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Process and Reliability Advantages of AuSn Eutectic Die-Attach
Keywords: eutectic die attach, wafer scale packaging, gold-tin solder
High-power semiconductor devices must be mounted using a robust die-attach material that can handle the temperature fluctuations generated by the chip and mechanical stresses due to CTE mismatches between the die material and the substrate it is mounted to. Traditionally, various die-attach products such as metal-filled conductive epoxies, high lead solders, and gold-silicon solders have been sufficient to mount the chip and have it perform reliably for the life of the device it operates. However, the trend of increasing heat generation, the demand for compact devices, the enactment of RoHS and REACH legislation, and the transition to GaAs chips, limits the use of conventional materials. The demand for high reliability in power devices in light of these industry trends has led engineers to evaluate various new materials for their die attachment. The use of a high temperature solder preform is proposed and demonstrated for use as a die-attach material in high power devices. The suggested solder preforms are eutectic gold-tin and may be implemented for high volume or lab quantity adoption using a Palomar Technologies’ Component Placement Work Cell. This equipment is capable of the complete die-attach process including high-accuracy pick-and-place of substrates, eutectic gold-tin preforms, and components, eutectic die attach, and pulsed-heat reflow using a computer controlled Pulse Heat Stage (PHS). Each of these steps is precisely controlled to offer a near void-free eutectic die attach between the device and its substrate. This is critical for thermal and electrical stability in high power applications. When the substrates, preforms, and components are supplied in high volume packaging, the assembly line can be fully automated, which enables a reduction in the cost of ownership and improves process yields. Assembly applications suited for this process include but are not limited to high-brightness LEDs, power amplifiers, LASER diodes, VCSELS, Lid Attach, MEMs, RF packages, IGBT modules and Wafer Scale Packaging. Keywords: Gold-Tin Solder, preform, automated pick-and-place, eutectic die attach, Wafer Scale Packaging, thermal conductivity, tensile strength, CTE, alternative die-attach materials
Amanda Hartnett, Applications Engineer
Indium Corporation
Clinton, NY

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