[SI-LIST] Re: Vias on decoupling pads
- From: "George Tang" <gtang@xxxxxxxx>
- To: <vincenzo@xxxxxxxxxxxxxx>, <Raymond.Anderson@xxxxxxx>,<si-list@xxxxxxxxxxxxx>, "'Sol Tatlow'" <Sol.Tatlow@xxxxxxxxxxxxxxx>,"'Patrick Jabbaz'" <patrick@xxxxxxxxx>
- Date: Tue, 6 Apr 2004 22:54:51 -0700
One of the assembly house that we have been using informed us that they have
found a way to fill the via holes by reflowing the solder on a blank board
first. But this will only work for vias of discrete components and not
BGAs, since too much solder under BGAs can cause adjacent balls to short.
It seems that conductive via plugging is still needed for small pin-pitch
BGAs.
Best regards,
George
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Vincenzo Kreft-Kerekes
Sent: Tuesday, April 06, 2004 9:41 AM
To: Raymond.Anderson@xxxxxxx; si-list@xxxxxxxxxxxxx; 'Sol Tatlow';
'Patrick Jabbaz'
Subject: [SI-LIST] Re: Vias on decoupling pads
Is there a critical aspect ratio for drilled through vias at which the
solder wicking becomes self-limiting to get an "auto-plugging" effect or
would the via diameter have to be so small that it won't even plate? And I'm
assuming there's not much point in first reflowing the board without
components to fill the vias, i.e. plugging for the resource challenged?
Best,
Vincenzo
-----Original Message-----
From: Ray Anderson [mailto:Raymond.Anderson@xxxxxxx]
Sent: Tuesday, April 06, 2004 12:00 PM
To: vincenzo@xxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Vias on decoupling pads
Vincenzo Kreft-Kerekes wrote:
> I've always wondered about this, from both the design and manufacturing
> standpoint, how is a via-in-pad any different from a via with a
non-circular
> capture pad? Why would you use a microvia instead of lets say a 14 mil via
> in the center of a 40x40 mil 0603 pad which would practically be a large
via
> capture pad with corners? Why would a fab house worry about the shape of
the
> capture pad, they don't seem to handle octagonal capture pads for through
> hole vias differently? Or plane stitching vias with practically board size
> capture pads? Thanks a lot for your help.
>
> Best,
> Vincenzo
>
The issue is with the solderability of components to the pads after the
bare pcb is fabbed.
If the via hole is too big or unfilled, your solder may wick down the
hole causing insufficient solder on the pad.
-Ray
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