One of my favorite unexpected childhood gifts was a rock tumbler kit; with some water and a few hours of runtime, I could fill a shelf full of brilliantly polished and lustrous stones. Not only did this start me down a path of appreciation for chemistry and materials, but it also introduced the importance of finishing a project with a polishing step. While these polishes are more aesthetic than anything else, some instances in PCB manufacturing become more of a necessity to support the design or improve processing outcomes. PCB beveling removes material at the routed edges following depanelization, often as a precursor to plating for edge connectors.
Weighing the Pros and Cons of PCB Beveling
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The Benefits of PCB Beveling
PCB beveling is part of board manufacturing that can clean up the rough surface from various depanelization techniques or enhance compatibility with different board-edge connectors for optimal mechanical coupling. On fabrication datasheets and other critical manufacturing documents, designers can indicate the angle for beveling on either side of the board; before fabrication is complete, beveling equipment rounds both sides of the board according to the desired angle – standard values are 20/30/45/60°. Advantageously, beveling is a rapid process with an appreciable feedthrough rate, making the process compatible with mid- and high-volume production lots.
Beveling operations adhere to one of three possibilities depending on feedthrough orientation relative to processing:
- A closed bevel fully contains the design of the mechanical body for the connector.
- An open-ended or open-beginning bevel is missing some of the connector’s mechanical body, with the exact designation depending on where the discrepancy occurs and the feedthrough direction.
Why beveling? Beveling ensures edge connector cards (a connection method where a PCB integrates with another board using pads that run to the edge of the board) adhere to two key metrics: reliability and durability. First, beveling creates the angle that matches the edge connector so that the connector can better grip the daughter card while matching with pin angles to ensure rugged connectivity. Second, beveling improves the number of insertion/removal cycles before failure, which could impact the long-term service life if rapid or repeated card switching is necessary.
The beveling process also improves board testability through an associated edge connector, allowing the mating boards to connect to hundreds of pins with a single insertion. The high level of reliability in the mating connection itself (in terms of mating/demating cycles) means that the contacts or connector pins are unlikely to experience failure even during prototyping periods where connection/disconnection may be high. Integrating standard fabrication and assembly test procedures through an edge connector can also rapidly accelerate per-board testing times, a vital consideration for high-volume production lots. Reducing the number of individual connectors during testing can also improve the accuracy of results (or time lost due to missing or incorrect connections).
Additionally, beveling can be a clean-up tool that ensures a smooth finish on the cut edges of the board, with the added benefit of further limiting exposure of the inner layers to the environment. It is a repeatable process for any production that minimizes damage related to board edges or chemical baths. Standard routing can produce jagged edges that can damage other boards in transit or equipment and technicians during handling. Partially separated epoxy resin and fiberglass substrate can collect as a residue in plating tanks, which requires removal while slowing overall throughput. Processes that rely on straight edges for positioning/reference may also suffer. Generally, beveling improves manufacturing work while limiting unintentional process exposure that could jeopardize the board’s quality.
Designing Mechanically and Electrically for Beveling
Regarding design parameters, beveling produces a residual thickness from the angled shaving on either side of the board edge. This residual thickness is a function of the total board thickness, the depth of the beveled edges (from residual thickness to total board thickness), and the angle from the horizontal (positive or negative). In equation form,
where tr, t, d, and a are the relative thickness, total thickness, bevel depth, and beveling angle, respectively.
Design at the board level will need to compensate for beveling adequately; however, adjustments to the design rules are relatively minor and are analogous to an extension of the board-edge clearance. These clearance rules ensure the conductor features and components do not come close enough to the edge, as generally speaking, signal integrity decreases at the extent of the board (this is due to wide-ranging factors, such as copper pull-back on internal plane layers resulting in significant EMI when traces pass over plane boundaries/gaps). The beveling angle will impact the necessary board-edge clearance, as smaller angles (measured from the horizontal) intersect the copper layers at a shorter distance. Beveling can even include placement inside the outermost edges for boards containing slots or cutouts.
Your PCB Manufacturer Knows All the Angles for Production
PCB beveling has a high applicability to many boards, improving the edge quality of the board (whether for additional processing or regular handling) without having a noticeable impact on throughput. While it’s not mandatory during manufacturing, designers may find the cost-benefit suitable for their production. Speaking with a manufacturer early in the PCBA design stage can aid development teams by guiding design rule parameters and board layout to optimize performance, cost, and manufacturability. At VSE, we’re a team of engineers committed to building electronics for our costumes; alongside our manufacturing partners, we’ve helped aid the design of life-saving and life-changing electronics for over forty years.
