Study of thermally reworkable epoxy materials and thermal conductivity enhancement using carbon fiber for electronics packaging

Epoxy resins are widely used as the underfill materials for the integrated circuit (IC) chips for the reliability enhancement and as the binder of electrically conductive adhesives (ECA). However, cured epoxy materials are infusible and insoluble networks which is a problem for the repair of a printed circuit board assembly packaged with epoxy materials.; In this study, six diepoxides containing aromatic moieties and low temperature degradable linkages, secondary and tertiary benzoates, and carbonates, were synthesized and characterized. Underfills based on four of these epoxides were developed and evaluated respect to their properties and reworkabilility. One of the reworkable underfills was evaluated with the 85°C/85% relative humidity test as the underfill of several ball-grid-array components on a organic board, which showed a high enhanced reliability.; Underfill materials based on a synthesized bisphenol-A diepoxide were developed for the no-flow underfill process and were evaluated regarding the application on both tin/lead and lead-free solders. The latent curing mechanism of the catalyst and the influence of fluxing agents were studied. The reworkable underfills showed satisfying overall properties on both Sn/Pb and Sn/Ag/Cu solders.; A unique approach for solving the problem of low reliability of ECAs was demonstrated. Small amount of sacrificial metal and alloy powders were added in silver flake based ECA and applied on six pad surfaces. The aging of bulk resistivity and contact resistance of ECA/metal surface pairs were studied and two alloys stabilized the contact resistance on all tested metal surfaces.; The internal heat generation of IC devices quickly increases which leads to deteriorated performance and low reliability. The thermally insulating property of polymeric underfills make this even worse with slow heat dissipation. In this study, a carbon fiber of high thermal conductivity was used together with silica in epoxy underfill materials and a 300% enhancement was observed as compared to a 45 vol.% silica filled material with comparable storage modulus and electrical resistance.