1. It is easy for copper foil manufacturer to achieve
the thickness requirement by adjust drum speed. The
problem here is the cost. Copper foil vendor sell
copper foil by weight rather than length;
2. May I know the test method you implied, by basis
weight or by micro-section?

Thanks and best regards
Shirley








--- "Mcmaster, Michael" <[log in to unmask]> wrote:
> Ed
>
> I don't interpret the values for starting thickness
> from Table 3-8 in IPC
> 6012A as "required" or "minimum" in anyway.  I
> interpret that column as only
> the nominal foil thickness.  You'd find it very
> difficult to find a board
> fabricator who could comply with those as minimum
> thickness requirements for
> the foil underneath the plating.  Here's why.
>
> The copper foil specification itself (IPC-4562)
> allows for a 10% variation
> in electrodeposited copper foil area weight.  So
> even though 0.5oz foil has
> a nominal thickness of 0.67 mils, it vary between
> 0.74 and 0.60 mils as an
> incoming raw material.  In reality, it's very
> difficult to find anyone who
> makes 0.5 oz foil that's at the nominal value.  Most
> foil fabricators
> intentionally skimp on the copper thickness to
> minimize costs.  We expect
> the foil receive to be below the relevant nominal
> thickness.  Processes such
> as preclean scrubs and microetches further reduce
> foil thickness.  That's
> why table 3-7 calls for a minimum finished 0.5 oz
> foil thickness (on IL) is
> only 0.47 mils.  It's expected that the processing
> of the boards will
> further reduce the copper foil thickness on both
> inner and outer layers well
> below the nominal thickness.  It's the minimum
> finished copper thicknesses
> from the right hand columns of Tables 3-7 and 3-8
> that are relevant.  If you
> really wanted a fabricator to comply with a minimum
> starting thickness of
> 0.67 mils for 0.5 oz copper, they'd have to use a
> thicker foil to achieve
> it.
>
> The good news is the foil thickness is relatively
> irrelevant.  The integrity
> of the copper plating is what really determines the
> reliability here.
> That's covered by the minimum  plated conductor and
> the through hole plating
> thickness requirements.
>
>
> > ----------
> > From:         Jack
> Crawford[SMTP:[log in to unmask]]
> > Reply To:     TechNet E-Mail Forum.
> > Sent:         Wednesday, September 19, 2001 9:52
> AM
> > To:   [log in to unmask]
> > Subject:      Re: [TN] External conductor starting
> thickness prior to
> > plating???
> >
> > >>> "May William D (Dean) CNIN"
> <[log in to unmask]> 09/19/01 11:17AM
> > >>>
> >
> > Reading from IPC-6012A, I noticed the required
> starting thickness of an
> > external conductor prior to plating for 1/8 oz
> base copper foil is 0.00020
> > inches and the starting thickness for 1/2 oz base
> copper is 0.00067
> > inches.
> > Does anyone have an idea on how minimum starting
> thickness is determined
> > for
> > each weight of base copper?  If minimum base
> thickness is exceeded by
> > chemical milling and micro-etching processes, will
> it compromise board
> > reliability assuming that there is sufficient
> electroplated copper to meet
> > minimum total finished copper thickness? What
> possible problems may arise
> > if
> > these base minimums are exceeded?
> >
> > Thanks for your consideration!
> >
> > Ed McAtee
> > NAVSURFWARCEN
> > PHONE 812-854-3892
> > FAX 812-854-1174
> >
> >
> >
> >
> >
>
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