Soldering Best Practices

Autor: Bill Gilbert (e 5 outros contribuidores)

Welcome to our guide on Soldering Best Practices. Here you'll learn the basics of how to solder the right way, some tips and tricks to help you get the best joints, and what you should avoid or be aware of moving forward.

Soldering can get hectic—hot elements, molten metal, and sensitive electronics are at play—so it's important to have a good set-up to help you get the results you want. Here are some aspects of a good soldering station:

Eye Protection - Good safety glasses with side and top shields or goggles are a must. Small fragments of molten solder can fly off from a joint and cause injury.
Good Lighting - It is hard to do a good job soldering when you can't see what you're doing. Proper lighting helps inspect the joints you make, and see when the solder starts to flow. You will work more safely, too.
Good Ventilation - Soldering can produce fumes that you shouldn't breathe. Having a fume extractor is important. You can buy one, or try building your own. A continuous source of fresh air like an open window or a fan blowing to the outside also helps. Here's a slo-mo video of fume production.

A heat resistant surface to work on. Soldering uses high temperatures that can damage most surfaces.
- A sheet of plywood or particle board works well.
- Silicone mats designed for soldering are available. These provide good protection and often have pockets for tools and fasteners.
Use a stand for your soldering iron. You are risking a burn if you don't.

Elbow room - It's one thing to have to solder in a small space because you are repairing something. You will do a better job when you have the chance to solder with room to maneuver.
Use a good grip - Hold your iron like a pencil in your dominant hand for best control. Orient your work so that you are in the most comfortable position and have support for your soldering hand. It's much easier to rotate the board than rotate yourself to accommodate a poor angle.
Stabilize your arm/hand - Resting your hand or elbow on a stable surface can greatly increase your steadiness and accuracy—which is vital when working with delicate components!
"Helping Hand" tools - These tools assist greatly in keeping the project you're working on stable as you solder. You need two hands to solder after all—one to hold the iron, and one to feed solder into the joint. Having a "helping hand" to keep things at the perfect angle can reduce errors and frustration. When the joint moves around, you can't maintain the kind of contact needed to heat the joint rapidly. Using a soldering splint, omnivise, circuit board holders, a vise or helping hands is often essential.
A better view - Sometimes the joints or parts are small and a magnifier improves your ability to to do a quality job. A magnifier can help you find and correct flaws that you might otherwise miss.

A Quality Soldering Iron - Among the features to choose:
- At least 60 watts of power.
- Fast heating; slow heating wastes time and also means temperature recovery will also be slower.
- Accurate, Settable, Temperature - The right temperature for your work. Small joints can be done with lower temperatures; larger ones require higher temperatures for more rapid heating.
- Silicone Insulated Handpiece Cord - Silicone insulation provides heat resistance and great flexibility. A flexible cord helps the iron to behave more like a pencil or pen for ease of work.
- Interchangeable tips - Different shapes for different jobs. also replacing a tip only if it burns out is much better than replacing the whole iron.
A Tip Cleaner - Coarse brass wool will remove excess solder and oxide films from your iron without the thermal shock of a wet sponge. Some do prefer a damp sponge, and if you choose to use such, make sure that you get a cellulose sponge, not one made from a polymer.
Tools to manipulate parts - You need tools to either to hold or move things when you are soldering. Tweezers, needlenose pliers and hemostats (like small pliers that clamp) are all good choices. Generally metal tools are preferable,

Quality Solder (Lead-free is best to start with) or solder sold by reputable sources are best.
- Be cautious buying from online auction sites as the solder being sold may be something meant for manufacturers with controlled conditions and potentially corrosive fluxes.
Quality Flux Seek to obtain flux meant for electronic soldering. A tacky flux is often a good choice especially if it comes in a syringe. A flux pen allows for easy application . Don't use plumbing fluxes as they are often far too corrosive.
Desoldering Braid. Also called solder wick, this is an essential tool for correcting errors or removing defective components.

A desoldering tool (solder sucker) is very handy especially with some repairs. It can desolder things more easily than desoldering braid on large components.
A vise for holding larger items rather than chasing them around the work surface.

Soldering is a simple process at its core, but with many nuances. At its most basic, the process consists of the following steps:

Turn on the soldering iron and allow it to come to operating temperature.
Tin the tip by melting a small amount of flux core solder onto the tip. Clean off the tip
Apply the hot soldering iron tip to the metal connection point on the board.
As it starts heating up the connection and wire, dab the solder against the connection until it starts to melt into the connection.
When the solder has flowed into the joint, remove the solder, then remove the iron. Hold the joint still until the solder solidifies.

