An experimental investigation was conducted to study potential degradation characteristics of FR-4, bis-maleimide triazine (BT), and cyanate ester (CE) printed wiring board materials subject to four thermal cycling experiments, including 25 to 85° C temperature cycling, 25 to 150° C temperature cycling, 25 to 200° C temperature cycling, and combined temperature/humidity cycling of 25° C/20% relative humidity to 85° C/85% relative humidity.  Environmental scanning electron microscope (ESEM) photography was used to study degradation effects.  Resin/fiber interface debonding was observed. Primarily on the edges of the glass-fiber bundles.  Explanations involve the moisture sorption of epoxy, the mismatch of the coefficient of thermal expansion of the epoxy-resin and glass-fiber, and the geometry of glass-fiber bundles.
 

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