Wave solder question

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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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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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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