To improve the stability and reliability of electronic systems, electronic engineers often focus on optimizing PCB stack-up design. To ensure the normal operation of electronic equipment, PCB stack-up design must comply with two mandatory rules. What exactly are these two rules, and what will happen if they are violated?
To improve the stability and reliability of electronic systems, electronic engineers often focus on optimizing PCB stack-up design. To ensure the normal operation of electronic equipment, PCB stack-up design must comply with two mandatory rules. What exactly are these two rules, and what will happen if they are violated?
Rule 1: Uniform Thickness for Identical Layers
The first rule for PCB stack-up design is to ensure that identical layers maintain a consistent thickness. When a PCB is subjected to external pressure or mechanical shock, stacking dielectric materials of varying thicknesses may cause board deformation or physical damage. Maintaining uniform layer thickness reduces the probability of such failures and enhances the overall structural stability of the PCB.
In addition, inconsistent layer thickness degrades signal transmission quality. Signals propagating through dielectric layers of different thicknesses are affected by varying impedance values and transmission velocities, which can trigger signal integrity issues and even signal distortion.
Violation of this rule will lead to unpredictable failures in electronic equipment during operation, including dielectric cracking, circuit malfunctions, and permanent equipment damage.
Rule 2: Alternating Arrangement of Dissimilar Layers
The second rule is to arrange dissimilar layers in an alternating configuration. The primary objectives are to enhance the mechanical strength and stability of the PCB, as well as to reduce electrical noise and electromagnetic radiation.
Without alternating dissimilar layers, the overall mechanical strength of the board is compromised. The PCB becomes more susceptible to deformation or fracture under external pressure or shock, resulting in a significant reduction in stability.
Furthermore, PCBs with non-alternating layer arrangements generate higher levels of electrical noise and radiation during signal transmission. This occurs because the electromagnetic properties of different materials are not accounted for; signals passing through dissimilar materials may experience reflection, refraction, and other phenomena that increase noise.
Violation of this rule results in frequent operational instability of the equipment. For instance, noise interference degrades signal reception and transmission quality, leading to degraded or substandard equipment performance. In addition, the coefficient of thermal expansion (CTE) mismatch between different materials must also be considered.
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