New Thermal Gasket for Mounting Multiple Power Modules to Singular Heat Sink

摘要

The elimination of random high thermal impedances has been a major factor in reducing the PSM failure rate; compare the -03 curve in Figure 9 to the PSM-11 curve. Additionally the average power module temperature reduction of 1.5℃ to 6℃ has improved the PSM MTBF, which will improve long-term reliability. Note that the -03 curve is beginning to flatten out indicating the beginning of the flat portion of a traditional bathtub reliability curve for electronic equipment. In parallel with developing the new thermal interface the team also worked with the supplier in improving his assembly procedures. Also shown in Figure 9 is the Field Survivability rate for the new interface combined with power modules manufactured with the supplier's new assembly techniques. Note that the flat part of the traditional bathtub reliability curve begins at six months, instead of fourteen months, and is >96%. Additionally a follow-up team (Dave Greene and Jim Marano---Test Engineering) implemented a modest thermal stress-screening test (RTC), which has further improved the first year Field Survivability Rate to nearly 99% (Figure 10). Presently half of all field returns are diagnosed as No Trouble Found and ～ 1200 PSMs have been shipped to the latest configuration. Finally there have been no incidents of contamination on the production line, which is mainly attributed to the training classes conducted by manufacturing engineering for assemblers on how to handle the thermal grease.