How to Solder
Effective soldering requires a combination of skill, patience and a sharp eye for detail.
Soldering is a relatively simple skill to learn. You will naturally progress in proficiency as you become intuitively familiar with the basic techniques of soldering and desoldering.
Materials Needed for Soldering
Small electronics pencil-grip iron.
Important note: You’ll want an iron in the 15 to 25 watt range for sensitive components (like IC’s, and small transistors).
For larger components, and thicker diameter wiring, an iron in the 25 to 40 watt range is best-suited.
Avoid using a solder “gun” type of iron for any small, consumer electronics. These tend to be far too hot. They are best suited for non-critical solder tasks and automotive use.
The steps are basically the same in either case. However, a solder gun usually heats up within several seconds.
It will also bring any component it is used on to critical heat in several seconds. It should be used on actual components only after practicing on numerous non-critical wire joints.
Eye protection.
Rosin-core solder.
Warning: Solder fumes are extremely toxic.
Important note: Avoid all types of acid core solder (i.e. Plumber’s solder). Acid core solder is highly corrosive. It will literally eat through standard electrical components, wiring and circuit boards.
Lightly-dampened sponge.
A cup with a small amount of water set off to the side.
This will be used for dipping your fingers into and moisturizing your sponge, as needed.
Tip: Avoid a wet sponge, as well as a dry sponge. Keeping your sponge lightly damp is just right.
Metal iron stand, for safely holding your iron while heating up (and when not in use).
Though it is not always the case, iron stands are often in the shape of a spiral mounted onto a base. The spiral is referred to as a “holster”. When not in use, you slide your iron into the holster.
Tip: If you do not already have an iron stand, then an old tuna can works very well.
You will want to install a bent-in crimp (as if it were going to be used as an ashtray) to actually rest the iron.
Avoid contacting the tip (and at least an inch below the tip), directly with metal when the iron is not in use.
Otherwise, you will be required to wait noticeably longer, before soldering.
This is because if too much of your iron (and especially the tip) is contacting metal when not in use, it will make your iron too cool for proper heat transfer to melt the solder.
Flux-scraping tool (for removing leftover flux).
Leftover flux can induce random circuit failure, especially at higher operating temperatures.
A thin-handled modeler’s “pencil” knife (with a flat chisel-style blade), works good for this purpose.
When using a thin-handled modeler’s “pencil” knife to remove the excess flux from your work, avoid scraping in an outwardly pushing manner.
You’ll want to use light, gentle inward “shaving” strokes, so as not to cut into the copper cladding or wire insulation. This also prevents damage to your components.
A small, tight-bristled nylon brush for knocking off the rosin scrapings as well as removing any dust, light tarnishing and oxidation.
Tip: An old tooth brush works well.
Clamps, vice, etc. for securing your work.
A small fan (if in a poorly ventilated area).
Important Note: Avoid blowing air directly upon your work. The tip will not heat up to the proper working temperature. Also, your solder joints will cool down too fast.
This makes them become “cold” solder joints. They will appear a dull gray, or dull grayish white (as opposed to clean, shiny solder joint).
Cold solder joints impede current flow, and can cause undue over-heating and random circuit failure.
A heat sink (if soldering or desoldering smaller, sensitive components).
Tip: A commonly-available alligator clip works well. What also work well is to gently grip the end of the component lead with a pair of slim-line needle nose pliers.
Preparation
Plug in your iron and allow it to heat up for two to five minutes. You should wait until you can touch a strand of solder to the tip and it rapidly becomes molten.
Once your iron has fully heated, melting a bead of solder on the tip and just above the tapered point of the tip is referred to as “tinning” the tip. Your soldering tip is also called a ‘bit’.
Tinning removes all surface tarnish and dust. It also allows for maximum efficiency in the transfer of heat to your component or wire splice to be soldered.
Wipe excess solder bead and flux onto lightly-dampened sponge. No tarnish or oxidation should be present. You want only a shiny tip.
Basic Soldering Techniques
Always wear eye protection. One molten micro-bead of solder could conceivably take out your retina.
Practice on many dozens of non-critical wire splices, first.
After initially tinning your tip, and prior to soldering any joint, always briefly touch a strand of solder to the tip.
You only need to do this until it just starts to freely melt and bubble, and releases visible solder vapor.
If your iron makes the solder molten almost instantly, then it is at working heat temperature.
Important note: Your iron should always be ready at working heat temperature, before bringing the tip to your work and performing any actual soldering.
While causing the solder to become molten, gently blow the vapor away from your immediate breathing space. Avoid actually blowing on the tip.
In moderate weather, opening a window (enough for a noticeable airflow) is advised.
Always be sure to wipe any excess solder onto your sponge before soldering your joint.
Secure your work firmly with clamps or a vice (avoid applying excess pressure to the board).
