Hand-soldering is one of the most difficult tasks in electronics, but after reading this article and carefully following our guidelines, the quality of your soldering should improve considerably. 
If you think soldering plays a minor part in the development of electronics, we will change your thinking.  We will also cover some of the items and equipment you can purchase to help you improve your skills in this area. 
The art of soldering has improved over the years, to a point where it is 99.9999% perfect. Every electronic product has hundreds of solder connections in its construction and a computer board, for example, has thousands of connections. The chance of a board failing in a 5 year life-time is less than 1%. Consider the enormous challenge this presents. 
I have watched soldering improve from the days of early colour television receivers when printed circuit boards were filled with dry joints and sets failed every 6 months or so. When these sets came in for repair, the only solution was to completely re-solder the board!
If the art of soldering had not improved, computers would NEVER have got off the ground. On a similar ratio, a modern computer would fail every 5 minutes!
It seems incredible that a simple facet such as soldering would hold-up such a development. 
Over the past 20 years, the quality of soldering has improve to a point where even the smallest, cheapest, throw-away product has a perfectly soldered PC board. 
It's all a matter of CLEANLINESS, using the right cleaning fluids (fluxes), the correct solder and soldering at the right temperature. The composition of the solder is extremely important. A change of less than 1% in the composition can make the difference between a joint that binds correctly and one that "fails."   All printed circuit boards heat and cool during the course of operation and depending on the actual temperature rise, the solder connection can "internally fracture." Solder is actually a very fragile material, possibly due to its low melting point, but also due to its composition, and is very susceptible to fracturing. This is why it is very easy to produce cracks in a connection, due to vibration or heating and cooling and movement. 
There is nothing worse than finding a PC board with solder-cracks that develop over a period of time due to faulty soldering. Sometimes dry joints can develop due to the components heating up and expanding. This action puts enormous stress on the solder connection and eventually it "breaks." In the worst cases you can "wiggle" the component lead and remove it without the need to de-solder! 
The answer is to re-solder the connection with a different type of solder or add more solder so it is stronger. You can also move the component away from the joint so that the joint does not get so hot. 
Sometimes the joint can become dry for no apparent reason. It could be poor cleaning in the first place, solder not being hot enough to form a bond between the surfaces or insufficient solder. 
There are possibly 100 reasons why a solder connection fails and if you think soldering is a simple science, I can assure you a multi-million dollar business has developed in response to industry need. This business has actually saved the electronics industry from ruin! 
But the art of soldering has expanded a lot further than simply making connections on a standard through-hole PC board. It has expanded into MICRO CONNECTIONS (soldering very small connections) and DESOLDERING as well as flood soldering (wave soldering) where the board is totally immersed in solder for a very short period of time and all the connections are soldered at the same time.   

THE ART OF SOLDERING 
Before we start, there are three facts that will surprise you. 
No matter what your level of skill at soldering, the quality of your workmanship will improve considerably by:
1: Using a small, temperature-controlled soldering iron, 
2: Using a wet sponge to clean the tip of the iron, and tapping off any excess solder before starting a joint, and
3: Using fine solder. 
You will be absolutely amazed at how the quality of a joint will improve by following these three pointers. 
A normal, low-cost soldering iron is far too hot for delicate electronic work. The manufacturers of these irons usually allow the temperature to stabilize at a high level so that the iron can be used for a number of applications, including fairly heavy copper-wire connections.  
The high temperature of the tips makes the rosin (resin) in the centre of the solder "burn off" too quickly and it does not get sufficient time to clean the connection. To compensate for this you need to apply extra solder and the end result is the joint can get too hot and damage the component - especially a LED or transistor or other semiconductor device. 
The other major problem with a constant heat iron is the resin forms a burnt carbon layer on the iron and this must be tapped off before starting each connection. 
By simply changing to a temperature-controlled iron, your soldering skills will produce a much better "technical connection." 
The joint will be smaller and more shiny (indicating the correct temperature has been delivered during the soldering process), less solder will be used and the resin in the centre of the solder will have more time to clean the components.  
You will find the time taken to carry out the soldering process will be shorter and this puts less heat-stress on the component. 
Fine solder doesn't really go further however it may appear to go further because less is required for each connection. 
But the surprising point is the fine solder produces a joint that has a better appearance. 
Here's a question:
What is the life of solder?
The useful life for solder is less than one second. 
When solder is heated to melting-point, the resin (or rosin) inside it melts and starts to evaporate. It is during this liquid phase that it has a cleaning effect on the surrounding components. The vapour-phase is already too late. It has already left the connection. So, you can see, you want the liquid phase to be as long as possible. It is only during this time that the cleaning action takes place. The resin is able to lift the oxide coating and allow the molten solder to flow over the leads and pads and make a firm attachment to the BARE metal surfaces. 
That's why solder must be added directly to the joint and not taken to the joint on the tip of the soldering iron. 
If you add solder to the iron then take it to the joint, the resin has already evaporated and the solder will try to stick to the oxide layer on the component lead and pad. This oxide layer can fall off very easily and that's why the connection creates a DRY JOINT. 
Old solder on the tip of the iron is not wanted for ANY connection and must be tapped off the tip so that new solder can be applied. Old solder actually forms a new layer of oxide on itself very quickly and is absolutely worthless. 
When making a solder connection, the main component you need in "solder" is NOT the solder but the flux in the centre of the solder. When you start thinking along these lines, your soldering will improve considerably. 

