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From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 2 Mar 2000 11:43:10 +0200
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Cecilia

Whereas I agree with the others that a saponifier may be worth considering, your 0,04 mm spacing is worrying me. Saponifier solution will be pulled in to under
the components by surface tension, but it will be **extremely** difficult to rinse it out again, especially if the components are bigger than a few mm2.

We have recently done trials in such circumstances with a relatively new German saponifier in an expensive Swiss-made high-throughput batch cleaner with very
good results. This has a cycle time of 6-8 minutes in each of three stages (they can be done simultaneously on succeeding batches), so that typically 6 loads
can be outputted per hour. The first stage is, say, 7 minutes saponifier cleaning with jets: the second is 5 minutes recirculating hot DI water jet wash plus
several open-circuit DI fine spray rinses (the particle size smaller than the component to board space) and the third stage is controlled hot-air knifing for
drying over 7 minutes, producing bone-dry assemblies. The saponifier is organic but does not use the usual 2-C MEA and actually has a 4-C amine formulation. It
is slightly less aggressive than the usual ones, but it has a higher proportion of solvents. It seems remarkably effective.

However, I would be **very** cautious about using any saponifier on a ceramic substrate without very extensive trials. Many of the frits used in making up both
conductive, resistive and insulating inks and pastes are sensitive to basic (or acid) solutions, after firing. In fact, even DI water alone can often dissolve
some of the glaze, but the dissolution rate may increase enormously once the pH exceeds about 8,5 or 9. This is why, on my first post, I queried whether you
were meaning organic solvents, rather than water. Another problem with ceramic substrates is that belt reflow is quite a popular method. This tends to cook the
flux residues, especially rosin, rendering them *very* difficult to clean off under components, where the limited space makes them act as a mini-oven: where the
temp around the leads of a QFP may rise to 220° or 230°C with a belt reflow, the temp under the components may go up as high as 280° or more (measured using
paints). Also the slower profile does not help either, due to the thermal conductivity of the substrate playing a role.

I hope this additional info will help

Brian

"Cecilia Alkhagen (EMW)" wrote:

> Hello!
>
> Could anyone tell me the most effective way of cleaning RMA-flux on FR4-boards as well as ceramic substrates. Both inline and batch cleaning is of interest.
> Component stand-off is 0.04mm in some cases and micro-BGA:s are soon in the production line.
>
> Cecilia Alkhagen
> Ericsson Microwave Systems AB
> SE-431 84 Mölndal
> Sweden
> Phone: +46 31 747 02 88
> Fax: +46 31 747 26 35
>
>
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