Hand-soldering connectors to planes on 6-layer 2 oz. copper PCB? - Page 1
Forum section: electronics / general

author: tinfever
author_rank: Regular Contributor
timestamp: November 10, 2023, 09:28:07 pm
content: Is there a threshold where it becomes no longer realistic to hand solder THT connectors to a PCB?I'm working on a PCB design (power distribution board) with at least 6 layers of 2 oz. copper. It will have connectors on both sides in close proximity and over 700 THT joints, most of which connect directly to copper planes on three layers that cover the entire board.Even with thermal reliefs on the THT pads, is such a thing even possible to hand solder for the first prototype or two? I'm not sure how I could preheat the board enough from the bottom without roasting the bottom-side connectors, or solder the joints fast enough to not have the connector pins start melting the connector housing.I have a Metcal MX5000 with a STTC-117 5mm tip, hot air station, and bottom side preheater. I've run into issues before soldering connectors just to a 1oz 2-layer PCB where the connector pins would start melting the housing plastic before the solder would wet the entire PCB pad.

author: thm_w
author_rank: Super Contributor
timestamp: November 10, 2023, 10:10:01 pm
content: You have one of the best setups possible for this task. If you are already melting the housing on a 2 layer PCB, it makes me think either: technique needs work, or, cheap low temp plastic connector was used. Are you trying to apply the tip to just the pad first?What are you preheating with and to what temperature (measured on the board itself)?

author: asmi
author_rank: Super Contributor
timestamp: November 10, 2023, 10:51:14 pm
content: With my PACE ADS-200 I was able to solder an SMA connector to a steel plateso it's all about using the right tools for the job, and knowing what are you doing.Quote from: tinfever on November 10, 2023, 09:28:07 pmYou should always heat up a connecting pad and never the pin. Once the pad is hot enough, the solder will flow automagically (provided there is enough flux). Also make sure you're using the right tip for the job - for large pads you need to use larger tips as they transfer heat to a pad more efficiently.

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 10, 2023, 11:42:49 pm
content: A high power iron like C470 will melt it like butter, with thermal reliefs it might be doable with a 80W iron, but I would use at least the C245 (~150W).Using a hot plate/heater will make things much easier.A increase of 50°C will be very noticeable, while 100°C should be still a safe temperature and ease things out even more.

author: thm_w
author_rank: Super Contributor
timestamp: November 10, 2023, 11:52:53 pm
content: OP already said they are usingSTTC-117, which is about the best tip possible if the width is acceptable. 390C 5mm chisel.They could try theHTC-7CH0053Sbut I don't think its much better, just might last longer.Quote from: DavidAlfa on November 10, 2023, 11:42:49 pmThe 80W metcal will outperform C245's 130W in many cases.

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 11, 2023, 12:13:22 am
content: Sorry, I'm not familiarized with metcal

author: uer166
author_rank: Super Contributor
timestamp: November 11, 2023, 01:50:14 am
content: With a Metcal it should be quite easy with a bit of preheating. I've soldered 2oz x8 layers without thermal relief with that exact tip. It takes some time and is definitely a little annoying without preheat.

author: loki42
author_rank: Frequent Contributor
timestamp: November 11, 2023, 09:01:52 am
content: Make sure you're using plenty of flux and hitting the pad and first. If you're still having issues you could try low temp solder like bismuth.

author: tooki
author_rank: Super Contributor
timestamp: November 11, 2023, 10:14:49 am
content: I’d consider preheating the board in an oven and giving it a good long soak to ensure it’s thoroughly preheated. Heating to 100-130C should be no problem at all. If possible, heat the connectors too, so their mass is also nice and warm. If available, an infrared or hot air preheater can then be used to prevent the board from cooling down too rapidly as you solder.Use a powerful ironwith as large a tip as is practical, but not set to an insanely high temperature. If the preheating is adequate and the tip big enough, you shouldn’t need a crazy hot iron. But you want the power there so that the temperature regulation can resupply the lost heat without delay. (For example, I use a 10mm chisel tip to solder BNC connectors to a 4-layer PCB. The huge mass ensures the tip doesn’t become a thermal bottleneck.)Flux is helpful. A good clean, freshly tinned tip with a sufficient amount of solder to act as a thermal bridge is essential.Another thing to consider is a selective solder bath. You would flux and preheat the board, then dip each connector’s pins to join them. The comparatively huge thermal mass of even a small solder bath can get the solder to flow well quickly.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 11, 2023, 11:08:17 am
content: Should be doable with that Metcal tip. Use leaded solder.

author: nctnico
author_rank: Super Contributor
timestamp: November 11, 2023, 06:40:51 pm
content: I use hot-air for these kind of jobs. Especially when there are many connectors involved. Works way quicker and more consistent compared to soldering each joint one-by-one.

author: ajb
author_rank: Super Contributor
timestamp: November 14, 2023, 09:45:28 pm
content: If all else fails, you could try a lower-temp alloy. You can go as low as 118°C with In52/Sn48, which is readily available from Chip Quik. May be good enough for a prototype.For production, consider reflowing the connectors (aka "pin-in-paste") if you have the option. Although if your assembler can do selective wave soldering that may be just as good and won't limit your connector options as much.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 21, 2023, 05:43:57 pm
content: Pre-heating combined with right soldering technique shoulddefinitelydo it. If not, you are not preheating or soldering properly. Instead of high preheat temperature, focus on gettingeverythingheated. If you use a hot plate, it needs to be big enough. Oven is even better. With oven, you have to be quick before the board cools down. Combination of oven then hot plate might be needed. Or hot plate plus adjustable hot air gun from above.Set pre-heating temperature something below damage level of connector plastics etc. Then you can preheat long enough.For one-offs or specialty equipment where you can ignore RoHS, standard 63/37 leaded solder helps significantly without having to resort to special alloys.