Guest Blog – MEMS New Product Development, Importance of Product Validation (Part 5)

Written by: David DiPaola, DiPaola Consulting, LLC, www.dceams.com

Product validation is an essential part of all successful MEMS new product developments.  It is the process of testing products under various environmental, mechanical or electrical conditions to simulate life in an accelerated manner.  Testing early and often needs to be a daily routine and not just a popular phase used in meetings.  This blog will cover proven methods to accurately perform MEMS product validation while mitigating potential issues resulting in repeated tests and non accurate results.

Measurement system analysis or MSA is a methodology to qualify the measurement system that will be used to characterize the product.  In the context of MEMS, this could be a function test system for characterizing the performance of a MEMS pressure sensor by applying known pressures / temperatures and measuring sensor output.  The first step of MSA is to calculate total system accuracy determined by a tolerance stack of subcomponent errors traceable to NIST reference standards.  This will ensure your test system has the accuracy needed to properly characterize the samples.  In addition, system linearity of the true and measured value with minimal bias change and stability of the measurement system over time should be demonstrated.  Lastly, a Gage R&R (using average and range or ANOVA methods) in percent of process variation (not tolerance) should be completed to demonstrate repeatability and reproducibility for each test system utilized.  An excellent reference for MSA is aiag.org, Measurement System Analysis.

Verification of the test system setup and function of the equipment is an important step prior to the start of validation.  Often times, improper test set up or malfunctioning equipment results in repeated tests and delayed production launches.  This is easily avoidable by documenting proper system setup and reviewing the setup thoroughly (every parameter) prior to the start of the test.  Equally important, the engineer should verify the system outputs are on target using calibrated tools after the tools themselves are verified using a known good reference.

We all like to believe that customer specifications are well thought out and based on extensive field and laboratory data.  Unfortunately, this is not always the case.  Hence it is prudent for engineers to challenge areas of the customers’ specifications that do not appear robust.  Neither the customer nor the supplier wins if the product meets the defined specification but fails in the field.  The pain of such events is pervasive and extremely costly for all parties.   As parts complete laboratory tests, take the added step of comparing the results to similar products in the field at the end of life and ensure similar degraded appearance.  When ever possible, test products to failure in the laboratory setting to learn as much as possible about failure mechanisms.  When testing to failure is not possible, perform the validation to 3 – 5X the customer specification to ensure proper margin exists mitigating the risk of field failures.  Furthermore, always take advantage of field tests even if limited in duration.  They can provide valuable information missed in a laboratory validation.

As briefly stated earlier, a function test or product characterization is the process of applying known inputs such as pressure, force, temperature, humidity, acceleration, rotation, etc. (sometimes two or more simultaneously), measuring the output of the MEMS product and comparing it to the desired target.  This is completed to ensure the product is compliant with the stated performance specification from the manufacturer.  As product life is accelerated through the validation, the device function should be characterized multiple times during the test to understand product drift and approximate time of failures.  It is recommended to perform function tests 3 – 8 times at periodic (equally spaced or skewed) intervals during the validation after the initial pretest characterization.  As an example, I often test products at intervals of 0, 25, 50, 75 and 100% of the validation.

Use of test standards is highly encouraged as it brings both consistency and credibility to validations performed.  Several organizations develop test standards for general use such as ASTM, JEDEC, AEC, Military and more.   When a product is tested to standards widely excepted in the industry, the intended audience is more likely to accept the results than if a non-familiar possibly less stringent test method was applied.  Some commonly used standards include ASTM B117 (salt spray), JEDEC JESD22-A106B (thermal shock), Automotive Electronics Council AEC-Q100 (stress test for integrated circuits) and MIL-STD-883 (various environmental tests) just to mention a few.  A list of validation standards used across the MEMS industry can be found in the MEMS Industry Group Member Resource Library, Standards Currently in Use at MEMS Companies.

In the validation of MEMS products, it is tempting to perform the testing on units from one wafer that has yielded 1000 pieces.  However, this is a single window in time and does not properly reflect the true process variation that can occur.  A better sampling approach for validation is taking units from multiple wafers within a lot and across multiple wafer lots.  Equally important, differing raw material lots should be used (one example is the starting SOI wafers).  This will ensure supplier, equipment, process, operator and time sensitive factors are well understood.

Controls are another method to learn valuable information about the products being validated and the equipment being used.  A basic control could be as simple as a product that is function tested at each stage of the test, but does not go through any of the validation (i.e. sits on a shelf at room temperature).  This will give an indication if something has gone wrong with your test system should the same errors be seen in both experimental (parts going through validation) and control groups.  Another use of a control is testing a product that has previously passed a given validation (control group) while simultaneously testing a product that has under gone a change or is entirely new (experimental group).  This will provide information on whether the change had any impact on the device performance or if the new device is as capable as a previous generation.

Lastly validation checklists are a valuable tool to ensure each test is set up properly before the test begins.  Without the checklist , it is easy to over look a step in pursuit of starting the test on time to meet a customer’s schedule.  Below is a sample validation check lists for thermal shock.  This can be modified for other tests as well.

Thermal Shock Validation Checklist

  • Perform proper preventative maintenance on the environmental chambers before the start of the test to prevent malfunction during the test
  • Identify appropriate control and experimental groups and ensure proper sampling from multiple wafers and lots

Document sample sizes

  • Identify a proper validation standard or customer specification to define the test
  • Document pass / fail criteria for the devices under test
  • Create a test log and record any time an event occurs (i.e. start of test, end of test, devices removed from thermal chamber for testing, etc.)
  • Verify calibration of measurement reference and trace it back to a national standard
  • Verify the measurement reference with appropriate simple test.  (i.e. thermal couple’s accuracy and repeatability with boiling water, room temperature, ice water and other known sources)
  • Measure the temperature of the hot and cold chambers with an accurate and verified reference prior to the start of the test (i.e. thermal couple ± 1°C)

Verify chamber temperature is consistent across the part loading

  • Verify the time it takes the thermal load to reach the desired temperature (i.e. -40°C) and that its within test guidelines
  • Measure the transition time between hot and cold chambers and verify its within test guidelines
  • Complete all necessary MSA on test equipment and document the results
  • Engrave serial number on each device (paint pen can be easily removed)
  • Document the location of devices in environmental chamber with digital photograph
  • Record serial number and manufacturer for environmental chambers used
  • Determine and document periodic intervals for device function test
  • Continuously monitor environmental chamber temperature for the duration of the test using an appropriate chart recorder

Document location of thermal couple (photo) and verify it is located close to parts

  • Monitor device output continuously during the test
  • Check on the environmental chamber daily to ensure no malfunctions have occurred and monitor daily cycle count
  • Create a test in process sign with appropriate contact information for support staff

This will likely prevent individuals from accidentally turning off the environmental chamber or changing temperature profiles without notifying you

  • Document any changes to this specification for future reference

Product validation is a critical tool to learn about MEMS performance over a laboratory based accelerated life.  Its an excellent method to validate theory and ensure product robustness in the field.  The due diligence presented in this blog will help engineers avoid seemly small mistakes that cause repeated tests, inaccurate results and missed customer deadlines.

