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Resistors associated with insulated gate bipolar transistor (IGBT) modules were inspected and analyzed to determine the cause of poor bond development in the chip to substrate solder joint. All failed devices delaminated at the surface defined by the titanium layer and a nickel solder phase. Titanium is not considered a solderable material, so the solder contact should have been the nickel layer. The source material for the titanium deposition contained a high percentage of oxygen. This likely affected the surface characteristics of the deposited layer and contributed to the poor bond. The poor bond quality of the resistors appeared to be related to contaminated source metal for deposition and the soldering process. The titanium source material apparently absorbed contaminants while in service which produced a contaminated titanium layer and a poor surface for deposition of subsequent metal layers. The soldering process dissolved the entire nickel layer thus further contributing to a poor bond at the titanium interface. RJ Lee Group (RJLG) determined the solder joint failures were related to the manufacturing process, specifically the backside metallization of the resistors.
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