Micron copper needles prepared by electrodeposition for low temperature bonding

Abstract

The needle structure plays a key role in the new low-temperature bonding technology. A electrodeposition route was used to directly obtain large copper needles up to the micron size. The copper needle was hexagonal pyramid with (111) preferred orientation. In order to regulate the size and density of copper needles, the effects of various electrodeposition methods and additives were studied. The slower the sweep speed of linear sweep voltammetry, the longitudinal growth was much faster than lateral growth. And with the scanning interval lengthening, copper needles changed from needle-like to columnar and then into broccoli. When adopted the galvanostatic method or cyclic voltammetry respectively, copper needles became larger as the current density or the number of cycles increased. The higher the frequency in pulse method, the copper needles were no longer obvious. Accelerators can increase the nucleation of copper needles for higher density, while both inhibitors and levelers were detrimental to copper needles.