Cu-Sn Solder Sealing for Hermetic Optical MEMS Devices Package

Optical MEMS devices have been developed for the various applications, such as display, communications, computing and Bio systems. These MEMS devices require the hermetically sealed packages to keep the device driving movement stable regardless of any environmental changes.

In this paper, the Cu-Sn solder system was chosen to seal the package pursuing to get the low cost, low temperature hermetic package. The Cu-Sn solder metallurgy in the joint structure and the sealing process conditions were designed to get a final uniform solder layer of only a Cu3Sn phase avoiding the concern about the kirkendall voids formation at the interfaces. The optimal sealing condition was achieved to examine the interfacial microstructure, shear strength, and He leakage.

The packages sealed with an optimal condition were also undergone through reliability tests, such as the high temperature storage test at 125oC for 1000 hrs, the high temperature and high humidity test at 85 oC and 85%RH for 1000hrs and the accelerated thermal cycling test (-55~125 oC) for 1000 cycles. After reliability tests, it is confirmed that the Cu-Sn solder sealed hermetic packages was reliable enough to pass the Mil-STD-883E specifications. The hermeticity was about 1~5 E-8 atm×cc/sec He leak rate and the shear strength was as high as ~5~10 MPa.