Solder Paste Printing Technology and Process Parameter Setting (4)

4 scraper and metal formwork

Squeegee shapes are flat type, diamond type, and sword type. The structure and shape of the squeegee are shown in Figs. 10 and 11. The material of the scraper, the installation angle and the operating speed can be found in the above analysis. It is no longer burdensome here.

In the stencil printing, in order to ensure the printing quality, high requirements are made for the production of metal stencil printing plates. The following are the main points:

a. The frame can not be deformed

b. Uniform and high tension, preferably above 30N/mm2

c. The metal plate must be flat and the surface roughness must be low

d. Plate thickness error within ± 10%

e. The opening must be aligned with the circuit board in the "Electronic Industry Process Standards Collection" provisions, the general dislocation shall not exceed 0.2mm, the fine pitch shall not exceed 0.1mm

f. Open the cutting surface of the steel plate to be vertical, and the middle protruding part can not exceed 15% of the thickness of the metal plate.

g. Opening Size Accuracy ±0.01mm Template Making Methods Laser painting, chemical etching and electroforming are common methods. Table 1 compares the overall performance of some of the production methods.

The following is a brief description of chemical etching. Taking a 0.15mm thick beryllium bronze material as an example, the process flow is as follows:

Original Illustration Design CAD Light Drawing Board Bronze Cleaning Drying Photoresist Double Side Exposure Development Hard Etching Chemical Polishing

During the entire template fabrication process, there are many factors that affect the quality of the etching. Among them, the composition, the ratio, the etching temperature, the etching time, and the etching mode of the etchant are most important. It is generally believed that the addition of a small amount of MgCl2 to the etching agent FeCl3 of the beryllium bronze is better by the spraying method.

The etched bronze stencil has a slight taper at the opening. The smoothness and geometry of the sidewalls of the apertures have a great influence on the etched stencil. Electropolishing is often performed at the openings of fine-pitch devices, and, in order to achieve smaller aperture sizes, Ni 10 μm is necessary for plating. The templates processed by these methods have a good effect.

The thickness of the template is generally selected according to the pitch of the component. Table 2 shows the relationship between the thickness of the steel plate and the distance between the feet.