Ask the Experts
December 1, 2008
PCB Cleaning After Long Term Storage
We need to assemble fine pitch PCBs that have been stored for 5 years. Is there a method for cleaning them to improve solderablity?
The PCBs have hot air solder level with 63/37 solder finish. They are 4 layer .062 inches thick FR4 laminate.
Expert Panel Responses
63/37 HASL finish degrades with the growth over time of an intermetallic layer Cu6SN5. Usually the thickness of the HASL coating is enough to give good solderability for an extended period. If this intermetallic layer has broken through the surface then these boards will be difficult to solder.
As for cleaning, this will help in removing any surface contaminants along with the oxide coating which will help but won't solve the solderability issue if again the intermetallic layer has grown to the surface.
You can test this coating for solder and intermetallic thickness with a Sequential Electrochemical Reduction Analysis Instrument (SERA). Good luck.
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.
As a consulting service and test laboratory we get this question regularly. We have use a specific saponifier at 5% concentration to remove the surface oxides to improve solderability or we use a gas plasma treatment if the oxidation is not to thick. If you want to discuss details or our service to do the cleaning please contact me off line.
President/Senior Technical Consultant
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.