Conformity Magazine - April 2008 - (Page 38)

test was performed using the skewed fixture system in order to minimize the number of variables. When this unit was tested on the pneumatic hammer system, the power supply failed at 15 Grms, and no other failure modes were found. However, under testing with the skewed fixture ESS system, we found the compact flash memory came loose at 7 Grms (a weakness not uncovered by the pneumatic hammer system). Then, at 8 Grms, there was a failure of one of the power supplies, but it came back when the vibration was stopped. When the random vibration level was stepped up to 10 Grms (less than 10 seconds after the start of the vibration), both power supplies failed and could not be revived. Because of different vibration imposition approaches taken for each test, it was not possible to compare the total time it took to propagate the weaknesses by each of the systems. But the whole ESS process including the high/low temperature tests took the pneumatic hammer system roughly 3 days. It took the skewed fixture ESS system only about 25 minutes of vibration time to find the backed-out compact flash memory problem, and 28 minutes to fail the power supplies. The testing time required with the skewed fixture system was considerably shorter than the pneumatic hammer system, and failures were identified at a much lower vibration level. Conclusions The test results for the three different products demonstrated that the skewed fixture chamber system precipitated the weaknesses in a product in much shorter time and at lower vibration levels than the pneumatic hammer shock system. In addition, the skewed fixture chamber system also found additional defects that were not uncovered by the pneumatic hammer system. The reason is that, for the same G level, the displacement is much larger at low frequencies than at high frequencies. For example, bending a wire (or any structure) thousands of times at a small displacement will not break it, but bending it at a large displacement a few times will break it. A shorter time to precipitate hidden defects can mean lower cost for the ESS process and a shorter product development cycle, as well as greater throughput during manufacturing. In addition, effective lower random vibration levels would use less of the product’s life during the HALT process, leaving more useful life in the product for the customer. Figure 7: Unit on the skewed ESS system Figure 8: Accelerometer mounted on the capacitor ESS Testing System Profile Vibration Intensity Level (Grms) Duration of Vibe at Each Level Failed at Total Time to Failure (min.) Figure 6 38 Conformity April 2008 ED Shaker with Skewed Fixture Flat Spectrum from 5-500 Hz 5 5 min. 5 Grms 5 Pneumatic Hammer System Uncontrolled 5, 10, 15, 20, 25, 30, 35 10 min 35 Grms 70 Table 1

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Conformity Magazine - April 2008 NewsBreaks Editor’s Note Mandatory Analog Cellular Service Ends FCC Releases Quarterly Reports on Consumer Inquiries and Complaints New Standards List Released for The EU’s Low Voltage Directive FDA Issues Notification on Unretrieved Device Fragments FDA Offers Guidance on Waivers for In-Vitro Diagnostic Devices ESD Open Forum Emerging Issues in Standards Challenges in Testing Design Fundamentals Focus on... New Products Product Reviews Premarket Approval Application Guidance Issued by FDA New Jersey Enacts Electronic Waste Recycling Regulations A New U.S. Standard for Workstation and Computer Design Might the CPSC Hold Retailers Accountable for Safe Products? CPSC Loses “Sole Toy Tester” CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - April 2008

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