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Electroless Nickel Tin Process

IP.com Disclosure Number: IPCOM000086269D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Schmeckenbecher, AF: AUTHOR

Abstract

In this process, tin is codeposited in an electroless nickel plating bath to improve the solderability of the nickel, particularly after the nickel has been subjected to a heat treatment.

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Electroless Nickel Tin Process

In this process, tin is codeposited in an electroless nickel plating bath to improve the solderability of the nickel, particularly after the nickel has been subjected to a heat treatment.

Phosphorous is codeposited with nickel in the conventional electroless deposition of nickel if hypophosphite is used as the reducing agent. For example, in using a typical ammoniacal nickel bath with a pH of 9 to 11 for selective plating of molybdenum pads on ceramic modules, a deposit of approximately 3.5% by weight of phosphorous is obtained. When the resultant nickel plated pads are heat treated, typically at 680 to 750 degrees C in a forming gas, the phosphorous tends to migrate to the surface of the nickel plate making the nickel surface very difficult to solder. It is, therefore, desirable to keep the phosphorous content as low as possible in the nickel plated areas.

Codeposition of tin in a nickel plating bath can be achieved by the addition of sodium stannite to the solution. For example, in a nickel plating bath containing
0.113 mole nickel sulfate, 0.235 mole sodium hypophosphite, 0.115 mole sodium potassium tartrate and 0.885 mole sulfuric acid, 20 milliliters of a 0.1N sodium stannite solution can be added to one liter of an electroless bath. Ammonia is added to bring the pH value to 9.

When a copper strip was dipped in a 0.1% PdCl(2) solution, rinsed and dipped in the above-described solution at 5O degrees C for 23 minutes, the plate o...