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February 1997

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Subject:
From:
"Leo P. Lambert" <[log in to unmask]>
Date:
Sat, 15 Feb 1997 07:53:32 -0500 (EST)
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>From my understanding the Ohmegameter was design to measure residues left
behind from the use of rosin fluxes.  The solvent was chosen to dissolve the
rosin and measure the change in conductivity of the solution based upon the
amount of activators remaining on the product.  It was also design to see
how clean the board was in relation to its preparation to be conformal
coated. It was not originally design to check if any electrical failures
would occur if the product was dirty with flux.

We did experience your dilema some time ago when we converted from Rosin to
water soluble fluxes.  Many inconsistent readings and all that stuff.  The
bottom line was that the residues from the water soluble fluxes were not
soluble in the Ohmegameter solution, therefore they did not change the
conductivity of the solution. This proved to be a major problem as these
residues were susceptible to absorbtion of moisture and could and would
cause electical failures of the product.  Another issue we found was the
ability of the solution to dissolve some of the bromides in the FR-4
material, which also changed the readings.  So the bottom line is another
method had to be developed or utilized which would in fact check for
contaminant which would be detrimental to the electrical functionality of
the product.  

I recommend the use of SIR testing at various humidity and temperature
levels to see if the flux residues left behind will be detrimental to your
product.  IPC has test coupons which could be used for this analysis and I
believe ALPHA Metals has a piece of equipment which could be used to measure
the results.

When you do conduct SIR testing make sure you have a control sample, two
samples processed, one which is cleaned and one which is not cleaned to get
comparative information.

Good luck

Leo Lambert
EPTAC Corp.
At 03:09 PM 2/14/97 -0600, [log in to unmask] wrote:
>
>
>
>
>
>Charles Barker
>02/14/97 03:09 PM
>
>We are investigating switching from RMA and SA based fluxes to WS fluxes.
>We notice much higher and inconsistent Ohmegameter readings with the WS
>fluxes. Is there a better means of measuring Ionic contaminants when using
>WS flux? What are others using to check how "clean" a WS processed assembly
>is after wash?
>
>Thanks in advance.
>
>Charlie Barker
>
>
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