Greg, 

Even though it looks to me like you are a competitor as a proprietary chemistry distributor in Southern California, I will try to get you pointed toward an answer.? I will mix questions with suggestions . 

You say you can see this gold tarnish after etch, implying you can see it on the copper trace sidewalls before resist stripping.? Right?

I presume you have a mixed process between the cupric etch from your TriTek controller, and the Electrochemicals Cobra Bond supplied by another vendor.? There is more than one Cobra-Bond, and you should find out if that has some letter designations following the "Cobra-Bond".? From the Electrochemicals web site, I suspect that Electrochemicals formulates different organic additives with their various peroxide sulfuric oxide alternatives trademarked Cobra-Bonds. These organic additives are obviously stable in acid environment and probably woudl be stable in your cupric. 

You certianly could have a build-up of the organic adhesion promoter from Cobra-Bond.?However, I am surprised that the additive would not come off in the Cobra-Bond application line itself.? What does the account do with an inner layer that is poorly covered with Cobra-Bond - how do they re-work the layer to pass it down the line a second time?? Ask them and consult the data sheet for the Cobra-Bond used at the shop.? The interference you are seeing would prohibit Cobra-Etch re-work down that line.

Finally, to see if you have an organic build-up, you may want to run a solvent extraction and then Infra-Red spectrum analysis on fresh cupric chloride (no organics) and problem cupric chloride -should show extra IR peaks.? A simple immiscible solvent like choroform or carbon tetracholride should extract organics from the cupric.? If you really want to know what it is, let the solvent evaporate in a hood and run another analysis on the residue after solvent extraction. Finally, your customer may want to lock you and the Electrochemicals rep in a room, until you can decide between you what is really happening. 

Denny Fritz
MacDermid, Inc. 


-----Original Message-----
From: Greg Triggs <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, 22 Jul 2008 5:52 pm
Subject: [TN] Cupric & Cobra-Bond question



I have a customer who gets a gold tarnish on copper traces after cupric
etch. It is usually worst with higher weight copper, and looks to be
related to rinsing. The tarnish is not removed in the strip/rinse /dry
process after etch. When the tarnish becomes extreme it effects the
coverage of the Cobra-bond. The alkaline cleaner prior to the Cobra-bond
does not remove the tarnish. I'm trying the maximize the rinsing as much
as possible. I'm also thinking about upping the normality of the cupric
(currently .3). They also etch a lot of boards that been put thru
Cobra-bond to help with the adhesion of the dryfilm. This is a new
process. Would this cause a problem with the cupric? Any thoughts.
Thanks in advance.

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