[martinw]

Dear all,

We are making two-sided copper PCBs, through hole, not surface mount, with all components on the top layer.

At the moment these can be hand assembled in limited batches of, say, five each week. We use low residue flux, but we still need to get rid of flux residues.

So far, we can just about get by with scrubbing the solder joint side with a stiff nylon denture brush soaked in isopropyl alcohol, wiping with tissues, removing the tissue dust, and repeating the process. This is pretty painful.

It does not help that the solvent/flux residue migrates to the component side through open holes and track vias, and has to be cleaned up around the components.

Each board is only about 4" by 8" and we only need to clean one at a time.

All components are immersion proof as regards ultrasonics, solvent and distilled water.

I guess, having rambled on for too long, my questions are ....

1) Is there a cheap and cheerful DIY design for a small ultrasonic solvent bath?

2) Any other suggestions?

Thank-you.

Best wishes,
Martin

[tpworks]

http://search.digikey.com/scripts/Dk...?name=SD74H-ND

[mc-motorsports]

I remember years ago in electronics class when I started we had some product simply called "flux remover" which worked awesome! Squirt a little on and just wipe with a small brush, clean as can be. Then the trade school decided to cut our budget and we started using denatured alcohol. Works, but not nearly as well. I would use the bottle/brush in the link above and denatured alcohol unless you can actually find a solvent made for removing soldering flux. Good luck.

[Mariss Freimanis]

Your best bet is to use water soluble flux solder. It makes solder joints as well or even better than the stuff you are using but the board rinses perfectly clean in hot water in just a few seconds. No need to touch it with a brush or anything.

Mariss

[martinw]

Dear tpworks and mc-motorsports,
Thank-you for your help.

I have used aerosol flux solvents with integral brushes. These are really good at removing spots of flux residues around each soldered joint.

The problem remains , however, that the whole of the board is left with a very thin film of residue. Hence the need for washing the whole board to get rid of it.

I thought that ultrasonic tanks cost a fortune, but I was mistaken until I looked into it further today. A tank that can take a 4" by 9" board only costs about £ 100 ($220) .

Choosing a solvent to use in it, frankly scares me to death.

Plastic components, OK. Sealed switches, OK. Clock crystals NOT OK.

For any other tips, I would be really, really grateful.

Best wishes,
Martin

[martinw]

Your best bet is to use water soluble flux solder. It makes solder joints as well or even better than the stuff you are using but the board rinses perfectly clean in hot water in just a few seconds. No need to touch it with a brush or anything.

Mariss

Mariss,

Our messages crossed in the vastness of Cyber-space.

Thank-you for your suggestion. Please bear with me a bit further....


Right now, we are hand soldering , in-house, a dozen or so two-layer boards using low residue solder. This is done with 0.7 mm diameter multicore solder with integral flux. Is such a solder available , for manual soldering , with something that can be cleaned in warm water?? If it is, that would make our lives a lot easier.

For production runs, the cleaning issue is another matter. To some extent, we can delegate the problem.

Thank-you for your reply.

Best wishes,

Martin

[Mariss Freimanis]

I would avoid using no-clean solder fluxes. They have a tendency to form tenacious surface films that are electrically conductive if cleaned. Alcohol based solvents are hygroscopic to some degree and the attracted water tends to bind with the no-clean flux residue to create really nasty conductive films that can only be partially removed with very aggressive cleaning.

No-clean solder literature should say "don't clean or you'll be sorry solder".:-)

By contrast, water soluble flux residue is very easily removed by water rinsing. Even a few seconds under a hot water tap in a sink is effective.

I looked up in our archives a picture of an ROHS soldered board washed with hot tap water only. We keep data archives of all production procedures as we qualify them for use here. The data on this picture is:

AIM WS485 solder paste. The time under the water stream was 15 seconds, no mechanical scrubbing was used, the board was shaken to remove excess water and then hot air dried. The hot air dryer helpfully added the dust you see on the board. The picture resolution is 20 micrometers. Please note the complete absence of any residue except for very faint calcium deposits (hard water here) and the aforementioned dust.

We use lead-free SnAgCu AIM water soluble solder paste (WS485) and cored wire solder (WS482). They also have regular 63/37 solder products (paste and cored wire) that are very good.

Mariss

[martinw]

Dear Mariss,

That was a quite extraordinarily helpful post.

AIM have people on this side of the pond, and their data sheets look helpful. It looks like water-soluable flux could be the way to go.

