Phenolic formaldehyde(PF)and epoxy(EP)resins are commonly used in electronic packaging. In this paper, high-ohmic resistors(2.2 M?, ±0.5%,)with Cr-Si film were coated by PF/EP paint, and the resulting coated resistors were used for heat and humid(HH)experiments. The experimental results show that the corrosion of bandlike resistive films is selective and isotropic, and that the corrosion spots in resistive films all form along grooves and extend in the same direction. It is revealed that OH^- ions are generated due to the electrochemical reactions of resistive film in HH experiments, so a NaOH aqueous solution with pH about 10 was used to study the effects of absorbed water and OH^- ions on PF/EP polymer film. The results indicates that the color of some part on PF/EP polymer film changes due to corrosion, and that the corrosion part of the polymer film is easy to be peeled off. It can be inferred that OH^- ions generated in HH experiments may play a catalytic role in the chemical reactions between polymer film and the absorbed water, which accelerates the degradation of PF/EP protection film for a resistor.
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