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January 2004

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Subject:
From:
Ted Stern <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 27 Jan 2004 13:35:05 -0600
Content-Type:
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Dear Ms. Smith:

In no particular order of probability, a few possible causes are as follows:

1.  Accumulation of leached photopolymer residue in the cupric bath,
particularly at the concentration of hydrochloric you are employing;
2.  Incomplete removal of photopolymer during develop; and
3.  Absorption by copper of a hydrophobic organic contaminant, sometimes the
result of excess, or improper type, of antifoam used when developing.

Some possible clues to determine to look for:

1.  The sticky residue you referenced is characteristic of photopolymer
leaching in the cupric etch, which is often black in color and has a gum
like texture.  Some photopolymers are more prone to leaching than others,
hence a change in photopolymer etch resist may give rise to a change in the
frequency of the problem.  You can recirculate the cupric bath through
carbon impregnated filters, which should remove the contaminant, to test
this possibility.  Be sure to be overzealous in quantity; i.e. 5 x 30"
filters for a 100 gallon bath.

2.  Etch a sample that has not had photopolymer applied to ascertain if
incomplete photopolymer removal prior to etch is the cause, or is
contributing to the observed excess copper.

3.  Copper is very oleophilic (oil loving), the absorption of which
significantly slows the cupric etch rate of copper.  If you see the problem
come and go, it could be related to the maintenance frequency (bath make-up
and replacement) of a previous process (typically developing); making the
assumption a new developer has no antifoam.  If you try suggestion 2. and
the sample etches clean, process a second non-photopolymer laminated sample
that has had antifoam applied to the surface.

Good Luck,
Ted Stern
HAWKINS, INC.


-----Original Message-----
From: Catherine Smith [mailto:[log in to unmask]]
Sent: Tuesday, January 27, 2004 12:15 PM
To: [log in to unmask]
Subject: [TN] Low level shiny copper spots after cupric chloride etching


Hello, can anybody help me please?  We are getting low level (up to 5
microns high) copper spots left on inner layer panels after the cupric
chloride etch.  It happens on most kinds of laminate.  We have put panels
through our chemical clean line and the etch only and the effect is still
there.  Leaving out the chemical clean line or pumicing the panels first
still leaves the spots.  The surface is shiny copper and sometimes there
appears to be some residue which we believe to be organic from a slight
carbon peak on an EDAX scan.  We found some sticky residue on the rollers
in the etcher which we removed, but the problem didn't go away.  We run at
4N HCl and 520mV, regenerating with hydrogen peroxide.
Has anyone experienced this before?  Did you discover where the organic
residue came from and the best way to remove it?

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