Baffling soldering problems!

Still cant get a fix to SMD soldering problems, Joints still look strong shiny and well wetted, although when pulled lead still coming away from pad, leaving a dull grainy looking space. This is occuring just after reflow (convection), no other process involved. Reflow profile when intuned and within paste supplier spec, alright printing characteristics, alright ambient temperature. Using a water soluble paste which is 'active', tried different batches, paste supplier puzzled. Solderability of PCB's and SMD components seem fine. Confusing, help much appreciated, regards Jack.

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Assuming that your components and PCB's have good solerderabillty and are stored in an air conditioned environment and kept free of contaminants then your problem sounds as though there is insufficient wetting of the component leads due to low temperatures. We found that on large 'J' leaded components increasing the solder lands helped with conducting heat under the component and solved the problem. If you are finding this problem on all components then it is probable that the temperature profile you are using is incorrect, check it with a data logging device. If this fails try using a paste with a more agressive flux.

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Assuming that you do not have a solderability problem with the board or part it sounds like you are not pumping the solder up high enough to contact the board plus push into the board by about 1.8mm. Are you using a chip wave in front of the normal solder wave? Are you experiencing shadowing because large parts are placed close to the leads that are failing? Is your entire board experiencing this problem or just a portion of the board? If this is occuring on a corner of the board is your wave equal on the right and the left? Are the speeds and feeds through the preheaters getting the board hot enough? And last but not least in you are not using an alcohol based noclean flux try it. The alcohol is driven off at a much lower temperature and water entrapment under these small leads is not an issue. This water might also be your problem. Hope I could help! regards FRANK

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