There is an old saying that something is a “drop in the ocean”. This is how I felt with the prospect of replacing a 12 V heating bed on my printer with a new 24 V bed. The old bed had a nice plug from the factory, although I had replaced the cable a long time ago due to heating issues with this particular printer. However, the new bed only had bare copper pads.
I’m not a soldering beginner: I made my first solder joint sometime in the early 1970s. So I felt up to the challenge, but also knew that I couldn’t use my usual Edsyn iron for a job like this. Since the heated bed is essentially a giant heat sink for these pads, I knew it would require the big guns. I dug up my old – and I my super old – Weller 140 W soldering gun. That would be enough, wouldn’t it?
Well the Weller …
Obviously not, otherwise you wouldn’t be reading this now. It could be that it just needed a new tip – this thing is seriously old, but it just wouldn’t get the pads hot enough for the solder to really flow. I finally got the wires glued, but the solder joints were so bad I couldn’t imagine they would withstand the constant bending.
I wondered if I should try a heat gun, but decided to try something completely different: flame. You can get butane soldering irons and torches from a variety of locations at many different price points. Since I was cheap, I picked up a Schneider brand iron from Harbor Freight. The handle has three attachments that nest. A collar just shoots flames like a torch. A small tube that fits the collar will keep the flame out and you will get hot air at the end. This tube can also accommodate a soldering iron tip.
We think the promotional image on the Harbor Freight website (see opposite) is a bit optimistic. We do not recommend this iron for surface mount work on a circuit board. I took a lot of heat, however, and as the video discusses below, the thing almost extinguishes too much flame. You can modify it like this [marshkid1] does in the video so it comes out less, but that wasn’t my problem.
It turned out that getting butane is not as easy as it used to be. That being said, you really want butane to be made for this type of tool so it doesn’t clog. I chose to only use lighter refill butane and took my risk. So far, so good.
There was only one problem. Despite the fierce flame, the solder just wouldn’t really melt enough to flow. The tinning of the wire would melt and remove some of the top surface of the pads, but since the entire surface of the circuit board resisted the heat it was impossible to get a good connection.
What should I do?
I considered heating the whole board in an oven or on a hotplate. I even thought of soldering under an IR lamp. In the end, I used a two-pronged approach. I removed the soldering tip from the iron and squirted hot gas over the connections. Then I used the Weller and finally got a reasonably good solder flow. However, the hot air alone was not enough.
The joints aren’t the best looking I’ve ever done, but they seem to hold up when used. Of course, I soaked everything with rosin, tinned everything and made sure that everything was clean. It was just too much heat capacity.
I can try again even if it works well enough at the moment. Maybe I need one of those giant car soldering irons. Or maybe I should use the SMD heat gun to preheat the connections. I’m sure I’ll get some things to try out in the comments.
I don’t think that’s the answer. Maybe it takes a PCB heater to solder a PCB heater?