The welding process is related to the welding method and other factors. The operation needs to be determined according to the material, brand, chemical composition of the welded workpiece, the structure of the weldment, and the welding performance requirements, and the soldering process is adopted.

     Soldering is a welding method that uses low-melting metal solder to heat and melt, and then penetrates and fills the gap between the metal parts. Because the solder is often a tin-based alloy, hence the name. Soldering iron is commonly used as a heating tool. It is widely used in the electronics industry.

Weldable range

Not all materials can be connected by soldering. Only some metals have good solderability (strictly speaking, they should be solderable) before they can be connected by soldering. Generally, copper and its alloys, gold, silver, zinc, nickel, etc. have good weldability, while aluminum, stainless steel, cast iron, etc. have poor weldability. Generally, special fluxes and methods are required for soldering.
Solder qualified
Substandard lead-tin solder composition or excessive impurities will affect the quality of solder, especially the content of certain impurities, such as zinc, aluminum, cadmium, etc. Even the content of 0.001% will significantly affect the wettability and fluidity of the solder, and reduce Welding quality. No matter how smart a chef is, it is impossible to use inferior raw materials to produce delicious dishes. This is obvious.
Suitable flux
Different fluxes should be used for welding different materials. Even if the same material is used, different fluxes are often used when the welding process is different, such as manual soldering iron soldering and dip soldering, and different fluxes are required for cleaning and non-cleaning after soldering. . For manual soldering, the use of rosin and active rosin can meet the assembly requirements of most electronic products. It should also be noted that the amount of flux must also be paid attention to, too much or too little is not conducive to soldering.
Solder joint design
Reasonable solder joint geometry is very important to ensure the quality of soldering.

heating time
Different heating times can be used when soldering. For example, the shape of the soldering iron tip is poor, and we have to extend the time to meet the requirements of the tin material temperature when soldering large soldering parts with a small soldering iron. In most cases, extending the heating time is harmful to the assembly of electronic products. This is because
(1) The bonding layer of the solder joint is heated for a long time and exceeds the proper thickness, which causes the performance of the solder joint to deteriorate.
(2) Printed boards, plastics and other materials will deform and deteriorate due to excessive heat.
(3) The performance of components changes or even fails after being heated.
(4) The surface of the solder joint loses its protection and oxidizes due to the volatilization of the flux.
Conclusion: The shorter the time, the better under the premise of ensuring that the solder wets the weldment.
Suitable temperature
If in order to shorten the heating time, a high-temperature soldering iron is used to solder the calibration joints, it will bring another problem: the flux in the solder wire does not have enough time
Overflowing on the surface to be welded causes premature volatilization and failure; too fast solder melting speed affects the performance of the flux; because the temperature is too high, although the heating time is short, it will also cause overheating.
Conclusion: Keep the soldering iron tip in a reasonable temperature range. The general experience is that the temperature of the soldering iron tip is 50°C higher than the melting temperature of the solder.
The ideal state is to shorten the heating time at a lower temperature. Although this is contradictory, in actual operation we can obtain a satisfactory solution through operating techniques.
Welding method

Fusion welding is a method in which the joint of the workpiece is heated to a molten state during the welding process, and the welding is completed without pressure. During fusion welding, the heat source rapidly heats and melts the joint of the two workpieces to be welded to form a molten pool. The molten pool moves forward with the heat source and forms a continuous weld after cooling to connect the two workpieces into one.
In the fusion welding process, if the atmosphere is in direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize metals and various alloying elements. Atmospheric nitrogen, water vapor, etc. enter the molten pool, and will also form pores, slag inclusions, cracks and other defects in the weld during the subsequent cooling process, deteriorating the quality and performance of the weld.

