When it comes to preparing for trips, I get satisfaction from rearranging my bag just right. It must be that same feeling Alexey Pajitnov tapped into with Tetris — something about filling a space to maximize efficiency makes us feel productive and accomplished. While there’s no addictive tune playing in the background during panelization (not yet, at least!), the manufacturing process scratches a similar itch. Panelization is the arrangement of individual PCB boards on a panel to maximize the number of PCBs. Another way to look at this is that panelization is paying for the panel, so there’s no reason not to try and maximize the production lot. Panelization, therefore, balances efficiency against spacing concerns, seeing as we want to ensure the boards are provided enough space for manufacturing processes and their finished dimensions.
Process work must be done to prepare the boards to be separated mechanically. This work is done through two methods: V-Scoring and tab routing. Both panelization methods find use depending on different design elements of the board. Below, it will be explored in greater detail and comparison-contrast.
V-Scoring: An Everyman’s Approach to Array Panelization
V-scoring is a relatively straightforward and, therefore, inexpensive method of PCB arraying. For rectangular-designed PCB arrays, a cut is made to a depth of a third of the board’s thickness on the top and bottom sides. Like tab routing, using hands to break the circuit board along the scoring is frowned upon unless strain-resistant components such as surface mount devices are absent. Excess stress and flexing of the finished board could lead to crack formation in the solder or complete disconnects between solder and pin if the shear force/moment is great enough. Additional depanelization methods include traditional mechanical designs such as saws, punches, and routers. Laser cutting is also an option for boards of 1 mm thickness or less.
In particular, both laser cutting and routing open up additional V-Scoring depanelization designs via flexible contours. Laser cutting has an additional marked advantage as it introduces an extremely low mechanical-stress option for cutting boards under 1 mm thick. Routing is far less cost-prohibitive than a laser cutting setup, but because the router generates oscillations at the same rate as its rotation speed, it can cause damage to vibration-sensitive components.
Tab Routing Shines for Off-Board Connectors
Tab routing is the process of drilling small series of holes along the edge of the board where the material between the board and the greater panel remains for structure. This process is similar to how plastic models would be held together before the user would break them away for assembly. Much like these plastic model arrays, breaking the perforated tabs by hand is not advised due to the stress you can put the PCBs under. After breaking these tabs, the sections of fiberglass still attached to the board are fittingly referred to as mouse bites. The mouse bites should be cleaned up to remove any excess material from the board that could interfere with fixture design or perhaps splinter and create debris in a hard-to-access field environment.
The placement of tabs should be beyond the extent of the board to ensure that after removing them, the board meets the original design specifications. From a mechanical standpoint, keeping tabs past the board edge keeps material voids and vacancies off the finished board that could negatively contribute to the vibration susceptibility of nearby components. Additionally, breakaway tabs should be:
- 3-5 drill hole line (typically)
- Hole size: 0.5 mm
- Hole-to-hole spacing: 0.75 mm
- Center-hole to center-hole spacing (spacing between tabs): 60 to 90 mm, must be less than 100 mm
- Components should be no closer than 6.5 mm to the nearest tab
Tabs placed infrequently can cause additional flex in the material that can especially cause issues during wave soldering. Tabs placed too frequently will cause machines and tools used to cut breakaway tabs to dull or break quicker.
Choosing the Appropriate PCB Panelization Method
Generally, tab routing is less utilized than V-Scoring, but it has a distinct advantage: boards with connectors extending beyond their measurements. V-Scoring can only make straight-line cuts from a panel-to-panel edge, whereas the layout or CAM designer can place the breakaway tabs wherever they are best suited (following the above best practices). This scenario is common with USB connectors (and other data transfer protocols) where the connector extends past the board for ease of cable interfacing.
Ultimately, panelization and depanelization may be decided by the tools available to your fabricator. It’s important to have access to different tools depending on the needs of your board — you don’t want to damage your near-finalized board with a process that is ill-suited for its design. When it comes time to build, look for a contract manager that will be able to source panelization that will maximize your production and a depanelization method that provides the least amount of disturbance to your boards. At VSE, your board will be handled as if it were our own.