Authored By:
Naoshi Nishimura, Mutsumi Komeyama, Tsuyoshi Maeda,
Katsuhisa Tanabe, Shigeo Hashimoto
C.Uyemura & Co., Ltd.
Osaka, Japan
Scott Larson
UIC Technical Center
CT, USA
Summary
Compact high-power density, high-efficiency, and low cost have been desired for power modules and high temperature operation reliability has been required for all materials for power modules and bonding interfaces. Because operating temperatures became higher as chip materials changed from Si to SiC, the material for die attachment has been especially focused on. As the material for die attachment, Ag sinter is one of the leading candidates because of the desire to remove lead for environmental measures, superior electric conductivity and thermal conductivity, and higher melting temperature after sintering.
There are pressure-assisted and pressure-free methods used for Ag sintering. It’s widely known that the Ag deposit has good reliability with Ag sintering material when using the pressure-free method, which isn’t affected by warpage and the steps of bonding surface. Generally, Ag deposits for the chip backside have been formed by a sputter coating process.
In this report, we confirmed the possibility of electroless Ag plating, which can process both sides at the same time. Solder joint reliability for the top side and Ag sintering joint reliability for the backside were evaluated for electroless Ni-P/electroless Pd-P/immersion Ag with displacement reaction (ENEPIS) and electroless Ni-P/electroless Pd-P/immersion Ag with autocatalytic reaction (ENEPES), compared with electroless Ni-P/electroless Pd-P/immersion Au with mixed reaction (ENEPIG). It was confirmed that ENEPES with a Ag thickness of 0.3 μm had good reliability both for the solder joint and Ag sintering joint. In the future, thermal cycle test after Ag sintering will be examined.
Conclusions
Several reliabilities of ENEPIS with a displacement reaction Ag bath and ENEPES with a autocatalytic reaction Ag bath were compared. ENEPES had better thickness distribution, and less Ni-P corrosion which resulted in better solder joint reliability. Both ENEPES and ENEPIS had good wire bonding reliability for Al wire. Also, when the Ag thickness of both ENEPES and ENEPIS was 0.3 μm and more, Ag sintering reliability could be satisfied. Thermal cycle testing after Ag sintering will be examined for ENEPIS and ENEPES as next steps.
Initially Published in the SMTA Proceedings
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