Background:

PCB manufacturing has evolved into a highly advanced high-tech industry. The rapid development of silkscreen technology has injected new vitality into the field, bringing significant changes to the electronics industry. It has become an indispensable component of various electronic devices and instruments. Today’s silkscreen technology can meet the high-density requirements of PCB production.

Youtube: https://www.youtube.com/watch?v=mwy9Kigv9Mg

Materials:

• 1) Stencil:

The stencil is a critical component in the silkscreen process as it controls the flow and thickness of the ink, ensuring the durability of the silkscreen print. The interaction between the stencil and photosensitive materials is also crucial for producing high-quality, high-precision prints. To achieve this, stencils undergo coarse treatment and degreasing to ensure good adhesion and extend their lifespan.

• 2) Light-sensitive Materials:

The most commonly used light-sensitive materials are diazo photosensitive agents and photosensitive films. Diazo emulsion is widely applied due to its uniform film thickness, high resolution, wear resistance, and strong adhesion to the screen. This makes it ideal for silkscreen printing of characters on printed circuit boards.

• 3) Stencil Frame:

The material and structural design of the stencil frame are essential. If the stencil frame lacks sufficient strength, it cannot maintain consistent tension, leading to poor quality. High-tension aluminum stencil frames are now commonly used for their strength and reliability.

Silkscreen Printing:

• 1) Silkscreen Printing Process:

The silkscreen process involves several key steps:

• Prepare soldering film negative
• Punch position holes for the film negative
• Surface cleaning
• Configure printing ink
• Print both sides of the PCB
• Preheat the board
• Exposure
• Develop
• Hot-set
• 2) Key Processes in Silkscreen:
• A) Preheating:

Preheating evaporates the solvent in the ink, transforming the soldering film into a non-sticky state. The preheating temperature and duration vary depending on the ink type. If the temperature is too high or the time too long, it can degrade the resolution and hinder development. Conversely, if the time is too short or the temperature too low, the film may stick during exposure, causing the soldering film to degrade during development.

• B) Exposure:

Exposure is the most critical step. Overexposure can lead to image distortion and a reduction in resolution, while underexposure may cause the developed image to become larger, with thicker lines. This can be monitored using a “light energy integrator” to determine the optimal exposure time.

• C) Ink Viscosity Regulation:

The viscosity of the liquid photoresist ink is primarily controlled by the ratio of hardener to the main agent, as well as the amount of diluent added. Insufficient hardener can result in imbalanced ink properties. The viscosity varies over time after mixing:

• Within 30 minutes: The ink is not fully integrated, causing poor flow and potential stencil blockage.
• 30 minutes to 10 hours: The ink achieves optimal flow and consistency for printing.
• After 10 hours: The ink becomes too fluid and harder to print, with reduced gloss.

Excessive thinner can affect the heat resistance and curing properties of the ink. Proper viscosity regulation is essential for quality silkscreen printing.

Conclusion:

The silkscreen printing process is relatively straightforward, yet requires precision. To ensure high-quality prints, operators must follow the established standards carefully to avoid defects that may arise from improper handling.

If you have any questions about PCBs or PCBA, feel free to contact me at info@wellcircuits.com.