How Do I Choose the Best Circuit Board Solder?

Circuit board mounting is a process in reflow soldering. Reflow soldering, also called reflow soldering, is a soldering technology developed with the advent of miniaturized electronic products. It is mainly used for soldering various surface-mounted components. The solder for this soldering technique is solder paste. Apply the appropriate amount and appropriate form of solder paste on the pads of the circuit board in advance, and then place the SMT components in the corresponding position; the solder paste has a certain viscosity to fix the components; The board enters the reflow soldering equipment. The conveying system drives the circuit board through each set temperature zone in the equipment, and the solder paste is dried, preheated, melted, wet, and cooled to solder the components to the printed board. The core part of reflow soldering is to use an external heat source to heat, so that the solder melts and flows again and wets to complete the soldering process of the circuit board.

Circuit board mounting

Selecting solder with strong adhesion, the printing accuracy of the solder and the placement accuracy of the components also need to be improved;

The external electrodes of the component need to have good wettability and wet stability. Recommendation: temperature 40 , humidity 70% RH, the service life of incoming components should not exceed 6 months;

Use a small pad width to reduce surface tension on the component end when the solder is melted. In addition, the printing thickness of the solder can be appropriately reduced, such as 100 m;

The setting of welding temperature management conditions is also a factor of component upright. The usual goal is to make the heating uniform, especially before the welding fillet of the two connection ends of the component is formed, the balanced heating must not fluctuate.

1. Establishment of temperature curve

Poor wetting refers to the solder and the pad (copper foil) of the circuit board or the external electrodes of the SMD during the soldering process. After wetting, no mutual reaction layer is formed, resulting in missing soldering or less soldering failure. Most of the reasons are caused by contamination of the surface of the solder joint or adhesion of solder resist, or the formation of a metal compound layer on the surface of the joint.

For example, sulfide on the surface of silver and oxide on the surface of tin can cause poor wetting. In addition, when the residual aluminum, zinc, cadmium, etc. in the solder exceeds 0.005% or more, the degree of activation is reduced due to the hygroscopic effect of the flux, and poor wetting may also occur. Therefore, anti-fouling measures must be taken on the surface of the soldering substrate and components. Select the appropriate solder and set a reasonable soldering temperature curve.

The reflow process is divided into lead-free and leaded. Lead-free devices have very different soldering components. The temperature control, especially the process, requires higher temperature curves than the leaded process. In actual applications, repeated process tests are required to achieve this. Satisfactory effect.