For as long as flip-chip technology has been around, under-fills have been necessary. Continually decreasing die thick-nesses and standoff heights have worsened the challenges associated with using underfills to the point where new processes must be investigated. Several creative approaches for using pre-applied underfills were presented at this year's Electronic Components and Technology Conference (ECTC). The biggest problem with dispensed underfill processes is low throughput. Dispensing the material at the edges of a die and waiting for it to wick underneath the die can be time-consuming. People still perform it because the processes are established, and there are some problems associated with pre-applied and no-flow processes. In some stacked-die applications, underfill is dispensed between the die after the stack passes some electrical tests, so the stack can be reworked more easily if necessary. Even with recent advances in dispensing and jetting technologies, pre-applied technologies still have a throughput advantage.
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