Soldering tutorial

Learning how to solder is pretty much an essential skill for a diy stompbox builder. Here's an introductory tutorial (adapted from one post from the thread linked below), for visual guidance search Youtube for "soldering" or find links to videos further down on this page.


It is not technically correct, but you can generally ignore the specific temperature, and only go by my view of how the solder behaves.

You have to know a little thermodynamics (very little!) to understand skilled soldering. Every material reacts to heat by two processes - thermal resistance and thermal capacitance. The resistance/capacitance makes a small time lag for the heat to get through each little piece of the material. The lower the resistance (that is, the material the heat is conducting through makes a difference) and smaller the capacitance (lower mass) of each section, the faster heat gets from one end of the chunk o' stuff to the other end. The more mass involved, the slower everything works. The way this works out is that every wire is a chain of these little conduction/slowing sections.

If you have to reach a specific temperature at one spot (the joint you're trying to solder), then you have to put in enough heat to get the joint's mass up to temperature; in addition, you have to supply enough heat energy to offset the heat that's flowing away down the wires. Heat flowing away from the joint on the wires is wasted for your purposes in soldering. All it does is heat up other things on the other end of the wires, and cools down your joint, making soldering harder.

A lot depends on the temperature of your soldering iron. If the iron is just barely hotter than the temp to melt the solder, then the joint temperature only approaches soldering temperature slowly, as the long term end result of the joint "filling up" with heat. If the iron is significantly hotter than the melting point of solder, then the joint passes through soldering temperature with less elapsed time, on its way to a way hotter temperature. The reason this matters is that the heat conducting down the wires to other places has less time to heat up, because the short time the joint heats gives the heat less time to travel. So you can heat the joint to soldering, get the solder to wet and flow, and get the soldering iron off the completed joint before heat has time to travel very far down the wires.

The higher temperature of the soldering iron lets the joint get to temperature, flow and wet the solder, and let you remove the iron **before the heat can travel to and heat anything else**.

Think of the difference between grilling steaks and boiling stew meat. If you grill a steak, the outside can be charred before the inside is fully cooked. If you boil a piece of stew meat, the inside and outside of the chunks of meat get cooked at about the same time. Heat takes time to travel. Likewise, you can burn rice in the bottom of a pan before the water boils if you have the heat too high under the pan. If you turn the heat down to low, the heat has time to travel to all parts of the water before the bottom layer scorches. Same principle: the heat gradient is steep with big temperature differences.

So to solder well by hand: use a temperature that's just low enough to not cause massive oxidation on your soldering iron tip. Get the joint ready to solder (clean, all parts in place, wires pre-tinned, etc.) and then touch the smooth-mirror-shiney tip of the iron to the joint, adding solder just as the heat comes up. You can **see* the solder temperature rise to molten as it travels across the few mm of the joint. When it's all flowed smoothly, get the iron off the joint. A good solder joint on resistor leads takes about two seconds.

Thread on soldering - Especially posts 9, 11 and 15.


Really nice video on soldering