Device Packaging 2019

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Warpage Behaviors of System-in-Packages on a Substrate Strip
Keywords: System in Pacakge, Mold Compound, Warpage
Although System-in-Package (SiP) technology has been used for a range of electronic devices, the warpage behavior of the package can be difficult to control and predict due to complex manufacturing parameters, design rules, and material properties. Previous research on this topic primarily focused only on either strip warpage or on the unit package while the combination of these two different warpages has not been studied and seems almost to be completely ignored in the industry. In this paper, the impact of these two different types of warpage are considered and studied, both experimentally and numerically. The focus of the paper is to study the impact of epoxy mold compound, strip warpage, and how the locations of individual SiP packages on the substrate strip affect their individual warpage. An advanced material characterization method is also conducted to study the curing reaction and Pressure-Volume-Temperature-Cure (PVTC) kinetics of the package. The curing reaction of epoxy resins, as a function of temperature and activation energies, is experimentally determined. During the curing process, the viscosity of epoxy resins change with temperature and conversion rate. The Castro-Macosko model is adopted to describe the rheological properties of epoxy resins. After the device is ejected from the mold, a viscoelastic model is used to consider the shrinkage effect. Thermal and cure induced strains are calculated from the chemical volume shrinkage by PVTC model. The combination of the volume shrinkage data, which is measured by the PVTC Tester, with the DSC conversion data, is used to formulate the specified volume of resin. Experimentally, we have prepared twenty substrate strip samples with different component density, mold clearance and keep-out designs. Each substrate strip contains eighteen system-in-packages. The warpages of all substrate strips and all the unit system-in-packages were measured, compared, and correlated. We have found that the warpage data was impacted by the component density, mold clearance, and keep-out designs. There was a strong coupling of strip warpage and unit package warpage. Furthermore, the warpages of unit system-in-packages may vary according to their locations. In this regard, we propose a theory to explain the behavior. Besides the material characterization, a Finite Element Method (FEM) was developed to simulate the kinetic and viscoelastic behaviors of epoxy compound, and the warpages of strip and unit packages. The developed FEM considered the detailed transient kinetic reaction of epoxy mold compound during the encapsulation process. The paper includes a comprehensive study of the warpage behaviors of SiP units on a substrate strip. We will discuss the impact of geometries, densities, gaps and clearance of SiP components. Different mold compound materials will be characterized and used to check the impact of warpages. With the work described in this paper, we will provide a unique characterization and numerical scheme to better understand the warpage behaviors of strip warpage and unit package warpage, which may be crucial to manufacturing next generation SiP packages.
Eric Ouyang, Deputy Director
STATSChipPAC
Fremont, CA
USA


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