Method for low temperature, low pressure metallic diffusion bond

Metal fusion bonding – Process – Bonding nonmetals with metallic filler

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228122, 22826312, B23K 3102

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active

045822409

ABSTRACT:
A method for intermetallic diffusion bonding of piezoelectric components, wherein ceramic pieces with fired-on silver electrodes are stacked with a thin shim of solid indium alloy therebetween. The indium alloy preferably comprises 25% indium, 37.5% lead and 37.5% tin. The stack is placed under 150 psi compression and heated at a temperature of about 350.degree. for 30-48 hours in an inert gas. Almost immediately upon being heated, a liquid-solid diffusion takes place in which a small amount of the silver diffuses from the electrodes into the now liquid indium alloy. The alloy in the interface becomes saturated with silver producing a new quaternary alloy which has a higher melting point than the previous indium alloy shim. Thus, there is a gradual solidification of the alloy as the concentration of silver increases. After solidification of the new alloy during the remainder of the heating time, there is a gradual diffusion of the indium into the silver and vice versa. The bi-directional solid-solid diffusion of the indium and silver gives the bond a strength higher than known in the prior art.

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Article in Physical Review, vol. 151, No. 2, Nov. 11, 1966, entitled "Interstitial Diffusion of Gold and Silver in Indium", by Anthony et al.
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Chapter 4 entitled "Fast Diffusion in Metals" from book entitled Diffusion in Solids, published by Academic Press, 1975; Chapter 4 authored by Warrenton et al.

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