Radio Frequency PCB Prototyping and batch manufacturing
What is an Radio Frequency PCB Board?
Radio Frequency is short for RF, which is a kind of high frequency AC variable electromagnetic wave. The alternating current that changes less than 1000 times per second is called low frequency current, and the high frequency current that changes more than 1000 times is called high frequency current, and radio frequency is such a high frequency current. Cable TV system adopts radio frequency transmission mode.
When the frequency of electromagnetic wave is less than 100 khz, the electromagnetic wave will be absorbed by the surface and can not form effective transmission. But when the frequency of electromagnetic wave is higher than 100 khz, the electromagnetic wave can propagate in the air and be reflected by the ionosphere at the outer edge of the atmosphere to form long-distance transmission ability. We call high-frequency electromagnetic wave with long-distance transmission ability. For radio frequency, English abbreviation: RF
High frequency circuit is basically composed of passive components, active devices and passive networks. The frequency characteristics of components used in high frequency circuits are different from those used in low frequency circuits. Passive linear elements in high frequency circuits are mainly resistors, capacitors and inductors.
General Characteristics of Radio Frequency Circuit Board
- CTEr = +40/+50 ppm per °C (low); Tg (glass transition temperature) is 280°C
- ER = 3.38/3.48 at 10.0 GHz
- ER is constant to 40.0 GHz
- ED (electro-deposited) copper only
- Layer-to-layer thickness control = +/- 0.001
- Fabrication costs are typical to slightly increased
Several Common Types of RF Circuits Board
1.Low Noise Amplifier (LNA)
LNA is a special amplifier, which is mainly used in the front end of radio frequency receiver. It amplifies the signal received by antenna with small noise and large gain. It is of great significance to improve the quality of received signal, reduce noise interference and improve reception sensitivity. Its performance is related to the quality of the whole communication system.
The main indicators of low noise amplifier are noise factor (NF), gain (Gain), matching degree of input and output impedance (S11, S22, input and output echo loss or input and output VSWR), linear performance (third-order intersection point and 1dB compression point), reverse isolation (S12), etc. Because LNA is located at the front end of adjacent antenna, its performance will directly affect the quality of received signal. In order to ensure the signal received by the antenna can be recovered at the last stage of the receiver, LNA needs to generate as low noise and distortion as possible while amplifying the signal. Therefore, in production testing, we mainly focus on the gain and noise figure of LNA.
2. Radio Frequency Power Amplifier (PA)
RF power amplifier is used in the last stage of transmitter. It amplifies the modulated frequency band signal to the required power value and transmits it to the antenna to ensure that the receiver in a certain area can receive satisfactory signal level and does not interfere with the communication of adjacent channels. For example, the transmitting power of mobile communication base station can reach hundreds of watts, the transmitting power of satellite communication can reach kilowatts, while the portable wireless communication equipment only needs tens of milliwatts to hundreds of milliwatts.
The main indicators of RF power amplifier are working frequency band, output power, power gain and gain flatness, noise figure, input-output standing wave ratio, input-output third-order intermodulation point, adjacent channel power ratio, efficiency and so on. Compared with low noise amplifier, RF power amplifier not only needs to satisfy certain gain, standing wave ratio and bandwidth, but also has high output power, conversion efficiency and small non-linear distortion.
3. Radio Frequency Filter
Radio frequency filter is mainly used to filter unnecessary signals and retain useful signals. It is a two-port device with frequency selectivity. It transmits matched frequency signals in passband, and attenuates the stopband frequency signals to achieve the function of signal spectrum filtering.
According to different frequency selection characteristics, filters can be divided into low-pass, high-pass, band-pass and band-stop filters, which are the four most basic filters.
Mixer is an important component of communication system. It is mainly used for frequency conversion of signal, that is, the frequency of signal is converted from one value to another value.
Mixer can be divided into active mixer and passive mixer. Passive mixers are usually composed of diodes and field effect transistors operating in variable resistance region (without DC bias). The gain is less than 1, the linear range is large and the speed is fast.
Active mixer is composed of field effect transistor (plus DC bias) and bipolar transistor. The gain is greater than 1, which can reduce the influence of noise at all levels on the total noise of the receiver after mixing.
