How does SMT solder paste affect soldering quality?

Solder paste affects soldering quality

How does SMT solder paste affect soldering quality?

Abstract: Solder paste is composed of solder alloy powder and flux, and flux is composed of solvent, film-forming substance, activator, and thixotropic agent. Solder paste is a very important part of the SMT placement process. The size of the metal powder in the solder paste, the ratio of metal content, the ratio of flux components, the time of warming up before use, the stirring time, and the storage environment and storage time of the solder paste will all affect the soldering quality. The following SZTech-SMT will briefly talk about the components of SMT solder paste and what are the effects on soldering quality.

The flux mass ratio and composition of solder paste flux components:

(1) Film-forming substances: 2%~5%, mainly rosin, and derivatives, synthetic materials, the most commonly used is water-white rosin.

(2) Activator: 0.05%~0.5%, the most commonly used activators include dicarboxylic acids, special carboxylic acids, and organic halide salts.

(3) Thixotropic agent: 0.2%~2%, increases viscosity and acts as a suspension. There are many such substances, preferably castor oil, hydrogenated castor oil, ethylene glycol mono butylene, and carboxymethyl cellulose.

(4) Solvent: 3%~7%, multi-component, with different boiling points.

(5) Others: surfactants, coupling agents.

Influence of solder paste flux composition on soldering quality:

Tin bead splash, flux splash, ball book array (BGA) void, bridging, and other poor SMT chip processing and welding have a great relationship with the composition of solder paste. The selection of solder paste should be selected according to the process characteristics of the printed circuit board assembly (PCBA). The proportion of solder powder has a great influence on improvingslump performance and viscosity. The higher the solder powder content, the smaller the slump. Therefore, the solder paste used for fine-pitch components should use 88%~92% more solder powder content of solder paste.

1. The activator determines the solderability or wettability of the solder paste. To achieve good soldering, there must be an appropriate activator in the solder paste, especially in the case of micro-pad soldering, if the activity is insufficient, it may cause grape ball phenomenon and ball-socket defects.

2. Film-forming substances affect the measurability of solder joints and the viscosity and viscosity of solder paste.

3. Flux is mainly used to dissolve activators, film-forming substances, thixotropic agents, etc. The flux in solder paste is generally composed of solvents with different boiling points. The purpose of using high boiling point solvents is to prevent solder and flux from splashing during reflow soldering.

4. Thixotropic agent is used to improving printing performance and process performance.

Summary of solder paste affects soldering quality.

The above content is related to the components of SMT solder paste and the impact on soldering quality shared by the SZTech-SMT processing factory. I hope it will be helpful to you. To learn more about SMT chip processing, welcome to visit

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top