Thermo-mechanical Characterization of Electronic Packaging Materials

摘要

Cross-linked polymers are commonly used in the assembly of electronic packages.rnParticular examples are thermal interface materials (TIMs) used to diffuse heat from the device,rnand underfills (UF) that stabilize solder connections between the silicon die and the package.rnChallenges encountered with TIMs are related to their thermo-oxidative stability at userntemperatures and the resultant loss in mechanical properties. This adversely impacts thernreliability of the electronic packages. This paper will present representative case studies torndetermine thermal stability of TIMs in an oxidative, microprocessor environment, along with therndegradation of thermo-mechanical properties in use conditions. The study demonstrated thatrnthermo-gravimetric analysis could be used to determine degradation activation energies of phasernchange systems. Knowledge of activation energy in turn proved to be a valuable screening toolrnfor various materials, and as a predictor of reliable thermal performance. For gel type TIMrnsystems, thermo-mechanical characterization showed that the residual curing of the materialrnduring use compromised the strain to failure of the material, leading to poor thermalrnperformance. A second class of popular thermosets are UF. Underfills are in intimate contactrnwith the silicon die and as a result are continuously exposed to high temperatures. Consequently,rnthe thermal aging process changes the mechanical properties of these UFs, impacting theirrnperformance. We present a case study that shows the impact of high temperature dwell on thernability of the UF to relax stresses, and hence cause premature failure. The study found that for arntypical UF system, the ability to relax stress post aging diminished approximately 40% underrnnormal operating conditions, leading to premature fracture of the material and thus, packagernfailure. Using both case studies we wish to demonstrate how understanding the thermomechanicalrnbehavior of these cross-linked systems allows for design of robust electronicrnpackages.