It has been reported by several laboratories that the time to delamination or decomposition of a printed circuit board specimen at 260°C decreases with the specimen thickness. A temperature gradient across the thickness of the sample within the furnace of the Thermomechanical Analyzer (TMA) was the suspected cause. Testing laminate specimens with embedded thermocouples, the temperature gradients within two major brands of TMAs and at several laboratories was determined to be approximately 2.5 to 3°C per millimeter. This temperature gradient results in a 20°C difference between the top and bottom of a 7 mm thick specimen. Modifications of the T_(260) test parameters, such as thermocouple location during the test and thermocouple calibration procedure are recommended.
展开▼
