There are several reasons to use SS:

• The SS marking helps the PCB assembly personnel during the Assembly Testing and Repair process to recognize:
  • Components.
  • Component orientation.
  • Board Name, Revision, Part Number etc.
  • Process type Like RoHS or SnPb.
• The SS may help authorities to recognize:
  • Registration number.
  • Standards.
  • Company name.
  • RoHS compliance.
• The SS will also help maintenance and field installation personnel to recognize:
  • Key Components.
  • Board Name, Revision, Part Number
  • Hazard marking, like High voltage.
  • Marking like dip switch, voltage, function, wave form.

Although SS is helpful, some dense boards do not allow all components to be marked. In this case we recommend marking only key components. If you are a designer, and your normal board is dense by definition, you may want to consider building your part library in such a way, that you will not need to remove / shrink the marking – it will come from the library without it.

And the board will look like this (SS marked in green)..

Versus

In the last picture there is much more information on the board. But, as not all the information (Reference Designator) exists, the user must use a layout file PDF, thus most of the advantage of having SS become disadvantage (can you say where is R242 or R241?).

Some of the important locations to apply SS:

1. Polarity marker for capacitors, diodes, LED IC's.
2. Major components on the board (IC's and others large parts).
3. PCB marking.

How and when to add the SS

The SS is added automatically by the different CAD tools. Normally, after the design is finished, the last stage is to relocate (or remove) the SS marking.

Some special marking you may consider adding:

• RoHS status
• Company name, Web Site or Logo
• Dip Switch explanation
• Voltage or Signal Name at special point 
• Connector Name
• Screw positing (to make assembly inspection easier )
• Label(s) position for S/N and Barcode
• PCB Manufacturer Date Code 
• Other markings

SS and Manufacturing

• SS will sometimes be used as solder barrier, in order to reduce or eliminate the amount of solder shorts.
• Sometimes, SS will be used as background (underneath the component), just in order to better identify missing components. Normally, this technique is used on very low-cost devices.

How should SS look like?

• Line width: 6mil min. (5mil is also possible at additional cost)
• String height: 30mil min. Lower value will make some letters unreadable.
• Distance to copper: 5mil. Anything less will normally be clipped
• Fonts: Use simple clean one

PCB manufacturers have tools for clipping Silk Screen, so it does not go over pads, test points and vias.

What can Valor (Mentor) detect during inspection?

• SS over SMT pad
• SS over PTH (Plated Thru Hole)
• SS over NPTH (Non-Plated Thru Hole)
• SS over FM (Fiducial Mark)
• SS over TP (Test Point)
• Mismatched SS to Reference Designator
• Missing polarity marker
• Distance to the part itself
• Small font
• Line width
• Multiple Reference Designator
• Clearance to route
• Overlapping String

And much more…