PCB Panelization Guidelines

      Automated circuit board assembly equipment often has trouble working with smaller boards, resulting in more frequent defects during the assembly process. To minimize these defects and improve the throughput of the manufacturing process, many companies use a process called panelization, resulting in a PCB panel.

What is a PCB panel?

      A PCB panel, also called a PCB array, is a single board consisting of multiple individual boards. Once assembled, the panel is then broken apart, or depanelized, into the individual PCBs during the breakout process. The benefit of the printed circuit board panelization process is a decrease in defects as automated assembly machines tend to encounter fewer problems during the assembly process. In addition, panelization also reduces cost by improving throughput.

      Successful PCB panelization requires multiple design specifications to work properly, including considerations surrounding panelization methods. We’ll detail these panelization methods and their specific requirements more thoroughly in this WHERE set of PCB panelization guidelines.

Panelization Methods

      Multiple panelization methods exist, each with its own drawbacks and benefits. The design of the boards on the panel and the panel itself will often play a large role in which panelization method best suits the application. The most notable of these factors include:

• Design: The design of the board plays the largest part in determining the most appropriate panelization method. The amount of clearance between components and the edge of the board may make certain methods much less suitable than others, as does the presence of edge-hanging components.

• Components: The types of components used on the board are just as important as their placement. Particularly sensitive components and connectors may play a factor in the most appropriate breakout and panelization method.

• Materials: The materials used in a PCB may limit which type of panelization method is most appropriate, as some materials are more prone to splintering during the breakout process. Board thickness is also a factor, as particularly thin boards may be more likely to break during assembly, and thick boards may prove more problematic during the breakout process.

      These factors limit the choices available to any one application. In fact, many assembly companies may use a combination of methods on any one project to ensure the structural integrity of the array while still mitigating issues during the breakout process.

      There are three panelization techniques in use today, though only two are commonly practiced. They are:

    1. V-Score Panelization: This common method of panelization separates individual PCBs with V-shaped grooves. These grooves remove approximately a third of the board’s thickness from the top and bottom of the board with an angled blade. A machine is commonly used to finish the breakout process, considering the remaining third of the board between the grooves is surprisingly strong, and hand-breaking can put stress on the PCB and surrounding components.

    2. Tab Routing Panelization: PCB arrays that can’t feasibly use a V-groove method will instead use a tab routing method. With this method, PCBs are pre-cut from the array and held in place on the board with perforated tabs. Three to five holes are often used in these perforation patterns. This method is often beneficial for its ability to support designs with edge-hanging components. It can also be broken by hand instead of with tools.

    3. Solid Tab Panelization: Arrays can be designed with solid tabs between each board, improving overall strength. However, the depaneling method for this type of panel requires either a depaneling router, a laser-cutting machine or a hook-shaped blade tool. The router can result in dust and vibration, while the laser-cutter is extremely expensive and ineffective on boards over 1mm thick. The hook-bladed option is less expensive but inefficient and prone to blade rotation. This method tends to be less common than the other two.

      V-Score and Tab Routing are the preferred panelization methods for most applications. The most important thing for PCB designers is understanding which of the two methods is best for their application. The next step is to design their array for maximal strength and breakout success.

      Many prefer the V-groove panelization method when possible for its efficiency and reduction in surface stress. Depaneling machines for this type of array are also relatively inexpensive and cost-efficient. Even better, they’re portable and require minimal maintenance. Though the method tends to result in rougher board edges, this is rarely a concern for applications where V-groove panelization is used.

      However, while V-groove panelization is preferable for various applications, it is rather restrictive in terms of panel design. For example, V-groove panelization is not ideal for designs where components are placed too close to or hang over an edge. They also introduce various manufacturing concerns that must be considered during the design process, such as:

• Clearance: To ensure components are not affected during the cutting process, a clearance of 0.05 inches must be maintained between components and any V-grooves. Taller components may need to be placed further away to ensure the cutter doesn’t interfere with them. For example, surface-mounted multilayer ceramic chip capacitors must be kept at least 1/8 inches away from the score line. Components with larger connection areas should also be placed further away from the groove, as the stress of depanelization can fracture solder joints if they’re placed too close to the V-groove.

• Jump-Scoring: V-grooves can reduce the structural integrity of a PCB array, causing the leading and trailing edges to sag when run through a wave-solder machine. This can cause the array to warp or get caught in the wave-solder machine. To strengthen an array and prevent these issues, designers can add jump scoring to the leading and trailing edges of the array. This can be accomplished by including a ? inch breakaway edge on the leading and trailing array edges and running the V-groove approximately halfway through these edges. Just instruct depaneling operators to remove these breakaway edges before separating the boards.
  

