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The ECN Roundtable - Harsh Environment Needs

Mon, 02/01/2010 - 10:38am

This month's Roundtable Question is: Given the improved performance of modern parts and packaging, how much certification and categorization does a product intended for operation in a harsh environment require?

Mont TaylorFrom Mont Taylor, Strategic Development Manager
High Temperature, Die and DSP, HiRel Defense and Aerospace
Texas Instruments

Although the performance of the latest parts and packages is very good, there are still reliability requirements that need to be addressed before new devices can be used in many harsh environments. For extreme high temperature applications, both silicon and package qualifications are needed to insure that devices will operate to the required lifetime and not just functional at temperature. At 200C for example, there a physical effects that need to be understood that vary by design and special packaging is required.

Silicon adjustment for harsh environments can include new functional design changes such as modifying die to remove thermal shutdown and special process setups for parametric changes such as HFE, Beta, and Resistance. Electromigration, Negative bias Temperature Instability, Time Depended Dielectric Breakdown (TDDB), and Hot Carrier Injection all are concerns for high temperature semiconductors and have to be understood for extended temperatures that go beyond a standard commercial or industrial part qualification. Package qualifications are also required for bond strength and die attach and are going to be different from typical package requirements.

Dick ToftnessFrom Dick Toftness, VP of Engineering
Vision Research

We at Vision Reearch find the reliability of commercial parts to be exceptional. Today when a board fails a bad part is not what you look for. Additionally more functionality has been designed into modules which eliminates the large variety of additional passive components which used to support our analog designs. This creates compact products with huge functionality and many less connections per function. What used to fit on three boards now is integrated on one board which eliminates cables and connectors, a well known cause of poor reliability. All this leads to very reliable systems that function on initial integration.
While this is true of commercial components our proprietary parts take special attention to maintain a high level of reliability.

Today we spend much more time working through thermal and mechanical issues. Structures still have natural resonance modes and with the increase in density of components, correct thermal design is a major concern. Our products are now used in many different environments with outdoor operation being the norm versus the exception. Temperature variation, vibration and moisture are major design considerations as products migrate from a controlled environment to being used in wind tunnels, attached under the wing of planes and on the top of snow covered peaks.

We have instituted a much more stringent regimen of qualification testing of our products. From the image sensor to the finished product environmental, mechanical and safety testing is executed to a well developed but ever improving set of specifications. To support our product improvement efforts thermal design has become a part of the initial design rather than an after thought as has design for EMI compliance and ESD tolerance.

Our major proprietary component is our image sensors. Each is designed specifically for VRI and is produced in small quantities when compared to commercial components. The challenge then becomes how to detect and eliminate defects with a small statistical sample. VRI has developed an in-house screening program which has had a significant impact on our sensor reject rate. Over the past two years our reject rate has fallen by 30x. This effort has reduced our production costs and greatly affected our field failure rate.

All this work has produced a product which has greatly improved reliability. Tracking one product over the last 4 years indicates a statistically significant improvement in field failure rate. Our initial turn-on rate in production has also improved and we have again proven the old adage that “production yield is a good indication of product reliability”.

Robert SeubertFrom Robert Seubert, Product Manager
Automotive Electronic Components/Relays & DC Power Relays
Omron

For automotive applications, component performance is critical and manufacturers must test to OEM specifications set by the OEM. The components must be validated to a GM, Chrysler, Ford, Toyota or Honda Spec. Manufacturing processes must follow the automotive quality standards in order to meet harsh environment demands, and manufacturing plants should be certified to ISO9001, ISO14001, and ISO/TS 16949.

When Omron designs a component for automotive use it is designed to meet or exceed the OEM specification. Numerous validation tests are preformed to the components. These tests include extreme temperature cycle testing, salt spray testing, shock and vibration.

In order to meet these specifications Omron does in-line testing to maintain the specifications required by the OEM. An example of this is each automotive sealed switch is tested to make sure it is sealed to IP67. By doing this Omron can guarantee 100% of the switches produced are sealed to IP67. Sealing of switches is very critical. If salt spray should get into the internal parts of the switches it will cause the switch to fail. Furthermore, all switches are also validated for compatibility with various chemical solutions (such as window cleaners, solvents, gasoline, and greases) to make sure there are no adverse affects on the materials used to manufacture the switch.

Most electrical junction boxes are positioned as under-the-hood applications in vehicles and are expected to work at high temperatures. Thus, certain relays are designed specifically for this type of location to meet the extreme requirements. Since most electrical junction boxes are protected from salt spray and chemicals, it is not as important to have the relays meet these conditions, however. Current relays are also designed to meet specific load conditions required for motors used in power windows and door locks, or for head lights and rear view defoggers. Each relay type has to meet an OEM spec and is designed specifically to meet those conditions.

Before Omron certifies a component for automotive use, a thorough investigation of the customer application is completed. By doing this, Omron can then make recommendations on how the component should be used in various environments and still work within the product specifications. In turn, the product will meet the Harsh Environment requirements found in the automotive and transportation industry.

 

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