Zymet Launches Reworkable Underfill Encapsulant for 0.4-mm Pitch POP Assemblies

EAST HANOVER, NJ -- Zymet has introduced a new reworkable underfill encapsulant, CN-1736, designed to underfill 0.4-mm pitch Package-on-Package (POP) assemblies. It has low viscosity and a lower CTE than its predecessors. Plus it has greater flux compatibility, making it suitable for use with a broader range of solderpastes and tacky fluxes.

With finer pitch devices, flow of an underfill is slower. To retain superior flow speed for 0.4-mm pitch POPs, CN-1736 has a viscosity of 650 cps, compared to 900 cps for its predecessor.

Also, finer pitch solder joints are more fragile and could be more susceptible to underfill-induced thermal cycle failure. Consequently, CN-1736 has been designed with a CTE of 55 ppm/°C , compared to 64-75 ppm/°C for its predecessors.

Rework is accomplished by use of elevated temperature, 170°C to 180°C, to remove the underfill fillet. Then, the BGA is lifted from the board after heating it to reflow temperature. Underfill residue is easily scraped off, again at 170°C to 180°C.