PCB Panel Size, Utilization And Cost Drivers

A printed circuit board is not manufactured as an individual part. It is manufactured as a panel that carries several boards, or several hundred small ones, and the price of a board is the price of its share of that panel. Two designs with the same circuit, the same layer count, and the same area can therefore cost very different amounts, because one tiles efficiently on the fabricator standard panel and the other leaves a strip of waste along every edge.

This article explains how fabrication is priced, how panel size and utilization work, which features drive the cost of a panel, and what a designer can change to reduce the price without changing the function.

How Fabrication Is Priced

The quotation is built from the panel rather than from the board. The fabricator starts with a standard panel size, works out how many boards fit on it, and prices the panel from its layer count, its material, its hole count, its line width, and its finish. The board price is then the panel price divided by the number of good boards that the panel is expected to yield, which is where utilization and yield enter the calculation.

That structure explains why a small change in a board dimension can have a large effect. A board that is a few millimetres too wide to fit a fifth column on the panel loses that entire column, and the same board shrunk by the width of a rail and a web suddenly fits. The effect is largest for small boards, where a panel carries many of them, and it is invisible in a quotation that only shows a unit price.

Panel Size And The Border Area

Panels come in a small number of standard sizes, chosen to suit the laminates and the equipment of the industry, and a fabricator works with the sizes its own lines handle. Around the array of boards there is a border that carries the tooling holes, the fiducials, the plating bus, and the coupon used for process control, and that border is not available for product. The border width is a fixed cost per panel, so its share of the panel rises as the boards become smaller.

Between adjacent boards there is a web, which is the material consumed by the router or the scoring wheel and the space needed for the tabs. Like the border it is a fixed overhead, and the number of internal edges in a panelization determines how much of it there is. A panelization with many small boards has more internal edges and a lower utilization than one with a few large boards of the same total area.

Utilization And Tiling

Utilization is the ratio of the board area to the panel area, and it is calculated after the border, the webs, and the unusable strips are removed. A design that achieves ninety percent is doing well, and one that achieves seventy percent is paying for material that becomes scrap. The calculation is worth doing explicitly, and it is worth asking the fabricator for the panel drawing rather than assuming that the boards are simply stacked in a grid.

Orientation is part of the calculation. A rectangular board often tiles better in one orientation than the other, and a board that is close to a simple fraction of the panel dimension may be worth adjusting by a millimetre to reach it. A designer who can change the outline slightly, or who can accept a different panelization from the fabricator, is usually rewarded with a lower price. Where the board is very small, the fabricator may propose combining several circuits on one panel with a shared border, which raises the utilization considerably.

Yield And Complexity

Yield falls as the panel becomes more difficult to build. The layer count is the strongest single factor, because each lamination cycle adds a chance of misregistration and of delamination. Line width and spacing matter next, since a fine line process has a wider distribution of results and a higher scrap rate, and the hole size and the hole count follow, because small holes with a high aspect ratio are difficult to plate uniformly.

The practical consequence is that the price per board is not linear in the board area. A feature size that halves the yield doubles the effective panel price, so a design that uses a slightly wider line or a slightly larger via can be cheaper even though the board is the same size. A design that uses fewer layers, or that moves the fine features onto a smaller area of the board, also reduces the cost.

Cost Drivers Beyond The Panel

The finish is a visible cost driver. A hot air levelled finish is the cheapest, an organic finish and immersion silver are close behind, and an electroless nickel immersion gold finish costs more because of the process control it needs. A controlled impedance requirement adds a coupon and a measurement, an acceptance class adds inspection and records, and a special material such as a high glass transition or low loss laminate costs more than the standard grade and is usually available only in defined constructions.

Testing is the last major item. A flying probe test is included in many quotations and costs time per net, while a fixture test moves the cost into tooling, and an electrical test with a fine pitch requirement takes longer than one on a coarse board. Delivery time is a commercial variable rather than a technical one, but an expedited order carries a premium because it disrupts the line schedule.

What A Designer Can Change

The levers that are available at the layout stage are the layer count, the line width and spacing, the via size and count, the finish, the outline dimensions, and the acceptance requirements. None of them can be changed after the artwork is released without cost, and all of them are cheap to change while the layout is still open. A design review that asks what the panel looks like, and not only what the board looks like, is the cheapest cost reduction available.

The conversation with the fabricator is the other lever. Most fabricators will propose a panelization and a set of design rules for the price band that suits the product, and a design that is drawn to those rules will be cheaper than one that is drawn to tighter rules and then reworked. The fabrication sequence that turns those rules into a board is described under PCB design and fabrication, the layout decisions that affect the process under layout decisions that affect production, and the layer strategy under layer stack up from one to eight layers.

FAQ

Why does a small change in board size change the price so much? Because the boards are cut from a fixed panel. A dimension that prevents another column or row from fitting wastes the material in that strip, and the cost of the scrap is spread over the boards that do fit.

Should the designer panelize the boards? The designer should consider the outline and the utilization, but the panelization itself is usually left to the fabricator, who knows the panel sizes and the equipment. Asking for a panel drawing is the useful step.

Is a standard finish always cheaper? Yes, when it meets the assembly requirement. A more expensive finish is justified by solderability, by the number of reflows, or by a shelf life requirement, and not by a general preference for gold.