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'Stackable bus connectors' are common nowadays on Arduino and other boards where a single connector has both the male pins (for the board below) and female sockets (for the board above)

enter image description here

In DIY sites there are instructions on how to solder these to the board. This isn't tooo hard.

But what do you do when you have a PC104+ 4x30 (120 pin) connector?

enter image description here

Soldering these by hand isn't easy and very time consuming but possible.

BUT, what do you do in mass production? you can't move these connectors through wave soldering as solder will get attached to the male pins and you can't have paste on the holes.

Any ideas on how this is done? I have a hard time believing this is done by hand. In the past there were press-fit connectors (still available today) but these are rare and quite expensive.

enter image description here

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  • \$\begingroup\$ The third image almost appears to be made up of pairs of surface mount headers (maybe with pads underneath), one on either side of the board - notice the plastic on the pins of the connector. \$\endgroup\$ – Tom Carpenter Nov 24 '15 at 14:28
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    \$\begingroup\$ As for the pins version, you can do reflow soldering - put paste around the holes, put the connectors through, then when it reflows the solder wicks down the hole. \$\endgroup\$ – Tom Carpenter Nov 24 '15 at 14:29
  • \$\begingroup\$ Theoretically I agree but it is not practical. How do you put solder on the holes? through the solder mask? I don't think the amount of solder paste passed by a mask is enough for a TH and probably wont work for all of the 120 pins, some might fail. So make a thick mask? but then other components will have too much solder paste. \$\endgroup\$ – Gilad Nov 24 '15 at 14:44
  • \$\begingroup\$ You don't need masses of solder paste, a ring around the pin should be fine. As each ring heats up it will want to blob together which will in turn pull it against the pin and cause it to wick down the hole. \$\endgroup\$ – Tom Carpenter Nov 24 '15 at 14:55
  • \$\begingroup\$ I haven't tried this but I don't think it will work... \$\endgroup\$ – Gilad Nov 24 '15 at 14:59
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So to summarize what I said in comments, the big manufacturers like TE and 3M make these in press-fit and "common" wave soldering version. 3M doesn't actually say much about the soldering process (at least in here, just "230°C for 60 seconds, 260°C for 10 seconds"), but TE goes in more detail besides specifying 260C and they recommend "Corpane Batch Vapor Phase (Model VVP 10 BU) and Vitronics IR (Model SMD 718) equipment", FWIW. As an aside, TE also sells presses (both manual and pneumatic) for their press-fit variants.

Teka makes a "self-soldering" version of these for reflow, which comes with solder balls pre-attached, and they have a more detailed article in which they compare their innovation with the alternatives. They recommended

Since both the solder and flux (in the form of the solder clip) and the connector are placed on the PCB at the same time, all that is required for reflow is the application of localized heat. This can be accomplished with the use of a benchtop hot-air fountain such as the one produced by Zephyrtronics. (Pomona CA, http://www.zeph.com/pc104)

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