thanks for your most helpful comments Bob
but the 13 mil hole via in pad certainly is a surprise to me
is that a finished size after plating or the drill size ?
i certainly understand the relation to the pad size and minimum annular
ring reqs
getting rid of the dog bones without resorting to laser drilling would
be a major boon
heck it would be great to put them in bypass cap pads for that matter,
you would get better performance and more routing room
bob, how was your 6 mil (i assume finished size) hole fabricated, laser
or mechanical drill?
and the cleaning question re QFN and BGA still interests me, whether
lead free or not
it seems to me that using the good old OA water soluble flux this is too
risky to use due to the difficulty of cleaning under these things
so is 'no clean' flux the typical method ?
does anybody still use RMA for this sort of work?
BTW, Bob, what is 'DAP' ?
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
Bob Benjamin wrote:
All,
I get the digest version, so I'm responding after reading a number of
messages regarding via sizes. The answer to Brad's original question is
yes, via in pad is the recommended connection for fine pitched BGA. Believe
it or not, the via size is going to be dictated by the pad size more than
by the solder thieving problem. The last one I did had a 6mil hole. We
have used 13 mil holes as the largest, and that is the info we have been
putting into app notes for our devices.
You will also see this with QFN devices that have the large pad used to
stabilize the package, as well as adding thermal relief. This tiny pad on
devices, such as op amps, can be tied through vias to ground planes to draw
off heat from the device. This is one of the places I have used the 13 mil
holes.
So is it recommended?..yes,..and does it work?....yes. If it really bothers
you, plug the holes with silver or epoxy.
And by the way, there is lead-free BGA that works well with no-clean
flux..or so I'm told by Kester. Dell, Nokia and Motorola are using LF
processes, and many of the parts they are using are BGA. One thing to
consider is LF parts are going to be the norm in the not too distant future.
There may be problems procuring leaded parts so keep this in mind.
If you would like to discuss this further, I am willing to do this, just
contact me directly.
Bob Benjamin
DAP - Texas Instruments
Tucson, AZ
[EMAIL PROTECTED]
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