One common mistake that beginners make when they first start out with a soldering iron is believing that the soldering iron should be applied directly to the solder to melt it onto the components. Unfortunately, solder doesn't bond well to cold metal, so this often results in poor joints. Instead, heat should be applied to the joint location before any solder is introduced to the joint.

You may want to melt a small amount of solder on the tip of the iron and then apply it to the joint and hold it there, as this helps with heat flow into the joint. But don't try to use the soldering tip as a heated trowel to smear solder. Have patience, the joint will heat up and then the solder will flow. Holding your iron steady is the best thing.

Over time you'll start to accumulate a feel for what good solder flow looks like, how much solder to use for various applications, and how to create ideal solder joints every time. Much like any skill, soldering takes time and practice to master, so trust that your soldering will improve the more you do it.

Here's a detailed guide to both through-hole and surface mount soldering. It's well worth a read-through, even if it might seem like a bit much at first.

Contrary to what you might think, application of a hotter iron for less time is easier on components than a lower temperature applied for a longer time.
Hotter for less time also keeps you from heating wires or traces to the point that coverings melt away from the joint.
Beware of excessive heat if you are having trouble getting the solder to flow. A larger or different shape tip that can do a better job getting heat into the joint may be a better solution than maxing out the temperature.

For lead-based solder around 300°C (~570°F)
For lead-free solder around 375°C (~700°F)
Don't be afraid to go to 400°C sometimes for larger joints like joining heavy copper wires. Use a bigger tip for these situations rather than cranking the temperature if your tip is small.
The calibration of both irons and stations are not always 100% accurate, so don't feel like you will be arrested for going higher, or that you can't try lowering the temp if it seems to be too hot and is burning off flux quickly.
- Your own style and preference is valid. Some fixers will need a higher temperature with their technique, some may need less. It's often discovered by feel
Going too hot will lead to oxidation, so it is a race to get heat into the joint so the solder flows before oxidation becomes significant.
- Use a sufficiently sized tip so that it can contact enough of the joint to allow good heat flow. It should be matched to the joint size. This diagram from Hakko is excellent!
- Too small a tip for a given joint will not get enough heat into the joint. You may even find the tip corroding from oxidation if the temperature is extreme.

Stuff takes time to heat up, and more stuff takes more time or more energy flow. Less stuff heats faster, but...Things to remember—
- A small iron tip heats up quickly, but has potential issues:
  - It doesn't have much mass so can't hold as much heat
  - It is also small, so it can't transfer as much heat
- A larger iron tip MAY be a solution, but shape could be just as important.
  - Here's a diagram from Hakko that has a good summary.
Your soldering iron may have small tips, as mentioned above, but may also have considerable power available to overcome the difficulties mentioned above.
A pad on a printed circuit board (PCB) if it is part of a large copper area will need much more heat input to solder than an isolated pad.
A pad on a PCB that is connected to large (or many) traces (printed circuit wires) will take more heat input to properly solder.

Two operations are called tinning:

Pre-applying a small amount of solder to each item that you are going to join. Usually this is to the leads of components or to wire.
Making sure your soldering iron is coated with fresh solder. This is both a maintenance procedure, and something you do as you are using your soldering iron after wiping off oxidation and cleaning the tip. Do this especially when you are done before storing your soldering iron.

When you are using enough flux, the solder will wet the various parts of the joint more easily. Sometimes beginners will try to apply an excessive amount of solder to compensate for the solder not flowing.
A bit more flux, rather than more solder, is the best way to solve this problem.
A huge ball of solder is not the route to a good joint. When you try to solder this way, you will frequently create "solder bridges." These are inadvertent connections made by the solder joining two points on the circuit board. To fix these you can use desoldering braid (and a little flux) to wick up the excess solder and clean it up as shown below.

