SMTA International Conference Proceedings

Thermomechanical Reliability of Low-Temperature Solder Alloys for Mid-Power Led Packages

Authors: Niveditha Nagarajan, Matthew Siebenhuhner, Nicholas Herrick, Ranjit Pandher and Carl Bilgrien
Company: Alpha Assembly Solutions
Date Published: 10/14/2018   Conference: SMTA International

Abstract: Low temperature solders used in package-level assembly (L2) enable lower cost production of LED packages, by utilizing a temperature hierarchy process (higher process temperatures for L1, lower process temperatures for L2). However, the thermomechanical reliability of low temperature solders has not been studied in LED package-attach applications. This paper will present a study of the thermomechanical reliability of three low temperature solders (all based on tin bismuth (SnBi)) when used for L2 interconnects, as compared to an industry standard SAC305 solder.

In this laboratory study, a statistically significant quantity of commercially available mid-power LED packages was assembled onto aluminum core and FR4 substrates using three SnBi alloys and SAC305, on standard SMT equipment (stencil printer and pick-n-place). Shear strength, junction temperature, luminous flux, efficiency and spectral emission were measured. The samples were put through thermal-cycling, for up to 2000 cycles to induce thermomechanical stress. Samples were then re-measured after every 500 cycles, to evaluate the level of degradation of the solder alloy. We will present the results of this study and discuss possible applications for the use of low temperature solder alloys in L2 LED assembly.

Key Words: 

Low Temperature Solder, LED, thermomechanical reliability

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