Bio:

BioDavid DiPaola is Managing Director for DiPaola Consulting a company focused on engineering and management solutions for electromechanical systems, sensors and MEMS products.  A 17 year veteran of the field, he has brought many products from concept to production in high volume with outstanding quality.  His work in design and process development spans multiple industries including automotive, medical, industrial and consumer electronics.  He employs a problem solving based approach working side by side with customers from start-ups to multi-billion dollar companies.  David also serves as Senior Technical Staff to The Richard Desich SMART Commercialization Center for Microsystems, is an authorized external researcher at The Center for Nanoscale Science and Technology at NIST and is a Senior Member of IEEE. Previously he has held engineering management and technical staff positions at Texas Instruments and Sensata Technologies, authored numerous technical papers, is a respected lecturer and holds 5 patents.  To learn more, please visit http://www.dceams.com.

Guest Blog: RoboBusiness Conference Review

Originally posted by Michael E Stanley in The Embedded Beat on Nov 1, 2013

Last week I had the opportunity to present a tutorial on sensor fusion at the RoboBusiness Conference in Santa Clara.  It was my first time at RoboBusiness, and I thoroughly enjoyed attending sessions, wandering the show floor and talking with other attendees.  As you might guess, this conference is all about BUSINESS enabled by robotics.  Neat technology by itself is of only academic interest.  The attendees are interested in making MONEY.  The theme of this year’s show was “Invest, Innovate, Implement”.

One of my first destinations was to visit Baxter, developed by Rethink Robotics.  You might have read about Baxter in the IEEE Spectrum article “How Rethink Robotics Built Its New Baxter Robot Worker“.  Baxter represents a new breed of robot intended to work along side people.  If a human gets in Baxter’s way, he yields instead of knocking the dumb human on his or her keister.

It’s also easy to tell Baxter what you want to do.  Simply grip both sides of his “wrist” and Baxter’s arm enters a “weightless state”.  You simply move his arm where you want it to go and program waypoints via a number of buttons on his arm.  No computer needed.  I experimented with the weightless mode, and it really is easy to move him about.

MikeAndBaxter.jpgMike meets Baxter

Freescale had a booth on the show floor.  Immediately across from us was Velodyne. These are the folks that make the Lidar system you’ll see on top of the Google map cars that roam the nation.  Velodyne had one of their systems set up on the show floor, generating a real-time image of the surrounding area (see image below).  The system is responsive enough that you can clearly see people walking around the floor.  These same systems will be similar to those used in high-end robots for mapping and collision avoidance.

Veladyne.jpgVelodyne Lidar Display

I’ve seen telepresence robots at the last couple Consumer Electronics Shows that I’ve attended.  As you might expect, they were out in force at this event, courtesy of Robotics Trends and Suitable Technologies in the form of Beam robots (below).  At one point in the show, I found myself in a conversation with two other individuals, both attending via Beam.  One from India and another from the U.S. east coast.  There were no noticeable bandwidth or delay issues.  And my remote friends informed me that the Beams have multiple cameras, including one that enabled them to see my feet – so they would not bump into things.  With a top speed of over 3MPH, that’s a good thing!

IMG_20131023_174907.jpgBeam telepresence robots at their charging stations

One of the keynote sessions was entitled “Deploying 20 Autonomous Mobile Robots in a Hospital” by Aldo Zini of Aethon and Ken King of El Camino Hospital.  They mentioned that nurses spend, on average, 50% of their time on logistical and administrative tasks.  A lot of this time is spent dealing with the hospital supply chain: medication, supplies, food, linen and trash.  Delivery of these is complicated by the large size of the average hospital campus, variation in delivery size (a few pills versus a stack of clean linen) and the need for timely delivery.  The Aethon tug (shown below) can be customized for different tasks.  Some of the machines at El Camino deliver drugs, others handle linen, etc.  Because the machines are able to work 24/7/365, the hospital found that they needed less floor space devoted to “staging areas”, and could re-purpose that space for revenue generating purposes.

AethonTug.jpgThe Aethon Tug

Field robotics is another huge area of growth.  This might include field preparation, spraying for pests, herding, harvest automation and more. Autonomous Solutions, Inc. is one of the companies working in this space.  They offer kits to retrofit vehicles for remote use.

asirobotsDotCom.jpgASI Robotic Vehicle

Another interesting keynote was entitled “Big Data Meets Big Agriculture: UAV Solutions for Modern Farming” by Bandon Basso of 3D Robotics.  Brandon presented example data sets collected via UAVs that clearly identify variation in plant health across a farm’s growing area.  Because the UAVs are self-guided, a farmer can launch the vehicle and then go for coffee while data is collected.  The farmer can then make intelligent decisions with regard to where to fertilize, add/decrease water, etc.   Decreases in UAV costs as well as the ease of data analysis (which can now be done in an hour or two), mean that farmers now have the option to perform this type of analysis multiple times over the course of a single growing season.

I got a chance to play with a really interesting haptics demonstrator by Barrett Technology Inc. You grasp a ball at the end of a robot arm mounted on a tripod (below left).  Moving that ball in space causes a virtual ball on a computer screen (below right) to move about an enclosed “room”.  Each surface (4 walls, ceiling & floor) of the room are modeled as being composed of some different material.  For instance, the floor was grooved and the right wall as magnetic. When you “rolled” the ball across those surfaces, you could feel the interaction of those surfaces with the ball you held in your hand.

BarnettTechnolgy.jpgBarrett Technology haptics demonstrator

Robotic arms have been a staple of the industry for generations, and there was no shortage at RoboBusiness.  c-link Systems (not shown) actually shared space in Freescale’s booth.  Others shown below (from left to right) include ABB Robotics, Schunk, and Universal Robots.  ABB has a 43 page catalog of robot solutions, ranging from controllers, track systems, positioners, point robots and more.  Another company to look at in this space (again, not shown), is Synapticon.

abb.jpgRobot Arm from ABB Robotics

Schunk.jpgRobot Arm from Schunk

UniversalRobots.jpgRobot Arm from Universal Robots

The roving robot shown below was developed by Unbounded Robotics. That company was the winner of the PITCHFIRE event, where startup firms pitched their companies and products for the venture capital community.  Unbounded Robotics has a nice video of the UBR-1 robot in action, which you should definitely view.

UnboundedRobotics.jpgUnbounded Robotics UBR-1

The VEX Robotics Design System (below) brings the old erecter set into the 21st century, offering everything from complete robot kits to a-la-carte ordering of individual components.  Their products are tailored for STEM education, but will make even experienced engineers drool in anticipation.

