After completing a PCB layout, a designer can rest (at least momentarily) knowing that their active contribution to the project is complete. However, since PCB productions rely strongly on the design process as both a collaboration and guide for the manufacturing process, designers must be confident in the accuracy of their work and the unambiguity it conveys. Carefully annotated and detailed PCB artwork serves as the master copy for most of the fabrication and parts of the assembly, so designers will want total confidence in their manufacturing files before sending them to the shop floor.
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PCB Artwork and Other Manufacturing Files |
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|---|---|---|
|
Type |
Function |
Format |
|
Artwork |
Provides a layer-by-layer view of the design |
Gerber, ODB++ |
|
Drill File |
Indicates the various drill hits by hole size, shape, plating, and depth |
NC drill file |
|
Stackup |
Shows a cross-section of the board indicating the different thicknesses and materials used during lamination and via/impedance structures |
Varies by ECAD tool, sometimes spreadsheet |
|
XY-data |
Gives placement information to automated placement equipment (i.e., pick-and-place) |
Plain text file |
|
Bill of Materials (BOM) |
Lists all of the components used in the assembly, including manufacturers’ part numbers, quantity, and package details |
Spreadsheet |
Translating Design from an ECAD Environment to Manufacturing
PCB artwork is the etch pattern designers submit to the manufacturer for fabrication. For ease of inspection, the individual layers of the board represent separate artwork files. These layers include the signal/plane layers of the stackup and distinct layers of the manufacturing process, like the solder mask, silkscreen, and more. For signal layers, the artwork represents the remaining copper after the etching process, i.e., what is left behind. However, this is not true of all layers; some represent negative or positive images.
- Positive artwork shows the final image of the layer as it should appear post-processing.
- Negative artwork shows the inverse of the layer post-processing, i.e., the color in the artwork on the corresponding layer represents space (and vice versa). Negative artwork is primarily a relic of the early layout tools and file size restrictions when it took less data to indicate a layer’s features.
However, the designer is responsible for the artwork and may describe the layers as they like, so long as the documentation for the manufacturer is unambiguous. This is especially true for layers that are not part of the “standard” documentation output (think of additional processes like tenting, plugging, etc.). More generally, the artwork anchors the manufacturing process in several ways:
- Tooling holes punched or drilled in the artwork ensure layer registration (layers are correctly oriented relative to one another and some hypothetical origin). Registration is necessary to ensure drilled hole hits strike their intended pads and prevent the drill from shorting/opening other subcircuits.
- The artwork defines the circuit’s copper features. By applying the artwork to the laminate with a dry film photoresist, technicians can obtain a copy of the artwork on the copper through a UV-light polymerization reaction.
- A second photoimaging step uses the artwork to create the solder mask reliefs (i.e., the solder mask opening for component lead/pin soldering).
How the Manufacturer Uses PCB Artwork
For the manufacturer, the artwork is the first look at the PCB designed by the layout. While a discovery call at the beginning of communications between the designer and manufacturer provides a rough guide on what the manufacturer should expect, the manufacturer can more granularly investigate board elements (and potential challenges) within the artwork files. The artwork acts as the manufacturer’s legend; as such, it is the most critical document to produce a quality build adhering to design intent.
Because the artwork will indicate board features, including dimensioning, tolerance is significant for communicating the design to the manufacturer. Consider some of the following ways tolerancing impacts the artwork:
- Tolerancing the board dimensions requires additional documentation to ensure the board can interface with automated assembly processes and transport. Generally, these tolerances are necessary on both sides of the board to provide parallelity.
- Tolerances for surface-mount device (SMD) boards may require additional information and restrictions, such as for processes like solder leveling. Designers should discuss these special cases with a manufacturer as soon as possible.
- With reflow soldering, the artwork provides the opening measurements for solder paste deposition on the pads. Precision is necessary to ensure the reliability of the solder joints and overall board continuity. Smaller or larger openings can inhibit the formation of an ideal solder joint.
Your Contract Manufacturer Has PCBs Down to a Fine Art
PCB artwork acts as the handshake between the designer and manufacturer, indicating the overall scope of the layout while fully detailing the necessary processes, features, and precision to realize the design intent. Designers must refrain from under- and overspecifying in the artwork to prevent frustration and delays in the manufacturing process. For designers feeling overwhelmed by the PCB manufacturing process, VSE is here to help. We’re a team of engineers committed to building electronics for our customers, including a full review of the design pre-manufacturing to ensure cost-efficiency and performance. We’ve been realizing life-changing and life-saving devices for over forty years with our valued manufacturing partners.