SOLDERING
We can describe the procedures required to perform the perfect soldering connection and outline all the equipment needed to carry out the task, but the final result will depend on your dexterity and timing. 
I have seen some workers move a component while the solder is cooling and this produces a fractured connection. Othertimes the iron is removed too quickly and the solder is not given enough time to flow over the joint and create good adhesion. 
It's a lot to do with WHERE you place the tip of the iron on the connection, to get the best transfer of heat in the shortest time. 
These are all things that come with time and experience. 
In this discussion we can only point out SOME of the things to avoid and provide you with a range of  equipment that will help you produce a result to the best of your ability. 

MY EXPERIENCE
Some years ago I had to make a repair on a $1,000 piece of equipment that involved soldering a wire to the END of a 0.002in wire that was flush with the edge of a high-voltage transformer. The wire had been eaten away by the ozone produced by the transformer and it was impossible to buy a replacement. The imported TV would be worthless if a new wire could not be attached.  By careful scraping of the potting it was possible to create a small depression around the wire so that it could be tinned. Eventually, a small wire attached. 
This is one of the most delicate soldering operations I have been required to do in the field but now this type of work is STANDARD for anyone servicing surface-mount equipment. 

THINGS HAVE CHANGED
I recently asked the assembly team at Talking Electronics if they preferred soldering through-hole components or surface-mount. 
The reply was most encouraging. 
They all preferred surface-mount. They said it was quicker to solder a surface-mount board. The main reason is the board does not have to be turned over and leads do not have to be snipped. 
Boards are lined up 20 to 50 at a time and a single component is fitted to each board. The next component is removed from its taped carrier and placed on the bench. It is picked up with fine tweezers and added to the board. 
One component is added at a time and eventually each board is loaded. 
You don't need any glue or solder paste. Fine solder and a soldering iron is all that is needed. 
You can see our article on Surface Mount soldering by clicking HERE.
For small runs it is cheaper than sending the boards to a "loading facility."
This is the way of the future and any equipment we will be suggesting in this article must be able to be used with standard through-hole components as well as surface-mount. 

