Reworkable rehealable packaging materials from the introduction of orthogonal dynamic covalent chemistries
As the physical complexity of multi-chip modules (MCMs) and demand for improved thermal management increases, traditional electronic packaging materials may reach fundamental limitations. For instance, capillary underfills when subjected to thermal stresses from typical operating temperatures are susceptible to fatigue, crack formation, adhesion loss and related failure mechanisms - all of which have significant consequences to package lifetime and performance. In general, packaging materials are complex formulations that includes: filler, matrix polymers, catalysts and adhesion promoters - however, the curing chemistry is reliant on irreversible bond formation (often thermosetting epoxy resins) where efforts are directed to minimize the rupture of these bonds. The incorporation of chemical moieties capable of bond formation under an equilibrium (e.g., reversible bond formation) provide access to macroscopic behaviors such as mechanophores, shape-memory behavior and autonomic self-healing, to name a few. By judicious selection of dynamic bonds multiple material responses can be generated by orthogonal stimuli. With an eye towards wide ranging electronic packaging applications, a dual responsive dynamic motif was designed, synthesized and incorporated into a material system that exhibits both autonomic rehealing properties, triggered by a thermal stimulus, and reworkability from a chemically triggered depolymerization. These are attractive properties for packaging materials as they can extend the lifetime of material, through damage repair, offer a pathway for improved yields and more complex MCMs through a facile chemical method of reworkability (e.g., depolymerization). This material system will be described towards its application as a capillary underfill.