High Performance Anistropic Conductive Adhesives for Lead-free Interconnects

To improve the electrical property of the anisotropic conductive adhesive (ACA) joints, self-assembled monolayer (SAM) compounds are introduced into the interface between the metal filler and the substrate bond pad. The formation of the SAM on gold and silver and the thermal stability were investigated by measuring the contact angles of SAM compounds with a hydrophilic or hydrophobic tail groups such as octadecanethiol (ODT), mercpatoacetic acid (MAA), 1,4-benzenedithiol (dithiol) and malonic acid (Acid M) on Au and/or Ag surfaces. Epoxy resins with two different curing temperatures were used as polymer matrices of the ACA formulations. SAM treated ACA joints showed much lower resistance at the same applied current than non-treated joints, and the effect on the low curing temperature epoxy matrices was more significant. Nano-Ag filled ACA showed more significant improvement of electrical properties due to the more surface area and higher surface energy of nano particles and consequently the higher thermal stability with SAM