RF PCB Board Applications
RF boards have a multitude of different applications, including wireless technologies, smart phones, sensors, robotics and security. With the advent of new technologies that are pushing the limits of electronics, the demand for RF boards is on the rise.
Finding a capable RF PCB manufacturer is critical to make sure the boards are fabricated to high quality standards and on-time. Our reputation speaks for itself. We pride ourselves on bringing the most demanding layout concepts to reality.
Design Skills of Radio Frequency Circuit Board
In recent years, due to the demand and growth of Bluetooth devices, wireless local area network (WLAN) devices and mobile phones, more and more attention has been paid to RF circuit design techniques. From the past to the present, RF circuit board design, like electromagnetic interference (EMI) problems, has been the most difficult part for engineers to control, even a nightmare. If you want to succeed in design at one time, you must plan carefully and pay attention to details before it works.
Radio Frequency (RF) circuit board design is often described as a "black art" because of many theoretical uncertainties. However, this is only a partial view, RF circuit board design still has many rules to follow. However, in practical design, the real practical skill is how to compromise these rules when they cannot be implemented due to various constraints. Important RF design topics include impedance and impedance matching, insulation materials and laminates, wavelength and harmonics, etc.
In addition to the general principle of considering the current size, the characteristic impedance of the Radio Frequency printed line must be taken into account, and the impedance matching must be strictly carried out. The impedance control of the printed line must be considered when making the PCB.
The characteristic impedance of printed circuit is related to the material properties and physical parameters of PCB, so the PCB designer must know the performance of PCB sheet.
Types of micropore
Circuits of different Natures on circuit boards must be separated, but they must be connected in the best condition without electromagnetic interference, which requires the use of microvia. Usually, the diameter of micropore is 0.05 mm to 0.20 mm. These micropore can be divided into three categories: blind via, bury via and through via.
Using partitioning techniques
When designing RF circuit board, high power RF amplifier (HPA) and low noise amplifier (LNA) should be separated as far as possible. In short, high power RF transmitting circuit should be kept away from low noise receiving circuit. If there's a lot of space on the PCB board, it's easy to do that. But usually when there are many components, PCB space becomes very small, so it is difficult to achieve. They can be placed on both sides of the PCB board, or they can work alternately rather than simultaneously. High power circuits sometimes include RF buffers and voltage controlled oscillators (VCO).
Design partitions can be divided into physical partitioning and electrical partitioning. Entity partition mainly involves the layout of components, orientation and shielding, etc. Electrical partition can continue to be divided into power distribution, RF routing, sensitive circuit and signal, grounding and other partitions.
Sometimes, it is impossible to retain enough segregation between multiple circuit blocks. In this case, it is necessary to consider using metal shield to shield RF energy in RF area. However, metal shield also has side effects, such as high manufacturing and assembly costs.
Power decoupling circuit
Appropriate and effective decouple circuits for chip power supply are also very important. Many RF chips integrated with linear circuits are very sensitive to power supply noise. Usually each chip needs up to four capacitors and one isolation inductor to filter out all power supply noise.
Thickness of Radio Frequency Printed Circuit Board
The thickness of PCB in radio frequency printed circuit boards is usually 0.2mm integer times, such as 0.8mm, 1.0mm, 1.6mm and so on. Sometimes, the thickness of PCB is expressed in inches. The specific thickness should be calculated according to the impedance control results.
Manufacturing of Radio Frequency PCB
The precision of characteristic impedance must be strictly controlled in the manufacture of RF circuit boards. The accuracy of dielectric constant is closely related to the uniformity of resin content in the substrate material (semi-cured sheet). The technical index of resin content in semi-curable sheet is formulated by each substrate material manufacturer according to the actual processing technology and production level of PCB factory. Because of the different amount of resin, the melt viscosity of semi-cured sheets is different and the lamination process is different. These will lead to differences in insulation thickness and accuracy of PCB. The dielectric properties, especially the dielectric constant values, of the multilayer plates produced by different manufacturers and semi-cured sheet materials with different resin content indicators show different levels and accuracy. Therefore, in order to improve the characteristic and high precision control of PCB, it is necessary for the substrate material manufacturer to cooperate well with the PCB manufacturer in the index control of resin quantity in the production of semi-curable sheets.
