As a partial reparation for my previous question today.
Please allow this rather esoteric/ but on topic question.
I was sending out a pcb that will have gold wire bonding pads.
It was a option at our board house. I got a call when I was requesting a quote.
"How thick do you want the soft gold bonding layer?"
"I have no idea." I said, which is my normal response.
"What's your "standard" thickness.?", I asked.
I was shifted to engineering. 30-50 micro inches was the answer, after a nice discussion.
(It's always a pleasure to talk with the engineer's.)
So that's what I ordered.
I could order a thicker layer.
Has anyone done this?
I'll be wire bonding soon, so I can let you know if it works.
Edit: Well I got the quote back and my jaw dropped. The price is more than $2k for a few pcb's. For that cost I could evaporate my own Ni and gold layers.
Edit 2: (Adding more to the question.)
So the reason for the high price is that the board house needed to send it outside for processing. I asked for quotes on their other types of Gold finishes.
The first is called Deep Gold. This is an electrolytic process and puts down 30 u inches of gold. (I don't know if there is any underlying Nickel.) This is also called hard gold and from limited reading I don't think it works for wire bonding.
The second is Immersion Gold. or ENIG and puts down 3-10 u in (75-250 nm) of gold over a thicker nickel layer. Again from limited reading it seems that one can not wire bond to this with gold. But maybe with aluminum. (Though there can problems with the Al/Au interface.)
And my final crazy idea is to make a mask for my pcb and evaporate my own Ni/Au layer.