Vex.jpgVex Robot Kits

As I mentioned earlier, this was my first RoboBusiness conference.  As a novice in the field, I came away with a number of lessons learned:

  • Robots have gone mainstream, affecting many more areas of the economy than just manufacturing.
  • The community seems to think that they’ve solved the navigation problem.  Autonomous UAVs can now navigate a pre-defined flight plan, avoiding unplanned obstacles on their own initiative, and even selecting their own landing sites.  Ground-based TUG robots can roam buildings on their own, with no major infrastructure to enable that navigation.  And SLAM (Simultaneous Localization and Mapping) techniques have progressed to the point where one presenter was able to show a full three dimensional model of the Tower of Pisa that was generated in 20 minutes.
  • The Robot Operating System (ROS) is the dominant toolset used by the industry today, although other options are still in use.  ROS is also consistent with the concept of Cloud Robotics.
  • iRobot and ABB were two of the big players at the show.  Most of the other companies I saw were much smaller.  There is still a lot of innovation and entrepeneurship going on.
  • The industry DOES have an up to date, and detailed roadmap: A Roadmap for U.S. Robotics From Internet to Robotics, 2013 Edition
  • 50% of the pilots in training today will be drone pilots
  • The adoption of co-worker robots is leading to re-shoring of jobs.  That is, bringing jobs BACK to the U.S.
  • Some industries (particularly fast food) may face job losses as robotic technologies are adopted.
  • In 20 years, coast-to-coast air freight shipping will be unmanned in the U.S.
  • Take a few minutes to visit the website of the Robotics Virtual Organization
  • If you are interested in personal UAVs, visit http://diydrones.com/
  • Primesense and the Microsoft Kinect have revolutionized robot vision, navigation and mapping by dramatically lowering the cost of vision hardware.
  • ROS Industrial is extending ROS into industrial settings.

I arrived on site in Santa Clara around mid-day on Wednesday the 23rd of October and headed home about 4PM the following Friday.  Hopefully the information above gives you a rough idea of just how jam-packed the conference and show were with information.  A good time was had by all!

Guest Blog: Design Enablement and the Emergence of the Near Platform

Guest blog post written by: Peter Himes, Silex Microsystems;
Introduced by: Karen Lightman, MEMS Industry Group

I am pleased to bring you this blog by Silex Microsystem’s Peter Himes, vice president marketing & strategic alliances. Peter reflects on MEMS and while other might lament at the conundrum of the uniqueness of all MEMS process (you can hum it to the tune initially coined by Jean Christophe Eloy of “one process, one product”) Peter instead sees opportunity. Through this challenge, Peter sees opportunity for innovation and collaboration. And what pleases me the most about his musings on MEMS is that the basic thesis that is my mantra:  “to succeed in MEMS, you can’t go at it alone – you must partner.” In this example he describes Silex’s partnership with A.M. Fitzgerald and Associates and their Rocket MEMS program. Read on, plug in and share your thoughts on how you’ve creatively sparked innovation in your own company; especially if you come up with the same reflection: in MEMS, it takes a village; you can’t go at it alone.

Design Enablement and the Emergence of the Near Platform

What does it mean to enable a MEMS design? Is it enough to have silicon wafers, a clean room and some tools? What bridges the idea to product?

Traditionally it has meant a series of trials based on past experiences on conceiving of a process flow which results in the final desired structure. What steps are possible? What materials can be used? How will it react to the process and how will it perform after all processing is done? All of these questions need to be understood simultaneously. Being able to do this consistently over many different projects is how Silex helps the most innovative MEMS companies get their ideas to high volume manufacturing.

But in markets where MEMS is becoming mainstream, where acceptance of MEMS technologies is encouraging traditional and non-traditional customers alike to consider their own MEMS programs, is this enough to enable the rapid growth of MEMS going forward? Is every MEMS device trapped in a paradigm of custom process development and new materials development? Does everything require MEMS PhD expertise to engineer a perfect solution? In a market where customers are looking for customized MEMS devices AND rapid time to market, can they have both?

The core of MEMS still lies in the custom process integration and the universe of MEMS devices is still expanding, pushed by the dark energy of innovation. Our SmartBlock™ approach to process integration is why we can execute on these challenges in a consistent and high quality way. But it still takes the time and effort of customized processes to achieve full production qualification, so we also believe that another model is possible, and we are beginning to see it emerge.

Process integration into a foundry environment is something we also call Design Enablement, because a successful MEMS process enables designs to be turned into an actual product. But the power of design enablement is somewhat muted if the echo only rings once. The true power of Design Enablement is when the process can resonate over many products or many redesigns of the same product. This would break the “one product, one process” paradigm and is what we believe is the next phase in the MEMS industry.

Rocket MEMS

Alissa Fitzgerald of AMFitzgerald & Associates had a dilemma and an idea. To her, the normal route for MEMS development was difficult from the start: begin with an idea and use a university or research lab to get a prototype out. Once it is successful, contact a production MEMS foundry to manufacture it – only to find out that there are still months or years of process qualification ahead. What if she could collaborate with a foundry from the start and define a product design platform and a process flow simultaneously? Using known process capabilities of an existing foundry, build and characterize the product to that process, so that both the processing window and the product spec windows are defined simultaneously. Then you have a process platform that is solid, “de-risked,” and ready to take customers to market quickly.

This is the idea behind the AMFitzgerald RocketMEMS program and Silex’s support and partnership in the initiative. And it results in something which is not fully customized for each new product, yet is not completely and rigidly fixed either. Rather, it is a “Near Product Platform” made possible by the design enablement of the Silex process integration approach and AMFitzgerald’s product design framework and methodology. It allows for product specific variability without breaking the mold out of which the process was cast.

And it works.

Guest Blog – MEMS New Product Development, Necessary Attributes of a MEMS Engineer for New Product Development (Part 4)

Guest Blog – MEMS New Product Development, Necessary Attributes of a MEMS Engineer for New Product Development
Written by: David DiPaola, DiPaola Consulting, LLC, www.dceams.com

In the development of new MEMS products, the team is the most important factor.  Executive management and investors will always evaluate teams and will only take large risks with teams that have earned their trust.  In response to a question I asked Rich Templeton (CEO of Texas Instruments) regarding how he made the decision to invest in a new technology, a portion of his response highlighted the evaluation of and betting on teams.  This is driven by the fact that it is actually quite common for engineers and entrepreneurs to lead multiple successful projects or startups over their career.  With this in mind, let’s review the necessary attributes that make these engineers and entrepreneurs so successful in MEMS new product development.

Integrity:  This is the foundation upon which all other attributes are built.  Truthfulness, consistency and accuracy of one’s actions is of utmost importance as without it you have nothing. This is not something that is exercised in part or stretched.  Its needs to embody who you are.