THE SOLDERING STATION 
The only real answer for a soldering implement is a SOLDERING STATION. 
If I gave you 10 reasons why a station is the only choice, the top reason would have to be QUALITY.
It improves the quality of your workmanship 100%. 
Just as a bicycle keeps you upright due to the gyroscopic effect of the revolving wheels, the correct temperature of the tip prevents the resin evaporating too fast and allows the solder to flow over the surfaces and clean them.  
The result is a pleasant surprise. Your skills are instantly improved. 
The ninth reason would have to be tip-size. If you have ever seen a surface-mount transistor, you will understand why a very fine tip is essential. You must be able to get the soldering iron onto the pad so that most of the heat goes into the pad to heat the joint and not via the lead of the transistor. 
There are other advantages of a station too. It is a convenient place to rest the iron, it has a wet sponge and a tray to take the old solder. Old-style soldering irons are left on the bench and touch other components. They sometimes burn holes through plastic items and create smoke, smell and carbon. 
Once you have settled on investing in a STATION, the cost is up to you. 
I am out of the picture on this issue however I will help you with some suggestions. 
Some stations have a very good range of tips. Some have a replacement guarantee and spare-parts availability. Some have "Zero Voltage" circuitry to eliminate both high voltage spikes and magnetic field generation at the tip to prevent unnecessary damaged to electronic components.
Some have a better-quality silicon lead to the iron that is very flexible. Some have a plug-in cord. 
Some have a digital read-out, while others have a panel meter read-out. Some have only a knob for the temperature setting. Some let you know the tip temperature. Some have a slightly higher wattage and this creates a better tip-temperature regulation. Some have a cooler handle while some simply look smarter. 
I want one that turns itself off after 10 minutes of non-use! 
It's up to you to look over the range and decide for yourself. Some manufacturers allow you to test their equipment via a demonstration while others allow a 2-week trial period. 
All this must be taken into account and will influence your final decision. 
No matter what you do, the end result will make you very happy. 
The only other thing you need is fine solder. 
I have had a lot of ignorance on this topic. Not everyone knows the enormous advantage of using fine solder. 
It's a quantum leap. Just as a station improves your soldering, the same improvement will be gained by using fine solder. 
Adding these two together results in a 200% improvement. 
Fine solder leaves considerably less flux on the connections and you produce a smaller, neater connection. (This is only a physical observation and is really not totally accurate. It's mainly due to the control you have over fine solder. You tend to use less.)

CHINESE SOLDER
I bought a number of spools of solder of different diameters on eBay and AliExpress and all of them were RUBBISH.
They claim the solder was 60/40 or even eutectic solder (63/47) but none of the solder melted at the same temperature as the solder I currently use. I had to increase the temperature of the iron considerably but the solder did not run smoothly and did not produce a shiny joint. Later, when I tried to add a wire to the joint, the result was just like a cold-connection.
In the end I threw the spools in the trash and got a refund from the suppliers.
If you are a beginner, you would think your soldering skills were the problem, but this solder was so frustrating that it was not worth the effort.
So, be warned.  CHINESE SOLDER IS RUBBISH.  

SOLDERING TEMPERATURE
One of the articles at the end of this discussion deals with soldering temperatures. The only point I need to mention is the melting point of 60/40 solder is 188°C but this is its PLASTIC REGION and it does not actually become liquid until about 260°C. To convert to Fahrenheit use the following converter:
Temperature Conversion
Enter a number in either field, then click outside the text box. 
Convert from Celsius to Fahrenheit and vice versa.

Solder below 260°C is in the PLASTIC REGION and will not produce a good connection. It must be heated above this temperature. 
I could provide a full page on the SOLID, PLASTIC and LIQUID regions of solder, according to the composition, but the bottom line is to raise it above 260°C.
The minimum setting for a soldering station is 280°C. 
For slightly heavier work (including de-soldering), the temperature can be increased to 320°C and for very heavy work the temp can be increased to 360°C. 

         Normal operation                                                      270-320ºC (518-608ºF)
         Desoldering operation for smaller joint                320-360ºC  (608-680ºF)

The station must be turned down immediately after carrying out the work as the tip will get stressed at this high temperature and this is when the coatings on it start to deteriorate and become pitted. As soon as a hole develops in the coating, the tip gets eaten away exactly like a hole in a tooth. (The copper inside the tip is eaten by the hot solder and eventually the extreme top part of it drops off.) 
A very good article covering the removal of surface mount devices with a very low melting-point solder called "Chip Quik," (made by Chip Quik) can be found HERE. About half-way down the article it says: When tin and bismuth are "amalgamated," it reduces the melting point of the solder to a very low 136°F, as opposed to the 361°F melting point of 60/40 solder. When you meld the two together —- that is, melt the new solder with the old — the resultant alloy has a melting point of about 150°F (well below the boiling point of water). At temperatures this low, it's nearly impossible to damage the solder pads. 
This is worth remembering! 

This covers the two essential items you need to carry out the physical side of construction. Don't forget a pair of side-cutters, and you are ready.

We now come to the repair and service-side of things. 

