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I work for a small company as an apprentice. We build mostly mass produce double sided PCBs. We are having trouble keeping the pin headers flat to the PCB through the reflow oven process.

  • The first side is pasted through a printer and populated by two machines (smaller parts.)
  • The board is reflowed and put ready for the second side.
  • We then print the second side and populate it through one or two machines. (job dependant)
  • The PCB is then taken and flipped upside down, before reflow, and the pin headers are placed through hole by hand (not soldered) into the first side so that the legs will solder from the second side paste.

As you could imagine, flipping the board back over to reflow would then would cause the pin headers to drop out. We have tried using a type of glue that dries fairly quickly and will hold the headers down while the PCB is in the oven but we haven't had much success and are still getting headers raising in the process causing us a lot of time and money on rework.

If anyone has a similar problem or has a solution I'd love to hear what you have to offer.

Update: we build these for a customer who will not change the pins or the board as they will not spend any money. we are happy to spend some money pur end though to improve our process.

I think we are now looking at some type of adhesive or something to support the pins through the oven.

These are the pins:

enter image description here

Here is an example of a board:

enter image description here

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  • \$\begingroup\$ You’re probably aware of the peel away white goo you use to selectively mask areas of the pcb from soldering - a blob of that on the pins might help. Or some kapton tape? \$\endgroup\$
    – Kartman
    Commented Oct 20, 2021 at 10:19
  • \$\begingroup\$ The second side could stay underneath and be wave soldered, parts on that side should survive immersion in the wave. It may require experimenting with board tolerances, but the pins could press-fit into the right size hole. You could build an assembly jig to hold the pins. \$\endgroup\$
    – Neil_UK
    Commented Oct 20, 2021 at 10:26
  • \$\begingroup\$ @Kartman yes we have techspray wondermask which is pink. we tried that but takes quite long to dry and the strength isnt great. kapton tape would be good for small runs but we mass produce these boards with 2 headers a board and around 16-20 boards in a panel and then anywhere between 1000-10000 boards total produced in one run. ill add a photo so it is easier to see. thankyou \$\endgroup\$
    – Korb
    Commented Oct 20, 2021 at 10:43
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    \$\begingroup\$ Alternatively, show the customer how much it costs to deal with incorrectly soldered headers and compare that with the price difference to headers that stay put during the reflow and let them see that the more expensive part results in cheaper manufacture that saves them money. \$\endgroup\$
    – JRE
    Commented Oct 20, 2021 at 11:43
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    \$\begingroup\$ your problem seems to be that your customer has provided you with a design that is not easily manufacturable by you. are they aware of this? are they paying extra because of it? if not why not? \$\endgroup\$
    – Jasen Слава Україні
    Commented Oct 20, 2021 at 19:09

3 Answers 3

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As an assembly jig could most easily be made from a number of blank boards, they will already have the holes in the right places, and be available.

enter image description here

The top light green board is the one you are assembling. The dark green boards are a stack of blank boards, epoxied together, with clearances routed out from the upper boards to avoid components on the underside.

The pin on the left is loose, and retained to height by dropping to the bottom of the hole. The pins to the right are plastic stripped assemblies, retained to height by resting on the top of the jig.

In use, you would either assemble the pins into the jig, and then drop the board on. It may be difficult to line up a large number of pins all at the same time. Alternatively assemble the pins into the board, drop the jig on, then invert. You could drill out the jig holes for greater clearance to make the second way easier on alignment.

You need to make sure that the thermal mass of the jig doesn't interfere with the (assumed IR) reflow process.

If epoxied PCB doesn't withstand multiple passes through the oven, then you could use the same PCB drill files to make something from metal or ceramic.

