We are doing a PCB which has both surface mount components and through hole components on it.
The surface mount components are on both sides of the PCB.
What’s the closest that a surface mount pad can be to a through hole pad?
0.0mm, if you don't mind your assemblers screaming at you.
Anything more than that, depends on target cost, process, reworkability, reliability, etc.
Tim
A assembler that works for our us, recommended once 4mm distanze between smd components on the bottom side and pth-pins.
But i think that recommendation is to keep it most easily for the assembler. I think less is also doable, but i think you need to keep in mind, that the harder time the assembling guys have, the more expensive it will be.
The DFM service I use, flags anything less than 150mil (~= 4mm). The guys who run the service, say that's a worst case condition for their house process, which is to use wave solder (preferring full wave, with selective wave as alternative). The clearance is for the fixture covering the SMT components. So the clearance is actually a cone frustum around the THT pad. The size of the cone depends on the fixture technology used: milled fixtures are cheaper but thicker than, say, formed titanium sheet.
Or you can do a full-wave process (no reflow), which I think is going to be more common with wider pitch SMTs and high volume production.
Tim
For the production of the printed circuit board 10 mils are more than enough; I use 1mm and even less
What’s the closest that a surface mount pad can be to a through hole pad?
Determined by the two pads voltage differential and nothing else.