Micross

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Off the shelf chip and die extraction for long term reliability.
Keywords: high temp, die extraction, bond pads
Die extraction, COTS and small production builds are common. Die can be extracted when chip sales are not an option. Extracted die help reduce the foot print on a PCB and improve performance. Typically those die are extracted with the bumps intact for subsequent wirebond to the PCB. Unfortunately those die bring along the negatives of the original die plus the extraction detriment. . The image below shows the die that have been extracted and stripped down to the bond pad. CVI has perfected the technique to not only extract those die but then remove the pure gold leaving only the Al-Au intermetallic. (An interesting note is that almost no pad we have extracted shows a gold bump with 100% IMC under the area of the original bump.) The pad can then have a UBM attached the supports improved reliability and flip chip bumping. By adding a UBM layer to the die pad the corrosion layer on the aluminum pad has been removed and replaced with a “clean” metal and gold oxidation barrier. The oxidation barrier can also be PdAu or pure Au to support wirebonding as needed. Regardless of the oxidation barrier layer, reliability results to date show improved performance at 10k hours at 200C (0 failures) compared to initial failures at <100 hours on a typical wire boned pad. 5k hours at 250C (0 failures) has also been demonstrated. What does this mean? Long term reliability at high temperature can be achieved using standard CMOS chips. Those chips are readily available and more economical. This modification supports build where extreme temperature and performance are critical.
Terence Q. Collier,
CVInc
richardson, texas
USA


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