Although it is easier to control when soldering on a circuit board with a large layout size, if the size of the circuit board is too large, the printed lines will become longer, the impedance will also increase, the noise immunity will decrease, and the cost of the board will increase; The size is too small and the heat will dissipate. The ability is reduced, the welding process is not easy to control, and the adjacent lines interfere with each other. Therefore, the design of the printed circuit board must be optimized:

(1) Try to shorten the connection between high-frequency components and reduce electromagnetic interference.

(2) Heavy parts over 20g should be fixed with brackets before welding.

(3) The heating element should consider the problem of heat dissipation to prevent defects caused by high surface temperature of the element, and the thermal element should be kept away from the heat source as far as possible.

(4) In order to make the circuit board beautiful and easy to solder, the components should be arranged in parallel as much as possible, which is also conducive to mass production. The optimal ratio for the board design should be a 4:3 rectangle. Line widths should be as balanced as possible to prevent routing discontinuities. Large areas of copper foil should be avoided to prevent the board from expanding and falling off when heated for a long time.

Fusion welding is a method in which the workpiece interface 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 interface between the two workpieces to be welded, forming a molten pool. The molten pool moves forward with the heat source and cools to form a continuous weld that connects 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 the metal and various alloying elements. Nitrogen, water vapor, etc. in the atmosphere enter the molten pool, and in the subsequent cooling process, defects such as pores, slag inclusions, and cracks will be formed in the weld, which will deteriorate the quality and performance of the weld.

To improve welding quality, various protection methods have been developed. For example, gas shielded arc welding is to isolate the atmosphere with argon, carbon dioxide and other gases to protect the arc and molten pool rate during the welding process; for example, when welding steel, titanium iron powder with high affinity for oxygen is added to the electrode coating. deoxygenation. It can protect the manganese, silicon and other elements in the good man electrode from oxidizing and entering the molten pool, and obtain high-quality welding seam after cooling.

Pressure welding is to make two workpieces in a solid state under pressure to achieve atomic bonding, also known as solid state welding. A common pressure welding process is resistance butt welding. When the current passes through the connection end of the two workpieces, the temperature there rises due to the high resistance. When heated to a plastic state, the connection becomes one under the action of axial pressure.

A common feature of various pressure welding methods is the application of pressure during welding without the need for filler material. Most pressure welding methods, such as diffusion welding, high frequency welding, cold pressure welding, etc., do not have a melting process, so there is no burning of beneficial alloying elements like fusion welding, and there is no problem of intrusion of harmful elements. welding, thus simplifying the welding process. Improve welding safety and hygiene. At the same time, since the heating temperature is lower than that of fusion welding, the heating time is short and the heat affected zone is small. Many materials that are difficult to weld by fusion welding can often be welded into high-quality joints with the same strength as the base metal by pressure welding.

Brazing is to use a metal material with a melting point lower than the workpiece as the solder, heat the workpiece and the solder to a temperature higher than the melting point of the solder but lower than the melting point of the workpiece, use liquid solder to wet the workpiece, fill the interface gap, and realize the connection with the workpiece. A method for realizing atomic interdiffusion welding.

The seam formed during the welding process that connects two connectors is called a weld. Both sides of the weld are exposed to welding heat during welding, and the structure and properties will change. This area is called the heat affected zone. During the welding process, due to different workpiece materials, welding materials, welding current, etc., the weld and heat affected zone after welding may be overheated, embrittled, hardened or softened, which will also reduce the performance of the weldment and make the weldability worse. This requires adjustment of welding conditions. Preheating the interface of the weldment before welding, heat preservation during welding and post-weld heat treatment can improve the welding quality of the weldment.

Solderability means that the metal surface is wetted by molten solder, that is, the metal surface where the solder is located forms a continuous, relatively uniform and smooth adhesion film. The solderability of the circuit board holes is not good, which will cause virtual welding defects and affect the parameters of the components in the circuit. Unstable multi-layer board components and inner conductors conduct electricity, which will lead to the failure of the entire circuit function in severe cases.

(1) The composition of the welding material and the properties of the material to be welded. As an important part of the welding chemical treatment process, the welding material contains chemical materials with flux. Generally, the low melting point eutectic metal is Sn-Pb or Sn-Pb-Ag, and the impurity content cannot exceed a certain proportion to prevent impurities from oxidizing materials. and dissolved by the flux. Flux generally uses white rosin and isopropyl alcohol solvent to remove rust on the surface of the circuit board through heat transfer, helping the solder to better wet the surface of the circuit board to be soldered.

(2) The solderability of the circuit board is also affected by the soldering temperature and the surface cleanliness of the metal plate. Excessive temperature will accelerate the diffusion of the solder, increase the activity of the solder, cause rapid oxidation of the circuit board and the molten surface of the solder, and cause welding defects; the contaminated surface of the circuit board will also affect the solderability of the circuit board, resulting in tin beads, tin Ball, open circuit, poor gloss and other defects.