Effect of temperature and humidity cycling on FR-4, BT, and CE PWBs

EFFECT OF TEMPERATURE AND HUMIDITY CYCLING ON FR-4, BIS-MALEIMIDE TRIAZINE, AND CYANATE ESTER PRINTED WIRING BOARDS Mary J. Li, Kamran Gohari, and Michael Pecht CALCE Electronic Packaging Research Center University of Maryland College Park, MD 20742

ABSTRACT

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.