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Atmega32 footprintI have downloaded the footprint for ATmega32 SMD as in the figure my question what is the need for the mechanical layer with purple and green colors in this foot print (and after fabricating the board is this layer will be appear on the pcb)

What do we have mechanical layers and what are they used for?

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  • \$\begingroup\$ Show a picture of that mechanical layer. \$\endgroup\$
    – Andy aka
    Aug 5, 2020 at 13:02
  • \$\begingroup\$ You can press the above link..i have a problem in uploading the picture..so i have inserted a link for it on google drive \$\endgroup\$
    – user255471
    Aug 5, 2020 at 13:04
  • \$\begingroup\$ No, that link requires access and I don't have access. Post a picture \$\endgroup\$
    – Andy aka
    Aug 5, 2020 at 13:07

3 Answers 3

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Mechanical layers do not appear on the final PCB. They are used for reference purposes only during the design process, as well as sometimes the setup process at the PCB manufacturer. The pink layer indicates the outline of the 3D body of the chip. This is used so that you, as the designer, can ensure that it does not collide with any adjacent components. The green outline indicates the "courtyard". This indicates a "bounding box" of the component, plus a bit of a "buffer". It helps you, as the designer, ensure that there is sufficient spacing around the component (as opposed to simply preventing direct collisions in 3D bodies like the pink layer).

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  • \$\begingroup\$ Ok sir...but if i removed them,is this will affect on the fabrication of the pcb?or not? \$\endgroup\$
    – user255471
    Aug 5, 2020 at 13:21
  • \$\begingroup\$ It will not affect the fabrication. They are mainly there to help you, as the designer, make sure that the board is manufacturable \$\endgroup\$
    – DerStrom8
    Aug 5, 2020 at 13:23
  • \$\begingroup\$ Ok sir...thank you... \$\endgroup\$
    – user255471
    Aug 5, 2020 at 13:23
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Mechanical layers of downloaded parts will vary from part to part. Including the information (like if they have part numbers, a pin 1 mark, a outline for the body of the part ect). There is no 'right way' to use mechanical layers, but your PCB manufacturer might request you to provide a board outline or stackup on a mechanical layer. Mechanical layers are stored as files when the board artwork is produced. You can have multiple mechanical layers.

(I use one for the board outline, one for assembly with all the component names)

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  • \$\begingroup\$ Ok sir..thank you \$\endgroup\$
    – user255471
    Aug 5, 2020 at 15:41
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The use of mechanical layers (you can, and should, have many of them) is up to the user to a large degree. In a footprint, one of the main purposes is to give a visual and (enforced by rules) bounding area to prevent interference during layout.

Another use in footprints is to create assembly diagrams more-or-less automatically. By adding a special string “.Designator” on a mechanical layer it can allow the diagram document to be created showing a box and something like “U3”.

3D bodies are usually on a dedicated mechanical layer, allowing full 3D modeling of the part and PCB and even almost photo-realistic rendering if your models are accurate enough. Most probably draw the line at creating a different model for each resistor value (say) to show the markings, but it’s completely possible, and a kit manufacturer might deem it worthwhile.

But there are many other uses that are commonly used in various parts of the design, documentation, fabrication and assembly process. You are free to invent new applications but Altium has some suggestions:

enter image description here

  • 3D Body - used for 3D body placement.
  • Assembly - used to hold the assembly data.
  • Assembly Notes - used to detail the component load order and/or important assembly instructions.
  • Board - used for the overall board size.
  • Coating - used to coat and protect the board.
  • Component Center - used for component placement.
  • Courtyard - used to define the space in which no other component should be placed.
  • Designator -used to place designators.
  • Dimensions - used to specify the outline of the board.
  • Fab Notes - used to detail important fabrication notes.
  • Glue Points - used to place glue points.
  • Gold Plating - used to provide a corrosion-resistant, electrically conductive layer on copper.
  • Route Tool Path - used to indicate the layer that contains the mechanical routing information. Note that a user-defined name is not permitted when using this layer type.
  • Sheet - used as a display feature and is designed to work with objects placed on a mechanical layer (such as dimensions, notes, and title blocks). The properties of a Sheet can be configured in the Properties panel in Board mode including the X/Y Axes, Width, and Height. You can customize all of the size values or enable the Get Size From Sheet Layer option to show the default size values from the Sheet.
  • V Cut - used to split circuit boards by cutting a "v" groove on the top and bottom of a circuit board while leaving a minimum amount of material in place to hold the boards together.
  • Value - contains the specific values for each component on the board.

For a simple board you would typically want at least several mechanical layers, and at least the outline one would go to the PCB fabricator.

If you are downloading random footprints from various sources you may need to make extensive modifications to have them all play well together in your particular environment. There is really no reliable standardization - for example, I typically combine routing paths and V-grooves on one layer.

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