Desoldering

So, you’ve learned to solder a couple of wires together and have practiced at soldering them to a circuit board or terminal.  But, you’re not happy with the outcome.  What to do? 

Well, now you’ll have to desolder the wires or component from their resting place and try again.  But, how do you desolder?  Let’s take a closer look and I will attempt to enlighten you on this pain “in the you know what”, procedure.  If you've soldered your wire to a terminal and the end result looks something like the examples below, then you need to desolder that sucker for sure and start over!

Examples of poorly soldered terminals

First things first - You have to decide what tool or tools to use to remove the soldered connection that you’ve just made or one that was made many moons ago by you or some other technician. 

Is the connection done professionally or is it a globby mess that just needs to be reworked?  No matter, you must decide how to tackle this job as you would any other.  Do you use a desolder sucker, desolder tip, wicking braid, or do you just heat it up and pull as hard as you can until the wire rips from its holding?

I hope you didn’t decide on the last method.  In my expert opinion, the best way to remove a connection from a PCB or through-hole terminal is with a desoldering gun. 

You can select different types of nozzle sizes for removing the solder.  These desoldering guns basically just heat up the solder as a regular soldering iron does.  Then you press a lever and the vacuum in the unit sucks up the molten solder and places it in a chamber.  No fuss, no muss. 

Desoldering Gun

When sucking up the molten solder you must be sure to hold the vacuum on for at least three seconds.  This allows all of the solder to reach the holding chamber.  If you release too soon the solder may fall back out through the  nozzle tip and glob your desolder site with melted solder.  Be sure to clean the nozzle before and after each use to ensure the tip remains oxidation free.  Just add a little dab of solder to the tip as you would a standard soldering tip and place it in the holder for the next job.

This system works well for most through-hole type solder jobs.  The nozzles can be selected to fit the soldered joint, thus ensuring that all of the solder is removed with one action of the desoldering gun.  Make sure that you don’t hold the nozzle on the joint for too long.  Just like soldering with a tip, if you overheat the joint damage may occur.  Below is an example video of the soldering gun I use in my own lab.

Desoldering a PCB

The next way of removing solder, and one that I have used many times, is solder wicking braid.  It is essentially copper braid on a spool.  Add a little flux to the wick and place the braid next to the joint or connection that you want to desolder.  Place the iron on the other side of the braid and watch as the wicking action soaks up the melted solder and displaces it on the braid.  

 Desoldering with Wicking Braid

This method works well for most jobs.  However, if the solder is thick and is stuck down inside an eyelet or via you may have a harder time using wicking braid.  In those cases I recommend sticking to the desoldering gun or maybe use some Chip Quik.  Chip Quik is a low temperature melting solder alloy that helps with removing stubborn solder connections.

Another way, not the way I prefer, is to use a mechanical solder sucker.  This tool is spring loaded and can suck up melted solder similar to the desoldering gun.  Just push the plunger mechanism down until it latches.  Place the desoldering tool nozzle next to the joint that you want to desolder.  Melt the solder and then push the release button.  This allows the spring to expand in the plunger and suck up the melted solder.  If done right, most of the time this works well with through-hole connections.

I don’t prefer to use mechanical solder suckers due to the static charge that can be generated when the plunger is released.  Static electricity can be very damaging to a circuit board if it is of a high enough charge.  You most likely will not encounter a problem with this happening on a home project.  However, if you work in the electronics industry you may want to avoid using this tool.

 Example Desoldering Pump

For surface mounted components you may want to use very small wicking braid, a hot air pencil, or a very small desoldering nozzle.  I have actually used a combination of both a hot air pencil and a soldering iron to remove stubborn solder joints such as ones that have been soldered with silver solder. 

Many small SMD components can be removed readily with a little bit of wick and some flux.  You can also use desoldering tweezers.  The tweezers heat up like a soldering iron.  Except in this case you have two irons that consist of tweezers.  They come in many shapes, temperature ratings, and sizes. 

Just add a little flux to your joint, heat the joint with the tweezers and under most circumstances the component will come right off.  Occasionally, you must employ  a pre-heater or extra heat on the joints of the component to remove it.  In those cases I recommend using a preheater.  I will discuss the uses of preheaters in another article.  

Example video of desoldering tweezers

So, hopefully this has helped you in selecting what best works for your own desoldering job.  Have fun and try not to burn anything!

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Soldering Wires Together

One of the first things I learned to do when I was being trained to solder was the proper way to tin and prepare wire for soldering.  You may think this would be easy.  However, even the most mundane of tasks, including soldering wire, can be daunting if you don’t know how to do it properly.