Good Judgment: An equally important attribute to integrity is a person’s ability to exercise discernment.  Its the skill of knowing what information is needed to make a sound decision, how to efficiently gather that information, being decisive and achieving positive outcomes a significant portion of the time.  It also entails the ability to lead when large gaps in information exist and managing the associated risk.  Engineers who use good judgment only reevaluate decisions for change as new information becomes available.  Furthermore, they study given information, decisions made and outcomes to hone this skill over time.

Details: The details are what make products robust with ultra high reliability.  A small detail can often make the difference in achieving or missing a specified performance target.  For example, overlooking the use of a getter in a MEMS device with a vacuum cavity could result in output drift if materials out gas over time.  Understanding the detailed physics of the problem at hand is also critically important.

Ability to Learn: Technology and human understanding of complex systems continues to evolve.  In order to be successful, a individual must have the desire and ability to learn as new information becomes available.  The MEMS industry is constantly changing with CMOS and nanotechnology integration, smaller feature sizes, optimized processes, standardization, sensor fusion and more.  Those who are unwilling to learn from not only their work but the credible work of others will have difficultly producing competitive products.

Problem Solving:  This is really a combination of proper methodology, attention to details and the ability to learn.  Experts in a field that know the answer before they start, rarely solve problems.  In running a design of experiments (DOE) of a MEMS sensor with a flip chip on flex laminated to a plastic substrate, pressure, time and heat were varied in a effort to eliminate voids in the laminate material and optimize process parameters.  The first DOE resulted in multiple large voids over all parameters showing no noticeable trends.  Through a methodology of identifying alternate factors and testing hypothesizes, it was then discovered that moisture impregnated in the plastic substrate and flex circuit itself was actually introducing voids in the laminate as it out gassed during the lamination process.  Once the moisture was removed either through a prebake or proper material handling, the voids were no longer present.  A subsequent DOE was completed including moisture as a factor and the process was optimized.  In a confirmation experiment, the predicted worst case process parameters resulted in large lamination voids and the optimized case demonstrated lamination with no voids and excellent adhesion.

Motivation / Passion:  The drive behind peoples’ actions and its alignment with project goals are essential.  Are they doing it because they love it and in essence it is a part of their DNA or is it simply a paycheck?  Does the subject matter wake them up in the morning because they can’t wait to get started?  Do their eyes light up, their voice become invigorated and their body language become expressive when they speak?  Do off shoots of their passion migrate into their personal time off?  These are some of the characteristics that highly motivated and passionate people display.   I had the privilege of discussing entrepreneurism and leadership with Ray Stata, founder and chairman of Analog Devices, a few years ago.  Through words and action, his passion is intertwined throughout ADI.  When their MEMS division was starting out and encountering difficultly, he showed his commitment to the business by becoming the general manager.  He figured the company would not fire the founder although they could.  In his spare time, he continues to show his entrepreneurial spirit as he lives vicariously through his investments in and mentoring of technology startups.  Everyone I have spoken to at ADI speaks highly of him.  Mr. Stata is an excellent example of the type of person you want on your team.

Creativity:  The ability to think in new ways is extremely important.  Its having the wherewithal to take an idea that appears crazy at the time and figuring out a way to make it work and provide a competitive advantage.  Devices that provide outstanding function and have an elegant, eye pleasing package with a captivating yet easy to use interface exude creativity.  An example of creatively in action is the first generation Apple iPhone.  When it was first released, it revolutionized the smart phone approach and the smart phone leader at the time is still recovering after large market share loss.

Experience: When looking at job descriptions, the top requirement is often education level.  This approach is not robust.  Let me explain.  If you were going to launch a MEMS device in production and wanted to hire an engineer, who would you choose: 1)  A person with a bachelors degree in physics who launched several profitable MEMS products in millions of units per year successfully or 2) a person with a PhD in the subject matter of interest and an MBA with little industry experience?  This is hypothetical but it illustrates a point.  Education is extremely important but the method through which it is obtained is less critical and can take many forms.  The CEO of Tumblr dropped out of high school in his freshman year because his school system had a weak computer science program.  Instead he and his parents agreed for him to pursue his education through alternative, more productive channels.  As recently highlighted in the news, he just sold his company for $1.1 billion to Yahoo.  He cites that he worked with and learned a tremendous amount from the smart people he surrounded himself with.

Persistence: The quality of steadily continuing despite difficult challenges along the way is a necessary characteristic of all accomplished engineers.  People who are persistence are often mislabeled as stubborn.  The key difference is persistent people listen to good reason and are cooperative.  However, being cooperative does not mean going along with the direction from those in authority that logical reason and data shows is the wrong path.  Instead staying the course and using influential communication with supporting data and analysis to gain needed support is a better approach.

Communication:  Proper communication is not only used to transfer information but also to persuade doubters with good reason.  This is an essential skill for interaction with customers, colleagues, investors and management.  An engineer with good communication skills can explain a complex problem in a well articulated, concise and simplified manner without skipping critical details.  In the end, the listener understands what was accomplished, how it was done, critical details and the resulting impact of the project.

Influence:  Individuals in MEMS new product development will encounter resistance from various people along the way.  This could be from management, investors or colleagues.  Hence the ability of individuals to affect the thinking and actions of others through sound reasoning, credible data, persistence and convincing plans is necessary to bring MEMS products to fruition.  For many years, there were critics who stated that standards for MEMS will never happen.  Instead of accepting the status quo, engineers from Intel and Qualcomm with the support of MIG and other companies worked together to produce the first MEMS standard on sensor parameters.  These actions are now influencing the MEMS community to accept that maybe some level of standardization is possible and beneficial.

Risk Tolerance: New product development and higher levels of risk go hand in hand.  Engineers who take on this challenge, need to have a greater tolerance for this risk and be able to manage it.  The key benefit of higher risk is the larger reward that is typically associated with it.  With any new product development, there is always the possibility for cancellation, low adoption, project delays and insufficient funding.  However, building teams on the principles above is the first step to lowering risk.

Other Points to Consider:  When choosing a team leader, vision is another important factor to consider.  Leaders with vision have the foresight to see the potential in an idea before it exists.  Not all team members have to be visionaries but it is important that trust is built between those who have it and those who don’t.  In addition, carefully consider the chemistry when building a team.  Having proper technical and business depth, meshing personalities and clear leadership is extremely important.

The team is essential for success in any MEMS new product development.  Focusing on the key attributes mentioned above will help companies hire the best individuals for MEMS new product development.  In next months blog, proper execution of MEMS validation will be discussed.

Updated Bio:

BioDavid DiPaola is Managing Director for DiPaola Consulting a company focused on engineering and management solutions for electromechanical systems, sensors and MEMS products.  A 17 year veteran of the field, he has brought many products from concept to production in high volume with outstanding quality.  His work in design and process development spans multiple industries including automotive, medical, industrial and consumer electronics.  He employs a problem solving based approach working side by side with customers from startups to multi-billion dollar companies.  David also serves as Senior Technical Staff to The Richard Desich SMART Commercialization Center for Microsystems, is an authorized external researcher at The Center for Nanoscale Science and Technology at NIST and is a Senior Member of IEEE. Previously he has held engineering management and technical staff positions at Texas Instruments and Sensata Technologies, authored numerous technical papers, is a respected lecturer and holds 5 patents.  To learn more, please visit www.dceams.com.

