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|Eutectic Zn-Al Die Attachment for Higher Tj SiC Power Applications: Fabrication Method and Die Shear Strength Reliability|
|Keywords: SiC, Zn-Al, Die attachment|
|SiC power applications, where small size, light weight, and cost effectiveness are key attributes, strongly require a package capable of withstanding higher junction temperatures (Tj) and greater thermal cycle (delta-Tj) stress. One of the most critical parts of the package is the die attach system because it is exposed to the same temperature as Tj. To date, die attachment systems such as eutectic Au-Si (m.p. = 363 degC) and Au-Ge (m.p. = 356 degC) have widely been used but unpromising in terms of cost. This paper comprehensively reports the fabrication method of a eutectic Zn-Al attachment system designed to provide long-term reliability over a broader Tj range by soldering SiC dies (2x2 mm2) with Cu foil on a SiN ceramic substrate. Four essential soldering conditions are presented and discussed for the formation of a strong and reproducible attachment. Die shear strength reliability data in the Tj range of 250 degC to 300 degC are reported here for the first time. Storage tests at 250 degC revealed that, after an initial slight decline, the die shear strength stayed virtually constant at a sufficient level (~115 MPa) for at least 2000 hours. Thermal cycle test results indicated that the attachments can withstand thermal cycle stress for 3000 cycles between -40 degC and 250 degC. The average die shear strength after 3000 cycles was 19.5 MPa, a value that is three times higher than the IEC standard of 6.2 MPa specified in Document 60749-19.|
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