First off, are you using solid or stranded wire?  Is the wire copper coated, zinc coated, aluminum coated?  The type of metal the wire consists of makes a difference as well.  You don’t necessarily need to tin the ends of solid wire.  Stranded wire on the other hand should be pre-tinned prior to splicing, soldering to a circuit board, or attaching to a terminal of some kind. 

When tinning wire always ensure that you don’t allow the solder to “wick” up under the insulation.  The solder should flow up the wire until it is about one wire diameter from the insulation.  This ensures that you don’t damage the insulation.  Remember to use the appropriate type of flux when tinning your wire.

Example of how to tin a wire

When you flow the solder up the wire ends do not touch the solder directly to the soldering iron tip.  Add a small dab of solder to the clean tip first and then heat the wire.  As soon as the heat transfer commences touch the solder to the opposite side of the wire away from the tip.  The heat from the tip and flux will allow the solder to flow.  Advance the tip and solder up the wire end until you reach the recommended stopping point just before the insulation.

I use a solder wick or heat wick just behind the area to be tinned to prevent too much heat from entering the insulation.  This is just a basic tool that attaches to the wire like a small pair of tweezers.  Below is an example of a solder anti-wicking tool.

Anti-Wicking Tool

Now that you’ve tinned your wire end what do you do with it?  Let’s see, are you attaching it to a board, splicing it to another wire, or installing it into a terminal?  Let’s cover the first one mentioned above.

When soldering a wire end into a circuit board there are some different ways to do this.  One way is to solder the end into an eyelet.  First, place the appropriate size wire into the eyelet.  If the wire is too large for the eyelet then you are using the wrong gauge wire.  Cutting strands off the wire ends is not a recommended method of fitting wires into eyelets or terminals.  It is actually a bad thing to do because you lose the current carrying properties that were recommended for that size wire.  You could cause power and/or signal degradation by performing this heinous act of hacking strands.  And lastly, you could cause the wire to be weakened at the end where it is soldered, ultimately causing the wire to break off.

Example of soldered wires to a circuit board

In the example shown above you can see the wires have been soldered in correctly.  However, the black wire exhibits some damage where it was held in place with a tool that created a heat bridge between the tool and the wire insulation.  This could have been avoided if an anti-wicking tool had been used instead.   You will also notice the eyelets are much larger than the diameter of the wire.  This is perfectly acceptable if so designated in the electronics industry by an engineering drawing. 

You will be fine as a home hobbyist to perform this action as well. 

So you’ve found the correct size wire, have tinned the ends, and now are ready to solder into the eyelet.  Place the wire into the eyelet with at least a half diameter wire size showing on each side of the eyelet.  If you can only solder from one side of the board, that’s fine.  Add some flux, add solder to your tip, and place the tip against the wire, then flow the solder on the other side of the heated wire.  The solder should flow uniformly and not glob up due to inadequate heating.  If you’re successful, the result should look something like the picture of the tinned wire on the right just below.

 

Example of the right way and the wrong way to tin a wire 

Of course, you may not be soldering to an eyelet.  Wires can also be soldered to component pads and traces as well.  If you want to learn how to do this properly I suggest taking a course on soldering such as the IPC-7711/7721 rework system.  I personally have taken this course and it helped me to become a successful certified IPC specialist in my field. 

Another method of soldering your wire to a circuit board is via a terminal.  You can wrap the wire around the terminal, through a terminal eye, or lay it through a channel.  Then you solder the ends to that terminal for a nice tight connection.  Refer to IPC 7711/7721 for proper soldering techniques and acceptable criteria for soldering to eyelets and terminals.

Example of soldering a wire to a terminal

The last method I want to cover here is wire splicing.  There are several methods for accomplishing this task utilizing soldering techniques.  The easiest way to splice a wire is with a lap splice. However, this splice does not provide a lot of strain relief in and of itself.  When creating a lap splice remember that both sides of the wire should be tinned at the same length.  The wires should overlap by at least three wire diameters and be parallel to each other.    You also have the option of adding a wire wrap around the splice for added strength.  After you have completed the splice clean the wire and then cover the splice with heat shrink or other material that will protect it from the environment or shorting to other equipment.

Example of a properly spliced wire

Shown above is an example of a properly spliced Lap Splice.  You will notice that the solder does not extend under the insulation, the wires do not exstend past the insulation, and the wire strands can still be clearly seen through the solder.  Another item of notice is that the wires are laid parallel to each other with no gaps or solder globs. 

Other methods of splicing wire include Mesh, Hook, Wrap, Western union, Rat-tail joint, and the  Knotted tap.  I'm sure that I may have missed one or two other's.  

If you would like a more in-depth breakdown on how to perform each type then refer to IPC/WHMA-A-620B (Requirements and Acceptance for Cable and Wire Harness Assemblies).  Or, you can read up on splicing at www.learn-about-electronics.com in the soldering section.

