Surface insulation resistance explained
Surface insulation resistance (SIR) quantifies the ability of an insulating surface to resist current flow under applied voltage. SIR values typically range from megaohms to teraohms and decrease with contamination and humidity.
SIR is a key metric in assessing long-term reliability. It is used in qualification cycles to ensure assemblies remain functional over intended service life. Combine SIR data with ROSE and IC for a complete picture.
Measuring surface insulation resistance
SIR measurement principles:
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apply a fixed DC bias between tracks on a test coupon
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expose to controlled temperature and humidity
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measure resistance over time or detect failure thresholds
Standards define test conditions and coupon geometry. ZESTRON runs controlled SIR tests tailored to customer operating conditions to deliver meaningful pass/fail criteria.
Importance in PCB design
Designers use SIR data to:
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set minimum creepage and clearance dimensions
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choose conformal coatings and potting materials
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specify acceptable residue thresholds for manufacturing
SIR results feed back into processes, cleaning choices, and design decisions to reduce field risk.