Lead-free flip chip: A comparison between lead-free solder and adhesives

As the time of the ban of lead-containing products in the electronics assembly industry comes closer, alternatives to replace the banned products are coming into place. This paper will describe the specific case of a flip chip on a printed circuit board where the standard lead-containing solder pastes will have to be replaced. Numerous alternatives have already been developed but the two main replacements, lead-free solders and adhesives, will be considered and compared with each other. For the first alternative, lead-free solders, a similar technology process flow as of the lead-containing process will be used but mainly focused on the bumping of the chips. The second alternative, adhesives, will use an original technology developed by IMEC to connect the chip to the printed circuit board. With this technology isotropic conductive adhesives will make the electrical connections, while non conductive adhesives will ensure the physical connection. After the description of both process flows, the results of electrical testing will be discussed in this paper.