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Ni Layer between Cu and Au In Solder Joint to Prevent Cu Dissolution and Solder Joint Failure as a Result of Reflows

IP.com Disclosure Number: IPCOM000085860D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

DiGiacomo, G: AUTHOR

Abstract

The drawing shows a portion of a chip made of silicon and a solder portion of lead-indium that joins the chip to a supporting module, not shown.

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Ni Layer between Cu and Au In Solder Joint to Prevent Cu Dissolution and Solder Joint Failure as a Result of Reflows

The drawing shows a portion of a chip made of silicon and a solder portion of lead-indium that joins the chip to a supporting module, not shown.

Conventionally the solder is formed on the silicon with intervening layers of chrome and copper. The chrome provides good adhesion to the silicon, and the copper provides good adhesion between the chrome and the solder. After the chip has been mounted on a module, it is sometimes desirable to remove the chip by again melting the solder and then to replace the chip by a subsequent solder reflow operation.

In modules in which the copper is initially in direct contact with the solder, the copper migrates into the solder during these reflow operations and the copper layer tends to break loose from the chrome. Thus, after several reflow operations, the mechanical and electrical connection between the solder and the silicon may depend on the adherence of the solder to the chrome.

In the solder joint of the drawing, a nickel layer is formed between the conventional copper layer and the solder. The nickel tends to dissolve in the solder in the same way that copper does, but it tends to prevent the copper layer from dissolving in the solder and from coming loose from the chrome layer. The intermetallics that are formed by the nickel and the lead-indium do not adversely affect the solder joint. This solder joint has...