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PCB shape design

2022-04-01

PCB shape design

Most professional PCB development and design sharing

In terms of PCB manufacturing and PCBA semi-finished product processing, it is suggested that the shape of PCB should be designed as a regular square, and irregular shapes should be avoided as far as possible, such as notched plate with large area, circle, triangle, etc.

From the aspect of PCB manufacturing, it will lead to the waste of board materials, which directly leads to the increase of cost, and is not conducive to the production of board factory. In terms of PCBA manufacturing, it will lead to inconvenient patch or furnace welding, because there is no suitable plate edge support or tin infiltration. If it is necessary to use irregular shape due to installation or design needs, we need to find a way to design the irregular shape into regular shape, fill the gap with splicing board, and put the irregular board into the regular board before splicing.

Selection of plate thickness: plate thickness generally refers to the thickness of finished plate (including copper foil, coating and solder resist). The commonly used substrate thickness is 0.5, 0.8, 1.0, 1.2, 1.6 and 2.0mm, with an error of ± 10%. The product thickness is mainly determined according to the product structure. 1.6mm is the most conventional thickness, and the thinner thickness is 1.2 and 1.0mm. The thinner, the lower the strength.
The plate thickness is inversely proportional to the difficulty of copper deposition. The thicker the plate, the longer the copper deposition channel. For holes with smaller pore diameter, the greater the difficulty of copper deposition, and the higher the defect rate and cost. Generally, the ratio of plate thickness to hole diameter shall be less than 8:1. For example, for a plate thickness of 1.6mm, the hole diameter is safer at 0.25mm. If the hole to be made is less than 0.25mm, the plate thickness shall be controlled below 1.2mm as much as possible. Therefore, when selecting the plate thickness, in addition to considering the structural installation strength, the hole diameter also needs to be paid attention to.
The thickness of multi-layer plate is mainly composed of the thickness of core plate plus insulating sheet and copper sheet. When the thickness of core plate is confirmed, it is generally adjusted by adjusting the insulating sheet (PP sheet) to achieve the required thickness, and the thickness of PP sheet directly affects the withstand voltage, insulation and impedance.

PCBA processing and production quality and efficiency are closely related to the design method of PCB circuit board itself. Good design can solve the problems of processing and production quality, efficiency and even cost. If the PCB design is not standardized or the problems are not considered comprehensively, it will seriously affect the production quality and efficiency, and directly or indirectly lead to the improvement of production cost.

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