Xiao Hei's eyes were a little confused, and he sighed lightly: "Welding." ”

"Sure enough, it's welding." Fu Xin smiled bitterly in his heart.

Welding, generally by heating two metal objects combined, if the welding process needs to melt the third substance, it is called "brazing", the third substance added to the melting is called "solder".

According to the melting point of the solder, brazing is divided into "hard soldering" and "soldering", usually with 450 °C as the boundary, and those below 450 °C are called "soldering". The so-called "welding" in the installation process of electronic products is a kind of soldering, which mainly uses tin, lead and other low melting point alloys as solder, so it is commonly known as "soldering".

To understand welding, you must first have an understanding of welding tools.

The first is the electric soldering iron, which is responsible for heating the soldered metal in the soldering area, melting the solder, carrying the solder and adjusting the amount of solder in the manual soldering process.

The structure of the electric soldering iron is very simple, and its main structure has five parts: the handle is made of wood or heat-resistant plastic, the hollow cavity can be opened, the cavity has the connection terminal between the heating wire and the power cord, and the power cord is locked by a plastic bolt or clip before being worn out of the rubber sheath at the rear end of the handle, which can withstand a certain tension for safety.

There is a soldering iron body made of iron pipe in front of the handle, the pipe body is close to the front end of the soldering iron core, the soldering iron core is wrapped on the thin iron pipe insulated by mica sheet with thin electric furnace wire in layers, the tail of the soldering iron head extends into the thin iron pipe, the front end of the thin iron pipe is embedded in a combined sleeve, and two screws, one large and one small, are tied horizontally on the sleeve, the small one is shorter, used to fasten the soldering iron core and the pipe body, the larger one is longer, used to bolt the soldering iron head, and the longer screw is to loosen the longer screw when adjusting the working temperature of the soldering iron.

The soldering iron tip is made of copper with a large heat capacity per unit volume and high thermal conductivity.

The working voltage, power and other parameters of the soldering iron are generally marked on the handle for identification when selecting.

The working principle of an electric soldering iron is simply a process of heating, heat transfer and heat dissipation of an electric heater under the action of electric energy: after the power supply is turned on, the power heat generated by the core of the soldering iron is determined by the resistance value of the heating wire at the rated voltage.

The heat is preferentially transferred to the tip to increase its temperature and then dissipated from the surface of the tip to the surrounding environment.

The speed of heat dissipation is directly proportional to the temperature rise of the soldering iron tip, and the greater the temperature difference, the faster the heat dissipation; When a certain temperature is reached, the power of heat dissipation will be equal to the power of heat generation and a dynamic equilibrium will be reached, the heating will stop, and the preheating stage of the electric soldering iron will be completed.

At this time, the temperature of the soldering iron tip is the no-load preheating temperature of the electric soldering iron, which is generally more than 300 degrees Celsius, which exceeds the melting point of the solder by a lot.

The heat of the heating core will also be transferred backwards to the pipe body part, because the pipe body part is made of a certain length of thin-walled steel pipe, the thermal resistance is larger, and some pipe back sections have heat dissipation holes or heat sinks, so that the temperature rise of the handle is not much.

At the no-load preheating temperature, each part of the soldering iron will store a share of heat in the relationship of heat = heat capacity x temperature.

During the soldering operation, when the working surface of the soldering iron tip is in contact with the solder and the workpiece, the original equilibrium relationship is broken, and the heat is immediately transmitted to the soldering work area through the contact part where the thermal resistance is much smaller than that of air, so that the temperature of the solder and the workpiece rises rapidly.

As long as the heat capacity of the soldering iron tip is large enough to be compared to the heat capacity of the workpiece in the soldering area, the soldering process can be completed in a very short time by making the temperature of the solder and the soldering part exceed the melting point of the solder, and the temperature itself drops very little.

The second is the soldering iron tip, the wearing parts of the electric soldering iron are the soldering iron tip and the soldering iron core, the soldering iron heating core is relatively single, as long as the size is the same, the power is the same, and it can be, so I will not introduce much here.

The shape of the soldering iron tip is mainly divided into straight and elbow. The shape of the working end is cone-shaped, spade-shaped, oblique split, special special shape, etc. However, usually on low-power soldering irons, most of them are straight-headed cone-shaped, and elbow-shaped soldering irons are more suitable for soldering irons with more than 75 watts.

The choice of tip shape can be decided according to the object of processing and the individual's habits.

Ordinary electric soldering iron tips are made of pure copper (copper) with a large heat capacity ratio and high thermal conductivity. There is a good affinity between tin and copper, so the molten solder can be easily adsorbed on the soldering iron head and left to be dispatched.

However, copper and tin form copper-tin alloys, which have a melting point much lower than that of pure copper and are partially melted at the operating temperature of the soldering iron.

The speed of its melting is proportional to the temperature, the temperature of each point on the working surface of the soldering iron tip will not be exactly the same, the copper metal consumption is faster in the place where the temperature is high, so that the working surface forms a depression, the concave surface makes the temperature more concentrated, and the speed of local melting is accelerated.

In this vicious circle, a deep pit will appear on the original flat working surface of the soldering iron tip, so that you have to rework and trim and tin. As a result, a soldering iron tip is scrapped in a short time, and the occasional trimming work is also a big problem.

