This paper is concerned with the design of hermetic, solder-sealed electronic modules. In particular, the thermal strains developing in the solder seal, potentially leading to solder cracking and module loss of hermeticity are analyzed using a 3D FEM model. It is shown that a full transient thermo-mechanical analysis of the module during power cycling is needed to be able to select the right lid material in order to maximize the solder fatigue life. This is especially true when the module power dissipation is too high for thermal cycling to be representative of module operating conditions.

The IBM AS/400 MCM, called Muskie, is considered as a model problem. This high performance MCM dissipates about 4–5 times the power of its predecessors. At this high power, it is shown via modeling that traditional alumina lids which match the ceramic substrate CTE will lose hermeticity prematurely in the field. Model verification was done by power cycling a set of nine modules and reading out their hermeticity level every few hundred cycles. The experimental results agreed well with the model. The model was then used to select another lid material with an optimized lid-substrate CTE mismatch. The new lid material, made of WCu, has been used successfully by IBM over the past two years.

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