Wear anti-static clothing and anti-static shoes when assembling parts
1. Soldering classification
(1) Fusion welding. Fusion welding refers to the welding method in which both the base metal and the solder are melted during the welding process. Common welding methods include plasma welding, electron beam welding, and gas welding.
(2) Brazing. The way in which the base metal does not melt during the welding process and the solder melts is called brazing. Brazing is divided into soldering and brazing. Soldering is a solder melting point of less than 450 ° C ~, brazing is a solder melting point of more than 450 ° C welding.
Pressure welding. Pressure welding is divided into heating and non-heating two ways anti-static shoes, anti-static clothing, such as cold pressure welding, ultrasonic welding, etc. are not heating. The heating method can be divided into two types, one is heating to plasticity, and the other is heating to local melting. In the manufacturing process of electronic products, the most common and representative form of soldering is soldering, which is an important soldering method. Soldering can achieve electrical connection, allowing two metal parts to be electrically connected. Soldering can also achieve mechanical connection of the parts and combine and fix the two metal parts. Common soldering methods include manual soldering, manual hot air welding, dip soldering, wave soldering and reflow soldering.
2. Soldering characteristics
The soldering method is simple and requires only simple tools (such as electric soldering iron) to complete the welding, solder joint repair, component replacement, re-welding and other processes. Specifically, the soldering process is to heat, let the solder melt, flow, and infiltrate the antistatic shoes on the soldering surface, and prevent the solder from penetrating into the surface of the copper base material (wire, pad), and A brittle alloy layer is formed on the contact faces of the two. In addition to some alloy materials containing a large amount of elements such as chromium and aluminum, it is not suitable to use soldering, and most other metal materials can be soldered.
Pick up. In addition, soldering has the advantages of low cost and easy automation. In electronic engineering technology, it is the welding method that uses the earliest and most extensive anti-static shoes and anti-static clothing. The main features of soldering are as follows.
The melting point of the solder is lower than the weldment.
When soldering, the solder and the weldment are heated together to the soldering temperature, the solder melts and the weldment does not melt.
The formation of the weld relies on the molten state of the solder to wet the weld surface, and the capillary acts to cause the solder to enter the gap of the weldment to form an alloy layer, thereby achieving the weldment joint.
3. The principle of soldering
Soldering is a typical brazing process in which the weldment and the solder having a lower melting point than the weldment are heated together to the soldering temperature. When the weldment is not melted, the solder melts and wets the soldered surface, relying on the atomic Diffusion forms the connection of the weldment. The physical basis of welding is
"Infiltration", infiltration is also called "wetting." If there is a dirt or oxide layer that blocks the wetting on the soldering surface, an alloy layer of two kinds of metal materials cannot be formed, or the solder is not sufficiently melted so that the solder is not sufficiently wetted. For soldering, it must be available
The conditions are as follows.
Weldments must have good weldability. Solderability refers to the properties of an alloy that is well bonded to solder by a soldered metal material at an appropriate temperature. Some metals have better solderability, such as copper and brass. In addition, due to the high temperature during welding, it is easy to make gold.
An oxide film is formed on the surface to affect the solderability of the material. In order to improve solderability, tin plating and silver plating are often applied to the surface of the material to prevent oxidation of the surface of the material.
The weldment surface must be kept clean. In order to achieve a good bond between the solder and the weldment, the weld surface must be kept clean. Even weldments with good weldability may have an oxide film that is harmful to infiltration on the surface of the weldment due to storage or contamination.
Oil stains. Always remove the dirt before welding, otherwise the welding quality cannot be guaranteed.
(3) Use a suitable flux. The role of the flux is to remove the oxide film from the surface of the weldment. Different soldering processes should choose different fluxes, such as nickel-chromium alloy, stainless steel, aluminum, etc. It is difficult to implement soldering without special special flux.
In the soldering of printed circuit boards, in order to make the soldering reliable and stable, a rosin-based flux is usually used.
The weldment should be heated to the proper temperature. When soldering, the role of thermal energy is to melt the solder and heat the soldered object so that the solder penetrates into the crystal lattice of the surface of the soldered metal to form an alloy. The soldering temperature is too low, which is detrimental to the penetration of solder atoms, and it is impossible to form an alloy.
It is easy to form a virtual solder; if the soldering temperature is too high, the solder will be in a non-eutectic state, accelerating the decomposition and volatilization speed of the solder, deteriorating the solder quality, and causing the pads on the printed circuit board to fall off in severe cases.
Suitable welding time. The welding time refers to the time required for the entire welding process, including the time when the soldered metal reaches the soldering temperature, the melting time of the solder, the flux functioning, and the time to form the metal alloy. When the welding temperature is determined
After that, the appropriate welding time should be determined according to the shape, nature, and characteristics of the welded part. The welding time is too long, which is easy to damage the components or the welding parts; if it is too short, the welding requirements are not met. Generally, each solder joint is soldered once for a maximum of 5 seconds.
4 solder joint quality requirements
Welding is the primary means of physically achieving electrical connections. Solder joints are made by an alloy layer formed by a soldering process. The alloy layer must be strong and reliable. If the solder is only piled on the surface of the weldment or only a small part of the alloy layer is formed,
In the initial test and work, there will be no problem with the solder joints, but as the conditions change and the time goes by, the contact layer gradually oxidizes, and the circuit may be interrupted or not working at all times. The appearance of the solder joints is still connected as originally.
This is the most headache in the work of electronic products, and it is also a problem that must be paid seriously in product manufacturing.