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.
Specially formulated Panacol underfill and edge-bonding adhesives are designed for simplified removal when required. For easy identification, these removable adhesives fluoresce yellow under UV light despite their black coloration. The aim is to enhance process control, and improve reworkability and recycling opportunities in electronic equipment manufacturing processes.

Adhesive as underfill for flip chips on PCBs
The table below provides an overview of Panacol adhesives that are used as underfill.
To download the technical datasheets (TDS) please click on the adhesive name.
Adhesive/ Underfiller | Viscosity [mPas] | Base | Curing* | Properties |
---|---|---|---|---|
Vitralit® 2655 | 150-300 | epoxy |
UV secondary heat cure |
flexible capillary flow high ion purity |
Vitralit® 2667 | 3,000-5,000 | epoxy |
UV secondary heat cure |
Low thermal expansion low ion content No outgassing |
Structalit® 5751 | 200-500 | epoxy | thermal | Black color, fluorescent yellow, jetable, low ion content, reworkable above 150°C |
Structalit® 8202 | 300-400 | epoxy | thermal |
Black, fast curing Capillary flow behavior Compatible with flux materials Low CTE, high glass transition temperature Low ion content (Cl- <900ppm) |
*UV = 320 - 390 nm