Avoid bringing the solder to the tip.
Bring the tip to one side of the joint to be soldered, along the tapered edge of the tip (not the point).
Allow the joint to heat up for approximately two to three seconds. This is referred to as “sweating a joint”
Bring the solder strand to the other side of the solder joint (directly adjacent), and at an angle.
Your iron should be offset at a roughly opposite angle that allows for maximum taper contact with the joint.
Good soldering technique involves allowing the solder to rapidly “suck into” the junction or splice.
Avoid keeping your iron tip directly in contact with your work any longer than is required; only long enough to establish a solid, clean solder joint.
Thermal stress (overheating a component) can lead to premature component failure and intermittent circuit failure.
Let it cool down naturally for several seconds – five to ten should be sufficient. Avoid the temptation to blow on it, as this can damage your work.
After your work has properly cooled down, inspect your work for excess flux and solder splash.
Especially take note of any solder splash that has made contact with surrounding junctions and components.
Also inspect your work for visible solder fractures within your joint. Fractures can be a cause for excessive component overheating, and ultimately causes intermittent circuit failure.
If you determine that you need to re-sweat and re-do a solder joint, always let it completely cool down first.
Be sure to remove both the excess flux and solder splash.
Tip: The solder splash can be also be gently scraped away with your modeler’s knife, and then knocked off with your brush. Be sure all residue is completely removed from the surrounding connection and board.
Loose metal flakes can become a fire hazard by causing an intermittent arc, often due to vibration (called a short).
How to Desolder
In many respects, desoldering is similar to soldering. This is especially true, when it comes to wearing eye protection, tinning your tip and removing all tarnish, dust, etc. from the component contacts (to be desoldered).
To desolder a component from a circuit in need of repair, you will need most of the above materials required for soldering, as well as the following:
Materials Needed for Desoldering
Desoldering bulb (suitable for most general, non-critical desoldering tasks).
Warning: Avoid using a bulb for electrostatically-sensitive circuits. If you must use a bulb, make certain that you are well grounded at all times while using it.
Optionally, you can also use a desoldering (vacuum) pump.
A desoldering pump is typically two to four times more expensive than a bulb.
However a desolder pump also tends to be much more efficient and requires less work.
The bulb is all you truly need to perform most standard desoldering tasks.
Important note: If you are primarily working with electrostatically-sensitive components and circuits, then you will definitely want to invest in a pump.
Most desolder pumps in the market are ESD safe.
Desoldering braid (which is best-suited for tightly-spaced components and IC desoldering).
Desoldering braid is also useful for awkward joints that would take several attempts with a bulb
Grounding strap (if desoldering electrostatically-sensitive components).
Basic Desoldering Techniques
Prepare your work, just as if you were soldering a joint, and remove all visible oxidation and dust first.
You should have the tip of the desoldering bulb or pump at an off-set but adjacent angle.
It is very similar to the above technique for bringing your solder strand and iron at opposite off-set angles to your work (covered above).
The only real difference is the way you are holding each tool, considering that your are merely replacing a strand of solder with a bulb or pump tip.
There are times when you will run into “stubborn” joints. It can prove highly effective in these cases to actually add just a bit more solder to the joint requiring desoldering.
The joint (the one with more solder added) should be desoldered to be shiny.
Allow your work to completely cool down, and then proceed to desolder the newly created joint (this is also where desoldering braid can come in very handy).
The most effective way to use desoldering braid is to press a short length of braid down onto the joint to be de-soldered with the tip of the hot iron.
It will typically take two to six seconds (depending on the wattage rating of your iron and the thickness of the braid being used) for your the braid to reach working temperature.
You will know that it is very close to working temperature, as it will start to draw the solder bead into itself.
After the braid has reached working temperature, the iron will rapidly melt the solder, which continues to gets sucked into the braid.
Once the specific portion of your braid has become saturated, you should move it just slightly to expose a fresh section of braid and continue desoldering.
Warning: Avoid allowing the solder to cool while the braid is making contact with your work.
Doing so greatly reduces the risk of causing excessive damage to the circuit traces (copper tracks) when you go to remove the braid from the joint.
If this happens, do not panic. Also, do not proceed any further until your work cools down completely.
Only then do you re-apply your iron tip to the braid. It will take several seconds to reach operating temperature.
Basic Soldering and Desoldering First Aid Awareness:
In the event you inadvertently splash your skin with molten solder, and receive burns which require treatment, here’s is a simple set of instructions to be aware of at all times:
Immediately cool the affected area for several minutes with cold running water.
Remove any jewelry (i.e. rings, bracelets, watches, etc.) before the swelling sets in.
Gently pat dry the affected area and proceed to apply a sterile dressing. This will help to protect you against infection.
Do not apply lotions, ointments etc., nor prick any blisters which form later.
Seek the professional advice of a medical doctor, if necessary.