Brazing technology for low temperature cofired ceramics and its application to MCM

A brazing technique for low temperature cofired ceramics (LTCC) has been investigated for the construction of hermetic MCMs. Ag/Cu was studied to achieve secondary brazing as well as to establish a cost effective process. Multilayer thin film metallization was used for brazing because of its superior heat resistance and adhesion strength. For I/O pins, brazing metal characteristics were investigated to ensure good reliability at pin joints. As a result, pin pull strength with Ag/Cu alloy was more than 7.0 kg/pin, which is comparable with that of Au/Sn alloy. The minimum pin pull strength increased as the diameter of the pin head increased from 0.7 mm to 1.00 mm. For the heat slug, MCM structure designs were investigated by stress simulation analysis to reduce inherent residual stress caused by Ag/Cu brazing. This revealed that a Cu buffer inserted between Cu/W heat slugs and LTCC or changing the heat slug material to Mo can reduce the residual stress generated by brazing. Thermal resistance simulations were performed for heat slugs. Electrical properties of LTCC were much superior to those of alumina