High-layer Count (HLC) PCB Technology for the 5G Era
One effective solution to the requirements of 5G technology is the use of HLC (High-layer Count) PCB boards that integrate key features such as skip vias, POVF manufacturing, advanced raw materials, and impedance control.
Special attention must be paid to PCB design and manufacturing to meet the demands of 5G era applications and beyond. Issues related to PCB size and thickness, reliable vias, accurate registration, reliable and accurate manufacturing methods, signal integrity, and effective raw materials must be addressed beginning in the design phase and throughout manufacturing.
One effective solution to the requirements of 5G technology is the use of HLC PCB boards, such as the one shown in Figure 1, that integrate key features such as skip vias, POVF manufacturing, advanced raw materials, and impedance control.
Figure 1. High-layer count PCB manufactured by Kinwong for the 5G industry. Image used courtesy of Kinwong
PCB Changes in the Era of 5G
5G involves a much more advanced integration of components such as antennas. This, in turn, leads to a demand for reduced component size to better support integration. In addition, antennas now require high-frequency materials and strict RF trace tolerance.
Furthermore, the transmission power of 5G base stations is considerably higher than that of 4G, requiring solutions that can achieve reduced losses and excellent thermal management while still supporting high speed, high-frequency solutions with reliable signal integrity.
Another way of looking at the challenges involving 5G technology would be to focus on three key performance characteristics that PCBs must provide:
- High speeds
- Fast transmission rates
- Reduced losses.
HLC PCBs have been found by engineers as an excellent approach to meeting the demanding requirements of 5G technology. HLC PCBs already support size constraints as well as manufacturing methods that include accurate registration and reliable vias. However, engineers have also discovered that they can provide enhanced signal integrity and enhanced impedance control as well as implement raw high frequency and low-loss materials.
HLC PCBs, which refers to PCBs with 12 or more layers, is one solution to staying on top of the 5G adoption boom. Such PCBs are thicker than conventional PCBs and often involve a large panel size with a small hole back drilled such as the example shown in Figure 2.
Figure 2. Example of the stack up for an 18 layer back drilling PCB. Image used courtesy of Kinwong
For these PCBs to provide the necessary level of performance, impedance control, and insertion loss are critical.
Considerations for HLC PCBs
As mentioned, to get the proper levels of performance required for 5G applications, there are a few things to consider when using HLC PCBs, which are:
- Skip Vias
- Layer to Layer Registration
- Impedance Control
- Upgraded Raw Materials
One of the challenges in manufacturing effective HLC PCBs involves successfully making interconnects through multiple layers. Skip vias have become necessary as they can pass through multiple layers without making electrical contact with each layer. These vias are, like most vias, vertically laser drilled and require high precision, but the process is quite complex if acceptable results are to be had.
Layer to Layer Registration
In HLC PCBs, the importance of tight layer registration tolerances cannot be overstated. And during manufacturing, various things can distort registration and alignment, including temperature, humidity, and the accuracy of registration hole placement. The careful selection of manufacturing processes and calibration of critical equipment allows extremely tight registration tolerances to be achieved.
A process called POVF (also known as VIPPO or VIA) in pad is often used to reduce the area of the board by narrowing the hole spacing and the holes themselves while also increasing wiring density, as shown in Figure 3.
Figure 3. An HLC PCB board made using the POVF methods by Kinwong Industry. Image used courtesy of Kinwong
This aids in reducing the board’s footprint and achieving a lighter-weight solution without compromising the performance. And more importantly, it works extremely well with the use of skip vias. POVF is more complicated from a manufacturing viewpoint but results in a much more reliable, accurate HLC PCB.
When high-frequency signals are propagating on PCB signal traces, which is often the case in 5G applications, those signals essentially turn the traces into transmission lines. Each point on the signal trace has a particular impedance, and when there is a difference in impedance going from one point to another, distortion of the signal can occur. To preserve signal integrity, PCBs must be designed with impedance control.
Upgraded Raw Materials
Because of the high data rates involved, upgraded raw materials are also necessary. These include high-speed materials such as TU862, a halogen-free composite of epoxy resin, and E-glass fabric. This is considered a mid-loss material and is commonly used with 14 layer PCBs.
Another example is S7439, which can be used with 10 layer PCBs and is considered a low-loss material. M6G is an example of a very low loss material, while M8 is considered an ultra-low loss material. For applications that require high-frequency materials, there are hydrocarbon-based options such as Aerowave 300 and PTFE-based options such as Rogers TC350.
HLC PCBs: 5G and Beyond
High-layer count PCBs are one of the necessary elements as 5G technology continues to develop. Speed and losses related to the chosen raw materials, high accuracy and low tolerance manufacturing methods, and signal integrity are key solutions to achieving the performance and reliability required for 5G.
And there are other applications that could benefit from these approaches, such as:
- File servers
- Data storage
- GPS technology
- Satellite systems
- Weather analysis
- Medical equipment
Kinwong Solutions: A Source for 5G HLC PCB solutions
Kinwong Solutions manufactures high-performance HLC PCB solutions for 5G challenges with high layer count (24, 32, and 40) boards.
Kinwong offers boards that:
- Implements skip vias with POVF
- Have a low registration tolerance of 5mil
- Have a back-drill stub length between 2 mil and 10 mil
- Achieve trace width/spacing tolerance of ±20% with ±10% for signal trace areas by special control and impedance control
- Have very low insertion losses with impedance tolerance of ±8%
The PCBs are available in a selection of high-speed materials, including ultra-low/very low/low/mid-loss materials and high-frequency materials. Additional options include embedded capacitor (except for 24 layer), resistor, or embedded copper coin. Finally, these HLC PCBs are also available as HDI PCBs and optical modules.
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