PCB Panelization: Size, Spacing and Material Utilization
The panel a board is built on is a shared resource, and the way a design is arranged on it decides how much of the raw material is converted into product and how much is thrown away. That arrangement is usually the shop’s decision, but the designer controls most of the variables that make it possible.
Panel Sizes and Why They Are Standard
Fabrication equipment is built around a small number of panel sizes, and the most common in the industry is roughly eighteen by twenty-four inches, with a smaller format around twelve by eighteen used for prototypes and short runs. The equipment that images, etches, plates and drills is sized for those formats, and a panel outside them either cannot be processed or has to be processed at a poor utilization of the machine.
Standard sizes matter because a job that fits them can share a panel with other work, which is how a small order gets a reasonable price. A job that does not fit has to occupy a whole panel of its own, and the cost of the unused area is charged to that customer. Our cost reduction notes describe how the panel is costed.
How Panelisation Is Built
A panel contains the customer’s boards, a border around them, and the features the production line needs: tooling holes for registration, fiducials for the placement machine, a test coupon for verification, and space for the panel identifier. The border is typically between a quarter and half an inch wide, and it is consumed by the tooling and the coupon rather than being wasted.
The boards are separated by a routed gap or by a pair of score lines, and the choice affects both the spacing and the way the boards are depaneled. A routed gap needs a router path between boards, which costs more area than a score line, while a score line limits the geometry to a straight edge.
Spacing Between Boards
The gap between adjacent boards is set by the separation method and by the tolerance of the process. A routed gap of around a tenth of an inch is typical, and it has to accommodate the router diameter plus clearance on both sides. A scored panel needs far less, because the material remains continuous until the two halves are broken apart.
Narrower gaps improve utilization but reduce the mechanical support during processing, which matters for thin boards. Where the panel is thin, a wider gap or a stiffening frame is used so that the panel does not flex as it moves through the plating line.
Utilization and Its Arithmetic
Utilization is the area of finished boards divided by the panel area, and it is expressed as a percentage. A panel that yields eighty per cent is doing well for a board with an awkward outline; a rectangular board with a sensible border can reach ninety per cent or more.
The arithmetic is sensitive to small changes. Adding a tenth of an inch to the border of a panel carrying small boards can remove a whole row, and the loss may be larger than the gain from a cheaper separation method. The calculation should be redone whenever the panel arrangement changes.
Board Size and Aspect Ratio Effects
A very long, narrow board wastes panel area whatever the arrangement, because the strips do not tile efficiently. Where the design allows, splitting a long board into two joined sections that are separated after assembly can improve utilization substantially.
An unusual outline has the same effect. A circular board leaves corners that cannot be used for anything except the border features, and a board with a large cut-out leaves an island of material in the middle of the panel. Our board outline notes describe how the outline is specified.
The Cost of Material
The laminate is only part of the material cost. The copper foil, the prepreg, the solder mask and the surface finish metal are all consumed in proportion to panel area, so a panel that is twenty per cent more efficient saves roughly twenty per cent of the material cost of the job.
At volume this dominates the price, which is why large programs revisit the panelisation after the design freezes. At prototype volume the setup cost dominates instead, and the panel is chosen for availability rather than for efficiency.
Assembly Considerations
A panel that is efficient for fabrication may be impractical for assembly. Placement machines need fiducials on the panel, the conveyor needs a straight edge to grip, and the board has to fit the machine’s maximum size. Where a panel exceeds the assembly equipment, the boards must be depaneled before assembly, which adds a handling step and cost.
Keeping the panel within the assembly equipment’s limits is usually worth a small loss of material, because the alternative is a manual depanelisation step that costs more than the material saved. Our breakaway tab notes describe the mechanical design of the separation.
What the Designer Can Control
The designer controls the outline, the position of the connectors, the height of the tallest component and the direction in which the board can be split. Marking the preferred panel direction on the drawing, or simply telling the shop that a particular arrangement is acceptable, often improves the panel more than any other single action.
Where the product has a family of variants, designing them to share a panel improves utilization further, because a single panel can carry several part numbers that are separated at the end. Our fabrication notes guidance describes how that instruction is recorded.
Additional Considerations for This Build
Practical attention to panelization pays for itself here, because it is one of the items that decides whether the finished board behaves as the drawing intended. Where the requirement is not stated on the fabrication drawing or in the assembly notes, the shop has to assume a default, and that default is rarely the value the design was simulated with. Stating panelization explicitly, together with the tolerance that applies, removes the assumption and keeps the result predictable from batch to batch.
Process Control and Verification
Reviewing the design before the data is released is far cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.
The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.
FAQ
Should the customer panelise the design? Either arrangement works, and the choice usually depends on who knows the assembly equipment best. Where the customer panelises, the shop should confirm that the panel fits its process before the job starts, because a panel that is too large has to be re-made as data rather than merely re-cut.
Does a tighter spacing reduce cost? It reduces material consumption and therefore the material cost, but it also reduces the process margin, and a panel that is difficult to handle may cost more in yield than it saves in laminate. The sensible spacing is the one the process can support reliably.
What does gopcb report for a panel? We report the panel dimensions, the number of boards per panel, the utilization, the border and spacing used, and the arrangement of the tooling and coupon features. Where an alternative arrangement would improve the yield, we quote both so that the customer can choose.
