De-soldering is required when any electronic component needs to be removed from a PCB, usually because it is faulty. Ideally, the aim is to remove all the solder from a component and detach the component from the PCB without damaging the de-soldered component, the neighbouring components or the PCB itself, either due to excessive heat or rough handling. There are also improperly-made soldered joints that are called dry joints, which are electrically noisy, unreliable and likely to get worse, in time. They may work well initially but can cause equipment failure at any time in the future. There will then come a time when you need to remove the solder from such a joint.
You can get a number of de-soldering guides on the Internet teaching old-school methods such as using a solder braid, a manual de-soldering pump, or the impact method to remove components from the PCB board. But these methods are really tedious and unproductive. The results only depend on your experience, and there is a high chance that you may damage the board beyond repair.
Over the years, these methods have served their purpose very well. They have been in use for a long time and are very cost-effective, especially the use of solder braid, which is a ribbon of extremely fine copper strands woven together. It is usually supplied in small reels and comes in a variety of widths. The braid is pressed against a molten soldered joint, and capillary action draws the solder out of the joint and into the braid. The portion of the braid that contains solder is then cut off the reel and discarded. The solder braid is usually treated with a flux, so that the solder is drawn up more effectively. But as the technology is changing and electronic components are shrinking in size, these methods have become less effective.
The prices of professional de-soldering tools have also come down over the past few years, which gives us every reason to buy one and save ourselves from all those losses that may occur with the tedious methods mentioned above.
Types of de-soldering stations
There is a wide variety of de-soldering tools available in the market, and each type is designed to cater to specific needs. Manufacturers offer different models in each category with various features and specifications, so selecting what’s best for you can get confusing. You can address this issue in two stages—first decide on the type of de-soldering station you need and then pick a model from the selected category.
De-soldering stations can be divided into different types:
1. The first type is for de-soldering through-hole components and is called suction type de-soldering station.
2. For SMD (surface mount devices) components, you need a different de-soldering tool known as the hot-air rework system.
3. Another tool called the heated tweezer has a more targeted approach, just as its name suggests.
4. The above tools cannot de-solder BGA (ball grid array) components. BGA packages need BGA de-soldering station specifically designed for the purpose.
Suction type de-soldering stations
Suction type de-soldering stations are used primarily to de-solder through-hole components or to remove solder from the pads after the SMD component is removed with the help of SMD de-soldering equipment. These de-soldering stations are based on the principle of suction of the melted solder from the PCB with the help of vacuum. Its heated nozzle is put over a joint with the pin at the centre to melt the solder and, once it has melted, a button is pressed to initiate the suction of the melted solder.
There is a huge variety of such de-soldering stations available in the market, but they mainly fall into two categories:
1. Integrated de-soldering units
2. Vacuum pump type de-soldering stations
Integrated de-soldering units. These are equipped with a nozzle, built-in heating element and suction unit, and most of them run directly from the mains. Such units are comparatively cheaper than a complete station but lack various features. Most of them do not even have the temperature-control function. So the tip can go up to very high temperatures while in the stand. and when you try to de-solder the joint you might even take out the pad—permanently damaging the board. Fig. 2 shows an integrated type de-soldering unit.
Vacuum-pump type de-soldering stations. These also work on the same principle as that of integrated units, but the power and suction is delivered through a different unit and is not integrated in the hand piece. Such stations come with better features like a digital display to ensure easy and reliable temperature control, power saving, auto shut-off and excellent thermal recovery. Such a unit can make your rework efficient and safe. Fig. 3 shows a vacuum pump type de-soldering station.
If you choose to buy a vacuum pump type de-soldering station, the next thing you need to decide on is the type of hand piece. There are different types of hand pieces available, such as gun type, pen type, straight, etc, and everyone will have a different opinion on which is the best. So go by your own gut feeling. Personally, I find the pen type more comfortable for precision work.
Once you have made all the above decisions, it’s time to work out the specifications for each model and choose one that best suits your requirements. Specifications for a de-soldering station are not too complicated but understanding them can make a big difference in making the right selection. Given below are the specifications and their descriptions to help you understand what they indicate about the de-soldering station.
Temperature control. The simplest and the cheapest de-soldering stations do not have any kind of thermal regulation. They are directly plugged into the wall socket and heat up to high temperatures in their holders. There is some amount of natural thermal regulation due to the physical environment. As the tip gets hotter, it dissipates more heat, and as it gets cooler, it dissipates less heat. Such stations may be described as thermally balanced but their output is neither controlled nor stable. Their high temperatures can cause permanent damage to the PCB.
