There are more than 40 kinds of metal welding methods, which are mainly divided into three categories: welding, pressure welding and brazing.
Fusion welding is in the welding process of the workpiece interface heating to the melting state, no pressure to complete the welding method. When welding, the heat source will rapidly heat the interface between the two workpieces to be welded, forming a molten pool. The molten pool moves forward with the heat source, forming a continuous weld after cooling and connecting the two workpieces into one.
In the welding process, if the atmosphere and the high temperature pool direct contact, atmospheric oxygen will oxidize metal and various alloy elements. Nitrogen and water vapor in the atmosphere will enter the molten pool and form defects such as pores, slag inclusion and cracks in the welding seam during the subsequent cooling process, worsening the quality and performance of the welding seam.
In order to improve welding quality, various protection methods have been developed. For example, gas shielded arc welding is to use argon, carbon dioxide and other gases isolated from the atmosphere, to protect welding arc and pool rate; For example, when steel is welded, titanium iron powder with high affinity for oxygen is added to the electrode coating to deoxidize, which can protect the beneficial elements such as manganese and silicon in the electrode from oxidation and enter the molten pool to obtain high quality welding seam after cooling.
Pressure welding is under pressure conditions, so that the two workpiece in the solid state of atomic bonding, also known as solid welding. The commonly used pressure welding process is resistance butt welding, when the current through the connection of the two workpiece end, where the temperature rises because of high resistance, when heated to the plastic state, under the action of the axial pressure into one.
The common feature of various pressure welding methods is that pressure is applied during welding without filling material. Most pressure welding methods, such as diffusion welding, high-frequency welding, cold pressure welding, etc., have no melting process, so there is no good alloy elements like welding, and harmful elements into the welding seam, which simplifies the welding process and improves the welding safety and health conditions. At the same time, the heating temperature is lower than that of fusion welding, and the heating time is shorter, so the heat affected zone is smaller. Many difficult to use fusion welding materials, often pressure welding can be welded into the same strength as the base of quality joints.
Brazing is a method of using metal material lower than the melting point of workpiece as solder, heating the workpiece and solder to the temperature higher than the melting point of solder, lower than the melting point of workpiece, wetting the workpiece with liquid solder, filling the interface gap and realizing mutual diffusion between atoms with the workpiece, so as to realize the welding method.
The joints formed during welding to join two jointed bodies are called welds. During welding, both sides of the weld will be affected by welding heat, and the microstructure and properties will change. This area is called heat affected area. Due to the differences of workpiece materials, welding materials, welding current, etc., the phenomenon of overheating, embrittlement, quenching or softening may occur in the welding seam and heat affected zone after welding, which will also reduce the performance of the welding parts and worsen the weldability. Therefore, it is necessary to adjust the welding conditions. Preheat the welding joints before welding, heat preservation during welding and heat treatment after welding can improve the welding quality of welding parts.
Three major causes of circuit board welding defects
Effect of weldability of plate hole on welding quality
Weldability is that the metal surface is wetted by molten solder, that is, the solder on the metal surface to form a continuous, relatively uniform, smooth adhesion film. Circuit board hole weldability is not good, will cause virtual welding defects, affecting the parameters of components in the circuit. Unstable multi-layer board components and inner wire conduction, serious will lead to the function failure of the entire circuit.