Milling Artwork in Copper: PCB Router Bit Diameters Get the Job Done

Altium Designer
|  Created: March 23, 2018  |  Updated: December 7, 2020

Routing good ideas to copper

Spring is a busy time of year in the garden. The yard brings chores, but with the right tools, time passes easily and pretty soon I’m enjoying my lawn chair. One of those chores is picking up all the dead leaves left from Autumn that remain in places they fell, blanketing areas of shrub beds and cement patio.

For shrub beds, I use rake and hands to pick up leaves and throw them in the compost. For the patio, I fire up the pressure washer and scrape stuck material from concrete with water. Thicker deposits require differing pressure and my washer has options for changing the thickness of water stream to get the most stubborn spots. When finished, I’ll put out the lawn furniture and open a book. Ah, earned downtime is the best.

Making signal layers on printed circuits boards happens in a similar fashion, either through etching with chemicals, laser, or milling machine. Use of milling machine includes PCB router bits to remove copper in areas unnecessary to the design. For the DIYer, this may be done manually, but for large production, image files provide programming data to drive the computer numerical controlled (CNC) milling machine.

When the signal nets and pads remain, printed circuit board layers are laminated together and plated. Assembly follows when components are soldered onto the resulting PCBs and sent on their way to the engineer for test and validation of design.

Output Files Define Image for Etching

Just as your patio edges are defined by concrete forms when poured, your PCB layer patterns are defined in output files. These files contain information the milling machine uses to program router bit movement to realize the design.

A DIYer may use the files to overlay on copper and follow by manually moving the router bit for their desired result. Just as you avoid power washing the topsoil from flower beds adjacent to the patio, programming data in output files prevents your router from removing copper, either manually or automatically, where you want traces to remain. What’s left is the PCB layer image.

PCB Router Bits For Etch During Milling

An image is made when router bits are used by milling machines to etch copper from layer cores and prepreg stacks, leaving intended nets and pads for design realization. Bits come in differing sizes, shapes, and materials to enable manufacturers to produce fine or fat traces, sharp or round edges, and landing pads or fills for eventual use in assembly.

As pressurized water is immune to destruction against concrete while power washing last year’s leaves from the patio, tungsten carbide bits hold up against many hours of use against fiberglass cores and prepreg that make up printed circuit board non-conductive layers. The tungsten carbide bits move along pathways defined in image files, leaving clean fiberglass. Untouched copper remains as defined in the gerbers.

Milling machine in PCB manufacturing using pcb router bit diameters
Milling Machines Use PCB Router Bit Diameters to Fabricate Boards

Gerber Information Defines Image For Programming

The gerbers provide programming data used by CNC milling machines to move router bits at fast rotational speeds to remove copper. Similar to high water pressure removing debris from your patio and cleaning the cement to remove unwanted layers of dirt. The fast rotational speeds accurately remove copper, leaving each PCB layer with patterns specified by the gerber and represented in the artwork.

Manufactured sheets of core and prepreg are cut into panelized shapes and each layer is milled specific to the gerber information provided in output files. The panels are shaped for handling on CNC machines’ large, manufacturing tables. This allows stable and accurate milling for production of layers whose vias and through holes match within microns when laminated together.

Milled Layers are Laminated Into PCBs

Once the bits complete milling, layers move across the manufacturing floor collecting at end of runs for eventual organization into laminated stacks. It reminds me of moving across the patio, pushing layers of crud out of the way so I can bring in the lawn furniture and ready myself for warm summer evenings.

The PCB fabrication process continues as more sheets move through milling and image creation, ready for next steps in the board build and eventual assembly. With unwanted copper removed and layers laminated, the PCB is ready for arrangement of components onto the remaining copper pads.

Removing dead leaves and unwanted copper result in new seasons for patios and circuit boards. As the patio furniture is brought in for summer meals and lazy reading, so is the printed circuit board readied for component placement and assembly to enable board power on and use in products.

A printed circuit board starts as an idea that is captured in schematics and PCB layout files for manufacturing. Through manufacturing, a milling machine moves router bits across unnecessary copper for removal, leaving clean, copper areas for installation of components.

A dalmation lays on tile outside
A Unified Platform Makes PCB Fabrication Compare to the Dog Days of Summer

You can use the Manufacturing Output Features of Altium Designer® Unified Platform to produce output files in the style that your fabrication house appreciates. New to Altium 18 is the output media selection bar which can be used to provide preferred formats of output files to your fabricator. This eases sharing of complex data and your designs are brought to market in a neighborly way, free of complication and full of satisfaction.

With this type of satisfaction built into drill bit routing instructions via the gerbers, who wouldn’t want to use Altium’s unified platform to generate manufacturing output files. Seriously, if you know anybody have them call Altium’s team of experts to talk about why.

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PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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