11. Stress-sensitive components should not be placed at the corners, edges, or near connectors, mounting holes, grooves, cutouts, gashes and corners of printed circuit boards. These locations are high stress areas of printed circuit boards, which can easily cause cracks or cracks in solder joints and components.
12. The layout of components shall meet the process and spacing requirements of reflow soldering and wave soldering. Reduces shadow effect during wave soldering.
13. Printed circuit board positioning holes and fixed support should be set aside to occupy the position.
14. In the design of large area printed circuit board of more than 500cm2, in order to prevent the printed circuit board from bending when crossing the tin furnace, a gap of 5~10mm wide should be left in the middle of the printed circuit board, and the components (can walk) should not be put, so as to prevent the printed circuit board from bending when crossing the tin furnace.
15. The component layout direction of reflow soldering process.
（1） The layout direction of the components should consider the direction of the printed circuit board into the reflow furnace.
（2）in order to make the two end of chip components on both sides of the weld end and SMD components on both sides of the pin synchronization is heated, reduce the components on both sides of the welding end does not produce the erection, shift, synchronous heat from welding defects such as solder welding end, require two end of chip components on printed circuit board long axis should be perpendicular to the direction of the conveyor belt of the reflow oven.
（3）The long axis of SMD components should be parallel to the transfer direction of the reflow furnace. The long axis of CHIP components and the long axis of SMD components at both ends should be perpendicular to each other.
（4）A good layout design of components should not only consider the uniformity of heat capacity, but also consider the direction and sequence of components.
（5）For large size printed circuit board, in order to keep the temperature on both sides of the printed circuit board as consistent as possible, the long side of the printed circuit board should be parallel to the direction of the conveyor belt of the reflow furnace. Therefore, when the printed circuit board size is larger than 200mm, the requirements are as follows:
（A） the long axis of the CHIP component at both ends is perpendicular to the long side of the printed circuit board.
（B）The long axis of the SMD component is parallel to the long side of the printed circuit board.
(C)For the printed circuit board assembled on both sides, the components on both sides have the same orientation.
(D)Arrange direction of components on the printed circuit board. Similar components should be arranged in the same direction as far as possible, and the characteristic direction should be the same, so as to facilitate the installation, welding and detection of components. If electrolytic capacitor positive pole, diode positive pole, transistor single pin end, the first pin of integrated circuit arrangement direction is consistent as far as possible.
16. In order to prevent short circuit between layers caused by touching the printed wire during PCB processing, the conductive pattern of inner layer and outer layer should be more than 1.25mm from PCB edge. When a ground wire has been placed on the edge of the outer PCB, the ground wire can occupy the edge position. For PCB surface positions that have been occupied due to structural requirements, components and printed conductors should not be placed in the underside solder pad area of SMD/SMC without through holes, so as to avoid the diversion of solder after being heated and remelted in wave soldering after reflow soldering.
17. Installation spacing of components: The minimum installation spacing of components must meet the requirements of SMT assembly for manufacturability, testability, and maintainability.
Post time: Dec-21-2020