How To Use A Heat Sink When Soldering: A Quick Guide

Soldering is one of the most useful skills to have when doing DIY electronic repairs around the house. It’s saved me hundreds of dollars in electrician bills, and one particular soldering tool, the heat sink, helps me save on components too.

When soldering, make sure the heat sink is clipped between the joint and the rest of the component or wire. The heat sink will divert attention away from the component so that it doesn’t get damaged from overheating.

Heat sinks are a secret weapon that you can use to up your soldering game. They work especially well when you’re working on wires or heat-sensitive components with leads. In this article, I’ll give you the rundown on how, and why, to use a heat sink.

What is a Soldering Heat Sink and Why is it Important?

Soldering (pronounced “sodd-er-ing”) is a useful method for joining electrical components and wires. It adds a filler material – the solder – to a joint to make a clean, efficient electrical connection.

Soldering is a low-temperature method of making such connections. Unlike welding or brazing, which heat metals to 600 °C or greater to melt them and literally fuse them together, soldering only needs to reach 200-300 °C to make good connections. This makes it much more useful for electrical applications.

For electronics, excessively high temperatures can be particularly destructive, causing components to burn, behave erratically, or shorten their lifespans. Even though soldering is a low-temperature method, overheating is still an issue, particularly for small components.

Heat Sinks

Over the years, engineers invented a tool to solve the problem of overheating when soldering: the heat sink. Dedicated heat sink tools look like little clamps that are placed between the soldering joint and the heat-sensitive component. Heat sinks can also be improvised using alligator clamps.

Heat sinks are usually made of a low-mass metal with a high heat conductivity like aluminum. It gives a “path of least resistance” to any excess heat that is applied to the soldering joint. Instead of traveling down the wire or lead, any extra heat will travel into the heat sink and be mitigated. This prevents components from overheating.

Professionally-sold heat sinks typically come in two varieties: some have curved ends, and others have straight ends. The ones with curved ends can be more versatile for small joints and leads. Otherwise, most electricians recommend heat sinks with straight ends.

Other Soldering Tools and What They Do

In a second I’ll give you a step-by-step guide to soldering with a heat sink, but first, let’s introduce the tools that we’ll be using. Some of these are essential, like the solder itself, while others are optional (but recommended).

Soldering Iron

The soldering iron is pretty much essential to soldering. Some MacGuyver enthusiasts have soldered using a standard cigarette lighter, but let’s ignore them for now. If you want any precision in your soldering, you’ll want to buy an iron.

Soldering irons come in a variety of shapes and sizes. They can produce high heat (sometimes this is called high-wattage), upwards of 500 °C, or medium to low temperatures between 250 and 400 °C. Some soldering irons have an adjustable temperature using a knob, though these tend to be more expensive.

One particularly cool variety of soldering iron is the soldering gun. These usually have a tip at the joining of two metal leads, allowing them to heat up and cool down very quickly using an electric current.

Soldering irons and guns all come with a tip, but sometimes, you’ll want to buy a different one. Flat tips – sort of like the tip of a flathead screwdriver – are great for wires. Pencil-shaped tips are better for things like circuit boards.

Solder

If you want to solder, then you need, you guessed it…solder! What is this strange, shiny material?

Traditional solder is made of tin and lead, usually alloyed in a 60/40 ratio. This gives it a melting temperature of around 200 °C, making it extremely versatile for making low-temperature connections for things like wires and circuit boards.

Lead is pretty toxic, so in the modern, health-conscious world, new solders have been invented that doesn’t contain any lead. Instead, these lead-free solders contain alloys of tin, silver, copper, and sometimes a few other metals. They work just as well but usually melt at a slightly higher temperature, around 220 °C. 

Because of the metals, it’s made of, solder is highly electrically and thermally conductive. It melts easily when you’re trying to apply it, and once it’s solidified, you have a stable, electrical connection! Assuming you do it right, that is (more on that later).

Rosin Flux Core Solder

Some varieties of solder you encounter contain what’s called “rosin cores” or “rosin flux”. This is an acidic material that will clean the materials that you apply the solder to. For electronics soldering, I’d recommend using solder with rosin cores. It should be easy to find.

