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Selective Soldering

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#65157

Selective Soldering | 3 October, 2011

I have been getting solder balls on the leads of a transformer that I am soldering to my pc board. My parameters are listed below. The board PTH's are .039 The transformer leads are .0255 square. My solder pot temp. is 310C Solder is Lead Free AIM SN100C The flux is ALPHA 857 WS My Z height is -.130 it barely touches the board, just low enough so that the solder wicks up the lead. I am getting decent barrel fill. I am breaking away and down at a 45 deg. angle at a speed of F20. I've been brushing flux on the top side to help the solder wick up the barrels. I am soldering 12 holes per board. Most of the joints result in IPC "acceptable" condition but too many have rejectable solder balls requiring rework. Any tips that you can offer are greatly appreciated. Thanks.

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#65159

Selective Soldering | 3 October, 2011

It sounds to me that it's a heat transfer issue. The solder is only bonding to the lead on not the barrel correct? Does your selective solder equipment have any type of heating source? Can you "dwell" on that particular joint? On some of our products we have to strategically pick our paths so that we heat the area of the troubled joint. There are some cases where we are on a lead for almost 20+ sec. just so we can achieve the desired solder joint. Now this all adds to the cycle time of course.

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#65160

Selective Soldering | 3 October, 2011

The machine does not have pre-heating feature. I'm soldering a six-up panel...I've tried putting them a an oven and letting them soak for 20 mins or so at a low temp. But by the time I placed the panel in the machine and manually fluxed the top side it would be room temp by the time I soldered, so I stopped. It also increased cycle time considerably. I think it might be a heat transfer problem too. The transformer is a acting as a big heatsink. I think I will try adding a Z height pre-heat dwell time and then hit the lead for about 2 secs. Thanks, I will post if it works.

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#65162

Selective Soldering | 3 October, 2011

Does your machine have a step and repeat? Do you have the option to flux and solder boards individually on a panel? Hope this helps.

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#65163

Selective Soldering | 4 October, 2011

Having a selective solder machine without a preheat sounds ODD. Preheats are pretty important to drive off flux volatiles and activate the flux so it cleans the parts ready for the solder to wet to them. If you have no preheat then you must be expecting the contact with the solder to do all your flux solvent evaporation / activation and preheating the pcb top side for good hole fill. If the flux solvent isn't evaporated before contact with the solder then you may get solder balls spitting from the energy of the rapid evaporation of the solvent in a 310 C solder pot. Can you hear any sizzling when the part goes into the solder ?Also, 857 is a very active alcohol based water wash flux...are you doing thorough cleaning after soldering to remove the active residues ?

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#67317

Selective Soldering | 19 September, 2012

Are you sure that you are getting adequate nitrogen flow up through the cap? If your pump isn't seated properly, you may have nitrogen escaping. Also, I have two different height nitrogen bases. The shorter one does not allow as much gas to escape around the nozzle, especially with the smaller nozzles and N2 caps. If you don't have the option of a taller base, try the N2 cap that is meant for the 12mm nozzle. That will at least help with the nitrogen pre-heating effect.

Have you tried using a flux pen, to limit the amount of excess flux that runs across the board?

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