What are The PCB High Frequency Plates? How to Choose?

In the processing and testing of high frequency PCB boards, high-frequency antennas, there are often beginners, because of the selection of the incorrect high-frequency PCB leads to the product results are not as good as expected. Today we will briefly talk about, PCB high-frequency plate what? How to choose?

A. Definition of PCB High Frequency Board:

High frequency board refers to the electromagnetic frequency of the higher special circuit boards for high-frequency (frequency greater than 300MHZ or wavelength less than 1 meter) and microwave (frequency greater than 3GHZ or wavelength less than 0.1 meters) in the field of PCB, is in the microwave substrate copper-clad laminate boards on the use of ordinary rigid circuit boards manufacturing method of some of the processes or the use of special treatments and the production of circuit boards. Generally speaking, high-frequency board can be defined as the frequency of 1GHz or more circuit boards.

With the rapid development of science and technology, more and more equipment design is in the microwave band (> 1GHZ) or even with the millimeter wave field (77GHZ) above the application (for example, now very hot car 77GHz millimeter wave antenna), which also means that the frequency is higher and higher, the substrate of the circuit board requirements are also higher and higher. For example, the substrate material needs to have excellent electrical properties, good chemical stability, with the increase in power signal frequency in the substrate loss requirements are very small, so the importance of high-frequency boards came to the fore.

B. PCB High Frequency Board Classification:

a, To Material Points:

 a) Organic materials: Phenolic resin, glass fiber / epoxy resin, Polyimide, BT / Epoxy, etc. belongs to it.

 b) Inorganic materials: Aluminum, Copper-invar-copper, ceramic and so on belong to. Mainly take its heat dissipation function.

b, To The Finished Product Hard and Soft Distinction: 

 a) Hard Rigid PCB;

 b) Flexible PCB;

 c) Rigid-Flex PCB.

c, By Structure: 

 a) Single Panel;

 b) Dual Panel; 

 c) Rigid-Flex PCB.

d, By Application: Communication / Consumable Electronics / Military / Computer / Semiconductor / Electrical Test Boards...

C. Commonly Used High-speed Boards (Manufacturers)

National board cost-effective, performance is not inferior to imported products

Foreign Ones Are:

a, Rogers: RO4003, RO3003, RO4350, RO5880, etc. With the development of 5G millimeter wave, Rose Jie also introduced a variety of low-loss circuit boards suitable for millimeter wave.

RO3000 Series: Based on ceramic-filled PTFE circuit materials, models: RO3003, RO3006, RO3010, RO3035 high-frequency laminates.

RT6000 Series: Based on ceramic-filled PTFE circuit materials, designed for electronic and microwave circuits requiring high dielectric constants, models include: RT6006 dielectric constant 6.15, RT6010 dielectric constant 10.2.

TMM Series: Composites based on ceramics, hydrocarbons, thermosetting polymers, models: TMM3, TMM4, TMM6, TMM10, TMM10i, TMM13i. etc.

b, Taconic: TLX series, TLY series, etc...

c, Panasonic: Megtron4, Megtron6, etc...

d, Isola: FR408HR, IS620, IS680, etc...

e, Nelco: N4000-13, N4000-13EPSI, etc..

f, TUC: Tuc862, 872SLK, 883, 933, etc..

Of course, there are many other high frequency plates not listed. Among them, Arlon (has been acquired by Rogers, is also an old brand RF microwave board factory).

D. Selection of High Frequency High-speed PCB Materials What are The Important Indicators?

When selecting substrates for PCBs used in high frequency circuits, it is important to examine in particular the material DK, the characteristics of changes at different frequencies. For the focus on high-speed signal transmission requirements, or characteristic impedance control requirements, focus on DF and its performance in frequency, temperature and humidity and other conditions.

The general type of substrate materials in the frequency change conditions, showing a large change in the DK, DF value of the law. Especially in the frequency of l MHz to l GHz, their DK, DF value changes are more obvious. For example, the general type epoxy resin a glass fiber cloth-based substrate material (general type FR-4) in the frequency of l MHz under the DK value of 4.7, while in the frequency of l GHz under the DK value of 4.19. More than l GHz, the change in its DK value tends to be flat. The trend of change is with the increase in frequency, and become smaller (but the magnitude of change is not large), for example, in l0GHz, the general FR a 4 DK value of 4.15, with high-speed, high-frequency characteristics of the substrate material in the case of frequency change, the DK value of the change in the smaller, since the l MHz to lGHz changes in frequency, the DK more than to remain in the range of 0.02 changes. Its DK value in different frequency conditions from low to high, a slight tendency to decline.

