Activity: Learn how to Solder!

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Soldering is the process in which you join together two items by melting a conductive metal filler in between. In this case, the metal used is solder and - when cooled - creates a sturdy union between materials. In the Intro to Electronics workshop, you learn the fundamentals of electronics as well as how to safely solder electronic components onto a printed circuit board (PCB). This acts as a subset of that workshop by just giving the tutorial on on to solder!

Contents

The Materials

 
From left to right is the PCB, battery holder, 100 ohm resistor, clear 5V LED, SPST button, and 3V battery.

You're going to be soldering together the Basic Board (BB), which is blue. In order to do so, you need a few materials!

  1. Soldering Equipment Box, which contains:
    1. Soldering Station
    2. Soldering Iron and Cradle
    3. Needlenose Pliers
    4. Side-angle Cutters
    5. Vice
  2. Solder (Leaded or Lead-Free)
  3. Electronic Components:
    1. Blue PCB
    2. 10 Ohm Resistor
    3. LED
    4. Battery holder
    5. battery

The soldering iron and related equipment can be found in DaBL's soldering kits which are located within plastic containers found at the back of the lab under the tool wall. In DaBL, there are two types of solder: leaded and non-leaded. For the purposes of this activity either will do but keep in mind if you use leaded solder, lead is toxic and you should wash your hands after it is used. The electronic components can be found in the left most consumables chest nearest the sink. Ask a Creative and Technical Specialist (CaTS) if you need any help locating materials.

IMPORTANT SAFETY PRECAUTIONS

Soldering is hot! (Sometimes in excess of 600° Fahrenheit.) Solder contains carcinogens! (Specifically, lead.) The following should be kept in mind at all times when soldering:

  • keep the area around the iron clear of any objects
  • keep the cable connecting the iron to the base station clear so nothing gets snagged
  • be aware of your surroundings

Soldering Guidelines

While soldering, your mantra is:

  1. Clean the tip: vigorously rub the tip of the iron it in the brass shavings.
  2. Tin the tip: add a small amount of solder to the tip of the iron.
  3. Heat the leg and the pad at the same time: make sure you touch both things you are soldering together so that they both heat up.

Soldering Guideline 1: Setting up your workstation and parts

Put your iron in its cradle, plug in the soldering station, and make sure the area around both of these devices is clear. Then turn on your station. It may have actual temperature control, or it may just have a knob. Either way, ask your instructor what temperature setting to use.

While your iron is heating up, make sure you have all the necessary components.

Then, grab about 12” of solder from the spool and wrap it gently around your non-dominant thumb, leaving about an inch or two pointing outward from the pad of your thumb.

You’re going to be pushing components in from the top of the PCB and soldering them to the bottom. Secure the PCB in your vise (or both alligator clips of your third hand). Pick up one of the 470Ω resistors and find its corresponding shape on the top of the PCB. Push its legs all the way into the board from the top face so that the resistor is sitting flush with the board. (Remember that they don’t have polarity so it doesn’t matter which way you insert them.) Then gently bend the legs so the resistor won’t fall out when you let go!

Soldering Guideline 2: Clean and tin, clean and tin

Soldering depends on proper transference of heat, and heat transference depends on proper metal to metal contact. If there is anything in between, it will hinder the process. Oxidation will inevitably occur on any metal surface, and is especially likely on the tip the longer the iron remains on. So it is important to remove this oxidation regularly to keep the heat moving!

Pick up the soldering iron and hold it as you would hold a pencil. Cleaning the tip is as easy as simply rotating and dragging it across the brass shavings (or wet sponge).

The second part of this equation is to remember to add a very small amount of solder to the tip after you clean it; this is called tinning. You do this for the same reason you add oil to a pan when you are cooking: to increase the surface area of the fluid, and therefore more effectively transfer the heat into the two objects you are soldering together!

Soldering Guideline 3: Apply that heat!

It’s finally time! The goal with all your solder joints today is to use the solder to connect the leg of the component with the copper pad on the PCB. In order to do this, you’ll need to heat both the leg and the pad, and then get solder to flow over both of them. The most important point to remember here is that solder will flow toward the source of heat. So when you make your solder joints, you want to:

  • place the part of the tip with the “tin” you added onto both the component leg and the copper pad
  • apply more solder from the stash in your non-dominant hand on the opposite side of the leg to where the tip is.

Notice that the solder joints in the pictures above and below kind of look like Hershey kisses; this is what you are aiming for.

Take your time! Figuring out exactly how to do this is tricky at first, since this is basically an exercise in fine motor skills. You may have to add more “tin”, or move the initial application of the solder to somewhere a little closer to the tip. Ask your instructor for help if you are unsure. And when you are satisfied that all the component’s legs are secured on the PCB, use the wire cutters to snip off the excess leg.

Assembly Process

Each component is different; therefore, each needs to be taken into consideration individually. Make sure to take note of the components which have polarity (LEDs and the battery); you don’t want to solder them in backward! You’ll find that soldering becomes easier the more you do it.

The components should be soldered to the BB in the following order:

  1. Resistor (non-polarized)
  2. Button (non-polarized)
  3. LED (POLARIZED)
  4. Battery holder (POLARIZED)

When you're done: congratulations! You have just made a permanent prototype of your first circuit! Test it out to make sure everything works.

Now turn off your iron, and return all the tools back to their rightful positions in the shop - but be mindful of the iron, cradle, and station. The iron needs to cool down before storing it. Let it sit for five to ten minutes, and then pack it up as well.

Step by step