Light boards and circuit boards are core components of lighting equipment. The rationality of their via design directly impacts signal transmission quality and product stability. Flawed via design can lead to various signal interference issues, including impedance discontinuity, parasitic effects, signal reflection and attenuation, crosstalk noise, power integrity degradation, and reliability degradation caused by thermal stress.
Impedance discontinuity in vias is a primary factor causing signal interference. In light boards and circuit boards, vias serve as channels for interlayer signal transmission, and their equivalent impedance is typically lower than the characteristic impedance of the transmission line. For example, when a 50-ohm transmission line passes through a via, the impedance may drop by approximately 12%, causing signal reflection at the via. Although this reflection is small, in high-frequency signal transmission, small impedance mismatches can accumulate and cause significant interference, manifesting as signal waveform distortion and reduced eye closure, ultimately leading to data transmission errors or abnormal LED drive signals.
Parasitic capacitance and inductance further degrade signal quality. The via structure itself has parasitic capacitance to ground, the magnitude of which is related to the pad diameter, isolation hole diameter, and the dielectric constant of the substrate. Parasitic capacitance prolongs signal rise time and reduces circuit response speed. Furthermore, the parasitic inductance of vias weakens the filtering effect of bypass capacitors. This is especially true in power supply paths. The resonant circuit formed by via inductance and capacitance can induce power supply noise, leading to LED brightness fluctuations or driver chip malfunction. In high-frequency lighting control signals, parasitic parameters can also cause signal ringing, increasing electromagnetic interference (EMI) emissions.
Signal reflection and attenuation are direct consequences of improper via design. When a signal passes through a via with impedance discontinuity, some energy is reflected back to the source, where it interferes with the incident signal. This reflection manifests as inter-symbol interference in high-speed digital signals and can cause amplitude distortion in analog dimming signals. Multiple via layer switching can accumulate reflections, causing signal amplitude attenuation beyond the permitted range. This can prevent the LED driver chip from correctly recognizing control commands, resulting in brightness control failure or color deviation.
Crosstalk noise is particularly prominent in densely wired light boards and circuit boards. Fluctuations in the electromagnetic field around the vias can couple to adjacent signal lines through mutual capacitance and inductance, generating crosstalk noise. In RGB light strip control circuits, if the spacing between the vias for data and clock signal lines is too small, crosstalk can cause clock jitter and data sampling errors. Furthermore, densely packed areas with vias can create an "antenna effect," radiating high-frequency noise to surrounding circuitry and impacting the communication stability of the wireless control module.
Power integrity impairment is another impact of via design flaws. If the impedance of vias in the power path is excessive or unevenly distributed, voltage drops can result, causing fluctuations in the LED supply voltage. In multi-channel parallel LED drivers, inconsistent via voltage drops can lead to unbalanced current distribution, causing overcurrent damage to some LEDs. Furthermore, the parasitic inductance of power vias limits transient current response, potentially causing power supply oscillations during startup of the switching power supply or sudden load changes, impacting the reliability of the entire light board.
Reliability issues caused by thermal stress are also not to be ignored. The connection between vias and copper foil is susceptible to stress during temperature cycling due to mismatched thermal expansion coefficients. If the via design fails to consider mechanical strength, the copper foil or via fracture may occur after long-term use. In outdoor lighting panels, thermal stress caused by diurnal temperature fluctuations can accelerate this failure process, manifesting as intermittent LED blackout or a shortened overall lifespan.
Optimizing via design in light boards and circuit boards requires multi-faceted considerations, including impedance control, parasitic parameter suppression, layout rationality, and thermal management. By accurately calculating via dimensions, rationally planning interlayer switching, increasing ground via density, and employing backdrilling, signal integrity can be significantly improved, ensuring stable operation of the light board circuit board in complex electromagnetic environments and thermal stress conditions.
