The over bump applied resin (OBAR) process is a wafer-level underfill (WLUF) process in which a filled resin is applied over the bumps of a wafer, dried, diced into coated chip which are aligned and joined through a substrate resulting in an underfilled flip chip package. This process has been evaluated by IBM on several test vehicles in close cooperation with Henkel (formerly Abelstik) which developed a material specifically to fit this process. The critical steps to make this technology work are alignment of OBAR coated chip to a substrate, elimination of significant voids and formation of a fillet with appropriate shape and size. The reliability of the material was evaluated after capping and BGA ball mount through JEDEC level 3 pre-con followed by DTC (deep thermal cycling), T&H (temperature and humidity), and HTS (high temperature storage). While some difficulties still exist, the OBAR process has been shown to be a viable alternative to capillary underfill application.
By: Claudius Feger; Nancy LaBianca; Michael Gaynes; Steven Steen; Zhen Liu; Raj Peddi; Mark Francis
Published in: RC24851 in 2009
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