PCB Mechanics

Mechanical layers are used to define the overall appearance of the PCB. It includes the Shape, Boundary, Slots, Drill holes, Keep-outs, Milled cuts, V-score cuts, Pannelizing info, and the overall structure of the PCB.

Mechanical Layers are usually of 4 basic types

  • Routing layer : These layers are electrical layers, that have track routings on it for interconnections.
  • Drilling : This layer specifies the Drill holes, their placement, sizes and whether PTH or NPTH.
  • Milling : This layer contains information about Milling tool diameter, and the placement or path of milling.
  • V-score : This layer contains information for V-score cuts.

Some problems and common issues that we get from Customer’s and their solutions

  • Copper is very close to the PCB Boundary. Generally, copper is supposed to be “pulled-back” from PCB boundary to a certain gap level, as well as away from routing or milled slots on the PCB. A general rule of thumb is 0.5mm pull-back of copper from Milled slots and PCB Boundaries is a good number but the customer can specify their own. If they do not pull-back the copper from such boundaries, then we have to shave off a little of the copper to ensure there is no exposed copper burr when the process finishes.

  • Sometimes the Gerber data files set does not contain the PCB boundary or Keepout layers. This creates a problem for us since we have all the information to make the PCB but the boundary is missing. Normally, we use the GKO or the GM15 layer for this, but sometimes these are not included OR show conflicting boundary information. Hence, whenever you submit your designs for our review, please do include the GKO or the GM15 layers with PCB boundary information.
  • Some orders require the PCBs to be sent individually, but if they are too small, then we would panelize them and add features on the panel like Tooling holes to do Location and E-Test etc. This pannelized structure is also more convenient for the customer as they can use that panel for component assembly and easily de-panel the individual boards from it.

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  • If you want V-Cut grooves in the PCB panel, then the minimum rule of thumb to follow is keep the copper and component boundaries at least 0.4mm away from the V-cut line. Otherwise the V-scoring blade can damage the copper and features.
  • We generally follow the Gerber files submitted to us for PCB boundary and outline. Usually layers like GKO define that. If you use any other layer for Board shape / boundary (for example: GM1) then please include that in the set of Gerber files, otherwise we will use standard GKO layer Gerber file and thus your PCBs might turn out different from what you perceive.
  • If you are submitting a Panel for fabrication, please make sure the Fiducial marks have a Solder-Mask opening. This is another common issue that we get and thus it becomes hard to determine if they are Fiducial marks or any other intended feature. Standard Fiducial marks have a Solder-mask opening of 3.0mm Diameter. Please place symmetrical Fiducials usually at the extents of the Panel so that the Assembly machines and AOI machines can easily place components and check for defects.

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  • If you are submitting a Panel, do also include Tooling holes, or you can ask us to put tooling holes on the panel for machine handling during the process.

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  • If you are submitting a Panel, you may want to add a unique Part number to the Panel and/or serial numbers on each board in the Panel. You can use any layer for this – example the Top Overlay layer or Bottom Overlay layer. If none specified, then we will put it for you generally on the Solder-Mask layer.

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  • We generally add Process Edge leaders each side on your PCB for ease of processing. These are generally 5mm in width and help in machine processing the PCBs. If you have a different requirement, you can mention that OR add that to your Gerbers before sending to us.

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