Properly conducted panelling of electronic packages, although often underestimated, allows to optimize all production processes – from assembly, through tests, to subsequent depanelling. In addition, it helps to maximize the efficiency of the use of laminate surfaces, and thus – to manage production costs more wisely. How is the connection of PCBs in the array and their separation made? How to properly perform these processes to avoid damage to circuits? We talk about all this on the example of Comarch IoT Plant work.

Assembly of SMT and THT, automatic visual inspection of AOI, as well as functional tests, e.g. using Flying Probe – the success of these production processes is determined by many factors, among which the properly conducted panel of printed circuits is of great importance. Placing the PCB in the panel can also be helpful during selective application of the protective layer – varnishing.

̶̶̶ When designing a panel of printed circuits, we must have two main goals. The first is to facilitate and accelerate the technological processes that follow the design phase, i.e. assembly and control. The second goal is also to facilitate and accelerate, and additionally to increase the security, this time the process of separating the panel into individual tiles – says Mateusz Rosek, Quality Control Engineer at Comarch IoT Plant.

What is printed circuit board panelling and when is it used?

As part of a standard process, PCBs are typically designed as a single circuit. However, in order to make the most of the laminate material and to optimize surface and through-hole mounting, individual tiles are usually laid in a matrix.

– The use of a multiblock is necessary to perform automatic assembly, for example in the case of circuits with very small dimensions. The placement of the tiles in the panel allows you to add a technological margin facilitating the SMT and THT assembly process, as well as the following stages of control or depanelling. There are two main ways of connecting circuits in the matrix, scoring and milling – explains Mateusz Rosek.

What are the most common methods of PCB boards panelling?

Scoring

It consists of cutting the panel on both sides of the plate, the depth of the notch is roughly ⅓ the thickness of the board. This is the optimal way to panel PCBs with simple shapes (e.g. a rectangle) – in such cases, material waste is minimal. In case the tile has a more complicated, irregular shape, panelling by punching is still possible, but requires additional machining with the help of milling, in which custom shapes are cut. Then it is also necessary to separate the individual tiles with a envelope to leave room for the tool (cutter).

Milling

It consists in milling the shape of the PCB in the panel in such a way that depending on the size of the PCB, from several to a dozen so-called bridges. These are fragments of laminate holding single PCBs in the panel, to ensure sufficient rigidity for subsequent processes – assembly and inspection. Bridges can be separated into perforated (drilled holes) and non-perforated.

What is PCB depanelling?

Depanelling is the next stage of the manufacturing process, which is based on separating the printed circuit matrix into individual boards. We carry out it using technology, which depends on the way of panelling planned in the project.

– The separation of the PCBs can take place in different stages of the production process – after the SMT or THT assembly stage, after quality tests, and even before the circuit assembly itself in the target device. At Comarch IoT Plant, we have tools that enable depanelling of scored and milled multiblocks, such as CAB Maestro 2, CAB Hektor 2 or Asys Divisio 2100 Ergo – adds Mateusz Rosek.

What are the most common methods of PCB depanelling?

Cutting the panels with the CAB Maestro 2 punch

The Maestro tool can be used to depanel the V-CUT arrays, which, due to the two adjustable cutting plates, allows the parameters to be adjusted to the thickness of the PCB. This allows you to cut both very thin and very thick laminates. This is the fastest and cheapest way to depanel. This method of separation is to push the panel between the cutting plates, guiding them through the notches made in the PCB production process. This is recommended for printed circuit boards of very small sizes, which are particularly vulnerable to damage using other tools. 

– In the case of scoring, placing components flush with the edge of the PCB or outside the outline of the PCB makes it very difficult or even impossible to cut the panel, because the plates simply cannot cut the part of the laminate on which the obstacle is located. If this happens, the only way to separate the boards is to break them gently by hand. Despite the utmost care, this action may result in PCB damage. That is why it is important to design a good panel and, for example, to use cutouts in the vicinity of the connectors so that the plates do not reach them, or the spacing between individual PCBs – explains Mateusz Rosek.

CAB Hektor 2

Hektor is a pneumatic knife used for manual breaking of perforated bridges. Position the depanelled plate on the supports so that the cutting edge of the knife is above the bridge. The tool can handle laminates with a thickness of 2 mm without any problems. As in the case of punching, it is problematic to place bridges close to or directly below the connectors. Due to the length of the knife, it is necessary to provide a minimum of 12 mm of empty trimming path through which the knife must be moved.

– In the case of tiles with very irregular shapes, this can be difficult to achieve. In this case, it is not possible to position the board on the supports. Another risk is the dense application of components close to the edge of the PCB in the immediate vicinity of the bridges, basing the panel on the elements is not advisable and may damage them. Depanelling using the Hektor tool is safer than milling in the case of small tiles panelled on bridges – says Mateusz Rosek.

Asys Divisio 2100 Ergo milling machine

When we are dealing with panelled boards on non-perforated bridges, and where, despite the use of perforated bridges, there is no approach for the Hektor type hand depanelling knife, it is necessary to use a Divisio milling machine. To cut the laminate tabs on the milling machine, start with the preparation of the program for the CNC machine. For this purpose, a DXF file is generated from the selected layers of Gerber files containing the milling path on the routing layer, the outline of the entire panel and individual tiles and holes that can be useful for placing the pins fixing the panel in the machine. Then key parameters such as panel dimensions, single board dimensions, spacing between successive plates in X and Y axes, as well as fiducial coordinates are saved.

Then the DXF file prepared in this way is loaded in the CAM software, where bridge milling paths are created, as well as positioning the so-called support pins – pins supporting the PCB and holding them after milling. After preparing the file, G-CODE is generated – a CNC machine code, on the basis of which the machine places pins and performs milling. In the next step, a new program is created in the interface of the milling machine for a specific product, into which basic data such as panel dimensions, fiducial coordinates are entered and G-CODE is imported.

– Once the program is complete, you can start to set the pins – the machine automatically picks them from the bank with a vacuum gripper and places them in the places stored in the program. When the panel is mounted on the table, a simulation is run to ensure that all cutting paths are in the correct positions and that the mill does not collide with the components on the plate. As in the case of previous methods, it is recommended to move the bridges away from the connectors – comments Mateusz Rosek.

Cutting very small PCBs is a challenge for two reasons. The first is the technological limitation caused by the diameter of the base of the pins. In the case of tiles placed close together in the panel, it is difficult to properly position the dowels in a way that will provide sufficient support for the tiles. Sometimes one panel has to be divided into several programs to provide enough space for the placement of pins. The second factor is the vacuum, which takes up dust created during milling. The vacuum can cause an extremely small insert to be sucked into the wire or, worse, it can catch on the tool and, rotating with the mill, start to hit the next board, causing damage.

– In such cases, if the perforation of the bridges is used, it is a good idea to leave one bridge (you can also cut the bridge, for example, halfway) and break it using the Hektor depanellizer. The alternative would be a very careful manual break. The saved program can be loaded when launching another batch of the same product, and then proceed to depanelling – adds Mateusz Rosek.

Summary

PCB panelling offers a number of advantages, such as process optimization in automated production and testing, and with it – saving time and reducing costs. The proper implementation of PCB panelling – from the design stage, through the choice of method, to the execution – must take into account a number of factors that determine the safety of subsequent separation of boards for their further use.

This is perfectly understood by the team of experienced Comarch IoT Plant engineers, who as part of PCBA assembly services use equipment that allows depanelling using the most effective tools. From the design stage to the subsequent implementation, our goal is the final success of the project. You can read more about the support that we can give your company on the main Comarch IoT Plant website.