More applications need microcontrollers to operate at higher temperatures. ICs must survive faster corrosion rate and higher stresses. Improving wire bonding, mold compound or package design requires engineering effort, long evaluation and cost. Because packages are already optimized, further optimization often does not yield the needed improvements. Without changing either chip design or the packaging, one can achieve high temperature reliability by protecting ICs with a gold, over passivation metal (OPM).
Low cost CMOS liquid crystal display driver ICs are plated with gold bumps at high volume. Similar gold plating process can be quickly and cheaply implemented over all microcontrollers. Between ICs to the electroplated gold OPM is a barrier metal that slows gold diffusion into aluminum and thereby increases operating life before Au-Al intermetallic wire bond failure. Reliability is improved 6x to 94x under different test conditions.
Ball bonding to gold pads are 10% to 40% stronger than onto aluminum pads. Furthermore, gold-gold mono-metallic bonds are ductile and can withstand stresses of extreme package reliability tests consisting of: AATC, MSL1 preconditioning, autoclave and then 190C HTB for 1000 hours. Ductile bonds can strain under mechanical stress and shock. Gold is resistant against corrosion such that packaged ICs survive reliability tests causing mold compound delamination and then moisture ingress from autoclave.