Solder bridge circled in red

Applying desoldering braid and heating it

Higher heat applied quickly, less chance to cook things.
Don't be shy in applying some flux, excess can be removed afterward.
- Pro tip: while everything is still hot and liquidy use a wooden cotton swab to clean up as much flux as you can
- Then use a swab moistened with Isopropyl Alcohol 90%+ concentration (IPA) to remove more excess flux.
- You can use lint-free wipes moistened with IPA to scrub it off.
- A soft bristled brush with IPA also works to help loosen large portions of flux. Brushing without wiping afterward just spreads the flux, so be sure to wipe up.
Heat the joint items and let the solder flow onto them.
Use an appropriate iron shape for the joint. This is often better than higher heat.
- Tips with flat spots like a wedge or bevel shape are especially suitable for spreading the heat to all parts of the joint.
- Small conical tips are good for precise application of heat, but won't work well on larger joints.
Look for the solder to flow into the joint. Don't feed the solder into the soldering iron tip.
Make sure your soldering iron tip is tinned.
Remove excess flux with 90+% Isopropyl Alcohol. Use a wooden q-tip or lint free wipes.

You want the solder meniscus or fillet to have about a 45° angle for its sides from the board surface, and be slightly concave like a little round concave tent in the case of a through-hole joint. If it is like a bubble, you have too much solder. If it is more like a pancake, too little. Here's an example:

Left joint is very good, right joint has a square pad so more solder is there. It's good too.

Soldering irons are hot. They don't mix with flammable materials. Clear the work area of paper, tissues, and other flammable items like glues or paints.
Molten solder can sometimes fly out in small balls from a joint. Eye protection is important.
Solder containing lead is toxic. So are flux fumes Use a fume extractor or have very good ventilation.
Use a stand for your soldering iron. Avoid burning things (or yourself!) inadvertently with a loose iron. Don't set your soldering iron down on your work surface. You might mistakenly grab it.

If you mean balling up in spots on the iron it could be because your tip is dirty. Here's a fix.
If you mean it won't stick to the joint and just stays on the iron, the joint is likely dirty or has considerable oxidation. Use flux and you will likely see the problem disappear.

You are probably trying to push the solder into place and smearing it rather than letting it flow. You may also be using too much solder so the solder forms a blob.
- Try raising the heat setting on your iron to help keep the solder more liquid.
- Use flux (it really works miracles!)
- Remove old solder with desoldering braid and try again with flux and fresh solder.
- Keep the joint still when the solder is solidifying (see below).
- Make sure you are using solder that melts and solidifies uniformly. A eutectic alloy is best because like a pure metal it has one melting and solidification temperature. Other solders like 60/40 or 50/50 (not recommended) solidify by first forming a paste phase and don't fully solidify until the eutectic temperature is reached. This paste phase is very susceptible to movement of the joint which can cause a bad solder joint. Clumpiness is a sign of this problem.
- You may be trying to work on a joint for too long, burning away all the flux. This will result in flagging (spikes of solder) and poor quality joints. You may even oxidize the tin in the solder, leading to clumping.

You may have applied flux or flux cored solder to the tip. That flux will burn off, and the smoke will stop. Avoid breathing that smoke as it is unhealthy.
You may have a new soldering iron and it is burning off a coating applied by the manufacturer.
Your iron may be set too hot.
You may have melted some insulation off of a wire and it is now smoking on the tip. Clean your tip with the brass wool or a damp cellulose sponge.

This occurs when the iron is left on for an extended period, and the solder begins to oxidize. Wipe the tip on a damp sponge or on some brass wool and tin the iron.
Apply fresh solder. If looks like you need more cleaning follow this guide.
This is a sign of a badly overheated iron if the shiny chrome part looks like this all over.

If your joints aren't conducting, the solder is not properly wetting or bonding to the parts of the joint. There is likely an oxide layer interfering. This could be a cold solder joint. A cold solder joint occurs when a joint is not properly heated to allow the solder to flow into the joint, or the joint is moved while the solder is cooling.
- Apply flux to the joint and reheat the joint to allow it to reflow properly.
- Reworking/reheating a joint over and over can readily cause a cold joint.
- You might even want to remove existing solder with desoldering braid and flux, and start over.

Tip tinning is applying solder to the tip of the soldering iron to protect it, and make it function well. The idea is to remove oxidation and use the solder to limit tip oxidation. Check out this guide to see how.

Soldering Glossary of Terms

How to Solder and Desolder Connections

Soldering Iron Not Melting Solder

Soldering Iron Not Heating

Soldering Materials 101

Soldering Iron Tips

Soldering 101 Video

Information from Hakko regarding re-tinning soldering iron tips.

Information from Kester Solder regarding difficulties with lead-free hand soldering. A little dated (2006) but still helpful. Geared more toward industry, but worth the time if you want more detail.

Excellent video from Tektronix about soldering. Almost 30 minutes long but well worth the time. Some dated stuff (it's from the late 1970s to early 1980s), but the throughhole soldering techniques shown are excellent.