Mechanical Layer

Introduction

It is important to always include the correct Mechanical Layer data file as it is vital to the production of a PCB.

Generating the Mechanical Layer Data File

The Mechanical layer data file should only contain the mechanical information for all layers that is necessary for the production of your boards.

It must contain at least the following information:

  • The exact board outlines, ideally including dimensions (mm or inch).
  • Exact positions and sizes for all internal milling, slots or cutouts, ideally including dimensions (mm or inch).

Board Outline 1  Board Outline 2

It is best practice to create the outlines using a small line – e.g. 0.50mm (20mil) wide – where the centre of the line represents the exact outline of the board, cut, out or slot etc.

IMPORTANT
  • When no dimensions are given we will always take the centre of the contour lines to be the exact outline of the board, regardless of their thickness.
  • DO NOT scale your Mechanical layer, it should be 1:1 and reflect the exact dimensions of the PCB.
  • In case of cut-outs or slots in your PCB, this layer is essential for the production process!
  • The Mechanical layer is (as for all layers) viewed from top to bottom through your PCB.
  • Do Not mirror or rotate the Mechanical layer.
  • Only include the relevant information in the Mechanical layer data.

Routing and Milling Data

Do not provide actual routing or milling layers for board contours or internal cut-outs.

Routing and milling data is production specific and depending on the rout tools, tool compensations, routing order and direction used by each PCB fabricator.

This means that we cannot use customer provided routing or milling data.

We need to completely recreate them and this can lead to confusion or misinterpretations which may result in incorrectly routed PCB’s.

It is our job as board producers to prepare correct production routing and milling layers based on the information in your mechanical layer.

Additional Information

If required the additional information listed below should be included in your Mechanical Layer data.

Reference Hole

The distance from one drill hole in X and Y to the PCB outline.

This is particularly important when you only have NPTH holes without copper pads.

Drill Position Symbols

Positional indication of all drills using symbols (=drill map).

Use different symbols for each different drill size.

PTH/NPTH Indication

Indicate which holes and slots are PTH and which are NPTH.

Customer Panels

If you supply panelised data include proper indications for break-routing and/or scoring (V-cut).

Layer Sequence

A clear layer sequence or buildup drawing for all copper, soldermask and legend layers.

Include any additional layers such as peel-off or carbon.

Provide the correct sequence as viewed from top to bottom and with the correct corresponding data file names.

Special Buildups

If the build of your PCB requires material thicknesses, copper thicknesses or multilayer buildups which are different from our standard values then add this information to the layer sequence or buildup drawing.

This would result in your boards being non-Poolable and may result in a higher price.

Drill Maps

Drill Map 1Drill Map 2

IMPORTANT

We ONLY use a drill map to cross-check that the drill file(s) are correct.

A drill map will NEVER be used to generate a drill data for production as it gives too many opportunities for error.

Routing and Milling

The standard tool size used for all outline routing or milling is 2.00mm (79mil).

This means that the standard minimum radius for inside corners is 1.00mm (39.4mil).

Requirements for a smaller radius on inner corners should be clearly indicated in the mechanical layer.
Routing Radius

DESIGN TIP

If you require a sharp or 90 degrees inner corner this can be obtained by placing a correctly sized NPTH drill exactly on the  board outline center of the inner corner or by a clever design of your board outline.

Internal Corners

Routed Slots

The smallest width for any routed slot is 0.50mm (20mil) finished size (ENDSIZE).

Standard Mechanical Tolerances

Our standard mechanical tolerances are:

Routed boards
  • Board contour dimensional tolerances                                                       +/- 0.20mm
  • Position of contour/cutouts to holes tolerances                                       +/- 0.20mm
  • Slot dimensions tolerances
    • Length                                                                                                  +/-0.20mm
    • Width                                                                                                    +/-0.20mm
Scored (V-cut) boards
  • Contour dimensions (after board separation)  tolerances                      +/- 0.30mm (+/- 12mil)

If no tolerances are specified in your data, we will produce according to our standard tolerance specifications.

If you require tighter tolerances these should be clearly indicated in the mechanical layer and tool list.

They will increase the cost of the PCB so should only be used if absolutely necessary.


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