Can I solder a press-fit connector with large footprint holes?

Question

For my project, I designed a PCB using press-fit connectors. However, due to the footprint error, the holes were larger than they should have been, and these PCBs are 8-layer high-speed PCBs.

Therefore, I want to use these PCBs, but the press-fit pins are too small for the holes. Can I solder these pins, which normally need to be pressed, to these holes? Will this cause me a problem?

Answer 1

A 0.67mm hole was for a 0.55mm soldered round pin (it is round, right? Because a square is too large and won't fit) is actually higher precision than a normal soldered hole so I don't see foresee any problems there as long as you can overcome the heatsinking of the board to solder.

Use a giant tip. Even if the tip is larger than the pad if there are no surrounding components to prevent you from squeezing it in. I think you can do it as long as you can squeeze the iron in.

I've soldered 4-layer boards with 2oz copper on the outside layers using leaded solder without much issue as long as I could fit a large tip in. The only ones that gave me issue were tiny surface mount pads without thermal relief that connected directly to a plane and those required a preheater.

For those it turned out a flat faced bevel tip with tinning only on the face and not the sides really helped because it holds a solder blob right on the tip that that can squeeze into the nooks and crannies and make real good contact on the smallest pads. The blob pulls away with the tip so it behaves like a liquid metal tip.

But I never found through-holes to be an issue at all.

Answer 2

Your options are:

1. try it.
2. respin the board.

However, you might find that the pads are such a heat sink that you'll be unable to make a decent solder joint.

Answer 3

Short answer: it's most probably ok

Longer answer:

Your first question has to by: why did you opt for press fit on that board in the first place? There can be different reasons and sinve you mention that it's a high speed board, there might be "interesting" ones.

Typical reasons are:

• solderless connection
  • no additional heat load on assembly
  • no risk of "cold solder joints"
  • can be assembled from the front
  • cheap, easy, fast
• signal integrity reasons
  • no legs protruding from the back so no reflections from an open end (yes, this can be an issue, see "What is Backdrilling of Vias and why it matters"
  • connectors can be inserted from both sides (under certain circumstances) into the same holes "Wave solder vs Press fit"

So my suggestion would be:

• find out, why press fit was chosen over SMT or THT
• try it out
• you might run into problems with the solderability of the connector
  • the plating of the pins might not be compatible with soldering (might not "wet" with commonly used fluxes)
  • the material of the body of the connector might not hold up to soldering

So you might need to buy the solder variant of the connector in question instead of soldering in the press fit connector. Again: Try it out.