Mike:

We have seen poor developing leave SM residue on the pad, which can be/is plated over.  You leave SM residue on the pad, then bake it on, and it is extremely difficult to remove.

One answer to this, which is definitely a band-aid, but also good insurance, is to put an alkaline cleaner on to the pre-clean before plating to remove these residues.

This is a nice approach, but a lot of people are afraid of it, fearing attack on the SM.   Not all alkaline cleaners attack SM.... bet you can guess who offers an alkaline cleaner that is proof to attack on SM!

Rudy Sedlak
RD Chemical Company

Mike Wolf <[log in to unmask]> wrote:
We are experiencing some type of residue on PCB's with gold as a final
metal finish. The residue adversely affects wire bonding to the gold.
The residue is present on both in-house fabbed boards and outside vendor
fabbed boards. It appears to be related to the soldermask in that there
are recognizable patterns (bubbles maybe) in the soldermask, that are
visible in the residue on the gold.

An aggressive plasma cycle loosens the residue (does not remove) but at
same time attacks the FR4 & Smask. No amount of solvent cleaning
removes the residue. Nor does ultrasonics.

Our in-house fab is electro- Copper, Nickel, & Gold, I'm pretty sure
the outside vendors are using ENIG.

We vacuum bake all our bds as a precaution to avoid die attach
bleedout. Could this bring to the surface problems we might not
otherwise see?

Has anyone else seen this type of residue? Know what it is or how to
get rid of it/prevent it?

Michael Wolf
EH&S Manager
EVI Technology LLC
7138 Columbia Gateway Drive
Columbia MD 21046
Phone # 443-542-2826
Fax # 410-290-1925
[log in to unmask]
www.evitechnology.com

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