EFFECT OF VOLATILES FROM ENCAPSULANTS ON DELAMINATION

摘要

Plastic encapsulated components contain organics which turn into volatiles during heat exposures such as during solder reflow or during environmental testing. Moisture turning to steam is not the only vapor released from plastics during solder reflow. With the push towards lead-free and higher reflow temperatures, the identity and the understanding of these volatiles would be of interest so as to improve manufacturing yields. Some of the vapors evolved during eutectic and lead-free solder reflow profiles of mold compounds are identified in this paper. At eutectic reflow peak temperatures of 220℃, Epoxy Novolac mold compounds will release gases like carbon dioxide, moisture, methyl alcohol, benzene, isobutyl methyl ketone as the residue solvent, triphenyl phosphine and N,N-dimethyl benzenemethanamine from the catalyst, and sometimes siloxanes from stress releasing agent. Some of the more dominant vapors include triphenyl phosphine(TPP) and triphenyl phosphine oxide(TPPO), water and methyl alcohol. Also, it was found that temperature ramping rates affected the rate of gases released. There was not a substantial difference in the composition of gases released for mold compounds between eutectic solder reflow temperatures and for the higher temperature of 260℃ for lead-free reflow. As expected, much less gas was released if the mold compounds were postmold cured for 4 hours. Gas evolution from polymer during heat exposure is inevitable, however, understanding evolved gas behavior can help reduce the amount evolved such as through proper material selection, post-curing and slower ramp-up, consequently this will improve adhesion variability and pop-corn susceptibility.