Guest Blog – MEMS New Product Development, The Technology Development Process and Design Review Checklist (Part 3)

Guest Blog – MEMS New Product Development, The Technology Development Process and Design Review Checklist
Written by: David DiPaola, DiPaola Consulting, LLC, www.dceams.com

After a functional A-sample prototype is built, it doesn’t take long for a project to gain traction that has market pull.  This is usually the point that a project becomes highly visible within a company and it enters the Technology Development Process (TDP).   The TDP is made up of multiple phases including concept, prototype, pilot and production with gates at the end of each phase.  Design and process reviews are required at each gate but may also occur within a phase.  These reviews are an open forum for communication of project progress and gaps towards technological, business and schedule milestones.  Furthermore the product is constantly evaluated against the market need and potential changes in market that may have occurred.  The audience for the reviews at a gate include peers and management who provide feedback on the project to date and collectively decide whether additional work is needed to complete the current phase or the completed work is sufficient to allow the project to proceed to the next phase with additional funding.  In certain instances, a project that has not met all of the deliverables may be allowed to proceed to the next phase but under strict conditions that must be fulfilled within a given timeline.  The goal of the TDP is to focus the team on high quality execution, effectively screen projects allowing only the best to proceed and hence accelerate successful innovation and profitability.

The MEMS Industry Group (MIG) Technology Development Process Template is an excellent tool for companies to use to implement the TDP within their organization (Marty et al. 2013).  The goal of the TDP was to create a simplified frame work that could be easily customized to fit a company’s needs.  The TDP structure shown below is a slightly modified version of the TDP developed by MIG.  In this version there are four major phases including concept, prototype, pilot and production with three major gates.

figure 1

The concept phase is where ideas are generated and the initial A-samples are developed.  It is also where the business case is first generated and the market need is defined.  It is highly desirable to have market pull at this point.  The prototype phase is where the design is developed in detail and B-samples are fabricated to support various levels of validation.  The outcome of the prototype phase is to have design that can be manufactured in volume production.  Towards the end of the prototype phase, production tooling is often released.  The pilot phase is where production tooling is built and qualified.  In addition, the product is made on production tooling (C-samples) and revalidated.  It is important to note that there should be no change in the product design between the last revision in prototype and the first samples off the production tooling.  The production phase is low to high volume production ramp.   Often customers will require revalidation of products in production once a year for the life of the product.

At each gate, there is a design and process review for the project.  In order for the team to be focused and efficient, there needs to be a clear set of deliverables defined for completion of each phase.  These deliverables range from business and market definition to project technical details to production launch.  The following checklist provides an in-depth set of deliverables for the design reviews at each gate that can be tailored to the specific needs of an organization.  It is noted that a fourth gate is common 3-6 months after production launch to review project status but is not depicted in Figure 1.


Figure 2

Design Review Checklist

figure 2
This table can be downloaded from the following link in PDF format.  Many of the items listed above are self explanatory.  Others are explained in more detail in previous blogs posts such as DFMEA and tolerance stacks.

The Technology Development Process is an essential element of successful MEMS new product launches.  The Design Review Checklist can also provide a frame work for discussion between management and engineers on required deliverables to pass a particle gate.  With improved communication and efficient execution of technology development, the TDP is a great tool for accelerating innovation and profitable MEMS products.  In next month’s blog, the necessary attributes of a MEMS engineer for new product development will be discussed.

Works Cited:

Marty, Valerie, Dirk Ortloff, and David DiPaola. “The MIG Technology Development Process Template.” MEMS Industry Group, Mar. 2013. Web. 28 Apr. 2013.

Updated Bio:

BioDavid DiPaola is Managing Director for DiPaola Consulting a company focused on engineering and management solutions for electromechanical systems, sensors and MEMS products.  A 17 year veteran of the field, he has brought many products from concept to production in high volume with outstanding quality.  His work in design and process development spans multiple industries including automotive, medical, industrial and consumer electronics.  He employs a problem solving based approach working side by side with customers from startups to multi-billion dollar companies.  David also serves as Senior Technical Staff to The Richard Desich SMART Commercialization Center for Microsystems, is an authorized external researcher at The Center for Nanoscale Science and Technology at NIST and is a Senior Member of IEEE. Previously he has held engineering management and technical staff positions at Texas Instruments and Sensata Technologies, authored numerous technical papers, is a respected lecturer and holds 5 patents.  To learn more, please visit www.dceams.com.

In Search of the Energy-Efficient Family Car

Written by: Karen Lightman, Executive Director, MEMS Industry Group
(as published in Design News on 09/06/2013)

Buying a car just isn’t as easy as it used to be, especially when you know just enough about alternative-fuel-source vehicles to make that decision very difficult. As my husband and I debate the merits and faults of energy-efficient cars (as the end date of his leased Prius looms in the background), I feel as though we must make a smart choice that is right for us and right for the planet. Perhaps you relate to such a quest for the perfect car that balances safety, comfort, fuel efficiency, and style.

When I entered this decision tree of what fuel-efficient car to buy, I initially thought that an electric vehicle (EV) would be the simple solution. EVs, which run on chargeable batteries, seem to make sense for our family. We live in an urban area and rarely take long trips requiring a long charge. We’ll just plug the car in at night and stop using petroleum that pollutes the air. Right?

Not quite. As I started discussing the decision with my MEMS colleagues (all with their EEs and MEs), I quickly learned that it’s not that simple. First, the biggest limitation is the battery itself. The energy-to-weight ratio for EVs is quite abysmal compared with gasoline. Up to one-third of an EV’s total weight can be attributed to the battery pack alone, and most of the batteries hold a charge for a few hundred miles at best. That’s a deal breaker for many.

Tesla appears to be the only EV company that is seriously attacking the battery issue. Its CTO has said battery energy density is improving about 7 percent a year. This clearly shows that his company understands one of the biggest roadblocks to EV adoption. Tesla has designed a beauty of a lightweight car that is chock full of MEMS/sensors and showcases an iPad-like dash between the passenger and driver. Plus it has two trunks; that is just so cool. (It’s the reason my 12-year-old daughter insists we buy a Tesla.)

Until we have cars that run on solar panels, energy is never free. Even if you decide to buy a Tesla, you have to think about where the energy is generated to recharge the battery every night. For me in Pittsburgh (and for most of the Northeast), the source is typically coal. Uh, oh. That means I would deplete more fossil fuels and release more greenhouse gases if I bought an EV. Another important issue is the disposal of heavy-lead lithium batteries. Some EVs need to replace their batteries after three years. So if you are the average American who holds on to a car for five years, you’ll need to dispose of (and pay for) two batteries and consider the environmental impact of that decision.

