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I'm in the middle of designing a circuit with hopes of going to mass production (> 5000 units). I'm trying to think ahead in my part selection a little bit for reliability and cost effectiveness. My only metric is the cost on Digikey (or like distributors) and how much they cost when a reel is purchased.

If I have multiple PCBs (4x) in different locations in the product that need to be connected, are connectors still cost effective? There will be the connectors on the boards and wire harnesses would need to be made with the mating connectors. From an assembly standpoint, connectors make sense but of course increase the BOM cost. The other option would be to just have pads on the PCB and solder wires to connect from PCB to PCB. I would think the latter would be cheaper but a PITA for assembly.

Does anyone have any experience with this?

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  • \$\begingroup\$ get a quote on a wiring harness for 20k units to allow quick connection in assembly line, versus a quote for 5k units worth of hand-soldered and secured wiring point-to-point done during assembly. Also think about signal integrity and mechanical issues with pad-to-wire based connections.. Just something to think about \$\endgroup\$
    – KyranF
    Sep 16, 2016 at 17:28
  • \$\begingroup\$ You really have to look at all the costs including assembly and service. Connectors (depending on type) can be very cost-effective especially if the boards can come in from the assembly house with the connectors attached and you just snap harnesses from the harness supplier onto the boards or boards onto boards. Really high volume consumer products often have many connectors internally, and they're not doing it to waste money. \$\endgroup\$
    – Spehro Pefhany
    Sep 16, 2016 at 17:32
  • \$\begingroup\$ Design must consider,; cost; performance and reliability and ease of repair. Define the interfaces in terms of V,I, dv/dt,di/dt, distance, budget, number of signals, power and grounds....before asking for specifics \$\endgroup\$
    – Tony Stewart EE75
    Sep 16, 2016 at 22:33

2 Answers 2

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Things might depend on the signals your wires carry, the cost of labour, and the cost of PCB size (which might also drive enclosure size) but as a first suggestion I would go for simple shrouded 2.54 mm 2xN headers and matching crimp connectors for 2.54 mm ribbon cables.

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You didn't say how many wires are connected between the boards. The more wires, obviously the more it will cost to do the hand soldering. The 0.1" headers and IDC crimp connectors shown in Wouter van Ooijen's answer cost about 12¢ each in 5K quantities for ten positions, or lets say 2.5¢ per pin for both male and female sides.

At a fully-loaded labor rate of $15/hour, just an example, an employee would have to solder $15/$.025 or 600 pads per hour -- one very six seconds -- to equal this cost. So the cost is going to be pretty much a wash. (I realize with the IDC headers, there is some time involved in crimping the female connector on the ribbon cable, but there is also prep work to strip and tin the wires, so this probably is a wash also. I'm assuming the cost of the cable is the same in both cases.)

Going with connectors will have lots have advantages:

  • You can store the boards separately right up to assembly in the enclosure.
  • You can use the connectors to attach test equipment to do a board test.
  • After connecting the boards if something isn't working you can unplug them again, instead of unsoldering wires.
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    \$\begingroup\$ I sourced those 10-position thingies for ~ E 0.10 in quantity 1, but that was a few years ago. \$\endgroup\$
    – Wouter van Ooijen
    Sep 16, 2016 at 21:41
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    \$\begingroup\$ Go with assembled standard length cables for a labor light manufacturing. I know Samtec has standard IDC cable configurations and DIGIKEY carries them. \$\endgroup\$
    – Passerby
    Sep 16, 2016 at 22:41

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