Building a daughter board that plugs into an existing PCB - Page 1
Forum section: electronics / projects

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 05, 2023, 11:30:34 am
content: I'm trying to build a daughter board that fits into an old PCB and need to tap signals from quite a few existing devices. Some are socketed and others I have desoldered and socketed.Some of the original sockets are of the single wipe type.I mounted the circuit board using turned headers but cannot get a reliable contact across all the sockets.Is there a better way?Perhaps I should replace the existing sockets with something else? Dual wipe?I could just solder the PCB assembly direct to the PCB but will have to modify my design as I have solder jumpers that may need to be changed on the underside currently.I'm particularly interested to know about any alternatives to sockets in this scenario

author: Ian.M
author_rank: Super Contributor
timestamp: September 05, 2023, 11:42:06 am
content: Once a turned pin has been inserted in a single wipe socket, that socket is compromised, and will never make reliable contact to any thinner pin. Also as the contact has been deformed, as you have discovered, it may not be reliable even with the turned pin, especially if its aged due to oxide and tarnish buildup on the contact, + the point of contact shifting.Depending on a dual wipe socket's exact contact design the same may be true for it.You don't have many options other than replacing the old sockets. I'd go with turned pin to mate non-destructively with the turned pin headers on your daughterboard, but still allow it to be reverted to no daughterboard + ICs in the same sockets.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 05, 2023, 11:54:47 am
content: Interesting.Rather than turned pin headers are there more socket friendly options?

author: Ian.M
author_rank: Super Contributor
timestamp: September 05, 2023, 12:34:32 pm
content: Yes, you can (with some difficulty for small quantities) get flat pin headers suitable for PCB mounting, but as you've already tried the turned pin ones, the sockets on the main board are already compromised, so they wont do you any good unless you have more devices that need this daughterboard. Also, they are a lot more fussy about alignment than turned pins (where the rounded tip and conical recess of the socket entry make them hard to misalign), and I would expect a significant risk of mis-insertion resulting in curled pins, which with your board's limited access to the middle sockets would be difficult to inspect for or correct.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 05, 2023, 01:31:21 pm
content: Yeap. It's all very tricky with the middle section. Perhaps it was a poor approach and I should split the parts up and go for some kind of interconnect scheme... Quite hard in this case with data and address buses.... But do-able.I might give up and rid myself of sockets and hard solder the whole assembly.

author: DTJ
author_rank: Super Contributor
timestamp: September 06, 2023, 10:39:11 am
content: Another approach to this problem is to use flexible PCB or thin <<1mm PCB material and lay it onto the bottom surface of the board directly.Have larger holes so the old circuit's through hole leg can go through the mod board and be soldered.I've seen it done commercially using both very thin PCBs and flex PCBs.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 06, 2023, 01:39:49 pm
content: Try using these with the turned pin style sockets.https://www.ebay.com/sch/i.html?_nkw=2.54+round+header+maleI have always had good experiences with them making a good firm connection.I use them for making FRAM adapters for replacing Dallas NVRAM's etc and they are great.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 22, 2023, 02:43:28 pm
content: So in the end I went for "Machined Pin" sockets and matching headers... works really well.

author: SeanB
author_rank: Super Contributor
timestamp: September 22, 2023, 05:09:25 pm
content: Have had some wire wrap sockets with poor contact, and not wanting to try to undo the wire wrap, because it was both wrapped and soldered, I simply went and got turned pin sockets, and soldered them to the existing single wipe socket, soldering each pin in turn to get a good connection. Then took another socket, and took the original fusible link PROM, and soldered it to the socket, then inserted the new pin section into the other. No more issues, and no need to remove 16 sets of wire wrap, buried under other wire wrap, and with a big risk of creating further issues.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 22, 2023, 08:58:23 pm
content: Quote from: NivagSwerdna on September 22, 2023, 02:43:28 pmLooks great.Using like-with-like should give the best solution.To avoid damaging main board sockets, during emulation or test, we have stacked a 'sacrificial DIP socket' between the wrong-sized pin, and the PCB, to ensure the PCB socket only sees an 'IC-like' insertion.