Lead Free Solder

So, you’re wondering if lead-free solder would be the best choice for your project. You want to be environmentally friendly and think using lead-free solder would be a big help.  Woe is to the technician that loves the lead-free realm!  Let’s take a closer look and I’ll explain why lead-free isn’t all that it’s cracked up to be in the world of electronics.

First of all, lead-free solder was not the idea of any technician that I know, have known, or have heard of in my thirty years in the electronics industry.  The European Union Electrical Waste and Electronic Equipment, or (WEEE), “yes, it has that acronym”, and Restriction of Hazardous Substances Directive or (RoHS), came into effect prohibiting the inclusion of large quantities of lead in almost all consumer electronics produced in Europe. 

 

Most manufacturers in the U.S. still use tin/lead solder.  Some may receive a tax break if they reduce the lead content in their formulations. 

Lead-free solders on the commercial market may contain some amount of tin, copper, silver, bismuth, indium, zinc, antimony, and small amounts of other trace metals.

Most lead-free solders have a much higher melting point than conventional lead based solders with tin.   The temperature difference may be as much as 20 degrees Celsius higher in some formulations. 

Lead-free solder poses a unique challenge to the technician or manufacturer of electronic components when using lead-free solder.  Solder pots and wave soldering machines must remain completely free of any tin/lead solder due to the contamination that the lead will introduce to the lead-free environment.  Solder pots can literally blow out their sides when tin/lead and lead-free solders are mixed.

When using lead-free solder you may notice that the resulting joint does not display a shiny appearance as the tin/lead solder will.  You should observe a dull, grainy appearance after the joint has cooled and has been cleaned.  This is normal in lead-free soldering.  When using lead-free solder the solder tip must remain completely clean and uncontaminated from any tin/lead solder.  A small amount of lead-free solder must be placed on the unused tip to reduce extreme oxidation caused by the lack of lead in the solder.

Example of a lead-free soldered joint

Tin/lead solders were initially introduced to help prevent the effects of “whiskering”.  This is a phenomenon caused by the tin in the solder.  Tin will actually grow tiny fine little whiskers over time if left unchecked and can cause short circuits in electronics.  Lead-free solders have this potential for causing whiskering.  Shown below is an example of this phenomenon under a microscope magnified many times.

Lead-Free solder whiskering

I prefer to stick with my tried and true tin/lead solder.  Unless you decide to move to Europe in the near future, I recommend that you stick with standard solder and leave worrying about the environment to the solder illiterate out there in the world.  They may never know what we go through to ensure their electronics function properly the first time and continue to function for many years.

Lead-free solder is a fine concept.  However, in actual applications it’s not as reliable as we would like it to be.  Lead-free soldered joints have a tendency to crack under stress and loads.  They don’t provide high reliability in most aviation and medical applications either.  That’s why we use tin/lead formulations in most of our electronics in the U.S. and other non RoHS compliant nations. 

But, if you’re dead-set on using lead-free solder in your own applications, I highly recommend that you do thorough research and get trained up on how to use this solder the correct way.  Mixing your lead-free solder with tin/lead solder on a circuit board may have unwarranted effects in the long run. 

Shown below is an example of the differences between tin/lead and lead free.  You will notice that the joint on the left is shiny and smooth while the one on the right is dull and grainy.  The shiny one is tin/lead and the dull one is obviously lead-free.  

Comparison of tin/lead to lead-free

  

If you mix lead-free with tin/lead solder you may cause more damage soldering the components to the board than the initial damage that caused you to rework the circuits in the first place.

Take care and good luck on your lead-free journey if you so choose this dangerous and windy path.

Solder

So, you’ve selected your soldering system, have your tips on hand, learned a little about what flux to use, and now you’re asking what type of solder would be best for your own project or needs.  “That’s a very good question.”  Let’s see if I can shed some light on this. 

First of all let’s go over what solder is made from and then we’ll work on what you may need. 

Solder is basically a filler material for soldering parts together.  We will only cover electronic applications as there are other types of solder alloys for use in jewelry making, brazing pipes, and many other industries outside of electronics.

Solder is available in many alloys for differing applications.  In electronics, the alloy or “Eutectic alloy”, of 63% tin and 37% lead (or 60/40) which is close or almost the same in its melting point, has always been the choice that most technicians prefer.  “I use this mix on a daily basis in my own lab.”

This mix of tin and lead has its advantages.  When the solder is heated to its melting point the solder will flow smoothly at its lowest temperature.  This prevents the solder from going through what is known as the “plastic phase”.  Having the lowest possible melting point prevents heat stress to electronic components.  With little to no heat stress this prevents possible cracking of the electronic components. With no “plastic phase” present this allows for quicker wetting as the parts heat up and faster setup times as the solder cools.

