Hi Ofer,
plug one side only and design the solder mask for the other side so that it
fully covers the annular rings of the vias belonging to the BGAs. As a
matter of fact, all you need is a small orifice that would let the air
escape. If the annular rings are covered, there is no risk for the solder to
be drained away from the joint.
And you will have to specify some tight tolerances to the solder mask
registration. Of course this could increase the price of the PCB, but with
such design you must always budget a few bucks more for manufacturing.
Regards,
Ioan
> -----Original Message-----
> From: Ofer Cohen [SMTP:[log in to unmask]]
> Sent: Tuesday, May 27, 2003 11:19 AM
> To: [log in to unmask]
> Subject: [TN] Plugging under BGAs
>
> Technetters,
> Most of our boards carry BGA (pitch => 1 mm). The finish is HASL, which,
> from various reasons, can't be changed. The general rule is to plug all
> the
> through-hole vias from the print side, apart of BGA locations, where the
> plugging is from the BGA side (mostly components side).
>
> In a new design, there are pairs of identical BGA-packaged components from
> both PCB sides, using the same TH vias. I have two options:
> 1. To select one side to plug (danger of solder balls under the BGA
> of
> the other side), or
> 2. Plug from both sides (danger of over-stress on the hole plating
> during the reflow, because of the air pressure inside the hole.
>
> What is your opinion?
>
> Regards
> Ofer Cohen
> Quality Assurance Manager
> Seabridge Ltd.
>
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