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Soldering Iron Technique Question
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Please be positive and constructive with your questions and comments.

Soldering Iron Technique Question

by thelaughingfool on Sun Jul 08, 2018 7:28 pm

I have a lot of difficulty soldering circuits together. Due to some medical issues, my hands have a tendency to shake during fine motor work. The narrow grip required to hold a traditional soldering iron is difficult to maintain, and as a result, the hot tip of the iron will jump around beyond my control. Then I got an idea. What would happen if I lightly fixed the iron in a clamp or vise, and then maneuvered the circuit and the solder to affix the components together. I can't find any resources that discuss this as good or bad, but I feel like there's a reason people don't traditionally do this. Are there any hidden dangers associated with doing something like this (which I have not tried yet), and would this be a suitable alternative given that my dexterity improves with a wider grip. Or are there other soldering options that may not need the traditional iron grip.

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Re: Soldering Iron Technique Question

by adafruit_support_bill on Sun Jul 08, 2018 7:47 pm

With many types of tools, there are times when it is better to 'bring the work to the tool' instead of 'bringing the tool to the work'. Issues such as fine motor control may tip the balance on such decisions .

I have found occasions where bringing the work to the iron had advantages. In the past I have used things such as a Panavise Jr or an articulated arm similar to this one: to hold the iron.

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Re: Soldering Iron Technique Question

by adafruit_support_mike on Sun Jul 08, 2018 11:23 pm

The bottom line of all Making is, "if it works, it works."

One of the scary things about Making is that there are so many options. We have standard procedures to avoid being overwhelmed by the sheer number of ways things can be done. Nobody has the right to revoke your license for choosing to try a new/different technique though. If you can physically arrange the pieces to try something, that's all the permission you need to do it.

Grab ideas like that with both hands and see where they take you. Even if you decide you don't like it, you'll have to think about the process and solve problems along the way. That's always valuable, no matter how a specific project ends.

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Re: Soldering Iron Technique Question

by flounder on Fri Sep 14, 2018 2:52 pm

The secret of good soldering: The heat is applied to the components to be soldered, which melts the solder and causes it to flow and "wet" the components to be soldered.

Nowhere is it written that the components are the fixed position and the iron is moving. Or that the solder cannot be pre-applied (in fact, in reflow soldering, it is) As observed, any technique that accomplishes the goal of good soldering is a legitimate approach. The key is to not overheat the parts, because this can damage most semiconductor-based components. Passive components (resistors, capacitors, inductors) can usually withstand a bit more heat.

You might even consider using a hot-air rework station as the heat source, and use solder paste (no, not the acid flux used when soldering pipe, which was also called solder paste, but the new meaning of the term: a paste-like mixture of solder and flux). Solder paste is most commonly used to deal with reflow soldering, but I can imagine using it for discrete component soldering. Apply a drop of the paste, and apply the hot air to melt the solder, that is, treat the problem as if you have a reflow oven. I am having problems soldering, since at 71 my fine motor control is not what it used to be, and I have thought about applying this method myself. I even bought a hot-air rework station. Beware of the cheap kind you find online; I am told they have a nasty tendency to catch fire. A good-quality station costs a bit more, but is better than losing your shop and/or house.

I suspect the hot air rework station sold by Adafruit is a reliable product, since they tend to sell products they use. And they would probably not use something that tended to catch fire even occasionally. Once you have this, I think your best choice would be a low-melting-point solder paste. I have an Sn/Bi solder for reflow soldering that melts around 140°C, whereas standard Sn/Pb solder melts around 180°C. The paste I have comes in dispenser tubes, which work like glue applicators. You squeeze the paste out into a blob. In reflow soldering, the paste usually comes in jars, and is spread out on top of a thin plastic or metal sheet with holes cut in so you can limit the paste to just the pads. The result is a coating of solder just a few thousandths of an inch thick. I don't know if the idea of a reflow oven works with discrete thru-hole components.

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Re: Soldering Iron Technique Question

by adafruit_support_mike on Fri Sep 14, 2018 11:36 pm

Reflow soldering is controlled by surface tension. When the solder melts, capillary action will pull it into the spaces between the PCB and the components. For through-hole parts, the space between the lead and the hole will pull solder in.

The heating profile is an issue for reflow work because the surface tension of molten solder gets lower as it gets hotter. That's why solder flows toward heat, even with a soldering iron: the hottest part of the solder spreads along the surface of the metal fastest. For large joints (compared to surface mount) you need to give the copper time to heat up before the solder melts. Otherwise, the molten solder will cool down as it goes into something like a hole and will form a plug.

A reflow oven lets you control the heating curve, but for bench work you can control the preheating by moving the air nozzle farther away from the PCB. Hold it back for a while to let all the metal near the joint heat up, then when the solder starts to melt, then bring the nozzle up close to pump in a lot of heat while the joint forms.

It takes some trial and error to get a feel for the temperature and distances, but just like soldering with an iron, isn't hard to learn. It's mostly just a matter of getting some practice.

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