Surface Treatment of Welding Pad for Radio Frequency Circuit Board
Generally there are the following kinds:
1) In general, tin-sprayed lead alloy HASL process is used, and the tin surface should be smooth and dew-free copper. Just make sure the weldability is good within 6 months. In order to obtain better skin effect, electroless gold plating or OSP process can be selected for RF plate. At the same time, it helps to reduce environmental pollution.
2) Chemical nickel-gold (Ep.Ni2.Au 0.05) can be considered if the PCB has fine spacing devices (such as BGA with 0.5mm spacing) or if the thickness of the plate is less than 0.8mm. There is also an organic solderability Preservative process (OSP), which is not suitable for use for the time being because of its short solderability, stickiness and non-solderability.
3) Electroless nickel plating and gold plating (Et. Ni5. Au0.1) must be used for boards with bare chips (requiring hot-pressing or ultrasonic welding, commonly known as Bonding) or keys (such as mobile phone boards). Some manufacturers also adopt the whole plate gold plating process (Ep. Ni5. Au0.05). The former has a smoother surface, a more uniform coating thickness and weld resistance, while the latter is cheaper and brighter.
In terms of cost, electroless nickel and gold plating (Et. Ni5. Au0.1) is more expensive than tin spraying, while the whole plate gold plating process is cheaper than tin spraying.
4) For printed plugs, hard gold is usually plated, that is, gold alloy with 99.5% - 99.7% purity containing nickel and cobalt. The general thickness is 0.5-0.7 um, marked Ep.Ni5.Au 0.5
The thickness of the coating is determined according to the number of insertions and removals. Generally, the thickness of 0.5μm can be subjected to 500 insertions and removals, and the thickness of 1μm can withstand 1000 insertions and removals.
Due to the special packaging of RF components, when selecting a new package of RF components or compatible devices, developers must fully communicate with the process personnel in the early stage to ensure the manufacturability of the components.
RF components should pay special attention to the plating thickness and material of the soldered end of the device to avoid the occurrence of void soldering and cold soldering during the manufacturing process (especially ceramic devices with silver-plated solder ends).
The flatness of RF components should be less than 0.005", especially ceramic modules such as VCO, power amplifier and filter.
When choosing components to work in high frequency environment, use SMD as much as possible. This is because SMEs are usually small in size and have very short pins.
Common Raw Materials for Design and Manufacture of Radio Frequency Printed Circuit Board
Choosing the right material is arguably the most critical decision in the RF board manufacturing process.
The frequency for RF board is normally between 300MHz ~ 3GHz, RF / Microwave designs require specialization unique to themselves. These high frequency circuits have more stringent requirements in the material, signal speed, signal loss, tolerances, and circuit design. we need to use special material to achieve the high frequency.
According to the performance requirements of the circuit board, it can be ordinary FR4 epoxy glass fiber, or it can be a special microwave substrate such as Teflon.
- In the low-power RF PCB design, the standard FR4 material is mainly used (good insulation properties, uniform material, dielectric constant ε = 4, 10%)
Some engineers don`t think it is suitable as an RF material at all. Others think it has its place in things, for less demanding, lower frequency RF applications. Loss tangent is certainly worse in this material and it is not a good choice for high-power or broadband applications.
If the budget is tight and you are considering FR4 for a low power, low frequency application, contact us and we can help you evaluate your options with our engineering expertise.
- Rogers High Frequency Circuit Materials. (Copper from 1/4 OZ to 2 OZ). such as 3000 series, 4000 series, 5000 series, 6000 series, RO4233, RO4350, RO4003, Arlon, and so on.
- PTFE (Dupon Telfon)
The fabricate process is similar like FR4, but the copper plating is more complex than FR4, because material characteristics, it`s much harder to metalize the through hole (copper plating), and other process is complex than FR4, so need unique handling method and experienced workers.
Many thicknesses and copper types available.
The table below provides general recommendations, but to find the best PCB materials for your specific project, please contact our engineering staff.
|RF Application||RF Materials||Bonding Materials||Attributes|
|Consumer Electronics||RO3006|| RO3000 Series Bondply |
|Cost effective with dependable electrical and thermal characteristics|
|Military/Space||RT/Duroid||RO4450B / RO4450F||The best in electrical and thermal performance and environmental durability|
|High Power Applications||6035HTC||Superior thermal management|
|Medical||RO4350B||RO4400 Bondply / 2929 Bondply||Versatile high performance properties to suit a range of device types|
|Automotive||RO3003||RO4400 Bondply||Excellent electrical performance compatible with standard manufacturing processeses|
|Industrial||RO4835|| 2929 Bondply |
|Excellent durability and environmental resistances, including oxidation|
What is the price?
