Method for enhancing the solderability of a surface

Abstract

A method for enhancing the solderability of a metallic surface is disclosed where the metallic surface is plated with an immersion silver plate prior to soldering, which immersion silver plate is treated with an additive selected from the group consisting of fatty amines, fatty amides, quaternary salts, amphateric salts, resinous amines, resinous amides, fatty acids, resinous acids, ethoxylated derivatives of any of the foregoing, and mixtures of any of the foregoing. The immersion silver deposits created are resistant electromigration.

Description

IN CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a division of application Ser. No. 09 / 821,205, filed on Mar. 29, 2001, now U.S. Pat. No. 6,544,397, which is a continuation-in-part of U.S. patent application Ser. No. 09 / 698,370, filed Oct. 26, 2000, now U.S. Pat. No. 6,444,109, which is a division of U.S. patent application Ser. No. 09 / 251,641, filed Feb. 17, 1999, now U.S. Pat. No. 6,200,451, which is a continuation-in-part of application Ser. No. 08 / 982,980, filed on Dec. 2, 1997, now U.S. Pat. No. 5,935,640, which is a division of application Ser. No. 08 / 621,098, filed on Mar. 22, 1996, now U.S. Pat. No. 5,733,599.FIELD OF THE INVENTION[0002]This invention relates generally to a method of treating a surface which treatment enhances the solderability of the surface. The method is particularly useful in the fabrication and assembly of printed circuit boards.BACKGROUND OF THE INVENTION[0003]Soldering is generally used for making mechanical, electromechanical, or e...

AI Technical Summary

Benefits of technology

The current invention introduces a better solderability preservative for surfaces, particularly copper surfaces. The invention proposes the use of an immersion silver coating which is more durable against electromigration compared to conventional deposits. This process provides a cost-effective and versatile way to preserve solderability on printed circuit boards and other areas of connection.

Problems solved by technology

Of the three soldering applications, making electronic connections is the most demanding.

In printed circuit fabrication, however, this method has several drawbacks.

The use of hot air solder leveling may cause unacceptably high rate of defects due to shorts, particularly when dealing with small circuits.

If plating is used, since it is not easy to selectively provide these areas with solder, all conductive areas of the board must be solder plated causing severe problems with the subsequent application of solder mask.

In addition the foregoing processes are inefficient and relatively expensive.

These processes work well but are time consuming and expensive.

Soldering directly to copper surfaces has been difficult and inconsistent.

These problems are due mainly to the inability of keeping the copper surfaces clean and free of oxidation throughout the soldering operation.

It has been found, however, that when the foregoing method is used the immersion silver coating has a tendency to develop outgrowths or filaments via an electromigration mechanism when the circuits are being used (ie. with voltage potentials present) in the presence of moisture.

The disadvantages of this method are the expense of gold plating as well as the necessity for additional process steps.

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