Stress Analysis of Glass-to-Metal Seals
B. Mathieu, and A. Dasgupta
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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