There are several approaches to fluxing. The first approach is to dispense the flux, flood the chip site with the flux, and then place the chip down. A dipping method may also be used. It consists of dipping the die into a film of flux and then placing the chip onto the substrate. Introducing the low-solvent flux onto a rotating drum generates the film.
Doctor blades ensure a uniform thickness.
The presence of post-reflow residues is of major concern because of the subsequent interaction with the underfill. Even though flip chip has been in use for more than thirty years, it is considered an emerging technology. As such, new materials and processes are continuously being introduced into the marketplace. Underfill materials, for example, are being introduced that will combine the fluxing and underfill operation into one. Although limited in use because of reliability constraints, these flux encapsulant materials, as they are appropriately called, promise a significant cost improvement over existing underfill processes.