Inexperienced radio amateurs sometimes face the problem of replacing chips on a printed circuit board. Performing a seemingly simple process of dismantling radio components, often there is a detachment of the contact pads or damage to a serviceable element due to overheating of its case. This problem arises due to the need to heat a large number of legs at the same time or remove solder from the contacts one by one, which leads to their breakage.
Therefore, for high-quality dismantling, you need to study well the question of how to solder microcircuits, as well as which soldering iron to choose to remove radio components from the printed circuit board.
Basic ways to dismantle chips
Before you start soldering microcircuits, you need to determine what type of part case is used in a particular case. Despite the wide variety of radio components, there are two main types of mounting microcircuits on a printed circuit board:
- chip legs are inserted inside special holes on the board;
- surface mounting provides for the presence of contact pads on the board, to which the legs of the radio component are soldered.
There are several soldering tools that can effectively simplify the chip removal process:
- warming up the junction of the contact pad with the leg of the radio component with one soldering iron;
- dismantling the chip using a metal braid of a coaxial cable;
- use of a special suction that helps remove solder from the place of soldering;
- use of a medical needle for dismantling;
- soldering the chip using metal heat-conducting plates;
- use of special compositions with a lower melting point (Rose or Wood alloy).
The choice of dismantling method largely depends on the knowledge of the technical characteristics of the microcircuit (heating temperature, case type), as well as on the practical skills of the radio amateur.
Dismantling with one soldering iron
Unsoldering a chip with a conventional soldering iron is considered a difficult task. An experienced radio amateur can perform such work without damaging the contacts of the printed circuit board and a serviceable part.
The essence of the method is to alternately remove the molten solder from the legs of the microcircuit. At the same time, it is important that the tip of the soldering iron is wetted with liquid rosin (flux) each time, and after that the solder residues are removed by wiping on a damp rag.
Completion of chip removal is performed after solder removal. To do this, the part is hooked from the side of the board and separated, after a slight warm-up of the contactsites. The force should be negligible so as not to damage the contact tracks.
Copper Braid Application
Before soldering microcircuits in this way, it is necessary to perform several preparatory operations. To do this, carefully remove the shielding braid from a small piece of coaxial cable.
Next you need:
- clean and tin the soldering iron tip;
- moisten a piece of copper screen with flux;
- attach the braid to the contacts of the microcircuit;
- heat the protective screen with a soldering iron, while the solder will impregnate the braid and release the legs of the radio component.
The braid is a good heat dissipation element, which reduces the possibility of overheating of the soldering place. In the distribution network, you can purchase a ready-made braid impregnated with rosin. But due to the considerable cost and high consumption of material, for one-time work it is preferable to make it yourself.
Using a special suction
Vacuum suction greatly simplifies the process of dismantling microcircuits, and is also a very useful tool for soldering radio components, effectively removing excess solder from the junction.
Industrial suction consists of the following elements:
- housing with vacuum flask;
- heat resistant spout;
- working piston;
- reverse spring.
Beforeto solder the microcircuit, the suction must be brought into working position. To do this, press the piston and fix it with a locking device.
Dismantling technology is as follows:
- Heat the soldering iron to the optimum temperature.
- Melt the solder on the contact of the radio component.
- Press the suction nozzle to the junction.
- Press the release button. In this case, a vacuum is created inside the flask due to the movement of the piston, and the molten tin is sucked into the device.
When doing a lot of work, the suction needs to be cleaned periodically.
To perform one-time work, suction can be done independently. To do this, it is necessary to remove the piston from a simple medical syringe and insert a spring for a return movement. A metal tube of a suitable diameter must be put on the spout of the device. The device is ready.
Dismantling the chip with a needle
Often, radio amateurs use a needle from a medical syringe to solder microcircuits. The diameter of the needle is selected so that it is inserted into the hole on the board, and the leg of the part goes inside it. Having picked up such a needle, you need to grind off an oblique cut of the tip with a needle file to a right angle.
Putting the needle on the leg of the microcircuit, it is necessary to heat the contact point on the board with a soldering iron. Then, while the solder is in a molten state, rotate the needle with gentle movements and sink it into the hole. As a result of such actions, the leg of the part isisolated from the board. Next, the same operation is performed with the remaining legs of the microcircuit.
Also, special factory tools can be used to clean the contacts.
Soldering microcircuits with a plate
The presence of several legs on the microcircuit complicates the process of simultaneously desoldering them from the board. Therefore, radio amateurs often use special metal heat-conducting nozzles to heat several contacts at once.
The process of such dismantling looks simple. A special plate or a simple razor blade is applied simultaneously to several contacts. The blade is then heated to the melting temperature of the solder. Since the heating area is increased, you need to use a 40 W soldering iron.
During the heating of the heat-conducting plate, it is recommended to swing the microcircuit a little to simplify the process of releasing the legs from the solder. After removing one row of contacts, the plate is transferred to another row of legs and a similar operation is performed until the part is completely free from the board.
Using special alloys for dismantling
The distinguishing feature of Rose or Wood alloys is their low melting point. So, the Rose alloy has a melting point almost two times lower than tin, about 100 ℃. This property of the material allows it to be effectively used in the process of desoldering small radio components and microcircuits.
The soldering technology consists in applying alloy granules tocontacts, after which this zone is heated with a soldering iron. Thanks to the alloy, the solder melts evenly at low temperatures. It remains only to carefully pry the part with tweezers.
Wood's alloy has an even lower melting point (65-72 ℃), but it contains toxic cadmium, which significantly limits its use in the home.
It is worth noting that a beginner radio amateur, before proceeding with the dismantling of microcircuits, needs to figure out which soldering iron to choose for radio components. This will allow you to complete the task much better and more efficiently.
Design of soldering irons
A soldering iron for continuous operation should be light in weight, as a heavy device quickly loads the hand of a radio amateur, due to which its movements become inaccurate.
Structurally, the soldering iron consists of the following elements:
- The handle of the device can be plastic or wooden. Plastic handles can heat up significantly, so they are used in low-power soldering irons. Powerful devices are most often equipped with wooden holders.
- The heating element made of nichrome consists of mica, on top of which a spiral is wound. If the wire burns out, then it is very difficult to replace it yourself. A soldering iron with a ceramic heater does not have this drawback, but is a very fragile device. If you avoid dropping the tool, the ceramic will last a very long time.
- The soldering iron tip is the main working surface. The sting is usually made of copper. If the sting burns, produceits cleaning with a file with a fine notch. There are soldering irons with replaceable nozzles.
Classification of soldering irons by power
The power of the soldering iron is its main characteristic, which significantly affects the quality of the work. The heating temperature of the soldering tip directly depends on the value of this parameter.
By power, soldering irons can be divided into the following groups:
- Soldering irons up to 10 W are used to work with thin conductors and small radio components.
- Soldering parts on printed circuit boards is best done with soldering irons with a power of 15-30 W.
- 40-60W soldering irons are most commonly used for home use.
- Electrical wires of large cross section are connected by devices with a power of 80-100 watts.
- 200W soldering irons are designed for soldering metal structures using soldering acid.
There are several ways to solder microcircuits from a printed circuit board, which have their own advantages and disadvantages. Which method to apply in a particular situation should be decided by the radio amateur himself, based on his experience and the technical capabilities of the equipment.
