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|Evaluation of High Temperature Joining Technologies for Semiconductor Die Attach|
|Keywords: High Temperature Electronics, Sinterable Silver Bonding, Die Attach|
|The development of novel high temperature die attach methods for semiconductor packaging enables adoption of advanced electronic packaging concepts for harsh environments, giving unique opportunities for demanding industrial applications such as new controls and monitoring technologies for deployment of next generation engine and airframe platforms. Traditional die attach materials including lead solders and conductive adhesives cannot meet requirements of operation temperatures up to and exceeding 300°C due to their limited melting and glass transition temperatures (Manikam & Cheong, 2011). The Manufacturing Technology Centre Ltd (MTC) has evaluated high temperature die attach materials and processes for silicon and silicon carbide (SiC) semiconductors. Assembly processes were explored for bonding components with or without a back metallisation and with capability to support electrical back contact if required. Die attach methods evaluated include: 1) Sinterable silver materials for back metallised semiconductor components; 2) Silver glass for non-back metallised semiconductor components; 3) Gold-silicon near eutectic preform for non-back metallised semiconductor components. Two types of substrates were selected including high temperature co-fired ceramic (HTCC) packages and gold or silver plated Kovar substrates. Test assemblies were subjected to accelerated life tests consisting of thermal ageing at 400°C and thermal cycling of -40°C to 200°C. These tests enabled the evaluation of the die attach materials under accelerated conditions of use. Reliability performance of the die attach materials was assessed using visual and X-ray inspection, mechanical shear testing and microstructure analysis. For sinterable silver materials, the test assemblies constructed using HTCC packages showed no significant reduction in shear strength after 1,700 hours ageing at 400°C. However shear strengths of the test assemblies constructed using Kovar substrates reduced by 95% of the initial values after ageing at 400°C for 336 hours. All test assemblies showed no significant reduction in adhesion after thermal cycling of -40°C to 200°C for 1,000 cycles. In addition, no apparent difference in shear strength could be detected for sintered silver interconnection for gold and silver metallised semiconductor components. Gold-silicon eutectic bonding as performed using a near eutectic preform had limited performance as aged at 400°C. Silver glass test assemblies constructed using HTCC packages showed a 50% reduction in shear strength compared to the initial values after thermal ageing at 400°C for 1,000 hours. A similar reduction in adhesion was presented after thermal cycling of -40°C to 200°C for 1,000 cycles.|
|Siyuan Qi, Research Engineer
The Manufacturing Technology Centre Ltd