Let’s face it — the batteries for EVs (and for most consumer electronics) are still inefficient. Here’s where my MEMS brain starts to activate and I start thinking about energy harvesting. Can’t we find ways through MEMS to harvest the car’s vibrations at least to power its electronics?

I bet the folks at MicroGen Systems are already looking into this. I actually know of a few more companies (big and small) that are looking into ways to make vehicles smarter and energy efficient from the get go through a combination of MEMS and sensors. Examples include energy harvesters in the tire that capture the vibrations and power the tire-pressure monitoring system, as well as sensors embedded into an engine to maximize fuel efficiency. Take it one step further, and HVAC monitoring systems managed by an in-car sensor network could keep passengers comfortable as the vehicle passes through varying daylight and temperature conditions. MEMS will make this happen.

I guess I will have to wait until there’s smarter battery technology that recharges an EV by green energy. In the meantime, I’ll be asking my local car dealer how many MEMS and sensors are inside the vehicle. The car with the most MEMS wins.

MIG Visits the AUVSI Unmanned Systemss Conference

Written by: Monica Takacs, Membership Director, MEMS Industry Group

From robotic ground vehicles that enter areas too dangerous for humans, to maritime vehicles that explore and map underwater caves, and drones used for agricultural and environmental applications, the unmanned vehicle systems appears to be a growth industry for MEMS.

MIG attended the AUVSI (Association for Unmanned Vehicle Systems International) conference in Washington, DC, August 13-14 to check out all of the MEMS devices found in these unmanned vehicle systems. Inertial MEMS sensors were featured throughout the show and many of the exhibitors demonstrated the cost, size, and power consumption advantages that MEMS has over traditional inertial measurement systems (IMU) like fiber optic gyros.

Several MIG members were at the conference showcasing their technologies.

Analog Devices featured their signal processing technologies for advanced unmanned systems for defense & civilian applications, including their MEMS based inertial sensor technology.

Epson introduced their M-V340 IMU for unmanned vehicles and other space- and weight-sensitive applications.  They claim it’s smallest IMU among high-performance IMUs having gyro bias instability of 10 dph or less (as of the beginning of August 2013, according to Epson’s research.)

Honeywell presented their HG1930 IMU for flight control, navigation of UAVs, missiles, projectiles, and munitions that include inertial MEMS sensors designed, developed, and manufactured in-house.

Meggitt showcased their thermal management solutions for unmanned platforms, and projectile tracking technology that track bullets to large missile and can provide weapon performance data from a target platform or threat notification on a tactical platform.

PNI Sensor Corporation displayed their 9-axis sensor fusion pinpoint heading and orientation technology and algorithms for the consumer, military, and scientific markets.

Sensonor showcased their tactical grade STIM300 IMU, a non-GPS aided IMU, containing 3 MEMS gyros, that is suitable for various commercial and defense guidance and navigation applications.

Xsens demonstrated their MTi 100-series, their high performance product line that features vibration-rejecting gyroscopes and a sensor fusion algorithm that overcomes limitations in Kalman Filtering.

VetorNav Technologies displayed their VN-200 GPS-Aided Inertial Navigation System (GPS/INS) which incorporates a suite of MEMS-based 3-axis accelerometers, gyroscopes, and magnetometers, along with a barometric pressure sensor and a high-sensitivity GPS module in a surface mount package.

Guest Blog – MEMS New Product Development, Critical Design and Process Steps for Successful Prototypes (Part 2)

David DiPaola, DiPaola Consulting, LLC, www.dceams.com

The fourth article of the MEMS new product development blog is Part 2 of the critical design and process steps that lead to successful prototypes.  In the last article, the discussion focused on definition of the customer specification, product research, a solid model and engineering analysis to validate the design direction.  The continuation of this article reviews tolerance stacks, DFMEA, manufacturing assessment and process mapping.

A tolerance stack is the process of evaluating potential interferences based on the interaction of components’ tolerances.  On a basic level, a cylinder may not fit in a round hole under all circumstances if the cylinder’s outside diameter is on the high size and the inside diameter of the hole is on the lower size causing an interference when there is an overlap of their tolerances.  This situation can become complex when multiple components are involved because it results in the number of variables reaching double digits.  A simple approach to tolerance stacks is using a purely linear or worst case approach where full tolerances are added to determine potential for interference.  However, experience from producing millions of sensors shows this approach is overly conservative and a non optimal design practice.  If tolerances of the assembly follow a normal distribution, are statistically independent, are bilateral and are small relative to the dimension, a more realistic approach is a modified root sum of the squares (MRSS) tolerance stack technique.  In this approach the root sum of the squares of the tolerances are multiplied by a safety factor to determine the maximum or minimum geometry for a set of interrelated components.  The safety factor accounts for cases where RSS assumptions are not fully true.  This approach is only recommended when 4 or more tolerances are at play.  If only 2 tolerances are present as in the first example above, it is recommended to perform a linear tolerance stack.  In some cases, linear tolerances need to be added to a MRSS calculation (MRSS calculation + linear tolerances = result).  Pin position inside a clearance slot for anti-rotation is linear tolerance that is added to a MRSS calculation.  Reasoning for this is the pin can be any location in the slot at any given time and does not follow a normal statistical distribution.

An example of a MRSS tolerance stack is provided below to review this concept in more detail.    Let’s determine if the wirebond coming off of the sense element will interfere with the metal housing.  A modified RSS tolerance stack shows line to line contact and only a small adjustment in the design is needed to resolve the issue.  The linear tolerance stack shows a significant interference what requires a larger adjustment.  Dimensions and tolerances are illustrative only.

Figure 1

MEMS Sensor Package (mm)

Fig 1


Figure 2

Modified Root Sum Square Versus Linear Tolerance Stack Approaches

0.17 > SF*(((T1^2) + (T2^2) + (T3^2) + (T4^2) + (T5^2))^(0.5))        MRSS Approach

0.17 > 1.2*((0.01^2 + 0.05^2 + 0.025^2 + 0.10^2 + 0.08^2)^0.5) = 0.17

0.17 > T1 + T2 + T3 + T4 + T5        Linear Approach

0.17 > 0.01 + 0.05 + 0.025 + 0.1 + 0.08 = 0.27

An excellent text on this subject is Dimensioning and Tolerancing Handbook, by Paul J. Drake, Jr. and published by McGraw-Hill.

