PCB designers are well aware of the intricacies involved in through-hole design, but what about PCB national control technology? Today, I’ll delve into the technical nuances of PCB through holes and back drills.
**Through-Hole Design in High-Speed PCB**
In high-speed PCB design, the utilization of multi-layer PCBs is common, with through holes playing a pivotal role. A through hole in PCBs primarily consists of the hole itself, the soldering plate area surrounding it, and the POWER layer isolation area.
1. **Impact of Through-Holes in High-Speed PCBs**
In multilayer high-speed PCBs, signal transmission between interconnect layers necessitates the use of through holes. At frequencies below 1GHz, these holes establish reliable connections with negligible parasitic capacitance and inductance. However, as frequencies exceed 1GHz, the parasitic effects of through-holes become significant, impacting signal integrity. At this threshold, through-holes become impedance discontinuities in transmission paths, leading to issues like signal reflection, delay, and attenuation.
Furthermore, when signals traverse through-holes to different layers, the reference layer of the signal line also acts as the return path. Consequently, return currents flow between reference layers through capacitive coupling, resulting in ground bounce issues.
In high-speed PCB design, the seemingly innocuous through-hole can often wield significant negative impacts on circuit design. To mitigate the adverse effects stemming from the parasitic properties of these holes, several measures can be implemented:
(1) Opt for an appropriate hole size: For multi-layer PCB designs with standard density, a through-hole diameter of 0.25mm/0.51mm/0.91mm (drill hole/pad/POWER isolation zone) is advisable. In cases of high-density PCBs, consider 0.20mm/0.46mm/0.86mm through-holes or explore non-through-hole alternatives. Larger hole sizes can be employed for power supply or ground connections to minimize impedance.
(2) Maximize the size of POWER isolation zones. Generally, for a given PCB, D1 should exceed D2 by approximately 0.41, considering the through-hole density.
(3) Minimize changes to signal routing on PCBs to reduce the number of holes wherever possible.
(4) Employ thinner PCBs to diminish parasitic parameters associated with through-holes.
(5) Position power supply and ground pins closest to the holes, ensuring short lead lengths to minimize inductance. Additionally, use thicker leads for power and ground connections to reduce impedance.
(6) Place grounding through-holes near signal replacement layer through-holes to create short-distance loops for signals.
Moreover, through-hole length significantly impacts through-hole inductance. While the length of through-holes for top and bottom conduction equals the PCB thickness, in high-speed PCB design, through-hole length should generally not exceed 2.0mm, even though PCB thickness may surpass 5mm with increasing layer count. For through-holes longer than 2.0mm, increasing diameter can enhance through-hole impedance continuity. For lengths below 1.0mm, an optimal diameter of 0.20mm to 0.30mm is recommended.
II. Introduction to Back Drilling Technology in PCB Production
1. What is PCB back drilling?
