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Tin HASL finish soldering problems

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Tin HASL finish soldering problems | 14 September, 2010

We are having an issue with a PCB supplier. Their Tin HASL layer seems to be the problem. We have triedworking with them to correct their process. What seems to have helped is lowering their temperature of the Tin dip from 540 F to 510 F.We still have some plating issues in the fine pitch area of the board, on approx 20% of the boards.The bare copper solder perfect, so we know it the HASL layer. Is there a standard temp that should be used in the Tin HASL finish? It seeems the closer they get to Tins melting point the better. Any advice would help.

Thanks in advance


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Tin HASL finish soldering problems | 17 September, 2010

In HASL pcb coating you need to fully coat the pads with solder and then blow off any excess solder to leave a nice coating on each pad. Generally pcb manufacturers try to give you a flat pcb pad to make your solder paste printing more consistent. To do this they try and blow off most of the solder. But it is a fine line between leaving enough solder on the pad and blowing most of it off and leaving a tin/copper intermetallic on the pcb pad that is really poor for solderability. And if the solder pot is at a lower temperature then they will blow less off before it cools on the pad. So you'll get a better solder coverage....but it may be a dome shape on the pads....this is good for wetting but tricky to print fine pitch without getting bridging. Generally we see good HASL is the best for soldering but not the best for fine pitch as it is not flat, but bad HASL is terrible for solderability..

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