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several issues that should be considered when making pcb



PCB production needs to consider aspects such as PCB size, PCB shape, clamping edge, and MARK point. In some PCB designs, because the actual requirements of the automated processing and production stage are not fully considered, the produced PCBs cannot be immediately put into the automated placement machine for placement production and processing, but need to make additional tooling and other methods for automated production. , Even some PCB designs cannot be automated at all and can only be welded manually, which will not only lead to the extension of the entire product period, but also increase the labor cost.

One. PCB size

The existing placement machine equipment has certain requirements for PCB size, the maximum size is 460mm×460mm, and the minimum size is 50mm×50mm. If the size is too large or too small, it cannot be put into the placement machine equipment for normal placement processing. Manual placement is required, which not only increases labor costs, but also the production cycle cannot be controlled. Therefore, in the PCB design process, it is necessary to fully consider the requirements of the later automated patch production on the PCB size, and design the PCB size within an effective range. If the PCB size is too small, it is necessary to adopt an imposition method in the PCB design process. The design is within the effective range.

Figure 1 shows the effect of PCB imposition using EDА software. This board is a 3×2 imposition, in which the square area is a single board size of 35mm×30mm, and the v-cut process is used to connect the veneer to the veneer. The blue area is the size after the imposition of 70mm×60mm. The PCB size after imposition meets the requirements of automated placement machines for placement and production.

QQ screenshot 20200513144835.jpg

Two, PCB shape

The existing placement machine equipment also has certain requirements for the shape of the PCB, requiring the PCB to be a regular rectangle, and the length-to-width ratio of 4:3 or 5:4 is the best. If the PCB is an irregular pattern, it is necessary to make auxiliary tooling before the automated patch production, which will increase the production cost. In order to avoid this situation, the PCB is designed into a regular shape to meet the requirements of patch production. However, in some products, due to the limitation of structural space, etc., the final PCB shape is required to be an irregular shape. Therefore, the stamp hole + bridge is used to increase the process edge in the later stage of the PCB design. The part is removed from the PCB. This not only does not affect the requirements of automated placement, but also meets the requirements of structural space.

Figure 2 shows the effect of adding process edges to the irregular PCB by using the EDА tool. The size of this board is 75mm×48mm. The square area represents the actual PCB size. The square area in the upper right corner is the process edge added by the stamp hole + bridging process, and the size is 40mm×9mm.

QQ screenshot 20200513144847.jpg

Three, clamping edge

In order to meet the requirements of automated assembly line production, a clamping edge for automated production must be arranged on the PCB to fix the PCB.

During the PCB design process, it is necessary to reserve a 5mm width prohibition area on the clamping edge of the board. The front and back of this area are forbidden to place placement components, and it is best not to wire. Usually the two long sides of the printed board are used as clamping sides. For printed boards with a ratio of the short side to the long side greater than 80%, the short side can also be used as the clamping side. The clamping edge is only to assist in the production of the increased part of the PCB edge, which can be removed after the production is completed. The clamping edge does not need to be added in pairs, only the plate edge that does not meet the 5mm clamping width requirement is added. Figure 3 is a schematic diagram of adding clamping edges on the two long sides of the PCB.

QQ screenshot 20200513144856.jpg

Four. Optical positioning points

For PCBs with mounted components, attention should also be paid to the addition of optical positioning points. The optical positioning points are also called mark points, which provide a common reference point for all steps in the assembly process to ensure that each device used in the assembly can be accurately positioned The location of the component. The mark point is the reference point of SМТ production, so the mark point is necessary for automated processing and production.

The optical positioning marks of the components need two, but the optical positioning marks of the PCB need three. It is best to place them on the edge of the board and try to cover all the patch components. The center of the mark point is at least 5mm away from the edge of the board. The two mark points on the opposite corners should be placed asymmetrically in the center. If there are mounting components on both sides, optical positioning marks should be placed on each side. If the devices are densely arranged and the mark points cannot be placed on the PCB, the mark points can be placed on the edge of the process.