Soldering Electrical FAQ

Soldering/Electrical Tools & Sundries

Solder There are many, many types of solder. The best solder is one of a 63% tin, 37% lead composition. The reason for this is 63/37 solder does not have a eutectic (or plastic) state. This means that while the soldering iron is on the material, it is a liquid. The moment you remove the iron, it hardens instantly. Other solder ratios or types all have a plastic state where you have to solder the connection, remove the iron, and hold/wait for the connection to harden before continuing on. The downside to 63/37 solder is that it is actually hard to find, as most stores do not carry it. To find it, you generally need to go to specialized electronics stores (NOT Radio Shack) or purchase it online. You can use other types of solder, but it really is worth you time to use 63/37. Unlike many things in life, it truly is the best in the world of soldering. Many companies make 63/37, with Kester probably being the “big name” in the business. Lead based solder is sadly being phased out due to environmental concerns though, so don’t be fooled by the newer “blingy” silver or other types of solder.

Solder also comes in sizes such as .030, .060, and .090 depending on the manufacturer. If its more cost effective for you, it is wiser to get the “angel hair pasta width” .090 rather than the “spaghetti width” .030 as you can always double or triple up the width to make it equivalent to the thicker solder, or just use more of the thinner stuff. A “perfect” soldering kit would have .030, .060. and .090 for use in all occasions though.

As well, the 63/37 solder should have a RMA rosin core.

Flux Flux aids in the flow of solder. To put a visual on the benefit of flux, imagine joining two bare wires and soldering them. Without flux, the solder joint will on the outside with very little interior penetration. By using flux, it will aid in the wicking action allowing the solder to flow to 100% of the interior of the joint resulting in a stronger and longer lasting connection. The best type of flux to use is a liquid RMA (Rosin Mildly Activated) flux as it has the least amount side effects in wiring or electronics. While it can create a sticky mess, it is easily cleaned up using isopropyl alcohol.

Isopropyl Alcohol Used for cleaning solder, wiring/solder connections prior to working on them, and removing flux residue. This can be obtained at electronics stores or by visiting the make-up removal section of your local drug store. While 100% pure isopropyl would be the best, you can get away with 70-90% content for far cheaper that is sold in drug stores.

Low lint/lint free rags/wipes and Q-tips/foam swabs These are used in conjunction with isopropyl alcohol in the cleaning process. In a perfect world, you’d lean towards true lint free wipes and foam swabs as they totally assure a clean and dust/lint free surface during preparation. In actual practice, you can use common items such as Q-tips, cotton T-shirt material, or tissue paper as suitable substitutes. Kleenex and paper towels do not cut it.

Wire strippers Many manufacturers make these and all work about equally as well. Some of the bigger names are Klein Tools, Snap-On, Gardner-Bender, and Craftsman. There really isn’t a lot of variation in design or functionality, so choose what looks best to you. The key to remember is that a properly working wire stripper will not nick the conductor. A nick is a weak spot and a future failure spot. The best type of wire stripper is known as an automatic wire stripper.

The reason for this is this type of stripper comes with replacement blades for the stripping portion and are engineered so the wire is stripped at a 90 degree angle and from the correct side. Replacement blades mean you always have a sharp cutting surface and are cheaper to replace than an entire set of wire strippers.

Side cutting wire strippers are fine when used correctly.

These strippers must be used with the flat side towards the cutting side so the cut edge is a 90 degree angle.

These are the only two types of wire strippers worth spending money on. Universal, “as seen on TV”, or one size fits all strippers are NOT worthwhile and should only be used in emergencies. As well, always remember the wire stripping rule: use the tool to cut the insulation, use your fingers to remove it. Do not nick/strip in one sweeping motion as you can damage the conductor. Using a knife or your teeth is best left to hillbillies.

Solder wick Solder wick is a thin copper mesh on a round roll. When used in conjunction with flux, it is applied to areas of too much solder. Once heat is applied to the wick, it allows the solder to flow into it, removing excess solder from your joint. This is sold in various widths, but probably the most commonly used size is the 1/8” width. Many companies make solder wick, with Soder-Wick probably being the “big name” in the business.

Heat shrink Heat shrink is best bought in different sizes and is one part where quality matters. 3M makes the best heat shrink, hands down. No names give you inconsistent shrinkage, tend to split, and generally are more trouble than they are worth. Get off the wallet for your heat shrink. Black is generally the “go to” color, though you can color match with today’s colored heat shrinks. Also read the manufacturers instructions with regard to shrinking techniques, size of shrink to use with different wire gauges, and amount to use. Generally speaking though, you should use the smallest heat shrink that will fit over your wire and use a length that is twice the width of your open connection.

