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Dec 28, 2020

Panelization Guidelines from PCB Power Market

PCB manufacturers use panelization as a popular method for effectively arranging small PCBs to fit standard laminate sizes, thereby making it easier to manufacture them in large numbers. Panelization not only helps to reduce material waste significantly, at the same time it also reduces processing labor for manufacturing the PCBs.

Before discussing panelization in detail, it is necessary to understand some terms manufacturers and designers use in the panelization process. These are:

  • Fiducial
  • Rail / Web Border
  • Reference Hole / Tooling Hole
  • De-Panelization Techniques

Fiducial

Fiducials are targets or features on the PCB that provide common measurable points necessary to execute all steps in the assembly process. Designers place fiducials on the artwork of the circuit board. These features improve the precision of automated machinery and vision corrected placement equipment providing the highest accuracy from such equipment.

Vision corrected placement equipment use targets or fiducials on the PCB for determining the dimensional variation of individual circuit boards prior to assembly. The equipment uses a camera to view the fiducials and calculates the variations by comparing the actual position of the fiducial to the coordinates stored in the placement program in the machine. The machine uses the offset between the two to correct the placement locations of all the components it will place on the board.

Printed Circuit Board Manufacturers USA

Fig 1: Fiducial

Typically, the designer will place three fiducials, also known as panel fiducials, in three corners of the artwork. Panel fiducials act as targets for vision compensation. Designers may place additional local targets for fine pitch components or BGA style packages. They locate these local fiducials on a diagonal adjacent to and across the packages.

Designers place all fiducials on the top copper layer suitable for plating. This provides the fiducials adequate contrast for machine vision systems. For further contrast, designers provide a wider mask opening on fiducials than they do for other component pads.

Rail / Web Border

In general, PCB assembly equipment require an area, free of components or leads, on two opposite edges of the board. Equipment such as precision coaters, wave soldering machines, reflow ovens, and surface mount placement machines require these areas to engage with edge conveyors that transport the boards through the equipment during the various assembly processes.

Printed Circuit Board Manufacturers USA

Fig 2: Rails

Designers and manufacturers may add these areas to the PCB as rails on the edges of the circuit board, with an arrangement of discarding them after the processing is over. Placing rails or web borders eliminates the need for custom tooling and fixtures, which may be cost prohibitive for production runs at low volumes.

Reference Holes / Tooling Holes

These are holes in the PCB, generally positioned on the extra rail / border, with close tolerance for the hole diameter and accurately located in relation to the component insertion holes. Reference / tooling holes allow mounting the PCB in equipment for automatic placement and soldering of components.

Reference / tooling holes are generally non PTH drills free from solder mask. As their location depends upon standards/requirements of the assembly house, they cannot have fixed locations.

De-Panelization Techniques

De-panelization techniques help in recovering individual PCBs without damage from the panel after the assembly process is over. Three popular de-panelization techniques are in use—perforations, scoring, and routing.

Perforations: these are a series of small holes placed on the break-out area connecting adjacent PCBs. After the assembly process is over, operators separate the boards by breaking then apart along the perforations. While incorporating break-out tabs, designers must consider the weight of components on the board, and whether the tabs can support their weight without breaking during processing.

Printed Circuit Board Manufacturers USA

Fig 3: Perforations

Presence of break-out tabs give boards a rough edge to their profile after separation. Designers must consider this effect before incorporating them in the PCB design. Designers must also ensure there is adequate space between the break-out tab and adjacent circuit traces for minimizing the possibility of damage to the traces during the process of de-panelization.

Scoring: when the weight of components on board is high and break-out areas are not possible to implement, designers use the scoring technique. This technique is also useful when the boards must have a smooth edge profile such as when mounting them in a chassis or card racks. For PCB assemblies that require a complete covering of conformal coating, scoring is optimal as it presents a smooth edge.

Printed Circuit Board Manufacturers USA

Fig 4: V-Score

During the PCB fabrication process, manufacturers cut the v-score partially into the circuit board. After completing the automated assembly process, the operator performs a secondary operation for breaking the PCBs individually.

Routing: Routing removes most of the material between adjacent PCBs, leaving them connected only with small tabs. Designers shape the tabs to be strong enough to carry the weight of components on the board, allowing assembly of the sub-panels as a single unit, but weak enough to allow easy separation of individual boards after assembly.

Printed Circuit Board Manufacturers USA

Fig 5: Routing

The routing process depends on individual board size and shape, and requires custom fixtures and machine programs. The designer has greater flexibility in designing boards with irregular outlines when using routing between boards in an array. They can ensure smooth edge profiles where necessary by judiciously routing.

Customer Panel / Sub-Panel / Array

In a panel, designers can arrange several smaller PCBs in rows and columns. Manufacturers and assemblers handle the panel just as they do for a single printed circuit board.

Printed Circuit Board Manufacturers USA

Fig 6: Array

Arranging PCBs in arrays to fit standard laminate sizes results in significant reduction in both processing labor and material wastage. Handling and transport efforts during assembly for PCB panels / sub-panels / arrays eliminates those necessary for individual boards.

Advantages and Disadvantages of Arrays / Customer Panels

Advantages: Individual boards may need to use carriers during various assembly processes. Carriers are not necessary as panels are of standard sizes.

Component assembly machines can run at higher efficiency when assembling panels, as the machines do not need to wait for placement of each small board.

Handling several small boards can be problematic during high volume production, whereas handling a single panel consisting of several boards reduces handling issues.

Disadvantages: It may be difficult to break-out individual boards, requiring jigs and fixtures, and the process may add extra cost to the assembly process.

Designing large arrays with several routed slots or v-scores is a difficult process. Often the routed slots and v-scores make the panel weaker, adding to bow and twist during the various assembly processes.

As designers must leave some space between adjacent PCBs for routed slots, scorings, or perforated break-out areas, they are not fully utilizing the fabrication panel.

Customer Inputs for Generating Array (Customer Panel)

Customers must offer array drawings containing details such as:

  • Total array size
  • Individual PCB size
  • Gap necessary between PCBs
  • Rail requirement details (size and side)
  • PCB orientation within the array
  • Fiducial details
  • Details of tooling holes
  • Specifications of de-panelization techniques

In the absence of a drawing, a document with the following details is also acceptable:

  • Array size preferred
  • Rail requirement details (size and side)
  • Fiducial details
  • Details of tooling holes
  • Specifications of de-panelization techniques

Conclusion

The above guidelines from PCB Power Market provide an easy understanding of panelization and its usefulness when manufacturing and assembling several small PCBs. Using panelization, it is possible to improve the throughput and efficiency of the entire process, while reducing process labor and material wastage.

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