Solder is typically sold on spools containing a specified length or weight of the material. Depending on what you’re soldering, you should select a specific kind. If heat damage is a major concern, I recommend traditional solder, since it melts at a lower temperature. Otherwise, lead-free solder works just fine.

Holder and Cleaning Sponge

These aren’t essentials, but I’d recommend picking them up. A soldering iron holder is a nice little stand that you can rest the soldering iron on when you’re not using it. Remember, the soldering iron can heat up to hundreds of degrees, so it’s best to not leave it just lying around where you can accidentally touch it and burn yourself.

Some holders also have a holder for a sponge. You can dampen the sponge with cool water, and then wipe the tip of the soldering iron on the sponge to clean it off. This will help make sure you don’t get a bunch of gunky contaminants on your soldering joint.

Helping Hands

When you’re soldering, you’ll have one hand holding the iron and one hand holding the solder. Unfortunately, that doesn’t leave any hands left to hold the piece that you’re soldering, which can move when you apply the iron to it.

Thankfully, engineers have solved this problem too. You can pick up a stand that has little “helping hands” on it – adjustable clips that can be moved into a wide range of positions – to hold your wires or components while you solder.

Especially if you’re new to soldering, this will help you do consistent, good work. Nothing is more frustrating than a wire that keeps running away when you touch it with the iron.

Exhaust System or Fan

If you’ve ever soldered, you know that a little trail of smoke comes up when you melt the solder. Remember, this stuff is made of metals like lead, tin, and copper. You don’t want to inhale this gas. It’ll irritate your nose, and if you solder without ventilation too much, it can lead to dangerous health complications.

This problem is easily remedied by a simple fan or, ideally, an exhaust system. After all, a fan will only disperse the gas around your workspace in smaller quantities – it won’t get rid of it all together like an exhaust system.

You wouldn’t be the first person to do it if you soldered without ventilation, but generally, I would recommend having airflow of some kind.

Other Tools and Materials

Assuming you’re working with wires, you may need other tools to manipulate those wires, including (but not limited to) strippers, cutters, or pliers.

If you’re doing circuit work on a board, you’ll of course need a circuit board. These come in a variety of different shapes and sizes, and they all have different resistance to heat(!), so be sure to pick one appropriate for your applications.

Heat-Sensitive Materials: What You Need To Know

Before you go right on to soldering things together, let’s take a second to make sure you don’t blow anything up, or damage your components beyond repair by overheating them.

This goes without saying, but some materials are more sensitive to heat than others. When soldering, you don’t have to worry about melting your wires. You wire insulation, on the other hand… If you’re not careful, you’ll burn it, melt it, make it get all spongey, or you can even set it on fire.

Electrical components in circuit boards can also be vulnerable to overheating too. Many of these contain TO-92 or TO-220 plastic casings on semiconductors, which can melt easily. Other electronic components that can be damaged are germanium diodes, capacitors, resistors, reed switches, and transistors.

Fortunately for you, all of the things I just mentioned can be easily protected by using a heat sink, since they all contain leads. If you don’t use a heat sink, these materials are likely to overheat, especially the smallest ones. Even if you don’t notice damage at first, it is quite probable that they will function strangely and not work for as long as expected.

Heat Data for Components

If you’re not sure if a component is vulnerable to heat or not, you can usually find it out on its datasheet. 

The datasheet will indicate a maximum junction temperature. This is the highest temperature that you can heat the component to before it is damaged. Soldering joints usually reach between 200-250 °C, so make sure the maximum junction temperature is higher than that, or be sure to use a heat sink.

Datasheets also sometimes include a soldering profile. This lays out steps to solder the component safely, with details on how long to heat it and what temperature to heat it at. Some soldering profiles will specify that a heat sink should be used.

Soldering With A Heat Sink: A Guide

Now that we’ve talked about which components we need to be mindful about damaging, and acquired all of our soldering materials we can go ahead and talk about how to solder. This is where it gets fun! 

