As an indispensable part of electronic products, PCB plays a key role in realizing the functions of electronic products, which leads to the increasing importance of PCB design, because the performance of PCB design directly determines the function and cost of electronic products. A good PCB design can keep electronic products away from many problems, thus ensuring that the products can be manufactured smoothly and can meet all the needs of practical applications.
Of all the elements that contribute to PCB design, Design for Manufacturing (DFM) is absolutely essential as it links PCB design to PCB manufacturing so that problems can be detected early and resolved in a timely manner throughout the life cycle of an electronic product. The complexity of PCB design will increase as the manufacturability of electronic products is considered at the PCB design stage. In the life cycle of electronic product design, DFM can not only enable electronic products to smoothly participate in automated production and save labor costs in the manufacturing process, but also effectively shorten the manufacturing production time to ensure the timely completion of final electronic products.
Due to the combination of manufacturability and PCB design, manufacturing design is a key element leading to efficient manufacturing, high quality and low cost. The scope of PCB manufacturability research is broad and can generally be divided into PCB manufacturing and PCB assembly.
As far as PCB manufacturing is concerned, the following aspects should be considered: PCB size, PCB shape, process edge and Mark points. Once these aspects are not fully taken into account at the PCB design stage, automated chip mounters may not be able to accept prefabricated PCBs unless additional processing measures are taken. To make matters worse, some boards cannot participate in automated manufacturing with manual soldering. As a result, the manufacturing cycle will be extended and labor costs will also increase.
1. PCB size
Each chip mounter has its own required PCB size, which varies according to the parameters of each mounter. For example, the maximum PCB size accepted by the chip mounter is 500mm*450mm, while the minimum PCB size is 30mm*30mm. That doesn't mean we can't handle PCB assemblies smaller than 30mm*30mm, and when smaller sizes are required, we can rely on paneling. Chip mounters will never accept a PCB that is too large or too small when it can only rely on manual installation and labor costs rise and the production cycle runs out of control.
Therefore, in the PCB design stage, the PCB size requirements set by the automatic mounting manufacturing must be fully considered and must be controlled within the effective range. As a 5x2 panel, each square unit is a single board with a size of 50mm*20mm. The connection between each unit is achieved by V-cut/V-scoring technology. In this image, the entire square is shown with a final size of 100mm * 100mm. According to the above panel size requirements, it can be concluded that the panel size is within the acceptable range.
2. PCB shape
In addition to PCB size, all chip mounters have requirements for PCB shape. A common PCB shape should be a rectangle with a length to width ratio of 4:3 or 5:4 (best). If the shape of the PCB is irregular, additional measures must be taken before SMT assembly, resulting in increased costs. To prevent this from happening, the PCB must be designed in a common shape during the PCB design phase in order to meet the SMT requirements. However, it is difficult to do this in a practical situation. When the shape of some electronic products must be irregular, stamp holes must be used to make the shape of the final PCB have a normal shape. After assembly, redundant auxiliary baffles can be omitted from the PCB to meet automatic installation and space requirements.
Irregularly shaped PCBs with processing edges added by associated software. The whole board size is 80mm*52mm, and the square area is the size of the actual PCB. The size of the upper right area is 40mm * 20mm, which is the secondary craft edge created by the bridging of the stamp holes.
3. Craft side
To meet the needs of automated manufacturing, process edges must be placed on the PCB to hold the PCB. In the PCB design stage, a 5mm wide process edge should be reserved in advance, without leaving any components and traces. Technical rails are usually placed on the short side of the PCB, but the short side can be selected when the aspect ratio exceeds 80%. Once assembled, the crafting side can be dismantled as an auxiliary production role.
4. Reference point (Mark point)
For PCBs with components mounted, Mark points should be added as common reference points to ensure that each assembly device can accurately determine the component location. Therefore, the Mark point is the SMT manufacturing benchmark required for automated manufacturing.
Components need 2 Mark points, while PCB needs 3 Mark points, these marks should be placed on the edge of the PCB board and cover all SMT components. The center-to-center distance between the Mark point and the edge of the board should be at least 5mm. For PCBs with double-sided SMT components, there should be Mark points on both sides. If components are placed too densely to place Marks on the board, they can be placed on the craft side.
PCB Assembly, or PCBA for short, is actually the process of soldering components on a bare board. To meet the requirements of automated manufacturing, PCB assembly imposes several requirements on component packaging and component layout.
1. Component packaging
During the PCBA design process, if the component packages do not meet the proper standards and the components are too close together, automatic mounting will not take place.
In order to obtain the best component packaging, professional EDA design software should be used to be compatible with international component packaging standards. During the PCB design process, the bird's eye view area must not overlap with other areas, and the automatic IC placement machine will be able to accurately identify and surface mount it.
2. Component layout
Component placement is an important task in PCB design, as its performance is directly related to the appearance of the PCB and the complexity of the manufacturing process.
During the component layout process, the mounting surface of SMD components and THD components should be determined. Here, we set the front side of the PCB to be the component A side and the back side to be the component B side. Component layout should consider the form of assembly, including single-layer single-pack assembly.
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