Solder in roll form

Any “non-eutectic” formulations of solder, like lead-free solder, can result in unreliable joints if the parts don’t remain still during the soldering process. 

Some common formulations for solder that I use and have used in my own lab are shown below.

63/37 – This melts at around at 183  Degrees Celcius or 361 Degrees Fahrenheit  (eutectic: the only mixture that melts at a point, instead of over a range)

60/40 – This melts around 183-190 Degrees Celcius or 361-374 Fahrenheit 

50/50 – This melts around 183-215 Degrees Celcius or 361-419 Degrees Fahrenheit

So, as you can see the different mixes of solder generally melt within similar temperature ranges.  There are not a lot of differences in the formulations.

Some solders don’t contain lead at all.  These “lead-free” solders are more widely used in countries that adhere to lead-free restrictions for electronics or rather (RoHS) or “Restriction of Hazardous Substance Directive.”  This directive mostly covers European Countries and is not widely used in the United States or elsewhere. 

These lead free solder formulations were introduced in an attempt to lower the use of lead in the electronics industry.  It was thought that by using lead free solder the amount of lead that found its way into landfills, toys, and groundwater from discarded electronic devices would or could be reduced.  Unfortunately, for the electronics industry, the use of lead-free solder alloys has made it difficult to produce quality electronic devices.  Lead free solder does not contain any eutectic formulations.  This type of solder melts at around 250 Degrees Celsius or 482 Degrees Fahrenheit.  This high temperature needed to melt the solder makes it very difficult to create a reliable joint.

Some other common solders include low temperature formulations.  Some of these alloys contain “Bismuth”.  

 One type I use to help remove stubborn circuit board components is called “Chip Quik”.  This solder alloy melts at a very low temperature and is available in leaded and lead free formulations.   

Here is a quick video on how Chip Quik works

Some solders melt at a much higher temperature.  One such solder is “silver solder”.  This alloy is used where high strength joints are desired where common solders will just not work.  Silver solder is also used to solder assemblies that you don’t want to become unsoldered during rework of surrounding components.  There are also specialty solder formulations for soldering aluminum components. 

Solder comes in many forms as well.  The most common method of using solder is on rolls.  However, there are also bars and paste solder.  I purchase bar solder for my lab solder pots.  This is an actual heating pot made specifically for melting solder.  I use one when I have many wire ends to tin or leads that need tinned on a large scale.  You may want one for your own use if you solder and need to frequently tin wire ends or leads.

Solder sizes are as varied as there are types, from the very small of just .010” to the larger .125” for common rolls.  You can purchase bars as well in leaded and lead-free formulations. 

Solder wire also comes in some of these common formulations:

(10/88/2), (60/40), (62/36/02), (62/36/2), (63/37), (Classic Tin/Lead), (Sn60),( Sn62), and (Sn63/Pb37)

For a complete breakdown of each designation, refer to the manufactures specifications.   Solder can also come with no flux core or be manufactured containing no-clean,  rosin, mildly activated rosin, water soluble, Glow core no-clean, or activated Rosin.  

 Refer to my article on flux for more information on fluxes and how they work.

The last type of solder I want to cover is “solder paste”.  Solder paste is a mixture of solder powder and flux.  The flux acts as a tacky, viscous binding agent to help hold the solder in place as it is melted.  The wetting action of the flux as it’s heated helps to flow the solder.  This type of solder is used mostly for BGA and LBGA solder ball applications.  To put in laymen’s terms, it’s used for the types of chips you would find on a computer circuit board that has no physical leads showing.  The solder pads are hidden underneath the component. Usually manufacturers utilize stencils when using solder paste.  However, you can use solder paste on your own project if you follow the example shown below.

Simple video showing how to use solder paste

I personally do not like using solder paste.  The small solder balls mixed in the flux have a tendency to roam if not heated properly.  You’re more susceptible to solder bridges and getting solder under the leads.  So, I say stick to standard tin/lead solder for your home projects. 

Selecting the right size will be up to you.  I generally use a solder gage that is small enough to fit the size of the wire or component pad.  Anything larger and you risk using too much.  This usually results in a large glob of solder on the worked item.  I use .010 for soldering extremely small components such as a 0402 or 0603 SMD (surface mount device).   .015 works well for 0805 to 1206 SMD components.  For tinning wire I either use the solder pot for multitudes, or start at .025 and work my way up from there depending on the wire size. 

Whatever you use will ultimately be up to what you decide works best for your own project.  What I have presented to you in this article should help lay a good foundation for your own soldering selection and experience.