Replacement wire A nice selection of wire is man’s best friend when doing electrical work. You should have a suitable selection in the most commonly used gauges for your application. You should also preplan which colors match your scheme and always err on the side of the better insulation types such as Teflon. You never know when you will have to run wiring close to hot engine components rather than a cooler interior for example. While wire is wire, it is usually a good bet to lean towards Teflon jacketed wire as it is tougher and resists higher temperatures than it’s inferior cousins. Electrical problems usually occur at the weakest point in the circuit and aside from slightly greater costs, it is almost never wrong to lean on the side of bigger/better when it comes to wiring.

Wire nuts Just say no when it comes to automotive applications.

Electronics tester A simple volt meter is all you really need. The pinnacle company though is definitely Fluke. While using a Fluke ScopeMeter 190 graphing multimeter would be the best, all one really needs is an inexpensive Fluke like a 23 or 77, which may be obtained on eBay. If cost is an issue, you use any brand even an old school Simpson analog meter, but remember the more functions your meter has, they more use you will have for it. Testing AC and DC with a continuity check function should be considered the bare minimum when meter shopping.

Test light Terribly useful tool to determine the presence or non-presence of 12V in automotive wiring. Without a doubt, the essential tool for any wiring project. Need to find which wire in a 25 wire bundle actually controls the rear wiper signal? The test light is your friend. Though possible with a multimeter, a test light is smaller and easier to manipulate in tight spaces and provides an easier indication of the presence of voltage via a light vs a digital or analog readout from a traditional meter. Though cheaper alternatives exist, spending the extra money on a Snap-On/Blue Point test light is money well spent.

Electrical tape Same applies for this item. 3M is the best, buy no other brand than genuine 3M electrical tape. Black is generally the “go to” color, though you can color match with today’s colored electrical tapes. 3M also sells various types for specific temperature applications. When used with a tight, neat wrap, their normal electrical tape is suitable for 95% of your electrical tape needs though.

Sponge A wet sponge aids in the cleaning process of the soldering iron tip as well as thermally shocking the iron. Thermally shocking the iron forces it into it’s maximum heat cycle allowing faster soldering and less time heating the component.

Soldering iron A soldering iron is a pencil shaped device used to heat materials that need to be soldered. Notice the use of heat materials, as you should not melt the solder onto the material, but rather heat the material so that solder melts onto it. For most wiring, a soldering iron in the 25-35 watt range should be suitable. These can be obtained very inexpensively at almost any store. For more advanced users, strongly consider a unit with replaceable tips and an adjustable heat control. Weller is probably the best known brand for this application as they are good units with reasonable pricing. Other great and cheaper options are the “Tenma” line of products from MCM Electronics and the ZD Electronic Tools line of products from MPJA Online

Soldering gun A soldering gun is a larger pistol shaped device. Though the purpose and practical application is the same as a soldering iron, soldering guns should only be used on large applications where high amounts of heat are needed to get the solder flowing. Possible uses of a soldering gun are in car stereo power wires of 0 gauge as the thicker wire acts as a heat sink. For most automotive users, a soldering iron is preferred, but the gun is mentioned in case you plan on lots of large soldering jobs.

Soldering Technique

Cleanliness is terribly important with soldering. You should always clean the items to be soldered, your solder, and your soldering iron prior to any work. Any contaminants on these items may find their way into your solder joint creating a pit, crack, or other weak spot. Wipe down with alcohol your solder as it probably has a thin layer of corrosion from sitting around a warehouse. Wipe any/all connections to be soldered. It may seem silly (for example) to wipe down a freshly exposed wire, but corrosion can occur inside insulation.

Soldering iron cleanliness. To clean your soldering iron tip, use your thickest solder or double/triple up what you have. With the iron on and held with the tip pointing down, apply liberal amounts of solder to the tip area and let it melt and naturally flow off the tip surface. This removes 100% of the contaminants from the soldering tip as well as skim coats the surface with a fresh coat of solder. This process is also called tinning, and should be performed over a scrap piece of metal, but as long as it’s non-flammable, you should be OK. Once you have cleaned the tip, remove any “solder burrs” clinging to your tip, by drawing it across a moistened sponge.

