Stephen,
Just looking on the shape of interconnect,it looks,that the innerlayer is
not equally microetched comparing laminate side and prepreg side. It seems
to me,that on prepreg side the etching rate is higher.
What desmear process is applied? Permanganate is doing strange things with
acrylic adhesive in conjuction with different surface preparation before
lamination.
I would advice your friend to take a look on "regular" multilayer and than
ask himself what are the differences in process path ( laminating
conditions/drilling/desmear). The negative etchback is just result of
previous processes and to my opinion persulfate microetch has nothing with
the problem itself.
Edward


Edward Szpruch
Eltek Ltd
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel  ++972 3 9395050 , Fax  ++972 3 9309581
e-mail   [log in to unmask]

> -----Original Message-----
> From: Stephen R. Gregory [SMTP:[log in to unmask]]
> Sent: å ðåáîáø 09 2001 4:13
> To:   [log in to unmask]
> Subject:      [TN] Inner Layer Issues...
> 
> Hi Everybody!
> 
> I got a email from Rene Lopez who has a problem that want's looked at by
> the group. I've posted two pictures up on my web page at:
> 
> http://stevezeva.homestead.com/
> 
> Rene is having a bit of trouble getting posts from the TechNet, and I
> don't know if it's been solved yet, that's why I've included Rene's email
> address here, do a "reply all" so Rene receives your replies.
> 
> (Thanks Rene for being patient with me...) 
> 
> -Steve Gregory-
> 
> I've pasted Rene's email to me below:
> 
> Hi Steve, 
> 
> Here are the two pics of concern. These boards were processed thru a
> sodium
> persulfate solution for 45 seconds at 72 F. We know that if we reduce the
> time in
> solution we may have problems on the surface of the board/adhesion issue.
> 
> More time in solution may cause more negative etchback.The material next
> to the
> innerconnects is acrylic. Tank is agitated with enductors as opposed to
> air spargers.  
> 
> It also has good side to side mechanical agitation. Have tried running the
> tank with the enductors off and with them on with same results.
> 
> As noted on the pictures, there is some sort of rounding off of the
> innnerconnects.  Does anyone know what causes this and give some input on
> how it can be reduced or eliminated?
> 
> Any input from your peers would be of great help.
> 
> Thank you very much,
> 
> -Rene A. Lopez-
> 
> 
> 

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