Dear Marcelo,
Yes, it is possible to measure SIR under a flip chip. If the comb pattern you
use is beneath a flip chip then any influences on the SIR across that comb
pattern will be detected just as if it were a standard IPC or MIL coupon being
measured in a more standard style of test. In fact we mount QFP's over our
process validation test comb patterns to provide a contamination entrapment
space and cleaning challenge. We think this makes it a better model for SMT
process validation, and so your idea is not at all far fetched.
It may take longer for moisture to penetrate to the comb pattern and lower the
SIR (if this is what occurs) but then this reflects the real application. In
terms of voltage, and the comb design the important factor is voltage
gradient.
You must look at the minimum track spacing (not so much the track width) that
is present in your application and the maximum voltage that is likely to be
applied across this space. From this you get the maximum field gradient (V/mm)
for your application, and it is this field gradient that you should apply to
your customised comb pattern.
Thus the voltage will depend upon the spacing on the comb pattern you decide
to use. By using the field gradient appropriate to your application you are
less likely to promote failure mechanisms that would not be relevant.
As an example on a B24 coupon (spacing 0.5mm) a bias voltage of 50V gives a
field gradient of 100V/mm.
In terms of using a bare board as a control, this is a very good idea, and you
should put a control in the chamber and actually test simultaneously whenever
you run a SIR test. This way any external and unwanted influences due to
chamber failure, condensation etc. can be accounted for.
Using an Auto-SIR(tm) unit you could take frequent readings (e.g. 128 test
points, 10 minutes intervals) and monitor the SIR over the whole test period.
You should try and stick to a standard to make your readings more comparable
with others e.g. IPC-TM-650.
You should start monitoring, heat up the chamber, and then apply humidity.
This way the effects of volatile materials can be seen, and the progress of
moisture penetration may also be seen effecting the SIR as the test
progresses.
Alan Brewin
Concoat Ltd
Concoat Ltd Email: [log in to unmask]
Alasan House, Albany Park Tel: +44 (0)1276 691100
Camberley, Surrey GU15 2PL UK Fax: +44 (0)1276 691227
-----Original Message-----
From: Chan, Marcelo
Sent: Wednesday, November 05, 1997 10:01 PM
To: 'Graham Naisbitt'
Subject: RE: [TN] [AS] What parameters do other companies use when
evaluating the e ffectiveness of Assembly h ouses
builds
Hi Graham,
I have an interest on your Auto-Sir technology.... Is it possible to
verify the cleanliness under a flip chip prior to reflow if I place a
modified SIR pattern under the flip chip.... I do not need absolute
numbers, just relative to another SIR pattern that I would place on a
QFP and on the bare board.... how would I do it and how would you
measure it? What would be the widths and space on the SIR pattern and
what voltage would do it at...
Marcelo
> -----Original Message-----
> From: Graham Naisbitt [SMTP:[log in to unmask]]
> Sent: Wednesday, November 05, 1997 4:31 PM
> To: [log in to unmask]
> Subject: Re: [TN] [AS] What parameters do other companies use
> when evaluating the e
> ffectiveness of Assembly houses builds
>
> Max,
>
> Have you previously received info about our Auto-SIR tester?
>
> Our technique will facilitate an identification of when and where any
> defects
> occur.
>
> If you would like more, please contact me off line.
>
> Graham Naisbitt
>
>
> Concoat Ltd Email:
> [log in to unmask]
> Alasan House, Albany Park Tel: +44 (0)1276
> 691100
> Camberley, Surrey GU15 2PL UK Fax: +44 (0)1276 691227
>
>
> -----Original Message-----
> From: TechNet On Behalf Of Max Bernhardt
> Sent: Tuesday, November 04, 1997 10:23 PM
> To: [log in to unmask]
> Subject: [TN] [AS] What parameters do other companies use when evaluating
the effectiveness of Assembly house builds
>
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