1. Surface treatment of weldments
The weldments encountered in manual soldering iron welding are various electronic parts and wires. Unless electronic components within the "warranty period" are used under mass production conditions, the weldments encountered under normal circumstances often require surface cleaning Work to remove rust, oil, dust and other impurities that affect the quality of welding on the welding surface. In manual operation, simple and easy methods such as mechanical scraping, alcohol and acetone scrubbing are commonly used.
2. Pre-soldering
Pre-soldering is to wet the leads of the components to be soldered or the conductive welding parts with solder in advance, which is generally called tin plating, tin plating, tin enamel, etc. It is accurate to call pre-soldering because the process and mechanism are the whole process of soldering-the solder wets the surface of the soldering part, and the bonding layer is formed by the diffusion of the metal, so that the surface of the soldering part is "plated" with a layer of solder.
Pre-soldering is not an indispensable operation for soldering, but it is almost indispensable for manual soldering, especially maintenance, debugging, and research.
3. Do not use excessive flux
The right amount of flux is indispensable, but don't think that more is better. Excessive rosin not only causes the work that needs to be cleaned around the solder joints after soldering, but also prolongs the heating time (the rosin melts, volatilizes and takes away heat), reducing work efficiency; and when the heating time is insufficient, it is easy to be mixed into the solder to form "Slag inclusion" defect; for the welding of switching elements, excessive flux will easily flow to the contacts, resulting in poor contact.
The proper amount of flux should be such that the rosin can only wet the solder joints to be formed, and do not let the rosin to flow into the component surface or socket holes (such as IC sockets) through the printed board. For the welding wire with rosin core, there is basically no need to apply flux.
4. Keep the soldering iron tip clean
Because the soldering iron tip is in a high temperature state for a long time during soldering, and it is exposed to flux and other thermally decomposed substances, its surface is easily oxidized to form a layer of black impurities. These impurities almost form a thermal insulation layer, which makes the soldering iron tip lose its heating effect. Therefore, rub off impurities on the soldering iron stand at any time. Wiping the tip of the soldering iron with a damp cloth or sponge at any time is also a common method.
5. Heating depends on solder bridge
In non-pipeline operations, the shape of the solder joints for a single welding is various, and it is impossible for us to constantly change the soldering iron tip. To improve the heating efficiency of the soldering iron tip, it is necessary to form a solder bridge for heat transfer. The so-called solder bridge is a bridge that relies on a small amount of solder on the soldering iron to transfer heat between the tip of the soldering iron and the weldment during heating.
Obviously, because the thermal conductivity of molten metal is much higher than that of air, the weldment is quickly heated to the welding temperature. It should be noted that the amount of tin retained as a solder bridge should not be too much.
6. The amount of solder should be appropriate
Excessive solder not only consumes the more expensive tin unnecessary, but also increases the soldering time and correspondingly reduces the working speed. What's more serious is that in high-density circuits, excessive tin can easily cause undetectable short circuits.
However, too little solder can not form a firm bond, reducing the strength of the solder joints, especially when soldering wires on the board, insufficient solder often causes the wires to fall off.
7. Weldments must be firm
Do not move or vibrate the weldment before the solder solidifies, especially when using tweezers to clamp the weldment, be sure to wait for the solder to solidify before removing the tweezers. This is because the solidification process of solder is a crystallization process. According to the crystallization theory, external force (movement of the weldment) during crystallization will change the crystallization conditions, resulting in coarse crystals, resulting in the so-called "cold welding". The appearance phenomenon is that the surface is dull and has the shape of bean dregs; the internal structure of the solder joint is loose, and it is easy to have air gaps and cracks, which will reduce the strength of the solder joint and poor electrical conductivity. Therefore, the weldment must be kept still before the solder solidifies. In actual operation, various suitable methods can be used to fix the weldment, or reliable clamping measures can be used.
8. Pay attention to the evacuation of the soldering iron
The soldering iron should be withdrawn in time, and the angle and direction of the withdrawal have a certain relationship with the formation of the solder joint.

Welding point

1. The solder joints must have sufficient mechanical strength to ensure that the welded parts will not fall off or become loose when subjected to vibration or impact. Do not use too much solder to accumulate, which will easily cause false soldering and short-circuit between solder joints and solder joints.

2. Welding is reliable, with good conductivity, and virtual welding must be prevented. Virtual soldering means that the solder and the surface of the welded part do not form an alloy structure. It simply attaches to the surface of the welded metal.

3. The surface of the solder joints should be smooth and clean. The surface of the solder joints should have a good luster. There should be no burrs, voids, no dirt, especially the harmful residues of the flux, and the appropriate solder and flux should be selected.

Aluminum soldering

Aluminum is very easy to oxidize, and the surface is usually covered with a layer of aluminum oxide film. Even if the film is scraped off before welding, due to the high temperature of the soldering iron during welding, an oxide film is quickly formed on the welding surface, which makes the scraped new If the surface is not in contact with air, then the tin can be attached to the aluminum. Two methods of soldering aluminum parts are described below.

1. Polish the welding surface of the aluminum parts with sandpaper, and put some rosin and iron powder. Use a soldering iron with a power of 60W or more, soak a sufficient amount of solder, and rub it hard on the soldering surface. Due to the effect of iron powder, the oxide layer is worn away, and tin adheres to the aluminum surface. While the tin is not solidified, wipe off the iron powder on the soldering surface and the soldering iron with a cloth, and then the soldering can be carried out in the usual way.

2. Apply a layer of mercury nitrate solution on the welding surface of the aluminum wire or aluminum plate to be welded. Due to the chemical effect, a layer of aluminum amalgam is formed on the aluminum surface, which can be welded after washing with water. The tin that has just been soldered is soldered to the aluminum amalgam, and the welding strength is not high. Therefore, a 100W large soldering iron should be used when soldering, and the soldering iron tip mostly stays on the soldering surface to diffuse mercury in the aluminum, and the tin can be firmly welded to the aluminum substrate to strengthen the welding strength.

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