Topic: Silkscreen Process – Purpose, Equipment, and Common Issues
What is Silkscreen (Legend) Printing?
Silkscreen printing (also called legend printing) is a key step in PCB manufacturing used to print identifiers, marks, and simple circuit patterns on the board surface using ink and mesh screen technology.
It is primarily used for:
Printing product batch numbers, manufacturing dates, logos, symbols, and text
Creating blackout layers or simple traces on one or both sides
Assisting with assembly alignment and debugging by marking components
Main Equipment Used:
Screen Printing Machine (Mesh Printer)
Oven (for thermal curing ink)
UV Dryer (for UV-curable ink)
Screen Making Equipment
Used to create image areas and non-image areas using photoresist
Working Principle:
A pre-fabricated screen contains open areas for text and graphics, while the rest is blocked with photosensitive emulsion.
The PCB is aligned with the screen using positioning pins.
A squeegee presses ink through the open areas of the mesh onto the PCB surface.
After printing, the board enters a drying process:
Thermal ink → oven drying
UV ink → UV curing
Special Use Cases:
Some single-layer boards may require printed conductive traces to simulate dual-layer functionality.
Double-layer PCBs may have printed blackout layers for light shielding or insulation.
These special functions are realized via silkscreen printing using conductive or blocking inks.
Common Issues:
| Problem | Description |
|---|---|
| Missing Print | Ink fails to transfer in certain areas |
| Contamination | Dust or particles affect print clarity |
| Ink Gaps | Incomplete or broken printed lines or characters |
| Ink Bumps | Raised areas due to excess ink or debris under the screen |
| Peeling/Falling Off | Poor adhesion between the ink and the board surface |
Summary:
Silkscreen printing is not just for labeling-it also supports circuit function in special designs. Proper screen preparation, ink selection, alignment, and curing are crucial to ensure high-quality output and avoid downstream defects.