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  • \$\begingroup\$ Just taking a look into this now, ive edited the original post with examples that may help. \$\endgroup\$
    – Korb
    Commented Oct 20, 2021 at 11:37
  • \$\begingroup\$ Considering it's a 90-degree header, this doesn't appear to be a solution for this particular PCBA. \$\endgroup\$
    – Barleyman
    Commented Oct 20, 2021 at 12:12
  • \$\begingroup\$ Now we have more details in the question, yes, the answer isn't as simple as this. The OP will have to employ slightly more design work to come up with something that will hold the board and pins in the right juxtaposition. \$\endgroup\$
    – Neil_UK
    Commented Oct 20, 2021 at 12:57
  • \$\begingroup\$ I suggested a 3D printed jig, that can be arbitrary shape but obviously it'll take time to design. If the OP uses proper STEP models in e.g. Altium, it'd be possible to hand the output 3D file to a mechanical shop for 3D printing but they won't do it free as in beer. But it shouldn't be that expensive because the 3D model does most of the work for them. If they have to create a model themselves it'll cost more £££. It might be possible to do something quick and nasty like soldering sockets on a breadboard and using a piece of putty or something to make the PCBA stay put. \$\endgroup\$
    – Barleyman
    Commented Oct 20, 2021 at 13:02
  • \$\begingroup\$ @Barleyman we have a 3d printer here in work \$\endgroup\$
    – Korb
    Commented Oct 20, 2021 at 13:20
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Depending on your volumes and labour cost, simple hand soldering is a valid solution to this kind of assembly items, especially as the connectors are 90 degree and two different headers must align nicely to plug in cleanly to the socket(s). Constructing some kind of assembly jig for reflow is an option but that kind of thing costs money which apparently is a no go.

Customer not accepting any cost increases sounds like you(r employer) made a bad call at RFQ and didn't consider the hand assembly cost. The obvious answer is to swallow the cost this time and call it lessons learned.

One thing that could help with the hand soldering is creating a 3D printed jig that will keep the headers straight during the manual soldering. That will reduce problems with misalignment and make it easier to do the soldering, which saves money and reduces defects.

Edit: Cheap and cheerful solution might be to solder header sockets to a breadboard and sticking a wad of blue tack or similar sticky putty to the breadboard which will keep the PCBA from moving while soldering. YMMV.

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  • \$\begingroup\$ spending some money our end is okay as long as it doesnt affect the customer. hamd soldering would be impossible as around 3000 solder joints would have to be soldered an hour. i think a reflow jig is the way to go \$\endgroup\$
    – Korb
    Commented Oct 20, 2021 at 13:17
  • \$\begingroup\$ @Korb You have the 3D printer which would theoretically make it easy or at least easier but on the other hand things get melty in the oven and you'd presumably need a lot of supports. But it's an idea. 3k pins an hour isn't that huge amount depending how many people you have. There's 14 pins in two neat rows, GND/Power plane pins are obviously the worst but otherwise you can go right down that row rapidly. Only 1 pin has to be soldered to keep the whole stay put, with a breadboard header socket rows plus a 3D printed support that should be doable fairly rapidly. \$\endgroup\$
    – Barleyman
    Commented Oct 21, 2021 at 22:17
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I can think of a few options:

  • press-fit headers (they stay by friction instead of solder)

  • headers with kinked pins (they stay by friction but need soldering)

  • some sort of platform that supports the headers during reflow,

  • just solder the headers last

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  • \$\begingroup\$ Thanks jasen As we make these boards for a customer, we cannot change the design of the board. Although we did look into kinked pins and they worked perfectly, but as they were more expensive the customer wouldnt go through with it. We have tried building jigs on a metal plate with metal bars on top to support the pins but occasionally the boards are bent from the first side of production, not much but enough to allow the middle pins to drop slightly. i think with the right design and suitable materials this will work but im not sure what to do. soldering last isnt option as they are mass prod \$\endgroup\$
    – Korb
    Commented Oct 20, 2021 at 10:56
  • \$\begingroup\$ I think we will have to look more towards an adhesive. thanks for the ideas. \$\endgroup\$
    – Korb
    Commented Oct 20, 2021 at 10:57
  • \$\begingroup\$ maybe get a tool made to kink the pins so that you don't have to pay extra for the parts. \$\endgroup\$
    – Jasen Слава Україні
    Commented Oct 20, 2021 at 11:15
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    \$\begingroup\$ maybe put some of the holes for the header out-of line to increase friction \$\endgroup\$
    – Jasen Слава Україні
    Commented Oct 20, 2021 at 11:22
  • \$\begingroup\$ @Jasen I think that's what Adafruit or Sparkfun do for their kits so that they're easier to solder \$\endgroup\$
    – DamienWontContributeToAITheft
    Commented Oct 20, 2021 at 12:50

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