​In electronic manufacturing, it is inevitable to encounter welding of circuits and components. The quality of welding has a great influence on the quality of manufacturing. Therefore, to learn electronic production technology, we must master welding technology.
Pre-soldering process
Before welding, welding should be carried out on the welding parts of pin or circuit board of components. There are generally three steps: "scratch", "plating" and "measurement".
1, scratch
"Scratch" is to do a good job of cleaning the welding site before welding. The tools commonly used are knives and fine sand paper, which clean the pins and printed circuit boards of integrated circuits, but keep the pins clean.
For homemade printed circuit boards, the surface of the copper foil should first be polished with fine sandpaper, and the dirt on the printed circuit board should be cleaned, and then coated with Rosin alcohol solution, flux or "HP-1" before use. For gold and silver plated alloy leads, the coating can not be scratched off, rubber can be used to wipe off the surface stolen goods.
2, plating
"Plating" is tin plating on a shaved component. The specific method is to apply a Rosin alcohol solution to the welded part of the scraped component, press the hot iron head with tin on it, and turn the component to evenly coat it with a very thin tin layer. If the wire is multi-strand wire, should be screwed together after light, and then tinned.
A small amount of flux shall be applied immediately to the lead line of the "scraped" component, and then a very thin tin layer shall be plated on the lead line with a soldering iron to avoid reoxidation of the surface to improve the weldability of the component.
3, measurement
"Test" is to use a multimeter to detect the quality and reliability of all tin-plated components after "plating". If there are unreliable or damaged components, the same specification components should be used for replacement.
Welding technology
After the welding is done, it can be formally welded.
1, welding method
Different welding objects require different operating temperatures for electric iron. When judging the temperature of the iron head, the electric iron can be touched with Rosin. If the iron touches Rosin, there is a "squeaky" sound, indicating that the temperature is suitable; If there is no sound, only the Rosin can be barely melted, which means that the temperature is low; If the head of the iron hits a large amount of smoke when it hits Rosin, it means that the temperature is too high.
In general, there are three main steps for welding:
First melt a small amount of solder and Rosin on the iron head, and align the solder head with Hanxisi at the same time.
When the flux on the soldering iron head has not yet evaporated, the soldering iron head and Hanxisi will contact the soldering spot at the same time and begin to melt the soldering tin.
When the solder infiltrates the entire solder point, remove the solder head and Hanxisi or remove the tin wire first. After the solder point is full and beautiful, leave the solder head and Hanxisi.
The welding process is generally 2 to 3s. When welding integrated circuits, the amount of solder and flux should be strictly controlled. In order to avoid the damage of integrated circuits due to poor insulation of electric soldering iron or internal heat generator induction voltage to the outer shell, the method of hot welding of power plug of electric soldering iron is often used in practical applications.
2, welding quality
When soldering, ensure that each solder joint is firmly welded and in good contact. The tin spot should be bright, sleek and hairless, with moderate tin content. Tin and welds are fused firmly and should not be degenerated or malleable.
Virtual welding means that only a small amount of tin is soldered at the solder point, resulting in poor contact and time breaking. False welding means that the surface seems to be welded, but it is not actually soldered. Sometimes with a hand drawn, the lead can be pulled out of the solder.
3, welding materials
For materials that are not easily welded, the method of plating and welding should be used. For example, for aluminum parts that are not easily welded, the surface can be coated with copper or silver before welding. In particular, some CuSO4(copper sulfate) or AgNO3(silver nitrate) are first added with water to form a solution with a concentration of about 20 %.
The cotton ball absorbed by the above solution is placed on the aluminum piece polished with fine sand paper, and the aluminum piece can also be directly immersed in the solution. Due to the replacement reaction of copper ions or silver ions in the solution with aluminum, about 20 minutes later, a thin layer of metal copper or silver will be precipitated on the surface of the aluminum piece.
Use a sponge to suck the solution off the aluminum and bake under the light until the surface is completely dry. After completing the above work, the alcohol solution with Rosin on it can be soldered directly.
Note that this method also applies to iron and certain alloys that are not easily welded. After use, the solution should be covered and stored in a cool place. When the concentration of the solution decreases as the number of times of use increases, it should be reformulated. The solution is corrosive and should be avoided from contact with skin or other articles.

Mechanical maintenance：
Selection of electric iron
There are many kinds and specifications of electric iron, and the size of the welded workpiece is different. Therefore, the reasonable selection of the power and type of electric iron has a direct relationship with the improvement of welding quality and efficiency.
(1) When welding integrated circuits, transistors, and heat-sensitive components, 20W internal heat or 25W external heat iron shall be used.
(2) When welding wires and coaxial cables, use 45W ~ 75W external hot iron, or 50W internal hot iron.
(3) When welding larger components, such as the lead pin of the output Transformer, the lead pin of the large electrolytic capacitor, and the metal chassis ground solder, etc., electric iron above 100W should be used.
Electric soldering iron is better with adjustable Hengwen soldering iron; When you do not use a soldering iron, you must keep a certain amount of tin on the soldering iron mouth. You must not keep the soldering iron mouth on the sponge and store it on the soldering iron frame. The sponge needs to maintain a certain amount of water, so that the sponge is moist all day; When you pick up the soldering iron to start use, you need to clean the soldering iron mouth, but you do not need to bring the soldering iron mouth to the sponge to clean during use. You only need to place the tin on the soldering iron mouth into the tin hard paper box so that the temperature of the soldering iron mouth will not be maintained. Sudden drop, If there is still difficulty in extraction of tin on the IC, and some tin is added(because the tin wire contains a helping flux), it is easy to extract more tin; The temperature of soldering iron is normal between 340 and 380 degrees. If some sensitive components can only accept welding temperatures of 240 to 280 degrees; The soldering iron is black and can not be handled with a metal device such as a blade. Instead, it must be solved with Rosin or tin wire. After each day, clean first, add the tin, and then cut off the power immediately.

Dongguan Shuangmao Electronics Technology Co. Ltd. is a professional development, production and sales of high-performance thermothermal welding platforms. High-frequency high-power welding platforms, hot-wind drawing welding platforms, iron heads, iron frames, electronic connectors, switching power supplies, power adapters, soldering materials Electronic Technology Co., Ltd.: brand-SMT Shuangmao, SUOBA Speedmaster, ZLONG Intelligence

​