What is the PCB silkscreen?
The silkscreen is a layer of ink printed on the bare circuit board used to identify the electronic components, Rev. no.#,test points, marks, logos, symbols, etc.
Normally it is printed on the components side or on the solder side, but any side is no matter and can be freely defined by PCB designer as long as it will be as a clear identification to reader as it’s purpose.
What colors that PCB silkscreen have?
Normally, the silkscreen color is in White, which is a public color and friendly to manufacturing process. Also, other color such as yellow, red, black is popularly used in initial of PCB board design. Pink silkscreen color is also a favorite color to PCB designer but we do not recommend to use this color due to it’s special characterics with result that unfriendly to manufacturing process.
How it comes out by PCB manufacturing process?
Commonly there are two production ways to get PCB silkscreen:
One method is done by PCB manufacturers via auto ink printing process as below which a little blurry on the edge of the PCB board. Which sometimes have blurry around the edge of the silkcreen letter.
The other is to use laser printing process which can get a better cosmetic quality than traditional ink printing process. Which have perfect cosmetic performance.
Basic notes about PCB silkscreen design
When it comes to PCB layout in silkscreen stage, the design is better to follow this regular ratio that width/height=1:6, which can be sure the silkscreen presented on the complete PCB board at a high resolution performance.
Note that the width of the silkscreen is changing from it’s different base copper thickness listed as in below table:
| Base copper(oz) | Minimum Silkscreen width(mil) | Silkscreen height(mil) |
|---|---|---|
| 0.5 | 4 | 24 |
| 1 | 5 | 30 |
| 2 | 6 | 36 |
6 Key points in PCB silkscreen design
- Place and direction of the components:Commonly, it would be better to mostly place all the components in the same direction instead of different directions, or else which will take extra work to functional test, verification, soldering, etc.
- Dot not place the silkscreen on the through plated holes
- Do not place the silkscreen over on the RF track (Radio Frequency)
- The direction of the silkscreen should be the same as the orientation as the data sheet of the components (For example, IC, diode,Led,etc).This will avoid the misunderstanding to PCB assembly process.
- For multi-pin components, which have sequential no.# of pins, the pin no.# 1,2.3…. should be presented on the silkscreen.
- The silkscreen profile for some special package components (BGA, QFN,etc) should be the same size as it’s component profile.
General guidlines to PCB silkscreen design
- Width: the silkscreen width ≥4mil, (the silkscreen cannot be printed out if the width less than 4mil).
- Spacing: the silkscreen should have 6mil spacing to solder mask opening pad, component soldering holes, test points, fiducial marks, etc. It will be as an anti-solder resistance once the silkscreen overlapped on the SMT PADs
- Do not overlap each other.
- It must be presented as sequential turns (from left to right; from top to bottom)
- Each silkscreen designator should be matched with it’s component accordingly (do not confuse the reader)
- For some polarity or orientation components, the polarity point or the Pin 1 should be clearly and correctly marked.
- Some extra marks or signs can be moved to GM layer(Geometry)
- If the PCB boards have a limited spacing to put the silkscreen, the silkscreen layer can be cancelled in PCB fabrication process, but it must be present by another layer as assembly drawing (Top or bottom layer)
- The bottom silkscreen layer must be viewed in mirror format.