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Method for enhancing the solderability of a surface
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a surface and soldering technology, applied in the direction of anti-corrosion paints, resistive material coatings, chemical vapor deposition coatings, etc., can solve the problems of inefficient foregoing processes, unacceptably high defects rate, and the most demanding electrical connection, so as to improve the resistance to electromigration and improve the soldering effect. , the effect of improving the resistan
Inactive Publication Date: 2014-12-23
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[0014]The current invention proposes the use of an immersion silver coating as an improved solderability preservative for various surfaces, particularly copper surfaces. Preferred compositions for depositing the immersion silver coating are also disclosed. The novel immersion silver plating process produces a silver plate which is more resistant to electromigration than conventional immersion silver deposits. The process proposed is a versatile, low cost method for effectively preserving the solderability of surfaces, particularly copper surfaces and areas of connection on printed circuit boards.
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.
Method used
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example i
[0044]IPC-B 25 test circuit boards were processed with the following steps:[0045]a). Acid Cleaner, 5 minutes, 120° F.[0046]b). Water Rinse[0047]c). Sodium persulfate / sulfuric acid microetch, 1 minute, 95° F.[0048]d). Water rinse[0049]e). Water rinse[0050]f). Immersion silver plate using the following composition
[0053]The circuit boards were then tested according to the Bellcore GR-78-Core (13.2.5, 13.2.7) standard test method and the results are recorded in Table 1.
example ii
[0054]IPC-B-25 test circuit boards were treated as noted in Example I except that in this case the immersion silver plating bath also contained 5.0 gr / l of tallow amine ethoxylated with 15 moles of ethylene oxide. The circuit boards were then tested according to the Belcore GR-78-Core (13.2.5, 13.2.7) standard test method and the results are recorded in Table 1.
example iii
[0055]IPC-B-25 test circuit boards were treated as noted in Example I except that in this case the immersion silver plating bath also contained 1.1 g / l of Pamak 25-S which is available from Hercules, Incorporated of Wilmington, Del. and is a blend of fatty and resinous acids. The circuit boards were then tested according to Belcore GR-78-Core (13.2.5, 13.2.7) standard test method and the results are recorded in Table 1.
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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 to electromigration.
Description
RELATED U.S. APPLICATION DATA[0001]Continuation of application Ser. No. 10 / 341,859, filed on Jan. 14, 2003, now U.S. Pat. No. 6,905,587, which is 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 application Ser. No. 09 / 698,370, filed on Oct. 26, 2000, now U.S. Pat. No. 6,444,109, which is a division of application Ser. No. 09 / 251,641, filed on Feb. 17, 1999, now U.S. Pat. No. 6,200,451, which is a continuation-in-part of application Ser. No. 08 / 982,980, now U.S. Pat. No. 5,935,640, which is a division of application Ser. No. 08 / 621,098, 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, electromecha...
Claims
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