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Indium Lead Solder for Component Mounting

IP.com Disclosure Number: IPCOM000082018D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

DeBoskey, WR: AUTHOR

Abstract

One of the problems which arises in the mounting of semiconductor elements on lead frames and substrates, is due to a collapse of the solder balls used as connection and spacing elements. The procedure described eliminates such collapse by using indium as an alloying metal with lead or solder, to generate a temperature dependent phase-equilibrium alloy.

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Indium Lead Solder for Component Mounting

One of the problems which arises in the mounting of semiconductor elements on lead frames and substrates, is due to a collapse of the solder balls used as connection and spacing elements.

The procedure described eliminates such collapse by using indium as an alloying metal with lead or solder, to generate a temperature dependent phase-equilibrium alloy.

In the use of this process, the components to be mounted have lead or solder projections formed thereon to function as connections and spacers. The lead frame or substrate will have the metallic printed-circuit leads covered with indium. After the components are positioned, the circuits are heated to a temperature above the melting point of indium, but below that of the lead or solder projections.

The molten indium will wet the lead and alloy with it to form the liquid phase equilibrium alloy appropriate to that temperature, but leaving a core of solid lead. Lowering of the temperature will enable solidification of the alloy with the component securely mounted on the base, and the connection will not melt at any temperature lower than that at which it was formed.

This technique provides the advantage of ambient corrosion protection due to the presence of the indium coating; it prevents a total melting of the lead or solder projections, and thereby maintains a proper spacing of the component from the base. It also simplifies processing, since there is no need to provide the...