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Blog - Soldering 101

Special thanks to Bill Galloway, KF5YIV, for both the topic and the blog.

You rock, Bill~

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For this presentation topic, I want to discuss a few of the items needed and some techniques use for soldering. Soldering is a very easy skill to learn, but as with anything mechanical, the incorrect selection of tools can make the job unnecessarily difficult. In this session, we will be focusing on soldering electronic related mediums. By “mediums” I am referring to wires; connectors; or component leads to a PCB. These mediums are usually copper or tin. Aluminum and cast metals are not mediums that can be soldered.

The purpose of soldering is to make a solid electrical connection. Unlike crimping, a properly soldered joint doesn’t oxidize or become intermittent.

Here is a list of some of the items required. We will discuss some of these in more detail:

• Soldering iron – sized appropriate for the medium being soldered
• Solder – needs to be a diameter and at a melting point suitable for the iron being used
• Flux & Flux brush– especially helpful when medium is dirty or oxidized
• Sponge – a slightly dampened sponge, used to keep the iron tip clean
• Safety glasses
• A well-ventilated area. We don’t want to breath the fumes from the solder and flux
• A work surface with an extremely high or non-existent melting point

Choosing the soldering iron:

Soldering irons come in many heat ranges normally referred to in Watts. You can find “pin” type soldering irons as small as 15 Watts, and soldering guns ranging to 150 Watts or more. The most common iron size for electronics is: 30 to 40 Watts. Cost varies as with any tool. Small soldering irons range from $10 to several hundred dollars for soldering stations with temperature controls etc… There are also several styles of soldering irons used. For the casual user, the straight, 30 Watt iron you simply plug in and wait for it to heat up is used most common. For the avid kit builder, you would want to invest in a quality soldering station with temperature control and auto heating feature. This type of station keeps the tip from burning up when in use for several hours daily.

Choosing solder:

Solder made for electronics is made with a percentage of tin, lead, and has a flux core. In the past few years as lead is being removed from more items, we now have lead free solder. Lead free solder requires more heat to be applied and the use of additional flux becomes beneficial to get a good flow around the medium being soldered. Solder also comes on a spool in several sizes ranging from the diameter of course hair to about a 1/8-inch diameter. The most common size is about ½ the size of #2 pencil lead. NOTE: You can always use smaller diameter solder with larger wattage irons, but great difficulty ensues when trying to use large diameter solder with small wattage irons. All of your heat will be consumed by the solder and not the medium you are working on.

Choosing the flux:

Flux comes in two states, liquid and paste. Most solder designed for electronics work has some rosin flux in the core. As mentioned earlier, the newer lead-free solder doesn’t flow as well and we use flux to assist with that. Liquid flux usually comes in a flux pen applicator. This way small amounts can be easily dispensed and is used primarily on circuit board component work. Flux paste usually comes in a container similar to a Skoal snuff can, and we use a small flux brush to apply it to the medium we are working on.

Preparation before the project:

OK… We have the items we need for the project, now what? In this example, we are going to be using a 35-watt iron for this project.

Let’s get started:

1. Plug in the iron and let it get up to operating temperature. NOTE: If you are outside in a cool or breezy environment, this directly effects the performance of the iron. Make sure to take precautions to isolate the iron from sources that can cool it down unnecessarily.

2. Once the iron is up to temp, swipe the tip on the damp sponge a couple to times to wipe the complete diameter of the tip. This process removes excess solder and any charred flux and other impurities.

3. Apply a small amount of solder to the tip. This is known as “tinning the tip”. This will ensure proper heat transfer to the medium being worked on and keeps the tip from oxidizing.

4. Repeat the cleaning and tinning steps each time you reach for the iron or begin work on the next piece of your project. NOTE: A dirty, oxidized tip will cause you much frustration and can overheat components causing failure.

The project medium:

The medium needs to be prepared to make the soldering project a success. If you are working with wire, like the center conductor of LMR 400 or RG8X coax, you want to get it ready to solder.

1. Apply a glaze of flux paste to each piece of medium you will be joining together. Don’t blob it on, a little really goes a long way.

2. Assemble the pieces of medium in the order they are to be soldered. NOTE: Don’t forget to slide on the collars or the other non-soldered parts before you solder the items. No one wants to discard the connector or remove what they just soldered because of a silly mistake. Don’t ask me how I know this. (Big Cheesy Grin.)

3. This next step just takes practice. You touch the hot tip to the point on the medium you need to join with solder. NOTE: The size of the area being soldered is directly proportionate to how long the heat needs to be applied. This is also where you need 3 or more hands. We will assume the medium is secured and you have hands available to hold the iron and the solder.

Now, touch the solder to the medium directly beside the iron. If the solder doesn’t melt, you need more heat, or the iron tip is dirty and the “cleaning/tinning” process needs to be performed. Once the solder begins to melt, keep feeding it until just before it begins to flow out of the joint. You don’t want so much solder that a drip begins to form.

a. As mentioned earlier, the heat must dissipate through all the area to be soldered. Heating the area too long with an undersized soldering iron will cause items around the joint to melt or become deformed. This just takes practice to determine if the size of medium and the heating capabilities of your soldering iron will work together.

4. Remove the heat, but DO NOT move the soldered joint until it cools. CAUTION: the medium will remain way too hot for you to touch, but the solder will cool enough to bond within 2 seconds on small medium.

a. If you move the medium before the solder cools enough to bond, you can cause what is called a: “Cold Solder Joint”. Cold solder joints are your nemesis. However, they are easily resolved. Simply apply heat, feed a little more solder, remove heat, and Don’t Move the medium being soldered.

After the project storage and care:

Now that you have your soldering project all buttoned up, we need to perform a few steps to store our soldering iron.

1. Clean the tip on the sponge and unplug the iron.
2. After a minute, apply a generous amount of solder to the tip, just before a drip forms
3. Let the iron cool with the large drip of solder at the tip. This will protect the iron tip from oxidizing while in storage and it will be pre-tinned when you use it next time.
4. A tip will last for years with proper care, but if it becomes pitted or deformed, it’s time to replace it.
5. Seal up the flux container and place the flux brush in a snack size zipper bag.
6. Store all your soldering supplies in a small case or larger zipper bag for future use. It’s always best to store like tools together. You don’t want to be hunting all over the place attempting to assemble your soldering kit the next time it is needed.

Wrap up:

I know this doesn’t help you visual learners much at all, so don’t fear. There are excellent “How To” videos on youtube.com, just search “soldering techniques”.
Go to your favorite shopping site or local electronics retailer and purchase a soldering iron, solder designed for electronics, flux, and a set of flux brushes so you too can get started.