In answer to Kathy Palumbo:
1.
Water soluble fluxes will be detected in an ionic extraction tester. The
residues are not as strongly ionic (like NaCl) but the organic acids used
are likely to ionise in solution. Remember substances are not actually
clearly defined as ionic or non-ionic, there is a whole spectrum of ability
of materials to ionise in water. This is of course why the same amount of
different materials will have a different effect on the results in an ROSE
test, and why NaCl is taken as a reference.
Having said this it is very difficult to then relate the reading in terms of
NaCl equivalent into a reliability assessment.
SIR testing will show you the effect on the ionisable organic acids in the
flux as well as any non-ionisable materials used as carriers,
rheology/tackifiers etc.
The NPL in London did a lot of work trying to relate ionic testing to SIR
readings and drew a blank. Sure there is a general trend in that ionically
dirty boards will have a lower SIR, but no repeatable correlation was found.
This is because, of course, the effects of non-ionisable materials is not
seen with the ionic extraction method.
In short ROSE only detects ionic contaminants, SIR monitors the effects all
contamination.
2.
Ionic extraction testing is very quick and cheap and has its place as a
process control tool. SIR testing works best as a process validation tool,
and should be used whenever a new material is used, or a change in the
process is implemented (even a change in reflow profile for example).
3. 4. Replied off line.
Also:
GEC Hirst research collected a huge amount of data when working on the
original CFC elimination work involving SIR testing. Their work suggested
that test times for SIR could be reduced to provide an SIR test capable of
application to process monitoring.
We use a test procedure for process validation where model 'coupons' are
taken from each step of the production process and tested simultaneously.
I.e. 4 bare board, 4 solder masked, 4 reflowed, 4 reflowed and mounted etc.
etc. Then when the results are analysed the stage of production causing
problems (if any) can be isolated.
Also when taking data sample every 10 minutes or so through the test I have
seen some great effects such as cleaning solvent trapped underneath flat
packs slowly evaporating off, and taking longer if conformally coated, and
volatile flux residues creating an increase in SIR (well documented).
General ionic drift increasing SIR due to a back voltage, and of course the
characteristic spikes of dendrites in some bad cases.
SIR can tell you a lot about a process if you have a detailed SIR/time
curve.
Alan Brewin - Chief Chemist
Concoat Ltd., Alasan House, Frimley Road,
Camberley, Surrey. UK. GU15 2PL
+44(0)1276 691100 www.concoat.co.uk
'Any opinions expressed are not necessarily those of my employer'
-----Original Message-----
From: Kathy Palumbo <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 29 June 1998 21:53
Subject: [TN] Contamination Testing for Water Soluble Flux Residue
>I was told that water soluble flux does not leave ionic contaminants
behind,
>and if you want to test for contaminants you should do a surface
Resistivity
>test.
>
>My questions are as follows:
>
>1. Is this entirely true, or can some sort of correlation be made between
>the two different types of tests.
>2. If surface Resistivity testing is being done should ionic contamination
>testing ever be done?
>3. Are there any Ionic Contamination Testing systems available so we can
do
>this test in house?
>4. Are there any Surface Resistivity Testing systems available so we can
do
>this test in house?
>
>Thanks in advance for you responses!
>
>Kathy Palumbo
>Viking Components
>
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