Probably the most important thing to remember is “the bigger the blob, the better the job” is NOT the mantra of soldering professionals. I’m lucky in that I’ve been trained to NASA standards of soldering. This means when I look at a robotic welded motherboard, I can actually critique and find errors with the machine that did the soldering. Soldering is one area in life where humans are better than machines.

We’ll look at a common scenario to highlight how to solder. For a basic two wire connection, you will prepare both wires by stripping approximately ½” off of each side. Clean each end of the exposed wire with alcohol. Now is also the time you want to insert the appropriately sized shrink wrap over one end of the wire and slide it down so as to not interfere with the soldering process. After cleaning both copper ends, carefully insert each end into the other so there is approximately ¼” of overlap. This is not an exact science, but try to make each end go into each other as neatly as possible without making the excess exposed wire bulge out too much. Apply a small amount of liquid flux to the butted connection. This can be done with toothpick or Q-tip. Then apply your cleaned, thermally shocked via a sponge, soldering tip to the connection to start heating up the joint. The flux will sizzle and smoke; this is normal. Then touch your solder to the wire joint. If it’s the right temperature, it will start to melt immediately and wick into the solder joint. You should notice the exposed copper wire to become the silver solder color. Move the solder around to ensure the entire joint is silver in color. This process is called painting the joint.

Occasionally, you will run into a case where your connection won’t heat up correctly due to dirty components or perhaps you are in a hurry. If this occurs, you can build a heat bridge to speed up the process. This is where you touch your solder at the joint where the soldering iron tip and the wires meet. This should create a liquid solder ball that will then start to wick into the joint. As stated earlier though, the best bet is to heat the joint rather than to hurry things along by melting via using the soldering iron itself to melt the solder. If you are not in a hurry and the solder won’t flow onto the heated component, you have a cleanliness issue with either the soldering iron tip, the solder, or the component. If this isn’t the case, then you need to use a more powerful soldering iron in the case of fixed wattage units or turn up with heat in the case of an adjustable unit.

How much to solder? Think less is more. Once the entire ¼” overlap area is silver, you are finished. You should still be able to see each individual strand of the wires, with the smallest amount of filling in the areas where the strands meet. Does it look like a solid silver blob? Use solder wick to remove the excess. Pull out about 2” of solder wick and wet the end of the wick with flux. Place this directly over the joint and hold the wick down to the joint with the soldering iron tip. Once the solder below melts, you should see the end of the wick turn from copper to silver. Remove the wick from the joint and inspect. Trim off the soldered wick end and repeat the process if needed.

Once finished, allow the joint to cool before cleaning with alcohol. Any remaining flux will appear as a caramel or black colored blob or smear and will be very sticky to the touch. This is the main soldering byproduct contaminant that needs to be removed.

Now that your joint is finished, slide the heat shrink over the joint and shrink it by whatever means is feasible or manufacturer recommended. This can mean using a heat gun, the tip or heat shield of your soldering iron, or perhaps a cigarette lighter. Many methods can be used, and it’s best to practice on your brand of heat shrink to determine which methods gives you the best results.

If you do like me and forget to put the shrink wrap on until after your connection is finished, or you have it too close to your connection during soldering and it shrinks due to heat convection through the wire, you are left with electrical tape. It’s best to use the two layers, twice as wide as the connection you are soldering rule.

While this is a nice walk through for a wire to wire joint, I cannot possibly cover every soldering situation. I can however give you some advice on how to apply the proper thought process to assist you in your situations.

a. Think through your soldering task. You might even go as far as taping the joint together, looking at it, and asking yourself: What could go wrong with method of connection? What is another possibly solution? Which method would give me the best long term results with the most reliability? Many times the problem isn’t so much of what to solder, as it is how to solder say a four wire connection in the middle of one wire. Should I wrap each wire in a C shape around the one or open up the one slightly by compressing it, then feeding through the other wires. The C shape gives a nice connection, but feeding through the wires offers a greater mechanical connection, but do I have room to perform one or the other?
b. Now that you have the method, how much solder should you use? Once again, the less is more rule applies with any solder connection. 100% of the wire to wire (or whatever situation) should be painted with solder. There should also be a very slight amount of excess that takes time and practice to achieve. This amount of excess is known as the fillet and is generally applied to components soldered into a circuit board. An overall definition is the excess amount of solder should never exceed 50% of the height of the component being soldered. An example is say you are soldering a wire onto a post by bending the wire in a C shape around the post. If the wire measures 1mm in diameter, the amount of excess solder around the wire that flows onto the post should not exceed .5mm. Needless to say we are talking about an incredibly small amount of solder, hence the prevalent use of “angle hair pasta” solder in electronics.
c. The first and last step is to remember common practices such as advanced shrink wrap preparation, soldering iron safety, wire/lead/component preparation, and overall cleanliness.

