From: Paul M Fly

Hi all,

  When we still did our own assembly "in-house" we did as Mike described.
The via was tented
on the side of the board the BGA was soldered on, and left untented on the
bottom to allow test
probes to make contact.

  Now we work with a contract assembler who does not want us to tent vias
under a BGA. They
claim to have seen this practice cause defects in the past. They will allow
us to have soldermask
extend onto the via pad, but it is not supposed to cover the drilled hole.

  As far as I know we never had problems with tented vias under BGA's when
we did our own
assembly, but working with a contract manufacturer has changed lots of
things including this.

************************************
          Paul Fly

Eastman Kodak Company
Engineering Technology Center - PEDT
2nd Fl.  Bld. 205  K.P.
2400 Mt. Read Blvd.
Rochester, New York 14650-3007
Phone: (716) 726-5670
Fax: (716) 726-0275
E-mail: [log in to unmask]
************************************





"Hiteshew, Michael" <[log in to unmask]> on 04/19/2001 01:08:31 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Hiteshew, Michael" <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: Paul M Fly/243609/EKC)
Subject:  Re: [TN] Vias under BGA's - Tented or Not??




Rick,
 We've been using BGA's for about 3 years. When we started, we queried
other
divisions advanced packaging groups for guidelines. They suggested tenting
vias on the top to prevent bridging. We left the vias untented on the
bottom
to allow test folks to probe them. Our boards are IR. reflowed. We've never
experienced any problems as far as I know.

Michael Hiteshew
Lockheed Martin NE&SS Marine Systems
410-682-1259

> ----------
> From:         Rick Thompson[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Rick Thompson
> Sent:         Thursday, April 19, 2001 10:46 AM
> To:   [log in to unmask]
> Subject:      [TN] Vias under BGA's - Tented or Not??
>
> Hi,
>
> We're running several designs from a new customer with multiple BGA's.
The
> boards are laid out such that the vias under the BGA's are not soldermask
> tented on either side.  Our experience with this type of layout is for a
> greater tendency to bridge as well as requiring the bottom side to be
> masked
> prior to any wave solder operation.  The customer is resistant to
changing
> this layout but I'd like to get some other opinions.
>
> My questions are: What are others doing in terms of PCB layout of BGA's?
> Is
> the above layout common? What if any trends are there in the industry for
> these types of layout?
>
> Thanks in advance for any insights.
>
>
>
> Rick Thompson
> Ventura Electronics Assembly
> 2655 Park Center Dr.
> Simi Valley, CA 93065
>
> +1 (805) 584-9858   x-304  voice
> +1 (805) 584-1529 fax
> [log in to unmask]
>
>

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