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July 1997

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Wed, 16 Jul 97 21:48:20 EST
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     Then again, the reduced oxide is supposed to be plain copper, isn't 
     it?
     
     
     Matt Byrne
     HADCO-Owego
______________________________ Reply Separator _________________________________
Subject: Re: Part II: Mechanism of Wedge Void Formation
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    7/16/97 07:59 AM


     Hi TechNet -
     
     There is a tool available that can very accurately measure both the 
     type and the quantity of copper oxide present on a surface in a 
     nondestructive manner - Sequential Electrochemical Reduction Analysis 
     (SERA). The ANSIJ-STD-003 PWB solderability committee recently 
     completed a gauge R&R study on several SERA equipments and is in the 
     process of submitting the test method for inclusion in the IPC-TM-650 
     specification. Although the 003 committee's focus is on solderability, 
     the SERA test method can also evaluate copper surface oxides. Contact 
     the folks at ECI Technologies (201-773-8686) for more information. Use 
     of this method could be used to eliminate the subjectiveness or as a 
     supplement to copper oxide identification by visual appearance.
     
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     
     
______________________________ Reply Separator _________________________________
Subject: Part II: Mechanism of Wedge Void Formation
Author:  [log in to unmask] at ccmgw1
Date:    7/15/97 5:14 PM
     
     
Rudy Sedlak mentions that a reduction in oxide thickness from black to 
brown to red in color assists in deterring wedge voids.
     
This trend could lead to a cosmetic difficulty.  Am I correct?
     
Matt Byrne states that reduced oxide helps:  Here I take this to be 
reduction from cupric to cuprous ions which Rudy Sedlak confirms.
     
Richard Fudalewski states that reduced oxide brings in a problem of its 
own, but I am uncertain which definition that Sedlak mentioned he is 
referring.
     
****
     
New question:  At what minimal thickness does one entertain cupric ion 
post oxide reduction with DMAB?  What are the trade offs cosmetically 
versus functionality (w.r.t. wv's)?
     
Again thanks,
Josep
     
P.S.  In direct answer to Byrne's question of reduction problem,  we see 
wv problems intermittently.  The goal is to strive for a cosmetic black 
coating.  Thickness entering DMAB is typically 0.28mg/cm2 (black not 
brown before immersion).  Acid resistance (10% HCl) is greater than 2 
hours.  
     
These wv issues are not related to layer counts.  I cannot as yet pin 
the mechanism down but have not ruled out materials such as prepreg.
     
I'd like to understand more about the contact mechanism of prepreg 
during lamination, whether other's verify Tg of lots, and if this has 
ever been an issue in wv troubleshooting.
     
[log in to unmask]
     
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