Insulation-Resistance Measurements of Coated and Uncoated Printed Wiring Boards

摘要

Insulation resistance (IR) was measured between narrow spaced conductors on different types of printed circuit boards with and without polymer coatings. Measurement environments consisted of thermal cycling in a humid environment per MIL-STD-202/106, and room temperature with 5 to 100 percent relative humidity (R.H.). The variability of the IR of test patterns both within a board and between boards with the same coating, and the lack of consistent resistivity values, suggest that the measured IR in these environments is not inherent to the materials, but is related to the contaminates present on and in the materials. There was little difference in IR for different conformal coatings or laminate types or sources. Although the IR was found to increase significantly when a board was conformally coated, there was no coating type tested which could ensure a high IR. Porcelain enamel and multiwire boards had lower IR than conventional circuit boards. An association was observed between low IR and the tendency for dendritic filament formation between conductors in a 100 percent R.H. environment. (ERA citation 08:044453)