Underfills alternates

Alternate approaches that eUminate the capillary-flow underfill process currently used by electronics assemblers, involve pushing the problem back to the wafer stage. One process, wafer-level underfill (WLU) (Figure 5.12), consists of applying the underfill material to a bumped wafer and then B-staging the underfill. The wafer is then diced and the die are positioned on corresponding connection pads on an interconnect... 

During product test and some field conditions, the solder is subjected to temperature extremes of — 55°C to 150°C or higher. These temperature cycles result in the imposition of large cyclic stresses and strains that cause the solder to fail due to complex interactions of creep and fatigue fracture mechanisms. If a chip underfill is employed, the critical interfaces between the underfill and chip and chip carrier are subjected to high alternating stress that can cause fracture, especially in the presence of impurities and contamination. 

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