DESOLDERING
Anyone who has soldered will be faced with the problem of removing a component. Everyone eventually makes a mistake. 
Desoldering requires 200% more skill than soldering. 
The reason is STRESS. 
The act of desoldering a component is going to place an enormous amount of stress on the "land" (also called the "pad" or "donut") and if it comes off the board, the whole project may have to be thrown out. 
The "land" is the copper pad on the printed circuit board. It is attached to the board by glue. This glue is very strong but when it is heated, the adhesion is reduced considerably. 
Every time it is heated and cooled, the strength of the glue also reduces. 
Replacing a component requires 3 cycles of heating and that's why the operation must be carried out very carefully. 
There is a whole range of tools and equipment to assist in the operation of desoldering and the equipment you select will depend on a number of factors. 
Again, I am going to sound like a salesman, but the facts are true. Desoldering equipment ranges from $3 to $12,000 and these items would not be on the market if they were not needed. 
For now, I am only going to describe the simplest desoldering item . . . Desolder wick. 
This is a length of copper braid that has been soaked in resin. Once a portion of it has been used, it must be cut off so that the end is clean and fresh. This is very important as one of the main purposes of the wick is to supply resin to the joint to allow the solder to flow from the joint and into the wick. 
Place the wick on the joint to be desoldered and touch the iron on the top of the wick. 
You can turn the soldering station up 20°C  (50°F)  to increase the rate of heat transfer and overcome the heat-sinking effect of the braid. 
The solder will be drawn off the joint and run into the braid. You may have to repeat the operation on the other side of the joint. 
But this is the maximum you should do. 
The solder should be almost totally removed and the lead should be almost free. A slight sideways movement on the lead with a hot soldering iron will break (soften) the last remaining attachment of the lead to the pad. 
Repeat with the other lead and the component can be removed. 
This is the ideal situation.  
Turn the soldering iron temperature down and it's ready to solder a new component. 
This is a fairly slow procedure and if you are faced with a large number of operations, you may prefer to invest in a desoldering tool. 
There are two types of "solder suckers." One is a hand-held syringe. It is used in conjunction with a temperature-controlled iron or standard iron. 
The iron is used to heat the solder on the connection and the tip of the syringe is placed over the lead of the component and pushed hard against the connection while, at the same time, releasing the spring-loaded plunger. The plunger works in reverse to normal operation. It sucks the solder into the body of the syringe. 
The other type of solder sucker is a soldering iron with a hollow tip. It will have a sucker bulb attached or a vacuum pump, to draw the hot solder from the connection. 
This type of solder sucker is more expensive but carries out the operation faster than the syringe as the tip is heated and can operate so quickly that the joint is hardly heated at all. This is because the hot solder is removed from the action. 
These items are included in the comprehensive list below and you can see their appearance and cost.  

SURFACE MOUNT
The last item I want to cover is SURFACE MOUNT. 
Some of the projects we are presenting on this CD use surface-mount components. There are a number of reasons why they have been chosen. One is size but the main reason is to add to your skills in handling and soldering.
We have produced a separate article on soldering SURFACE MOUNT components and it can viewed  HERE. This article also includes a comprehensive listing of surface mount transistor markings. 

The following series of articles comes from other authors, they include many facts for the professional and include industrial applications. You need to be on the internet to view the pages.

Click HERE for an article on HOT TWEEZERS, HOT AIR PENCIL, and a guide on SMD replacement. 

Click HERE for an article titled SOLDERING MANUAL.

Click HERE for a short article on desoldering.

Click HERE for an equipment report on DEN-ON SC7000 Desoldering Tool @$395.00  This is a hand-held device similar to a soldering-gun with a self contained vacuum pump with reversible hot air blow for SM removal.

Click HERE for an excellent article on How to successfully Remove and Replace SMD Chips.

 Click HERE for excellent diagrams on removing and replacing a surface mount IC with a Rework Station.

Click HERE for Digi-Key details on all types of products. This is the best search engine on the net. 
For details on Solder  e.g: 1/2lb of 0.71mm solder KE1117-ND or KE1118-ND for approx $9.00. Load the part-number into the search engine for pricing.  

Click HERE for details on solder cream.

Click HERE for details on solder paste.

Click HERE for details on soldering stations, desoldering equipment, including SMD rework.

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