Any online soldering help? The absolute mother load of soldering information with pictures and more applications than you will ever see can be found on this link.

Any soldering safety precautions? Soldering irons are HOT! Treat every iron as if it’s hot every time. Use the “handgun rule”….it’s always loaded, therefore the soldering iron is always hot. Never eat, drink, or smoke in the presence of soldering equipment. The vapors/contact with solder is hazardous so ensure your work area is well ventilated or use a small fan to extract solder fumes. Never use your mouth as the “third hand” to hold the solder.

Crimp on connectors

What about crimp on connectors? Crimp on type connectors of various forms can still be soldered on. This provides an additional layer of connectivity, strength, and protection. While to many this seems redundant, it may be the step that puts you above the competition in a car show or when showing the differences in your business practices to customers. This is easily done by using sleeveless connectors that are crimped then soldered and new sleeves are fabricated with various colored heat shrink. This allows a better connection as well as allowing a custom look. OEM or aftermarket sleeved connectors are generally color coded by the manufacturer or have set standard colors based on wire gauge. By cutting off the existing sleeving material, this will allow you to customize your connectors’ colors to suit your existing color scheme. For highly technical users, this article highlights the benefits of using uninsulated connectors.

Aside from combining solder with crimp on connectors, they may be used as a standalone, easy solution to those with no soldering skills or in inaccessible areas where soldering is impractical. Generally speaking though, you get what you pay for with crimp on connectors. The better ones to purchase contain soft plastic sleeving so that it does not become deformed during the crimping process. While not a deal breaker for many, it’s really best to buy the better connectors as you never know when you will prefer their appearance instead of being stuck with one of the cheaper units. 3M makes wonderful connectors as a rule though there are other good manufacturers as well.

Another key is for best results you should always use the tool specified for crimping by the connector manufacturer. Yes, pliers will work, but for the best and longest lasting connection use their specific tool/crimper/die. This might be a good time to invest in a quality crimper with replaceable crimp dies such as ones manufactured by Paladin Tools. This allows you to use one tool on a variety of tasks. Though it has a higher initial expense, subsequent crimp dies are cheaper than a new, single purpose crimper.

Any online connector help? The absolute mother load of connector information with pictures and more applications than you will ever see can be found on this link.

What about gold connectors? Gold connectors are only primarily for show though they are more resistant to corrosion than other electrical conductors.

What about twist on or “no tools” connectors? Just say no. Yes, some have had luck with these types, but why take the chance?

What is dielectric grease? The primary purposes of dielectric grease is to keep out moisture and prevent corrosion. It’s a non-conductive silicone based grease that keeps primarily prevents corrosion and is mainly used on connector junctions. Many swear by this as cheap insurance against future problems.

General information

Where do I buy soldering tools? Probably the best and easiest resources are through Techni-Tool and Jensen Tools, both of which offer free catalogs. If nothing else, I’d recommend subscribing to these catalogs as they both offer a wide variety of unique tools that have automotive related functions though they are primarily catered towards the electronics industry. You should also visit your local electronics stores. The best ones are usually locally owned and are only found in the yellow pages.

What should I avoid?

a. Cold Heat soldering tool. Though I’ve personally never used it, it’s commonly known as junk.
b. Radio Shack. Consider this your last minute/last resort spot for item. It is typically overpriced, no-name stuff that will cause more problems that they solve. Remember their logo: You’ve got questions….we’ve got blank looks.
c. Cheap “Made in China” type products of any sort. Most of this stuff is sold at either Radio Shack or in the “electrical” aisle at Wal-Mart. Just say no.

Editors Note

This post was created because I wasn’t able to find a good Soldering/Electrical FAQ. Unlike my other FAQs, this post mentions brand names/types/styles of tools and sundries to aid people in google searching/ebaying for them as for many, these types of items are wholly foreign to many people.

As well, if you have a favorite brand/product, please post with the manufacturer URL so others can look at it. I’ve mentioned my recommendations of the “best” products, feel free to list yours.

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