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Gold plating defects

2007

I'm a process engineer trying to determine the origin of gas plumes and surface cavitation on an aluminum electronics housing that has been nickel (100-300 micro)and gold (50-120 micro) plated. Part size 4.5x3.5x.59 6061 t6 aluminum.

I machine, ultra sonic clean Simple Green ⇦this on eBay or Amazon [affil links] ),glass bead, nitric acid etch, rinse in tap water then send to plater. Parts appear flawless under 10x microscope after plating. Parts are then secondary machined on top and bottom to remove plating only, alcohol is used during the milling process as a coolant. Part will then be vapor degreased ultrasonically in a bromathane solvent.

This process in designed to prep the part surfaces for feed-thru installation, using gold plated kovar feeds matched to gold/tin preforms (solder rings). I'm using a BTU 7 zone oven spiking the profile to 340 deg C.I use a nitrogen atmosphere with flux. After feed-thru
installation is complete the part is taken directly to an Ionix/ultrasonic cleaner. Then the parts are rinsed in DI water/ultrasonic and dried at 70degF.

My problem is that final inspection is finding small gas plumes at many of the small pores in the gold plating, along with small cavitations on top side of some of the pocket and channels inside the part

Can ya see any obvious flaws in my process? e.g., can't ultrasonically clean aluminum !
Thanks,

John Griffin
prcoess engineer - Chicopee