I've seen this problem with laminates and prepregs where there are "soda
straw" voids inside the glass bundles. We also call them silver streaks
because that's what they look like. Adjacent to a drilled hole they can be
difficult to differentiate from crazing but when they extend away from the
barrel for more than few mils, it becomes obvious they are more than damage
from the drill process. Our most recent occurrence of this problem was
traced back to a modification in the prepreg manufacturing process at our
supplier.
Mike McMaster
RF Product Engineer
Merix Corporation
503-992-4263
----------
From: Timothy Reeves [SMTP:[log in to unmask]]
Sent: Thursday, April 06, 2000 12:58 PM
To: [log in to unmask]
Subject: Re: [TN] Laminate porosity
Thanks Pratap,
that's just what I wanted to know.
Now, how does one verify poor glass treatment, and where is it
addressed?
The IPC-EG-140 has a test for organic content, but it must apply
only to raw
glass fabric. And, lastly, is that test an accurate gauge of
adhesion
performance, and do laminate manufacturers use it?
Tim Reeves
> ----------
> From: pratap
> Reply To: pratap
> Sent: Thursday, April 6, 2000 14:18
> To: TechNet E-Mail Forum.; Timothy Reeves
> Subject: Re: Re: [TN] Laminate porosity
>
> Timothy and Wang,
>
> Wicking has been seen time and again by board fabricators. The
following
> factors may affect wicking during PTH plating -
> 1. Adhesion of epoxy to glass bundles/fibers. silane treatment of
glass
> fibers may be poor.
> 2. Stresses during hole drilling. Shattering of glass fibers may
occur if
> speed and feed ratio is not balanced for the spceific
construction, drill
> diameter, type of material being drilled.
> 3. Aspect ratio of the hole being drilled.
> 4. Drill geometry also affects as to how cleanly the material is
being
> cut.
> 5. Smear removal may impact wicking depending upon how aggressive
the
> etchant is in attacking the epoxy.
> 6. Lamination process may also contribute depending upon the
quality of
> B-stage bonding layers, epoxy flow etc.
>
> A carefully look at the xsection may reveal where the wicking is
occuring,
> in bonding plies or the copper laminate ply. If in the bonding ply
area,
> then composite lamination/laminator need to be looked. But if the
copper
> laminate area shows wicking, then contact the laminate supplier
for help.
> But if the hole looks rough, first start with drilling process and
drill
> bit
> investigation.
> ----- Original Message -----
> From: "Timothy Reeves" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, April 06, 2000 10:55 AM
> Subject: Re: [TN] Laminate porosity
>
>
> > I am quite interested in this problem, too. We had two lots of
clad
> laminate
> > which suffered from quite a bit of haloing after it was drilled,
and I
> had
> > it tested for resin content and Tg by DSC. The results were OK.
I
> suspect
> a
> > problem with the glass treatment (I don't know what else to
suspect),
> but
> > don't know how to find out if this is the problem. The supplier
is large
> > (and shall remain unnamed) and is taking their time to give an
answer.
> Any
> > ideas?
> >
> > Timothy Reeves
> > ECD Circuit Board Division
> > 13626 South Freeman Road
> > Mulino, OR 97042
> > (503) 829-9108 (800) 228-8198 FAX (503) 829-5482
> >
> >
> > > ----------
> > > From: Wang, William (Suzhou Laminate)
> > > Sent: Thursday, April 6, 2000 11:31
> > > Subject: Laminate porosity
> > >
> > > I work for a copper clad laminate manufacturer. One of
our
> customer
> > > (PCB shop) has wicking problem for plated through hole. They
said they
> > > found
> > > "laminate void in glass fabric " by microsection. (They mean
the glass
> > > yarns
> > > are not wetted by epoxy resin, not void in resin after
lamination.
> Usually
> > > wicking is related to rough drill or over desmear process). I
made
> > > microsection by myself and make real good polish. After that I
believe
> the
> > > so called "laminate void in glass fabric" is the result of
poor
> polishing
> > > i.e. scratches. (My microsection can see a single yarn but
their
> > > microsection can't). I attached some detail dimension for your
> reference:
> > > Glass yarns diameter: 1080 (5 microns), 7628 (9 microns)
> > > Extect abrasive paper P1200 grit: grit size 10 to 20
microns,
> average
> > > 15
> > > microns
> > > Multipolish Al2O3: 0.05 microns
> > > Specification for laminate void is < 3 mil. (IPC-4101 &
> MIL-PRF-5510
> > > F).
> > > Our product is 5 mil laminate so the "laminate void will be
far less
> than
> > > 3
> > > mil.)
> > > My customer show us a article dated at August 1982 by PC
FAB,
> > > "Laminate
> > > Porosity Causes". But the pictures are too blur after copy
many times.
> The
> > > authors are J.F. Nejedlik and A.M. DeSantis.
> > > My questions are as follows:
> > > 1. Anyone has the experience of "wicking" or "blow hole"
due to
> the
> > > wetting problem of glass fabric?
> > > 2. Is microsection technic with 100 X to 200 X
magnification
> capable
> > > of
> > > tell the wetting condition of single yarn of glass fabric?
> > > Any inputs will be greatly appreciated!!!
> > >
> > > William Wang
> > >
> >
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