Challenges of 5G technology to HDI PCB

Challenges of 5G technology to HDI PCB

Mixed signal receiving PCB design

Today, most systems handle 4G and 3G PCBs. The component's transmit and receive frequency range is 600 MHz to 5.925 GHz, and the bandwidth channel is 20 MHz, or 200 kHz for IoT systems. When designing PCBs for 5G network systems, depending on the application, these components will require millimeter wave frequencies of 28 GHz, 30 GHz or even 77 GHz. For bandwidth channels, the 5G system will process 100MHz below 6GHz and 400MHz above 6GHz.

These higher speeds and higher frequencies will require the use of suitable materials in HDI PCBs to simultaneously capture and transmit lower and higher signals without signal loss and EMI. Another problem is that devices will become lighter, more portable, and smaller. Due to strict weight, size and space constraints, HDI PCB materials must be flexible and lightweight to accommodate all the microelectronic devices on the circuit board.

For PCB copper traces, thinner traces and stricter impedance control must be followed. The traditional subtractive etching process used for 3G and 4G HDI PCBs can be switched to a modified semi-additive process. These improved semi-additive processes will provide more precise traces and straighter walls.

The material base is also being redesigned. Printed circuit board companies are studying materials with a dielectric constant as low as 3, because standard materials for low-speed PCBs are usually 3.5 to 5.5. Tighter glass fiber weave, lower loss factor loss material and low profile copper will also become the choice of HDI PCB for digital signals, thereby preventing signal loss and improving signal integrity.

EMI shielding problem

EMI, crosstalk and parasitic capacitance are the main problems of circuit boards. In order to cope with the crosstalk and EMI generated by the analog and digital frequencies on the board, it is recommended to separate the wiring. The use of multilayer boards will provide better versatility to determine how to place high-speed traces so that the paths of the analog and digital return signals are kept away from each other, while keeping the AC and DC circuits separate. Adding shielding and filtering when placing components should also reduce the amount of natural EMI on the PCB.

In order to ensure that there are no defects and serious short circuits or open circuits on the copper surface, advanced AOI and 2D metrology with higher functions will be used to check the traces of the conductors and measure them. These technologies will help PCB manufacturers look for possible signal degradation risks.

Heat dissipation

A higher signal speed will cause the current through the PCB to generate more heat. PCB materials used for dielectric materials and core substrate layers will need to adequately handle the high speeds required by 5G technology. If the material is insufficient, it may lead to copper traces, peeling, shrinkage and warping, because these problems will cause the deterioration of the PCB.

In order to cope with these higher temperatures, manufacturers will need to focus on the choice of materials that address thermal conductivity and thermal coefficient issues. Materials with higher thermal conductivity, excellent heat transfer, and consistent dielectric constant must be used to make a good PCB to provide all the 5G features required for this application.