DFMEA, design failure mode and effects analysis. is another tool that is extremely effective to identify troublesome areas of the design that need to be addressed to prevent failures in validation and the field.  Simply put this is a systematic approach to identify potential failure modes and their effects and finding solutions to mitigate the risk of a potential failure.  A Risk Priority Number (RPN) is then established based on rating and multiplying severity, occurrence and detection of the failure mode (severity*occurrence*detection = RPN).  The input to the tool is the design feature’s function, the reverse of the design function, the effect of the desired function not being achieved, and the cause of the desired function not being achieved.  There is also an opportunity to add design controls prevention and detection.  The outputs are the corrective actions taken to mitigate risk of a potential failure. Figure 3 shows an brief example of this approach for a MEMS microphone.

Figure 3

Design Failure Mode and Effects Analysis (click to view full size)

Fig 3

Further information on DFMEA can be found at Six Sigma Academy or AIAG.  Corrective action section left out of illustration for clarity.

It is also extremely important that the manufacturing process be considered from the first day of the design process.  Complete overlap of design and process development are the true embodiment of concurrent design.  The following illustration depicts this well:

Figure 4

Concurrent Design

Fig 4

Hence before a MEMS design is started, discussions should be initiated with the foundry, component fabrication suppliers and the process engineers responsible for the package assembly.  These meetings are excellent times to review new capabilities, initial ideas and explore new concepts.   Considering the design from a process perspective simultaneously with other design requirements leads to highly manufacturable products that are often lowest cost.    In essence, the design engineer is performing a constant manufacturing assessment with each step in the design phase.  This methodology also encourages process short loops in the design phase to develop new manufacturing steps.  This expedites the prototype process with upfront learning and provides feedback to the design team for necessary changes.  The additional benefit of this approach is the boarder team is on board when prototyping begins as they had a say in shaping the design.

Another tool to thoroughly understand the process in the design phase is process mapping.  Using this methodology, process inputs, outputs, flow, steps, variables, boundaries, relationships and decision points are identified and documented.  The level of detail is adjustable and to start there can be a broad overview with more detailed added as the design progresses.  This quickly provides a pictorial view of the process complexity, the variables effecting the design function, gaps, unintended relationships and non value added steps.  It can also be used as a starting point for setting up the sample line in a logical order to assemble prototypes, estimating cycle time and establishing rework loops.  To further clarify this method, a partial process map for a deep reactive ion etch process is provided:

Figure 5

Partial Process Map of Deep Reactive Ion Etch Process

Fig 5

This process map is not all inclusive but illustrative of the process flow, critical parameters, inputs and a decision point.  The personal protection equipment, tools used and relationships in the process are omitted for brevity.  With this level of process detail available to the design team, the complexity of feature fabrication can be evaluated, anticipated variation from process parameters can be analyzed and much more possibly prompting design changes.
Knowledge of and attention to detail in these eight critical, yet often overlooked steps are essential in the design of highly manufacturable, low cost and robust products.  These methodologies create a strong foundation upon which additional skills are built to provide a balanced design approach.  In next month’s blog, the design review process and a checklist will be discussed to help engineers prepare for this important peer review process.

Updated Bio:

Bio

David DiPaola is Managing Director for DiPaola Consulting a company focused on engineering and management solutions for electromechanical systems, sensors and MEMS products.  A 17 year veteran of the field, he has brought many products from concept to production in high volume with outstanding quality.  His work in design and process development spans multiple industries including automotive, medical, industrial and consumer electronics.  He employs a problem solving based approach working side by side with customers from startups to multi-billion dollar companies.  David also serves as Senior Technical Staff to The Richard Desich SMART Commercialization Center for Microsystems, is an authorized external researcher at The Center for Nanoscale Science and Technology at NIST and is a Senior Member of IEEE. Previously he has held engineering management and technical staff positions at Texas Instruments and Sensata Technologies, authored numerous technical papers, is a respected lecturer and holds 5 patents.  To learn more, please visit http://www.dceams.com.

Thinking Outside the Mobile ‘Box’

Written by: Karen Lightman, Executive Director, MEMS Industry Group
(as published in Design News, August 1, 2013)

By now you’ve probably figured out that there are a bunch of micro-electromechanical systems (MEMS) devices inside smartphones and myriad other mobile consumer devices. But did you know that MEMS is also revolutionizing how dairy cows are managed and that it’s a potentially $40 billion business?

I learned this recently from Dr. Alissa Fitzgerald’s presentation at Sensors Expo 2013, “Thinking outside the (mobile) box: Other important high-value applications for sensor fusion.”

The cows wear MooMonitor, a collar outfitted with a motion sensor (MEMS accelerometer) and a temperature sensor that indicates when the mama cow is hitting peak fertility and is ready for reproduction. It’s called a “bovine estrus cycle detection” app, and you can get updates from the cows via iPhone right there on the dairy farm. There are a staggering 265 million dairy cows in the world that could wear these collars, and whose farmers can benefit from this application. This is a fine example of someone figuring out a way to make a ton of money in MEMS with a non-consumer mobile device.

 144549_679865

The MooMonitor collar.
(Source: Dairymaster)

Fitzgerald identified several other MEMS-based applications in markets that some might call “unsexy” but that actually have big potential. In home maintenance equipment, we have robotic vacuum cleaners (Roomba), gutter cleaners (Looj), and even pool cleaners (Mirra) — all made by iRobot. Even the big home appliance makers like Whirlpool and LG are getting into the action with “smart-home” goods such as clothes dryers embedded with humidity sensors.

While the thermostats that control HVAC might not seem like a huge market opportunity, Fitzgerald encouraged us to think again about this humble piece of electronics. There are 10 million thermostats purchased in the US each year, and 250 million already installed in homes and light commercial buildings. That’s a market ripe for smart MEMS-enabled systems that can intelligently sense a home’s/office’s heating/cooling needs.

Enter the Nest Learning Thermostat that has multiple MEMS temperature sensors, IR motion detectors, and behavior analysis and prediction, and voila! You finally have a thermostat that can save you money on your HVAC. And the best news yet? Nest is intuitive, so you don’t have to read a huge manual on how to program it. Fitzgerald estimated that based on the annual sale unit numbers, and estimating the cost of a thermostat at $50 to $250, the total available market for thermostats to control household HVAC would be at least $0.5 billion and possibly as high as $2.5 billion annually in the US. It’s looking a lot sexier now, right?

The success of MEMS beyond the mobile-consumer space is still a well-kept secret. While health/fitness and medical devices are gaining some ground, Fitzgerald reminded us that there are many other huge industries that are often overlooked by MEMS product companies and market analysts. These include oil and gas, steel, agriculture, textiles, and mining, for starters. Fitzgerald believes that billion-dollar business opportunities are out there for companies that can think outside the box, instead of just providing more cool stuff for urban gadget hounds.

So let’s hear it for MEMS-enabled products that help people in other large industries to get their work done in the oil fields of Texas and on the dairy farms of Wisconsin.