No matter what you’re soldering, here are some general procedures to follow:

  • Preheat your soldering iron. Unless you’re using a soldering gun, this will probably take several minutes. Plug it in and be patient. You want the soldering iron to be a consistent temperature while you’re working, so allow it to preheat to its operating temperature before you begin.
  • Steady the joint. If you’re working with wires, twist the two wires together so that they are locked into one piece. If you are putting leads through a circuit board, bend the leads on the backside so that they don’t move. Secure the joint using helping hands if you have them available.
  • Cut solder from the spool. Holding the entire spool while you’re trying to work is a bit unwieldy. Instead, cut a piece off that you can apply directly to the joint using your non-dominant hand. Your dominant hand will hold the soldering iron.
  • Heat the joint, then apply the solder to the joint. This is probably the biggest mistake people make when soldering. Don’t touch the soldering iron to the solder itself! Instead, apply the soldering iron to the joint, heating it. Then, touch the solder to the joint. If the solder doesn’t begin to smoke and melt, then continue applying the iron until it does.
  • Allow the solder to cool naturally. Here’s another common mistake: don’t blow on the solder – let it cool naturally. If you blow on it, it can cool unevenly and break your leads. It also can crystallize in a different way that makes it less conductive. So relax – just let it sit for a few minutes to cool while you do (or solder) something else.
  • Wash your hands when you’re done. The metals contained in the solder are pretty nasty. You don’t want to ingest them, so make sure to clean your hands off when you’re done working.

Alright, now let’s talk about the specifics of soldering different things, and go over when and how you can use a heat sink to do a good job. You can solder a number of different things, but the ones I’ll be talking most about are wires and components for circuit boards.

Soldering Wires With A Heat Sink

The easiest way to learn to solder is using wires since they’re relatively large, can be secured, don’t overheat, and if you mess up, it’s easy to fix.

Preparation

To prepare your wires, you’ll begin by stripping them. About half an inch each should do. 

If you eventually want to cover your soldering job with a shrink cover, you’ll need to slide that over one of the wires next. This is a case where you’ll absolutely need a heat sink – I’ll come back to that in a second.

Next, take the exposed wires and twist them together into one, unified joint.

Secure the joint using helping hands, or if you don’t have any helping hands available to you, put them on a material that you’re fine with burning a little bit, like a scrap piece of wood.

The Heat Sink

When soldering wires, the heat sink is mainly used to prevent damage to the insulation on the wires. The heat sink also can prevent your shrink cover from closing prematurely.

All you need to do is clip your heat sink onto the wire between the joint and the insulation/shrink cover. This will prevent heat from being transferred down the wire and into the insulation/shrink cover and damaging it. 

Easy, right?

Soldering

Your wire joint is now ready for you to solder and seal the electrical connection between the two ends. Following the tips above, you’ll begin by preheating your soldering iron.

Once the iron is preheated, take it in your dominant hand, with solder in your other hand. Heat the wire joint (not the solder!) with the soldering iron. Occasionally tap the joint with the solder to see if it’s hot enough to melt. It should only take a few seconds to heat up hot enough.

When the joint is hot enough, the solder will melt and smoke upon contact. Apply the solder over the whole joint.

Allow your joint to cool, and it should be good to go!

Covering the Joint

Once the solder has cooled, make sure you did a good job by testing your device connected through the joint. If it works, you’re ready to cover it up. 

Take the piece of shrink covering that you slid on earlier, and slide it over, directly on top of the soldering joint. Use a heat gun to heat it up, closing the cover, and voila! You now have a nicely dressed, perfectly functioning wire.

Through Hold Component Soldering on Circuit Boards

Besides wires, the other most common instance for soldering is when you’re attaching a material to a circuit board. If the circuit board has holes to put the component leads through – this is known as through-hole component soldering. 

Soldering circuit boards is a little trickier than wires since the connections are smaller. With a bit of practice, you should be able to get this down pretty well.

Preparation

As before, you’ll preheat your soldering iron and secure the circuit board. If the component you’re soldering has long enough leads, bend them on the back of the circuit board to hold them in place.

The Heat Sink

You’ll be soldering the components on the back of the circuit board, which leaves room for the heat sink on the front of the board. In fact, the board itself acts as a bit of a heat sink, but don’t rely on it to dissipate all of your heat, as this can damage other components or the board itself.

Take your heat sink and clip it to the lead on the front side of the board. Any heat that is transferred through the lead will not make it to the component; instead, it will be sent into the heat sink.

