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Ask the Experts

September 1, 2010 - Updated
August 29, 2010 - Originally Posted

Flux Cored Wire Solder Shelf Life

We have a quantity of flux cored wire solder that is beyond the manufacturer's expiration date. How can we determine if this wire solder is still usable? Is there any data that suggests using older flux cored solder will be detrimental to the reliability of the product being soldered?

J. B.

Expert Panel Responses

Cored wire solder is generally very shelf-stable. The core flux is a nearly solid material and therefore is not prone to reaction-related degradation over time in the same way that solder paste is. The biggest impact to the performance of cored wire throughout the shelf life (and potentially beyond) is related to the oxidation of the solder; this oxidation will cause the product to have less flow than would normally be expected. The reason for this is that the flux would be forced to overcome a greater amount of oxidation from the wire itself, leaving less fluxing activity to help the solder spread to the metalized surfaces. The presence of additional oxidation may be visible on the surface of the wire. You may find that the oxidized surfaces are only on the outer portion of the cored wire, meaning that you could unspool the wire until you get down to the less oxidized material. You can determine if the expired cored wire is still usable by simply trying it � and if you aren't getting the typical amount of soldering action (wetting speed, spread) that you normally expect, this means that the age of the cored wire could cause a performance issue. I have never heard of a reliability issue related to using cored wire past the expiration date of the cored wire. The caveat to that statement is that if the solder is excessively oxidized, the operator may feel forced to supplement the cored wire with more liquid flux than would be considered typical or acceptable. If excessive liquid flux is applied and not properly heated, a reliability issue may occur for that reason. Proper training of operators and discipline to use the proper amount of liquid flux is critical here.

Brian Smith
General Manager - Electronic Assembly Americas, DEK International

Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.

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