I should be able to make the pads 14.65mils wide at 0.5mm spacing to keep a
5mil pad-to-pad spacing right?

  _____

From: TechNet [mailto:[log in to unmask]] On Behalf Of Happy Holden
Sent: Thursday, June 22, 2006 1:35 PM
To: [log in to unmask]
Subject: Re: [TN] via-in-pad design



Hi Ken,
A 0.5 mm uBGA usually has ball and pad sizes of 0.175 mm to 0.3 mm
(0.007-0.012").  Normal mechanical drilling is FHS + 0.010".  Even a 6 mil
FHS leaves you with a 0.016" pad (0.41 mm) and this is usually to large for
a 0.5 mm uBGA and the spacing would be less than 0.094mm (0.0037").  This,
on top of the fact that filling a 6 mil through-hole is near impossible.  I
think that you have to go back and convince the customer that laser-drilled
blind vias is the only COST-EFFECTIVE way to do 0.5 mm uBGAs.
 If they have had a problem with reliability of laser-drilled holes in the
past - - that is another story!  There are plenty of PCB Fabricators that do
an excellent job with laser drilling - then there are others that do not do
a good job.  If you need a list of the top HDI fabricators, send me an email
and I will send you a list back, as well as references for reliability data
on laser blind vias that shows they are much more reliable than normal
through-holes (WHEN PROPERLY BUILT!).

Happy Holden
Asian Pacific Services








kwood716 <[log in to unmask]>
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06/21/2006 04:04 PM


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Subject
[TN] via-in-pad design






Hi all,
I have a PCB that uses a BRF6150 uBGA (0.5mm pitch) that I need to redesign.
The current design uses very small blind and buried vias
and the customer want to use through-all vias. The only way I can do this is
by utilizing a via-in-pad method. Is that still
a good option? maybe used with a via-fill goo?
Thanks
Ken

 _____


Saturn PCB Design
Kenneth J. Wood CID
2737 Bishop Lane
Deltona, Fl 32725
Phone: 407-340-2668
email:  <mailto:[log in to unmask]> [log in to unmask]


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