/How to control the distance between two components during PCB assembly
When assembling PCB, we should take into account that there is a certain error when assembling the machine, and take into account the convenience of maintenance and visual appearance inspection, the adjacent parts and components should not be too close, and a certain safety distance should be left.So how close are the two components going to be?
In addition to ensuring the safety gap between the welding pads, the maintainability requirements of vulnerable components should also be considered.General assembly density requirements are as follows:
1.Between the chip components, between the SOT, between the SOIC and the chip components is 1.25mm.
2.Between SOIC and QFP is 2mm:
3.Between PLCC and chip components, SOIC and QFP is 2.5mm:
4.Between PLCC is 4mm.
5.When the assembly is mixed, the distance between the insert and the disc is 1.5mm.
6.When designing a PLCC socket, be careful to leave the size of the PLCC socket body (because the PLCC pin is inside the bottom of the socket body).
Rules for component layout
Under the condition of design permission, the layout of the components in SMT processing should be arranged in the same direction as far as possible, and the modules with the same functions should be arranged together.The same packaging components are placed equidistant for fitting, welding and testing.
Safe distance between components
QFP, PLCC.The common feature of these two devices is four-edge lead encapsulation, the difference is the shape of the lead has some differences.QFP is gull-wing lead, PLCC is j-lead.Because of the packaging of four-edge lead, wave soldering process cannot be used.
QFP and PLCC devices are usually distributed on the component surface of PCB board. If the cloth is to be re-refluxed on the welding surface, its weight must meet the requirement that the weight of welding Angle contact surface per square inch should be less than 30 grams.
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