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Plastically Deformable Stress Buffer Zones

IP.com Disclosure Number: IPCOM000076662D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Lynch, JR: AUTHOR

Abstract

The transmission of stresses to underlying layers in a multilayer metal structure upon a glass or ceramic substrate can be minimized. The thermal stresses imposed in processing are not fully eliminated, but are prevented from causing a stress - thickness product which would exceed the tensile strength of the glass and subsequently result in either adhesion loss or glass damage. An optimum deformable condition, limiting force transmission, is set up in the metal.

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Plastically Deformable Stress Buffer Zones

The transmission of stresses to underlying layers in a multilayer metal structure upon a glass or ceramic substrate can be minimized. The thermal stresses imposed in processing are not fully eliminated, but are prevented from causing a stress - thickness product which would exceed the tensile strength of the glass and subsequently result in either adhesion loss or glass damage. An optimum deformable condition, limiting force transmission, is set up in the metal.

A specific example of the technique follows. First step is to vacuum evaporate chromium (800 angstroms), then copper (80,000 angstroms) on top of a 2 to 3 mil glass or silicon dioxide surface. The next step is to anneal between about 350 to 800 degrees C. The annealing step causes the reduction of the forces into the glass during thermal cycling. These forces are the result of the thermal coefficient mismatch between the glass and chromium-copper layer and the subsequent metal layers deposited at near room temperature. The annealing produces slip planes within the copper layer so that, during thermal cycling, the expansion stresses of the copper are taken up internally, without the glass cracking as was experienced in the prior art. Subsequent wire bonding criteria is also increased using this method.

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