The printing result of solder paste plays an important role in SMT manufacturing. There are many factors that affect the printing quality of solder paste. The composition of solder powder, the composition of solder powder and the ratio of solder powder to flux are the key parameters to determine solder paste melting point, printing ability, weldability and solder joint quality. Generally, tin powder alloy components should reach eutectic or near eutectic as far as possible. The ratio of tin powder to flux is expressed as the percentage by weight of tin powder in the paste. The content of tin powder directly affects the viscosity and printing property of solder paste. Tin powder content is 75~90% in general. The content of tin powder used in no-cleaning solder paste and template printing process is higher, generally 85~90%, while the content of tin powder used in drip coating process is lower, 75~85%.
The size, shape and evenness of tin powder particles are important parameters that affect the properties of solder paste. Small particles of solder paste printing is better, especially for high density, narrow spacing products, because the template opening size is small, must use small particles of alloy powder, otherwise it will affect the printing and touch. The diameter of tin powder particle is about 1/5 of the size of template opening. The solder paste printing pattern of small particle alloy powder has high definition, but it is easy to produce edge collapse. Due to the large surface area of small particle, the degree and opportunity of oxidation are more. Therefore, when the assembly density is not high, a coarser alloy powder can be chosen appropriately without affecting the printability, which can not only improve the weldability, but also reduce the cost of solder paste. The shape of the alloy powder also affects the paste's printability, desorption and weldability. The solder paste composed of spherical particle alloy powder has low viscosity, easy to collapse after printing, good printability, wide application range, especially suitable for high-density narrow spacing screen and metal template printing, and also suitable for drop coating process. Spherical particles have small surface area, low oxygen content and bright welding spot, which is beneficial to improve welding quality. Therefore, spherical particles are generally used at present.
Solder paste is a thixotropic fluid, which can produce flow under the action of external forces. Viscosity is the main characteristic index of solder paste, it is an important factor affecting the printing performance: the viscosity is too big, solder paste is not easy to go out of the template hole, the printed graphics are incomplete, the main factors affecting the paste viscosity: percentage of tin powder: high alloy content, high viscosity; A high percentage of flux means a low viscosity.
TRUNNANO (aka. Luoyang Tongrun Nano Technology Co. Ltd.) is a trusted global chemical material supplier & manufacturer with over 12 years experience in providing super high quality chemicals and Nano materials. The Tin Powder produced by our company has high quality. Lower, please contact us if necessary.
