Influence of Bath Constituent on Microstructure and Joining Characteristics of Plating Layer at the Joining Interface : Micro-Parallel Seam Joining and Development of Joining Equipment (3rd Report)

Experimental evaluation of hermeticity and joining strength and an investigation of joints by SEM, EPMA, AES, were accomplished on hermetically sealed package by Micro-Parallel Seam Joining (MPSJ) using a lid (Fe-Ni-Co alloy) normally applied as hermetic seal of ceramic package for highly reliable LSI, nickel plated in both Watts bath and sulfamate bath. The results are summarized as follows : (1) A crack was observed at the grain boundary in a plated layer at the joining interface of ceramic package which was hermetically sealed with use of a nickle-plated lid in a sulfamate bath. The crack is considered to have been caused by sulfur segregation at the grain boundary from the result of investigation by SEM and AES. As a result, both hermeticity and joining strength were unsatisfactory. (2) Tendency of crack occurrence was observed to be especially notable at the seam joint after a thermal cycling test performed to evaluate reliability of joint rather than immediately after joining. Therefore, the thermal cycling test is considered to be an effective means for evaluation of crack occurrence. (3) No crack was observed at the joining interface of hermetically sealed package using a nickel-plated lid in Watts bath, indicating a sound joint structure. Both hermeticity and joining strength were found satisfactory. However, a peeling of the plated layer at an area of the lid slightly away from the joining section was observed on a lid applied with thick plating of 10 μm. Therefore, plating thickness of approximately 3.5 μm in Watts bath is considered to be adequate. (4) Correlation between hermeticity and peel strength was not found on a package hermetically sealed with use of a nickel-plated lid in sulfamate bath. Although the specified value for hermeticity was satisfied, peel strength was zero or a value close to zero in some specimens. Therefore, both methods have to be performed as an evaluation method for joint of hermetically sealed package by MPSJ.