Fu Xin has long known this defect, so he developed a longevity soldering iron head according to the memory of later generations, and it was not only widely used by Huaxing Electronics Factory and Xunyang Electronics Factory, but also combined with Zhongnan Copper Factory in Haicheng to form this technology into products, which are exported to home and abroad, bringing huge profits to Huaxing Industry and Zhongnan Copper Factory.

In order to maintain the adsorption of the soldering iron tip on the solder, a more active flux is used on the outside of the iron, such as Fuxin uses zinc chloride and hot-plated a layer of pure tin.

This problem is solved by the fact that the iron does not react with the tin at the operating temperature of the soldering iron.

When using longevity soldering iron tips, pay attention to protect the plating on its surface, do not sand on sandpaper like ordinary soldering iron tips, file with a file, and if there is something black attached to its tip, you only need to wipe it slightly on a special wet cellulose sponge to reveal the original bright tinned surface.

In addition, when pausing the operation, the tip should be flushed down and placed on the soldering iron holder, so that the tip of the soldering iron is always wrapped in the droplets of the solder, so as not to "burn to death" the soldering iron tip. The ability of long-life soldering iron tips to carry solder is slightly worse than that of ordinary soldering iron tips, but when used with solder wire, it has little effect.

The third is the soldering iron stand, the structure of the soldering iron stand is very simple. However, the area of the work table is limited during mass production, and the work efficiency must be emphasized, and the placement of the soldering iron is not exquisite. At this time, a good soldering iron stand is very important.

The soldering iron frames used by Huaxing Electronics Factory and Xunyang Electronics Factory are also improved by Fu Xin. This kind of small thing, Fu Xin did not have the leisure to design, he copied the later generations of Furant brand soldering iron stand, the base is drop-shaped, and the top is inlaid with a barbed wire mesh at a 45-degree angle.

After talking about soldering tools, the next step is solder.

Solder, also known as brazing filler metal, is the solder used in the soldering process, which is usually an alloy composed of tin (sn) and another low melting point metal, lead (Pb). In order to improve the physical and chemical properties of solder, a small amount of antimony (SB), bismuth (Bi), silver (AS) and other metals are sometimes intentionally added.

Tin-lead solders formulated in different proportions of tin and lead will have different physical properties such as melting point and mechanical strength. The higher the tin content in the tin-lead solder, the stronger its wettability. The higher the lead content, the better the corrosion resistance of the solder joint surface. Eutectic solders should be used as much as possible for manual soldering.

The shape of lead-tin solder can be processed into different shapes such as solder bars, solder strips, solder wires, solder rings, solder sheets, solder balls, etc.

It is also possible to mix a certain particle size of solder powder with flux to make paste solder, that is, the so-called "silver paste" and "solder paste", which is used for the installation and soldering of surface mount components.

Hand soldering is now commonly used with activated rosin flux cores. The diameter of solder wire is divided into more than 10 specifications from ¢.5mm to ¢.0mm.

For general electronic product installation and soldering, a φ0.2mm or less soldering wire is used, and a solder wire of less than ¢.5mm is used for the soldering of tiny components on the mounting circuit board with a high density.

After talking about the specifications of solder, the last one is the last one of the solders, solder paste.

Solder paste, commonly known as silver paste, is a paste made of a mixture of high-purity solder alloy powder, flux and a small amount of printing additives, which can be coated on circuit boards by steel mold or screen printing, and is the key material of modern surface mount technology, that is, SMT.

Now that the solder is figured out, it's time for the actual operation. Of course, in practice, the preparation must be done first, otherwise there will definitely be problems.

Tools such as solder, flux, etc., must be prepared before soldering begins. Trim the working temperature of the soldering iron, so that the working surface of the soldering iron tip is completely kept in the state of eating tin.

Before the first power on of the new soldering iron, the soldering iron tip should be adjusted out about two centimeters, after full preheating test welding, if the temperature is not enough, you can untie the fastening screw and send it back a little inside, test welding, not enough to send it back to the point again, so gradually adjust it up, try a few more times, at the beginning it is better to let it be low, not to let the temperature be too high, otherwise the soldering iron tip will be burned to death.

The so-called "burning" refers to the fact that the tin plating layer on the front end of the soldering iron tip is oxidized off at an excessively high temperature, and a black copper oxide shell layer is formed on the surface.

At this time, the soldering iron tip neither transfers heat nor eats tin, if it is barely pressed on the solder, the solder will suddenly melt after a long time, roll to the side, and never be friendly with the soldering iron tip. With such a soldering iron will not work.

Once the soldering iron tip is burned to death, the surface must be filed off and re-tinned, which is a fatal loss for the longevity of the soldering iron tip.

No matter what level of workers, they must pay full attention to this procedure, when changing a soldering iron, or changing the working environment, the power grid voltage changes, must pay attention to adjust the working temperature of the electric soldering iron: so that it is maintained at about 300 °C.

The practical guideline is: on the premise of not burning the soldering iron tip as much as possible. ―Make sure that the tip of the soldering iron tip is always in a silvery-white state. (To be continued.) )