Zymet Inc. has introduced a reworkable edgebond adhesive, UA-2605, that improves thermal cycle performance of CBGAs and plastic BGAs. In one trial, UA-2605 tripled the 0°C to +100°C performance of a CBGA, to nearly 2500 cycles. Previously, an underfill was needed to achieve this level of performance.
Figure 1: Edgebonded CBGA.
The edgebond adhesive is much easier to process than an underfill. When applying underfill, the board is preheated to facilitate capillary flow, and multiple dispense passes are used to deposit sufficient material. With UA-2605, only four beads of the adhesive are required, one at each corner (Figure 1). There is no need to preheat the board, no need to wait for underfill flow, no need for multiple dispensing passes.
Figure 2: After removal of underfilled BGA, underfill residues must be removed.