Microtech2010 2010

Advanced Virtual Qualification Methods to Reduce the Time-to-Market of Microelectronic Assemblies

M.H. Shirangi, M. Koyuncu, J. Keller, B. Michel
Bosch Mahle TS GmbH, DE

Keywords: interface delamination, moisture, plastic IC package, simulation


This work presents some recent progresses in reliability assessment of electronic assemblies in automotive industry and shows how coupled numerical-experimental techniques can help saving time and reducing the cost of IC package qualification. In order to fulfill the continuous trend in miniaturization of the electronic devices together with the demand to shorten the time to market, it is essential to use virtual qualification methods based on numerical methods. One of main concerns in electronic packages is the structural integrity of these devices during their fabrication, surface mount technology and service life. A prominent example of cracking in electronic assemblies is the interface delimitation between two dissimilar materials. This failure mode is accelerated when the polymeric materials absorb moisture in humid environments. Moisture results in degradation of material properties, induces additional deformation due to hygroscopic swelling and more importantly degrades the adhesion strength. The methodology developed in this study to investigate the interface delimitation between epoxy molding compound and the copper-based leadframe of a plastic IC package is as follows: 1. The process-induced stresses during the fabrication of the plastic encapsulated devices will be taken in to account. The method was previously benchmarked by comparing the warpage of a simple biomaterial beam with the results from Finite Element (FE) analysis [1]. 2. Next, the moisture absorption of the plastic package will be modeled by FE analysis. Several test specimens were used to investigate the diffusion of moisture in epoxy molding compound and novel simulation techniques were proposed and validated [2,3]. 3. The hygroscopic swelling of the polymers upon moisture absorption will be modeled. The value of the coefficient of hygroscopic swelling was determined experimentally and implemented in the FE code [4]. 4. The adhesion between the epoxy molding compound and leadframe was determined in terms of interfacial fracture toughness. Several test specimens, preconditioning and load setups were used to determine the toughness as function of temperature, moisture and mode angle [5]. 5. Finally the fracture mechanic method will be applied to analyze the interface reliability. The energy release rate will be compared against interfacial fracture toughness and the delimitation risk will be evaluated. This work provides conceptual understandings of the problem of moisture-driven interface delamination in plastic encapsulated microcircuits. In addition, it will be shown how the developed method can be used to select the materials more properly in order to improve the delimitation resistance in the package to preserve the package structural integrity.
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