Guest Blog – MEMS New Product Development, Critical Design and Process Steps for Successful Prototypes (Part 1)

David DiPaola, DiPaola Consulting, LLC, http://www.dceams.com

In the third article of the MEMS new product development blog, critical design and process steps that lead to successful prototypes will be discussed.  These items include definition of the customer specification, product research, a solid model, engineering analysis to validate design direction, tolerance stacks, DFMEA, manufacturing assessment and process map.  With the modeling and analysis tools available and short loops for both design validation and process development, it is possible and should be expected to have functional prototypes on the first iteration.

Thorough review of the customer specification and an understanding of the application are two of the most critical steps in developing a prototype.  Without this knowledge, its a guess on whether the design will be successful meeting the performance objectives with next to zero quality problems.  The issues often encountered are the customer specification is poorly defined, it does not exist or there are gaps between customer targets and supplier performance.  It is the responsibility of the lead engineer to work with the customer to resolve these issues in the beginning stages of the prototype design to ensure a functional prototype is achieved and is representative of a product that can be optimized for production.   Furthermore, this specification creates an agreement between the supplier and customer on expectations and scope.  Should either of these change during the project, the deliverables, cost and schedule can be revisited.  Expectations and scope include package envelope, application description, initial and performance over life specifications, environmental, mechanical and electrical validation parameters, schedule and quantities for prototype and production.  In this process the supplier and customer review each item of the specification and mark it as acceptable as written or needs modification to be met given current knowledge.  There can also be area of further research and development before an agreement on the topic can be reached.  This entire process is documented and signed by both parties as a formal contract.  Then as more is learned about both the product design and application, modifications to the agreement can (and likely will) occur with consent of both parties.

Product research is another area of significant importance to the prototype process. This research has several branches including technology to be used, existing intellectual property, materials, design approaches, analysis techniques, manufacturing processes to support proposed design direction and standard components available to name a few.  Product research will also involve reaching out to experts in different fields that will play a role in the product design.  This is the initial data collection phase of learning from previous works through reading patents, journal articles, conference proceedings and text books and building a team of qualified professionals.  This process is sometimes chaotic and over whelming while wading through mounds of information in search of a viable design path.  However, this only lasts for a short period as trends start to form, innovation is birthed and a path is forged.

Parametric, 3D modeling is no longer a luxury but a must have in the design and prototype process.  It is essential for visualizing the design, documenting it and analyzing function, geometric properties and potential interferences.  However, use of the solid model should not stop there.  The documented geometry can be imported through a live link or other means to various other tools such as CNC machining, finite element analysis, tolerance stack analysis, motion visualization, fabric pattern generation prior to stitching, mold flow analysis, electrical simulations, equipment interactions, process development and much more.  The solid model should be considered a starting point for a much larger analytical model that is used to describe the fabrication, function and performance of the product and its components.  Once the solid model is complete, it is also extremely helpful to make stereolithography (SLA) or 3D printed components that can be felt, observed and often times used for preliminary product testing.  For a trivial cost, SLA’s can provide a wealth of information prior to prototype and help sell the design to colleagues and customers.

As highlighted in the previous paragraph, engineering analysis is the process used to validate the design and process direction theoretically.  The analysis can take the form of a manual hand calculation of deflection to the sophistication of finite element analysis predicting the strain in the diaphragm of a MEMS pressure sensor due to deformation of the surrounding package under thermal conditions.  The key to successful analysis is not only proper engineering judgment on parameters and attention to detail in model creation but validation of the analysis through experimentation or other theoretical means.  For example, the FEA results of a MEMS diaphragm under large deflection can be compared to other theoretical calculations of a round plate under large deflection that has been validated with experiment.  Correlation of the results suggest your model is in the ballpark and can be used to evaluate other parameters such as stress and strain.  In this analysis phase, the global model is often comprised of several smaller models using different analytical means that are then tied back together for a prediction of performance.  With many live links between several pieces of analytical software and the power of today’s computers, this process is becoming more efficient with better overall accuracy.

To better illustrate the points above, a case study of a MEMS SOI piezoresistive pressure sensor will be reviewed.  This pressure sensor was designed for operating pressures of 1000 – 7000 KPa. Due to the pressure range used, the surface area of the sensor that was bonded to the mating package substrate needed to be maximized while minimizing the overall foot print to increase the number of sensors per wafer.  Hence a deep reactive ion etch was used to obtain near vertical sidewalls.  A thicker silicon handle wafer was used to provide additional strain isolation from the sensor package while staying within a standard silicon size range for lower cost.  The silicon reference cap provided a stable pressure reference on one side of the sensor diaphragm.  Its geometry was optimized for handling, processing and dicing.

A solid model was created of the design including the wirebond pads, aluminum traces, interconnects, oxide layers and piezoresistors on the silicon membrane wafer.  In addition, the cap and handle wafers were modeled.  Although not shown here for proprietary reasons, each layer of the membrane was modeled as though it was fabricated in the foundry.  This enabled the development of a process map and flow.  Finite element analysis of the diaphragm under proof pressure loads showed that the yield strength of the aluminum traces could be exceeded when in close proximity to the strain gages.  This can cause errors in sensor output.  Hence doped transition regions were added to keep the aluminum out of this high stress region.  A comprehensive model of the piezoresistive Wheatstone bridge was created to select resistor geometry and predict the performance of the sensor under varying pressure and thermal conditions.  Strain induced in the gages from applied operating pressure and resulting deflection of the diaphragm was modeled using finite element analysis.  A model was also created to determine approximate energy levels needed to dope both the piezoresistors and transition regions.  This information was critical in discussions with the foundry in order to design a product that was optimized for manufacture as doping levels and geometry were correlated.   Furthermore short process loops were developed at the NIST Nanofab to optimize etch geometry and validate burst strength.

It is important to note that the design of the sense element was designed with constant feedback from the foundry and their preferences for manufacturing.  In addition, the sense element and packaging were designed concurrently as there was significant interactions that need to be addressed.  Design of the sense element and packaging in series would have resulted in a non optimized design with higher cost.  In the end, a full MEMS sensor specification was developed and provided to the foundry for a production quote and schedule.  Through working directly with the foundry, optimizing die size and designing a sensor for optimum manufacture, over 60% improvement in cost was achieved over going to a full service MEMS design and fabrication facility.

fig 1

Due to the length of these topics, stay tuned for next months blog for Part 2 of this article.  In that segment other critical steps including tolerance stacks, DFMEA, manufacturing assessment and process maps will be reviewed.

 

Bio:

David DiPaolaDavid DiPaola is Managing Director for DiPaola Consulting a company focused on engineering and management solutions for electromechanical systems, sensors and MEMS products.  A 16 year veteran of the field, he has brought many products from concept to production in high volume with outstanding quality.  His work in design and process development spans multiple industries including automotive, medical, industrial and consumer electronics.  Previously he has held engineering management and technical staff positions at Texas Instruments and Sensata Technologies, authored numerous technical papers and holds 5 patents.  To learn more, please visit http://www.dceams.com.

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