SIR or to give it it’s full title, Surface Insulation Resistance Testing, is a method used to characterise individual electronic production process chemistries, such as flux, resist, coatings etc., from an electro-chemical standpoint.
The method has been with us for many years but has seen many improvements as science research has developed. Measuring changes to the surface insulation resistance under conditions of heat and humidity determines the materials propensity to react when under electrification. Both surface (SIR) and sub-surface (CAF) effects measurements permit a determination of field reliability of the end product.
Latest developments show that this technique can also be used to characterise a production process, by measuring the same effects on the combined behaviour of the total assembly process and taking measurements at each “wet” chemistry stage: Solder resist, SMT adhesives, solder flux, solder paste, cleaning, conformal coating and so on.
Doug Pauls is an internationally recognised expert in this field and here explains the fundamentals.
27th May 2009