[log in to unmask] wrote:

> I'm just wondering about a no-clean flux made by InterFlux called
> interflux2005M.

I'm not familiar with the formulation of that specific flux.

> Sometimes we need to put some extra flux on certain kinds of components,
> and if there's not enough heat it won't burn away and leave a white
> powder left on the PCB. This is to my knowledge Adipic acid (spelling?).

Possibly, is that what InterFlux said it was?
> 
> How does this affect the components and PCB if it's in one kind of a
> place where you can't brush it off?

It depends on the other materials in the flux, such as surfactants and
polyglycols, the circuit board substrate, i.e. CEM-1, FR4, etc., the solder 
mask and it's application and cure (or lack of it), whether the board was
HASL'ed, and other factors.  If you use FR4, good solder mask and have an incoming
board maximum ionic contamination requirement, and the flux's activator system
is just adipic acid, it is unlikely that you will have a problem.  If you use CEM-1,
cheap solder mask and poor HASL, you may have electrical reliability problems.
If you want to be double-sure, do Bellcore process SIR and electromigration 
(TR-NWT-000078) evaluation.  There are several independent test labs that 
will do this work, but it costs money.  Also do board life-testing at elevated 
temperature and humidity.
> 
> Of course we can use a waterwash or any similar kind of washer, but we
> don't wan't that extra step in the production. Many people here at
> Ericsson have diffrent theorys about if the flux do harm or not.
> Anybody have any experience in this matter?
> Yes, I sometimes get boards from Alpha Metals customers that have been processed 
with our no-clean fluxes.  I have seen electromigration failures even with flux
that use the non-hygroscopic dicarboxylic acid activators, such as adipic, succinic
and suberic acids.  However, these sorts of failures are more common for pc-boards
assembled with fluxes containing more hygroscopic acids, such as glutaric acid.  These
failures depend on many factors, such as those I listed above, and others, such as the 
specific service environment and the wave-soldering process conditions.  

I don't have any experience with InterFlux products and circuit failure,
but low residue, organic acid-type no-clean fluxes usually have similar 
formulae.

Before we see any more creative organic chemistry, adipic acid is:

	HOOC-(CH2)4-COOH

(I was taught "oh my such sweet APPLE pie" to remember these formulae)

The generic formula for dicarboxylic acids is:

	HOOC-R-C00H, where R is a hydrocarbon chain.

I suggest you call InterFlux and ask to speak to the chemist responsible for 
no-clean flux formulation or the chemist or engineer responsible for SIR and
electromigration testing.  Also talk to the person at Ericsson responsible for
electrical reliability testing.

John Sohn has written a few papers that you may wish to read comparing the SIR 
of a few organic acid flux activators.

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