Hi Emanuel,
i think what you are writing about here is a different issue than we
were discussing
i believe the discussion was about having the via inside the BGA pad
itself, not the 'dogbone' via typically used to fan out the BGA pad
this is often called 'via in pad'
if the via inside the BGA pad is small enough the solder paste will not
flow through it
the topic is at what size this is good practice
i would call what you describe here more something like 'bridging' than
'theiving'
i would yell at your fabricator
these days there is no room for sloppy solder mask registration
Dennis Saputelli
_______________________________________________________________________
Integrated Controls, Inc. Tel: 415-647-0480 EXT 107
2851 21st Street Fax: 415-647-3003
San Francisco, CA 94110 www.integratedcontrolsinc.com
Emanuel Zimmermann wrote:
Brad,
Since years we are using tented vias with drill (not final) sizes of 12mil
and smaller. Just lately we had the issue of tholder thieving on a board
below a 1mm BGA with vias between the balls. The manufacturer decided to
have a relatively large solder mask opening. He obviously needed this
large opening since the mask was displaced such that the wall of a via not
exactly centered between BGA balls was exposed on the side of the
connecting BGA pad resulting in no solder mask bridge between partially
tented via and connecting pad. This already was enough to cause solder
thieving! My experience is the opposite of what these articles state.
Regards,
Emanuel
---
MPL AG www.mpl.ch
Emanuel Zimmermann [EMAIL PROTECTED]
Manager R&D Phone: +41 56 483'34'34
Taefernstrasse 20 Fax: +41 56 493'30'20
CH-5405 Daettwil
---
[EMAIL PROTECTED] wrote on 08.12.2005 01:31:32:
Okay a lot of you out there have a lot more experience with BGAs and
micro sized devices than I have, I wanted to see if any of you have
heard of this issue. I know that I have only heard the opposite until
today.
What I was told today is that Linear Technology and some other
Semi technical articles are stating that for small vias (13mils or
smaller), one does not have to tent vias on BGAs or worry about vias
in pads because the hole is so small that it will not thieve solder
from the pad/joint. Now this goes against all I have ever heard
because all the talk of BGAs has always concerned themselves with
solder thieving from the pads and tenting vias/dogbones to stop
this. Now my thinking is that maybe that is old school and only an
issue on the larger/older BGAs where one may be using larger vias.
But with some of these new microBGAs you would be very hard pressed
to use anything larger than a 13 mil finished via hole. And with a
hole this small it is smaller than most solder paste balls and the
surface tension of the solder may restrict solder flowing into the
hole when it is reflowed.
Comments? Anyone confirm or refute this claim?
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
#14 - 1925 Kirschner Road,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
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