Some manufacturers require drill template drawings as part of the mechanical documentation of the PCB.
Routines for generating, editing, dimensioning and printing of drill templates are included in Fabrication.
The special purpose library
@TOOLS.PACKAGE contains ready made set of packages used to represent different hole
diameters and categories on the drawing. Each of these packages may be edited using Library Editor in package mode.
Names of these packages,tool numbers assigned to them and categories (patches) should not be changed.
Dimensions and Notes
Dimensions may be added to the board at any time but the dimensioning data is only accessible in Fabrication for editing and printing.
They are not visible in the Layout Editor mode. Two kinds of dimensioning are provided - distance dimensioning and angle dimensioning.
The distance to be measured is defined by two contact points
placed at the points between which dimensioning is required. System measures the distance and automatically
generates dimensioning lines, arrows and texts which may be added to the drawing optionally.
Angle dimensioning requires the placement of three contact points showing the vertex and the arms of the angle.
All additional information in the form of graphics and texts but not intended as part of the artworks may be included
in the PCB drawing as Board Description Notes. The editing procedure is similar to editing symbols/ packages,
but as in the case of Copper Planes and Copper Pour Areas, items are visible with the whole board in the background.
Display of Board Description Notes may be switched ON or OFF.
Printing Layout Documentation Drawings
Display of layers, copper planes, copper pour areas, dimensions and notes may be set by enabling any of these options
in the View dropdown list. The prepared views may then be sent to the printer.
This feature provides the flexibility to print and preview various views design of the PCB.
Extracting NC drill data
The pinned components have to be mounted on the board.
For this, the printed circuit board has drilled holes at every lead position of the component.
While creating libraries of packages, pads are used to represent the lead positions of the component.
Hence, these pad position provide the coordinate reference for drilling a hole to mount the leaded components.
The drill size information is a part of the padstack. NC-Drill generates the drill data and a template drawing used for drill inspection.
The Template generation is optional.
Information about the hole diameters and categories is included in via and padstacks. Dividing holes into categories may be required when more than one drilling operation is required. Holes may be needed for component pins and vias as well as for other purposes such as for screws fastening the boards in cabinets or securing connectors. Via holes and component holes are plated while mechanical holes are usually not and therefore these are not drilled at the same time. Hole categories enable to group different types of holes into separate patches for drilling operations to be performed at different stages of the PCB manufacturing process.
Editing and Printing of Layer Artworks
Editing artworks is the final stage in the preparation of PCB layout to obtain manufacturing documentation in the form of films. The artworks must be edited individually for all those layers for which the artwork films are required. A simple double layer board, for example, may require generation of four artworks:
- silk screen artwork - obtained from component print layer.
- component layer artwork
- solder layer artwork
- solder mask artwork
In this case, artwork editing operations are limited to these four layers.
Selected artworks may be previewed on the screen layer by layer. They may be also send to the printer at this stage.
Whether printed artworks can be used for obtaining production films depends very much on the printer quality.
With a printing density 300 dpi, a lot of precision of the artworks created with system resolution 1000 dpi may be lost.
In any case, the printed output may be used for validation purposes.
In cases where cards are not too dense or complicated printed outputs may be acceptable.
To assure quality of printing, photoplotters are used. This has been explained in the section on Photoplotting Concepts.
NC-drill data provides information regarding the size, X, Y coordinates and type of holes to be drilled in the board.
In generating the NC-Drill data, the system extracts information about the hole positions, sorts them according to drill size information.
The different hole sizes are grouped together and generally sorted to drill in a specific order.
This grouping may be done based on sizes, type of drilled hole, like through plated or non-plated, via type like buried or unburied etc.
A precision format of 2.4 for inches and 3.3 for metric is selected internally by the program. This is generated as a drill tape data.
The data may be used directly on any computer numerically controlled drilling machine. This NC-Drill data is provided in a specific format.
By default, EXCELLON format is the accepted industry standard.
Generation of Disk Files Containing Generic Data for Pick & Place Machines
Generic Pick & Place output contains all possible geometric data about the components on the PCB.
The scope of data generated may be selected by the user.
Output is generic which means that it may require reformatting to fit the specific Pick & Place equipment.
Generic format description is included in the file header.