Soldering

Joints on circuit boards tend to be a lot smaller and more delicate. You can typically use lower heat on your soldering iron because circuit boards tend to be very thermally conductive.

Once the iron is preheated, touch it to the intersection of the lead and the back of the board, heating the joint. Occasionally tap it with the solder to see if it is hot enough. When the joint is hot enough, the solder will melt and smoke.

You need to be careful how much solder you apply to circuit board joints like this one. If you apply too much, you can cause the board to short circuit. If you don’t apply enough, the connection may not be as good. You just want enough solder to pool around the connection and form a tiny little bump.

Pull the solder away before the soldering iron so that the solder doesn’t solidify onto the board. Allow it to cool normally, without blowing on it.

Cutting the Leads

Use a pair of wire cutters to cut any extra lead past the joint. If you leave too much lead on the board, it can make a short circuit and not function properly.

Cases Where You Can’t Use a Heat Sinks

While heat sinks are great for keeping components and wires safe when soldering, they can’t always be used. If the leads or wires are very short, for example, there may not be enough room to attach a heat sink between the component and the joint.

Tinning

The harder method to connect components onto circuit boards is called tinning. Unlike through-hole soldering, you don’t have enough lead space to attach a heat sink to.

Tinning is most common for circuit boards that don’t have holes in them. Certain components like IC chips don’t need holes to be soldered. This makes for a trickier, subtler solder, that must be approached in a more careful way.

Even though you don’t use a heat sink in tinning, I’ll give you a few steps on how to do it so that you can finish neat and clean circuit board solders. Be sure to consult the soldering profile to figure out how hot your iron needs to be, and how long you need to apply it to the board.

Preparation

Of the methods we’ve discussed, tinning requires the most preparation. First, you’ll preheat your soldering iron, and secure your circuit board.

When tinning, you apply some solder to the board before you attempt to attach the component. There should be a small pad on the board where the component will go.

Touch the tip of the iron to the pad, and apply a small pool of solder to it. This “tins” the board so that when you want to apply the component, the solder is already present.

Soldering

Take the component with a pair of tweezers. Use the soldering iron to heat the solder that was just pooled on the circuit board’s pad.

Lower the component onto the pad, and then pull the soldering iron away. If done properly, this should form a good connection between the component and the circuit board at one end of the component.

On the other end of the component, solder normally, heating the joint and then tapping with the solder.

The reason components like chips are soldered in this way is because you only have two hands available to do the job. You need to hold the chip with tweezers to put it onto the board, which means you can only hold the soldering iron (not the solder) in your other hand. To adjust for this, the solder is placed on the board before the chip.

How to Tell if you did a Good Soldering Job

Now that you’ve soldered your joint, you can inspect it to see how well you did.

For wires, it’s pretty easy to tell. The biggest indicator of a good (or bad) soldering job is the color of the solder. It should look shiny, not dull. Dull solder indicates that it wasn’t heated and cooled properly, and can lead to conductivity issues.

If you soldered to a circuit board, the color is still a good indicator. A few other rules apply, too. If you did a good job, the leads will not be loose, nor will you be able to see through the hole to the other side.

Especially with tinning, surface soldering jobs, you don’t want the solder to touch more than one pad on the circuit board at a time.

If your soldering meets all of these criteria, congratulations! You did a great job.

Summary

Heat sinks can be vital to doing a good job when soldering. They’ll prevent your wire insulation from catching on fire or closing before you want it to, and they can save your components and expand their lifespans.

To use a heat sink, you’ll attach it between the soldering joint and the component (or insulation). The heat sink will divert any extra heat away so that the insulation and component function properly.

Sources:

https://www.instructables.com/Save-your-components-with-a-heat-sink/
https://electronicsclub.info/soldering.htm
https://electronics.stackexchange.com/questions/3252/what-kind-of-damage-could-a-soldering-iron-do-to-a-component
https://www.instructables.com/How-to-solder/
https://www.quora.com/Can-a-transistor-or-other-components-be-damaged-due-to-the-heat-of-a-soldering-iron-during-the-soldering-process
https://www.instructables.com/How-to-Solder-a-Through-hole-Component/

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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