Soldering is the joining of two metal surfaces together using a metal filler called solder. Soldering is how we assemble a PCB by putting components on it.
To determine which components go where, you can reference the schematics and layout diagrams for the board you are soldering. In Altium, you can click on a component for its identifying information and linked datasheet. Some components will be obvious like ICs, connectors, and components with an associated identifier, but others will require to check for the proper values.
Many components like capacitors, inductors, and resistors are sized by a four digit sequence. The first two digits are the length in mm and the second two digits are the width in mm. The most common sizes you’ll encounter soldering at UW Orbital are 0603 (0.06 in x 0.03 in) and 0402 (0.04 in x 0.02 in).
Components are either surface-mount or through-hole. Surface mount components are those that should be soldered on one surface on the board (ICs, capacitors, inductors, resistors, etc.). Through-hole components are those that should be soldered through a hole on the board (headers, connectors, etc.).
Soldering can be done either by hand or using reflow methods. The hand method is what most people are familiar with, which is using a soldering iron to melt solid solder used to join a component to a pad. By contrast, reflow methods use other devices such as hot air stations, hot plates, and reflow ovens to melt solder paste previously applied to join a component to a pad. Hand methods are often better if you want more control over the soldering or to solder through-hole components.
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Soldering equipment reaches very high temperatures. Do not touch any surface that heats up, including the soldering iron tip, hot air station nozzle, hot plate, reflow oven insides, and PCB + components. Also, stay clear of the hot air nozzle’s output.
Also, keep away from any equipment sensitive to heat.
Solder is leaded, so we also want to take steps to avoid breathing in the toxic fumes as much as possible. Make sure you have a fan set up and ready.
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A soldering iron uses a metal tip that heats up to melt solid solder, which is stored in coils in plastic tubes. Begin by placing the component on the pads, making sure that it is in the correct orientation. You will then solder it one pad at a time. Apply a lot of solder flux. Solder flux helps the solder flow to make the connection. Use the soldering iron to melt some of the solder onto the tip and onto the connection point between the component and the pad. Be careful not to use too much solder as it may then short nearby pads or connections.
For through-hole components, apply solder all around the connection to make sure that the connection is complete. You should have a cone around the part of the component making the connection through the PCB. Since through hole components may interfere with the balance of the board placed on the bench while you are soldering, you may want to use a stand to hold the board while you are soldering. For soldering headers specifically, one trick you can try is to place the connection side of the header in a breadboard to fix it in place and hold the PCB in the air with tweezers if necessary.
Desoldering with the soldering iron can be a bit tricky. You will most likely need to add more flux to allow the solder to flow again. Then, heat up the connection between the component and the pad, including the component and the pad if necessary. You can then use the tweezers to remove the component.
If you apply too much solder, you will want to remove it so it doesn’t interfere with any connections (and also for aesthetic purposes). Much of the time if there is too much solder, you can heat up the excess solder and remove it with the soldering iron tip or the tweezers. You can also use solder wick, which is a ribbon of braided copper, to remove excess solder. To use the solder wick, first place the solder wick on top of the solder you want to remove. Then, use your soldering iron to heat up the solder wick, and it along with the solder should heat up. Solder will stick to the solder wick. Then, remove the solder wick along with the soldering iron tip. Make sure these are removed together as removing the solder wick without heat may result in ripping the pad off the PCB. Another tool you can use to remove excess solder is the solder pump which sucks up extra solder.
A hot air station outputs a stream of hot air through a nozzle to heat up components and melt solder paste. Begin by applying solder paste to all the pads of a component. Solder paste is a mixture of solder, flux, and other ingredients that help it make a good electrical connection. Then, place the component on the pads, making sure that it is in the correct orientation. Then, hold the nozzle output directly above the component such that it is normal to the joining plane. This position is very important as angling the nozzle may cause the component to drift out of its place. Keep applying hot air until the component is securely in place. If you applied enough solder paste, you should be able to visually see the solder paste retreat from the edges and perhaps even darken or bubble. Use your tweezers to poke at the component and make sure it is in place.
Desoldering a component can be easily done by heating up the component through the same procedure as above, and then using your tweezers to remove the component when possible.
Note that you should only use the hot air station to solder one component at a time.