RE: BGA Assembly

[Peter Ross <peter.ross@imshq.ftech.co.uk>]

Dimiter,


I was specifically recommended not to put vias or holes under the ball, by
someone with past experience of solder being drawn through the hole and away
from the BGA. I guess this isn't what you wanted to hear - sorry.


Regards


Peter Ross


> -----Original Message-----
> From:	Dimiter Popoff [SMTP:tgi_earth@yahoo.com]
> Sent:	24 November 2000 05:22
> To:	pci-sig@znyx.com
> Subject:	Re: BGA Assembly
> 
> John,
> thanks!
> 
> >What I can tell you is that there should be no need for any
> >form of limiting feet, etc. The surface tension of solder
> >balls on BGAs is sufficient to provide self centreing during
> >reflow.
> 
> Are you sure this would be the case also with the holes I have
> under each ball? I suspect it would be OK, but this was (is)
> my first board with BGAs and on top of this there is no room
> for errors... so I put the feet just to make sure I would not
> end up with a flat block of solder :-).
> 
> >Your problem (below) sounds very much like a lack of flux.
> 
> No, there was plenty of it. And the BGAs did not float in it
> because it did run through the holes. They did not solder well
> also the second time because the feet I had put were a bit too high
> (because of remnants of the glue, I suppose).
> 
> I am pretty sure I'll solder the second board free of problems, yet
> I need the first one working as well.
> 
> I suppose I'll go on with the feet for another while, because I noticed
> that through those holes, which have a pad for a decoupling capacitor
> at the opposite board side, more solder from the ball had flown just
> wetting the metal area; and having all the solder of such a ball
> run through the hole and destroy the connection (quite
> unlikely, I guess) is a mess I don't even want to think of :-).
> 
> Please advise (or speculate) on the above. I will be also very
> grateful if you have some other advice on that topic.
> 
> Dimiter
> 
> -----------------------------------------------------------------------
> Dimiter Popoff
> Transgalactic Instruments, Gourko Str. 25 b, 1000 Sofia, Bulgaria
> http://transgalactic.freeyellow.com
> Email: tgi@bulnet.bg, tgi_earth@yahoo.com
> Phone: 00359/2/9923340, 00359/2/9805997, Fax: 00359/2/9540384
> 
>