Separation of the internal layers of a laminate or printed wiring board is commonly referred to as delamination. Caused by internal stress when the sample is exposed to heat, delamination results in a change in the sample dimension measurable by a Thermomechanical Anaylzer or TMA.
Time to delamination is frequently measured at 260°C, 288°C and 300°C. Referred to as T-260, T-288 and T-300, the tests measure a material’s ability to withstand temperatures which are utilized in producing printed wiring boards. The precise temperature control of the TMA allows time to delamination to be measured at any critical temperature.
IPC-TM-650 18.104.22.168 defines the parameters for time to delamination tests. This method allows the sample to be heated to the temperature of interest at either 10°C/min or 100°C/minute. While the slower ramp rate allows for the measurement of other parameters such as coefficient of thermal expansion and glass transition temperature, this method is not commonly used by Isola's Analytical Services Lab. The faster ramp rate decreases run time and provides results more representative of the thermal shock seen in the manufacture of printing wiring boards. Unless otherwise noted, time to delamination results reported by the Isola ASL are measured at a ramp rate of 100°C/minute.
Each material has a characteristic time when delamination occurs at a given temperature within plus or minus approximately 2 minutes. Factors that affect the time to delamination results can be under cure of the resin, poor interlaminar bonds caused by insufficient pressure during processing , low resin content and poor bond between the oxide layer of the copper and the prepreg. Preparation of the sample can also affect the result. The edges of the sample must be free from any internal cracking caused by cutting the sample. Therefore, time to delamination samples must be at least 16 mm by 16 mm to allow for removal of edge damage. The recommended sample size is 2 inches by 2 inches to allow for any necessary retests.