Pan Pacific Symposium Conference Proceedings


Authors: Mark T. McMeen and Casey H. Cooper
Company: STI Electronics, Inc.
Date Published: 1/31/2007   Conference: Pan Pacific Symposium

Abstract: As the electronics industry moves toward smaller form and fit factors, bare die of both actives and passives are being incorporated into package designs such as Multichip Modules (MCMs), System-in-Package (SiP), Chip-on-Board (COB), and emerging system-level designs such as imbedded die within the printed circuit board (PCB). These design efforts are to miniaturize the electronics system into the smallest form and fit factor assembly. This move to miniaturize pushes the electronic industry’s manufacturing processes and assembly techniques to the limit of process controls and thus necessitates the need to understand the applied stress and strain to these components. Material characteristics of die attach adhesive, used to mechanically couple the die to the substrate, are affected by adhesive selection and cure profile parameters. The ability to understand the stresses applied to the die during the assembly process, as well as the resting strain level and shear value after thermal cure, sheds understanding into which processes and material sets provide the desired attachment characteristics. The result of low strain levels at the die surface combined with high shear values maximizes the overall robustness of the package or circuit card assembly (CCA) and builds a safety delta into the electronics system. This paper will study the material characteristics, such as applied strain levels, during processing and after cure in order to maximize the overall robustness of a package or CCA design. The test protocol is designed to evaluate various die attach adhesives and their cure schedules with process variables such as cure time, cure temperature, and cure schedule type (e.g. single step or multi-step). This data set will capture micro-strain measurements during and after cure of the adhesive as well as the shear strength of the cured die attach adhesive in order to correlate which process parameters deliver the lowest strain gage levels and highest shear values at the die level after thermal cure. The analysis of correlating shear test data versus strain gage measurements as compared to adhesive selection and cure profile will provide the process engineer the necessary data to determine the optimal material set and cure profile parameters. Key words: Die Attach Adhesives, Strain Measurements, Cure Profile, Shear Test, Strain Gage, Material Characteristics

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