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December 2003

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DesignerCouncil <[log in to unmask]>
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Designers Council Forum <[log in to unmask]>, "Kowalewski, Andy" <[log in to unmask]>
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Wed, 10 Dec 2003 11:46:03 -0600
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Chris Robertson <[log in to unmask]>
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Chris Robertson <[log in to unmask]>
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Lockheed-Martin
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I wanted to point out that many (maybe most) designs I saw come in
didn't specify external plating or hole plating. Manufacturers can very a good
bit on their default plating thickness.
If you specify 1 oz external copper, you may get .5oz starting copper and
.5 oz of plating or some variation.
Regardless of specs noted, manufacturers can plate holes at varying levels
Unless you specify the external plating, which is nearly the same as the
hole plating or visa versa, you don't know what the manufacturer will drill.
So be warned if you want to do current calculations then you had better
specify hole plating or external plating.

  ----- Original Message -----
  From: Kowalewski, Andy
  To: [log in to unmask]
  Sent: Wednesday, December 10, 2003 10:39 AM
  Subject: Re: [DC] Manufacture adjusting Gerber's


  It's to do with the plating of the barrel in a multilayer board.

  When the hole is drilled, the external surfaces have complete copper
  coverage and so the annular ring isn't evident until after imaging and
  etching. Hence you can add the thickness of the plating to the pad size
  for an annular ring requirement.

  On the inner layers, imaging and etching have already been completed so
  when the hole is drilled, it needs to 'see' enough copper around the
  hole so that the plating of the barrel makes good contact to the
  innerlayer pad. That hole size is the drilled hole, but the final hole
  size is the one specified by the designer and relies on an oversize
  drilled hole to be plated up. So the annular ring is specified 'worst
  case', which is before plating.


  Andy K.
  Sychip Inc
  Office (972) 202 8852

  -----Original Message-----
  From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Stan
  Radzio
  Sent: Wednesday, December 10, 2003 10:34 AM
  To: [log in to unmask]
  Subject: Re: [DC] Manufacture adjusting Gerber's

  Gary,
          I was following you right up to the point where you said "for
  inner layers".  I don't mind looking like an idiot asking questions that
  are obvious to everyone else.  Could you explain why you are using the
  drill hole size versus the finished hole size on inner versus outer
  layers?  Said another way: what is the manufacturing process that you
  are accommodating with this design decision?

  Thanks,
  -Stan


  -----Original Message-----
  From: Gary Ferrari [mailto:[log in to unmask]]
  Sent: Tuesday, December 09, 2003 5:12 PM
  To: [log in to unmask]
  Subject: Re: [DC] Manufacture adjusting Gerber's


  Ted,

  The board fabricator always drills with a larger drill bit to compensate
  for shrinkage of the laminate. This is why the designer uses the drilled
  hole size when calculating lands for inner layers. The finished hole
  size is used for calculating outer layer land sizes.

  The board fabricator is not requred to automatically adjust
  inappropriate spacing.  They usually will contact the designer and
  explain the problem. That is, if you use a decent board fabricator.

  Regards,

  Gary

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