What is SIR testing?
SIR stands for surface insulation resistance and measures the resistance between conductors on a PCB under defined environmental and bias conditions. SIR evaluates the electrical effect of residues over time and under stress, rather than just extractable amount. It is a more direct predictor of leakage, dendrites, and electrochemical migration risk.
SIR testing typically uses coupon boards with defined patterns and is run under humidity and temperature with applied voltage. Results show resistance degradation or pass/fail behavior, making SIR essential for validating cleaning processes and conformal coatings.
SIR testing methodology
Typical SIR protocol:
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Use standardized test coupons with grid patterns.
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Clean or contaminate coupons to defined levels.
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Apply DC bias across conductors and expose to temperature/humidity stress.
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Measure resistance over time and log any drop in insulation resistance.
SIR identifies threshold contamination levels that lead to failure and supports qualification of cleaning chemistries and coatings. ZESTRON performs SIR tests and interprets results to recommend corrective actions.
Importance of SIR testing
SIR testing is critical because:
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it reflects electrical consequences, not just chemical quantity,
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it reveals time-dependent phenomena like dendritic growth and electrochemical migration,
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it helps qualify processes, coatings, and assembly changes.
Manufacturers increasingly require SIR data for high-reliability products. ZESTRON integrates SIR testing into cleanliness qualification programs to ensure robust electrical performance.