[Repost] The impact and requirements of different manufacturing processes on the pads on PCB

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[Repost] The impact and requirements of different manufacturing processes on the pads on PCB [Copy link]

1. If there is no plug-in component connected to the two ends of the SMD component, a test point must be added. The diameter of the test point should be between 1.0mm and 1.5mm to facilitate the online tester test. The edge of the test point pad should be at least 0.4mm away from the edge of the surrounding pad. The diameter of the test pad should be more than 1mm and must have network attributes. The center distance between the two test pads should be greater than or equal to 2.54mm; if a via is used as a measurement point, a pad must be added outside the via with a diameter of 1mm (inclusive) or more. 2. Pads must be added to the locations of holes with electrical connections; all pads must have network attributes, and the network names of networks without connected components cannot be the same; the distance between the center of the positioning hole and the center of the test pad is more than 3mm; other irregular shapes but with electrical connection slots, pads, etc. are uniformly placed on mechanical layer 1 (referring to slotted holes such as single plug-ins and fuses).

3. If the pads of the component feet with dense pin spacing (pin spacing less than 2.0mm) (such as: IC, swing socket, etc.) are not connected to the hand plug-in pad, a test pad must be added. The diameter of the test point should be between 1.2mm and 1.5mm to facilitate the online tester test.

4. If the pad spacing is less than 0.4mm, white oil must be applied to reduce continuous welding during the wave peak.

5. The two ends and ends of the patch components of the dispensing process should be designed with tinning. The width of the tinning is recommended to use a 0.5mm wire, and the length is generally 2 or 3mm.

6. If there are hand-soldered components on a single-sided board, the tin bath should be opened in the opposite direction of the tinning direction, and the width of the viewing hole should be 0.3mm to 0.8mm;

7. The spacing and size of the conductive rubber buttons should be consistent with the actual size of the conductive rubber buttons. The PCB board connected to it should be designed as a gold finger, and the corresponding gold plating thickness should be specified (generally required to be greater than 0.05um~0.015um).

8. The size and spacing of the pads should match the size of the SMD components. a. Unless otherwise specified, the shape of the component hole, the pad and the component foot must match, and the symmetry of the pad relative to the center of the hole must be ensured (square component feet match square component holes and square pads; round component feet match round component holes and round pads), and adjacent pads must remain independent to prevent thin tin and wire drawing; b. Adjacent component feet in the same circuit or compatible devices with different PIN spacing must have separate pad holes, especially the compatible pads of package-compatible relays must be connected. If separate pad holes cannot be set due to PCB LAYOUT, the two pads must be surrounded by solder resist.

9. When designing a multilayer board, please note that for components with metal shells, when the shell contacts the printed board during the plug-in process, the top pads cannot be opened and must be covered with green oil or silk screen oil (e.g. a two-pin crystal oscillator, a three-pin LED).

10. When designing and laying out the PCB board, try to reduce the slots and holes in the PCB board to avoid affecting the strength of the PCB.

11. Precious components: Precious components should not be placed at the corners, edges, mounting holes, slots, cuts and corners of the PCB. These locations are high-stress areas of the PCB board, which can easily cause cracks and cracks in solder joints and components.

12. Heavier devices (such as transformers) should not be placed far away from the positioning holes to avoid affecting the strength and deformation of the printed circuit board. When laying out, heavier devices should be placed at the bottom of the PCB (which is also the last side to enter the wave soldering).

13. Devices that radiate energy, such as transformers and relays, should be kept away from amplifiers, microcontrollers, crystal oscillators, reset circuits and other devices and circuits that are easily disturbed to avoid affecting the reliability during operation.

14. For QFP packaged ICs (which require wave soldering technology), they must be placed at 45 degrees and tinned.

15. When the chip components are wave soldered, the board around the plug-in components (such as heat sinks, transformers, etc.) and below the body should not have heat dissipation holes to prevent the tin on the wave crest 1 (spoiler wave) from sticking to the upper board parts or part feet during the wave soldering, and generating foreign matter in the machine during the assembly in the later process.

16. Large area copper foil requires to be connected to the pad with insulation tape. In order to ensure good tin penetration, the pads of components on large copper foil areas are required to be connected to the pads with insulation tape. For pads that need to pass large currents of more than 5A, insulation pads cannot be used;

17. In order to avoid the deviation and tombstone phenomenon of the device after reflow soldering, the pads at both ends of the reflow soldered 0805 and 0805 chip components should ensure heat dissipation symmetry, and the width of the connection between the pad and the printed conductor should not be greater than 0.3mm (for asymmetric pads).

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