thru-hole connector on an SMD board - Page 1
Forum section: electronics / general

author: artag
author_rank: Super Contributor
timestamp: October 23, 2022, 12:29:43 pm
content: I have a board design with almost all the components on the top side.However, I also need to make a multiwire connection to the bottom side. Either a thru-hole or an SMD connector can ber used for this but the SMD one obviously makes it a two-sided assembly operation.If I use a thru-hole connector, the solder is on the top side along with all the other parts and could be soldered at the same time. But the connector itself protrudes from the bottom so the board can't lie flat on a hotplate or belt.Is there a way to overcome this and assemble the board as though it had components on one side only ?

author: Jackster
author_rank: Frequent Contributor
timestamp: October 23, 2022, 12:33:19 pm
content: Thinking somewhat out of the box as you are trying to go for a single-sided assembly.Have an SMD connector on the top side, and a large enough cutout (if permissible) for the cable wire and connector to pass through?There are also press-fit THT connectors. Not a massive fan but maybe an option?In the assembly process, the THT would be done after SMT, so this should not be an issue having a THT on the board.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 23, 2022, 12:41:27 pm
content: Quote from: artag on October 23, 2022, 12:29:43 pmThrough hole components are most of the time not soldered through the same process as SMD components. There are TH components that are suited for reflow soldering and there are SMD components that are wave soldering capable but in general you would have SMD components done through a reflow oven and you would have TH components through a wave soldering process. TH components can also be selectivly soldered, which is probably the way to go for a board such as yours ;-)

author: tszaboo
author_rank: Super Contributor
timestamp: October 23, 2022, 12:57:58 pm
content: You could add bottom entry SMD headers and have pins on the other board.Or use a FFC cable or similar.

author: artag
author_rank: Super Contributor
timestamp: October 23, 2022, 01:39:43 pm
content: Thanks for the suggestions !The components on the top side are WS2812 and capacitors laid out in a specific pattern. So although there is a moderate amount of space, I can't move parts around to make it the right shape. I do have space for a double row of 2mm TH pins but if I put a topside SMD connector there the cable would obscure the LEDs.So, I really want to have the cable on the bottom side and nothing more than pins coming through to the top. The bottom entry SMD headers might be the way, but I haven't found any yet. That could be because I wasn't using the right name when searching for them.update : Yes, I'd been looking for SMD pin headers where the pins go through the board. But a bottom entry pin socket with either wire-mounted pins or a pin header plugged into both cable socket and pcb socket might do the job.Do bottom entry FFC connectors exist ?

author: tomgat
author_rank: Regular Contributor
timestamp: October 23, 2022, 02:09:50 pm
content: Quote from: artag on October 23, 2022, 12:29:43 pmThis isnt an issue from a manufacturing standpoint. You just put the board in a jig when it goes through the belt (or a batch oven) just like you do with double sided component boards.From a manufacturing perspective its always better to use SMD, but from a designers perspective the main decision to going with a TH is deciding if you need that extra rigidity. If you dont and are limited on space on one side, then you can just put the SMD connector on the other side. You will get an extra cost because of a 2nd operation (ie. You must stencil, place, and reflow other other side)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 23, 2022, 02:21:15 pm
content: how many lines in the connector?is production qty high enough that hand-soldering isn't an option?I've never seen a bottom-entry FFC, or a male-pin bottom entry pin header - plenty of female ones though

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 23, 2022, 09:15:39 pm
content: Your options:Hand solder a TH connector placed on the bottomFind a bottom entry connector you like in the Samtec or Digi-Key or whatever catalogJust pay for two-sided reflow#2's the best if you see something you like. Otherwise there's not much difference between #1 and #3 if you're paying someone else to do the assembly. They never mind hand soldering if it's in low volumes.

author: tszaboo
author_rank: Super Contributor
timestamp: October 24, 2022, 07:56:49 pm
content: Quote from: artag on October 23, 2022, 01:39:43 pmThere you go, a few examples:https://www.we-online.com/catalog/en/PHD_2_0_SMT_DUAL_SOCKET_HEADER_LOW_PROFILE_6210XX21821https://nl.rs-online.com/web/p/pcb-sockets/1799037

author: mariush
author_rank: Super Contributor
timestamp: October 24, 2022, 08:11:00 pm
content: Another option could be castellations ... half circles on the edge of the pcb .... then just have some pins on the side and you can quickly drag solder to make solder joints between the half through holes and the pins.Don't know how much current ... you could also resort to how some multimeters connect speaker to pcb .. use some springs .. pads on the led strip and the bottom board, some plastic tubes or a small connector housing on the bottom just to keep individual springs vertical, then as you bring the pcbs together the springs contract a bit and you get good contact.could also have just some square or round pads on the top board, with holes in the center big enough to get pins from the bottom through those holes ... then it's just a matter of flux and solder covering the pads with solder (sort of how they do led bulbs)Or a rectangular slot through which a vertical pcb could be inserted ... pads to the edge of the rectangular cutout, pads on the vertical pcb .. some solder paste and you got a connection.Another option already mentioned .. flat flex ribbon cable and a surface mount connector on the edge of the board.