The Bare Board Drawing - 44xxx
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The Bare Board Drawing - 44xxx



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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.

Artwork data

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: -

ARTWORK DATA REFERENCE TABLE 1
FILE NAME FILE DESCRIPTION
44999-02.AST COMPONENT ASSEMBLY TOP
44999-02.ASB COMPONENT ASSEMBLY BOTTOM
44999-02.ELT ETCH LAYER TOP
44999-02.IN1 ETCH LAYER INNER 1
44999-02.IN2 ETCH LAYER INNER 2
44999-02.ELB ETCH LAYER BOTTOM
44999-02.SMT SOLDER MASK TOP
44999-02.SMB SOLDER MASK BOTTOM
44999-02.SPT SOLDER PASTE TOP
44999-02.SPB SOLDER PASTE BOTTOM
44999-02.BDR BOARD OUTLINE DATA
44999-02.RTG ROUTING DATA
44999-02.DDT DRILL DATA
44999-02.DDS DRILL SYMBOL TABLE
44999-02-XY.TXT COMPONENT PLACEMENT COORDINATES
44999-02-TOP.DXF TOP VIEW
44999-02-BOT.DXF BOTTOM VIEW
NOTE: EXCELLON DRILL DATA FILES IN NCDRILL FOLDER

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

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.

Copper layer thickness 17, 35 or 70 µm
Board thickness 0.6, 1.0, 1.6 or 2.0 mm
Board thickness tolerance ±10%
Bow & twist of PCB ±1%
Minimum copper track width 0.15mm
Minimum copper track separation 0.15mm
Minimum SMT pad to pad distance 0.4mm
Minimum copper track to hole/routed edge distance 0.3mm
Minimum copper track to punched edge distance 0.8mm
Minimum copper track to V-cut edge distance 0.5mm
Minimum non-plated through-hole (NPTH) edge to board edge 1.25mm
Copper artwork shift tolerance ±0.1mm
Minimum solder mask width 0.2mm
Solder mask misalignment tolerance ±0.15mm
NPTH diameter tolerance ±0.1mm
Plated through hole (PTH) diameter tolerance ±0.15mm
Through-hole misalignment tolerance ±0.08mm
Minimum drilled hole diameter 0.4mm
Minimum punched hole diameter 0.8mm
Routed edge tolerance ±0.15mm
V-cut edge tolerance ±0.3mm





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