Quite a few mechanisms have been advanced as possible means to improve CAF resistance, mainly glass finish and resin systems. While this testing has so far been able to confirm an impact from the glass finish on the magnitude of insulation resistance, the tests have also shown that resin systems have an even greater effect on the insulation resistance. The inability to produce actual CAF failure probably indicates that the CAF failures are perhaps more a product of the PCB fabrication process. The higher voltages and lower hole-to-hole spacings did not cause any reductions in time to failure or insulation resistance. To summarize, CAF enhancement solution lies in preventing the primary step of degradation of IR or debond-ing through: 1. Robust resin systems resistant to chemical attack. 2. Robust glass resin interface/robust finish. 3. Optimized drilling parameters and conditions. 4. Understanding and avoiding other fab-related causes such as thermal shock/stress. TARUN AMLA is director, operations specialty products with Isola Laminate Systems Corp. (La Crosse, Wl). He can be reached at 608-791-2317; tarun.amla@isolaag.com.
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