FPC Production: Five Panelisation Principles

Flexible circuits are almost never produced one at a time. A single FPC is too small for the handling equipment and too wasteful of material, so production starts from a panel that carries many units. How that panel is arranged, the panelisation of the design, determines the material cost, the accuracy of the forming step and the ease of every subsequent operation. Five principles cover most of the practical decisions.

Pack the Units as Tightly as the Process Allows

The first principle is to reduce the distance between adjacent units as far as the manufacturing steps permit. FPC production pays for material by area, so a panel that wastes space between units wastes money directly, and the saving accumulates over the whole production run. Tight packing is therefore the default, and the question is how tight the process allows.

The limit comes from the operations that follow. The forming step needs to separate the units accurately, the tooling needs a place to register the panel, and the handling equipment needs enough material around the units to hold them. Those requirements set the minimum spacing, and the design of the panel should start from them rather than from an arbitrary figure.

Maintain a Minimum Spacing Between Units

The second principle sets a floor on the spacing: adjacent units should be separated by at least around two and a half millimetres. In volume production the forming step is often a die punch, and the punch needs registration holes between the units to stay aligned. Sharing a registration point between units is what allows the punch to work precisely across the panel.

In prototype and small-batch production, forming is usually done by laser cutting instead. Even there the units must not be joined directly, because a small deviation in one cut would propagate and shift every downstream unit on the panel. Separating them means each unit is independent, so a deviation affects one part rather than the sheet.

Add Etched Identification Marks

The third principle is to include identification marks in the panel itself, etched into the copper rather than added as a label. The marks should record the panel dimensions and the number of units, which makes it possible to verify the panel against the documentation at each stage of production without opening a file.

Etched marks survive every subsequent process, whereas an adhesive label does not. They also make the panel self-describing when it is found on a shelf months later, which is a small benefit until the occasion arises.

Register the Whole Panel, Not Just the Units

The fourth principle concerns the panel corners. Registration holes belong at all four corners, and one corner should carry a distinctive hole pattern so that the orientation of the panel can be determined at a glance. Without that asymmetry, a panel can be loaded the wrong way round, and the result is coverlay bonded to the wrong face or a legend printed in the wrong orientation.

Orientation errors are expensive because they are usually discovered late. A single asymmetric registration feature removes the possibility, and it costs nothing beyond the decision to include it.

Control the Panel Dimensions

The fifth principle is a constraint on size. Panel width is commonly fixed at about 250 millimetres by the handling equipment, and the length should also be kept within that figure if possible. The reason is accuracy: the larger the panel, the greater the accumulated deviation, the worse the positional accuracy and the higher the defect rate. A panel that is too long may be within the equipment’s nominal capacity and still produce parts outside tolerance.

Where the quantity of units requires more area than a single panel can hold, using multiple panels is the correct answer rather than enlarging one.

The Three Arrangements

Within those principles there are three common arrangements. A regular array places the units in a simple grid, which suits rectangular, square, round or oval outlines. A slanted arrangement rotates each unit by a small angle to make better use of the panel area where the outline is a curved strip or a bent shape. A flipped arrangement combines units in alternating orientations so that a pair shares a boundary, which saves material where the outlines allow it. Our multilayer flex processing notes cover the additional considerations when the units are multilayer, and the breakaway tab material covers the removal method.

Whichever arrangement is used, the governing rule is the same: the most economical panel that the process can produce reliably. Our fabrication notes guidance explains how to record the panel requirements with the data, and the flexible circuit materials page covers the substrate choices that go with them.

Why Panelisation Is a Design Decision

It is tempting to treat the panel as a manufacturing detail that the fabricator decides. In practice the panel arrangement constrains what the design can do. The spacing between units limits how many fit on a panel, which determines the material cost per unit. The position of the registration holes limits where the forming can be applied, which affects the tolerance on the unit outline. The orientation marking determines whether a coverlay can be bonded the wrong way round.

Each of those constraints is easier to satisfy at the layout stage than to correct afterwards. A design that specifies the unit outline precisely, states the forming method, and leaves the panel arrangement to be agreed with the fabricator gets a panel that suits the process. A design that assumes the units can be arranged freely may find that the process needs eight millimetres between them rather than three, and that the quoted quantity no longer fits the panel.

There is also a handling argument that is easy to overlook. A panel that is well arranged can be processed through printing, placement and testing with the same reference features, so the alignment established at the first step carries through to the last. A panel that was arranged only to save material often lacks those common references, and each station then has to find its own, which adds setup time and introduces variation between operations.

FAQ

Why not produce single FPCs instead of panels? Because the handling equipment cannot manage a part that small with sufficient accuracy, and because the material utilisation would be poor. A single unit also cannot be held reliably during the forming operation, so the accuracy of the outline would suffer. Panelising is not only about cost; it is what makes the process capable of holding the tolerance the design requires.

How is the spacing decided in practice? From the forming method and the registration requirement, not from a rule of thumb. A die punch needs room for the registration holes between units, while laser cutting can work with less spacing but still benefits from independent units. The fabricator should be asked what spacing its process requires, and the answer will be specific to the forming route.

What does gopcb need to quote an FPC production panel? The unit outline, the quantity, the forming method, and any constraint on the panel dimensions imposed by the assembly equipment. The substrate material and the copper weight also matter, because they determine the minimum spacing that the etching process can hold. With those details the panel can be laid out to suit the process rather than being adjusted afterwards.