Distance of SMD component from through hole pad?

[treez]

Hello,
What is the minimum distance allowable for a through hole component from the drill hole of a through hole pad?
We are laying out a 60W offline SMPS which also has some basic monitoring circuitry on it.

 

[shaiko]

1. From a manufacturing point of view - you better consult the factory technologist.
2. From a design point of view - just make sure that the distance is enough not to cause an electric arc or dielectric breakdown of any kind.

 

[FvM]

If you are talking about PCB component side, regular PCB clearance and creepage rules for the respective operation voltage apply. Component metal cases have to be considered of course, obviously SMD components must not block throughole assembly.

For the solder side, observe the restriction by the used solder method, e.g. selective wave solder.

 

[treez]

thanks, We have the thru hole components on the top, and the SMD's on the bottom, I believe that any SMD pad should be at least 3mm away from the drill edge of any thru hole pad?
This , as such, is to stop the SMD's being deluged by the wave soldering process(?)

 

[FvM]

There are different ways to solder this design.

1. (Classical)
SMD components placed on the bottom side, fixed with screen printed or roboter dosed glue. Regular wave soldering after placement of throughplated components.

Disadvantage: Can only solder SMD components with sufficient pin spacing and specific orientation. No QFP or chip scale packages. Special wave solder footprints required.

2. (Modern) Reflow + Selective wave
Regular SMD placement and reflow solder of bottom side. Throughplated components are soldered with "selective wave", a X/Y moved solder jet. Clearance of SMD to troughplated pads depends on nozzle size, e.g. 3 to 6 mm. Ask the assembly house for exact placement rules.

 

[treez]

Thanks, 3 to 6mm is what I was expecting...I wonder if that distance means "edge of SMD pad to edge of thru hole pad" or "edge of smd pad to drill edge"?

Of course, we could violate the distance for wave solder of the thru hole parts and simply insist on the thru hole parts being hand soldered, but are not sure how much this would cost in comparison.?

 

[FvM]

You didn't yet tell about the used solder method. Is it selective wave?

I wonder if that distance means "edge of SMD pad to edge of thru hole pad" or "edge of smd pad to drill edge"?

Neither. In the simplest case, the distance throughhole center to SMD pad edge must be greater than the nozzle radius. You should really contact the assembly house.