Uniform adherent palladium contact bump production - by electroless plating on aluminium conductor of semiconductor chip.

: Meyer, H.; Mahlkow, H.; Aschenbrenner, R.

Abstract
Electroless deposition of uniformly thick, adherent Pd contact bumps (preferably of at least 2 microns height) on the aluminium conductor structures of semiconductor circuit carriers involves subjecting the conductor structure surfaces to (a) cleaning; (b) treatment with an acidic Pd ion-containing activating solution; and (c) electroless Pd deposition from a bath of pH 4-7 (preferably 5.3-5.8), containing Pd ions, formic acid (or derivative) as reductant and a nitrogen-containing complex former for the Pd ions. Also claimed are otherwise identical processes in which treatment with an aqueous zinc ion-containing solution is carried out between steps (a) and (b) and/or the Pd contact bumps have at least 2 microns height. Further claimed are (i) a semiconductor circuit carrier obtained by one of the above processes; and (ii) methods of contacting semiconductor circuit carriers with hybrid circuit carriers by the flip-chip technique using Pd contact bumps produced by the above processes. USE - Especially for contacting semiconductor chips with hybrid circuit carriers (e.g. circuit boards) by the flip-chip technique. ADVANTAGE - The processes allow reliable and adherent deposition of uniformly thick Pd contact bumps on aluminium surfaces. The bumps can be deposited to e.g. 20 microns thickness inexpensively and without the need for masks, have high adhesion, do not form surface oxide films on storage in air (so that the additional thin gold layer, used for Ni bumps, is not required) and are deposited in a pH range which does not cause attack of the aluminium.