Could the 50 ug figure relate to uncleaned boards which have been put into
the Ionograph?
If so the number is meaningless as a measure of reliability or anything else
when evaluated against the number for a cleaned board. The Ionograph was
developed as a means of process control for cleaning rosin based fluxes that
met a now obsolete military flux specification.
The best you could say is that it is probably an indicator for the amount of
no clean flux present. No clean fluxes are defined as harmless if the
residue meets certain criteria, none of which includes amounts of residual
extractable ionics.
If the number is for a cleaned assembly then all we can really say for sure
is that the boards have a lot more extractable ionics on them than they
could have, [as amply demonstrated by the fact that the other techniques get
lower numbers].
If you were using a high solids rosin based RMA flux (say 35%) of the type
around when the Ionograph was invented, and put an uncleaned board into the
Ionograph it would likely go off scale, the total extractables would be
huge. But RMA fluxes are considered safe if uncleaned. Poorly cleaned they
may not be safe and that was the point of the test: to provide a means of
monitoring cleaning process effectiveness.
Regards
Mike Fenner
Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Carroll,
George
Sent: Tuesday, July 15, 2003 9:09 PM
To: [log in to unmask]
Subject: Re: [TN] Ionograph reading for No clean v/s aqueous processed
(wa ter soluble flux)
Ken,
As the previous respondents have indicated, Ionograph results shouldn't be
used as a go-no-go. Taking the process approach, what were previous results
from this vendor? from other vendors providing similar boards? Are there
components that would tend to hold flux under or near them? That could
contribute to field reliability issues. There may be those that disagree
with me, but 50 sounds a bit steep in comparison with no-clean boards that
I've measured.
George
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