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Immersion Tin Lead Plating

IP.com Disclosure Number: IPCOM000084617D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Schmeckenbecher, AF: AUTHOR

Abstract

A tin-lead alloy can be deposited on gold by a fast exchange reaction. After deposition, the substrate is heated to above the melting point of the tin-lead alloy. The tin-lead wets the gold surface and forms a continuous coating. This assures wettability by solder even after prolonged storage.

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Immersion Tin Lead Plating

A tin-lead alloy can be deposited on gold by a fast exchange reaction. After deposition, the substrate is heated to above the melting point of the tin-lead alloy. The tin-lead wets the gold surface and forms a continuous coating. This assures wettability by solder even after prolonged storage.

For example, on multilayered ceramic modules for the packaging of integrated circuit chips, molybdenum chip vias are plated with nickel, followed by a thin layer of immersion gold (about 7-10 mu '' thick) which is deposited by an exchange reaction. The integrated circuit chips then are joined to the vias by solder reflow.

The gold layer is very thin and porous and the nickel underneath may be oxidized or otherwise contaminated, preventing wetting by solder. Therefore, it is desirable to provide an indication that the via is solder wettable before the chips are actually joined, and to maintain the wettability during storage and handling.

The following is an example of the immersion tin-lead process. Molybdenum chip vias on the surface of a multilayer ceramic module were plated with about 120 mu '' of electroless nickel and heated in forming gas to 680 degrees C for 4 minutes. The nickel was coated with gold from a commercially available immersion gold solution. The module then was dipped for 3 minutes at 90 degrees C in a solution containing: 2.0 grams/liter stannous chloride (SnCl(2).2H(2)O)

1.75 " lead acetate (Pb(C2H(2)O(2)(2))

5.6 " sodium hydr...