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June 2002

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Subject:
From:
"Tempea, Ioan" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 25 Jun 2002 08:32:50 -0400
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text/plain (244 lines)
Thanks for the insight.

So 1 mil is overkill, hehehe.

What about 2 mils tolerance for the registration? Is it standard stuff?

I am missing something here, the ganged openings. What is this, the absence
of the solder dams? If this is so, I have no problem with them, we
successfully build  a lot of boards with dams and lots of boards without
them.

It's just that I want to establish clear rules for our PCB designers and, in
my opinion, small things like registration, not forgetting about dams makes
them more involved in what they do. Pure psychological stuff. Of course,
this should not affect the costs.

Thanks again,
Ioan

> -----Original Message-----
> From: Mark Hargreaves [SMTP:[log in to unmask]]
> Sent: Monday, June 24, 2002 11:23 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Registration of soldermask
>
> Dougal,
> A little harshly stated perhaps, but this USA board fab agrees with your
> tolerance comment.  If used, I'd hope that tolerance would be limited to
> specific components.  Almost anything's doable, but +/- 1 would affect
> price
> and yield at our shop.
>
> Very little assembly experience here, so I can't respond to the soldermask
> dams comment, except to say that most of our customers require them, and
> sometimes relax registration tolerances rather than "ganging".
>
> Regards,
> Mark Hargreaves
>
>         -----Original Message-----
>         From:   Dougal Stewart [SMTP:[log in to unmask]]
>         Sent:   Saturday, June 22, 2002 7:30 AM
>         To:     [log in to unmask]
>         Subject:        Re: [TN] Registration of soldermask
>
>         Well, I'm impressed and I see why you USA board fabs stay in
> business ! Even
>         the best automatic printers with optical registration would find
> it
> hard to
>         achieve 0.001" positional tolerance - the heat from the lamps
> exposing the
>         artwork will make the artwork shift by more than this..... So, if
> this is
>         what you specify, you will have to pay the price, which is either
> scrap or
>         rework at the fab house, which they should add onto your board
> price, or is
>         absorbed by the fabricator, who then goes out of business trying
> to
> achieve
>         the physically near impossible. After that you will go to the far
> east for
>         your supply where they will ignore your requirement (sorry, not
> understand)
>         and you are back to having ganged openings or reduced pad width.
>         I have only come across one soldermask capable of achieving a
> soldermask dam
>         of less than 0.004", as normally the undercut will remove the dam
> if
> the
>         artwork is less than 0.006". To achieve dams on a 20 mil pitch
> device (which
>         is actually 19.685 mil), use a 10 mil pad, and just state that you
> require
>         solder dams.
>         Why don't you allow ganged openings - what part of your assembly
> process
>         can't you control? Is it solderpasting, position of paste screen,
> volume of
>         paste, or positioning of components?
>
>         Dougal Stewart
>
>         email:  [log in to unmask]
>         phone: +44 1896 822204
>         mob:    +44 7984 629667
>         ----- Original Message -----
>         From: "Greg Scott" <[log in to unmask]>
>         To: <[log in to unmask]>
>         Sent: Friday, June 21, 2002 11:19 PM
>         Subject: Re: [TN] Registration of soldermask
>
>
>         > Loan,
>         >
>         > What we do is design with 2mil per side opening with a solder
> mask
> note:
>         >      No finished solder mask over pad edge.  Annular ring of
> exposed board
>         material around pad edge to
>         > be .001 min, .003 max.
>         >      Maintain  a solder mask bridge of .004 min. wide between
> fine
> pitch
>         solder pads.
>         >
>         > Also the pad can not be wider then .012 with this approach.  Do
> not allow
>         for ganged soldermask
>         > relief.  We had all
>         > rework problems with that approach.
>         > Have not had problems since this note.
>         >
>         > Greg Scott
>         > Cray Inc.
>         > Seattle, WA.
>         >
>         > "Tempea, Ioan" wrote:
>         >
>         > > Hi technos,
>         > >
>         > > what would be a reasonable requirement for the registration of
> the
>         solder
>         > > mask on boards with 20 mils fine pitch having solder mask
> dams.
> We asked
>         for
>         > > 0.002" and it almost comes over the edges of the pads.
>         > >
>         > > Is 0.001" doable, with no impact on the price?
>         > >
>         > > Thanks,
>         > > Ioan
>         > >
>         >
>         >
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