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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Non soldered leads on ic's

Ernie Flamont

#12569

Non soldered leads on ic's | 18 February, 1999

During inspection and test we find leads which do not get soldered. Some are because of insufficient paste, but with others everything looks right. This will only happen on 1 to 2 pins, and it is not isolated to a specific type of ic or location on the pcb. If anyone has experience this before and can help, I would appreciate it.

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Pete Sorenson

#12570

Re: Non soldered leads on ic's | 19 February, 1999

| During inspection and test we find leads which do not get soldered. Some are because of insufficient paste, but with others everything looks right. This will only happen on 1 to 2 pins, and it is not isolated to a specific type of ic or location on the pcb. If anyone has experience this before and can help, I would appreciate it. | The possible causes I can think of are: 1. PWB solderability 2. Oxide on the component leads 3. Wave solder temp/time 4. Contamination from adhesives Perhaps you have or can eliminate some of these possible causes via test. The majority of problems I have seen where everything looks OK but the joint is bad has been caused by oxidation of the component leads. In some applications, the joint problem when caused by oxide has shown up in the field, or during environmental testing rather than functional testing. The major cause of oxidation was components that had been in stock for an extended period of time without protection against oxidation.

Regards, Pete Sorenson

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Justin Medernach

#12571

Re: Non soldered leads on ic's | 19 February, 1999

| During inspection and test we find leads which do not get soldered. Some are because of insufficient paste, but with others everything looks right. This will only happen on 1 to 2 pins, and it is not isolated to a specific type of ic or location on the pcb. If anyone has experience this before and can help, I would appreciate it. | Ernie, Pete is right. One of the causes could be solderability but I tend to doubt it. I think if it were a solderability issue, you would see much more of a fall out than one or two pins. I would suggest slowing the process for a few shifts and scrutinizing each process. I would bet that you have issues in the screen printing cell that need to be resolved. You had mentioned insufficient solder. Sit back and ask your self why. A.) Are your aperture geometries wrong? B.) Is your paste right for your process? C.) Do you have adequate controls on your solder paste? eg. how long does in sit on the stencil before it's scrapped? D.) Do you clean the stencil enough? E.) Are the stencils cleaned thoroughly after running a job? F.) What is the Cp / CpK of your printer? eg. How repeatable is it? G.) Are PM schedules kept up? H.) Are your squeegee blades in tact? I.) Are you printing too fast or with too much pressure? J.) Are you using SPC on your process? K.) What is the sampling frequency? Blah blah blah blah. There are a ton of variables affecting this process, that's why I always start there. Another issue may be the component lead coplanarity. Do you verify coplanarity on your placement machine? Hope I gave you some things to think about.

Regards, Justin Medernach

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Steve Schrader

#12572

Re: Non soldered leads on ic's | 23 February, 1999

| During inspection and test we find leads which do not get soldered. Some are because of insufficient paste, but with others everything looks right. This will only happen on 1 to 2 pins, and it is not isolated to a specific type of ic or location on the pcb. If anyone has experience this before and can help, I would appreciate it. |

This is probably not your problem since you see it randomly across the board, but you should check anyway in addition to the suggestions already made by others:

If you have via's attached to the end of your pads without a soldermasked trace in between, paste may be wicking away from the lead and down the via.

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