Flip Chip Underfill

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

Adhesives that are used as underfill for chips are usually epoxy resins with capillary flow behavior. This means they flow easily into even the thinnest gaps and can therefore be applied quickly and easily. The use of dual-curing adhesive systems is most effective: the adhesive is cured in the edge area using UV light and thus fixed; the shadow zones under the component are then cured in a second step using heat.

Adhesive as underfill for flip chips on PCBs

Sustainable thanks to reworkability and recycling

Reworkability makes it possible to process, repair or recycle products after assembly. This point is becoming increasingly important for manufacturers of electronic components as legislation and environmental associations continue to drive forward the minimization of electronic waste. One starting point for sustainable strategies is the reworkability and reparability of individual modules on printed circuit boards to counteract the scrapping of a complete component or module.

Some underfill adhesives from Panacol are specially designed for this "reworkability": they can be removed again when exposed to temperatures above the glass transition range of 150°C. The epoxy resins adhere reliably up to this temperature and application range. Only above this critical temperature threshold is it possible to process the product. To make the adhesives easily recognizable, the black adhesives fluoresce yellow when excited with short-wave light.

A black, yellow-fluorescent underfill under normal (left) and UV light (right) in comparison