PCB Blog - Methods of Flex cut PCB

The structure of flex cut PCB products is composed of a soft copper foil substrate and a soft insulation layer, which are bonded with adhesive and pressed together, and have many advantages that hard circuit boards do not have. By utilizing flexible circuit boards, the volume of electronic products can be greatly reduced, which is suitable for the development of electronic products towards high density, high reliability, and miniaturization. Especially under the current wave of 5G replacement, the production capacity of soft boards will jump, and laser cutting of soft boards will drive the rapid development of 5G terminal products.

Flex-cut PCB

The flex-cut PCB using traditional mechanical punching machines is prone to burrs and delamination. Due to the need to produce molds, it takes a long time to produce samples and small to medium-sized batch production, and high-precision molds are quite expensive. Using UV laser cutting can avoid these problems, with high flexibility and simple graphic design.

The forming method for soft boards generally includes drying punching, cutting, and manual forming. Choose different molding methods based on the number of flexible circuit boards required, the accuracy, and the delivery time required by customers.

Three common forming processes

1. Die stamping

Die punching forming is the main process of using molds to cut and process semi-finished flex-cut PCB, creating a soft board shape. Different soft board products require different molds.

1) The molds are divided by material, including steel molds and knife molds.

Steel molds are made of steel with high accuracy, and multiple stamping times, and are not easily deformed. They are the most commonly used molds. Due to their heavy weight, they often need to be moved during installation, and the cost is relatively high. Therefore, steel molds are generally used for flexible PCB punching of not-too-large flexible PCB with dimensions within 600mm; The steel mold is composed of an upper mold and a lower mold, with the lower mold as the base and the upper mold as the punching and cutting mold.

The blade mold is light in weight and low in cost, made of wood and steel blades with low accuracy. It is generally only suitable for forming products and auxiliary materials that do not have strict requirements for appearance accuracy, such as soft plate reinforcement sheets.

2)  According to accuracy, there are precision molds, ordinary molds, and simple molds.

This involves three production methods for soft board forming molds, namely slow wire, medium wire, and fast wire.

The mold made by slowly threading is a precision mold with an accuracy tolerance of ± 0.05mm. The steel is of good quality and not easily deformed, but it is expensive and takes a long time to make.

The mold made by wire cutting is a regular mold with an accuracy tolerance of ± 0.10mm, which can meet most needs. The price is moderate, and the performance is stable. It is the type of mold that is commonly chosen.

The mold made by fast threading is a simple mold with an accuracy of ± 0.2mm, which is slightly cheaper than ordinary molds. Generally, this mold opening method is only chosen for products with low requirements for appearance tolerance.

After the mold is installed to the punch, it is necessary to adjust the punching height of the mold with a test plate to select the most suitable punching force, to ensure that the flex-cut PCB can be separated according to the outline design drawing, and at the same time, it will not damage the soft plate cutting other parts that do not need punching.

According to the size of the soft board, the mold often adopts a one-out multiple methods, that is, stamping once to form multiple soft boards, thereby improving production efficiency. During the production process, without changing the appearance design of the soft board, the mold only needs to be made once and can be reused later, making it suitable for mass production and reducing unit production costs.

2. Cutting and forming

Generally only used for sample and very small batch production. Cutting forming includes CNC knife cutting forming and laser forming.

CNC cutting, input the cutting diagram into the computer, fix the flex-cut PCB assembly on the device according to the positioning hole, and move the cutting head on the device according to the drawing line to cut the soft board into the specified shape.

This cutting method, due to the small volume of the blade itself and the easy damage of the blade head, results in poor accuracy of the processed soft plate, long processing time, and improper adjustment of depth, which can lead to excessive burrs and incomplete cutting. Before the emergence of laser cutting machines, it was generally only used for cutting and forming soft plate samples, protective films, and electromagnetic films.

With the popularization of laser cutting machines, due to their high accuracy (≤ 0.05mm), smooth and square cutting surfaces, fewer burrs, and faster speed than cutting, they have replaced the CNC cutting method. Currently, the vast majority of flex-cut PCB samples are produced using laser cutting methods.

It should be noted that laser cutting uses high-energy red/ultraviolet wire harnesses for processing, so there may be burning marks on the cutting surface. To avoid affecting the appearance after production, it is best to use a dust-free cloth and alcohol to wipe.

3. Hand forming

The shape of the Flex board is manually formed using scissors and pens, which are only used for very few products that do not require precision in appearance.

In the production of flex-cut PCB, forming is the process before quality inspection and packaging, and it is also the last step in the production process. The above are several methods for forming soft boards, as well as their respective advantages, disadvantages, and usage environments. Regardless of the type of soft board produced, to meet the quality requirements of the product, it is necessary to attach great importance to the forming process of the soft board shape.

The use of laser technology for flex-cut PCB is currently the mainstream method and also a future trend. Laser cutting is a flexible and automated processing method. The high-precision processing effect and flexible and controllable processing process make it irreplaceable in the flex-cut PCB processing process. In addition, compared to mechanical stress processing, laser cutting has the advantage of lower losses during processing. Laser cutting is a non-contact process that does not consume cutting tools. The pace of automated production is short, the cutting speed is fast, and it can significantly reduce manufacturing costs in mass production.