Component Layout Design for SMT Chip Processing (2)

About the components and parts that need to be adjusted or replaced frequently, such as potentiometers, adjustable inductance coils, variable capacitor micro switches, fuses, buttons, plug-ins and other components, we should consider the structural requirements of the whole machine and put them in a position for easy adjustment and replacement. If it is adjusted inside the machine, it should be placed on the printed circuit board where it is easy to adjust. If it is adjusted outside the machine, its position should be adapted to the position of the adjustment knob on the chassis panel to prevent conflicts between three-dimensional space and two-dimensional space. For example, the panel opening of the toggle switch and the vacant position of the switch on the printed circuit board should match.

Fixing holes should be provided near the terminals, plug-in parts, the center of the long string terminals and the parts that are often subjected to force, and there should be a corresponding space around the fixing holes to prevent deformation due to thermal expansion. For example, the thermal expansion of the long string terminals is more serious than that of the printed circuit board, and it is prone to warping during wave soldering.

Some components and parts such as transformers, electrolytic capacitors, varistors, bridge stacks, radiators, etc. that have large tolerances and low precision in volume (area) and require secondary processing, and other components are at the original interval. On the basis of the setting, add a certain margin.

It is recommended to increase the margin of electrolytic capacitors, varistors, bridge stacks, polyester capacitors not less than 1mm, and transformers, radiators and resistors exceeding 5W (including 5W) should not be less than 3mm.

Electrolytic capacitors should not touch heating components, such as high-power resistance thermistors, transformers, radiators, etc. The minimum distance between the electrolytic capacitor and the radiator is 10mm, and the minimum distance between other components and the radiator is 20mm.

Do not place stress-sensitive components on the corners, edges, or near connectors, mounting holes, slots, cuts, gaps, and corners of the printed circuit board. These locations are high-stress areas of the printed circuit board. It is easy to cause cracks in solder joints and components.

The component layout should meet the process requirements and spacing requirements of reflow soldering and wave soldering. Reduces shadowing effects during wave soldering.

The positioning holes of the printed circuit board and the positions to be occupied by the fixing brackets should be reserved.

In the design of large-area printed circuit boards with an area of ​​more than 500cm2, in order to prevent the printed circuit board from bending when passing through the tin furnace, a 5~10mm wide gap should be left in the middle of the printed circuit board, and no components (can be routed), to be used to add a bead to prevent the printed circuit board from bending when passing through the tin furnace.