Influence of Scraper System on PCBA Processing

Introduction

The composition of scraper system is included by printing head (scraper lifting step control device and installation part), scraper beam and drive part (servo motor and synchronous gear drive), etc. The following will discuss the influence of scraper system on PCBA processing:

1. Angle of the scraper:

In the electronic processing production process, the angle of the scraper affects the size of the scraper's vertical force on solder paste. The smaller the angle, the greater the vertical force. By changing the angle of the scraper, the angle of the pressure scraper can be changed. If the angle of the scraper is greater than 80 degrees, the solder paste can only keep moving without rolling. At this time, there is little vertical force and the solder paste will not be pressed into the print template window.The optimum angle of the scraper should be between 45 and 60 degrees, when solder paste has good roll-ability.

2. Speed of the scraper:

The speed of the scraper increases the force on the solder paste.Considering the fact that solder paste is pressed into the window, that is, solder paste is pressed in less time. If the scraper is too fast, solder paste cannot scroll and only slides on the printed template.Because it takes time for solder paste to flow into the window, this is evident when printing fine gap QFP graphics. When the scraper runs along one side of QF, the solder paste graphics perpendicular to the solder plate of the scraper are fuller than the other side. Therefore, some printers have the function of rotating the scraper 45 degrees to ensure uniform and maximum solder paste volume on all sides during fine gap QFP meta printing.Ointment printing is uniform and full in both vertical and horizontal directions. Usually when the speed of the scraper is controlled between 20 and 40 mm/s, the brush works well.

3. The pressure of the scraper:

When solder paste is rolling, a positive pressure, commonly referred to as printing pressure, is applied to the vertical balance of the scraper unit.Insufficient printing pressure can cause the solder paste to scratch dirty. If the printing pressure is too large, it can also cause leakage behind the template and scratches on the surface of the board. Therefore, the pressure of the scraper is usually set at 5~12N/(25mm).The ideal scraper pressure should be to scrape the solder paste exactly off the surface of the board.

4. Width of the scraper:

If the scraper is too wide relative to the PCB, more pressure and solder paste will be required to participate in its work, which will result in waste of solder paste. Generally, the width of the scraper is PCB length (printing direction) plus around 50mm for the best, and to ensure that the scraper head falls on the metal template.

Conclusion

It can be summarized that the scraper presses the stencil to make the it contact with the PCB. Subsequently, the squeegee pushes the solder paste on the template to roll forward, while making the solder paste fill the template opening. When the template is separated from the PCB, the solder paste of appropriate thickness is left on the PCB corresponding to the template pattern. In additional, the scraper is divided into metal scraper and rubber scraper, which are used in different occasions.