Your comments about "no-clean" chilled me to the marrow. We made a sprung-loaded forty point test jig to test the boards. The "fault" on one board turned out to be a dodgy contact between the test jig and a very thin film of "no-clean" residue on the board being tested.

Many thanks for your advice.

Best wishes,

Martin

[Mariss Freimanis]

Martin,

Thank you. I have measured resistances below 1K / 2.5mm on cleaned "no-clean" soldered boards. That is low enough to upset logic circuits and cause complete havoc in analog circuits.

Mariss

[martinw]

I have measured resistances below 1K / 2.5mm on cleaned "no-clean" soldered boards. That is low enough to upset logic circuits and cause complete havoc in analog circuits.

Mariss

Dear Mariss,

Please stop! My tripes are turning to water at the implications of this "no-clean" nightmare. I will check the properties of our "no-clean" wire core solder today.

Thanks again.
Best wishes,

Martin

[Mariss Freimanis]

Dear Mariss,

Please stop! My tripes are turning to water at the implications of this "no-clean" nightmare. I will check the properties of our "no-clean" wire core solder today.

Thanks again.
Best wishes,

Martin

Sorry. It is frightening though. We had to trash some 200 G201 REV0's when Geckodrive was young and poor in 1999. It was very expensive and it nearly brought us down. We used no-clean solder then and we found out there was no way of cleaning it off after the boards were done and washed. The stuff was under the SMT parts and unreachable. Being hygroscopic, it would attract moisture from the air, electrolytic action from a powered-up circuit would add metal ions to the mix and royally short everything out. Trashing the drives was the only alternative.

We switched to water soluble flux and its been peaches and cream since then. Clean boards, no contamination at all, better than 10 gig-Ohms of board surface resistance. No-clean flux is evil. Really evil.:-)

Mariss

[martinw]

Sorry. It is frightening though. No-clean flux is evil. Really evil.:-)

Mariss

Dear Mariss,

Thank-you. We will use your excellent advice.

No need to sit on the John till morning.

Best wishes,

Martin

[martinw]

Dear Mariss,

I'm sorry to trouble you again.

For production runs, we can shy away from "no-clean" flux, but we still have a few boards that were hand assembled with the "evil stuff". Obviously we would like to make these servicable, so we still need to clean them.

My idea is to conduct a little experiment.....

Cut a few pieces of 0.1" stripboard into two inch squares and put down as much of our "no clean" solder onto the copper strips as possible without bridging the insulating areas between each strip. (The width of the insulation is about 0.7mm.).

After leaving the samples for a couple of days, we can use a variety of cleaning techniques to try to remove any residues. We can measure the insulation resistance between adjacent strips of solder to see if all is well or not.

My question is this: In your case, did the insulation problem appear immediately after cleaning, or did it build up over time as more moisture was absorbed by the hydroscopic "gloop"?

Best wishes,

Martin

[sigma relief]

It is a bit late to add this, but I have to come to the defense of some no clean solder in both the smt paste form and standard roll form as well as spray on flux used in wave solder process. I work for a mid size electrical manufacturer with ~10 modern high speed SMT lines, 6 wave machines, and thirty or more manual solder lines. I unfortunately do not have the specs for any of the solder at my disposal (I'm at home), but I can state for certainty that we have never washed a single of our 20 million boards we produce each year. Half of that volume is older single sided thru hole technology, with the remainder being "average" SMT complexity. At least a million boards a year are near state of the art (we don't do any 0102 or smaller components, the cellphone companies can have those things all to themselves) boards with hundred+ pin BGA micros and ENIG (electroless nickel - immersion gold) PCBs. While we are not in the motor control industry, we do power electronics similar in many ways to motor controls, but often with more advanced/delicate on board electronics. While I am a mech E, I am closely involved with manufacturing and electrical design and have never heard of a problem where this happened. Occasionally the wave solder spray flux applicators get turned up by over zealous operators and we get buildup which has caused problems, but this is not our "standard" operating procedure. While I have nothing but respect for Mariss who is far better informed on this topic than I, I felt it important to mention that leaving no clean flux on both standard and RoHS solders can be acceptable with judicious selection.

John

[Mariss Freimanis]

sigma-relief,

I have no argument with what you say. My point was never try to wash a 'no-clean' soldered board. That is when trouble begins. I agree an unwashed board is completely reliable.

Mariss