General type substrate material dielectric loss factor (DF), in by frequency change (especially in the high frequency range of change) and produce DF value change than DK. The rule of change is tending to increase, therefore, in the evaluation of a substrate material of high frequency characteristics, to examine the focus of its DF value changes. With high-speed high-frequency characteristics of the substrate material, in high-frequency changes in the characteristics of the general type of substrate material there are two types of obviously different types: a class is with the change in frequency, its (DF) value change is very small. There is also a class in the magnitude of change with the general type of substrate material is similar, but its own (DF) value is lower.

E. How to Choose High Frequency High-speed Board?

Selection of PCB materials must be balanced between meeting design requirements, mass production, and cost. Simply put, design requirements include both electrical and structural reliability. This is usually more important when designing very high speed PCBs (greater than GHz). For example, the FR-4 material that is commonly used today may not be suitable because the dielectric loss Df (Dielectricloss) at a few GHz is very high.

For example, a 10Gb/S high-speed digital signal is a square wave, which can be viewed as a superposition of sine wave signals of different frequencies. Therefore 10Gb/S contains many different frequency signals: 5Ghz fundamental, 3rd order 15GHz, 5th order 25GHz, 7th order 35GHz signals, and so on. Maintaining the integrity of the digital signal and the steepness of the upper and lower edges is the same as low-loss, low-distortion transmission of RF microwaves (the high-frequency harmonic portion of the digital signal reaches the microwave band). Therefore, in many ways, high-speed digital circuit PCB selection and RF microwave circuit needs are similar.

In the actual engineering operation, the selection of high frequency boards may seem simple but the factors that need to be considered are still very much, through the introduction of this article, as a PCB design engineers or high-speed project managers, the characteristics of the board and the choice of a certain understanding. Understand the electrical properties of the board, thermal properties, reliability, etc.. And the rational use of layer stacking, design a piece of high reliability, good processability of the product, the consideration of various factors to optimize.

F. The Following Will be Introduced Separately, The Main Considerations For Choosing The Right Plate:

a, Manufacturability:

For example, what is the performance of multiple pressing, temperature performance, etc., CAF/heat resistance and mechanical toughness (adhesion) (good reliability), fire rating.

b, With the product to match the various properties (electrical, performance stability, etc.):

Low loss, stable Dk / Df parameters, low dispersion, with the frequency and environmental change coefficient is small, material thickness and glue content tolerance is small (impedance control is good), if the alignment is long, consider low roughness copper foil. Another point, the design of high-speed circuits are required to simulate the pre-design, the simulation results are the design of the reference standard. "Xingsen Technology - Agilent (high-speed / RF) Joint Laboratory "to solve the simulation results and test inconsistent performance problems, have done a lot of simulation and actual test closed-loop validation, through a unique method to do the simulation and the actual test.

c, Timely Availability of Materials:

Many high frequency plate procurement cycle is very long, even 2-3 months; in addition to the conventional high-frequency plate RO4350 have stock, many high-frequency plate need to be provided by the customer. Therefore, HF plates need to communicate well in advance with manufacturers, as early as possible to prepare materials;.

d, Cost:

Look at the price-sensitive degree of the product, is a consumer product, or communication, medical, industrial, military applications;

e, The Applicability of Laws and Regulations:

To integrate with different national environmental regulations to meet the requirements of RoHS and halogen-free.

The above factors, high-speed digital circuits running speed is the main factor to consider PCB selection, the higher the rate of the circuit, the selected PCBDf value should be smaller. With medium, low-loss circuit board material will be suitable for 10Gb / S digital circuits; with lower loss of the board for 25Gb / s digital circuits; with ultra-low loss board will be adapted to faster high-speed digital circuits, the rate can be 50Gb / s or higher.

G. From The Material Df:

Df between 0.01 ~ 0.005 circuit boards suitable for the upper limit of 10Gb / S digital circuits.

Df between 0.005 ~ 0.003 circuit board material suitable for the upper limit of 25Gb / S digital circuits.

Circuit boards with a Df not exceeding 0.0015 are suitable for 50Gb/S or even higher speed digital circuits.