Authors: Siew Kee Lee, You Chye How, and YS Khoo Company: Texas Instruments Electronics Malaysia Sdn. Bhd. Date Published: 10/13/2013
Abstract: Solder extrusion had been identified as one of the chronic issues that causes high yield loss in lead-free assembly processes of module package or System-In-Package (“SIP”) with integrated passive components and solder bumped IC components. This phenomenon occurred at multiple reflows during SMT process usually at 245oC to 260oC peak reflow temperature, where the solder bump of IC components in the module or SIP package was re-melted at 217oC solidus temperature for standard lead-free tin-based alloys and expanded in solder volume to extrude through weakest interface and cause solder bridging with adjacent bumps or I/Os. This had resulted electrical short or device functional failures. Despite the challenge to improve adhesion of the weakest interface to eliminate solder extrusion, another challenge is focused on the selection of best solder alloys which able to maintain in solid form without re-melting during SMT reflow process. Recently, high temperature solder alloys had gained strong interest among IC manufacturers to develop a robust packaging technology to serve the rapid growth on module or SIP packages. There are few candidates of high temperature alloys were offered by solder suppliers, e.g. gold-tin alloys (80Au20Sn), tinlead alloys (90–95wt.% lead), bismuth-based alloys and antimony-based alloy (90Sn10Sb), each will have its pros and cons for adoption to meet regulations requirement, package reliability and cost.
In this paper, Sn10Sb with melting temperature ranging from 242oC to 256oC was selected for this study. Sn10Sb solidus temperature was validated using DSC/TGA and real time monitoring of solder phase transformation during reflow process. Experiment was planned and conducted to study the impact of intermetallic compound (“IMC”) with different flux chemistries and under bump metallization (“UBM”). Reliability of SIP package with Sn10Sb bump as interconnect under quick reliability assessment was also being discussed.
lead free, solder extrusion, UBM, flux, DSC, reliability