National Physical Laboratory

Surface Insulation Resistance (SIR) measurement

Dendrites formation around cathodeDendrites formation around cathodeĀ 

During Surface Insulation Resistance (SIR) measurement, the electrical resistance between metallic conductors on a substrate surface is monitored when a voltage is applied. These results give a measure of the likely reliability of the circuit assembly in the field. The equipment at NPL can detect leakage currents approaching pA, and can log resistance values every 10-20 minutes over a 3-7 day test period.

In practice test coupons incorporating track comb patterns are used that are representative of geometries found the PCA, and manufactured using the process chemistries, such as flux, paste, cleaners, resists etc. which are to be characterised.

Failure modes such as dendrite growth and cathodic anodic filamentation (CAF) are detected in the testing.

Common applications:

  • Determining the potential effects of new chemical processes on PCA electrochemical reliability
  • Ranking potential alternatives for flux, paste, cleaning media, surface finish in terms of reliability performance
  • Qualifying individual flux, paste or resist products (IPC, ISO test standards)
  • Assessing cleaning process performance


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Last Updated: 25 Mar 2010
Created: 29 Jul 2009