Thermal modeling for warpage effects in organic packages

Abstract

Maintaining the integrity of the heat dissipation path for high end microelectronic devices has become increasingly challenging as the industry migrates from ceramic to organic packaging. Typically, flip chip organic packages undergo significant thermal and mechanical stresses throughout the manufacturing process, including chip join, underfill, encapsulation, BGA attach and card join. As a result of the mismatch of thermal and mechanical properties between the components, significant warpage is generated in the organic substrate, the chip, and the thermal interface material (TIM1) on completion of the assembly. Warpage affects not only the substrate coplanarity but also the thermal performance of the TIM1. At room temperature, the center of an adhesive TIM1 is under compression between the lid and chip while the corners and edges are under tensile stress. The effective thermal conductivity for the portions of the TIM1 under tensile stress can be significantly lower due to the elongation of the gap and the narrowing of the heat flow area. The present paper describes an approach to model the thermal performance of an adhesive thermal interface material taking into account the warpage effects and the inherent out-of-flatness in the heat spreader. Reasonable agreement is obtained between the modeling results and thermal measurements for a representative thermal test vehicle. The present modeling approach can potentially be used to optimize the component design and the bond and assembly process to achieve optimum thermal performance.

An efficient lid design for cooling stacked flip-chip 3D packages

“…In the model, a constant TIM1 resistivity is used across the chip area, while it is known that for organic laminate packages the TIM1 resistivity at the chip edge is higher due to package warpage and assembly reasons. This has been discussed in Wei [10]. The thermal resistance for the 2D package was found to be insensitive to the resistivity of all the other package components such as the underfill / C4, seal, or laminate, and hence these results are not shown for clarity.…”

A hybrid approach to characterization and life assessment of trilayer assemblies of dissimilar materials under thermal cycles

“…In addition, the material behaviours generally deviate from those of their generic counterparts as the result of their physical or metallurgical interconnection to neighbouring materials [23]. As such, relevant laws governing these behaviours are complex to prescribe [24]; related parameters are difficult to determine for a specific application [25], and book values of the properties as published, show wide ranges of variation [6,26].…”