What Plays the Key Roles in Solder Paste Use?


Published by Pinsheng Electronics Co., Ltd April 29,2022

Solder Paste Printing is the first process of SMT Assembly. If not handled well, the next processes will get adversely affected. 

So what play the key roles in solder paste use?

1. Quality of the solder paste

Solder paste is a pulp mixed by alloy powder with flux. In solder paste use, good quality is required, in which several factors affect the viscosity of the solder paste: the amount of alloy powder, the size of the particles, the temperature, the pressure of the doctor blade, the shear rate, the flux activity, and the like. If the quality of the solder paste is not good, the SMT assembly is not well achieved.

solder paste's quality affect assembly

2. Store of the solder paste

The storage in solder paste use is also very important. If the solder paste needs to be cycle-used, it must pay attention to the temperature and humidity issues, which might affect the solder joint quality. The high temperature will reduce the viscosity of the solder paste, and too much humidity may cause deterioration. In addition, the recovered solder paste and the new solder paste should be stored separately and used separately if allowed.

3. Stencil in solder paste use

A SMT stencil is a tool that moves solder paste to the pads of a PCB. The quality of the stencil directly affects the solder paste printing quality. Before stencil cutting, the parameters such as the thickness of the stencil and the size of the opening must be confirmed carefully.
The distance between the components on circuit board is about 1.27mm, the components with a pitch over 1.27mm require a stencil of 0.2mm thick, and for the narrow pitch, it should be 0.15-0.10mm thick. Components layout determines the thickness of the stencil.

Solder paste printing

4. Equipment in solder paste use

PS Electronics utilizes high-speed machines to print solder paste, these devices have a great impact on solder paste printing quality. Printing machines are mainly divided into manual printing machines, semi-automatic printing machines and fully automatic printing machines, which come in a variety of different features and functions, depending on the needs, different machines are used to achieve optimum quality.

5. Printing methods

The printing methods in solder paste use can be divided into contact type and non-contact type printing. The printing with a gap between the stencil and circuit board is called non-contact printing, in which the gap is adjustable, the general gap is 0-1.27mm. Another method leaves no gap between the stencil and circuit board, which is especially suitable for fine pitch printing.

6. The speed in solder paste use

The high speed of the blade is good for the rebound of the stencil, but also hinders the transfer of the solder paste to the printed circuit board pad. While a slow speed will cause the poor resolution of the solder paste printed on the pad. On the other hand, the speed of the blade has a great relationship with the viscosity of the solder paste, the faster the blade speed, the smaller the viscosity of the solder paste.

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