DIY PCBs with no through plating - Page 1
Forum section: electronics / general

author: oliver602
author_rank: Regular Contributor
timestamp: August 04, 2016, 11:37:57 pm
content: I want to connect two traces on a double sided board using the lead of a through hole part(a USB connector). Sorry I don't know what you call this. What you normally use vias for. Is there a way I can get solder on the pad under the part to make the connection? I tried to get the solder to wick up through the board from the bottom side but it wouldn't happen. Is that even possible? Any good way to do this besides through plating or making a link elsewhere?

author: sleemanj
author_rank: Super Contributor
timestamp: August 05, 2016, 12:56:59 am
content: If you can access the pad, even if you have to use the finest tip you can, then that's of course no problem, just top-side solder it, for through hole resistors, diodes, transistors etc... no problem. Electrolytic capacitors you can always just have hovering above the board a couple mm so you can get the iron under. If it's a PCB header you are doing, that's easily enough resolved just by lifting the plastic base up a bit and solder underneath before pushing it back down, bit of a fiddle but works fine, for board-to-board interconnects you could consider using round-pin (aka machine pin) headers which you can solder top-side no problem.If you can't access the pad at all though then it's tricky.Using a hollow rivet is probably best, if the hole/pad is wide enough to accommodate the rivet large enough to get the pin through the rivet. But getting said rivets may be expensive though...https://www.megauk.com/through_hole_rivets.phpIf the hole is really tight on the pin, MAYBE, you could put a mound of solderpaste over the pad, insert the part, and heat the pin to melt the now hidden solderpaste and hope it works. Never tried it, just an idea.Taking some thin repair enamelled wire (0.1mm or whatever), you could wrap it around the top of the pin right under the component body and thinly solder in place, insert the part so the wire is between the part and board, and then affix the other end of said wire to somewhere on the top side trace in question which is more accessible.

author: oliver602
author_rank: Regular Contributor
timestamp: August 05, 2016, 01:36:17 am
content: Thanks sleemanj for your detailed answer, I will try the solder paste and wire ideas tomorow

author: uncle_bob
author_rank: Unknown
timestamp: August 05, 2016, 02:17:00 am
content: HiGrab a piece of flexable speaker wire and tear about 1" of it apart. That will give you an inventory of thin un-insulated copper wire. The technuque you will be using is called a "Z wire". One end lays flat on the top pad, the wire goes through the hole and the other end lays flat on the other pad. Viewed from the side the wire looks a little bit like a letter Z.Once the wire is in place, you tack solder it to both pads. The part then goes through the hole and you solder the part in place. If there isn't enough room in the hole, the hole needs to be drilled out.Bob

author: technotronix
author_rank: Regular Contributor
timestamp: August 05, 2016, 06:19:40 am
content: Try creating solder bridges.

author: uncle_bob
author_rank: Unknown
timestamp: August 05, 2016, 01:32:51 pm
content: HiThe real answer to this is don't do it.Since this is a DIY board, you control the layout. In locations that have blind through holes, put in a redundant non-blind hole. The other alternative is to simply not join the two traces under a part in the first place. Yes it's a little different than the design rules for a plated through board. Back in the days before plated through holes, we ran big lines of Berg machines that put ugly looking rivets in the holes. They pretty much worked most of the time .... I don't know of anybody who mourned their retirement.Bob

author: CJay
author_rank: Super Contributor
timestamp: August 05, 2016, 01:41:49 pm
content: Quote from: uncle_bob on August 05, 2016, 01:32:51 pmOh those rivets were hateful things too, they used to cause no end of problems in the TVs I repaired and the quality of the double sided boards they were used on was awful too, the top foil was prone to lifting if you lingered a few seconds too long with a soldering ironFortunately I came into that trade just as plated thru hole tech had become mature so I didn't have to deal with the rivets for too long.

author: MicroBlocks
author_rank: Contributor
timestamp: August 08, 2016, 05:19:50 am
content: Go with the 'Z wire' technique. Works pretty good.If the holes have enough room you could add more strands to improve the wicking action.I actually use wicking wire for that, cut of a piece and unravel the threads.

author: oliver602
author_rank: Regular Contributor
timestamp: August 09, 2016, 01:32:44 am
content: Thanks everyone. I really wanted solder paste on the top pad to work but have to put too much heat into the part before it would heat the pad enough to flow. I had some success using a heat gun instead of the iron but I always burned my PCBs.Z wire worked great