The Bare Board Drawing - 44xxx
The PCB bare board drawing is a separate drawing from the assembly drawings. The PCB 44XXX drawing will have a full title block and revisions control as shown in Figure 2. Since the PCB assembly refer to the single board, any changes will affect both drawings.
Figure 2: The standard bare board drawing border
This drawing shall detail all the mechanical dimensions and tolerances that are important to the design. It shall also clearly identify and label the Top and Bottom layers of the PCB. When applicable, intermediate inner layers shall also be identified and labelled. These shall follow the naming convention of Inner 1, Inner 2, etc..., with the first inner layer being the one closest to the top layer. Dimensioning of the holes shall only be included if critical to the assembly. The drawing shall also detail the following as applicable: -
i) Board material.
ii) Copper and all other plating thickness specification and tolerances.
iii) Areas of the PCB requiring additional plating processes.
iv) Solder resist finishes.
v) Silk screen and identification where applicable.
vi) Reference to any manufacturing standards that must be observed.
vii) Carbon finishes tolerances, potentiometer resistance and linearity.
viii) Edges or edge sections which shall be routed.
ix) Edges or edge sections which should be scored for snap-off.
x) Indicate if the circuit tracks should be tested for continuity.
xi) Indicate conformal coating if required and coating type and locations.
xii) Indicate where the supplier may place their traceability identification data.
xiii) Indicate an unused area for the panelisation reference co-ordinates.
xiv) Indicate ‘keep out’ zones
The panelisation details shall only be defined when Methode are to purchase PCBs in panelised form. Otherwise a note reading “Panelisation to be defined by PCB assembly supplier” shall be included with the general notes list.
The bare board drawing does not need to the show the artwork pattern unless it aids the understanding of the design.
Flexible PCBs shall be drawn with the same details.
The bare board drawing shall include a table containing the file names and description of the manufacturing data of the PCB. The table shall have the following format: -
Table 4: Artwork Data Reference Table
A ZIP file with the number of the PCB and revision shall be created for each PCB and each revision. The file will contain all Gerber files, Excellon drill files and any other output files needed for the manufacture of the PCB, as listed in Table 4. The Excellon drill files shall be called ‘ContourNonPlated.ncd’, ‘ThruHoleNonPlated.ncd’ and ‘ThruHolePlated.ncd’, and shall be placed in a folder within the zip file called ‘NCDrill’. The file name of the zipped file shall be 44xxx-nn.zip, where 44xxx is the bare board number and nn is its revision number, which shall correspond to the drawing revision number.
Tolerances on dimensions of PCBs, placement of components, hole diameters, etc… will vary between PCB suppliers, depending on their equipment. Thus, when tolerances are critical on particular dimensions it is recommended that these are specifically highlighted during a design review with the supplier, in order to verify that they can be maintained.
The table below gives an overview of typical dimensions that can be achieved by most PCB suppliers and can be used as a guideline.