      If these design considerations are kept in mind, a V-scored panel should experience minimal problems during the manufacturing and assembly process.

Design Considerations for Tab Routing Panelization

      Tab routing panelization tends to be preferred in applications where components are placed very close to or over an edge. It’s also preferable for PCBs made in non-rectangular shapes like circles. However, because the tabs are the breaking points for these arrays, several design choices must be made to ensure the strength and functionality of these arrays, especially during the breakout process. Some of these considerations include:

• Clearance: Because of the stress placed at the breakaway points and the potential for splintering, keep components and traces at least 1/8 inches away from the tabs. Surface-mounted multilayer ceramic chip capacitors must be kept further away, at least ? inches from the tabs to ensure minimal interference.

• Knock-Outs: If your PCB design includes holes greater than 0.6 inches, a placeholder, or knockout, may be required to prevent issues during the wave-solder process. Knockouts are particularly important in the middle of an array, where PCB arrays are more likely to sag. Smaller rectangular knockouts can have a wide, five-hole perforated tab on a single edge, while larger, more irregular shaped knockouts may require multiple three-hole perforated tabs.

• Tab Placement: Tab placement is important to maintain the integrity of your PCB array design. Tabs must be placed every 2 to 3 inches along a board edge for five-hole perforated tabs, and every 1.5 inches for three-hole perforated tabs. Tabs should be placed as close to the edge of a board as possible to avoid curving at the edge of a board, but should not be placed under overhanging components. The designer must also ensure the tabs are big enough to support the boards, but not big enough to interfere with the breakout process.

• Perforation Placement: If you want to avoid protrusions from the side of your board, never place tab perforations down the center of a tab – instead, run them close to the edge of the PCB, or on each side of the tab if placed between two PCBs.

• Array Arrangement: When arranging PCBs, be sure all tabs broken at one time are collinear so that there are consistent break-lines throughout the array. If break-lines aren’t consistent, some tabs will break while others are simply pulled perpendicularly to the board surface, which can tear the lamination.

      With these considerations kept in mind, your design should encounter minimal issues during the manufacture and breakout processes.

Instructions for Breaking Out PCB Boards

      Even if you design a PCB array perfectly, problems can still occur during the breakout process. From splintering and tearing to component damage, the breakout process can destroy a board if done improperly. That’s why proper board break out methods are essential to keeping costs to a minimum. Keep the following guidelines in mind during the breakout process to avoid any such issues:

• Breaking Tabs by Hand: A properly designed tab routed panel can often be broken with hand tools. For the best results with a hand tool, use wide-nose pliers to bend each tab in a break-line until it audibly cracks. To fully separate along the break-line, bend the tabs in the opposite direction.

• Breaking Tabs by Machine: In some cases, the board may be too thick to break entirely by hand. In this case, using a cutting tool may be preferable. A hook blade or depaneling router may be a good option here, as discussed previously with solid tab panelization.

• Breaking V-Grooves by Hand: Depending on the design of the board and how close components are to the edges of the board, V-scored panels can be broken by hand using a method like that used for breaking tabs.

• Cutting V-Grooves: V-Scored panels require a type of depaneling machine to break free. This machine uses a pizza-cutter-type blade, one that’s relatively inexpensive and requires little maintenance. The only drawback is that the edges will be somewhat rougher than routed options.

V-Score vs. Tab Routing PCB Panels

      Choosing whether to use V-score or tab routing methods in your panel will largely depend on the design of the PCB you’re working with. Consider the following factors when making your decision:

• Board Shapes: The shapes of the PCBs included in an array play a large role in the panelization method. For square or rectangle boards, V-scoring works well. Tab routing is more appropriate when working with unusual shapes.

• Edge Components: If your PCB relies on the presence of edge-hanging components, or components placed close to an edge, some variation of tab-routing may be more appropriate than V-scoring. Just be sure that the tabs are not located near these edge components.

• Edge Quality: If edge quality plays a factor, tab-routing may be preferable to V-scoring. Though the process leaves small rough nubs of laminate, these can easily be sanded off, and the remaining edges are smooth from the routing process. V-scoring, on the other hand, results in rough edges all the way around, which may require more sanding if smooth edges are necessary.

• Time Expense: Tab routing tends to take more time and labor to set up, as they require a lot of time on the router. V-scoring, on the other hand, requires much less time under the machines.

• Waste: If material waste is of concern, V-scoring offers the most benefit. The method wastes much less material than tab-routing, meaning much less overall cost per board.

      It’s also important to consider that Tab Routing and V-scoring methods are not mutually exclusive. These methods can be used in combination in certain circumstances. For example, tab routing can be used for PCB edges that have components close to or hanging over the edge, while V-scoring can be used on other edges.