I'd like to share some of my personal experience regarding this topic, hope it
can help.
I started to use backdrill technology from 2010 and no critical problem found
by now as long as the manufacture could follow the correct process, so
backdrill itself can be treated as a mature technology, I think.
While for backdrill the via-in-pad vias, we have successfully use it on our
FPGA board (FPGA with thousands of balls) for several projects from years ago,
note that these boards are not high volume product boards.
Typically before introducing a new technology into my design, I will evaluate
it together with my PCB and assembly vendor to make sure the risk is under my
control. So why not call your partner to get their suggestion?
Best Regards
Bruce Qin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf Of
Chuck Corley
Sent: Saturday, August 11, 2018 06:50
To: Ned.Dempsher@xxxxxxx
Cc: si-list@xxxxxxxxxxxxx; si-list-bounce@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Backdrilling Via-In-Pad
Via-in-pad has caused reliability problems with solder ball cracks and
failures.
There have been many boards in a lot that worked fine, but there is a failure
fallout. A number of companies had to respin boards later to eliminate it. I
recommend you try to avoid that painful experience.
Backdrilling is a reasonable and well-tested technique for reducing the
capacitance that non-functional stubs create.
Chuck Corley
National Instruments
On 2018-08-08 13:34, Ned.Dempsher@xxxxxxx wrote:
Good Afternoon SI LIST,
I have an additional question concerning via structures for very high speed
design.
Via-in-Pad is being touted, rightly so, as an improved breakout approach.
At the same time backdrilling or at least stub reduction is obviously
becoming more and more of a necessity.
I am being told by our very able PCB CAD folks that back drilling via-in-pad
is a NO GO because they cannot obtain any good long term reliability data.
I have seen a very high speed design with via-in-pad backdrilling but it was
very low volume, and a noncritical application.
And, just because I saw it and it worked doesn't mean of course that it's OK
to do.
There is an article that shows that a mix of BGA nonbackdrilled vias-in-pad
with non via-in-pad (surface routing) exhibits solder failures.
Also, that they expect that a mix of BGA nonbackdrilled via-in-pad with
deeply backdrilled via-in-pad (which would be similar to surface routing
above) should therefore exhibit similar failures.
(The problem is due to different CTEs between these two different
types of structures when they are adjacent to each other so there's no
problem if this doesn't occur - i.e. they all have similar backdrill
or no backdrill or they are not close to each other, Figures 7and 8.)
(http://iconnect007.uberflip.com/i/895789-smt-nov2017/60)
What are your experiences regarding this technology from both an SI and
reliability standpoint.
Are many or any backdrilling via-in-pad?
Thanks Much,
Ned Dempsher
L3 Technologies
Camden, NJ
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