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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Pat Copeland

#15632

Double sided smt | 3 June, 1998

Can anyone tell me if there is a reference for smt component height specs on the bottom side of a board, which will also go through wave soldering. A current design I am reviewing has tant caps(7343) and a crystal on the back side. Should I only be concerned about the temp spec or is there a height spec.

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Justin Medernach

#15635

Re: Double sided smt | 3 June, 1998

| Can anyone tell me if there is a reference for smt component height specs on the bottom side of a board, which will also go through wave soldering. A current design I am reviewing has tant caps(7343) and a crystal on the back side. Should I only be concerned about the temp spec or is there a height spec. Pat, I'm not sure of a height spec but I do know that you can "shadow" components behind taller profile components. You'll end up with solder skips if the design isn't right. You should be all right with TAN caps as long as there isn't a chip component right behind it with respect to the boards travel into the wave. I don't know the recommended distance. TH architectures really aren't my bag but I'm sure someone will help you out. Regards, Justin

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Chrys

#15634

Re: Double sided smt | 3 June, 1998

| Can anyone tell me if there is a reference for smt component height specs on the bottom side of a board, which will also go through wave soldering. A current design I am reviewing has tant caps(7343) and a crystal on the back side. Should I only be concerned about the temp spec or is there a height spec. Pat, The height requirement depends on the machine you are using to wave solder the components. Typically, wave solder machines will give you lead clearances of up to .440" or even .500" The process isn't quite as controllable at those heights, though. I'd stay around .300" or .350" max. Something to worry about, however, is tant caps on the bottom of boards in general. Their height and mass gives them a high center of gravity, and makes it easy for the flow of the wave to knock them off the board. (Some 0805's do this, too) And they shadow other components. Plus, the tant caps we see have teeny little terminations that are tough to wave solder. We try really hard to get our designers to keep the tant caps on topside. I'd rather have an SOIC than a tant cap going over my wave, any day of the week. It's less of a headache in the long run. Chrys

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Bob Willis

#15633

Re: Double sided smt | 7 June, 1998

| Can anyone tell me if there is a reference for smt component height specs on the bottom side of a board, which will also go through wave soldering. A current design I am reviewing has tant caps(7343) and a crystal on the back side. Should I only be concerned about the temp spec or is there a height spec. There is not a specific height limit it is the effect on the wave soldering process. You ideally want the wave to pump a small distance as this improves the dross production, gives a more consistent wave. Most people look for a setting from the base of the board to the wave ducting of 6-8mm.

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