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Title: A comparative study of die attach strategies for use in harsh environments
Author: Moreira de Sousa, Micaela Filipa
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2012
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Well-logging and aerospace applications require electronics capable of withstanding elevated temperature operation. A key element of high temperature packaging technology is the Si die attach material, and a comparative study of two die attach systems for use in harsh environment has been performed. Die bond sample packages, using commercial adhesives and an Au-Si eutectic solder, have been manufactured and were subsequently thermally exposed for various times at 250 and 300°C respectively. The adhesive die bond packages comprised a high temperature co-fired ceramic (HTCC) substrate with W, Ni and Au metallisations whereas the Au-Si die bond packages used thick film Au metallised on a Al₂O₃ substrate. Optimisation of the eutectic die bonding parameters was successfully performed for the Au-Si system by an experimental design method, which improved mean and spread of maximum bonded areas and consequently, the shear load to failure. Bonded area was systematically assessed by scanning acoustic microscopy (SAM) followed by digital image analysis (DIA). Accelerated testing comprised thermal cycling and thermal shock and although showing some degradation, Au-2wt%Si die bonds were surprisingly robust, showing excellent subsequent stability during industrial device testing investigations.
Supervisor: Grant, Patrick ; Johnston, Colin Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Sciences ; die attach materials ; Au-Si eutectic ; high temperature electronics ; reliability