I had a BGA via-in-pad design a few years ago where the assembler used
kapton (or some heat resistant tape)
on the back side of the pads so the solder wouldn't flow through, worked
well.
Ken
__________________________________________
Kenneth Wood
Saturn PCB Design, Inc.
www.saturnpcb.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Tuesday, February 05, 2008 1:23 PM
To: [log in to unmask]
Subject: Re: [TN] Open via in pad - any success?
Wayne,
If I had blind vias and a choice, I would spec over-plated vias...
With small vias you can't guarantee that the plugging operation will not
entrap additional materials in the closed end of the vias..
Besides I would rather have a single point of failure instead of having
2...
Paul
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
Sent: Monday, February 04, 2008 6:59 PM
To: [log in to unmask]
Subject: Re: [TN] Open via in pad - any success?
Dwight-
What's the difference between plugging and filling?
I'd heard overplating the vias was recommended in this case because
there was a high chance of voids/outgassing to originate at the site of
the fill/plug. I keep wanting to try this technique beneath QFN parts
but my CAM artist keeps "accidentally" specifying the overplate!
Wayne Thayer
________________________________
From: TechNet on behalf of Dwight Mattix
Sent: Mon 2/4/2008 8:20 PM
To: [log in to unmask]
Subject: Re: [TN] Open via in pad - any success?
At 04:55 PM 2/4/2008, Ryan Grant wrote:
>Hi All,
>
>I just got told by a design engineer that LaserJet printers are built
>using via in pad where the via is NOT plugged. He claims the via is
>filled with solder first, then goes through the normal SMT process.
>
>He intends to use this to connect a BGA ball on one side of the board
>to a cap on the other side using an mechanically drill via that is not
>plugged.
>
>Before I call BS on this, and tell him "do not pass go until that via
>is plugged, flattened and plated over", has anyone been successful with
>a via in pad that is not plugged?
>If so, was it double sided?
>And, was one side connected to a BGA ball?
Yes, yes, and yes.
However as you might imagine, the devil's in the details.
Filled (not plugged) with matched CTE non-conductive epoxy (ie SanEi or
Peters) and planarized (ie flattened) makes life easier and with less
unintended consequences to manage. However, there shouldn't be a need
to overplate the via fill. Unless you're probing filled pads that's just
needless extra plating process and adds risk of via failures (expansion
lifts pad and cracks via at knee).
>Thanks,
>Ryan
>
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