Flip Chip Underfill

Underfills are used for mechanical stabilization of flip chips. This is especially important when soldering ball grid array (BGA) chips. To reduce the coefficient of thermal expansion (CTE), the adhesives are partly filled with nano fillers.

Adhesives used as chip underfill have a capillary flow behaviour for quick and easy application. Usually dual-curing adhesives are used: the edge regions are fixed in position by curing with UV light before the shadow zones are cured thermally.

The table below provides an overview of Panacol adhesives that are used as underfill:

Adhesive as underfill for flip chips on PCBs
Flip chip underfilling

Adhesive/Underfiller Viscosity [mPas] Base Curing* Properties
Vitralit® 2655 150-300 epoxy UV
Vitralit® 2667 3,000-5,000 epoxy UV

*UV = 320 - 390 nm