As a micro-etch (either type) becomes saturated with copper, there is a 
tendency for it to redeposit copper sulfate crystals, especially when it 
hits a cold rinse.  These tiny copper sulfate crystals will cause dewetting 
in HASL. It is common practice to follow the micro-etch rinse with a 
sulfuric acid dip of 5-10% and rinse.  This redissolves the copper sulfate. 
 Another fix is to change (persulfate) or regenerate (peroxide-sulfuric) the 
micro-etch more frequently, to prevent copper buildup in the solution. 
 Also, maintain enough acid in the etch (see supplier) to keep the maximum 
amount of copper in solution.

Patty
 ----------
From: TechNet-request
To: TechNet
Subject: Re: HASL Microetch
Date: Thursday, September 26, 1996 1:30PM

     As a HASL service provider we see the entire gambit of solder mask
     residues.  We use a persulfate based etchant at a rate of 40-60
     microinches.  The trade off is that it is much more difficult to rinse
     than peroxide/sulfuric chemistries and can cause non-wets if not
     entirely removed before entering the HAL machine.


     Michael Holan
     Process Engineer
     Radian Electronics Div.
     [log in to unmask]


______________________________ Reply Separator
_________________________________
Subject: HASL Microetch
Author:  [log in to unmask] at INTERNET
Date:    9/26/96 12:57 PM


Does anyone have information, opinions or preferably data regarding micro
etching with persulfate vs sulfuric acid/peroxide chemistries? We are
currently using a sulfuric acid/peroxide based microetch at the HAL line, 
and
are considering alternatives. I have seen some information which suggests a
persulfate based chemistry is better at removing solder mask residues.  Any
feedback would be appreciated.

Jim Kenny

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