Power consumption. When the nozzle tip touches the joint, its temperature drops, as the heat is dissipated in the joint. If the part you are soldering can dissipate heat at a higher rate than what your tip can deliver, the temperature will keep dropping until it won’t melt solder any more. The wattage that you would require completely depends on the project at hand. Usually, bigger components absorb and dissipate more heat. If this rate is more than the heating rate of the de-soldering equipment, the joint starts cooling down. So the general rule is that you need more wattage for larger parts.
A higher wattage does not mean that the nozzle tip runs hotter. Instead, the heating is faster and there is more power in reserve, when required. Choose a de-soldering station with sufficient wattage to cover all types of joints. For large components and joints you would need more power, and you would not like to buy another station for that kind of work.
Temperature range. Different solder joints have different nozzle temperature requirements for de-soldering. Also, different solders have different melting temperatures (see Table I). So it makes sense for the de-soldering station to be temperature-controlled type. Check out the range of joints you would be de-soldering and select a station with suitable range. The wider the range, the better.
Temperature stability. This is a measure of how well the control circuit works, allowing for the heat losses into the environment and yet keeping the tip’s temperature stable. The stability specification is valid only when the iron is at rest, not when it is actually being used for soldering.
Nozzle-to-ground resistance. Tip-to-ground potential is also called millivolt leakage. This is the voltage existing between the soldering iron tip and the workstation common point ground. It should not exceed 2mV as defined by various standards.
Nozzle-to-ground potential. This is the resistance that exists between the tip of the soldering iron and the workstation common point ground. It should be between 2 ohms and 5 ohms.
Thermal recovery. This is also a measure of how well the control circuit works. When a joint is soldered, heat is lost from the tip through conduction and the tip’s temperature drops. Thermal recovery refers to how long the soldering station takes with a particular tip at, say, room temperature, to get back to the initial temperature. The better the thermal recovery, the faster the operator can work.
The characteristics in Fig. 4 were obtained by the manufacturer (HAKKO) by melting a solder consecutively on a 5×5mm PCB land size and simultaneously measuring the tip’s temperature with a thermocouple fitted on the tip.
ESD-safe. If you are interested in soldering a lot of static-sensitive parts such as CMOS chips or MOSFET transistors, you should look for slightly more advanced de-soldering stations that use static-dissipative material in their construction to ensure that static does not build up on the equipment itself. You may find these listed as ‘ESD safe.’ The cheap variants won’t necessarily be ESD-safe but, nevertheless, will still probably perform perfectly well in most hobby or educational applications, if you take the usual anti-static precautions when handling the components.
Hot-air rework system
To de-solder SMD components, hot-air rework systems are used. How they work is exactly opposite to how vacuum-pump type systems operate. Hot-air rework systems blow hot air on the target component, melting the solder. Once the solder has melted, the component is removed using regular tweezers or positioner. You will still have some solder on the pads, which is then removed by the vacuum pump type de-soldering system. Fig. 5 shows such a rework station.
There are normally two controls in such systems—the temperature control and air-flow control. You will need different temperatures and air pressure for different SMD joints. Normally, thick joints will need higher-temperature blown air to melt all the solder. The important thing here is that the solder on each pin should melt completely, otherwise it will be impossible to remove the component from the PCB.
The disadvantage of such a system is that the impact is not very targeted and even the neighbouring components are affected. Sometimes, the small components even get blown away in the more dense boards. Though there are different-sized nozzles available, and small nozzles work well in close areas, you may still damage other components if you are not careful.
The specifications for such systems are simple and self-explanatory. Temperature control, power consumption, temperature range and ESD-safe has already been explained in the case of vacuum-pump type rework systems, and those descriptions apply in this case too. As the name suggests, the airflow specification gives you an idea of the system’s capacity to blow air.
Heated tweezers have more targeted heat transfer than hot-air rework stations. They provide a fast, efficient method to solder and de-solder surface mount devices such as chip resistors, chip capacitors, SOTs, flat packs and DIP ICs. They normally have dual-insulated heating elements to ensure rapid heating and recovery. These devices come with a wide variety of interchangeable tips that are available in a range of widths, from 2 mm to 30 mm. Fig. 6 shows a pair of heated tweezers.
All the specifications for heated tweezers are the same as those discussed in relation to vacuum-pump type de-soldering stations.
BGA rework station
All the tools mentioned above will not be able to de-solder a BGA (ball grid array) from the PCB. De-soldering BGAs is much more complicated than other rework operations and requires more sophisticated equipment. The main differences in BGA rework stations are the heating source and mode. Rework stations with upper-heating and both-side heating are the two types available in the market. The both-side heating mechanism is more suitable, if one considers the component’s safety. Some also have a feature to set the temperature curve. The pre-heat function is also useful to prevent the PCB from warping during repairs.
The author is a technical editor at EFY