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.
Adhesive as underfill for flip chips on PCBs
The table below provides an overview of Panacol adhesives that are used as underfill:
| Adhesive/ Underfiller | Viscosity [mPas] | Base | Curing* | Properties |
|---|---|---|---|---|
| Vitralit® 2655 | 150-300 | epoxy |
UV thermal |
Flexible capillary flow high ion purity, |
| Vitralit® 2667 | 3,000-5,000 | epoxy |
UV thermal |
Low thermal expansion low ion content |
*UV = 320 - 390 nm