Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Wave solder question

#18916

Wave solder question | 19 February, 2002

We have had some discussions about what causes parts to lift out of the holes when going over the wave on our flow solder machine. The machine being used is a Treiber (700 series). There are two bottom pre-heaters and one top pre-heater. We try to pre-heat our boards to temp of 220F and the solder pot temp is at 490F. Track speed is at 35 ipm on most assemblies. We use Kester RMA 186 with a foam fluxer and 63/37 solder from Electrum. We had been doing a lot of masking then decided to try flowing with out masking. We found we had some very good results but the questions of what causes some parts to lift and some not even though they may be the same part just different location. Any input on this would be greatly appreciated. Thank you.

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Greg

#18917

Wave solder question | 19 February, 2002

Check the pcb layers. Maybe it gets hotter in certain areas of the board. Most parts being wave soldered should be clinched, crimped whatever to avoid this. What parts are lifting?

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#18919

Wave solder question | 19 February, 2002

Surface tension is a likely cause. Surface tension is a negative wetting force. You may have a solderability problem. Be sure your flux is properly activated according to the flux mfg. top side board temp. specification. When surfaces to be soldered, in this case the component leads, have more oxidation than the flux is able to de-oxidize you will get negative wetting. Also, could be a contamination problem. Are Operators touching the leads or PWB with greasy, oily, post-nose-picking fingers? Here are some other possibilities: 1. Conveyor vibration 2. Conveyor angle 3. If you're using pallets- check the pallets to be sure PWB is help properly and flat 4. Uneven wave- use a LevChek 5. Wave height too high 6. Leads too long

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#18923

Wave solder question | 19 February, 2002

You weren�t clear but I assume the problem is not widely distributed and affects only a few parts on each board.

Do this trick: * Cut a ~1� piece of fairly serious wire, like 18 or 12 AWG. * Strip the insulation. * Gear-up with gloves, glasses, and what ever else you use to be safe when working around a solder pot. * Grasp one end with a pair of pliers. * Slowly push the end away from the pliers into a solder pot. * Observe that the end of the wire indents the solder.

Repeat the experiment, but release the wire while it is indented into the solder.

Repeat the experiment, but flux the wire before pressing it into the solder.

Lifting (floating) parts during wave soldering. Causes: * Leads that can't be clinched (connectors, some header sticks, etc.). * Corroded leads that will not take solder. Flux is supposed to prevent this, but it can only do so much even if it is applied properly. * Flux that is too weak for the corrosion on some component leads. * Operators not paying enough attention to the topside solder fillet on these parts, because solder may not flow up the PTH, if the lead has a bad finish. * If the part with a floating problem has not been a floater in the past, check the lead finish and the flux application.

Solutions: * By far, the preferred solution is to make sure you're getting parts with a good lead finish, and not having to worry about holding the part down. * Using a more active flux. * Try adding just a slightly heavier application of flux to parts that "float" at wave, especially when using no-clean flux. * Shorter leads can help eliminate these defects at wave solder, sometimes. * Using weights to keep parts from floating: - Stuff the bags with anything that can take the heat exposure: glass [not plastic] marbles, aluminum pellets used in baking piecrusts, whatever. If the bags are cloth, pay attention that the bag is not damaged through the process, over time. Maybe fiberglass or leather bags filled with BBs. Not sand. It works through woven material bag too easily. Not steel shotgun shot, if you are going to get the bags wet. - Use the lightest weight that will do the job. Too much could cause the board to bow downward, with a variety of results, none of them good. - Area under the bag will not get the full exposure to your preheat, if you have topside preheaters. If this is a problem, consider getting small metal weights machined to fit on the problem part. * "Gluing" the components down with a water-soluble temporary solder mask * Clinching the component leads. * Solder tacking a lead and covering the tack with temporary solder mask.

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Shawn

#18926

Wave solder question | 19 February, 2002

I would like to thank all of you again for your input. It is greatly appreciated and really does offer excellent and different perspectives to problems.

Thanks

Shawn

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