Abstract:

Fracture of glass seals in metallic hermetic electronic packages is a significant failure mode because it may lead to moisture ingress and also to loss of load carrying capacity of the glass seal.  Seal glasses are intrinsically brittle and their fracture is governed by the stresses generated.  This study investigates stresses in lead seals caused by handling, testing, mechanical vibration, and thermal excursions.  Loads considered are axial tension, bending, and by superposition of these results.  Design and analysis of experiments in conjunction with finite element simulations are used to formulate pseudo-closed form equation to relate the maximum principal stress, within the glass-seal, to the type of loading and geometry.  The accuracy of the proposed closed-form equations are verified through analysis of residuals.  The analysis reveals the sensitivity of the magnitude of the seal stress to seal, lead, and package geometry.  The purpose of the closed-form model is to illustrate a systematic methodology to develop design guidelines from simulation studies in a multi-variable problem; and to apply this methodology for the reliable design of lead seals.  Manufacturing-induced problems such as defects and flaws are not considered.
 

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