Ask the Experts
December 1, 2008 - Updated
December 1, 2008 - Originally Posted

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
FCT Assembly
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.
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