Soldering

Soldering is the act of joining two metal parts together with a low melting temperature metal alloy in combination with a Flux, Typically done with an electric Soldering Iron. The joining metal alloy can be split into two seperate groups based off on the alloy containing lead or not, Leaded Solder and Lead Free Solder respectively.

Soldering Mechanics

Soldering relies on 3 primary parts. All of these parts are important in attempting to solder parts together and if one area isn't sufficient the resulting Joint can fail or never be created.

Temperature

Temperature plays a crucial role in soldering in two ways, Working Temperature in regards to the alloy being used and Heat Capacity in regards to the the object(s) being soldered.

Working Temperature

Working temperature is a straightforward part. This is temperature at which the alloy melts and will flow before it turns back into a solid again. Though just having a Soldering Iron that can reach this temperature is not enough for the work to be done. This is where Thermal Capacity comes in.

Thermal Capacity

This is the most dynamic part of soldering and leads to the most issues. Every object has two main properties, Thermal Conductivity and Mass.

Thermal Conductivity

Thermal Conductivity is the rate at which the material will accept or release heat. The higher this is for a material the faster this change will take place, this is why copper will heat quickly but the surrounding glass can stay much cooler. Glass is a poor conductor of heat. Oxide layers will also limit the ability of the materials to accept or transmit heat to surrounding areas.

Mass

Mass dictates the total amount of heat an object can hold. As an an object becomes larger the amount of heat required to bring the entire object up to temperature increases.

These values can all be thought of like containers and water, Mass is the size of our container, Thermal Conductivity is the pipes allowing water in and out. Together these make the Thermal Capacity. The amount of heat coming in must exceed the amount going out to reach a given temperature. If at any time the heat leaving one object exceeds the amount coming in the temperature will reach an equilibrium below the target temperature.

Thermal Table

Thermal Condition	Mass - Soldering Iron	Mass - Soldered	Result
Heat In > Heat Out	Small	Small	Stable Temperature is possible.
Heat In < Heat Out	Small	Small	Temperature will not be sufficient to solder the object.
Heat In > Heat Out	Small	Large	Stable Temperature is possible.
Heat In < Heat Out	Small	Large	Temperature will not be sufficient to solder the object.
Heat In > Heat Out	Large	Small	Stable Temperature.
Heat In < Heat Out	Large	Small	Temperature will be stable until the iron's held heat is depleted. Will work for short amounts of time.
Heat In > Heat Out	Large	Large	Stable Temperature is possible.
Heat In < Heat Out	Large	Large	Temperature will not be sufficient to solder the object.

Metal Preparedness

When soldering you want very clean metals, no oils, dirt, residues or oxides on the surface. All of these will interfere with the resulting joint or make the solder entirely fail to bond. This also applies to the solder alloy as the oxides will interfere with heat transfer and build up as Dross.

Flux

Flux does two things for the joint, First it cleans oxides off both the object being soldered and a the solder alloy itself, it then protects these surfaces from reacting with oxygen during the soldering operation.

Flux will also improve the Wetting of the solder alloy allowing it to smooth out and bond to the other metals.

If the metals are too dirty, flux alone will not solve the problem and stronger chemical or mechanical cleaning will be required to allow the soldering process to work.

Solderability

Solderability	Base Metal
Easy	Tin Copper Bronze Brass Lead Zinc Nickel
Possible	Carbon Steels Low-Alloy Steels
Hard/Not Worthwhile	Aluminum Aluminum-Bronze High-Alloy Steels Stainless Steels
Not Soderable	Cast Iron Chromium Titanium