Rectangular solder pot for 7x7 board with 500+ through-hole connector pins - Page 1
Forum section: electronics / general

author: jrowberg
author_rank: Contributor
timestamp: August 14, 2020, 04:47:40 pm
content: I'm working on a (more-or-less) universal test jig base PCB design, which is build primarily around submodules routed together through a variety of 0.1" 2-row IDC connectors on a base PCB. This base PCB is about 7 inches square, and basically all of the parts that go on it are those connectors. There are over 500 individual pins, possibly closer to 1000 by the time I finish the design. See the attached screenshot for reference.Ido notwant to solder these by hand. I've done a similar board before, and it's just ridiculously time-consuming.I considered SMT-style connectors since I'm familiar and comfortable with that process, but I'd rather stick with through-hole for this board because these connections will benefit from increased mechanical strength; I anticipate the plug-in modules will be inserted and removed regularly in at least some use cases. (If SMT-style IDC connectors do not suffer from mechanical issues with repeated insertion/removal, someone please let me know!)Anyway, if through-hole is required, this seems like a perfect candidate for a dip-soldering device such as this one:https://www.aliexpress.com/item/33008770419.htmlIs there a better tool for soldering 500+ connector pins on perhaps 5-10 boards at a time?

author: jmelson
author_rank: Super Contributor
timestamp: August 15, 2020, 01:35:28 am
content: I have a ChuangMeiWei 5 x 7" solder pot that I use for this sort of task. I have a board that is about 3 x 3" and has 40 through-hole parts on it.I mask of things that should not be soldered with Kapton tape, and then paint the back of the board with water soluble liquid flux. I drop all the parts in, and then preheat the board with a hotplate to about 100C for 2 minutes. Then, I made a kind of tongs that has claws spaced just right to hold the board without touching any of the parts. I dip one edge of the board in the solder and then tilt it down to be level on the solder. This prevents air from being trapped under the board. I hold it flat in the solder for 8 seconds and then lift the opposite end a bit. Then, I SLOWLY lift the board out of the solder, at just a couple mm per seconds. Lift too fast and you get solder bridges and icicles. The hand part of the process takes some trial and error, but I usually get close to 100% perfect soldering with it.I also folded up a little cover for the solder pot out of galvanized steel with an insulated handle. This keeps air off the hot solder and slows the oxidation.It sounds like you need the next size up pot for your board.Jon

author: jrowberg
author_rank: Contributor
timestamp: August 15, 2020, 02:55:59 am
content: Thanks, Jon! That is super helpful information. I don't suppose it would be possible to get a picture or two of your setup with the pot and your claw tool? I think I follow but a visual reference would be great. I wonder how easy it would be to rig up a small motorized winch system with thin stainless steel cable to help with the dipping process. Probably over-engineering this a bit.Are there any notable issues with noxious vapor or other nastiness before, during, or after the process? I have a smallish ventilation system that would probably work, but if possible I'd rather just do this step on a small table right in front of an outward-blowing window fan.Also, if you can share, how much solder (in bar form?) is usually necessary for your 3x3 job, and what does that cost you? I've never priced out that kind of raw material. Is it reusable if you cover it, or is whatever you melt for any single run of the machine only good until it cools off?

author: mariush
author_rank: Super Contributor
timestamp: August 15, 2020, 05:46:20 am
content: Could you maybe use solder paste and hot air gun , some infrared light of some sort to heat up the board?I'm thinking getting some sponge material, make cutouts in it for the connectors on the other side so that you can flip the circuit board and have all the connector pins stay in the holes.Another stencil / something applied on top , pour solder paste in the area where the pins are ... get hot air gun of some sort over the whole set of pins

author: jmelson
author_rank: Super Contributor
timestamp: August 15, 2020, 04:22:39 pm
content: Quote from: jrowberg on August 15, 2020, 02:55:59 amOK, first picture is the pot with the homemade cover. 2nd picture is the claw holding the board. Sorry about the blur, this was a 3-hands job to get a pic.No, there really isn't that much fumes. I have been using the same batch of solder since I set this up. It does take about 3 bars of solder to start up the pot. I have added one whole bar, at least, maybe two, in the time I have used this. You can get SAC305 bar solder on eBay surprisingly cheaply.To answer mariush, I think the hot air gun might blow parts off the board, unless done super carefully. Yes, I've thought about making a pallet to hold the parts and then using a soldering robot. I rigged a soldering iron with springs to my milling machine, and a motor to feed solder. It kind of worked, but had to be babysat to make sure it was actually soldering the joints. I do have two connectors on that board that have to be soldered on the component side, that would be a good job for a robot.Jon