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Low Profile and Large Size WLCSP in IoT Applications
Keywords: WLCSP, low profile, Internet of Things / IoT
Recently, Wafer Level Chip Scale Package (WLCSP) Package is being rapidly adopted in Internet of Things (IoT) and consumer mobile electronics due to its low profile, small form factor and relatively easy assembly process. WLCSP with large die size becomes the trend in fulfilling high performance product demands. However, the solder joint reliability performances of WLCSP is the key challenge and becomes critical as increasing die size, especially the size is larger than 6 6 mm2. There is also growing interest in low profile WLCSP packages to less than 300 microns, especially when they are placed in a limited space inside IoT devices. Thin wafers are fragile and must be supported over their full dimensions to prevent cracking and breakage. An increasingly popular approach to thin wafer handling involves grinding and taping thin wafers with in-line machines. A specific carry tape have been also developed for transferring thin wafers after thinning. In this paper, WLCSP board level reliability for both large die size and low profile was studied, an 8 8 mm2 test vehicle used for the large WLCSP package testing has 350um ball pitch and fully populated array. Solder alloy, passivation thickness and redistribution layer thickness were explored for reliability enhancement. In addition to board level reliability test simulation and data collection, processing challenges were discussed, as well as processing solutions for thin wafer handling.
Tom Tang,
Siliconware Precision Industries Co., Ltd.
Taichung, Taichung

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