Abstract: Soldering is a welding method that uses a low-melting metal solder to heat and melt, and then infiltrates and fills the gap between the metal parts. Because the solder is often a tin-based alloy, hence the name. Commonly used soldering irons are used as heating tools. Widely used in the electronics industry. As a kind of operation technology, tin soldering is mainly mastered through actual training, but following the basic principles, learning the experience accumulated by the predecessors, using the correct method, can master the operation technology with half the effort. So how do you use soldering iron for soldering? The following is a small introduction.
How to use soldering iron for soldering?
Technical points
As a kind of operation technology, tin soldering is mainly mastered through actual training, but following the basic principles, learning the experience accumulated by the predecessors, using the correct method, can master the operation technology with half the effort. The following points are essential for learning welding techniques.
Basic condition weldable range
Not all materials can be joined by soldering. Only a portion of the metal has good solderability (strictly speaking, it can be soldered) to be soldered. Generally, copper and its alloys, gold, silver, zinc, nickel, etc. have good weldability, while aluminum, stainless steel, cast iron and the like have poor weldability, and generally require special flux and method to be soldered.
Solder qualified
Lead-tin solder composition is out of specification or impurities exceeding the standard will affect the quality of solder, especially certain impurities, such as zinc, aluminum, cadmium, etc. Even 0.001% content will significantly affect solder wettability and fluidity, reduce Welding quality. It is obvious that the wise chef can't make delicious food with inferior ingredients.
Suitable flux
Different fluxes should be used for welding different materials. Even if the same material is used, different fluxes are often used when welding processes are different, such as manual soldering iron soldering and dip soldering. Different solders are required for post-weld cleaning and non-cleaning. . For manual soldering, rosin and reactive rosin can meet most of the electronics assembly requirements. It should also be pointed out that the amount of flux must also be noted, too much, too little is not conducive to soldering.
Solder joint design
Reasonable solder joint geometry is critical to ensure the quality of the solder joint. As shown in Figure 1 (a), due to the limited strength of lead solder, it is difficult to ensure sufficient strength of the solder joint, and Figure 1 (b) The joint design has been greatly improved. Figure 2 shows the effect of the through-hole mounting component leads on the printed board on the soldering quality when the hole size is different.
The following points of manual soldering are derived from the soldering mechanism and have proven to be universally applicable.
heating time
Different heating speeds can be used for soldering. For example, the shape of the soldering iron is poor. When soldering large soldering irons with small soldering irons, we have to extend the time to meet the solder temperature requirements. In most cases, prolonging the heating time is detrimental to electronics assembly because
(1) The bonding layer of the solder joint deteriorates the solder joint performance due to heating for a long time exceeding a suitable thickness.
(2) Printed boards, plastics and other materials will be deformed and deteriorated if they are heated too much.
(3) The performance changes or even fails after the components are heated.
(4) The surface of the solder joint is oxidized due to flux volatilization, loss of protection.
Conclusion: The shorter the time, the better the solder wett weldment is guaranteed.
Suitable temperature
If a high temperature soldering iron is used to weld the solder joint in order to shorten the heating time, there is another problem: the solder in the solder wire does not have enough time.
It flows prematurely and volatilizes on the surface to be welded; the melting speed of the solder too fast affects the action of the flux; and the excessive heating time causes the overheating phenomenon due to the excessive temperature.
Conclusion: Keep the tip at a reasonable temperature range. The general rule of thumb is that the tip temperature is 50 °C higher than the solder melting temperature.
The ideal state is to shorten the heating time at a lower temperature, although this is contradictory, in practice we can obtain a satisfactory solution by operating methods.
Tip
The tip of the soldering iron transfers heat to the solder joint mainly by increasing the contact area. It is futile to use a soldering iron to force the solder joint to heat. In many cases, damage to the weldment is caused. For example, potentiometers, switches, and solder joints of the connectors are often fixed on the plastic member, and the result of the afterburning is likely to cause the original to fail.
Operation essentials
1. Weldment surface treatment
The weldments encountered in manual soldering iron welding are a wide variety of electronic components and wires. Unless the electronic components in the "insurance period" are used under the conditions of mass production, the weldments encountered in general need to be surface cleaned. Work to remove rust, oil, dust and other impurities on the welding surface that affect the quality of the weld. Manually used mechanical scraping and alcohol, acetone scrubbing and other simple methods.
2. Pre-welding
Pre-welding is the soldering of the component leads or conductive soldering parts to be soldered, which is also commonly referred to as tin plating, tin-plating, antimony tin, etc. The pre-welding is called accurate, because the process of the process is the whole process of soldering. The solder wets the surface of the weldment, and the surface of the weldment is "plated" with a layer of solder after the diffusion of the metal forms a bonding layer.
Pre-welding is not an indispensable operation for soldering, but it is almost indispensable for manual soldering iron welding, especially for maintenance, commissioning and development.
3. Do not use excessive flux
The right amount of flux is indispensable, but don't think that the more the better. Excessive rosin not only causes the amount of work required to be cleaned around the solder joints, but also prolongs the heating time (rosin melts, volatilizes and takes away heat), reduces work efficiency; and when the heating time is insufficient, it is easy to be mixed into the solder. "Slag inclusion" defect; for soldering of the switching element, excess flux easily flows to the contact, resulting in poor contact.
The proper amount of solder should be that the perfume can only wet the solder joints that will be formed. Do not let the perfume flow through the printed board to the component or socket holes (such as IC sockets). For the wire using the rosin core, it is basically unnecessary to apply flux.
4. Keep the tip clean
Because the soldering iron tip is in a high temperature state for a long time during soldering, and is exposed to a thermally decomposed substance such as flux, the surface thereof is easily oxidized to form a black impurity, and these impurities almost form a heat insulating layer, so that the soldering iron head loses heating. Therefore, it is necessary to remove impurities on the iron frame at any time. It is also a common method to wipe the iron head with a damp cloth or a wet sponge at any time.
5. Heating depends on the solder bridge
In the non-pipeline operation, the shape of the solder joints in one soldering is varied, and it is impossible for us to constantly change the soldering iron head. To improve the efficiency of the tip heating, a solder bridge that generates heat is needed. The so-called solder bridge is to rely on a small amount of solder on the soldering iron as a bridge for heat transfer between the soldering iron tip and the weldment.
Obviously, since the thermal conductivity of the molten metal is much higher than that of the air, the weldment is quickly heated to the soldering temperature.
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