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.

graphical representation of a PCB flip chip with adhesive as underfill

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 (LVT, 25°C, Sp. 4/30 rpm) epoxy UV
secondary heat cure 		Low thermal expansion
low ion content
No outgassing
Structalit® 5751 200-500 (Rheometer, 25°C, 10s^-1) epoxy thermal Black color, fluorescent yellow, jetable, low ion content, reworkable above 150°C
Structalit® 8202 300-400 (Rheometer, 25°C, 10s^-1) 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