The arrangement of components must not only fulfill the electrical performance and mechanical structure requirements of the entire device but also align with the SMT production process standards. Since design-related quality issues are challenging to rectify during production, PCB design engineers should possess a fundamental understanding of SMT process characteristics and arrange component layouts according to the specific processes. Proper design can significantly reduce soldering defects.

1. Circuit design requirements for component layout

The layout of components significantly affects PCB performance. During circuit design, large circuits are typically segmented into unit circuits, with each unit’s position organized according to the signal flow direction. It is essential to avoid the overlap of input/output signals and different voltage levels; the signal flow should be orderly, maintaining as much consistency in direction as possible. This approach facilitates fault detection.


2. SMT Process Requirements for Component Layout Design

The arrangement of components must be designed according to the characteristics of SMT production equipment and processes. Depending on the method used, such as reflow soldering or wave soldering, the layout requirements will vary. Additionally, when dealing with double-sided reflow soldering, distinct layout requirements exist for both the primary and secondary surfaces.

How to achieve a reasonable PCB layout design and what are the requirements:

(1) The distribution of PCB components should be as uniform as possible.

(2) Similar components should be oriented in the same direction wherever feasible, with consistent alignment of characteristic directions to facilitate mounting, soldering, and testing.

(3) Adequate maintenance space should be maintained around larger components, ensuring the size of the SMD rework equipment’s heater head can be operated effectively.

(4) Heating elements should be positioned as far from other components as possible, ideally located in corners and well-ventilated areas within the chassis.

(5) Keep temperature-sensitive components distanced from heating elements.

(6) The layout of components requiring frequent adjustment or replacement—such as potentiometers, adjustable inductors, variable capacitors, micro switches, fuses, buttons, and plugs—should take overall structural requirements into account, placing them in easily accessible positions.

(7) Fixing holes should be located near terminals, plug-in components, the center of long terminal strips, and areas frequently subjected to stress. Adequate space around fixing holes is essential to prevent deformation from thermal expansion and warping during wave soldering.

(8) For components like transformers, electrolytic capacitors, varistors, bridge stacks, and heat sinks, which may require secondary processing due to large tolerances and low precision, additional clearance should be added beyond the original spacing.

(9) Avoid placing valuable components at corners, edges of the PCB, or near connectors, mounting holes, slots, and gaps. These areas are prone to high stress and can lead to cracks in solder joints or components.

The reasonableness of the layout directly impacts the wiring effectiveness, making a well-considered PCB layout the foundational step towards successful PCB design.
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