I accidentally sent the reply below without copying TechNet. Beg to differ
on below comments.
My Reply:
Pink ring is not a new problem. Check the literature for past articles.
Three that come to mind:
"Pink Ring: Beyond Surface Inspection," by Patricia Goldman (Enthone-OMI),
IPC Technical Paper # IPC-TP-741. (General discussion of causes and need
for complete process optimization)
"Mechanical Solutions to Pink Ring," by Glenn Heath (Tektronix/Merix), IPC
Technical Paper # IPC-TP-964. (comparison of drill geometries and effect on
pink ring - pretty interesting!)
"The Pink Ring Condition in Multilayer PCBs: an industrial collaborative
research programme," by S. Graham et al, published in Circuit World, Vol. 16
No. 4, 1990. (detailed, statistical treatment of causes and remedies for
pink ring - very good)
I have two of these. There are other papers, too.
P.S. - there is some pretty strong evidence that drilling does indeed
"cause" pink ring (at least start it), most likely by causing some vibration
and damage to the resin right around the hole being drilled. Read Glenn's
article!
Patty
----------
From: Lenny Kurup
To: mbyrne
Cc: TechNet; Miscantor
Subject: Re: Re[2]: Mechanism of Wedge Void Formation
Date: Wednesday, July 16, 1997 2:17PM
Hi Matt,
The problem of wedge void formation is, in most cases attributable to the
oxide process, little, if any blame can be ascribed to "shotty" drilling.
The oxide layer thickness is a key parameter to consider when trouble
shooting, as well as lamination settings such as shifts in planarity,
temp., pressure and even contamination issues, etc. Your description of
possible causes matches what we have experienced, and, corrective actions
have always resulted in process improvements. The pink-ring problem, indeed
only appears after wet processing.
Lenny Kurup
Technical Representative
EMX ENTERPRISES LTD.
On Tue, 15 Jul 1997 [log in to unmask] wrote:
> We found that a reduced oxide helped quite a bit. This means that
the
> inner layer processing is involved in the formation of wedge voids.
> I'll bet that lamination cycles can adversely affect the boards too.
> Drilling is, of course involved, & wet process brings out the defect.
>
> What problems do you have with reduced oxide?
>
> Matt Byrne
> HADCO-Owego
>
>
> ______________________________ Reply Separator
_________________________________
> Subject: Re: Mechanism of Wedge Void Formation
> Author: [log in to unmask] at SMTPLINK-HADCO
> Date: 7/15/97 06:37 AM
>
>
> wedge voids are usually a start of shotty drilling - then seepage of
solution
> through the voids and that solution then starts attacking oxide layer -
which
> inturn leads to pinkring. Dm will not make a difference - actually if
> drilling is still primary cause - will be the same or worse - since Dm is
> thinner coating. A reduced oxide layer can eliviate problem to a certain
> degree - but then - reduced oxide brings in a problem of it's own.
>
> regards
>
> Richard Fudalewski
>
> Atotech Canada
>
>
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