Hi Ivo

We did some research about this item. The work we did was on various solder
creams combined with several cleaning methods:

Flux  I          I     I     I     I             I
      I Cleaning I HCS I CFC I H2O I no cleaning I
-----------------I-----I-----I-----I-------------I
RMA              I  X  I  X  I     I     X       I
-----------------I-----I-----I-----I-------------I
RA               I  X  I  X  I     I     X       I
-----------------I-----I-----I-----I-------------I
Water soluble    I     I     I  X  I     X       I
-----------------I-----I-----I-----I-------------I
NoClean          I     I     I     I     X       I
-----------------I-----I-----I-----I-------------I

To analyse the results we made:

- Measurements of ionic contamination after soldering with one of these
measurement equipment that solve parts of the residues remaining after the
cleaning and measure the conductivity of the solution

- Measurement or the surface resistance underneath 0.5mm pitch QFP's which
are 28mm long with a comb pattern in various temperature / humidity
combinations during 1000h.

- Measurement of the thickness of the residues with microsections.

- Classification of the appearance with SEM and stereo microscopy.

As one of the results we found that the process with water soluble flux
followed by water cleaning gave good results. Not only where the
solder-joints very clean. But this combination showed the best valuable
results in the measurement of the ionic contamination. While all the other
flux residues are hardly soluble in water / alcohol and hence one is just
measuring the amount of free ions at the surface of the residues, the
measurement of the ionic contamination of water soluble fluxes gave
actually a measure of the total amount of residues. If you want to know
more, please feel free to contact me.

Cordially

Guenter Grossmann

ETH Zuerich  ETZ / H71
Reliability Laboratory
Gloriastr 35
8092 Zuerich
Switzerland
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