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Addressing Flux Corrosion and Reliability Concerns Early
January 28, 2014 |Estimated reading time: 1 minute
Flux corrosion is just one of the reasons an assembly might be rejected by the end customer or, worse yet, be returned from the field non-operational. Fortunately, there are steps that can be taken to minimize the risk of corrosion, even before the first component is placed.
Understanding how flux corrosion is assessed per industry standards is an important first step in selecting the correct flux-containing products for the assembly process. Additionally, understanding the different types of flux corrosion is useful in determining the best way to minimize the flux’s corrosive effects, which can be assessed using actual process chemistry on dummy circuits through testing that is termed “assembly process validation testing.” And what better way to avoid field failures than to learn from others’ mistakes? The following three case studies will provide steps for assembly process improvement.
There are two types of corrosion associated with fluxes, chemical and electrolytic. By definition, chemical corrosion is a process in which a solid, especially a metal, is eaten away and changed by a chemical action. Electrolytic corrosion, on the other hand, is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact in the presence of an electrolyte.
Flux corrosion on electronic assemblies was assessed in the 1950s. Unfortunately, it is a failure mechanism still observed today. Initially, flux materials were qualified for use on military products per MIL-F-14256. These were the days of the RMA (rosin, mildly activated) and RA (rosin, activated) fluxes. The first IPC specification, IPC-SF-818, came along in 1988, followed by a standard that was accepted by multiple organizations. Given the joint effort, it was renumbered IPC J-STD-004 (J-STD = joint standard).Read the full article here.Editor's Note: This article originally appeared in the January 2014 issue of SMT Magazine.