The layout of components should be designed in accordance with the characteristics and requirements of SMT electronic processing and production equipment and technology. Different processes, such as reflow soldering and wave soldering, demand distinct component arrangements. In double-sided reflow soldering, the A side and the B side require different layouts. Similarly, selective wave soldering and traditional wave soldering impose varying layout demands.
The distribution of components on the printed circuit board (PCB) should strive for uniformity. High-quality components possess significant heat capacity during reflow soldering. Excessive concentration may lead to localized low temperature and false soldering. Additionally, uniform layout aids in maintaining center of gravity balance, preventing component and metallized hole/pad damage.
Components on the PCB should be oriented consistently. Similar components should align in the same direction to facilitate mounting, welding, and testing. For instance, electrolytic capacitor anodes, diode anodes, single-pin ends of triodes, and integrated circuit first pins should ideally face the same direction. All component numbers should be printed uniformly.
Space around large components should accommodate the size of the heating head of SMD rework equipment.
Heating components should be isolated from other components, preferably positioned in chassis corners or ventilated areas. They should be supported by leads or other means to maintain distance from the PCB surface, with a minimum of 2mm. Multilayer boards should feature metal pads connecting heating component bodies to the PCB, allowing heat dissipation.
Temperature-sensitive components should be kept away from heating components, such as triodes, integrated circuits, and electrolytic capacitors.
Components requiring adjustment or frequent replacement, like potentiometers or fuses, should be placed for easy access. Internal adjustments should locate components for easy access on the PCB, while external adjustments should align with chassis panel knobs to avoid spatial conflicts.
Fixing holes should be near terminals, plug-in parts, or areas prone to force, with sufficient space to prevent deformation due to thermal expansion. For example, long series of terminals require adequate space around fixing holes to prevent warping during wave soldering.
Components requiring secondary processing due to size tolerances should be separated, with added margins.
Electrolytic capacitors should not touch heating components, with a minimum distance of 10mm between capacitors and heat sinks. Stress-sensitive components should avoid high-stress areas of the PCB to prevent damage.
Component layout must adhere to process and spacing requirements for reflow soldering and wave soldering, minimizing shadow effects during wave soldering.
Positioning holes and fixed brackets on the PCB should be reserved.
Large-area PCBs should include a 5~10mm gap in the middle to prevent bending during wave soldering.
The direction of component placement should consider the PCB’s entry into the reflow oven.
To mitigate soldering defects like tombstoning, the long axis of two-end chip components should be perpendicular to the reflow oven’s conveyor belt direction.
The long axis of SMD components should align with the reflow oven’s conveyor belt, with perpendicular alignment between two-end chip components and SMD components.
Besides heat capacity uniformity, component layout should consider orientation and order.
For large PCBs, alignment with the reflow oven conveyor belt ensures consistent temperature on both sides.
To prevent short circuits, the distance between conductive patterns on the PCB edges should exceed 1.25mm. Ground wires on the PCB outer layer can occupy edge positions. Areas occupied by structural requirements should not accommodate components or printed wires.
There should be no through holes in the bottom pad area of SMD/SMC to avoid solder remelting in wave soldering.
Component installation spacing should meet SMT assembly requirements for manufacturability, testability, and maintainability.
The distribution of components on the printed circuit board (PCB) should strive for uniformity. High-quality components possess significant heat capacity during reflow soldering. Excessive concentration may lead to localized low temperature and false soldering. Additionally, uniform layout aids in maintaining center of gravity balance, preventing component and metallized hole/pad damage.
Components on the PCB should be oriented consistently. Similar components should align in the same direction to facilitate mounting, welding, and testing. For instance, electrolytic capacitor anodes, diode anodes, single-pin ends of triodes, and integrated circuit first pins should ideally face the same direction. All component numbers should be printed uniformly.
Space around large components should accommodate the size of the heating head of SMD rework equipment.
Heating components should be isolated from other components, preferably positioned in chassis corners or ventilated areas. They should be supported by leads or other means to maintain distance from the PCB surface, with a minimum of 2mm. Multilayer boards should feature metal pads connecting heating component bodies to the PCB, allowing heat dissipation.
Temperature-sensitive components should be kept away from heating components, such as triodes, integrated circuits, and electrolytic capacitors.
Components requiring adjustment or frequent replacement, like potentiometers or fuses, should be placed for easy access. Internal adjustments should locate components for easy access on the PCB, while external adjustments should align with chassis panel knobs to avoid spatial conflicts.
Fixing holes should be near terminals, plug-in parts, or areas prone to force, with sufficient space to prevent deformation due to thermal expansion. For example, long series of terminals require adequate space around fixing holes to prevent warping during wave soldering.
Components requiring secondary processing due to size tolerances should be separated, with added margins.
Electrolytic capacitors should not touch heating components, with a minimum distance of 10mm between capacitors and heat sinks. Stress-sensitive components should avoid high-stress areas of the PCB to prevent damage.
Component layout must adhere to process and spacing requirements for reflow soldering and wave soldering, minimizing shadow effects during wave soldering.
Positioning holes and fixed brackets on the PCB should be reserved.
Large-area PCBs should include a 5~10mm gap in the middle to prevent bending during wave soldering.
The direction of component placement should consider the PCB’s entry into the reflow oven.
To mitigate soldering defects like tombstoning, the long axis of two-end chip components should be perpendicular to the reflow oven’s conveyor belt direction.
The long axis of SMD components should align with the reflow oven’s conveyor belt, with perpendicular alignment between two-end chip components and SMD components.
Besides heat capacity uniformity, component layout should consider orientation and order.
For large PCBs, alignment with the reflow oven conveyor belt ensures consistent temperature on both sides.
To prevent short circuits, the distance between conductive patterns on the PCB edges should exceed 1.25mm. Ground wires on the PCB outer layer can occupy edge positions. Areas occupied by structural requirements should not accommodate components or printed wires.
There should be no through holes in the bottom pad area of SMD/SMC to avoid solder remelting in wave soldering.
Component installation spacing should meet SMT assembly requirements for manufacturability, testability, and maintainability.
