There' s some validity to what they are asking.  If some of the vias are
isolated in the design, they can be high current density areas and end up
with more copper plating in the barrel.  Increasing the pad size would
reduce the local current density and the amount of plating.  Larger pads
might also allow for slightly thinner HASL deposits since the wetting area
is larger.

There's also a possibility that with larger pads they can bump up the drill
size, though if you already have a 12 mil annular ring that shouldn't be a
problem.

> ----------
> From:         Elensky, Richard[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Monday, January 07, 2002 1:52 PM
> To:   [log in to unmask]
> Subject:      [TN] PCB Fab Question
>
> Good Day to all,
>
>         My PCB fab house has been trying to correct an issue regarding the
> finished size of a PTH.  In our discussions, they mentioned an item I
> don't
> quite understand and thought I would utilize the vast knowledge of forum
> to
> get an Educated opinion... (I understand the risks involved with that
> method)
>
> We are using HASL finished boards, 8 layers, .125" thick.  Nothing too
> wild
> there.
>
>         The fab house stated they could better control the tolerance
> (+.003
> / -0) on a PTH if the annular ring were larger.  The current ring is about
> .012" larger than the radius of the hole (.213).  They wish to increase
> the
> ring by .010" to.015" as a means of controlling the amount of plating
> applied to the inside of the PTH.
>
>         Is this possible??  Does the annular ring have that much control
> on
> the amount of plating applied to the barrel of the PTH?  Are they blowing
> smoke to cover a process related issue?
>
> Thank you for your interest.
>
> Rich
>
>
> Richard Elensky
> Sr. Manufacturing Engineer
> [log in to unmask] <mailto:[log in to unmask]>
>
> Tel:  559-292-1111  x246
> Fax:  559-292-9355
>
> Dantel
> 2991 North Argyle Ave.
> Fresno, CA, 93727
> Visit our web site at:
> http:// www.dantel.com <http://www.dantel.com>
>
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