Underfill is a material used for filling the gap between a flip-chip and the PCB. Usually the material will be dispensed after reflow the solder joints. Driven by capillary force, it fills the gap and encapsulates the solder balls. No-flow underfills are a new technique to eliminate the time consuming flow and curing step of regular materials. These materials are dispensed before reflowing. The curing and soldering takes place at the same time in a reflow oven. As with all underfills, it is still almost impossible to rework a defective chip. The goal of our investigation was not to develop a re workable underfill material, instead to rework a flip-chip using an existing no-flow underfiller. We have been studied thermal, chemical and mechanical rework techniques. We have found a combination of thermal, chemical and a mechanical rework as a way to a successfully rework. But better results we got by using only a mechanical approach for removal of defective flip-chips. The poster presents the optimised process flow for a rework of flip-chips with no-flow underfiller.
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