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PCB board solder paste formulation design process considerations

From an ideal process point of view, we hope that the pcb board solder paste flux system will maintain the ability to deoxidize and prevent oxidation before the solder melts, and will completely remove the oxide on the surface of the soldered metal when the solder melts. At the same time, it is desirable to have a minimum of active components remaining after soldering to ensure the environmental reliability of the solder joints. However, this ideal requirement is subject to changes in the degree of oxidation of the surface to be welded and the welding time, and it is actually difficult to achieve a state in which “the oxide is removed without the remaining active agent”. To this end, the formulation of the solder paste should be based on the design of a multi-component activator, and a multi-component solvent system is also adopted to ensure that the flux system continues to be active and the amount of residue is minimal.

Solder powder: If the automatic coating process wants to fluidize the solder material, the solder metal pcb board must be made into spherical particles. Solder powder is usually manufactured by a spray method, and the size and shape of the solder powder to be produced must meet certain pcb board requirements. Solder powders for the PCB electronics industry are classified according to their particle size. Since the surface assembly tends to be high-density and miniaturized, the size of the solder powder used is also getting smaller and smaller, and the main consideration is the tin permeation property of printing. The solder powder particle size currently in common use is type 4, which is commonly referred to as powder No. 4.

In order to promote good flow of solder paste during the printing phase, the solder powder particles must be spherical. Spherical particles also mean less oxide on the surface of the solder powder particles.