In order to get an accurate and prompt quotation, you can provide some necessary information according to the following guidelines:
1. Quantities required
2. Delivery time
3. Materials Requirements (material type, thickness as well as copper requirements)
4. Finish requirements (type and thickness)
5. Panelization Requirements
6. File set
- Complete GERBER files including the Excellon Drill File (preferred)
- DXF or .DWG file (acceptable)
- PDF drawings (acceptable for quoting, but electronic file type above or existing films required for manufacturing).
RF transmission: RF cable, RF connector, RF components
Radio Frequency Cable: Radio Frequency Cable, which is used for signal transmission. It is widely used in common cable TV lines, radio communication equipment and related radio electronic equipment of electronic devices. Our semi-rigid, semi-flexible, RG series, rolling lines, KSR low loss, fine three-coaxial, advanced flame retardant and other types of cables are widely used in communications, aerospace, medical, IT equipment, rail transit, large data industries. Through TUV, SGS, UL, TLC and other industry certification, our high-frequency cables have excellent electrical and mechanical properties, good shielding, low attenuation, small standing wave, strong environmental adaptability, high and low temperature resistance, bending resistance, anti-corrosion and moisture-proof characteristics.
Radio Frequency Connector: Connector is a clutchable or replaceable component of the interconnected part. It is a bridge between all signals. The nature of connector will affect the operation quality of the whole system. Therefore, high standard connector is the first condition to ensure effective signal transmission. Jin Xinnuo provides a wide range of RF connectors: 4.3-10, 7/16DIN, N, TNC, BMA, SMA, SMK, APC3.5, SMC, SAA, SSMA, micro-rectangular, circular electrical connectors, glass beads and other types. It has good seismic resistance, high power, low standing wave ratio, attenuation and third-order intermodulation, high reliability and high sealing. It has been widely used in many fields such as macro base station RF output port, indoor distribution, radio equipment and electronic instruments, microwave equipment, aerospace and so on. At the same time, our connector can be suitable for wet and rainy weather, can effectively prevent gas, moisture or liquid into the connector shell, ensure product stability.
Radio Frequency Component: Radio Frequency Component is generally composed of a cable connecting two radio frequency coaxial connectors. It is a complete transmission capable of transmitting radio frequency signals and energy. Cable component is a key part of transmission system. Its performance will seriously affect the quality of transmission system. The performance of cable components depends not only on the performance of cables and connectors, but also on the connection technology of connectors. There are many examples of inappropriate connection of connectors which lead to the performance of cable components not up to standard. Therefore, it is better for competent users to purchase directly from professional cable manufacturers.
Radio-frequency (RF) and microwave (MW) circuits
In general terms, the PCB industry considers an RF circuit board to be any high frequency PCB that operates above 100MHz.
Within the radio frequency class, anything above 2GHz is a Microwave PCB.
Radio-frequency (RF) and microwave (MW) circuits can be found in countless wireless products from handheld devices for medical and industrial applications to advanced communications systems for base stations, radar and global positioning. The success of these high-speed products begins at the product design stage when the PCB laminate materials are selected. Rayming works with the product design team to insure that the project's cost/performance targets can be met by providing information on material options, relative costs and DfM considerations. Once the design has been completed, JHYPCB follows the boards from prototype through to production where key process variables such as line widths and dielectric spacing are measured and controlled to insure the product meets the designed requirements and delivers consistent performance throughout the products life cycle.
The RF frequency range is normally 500 MHz to 2 GHz, though designs above 100 MHz will typically be considered RF PCBs. If you venture above 2 GHz, then you`re in the microwave frequency range.
RF and microwave printed circuit board designs have a few major differences to consider - differences between themselves and your standard digital or analog circuit.
RF and microwave printed circuit boards operate on a frequency and pass signals within a certain band. Band pass filters are used to transmit signals in the [band of interest," and anything outside of this frequency range is filtered out. Bands can be narrow or wide and can be carried via high-frequency carrier waves.
RF and microwave signals are very sensitive to noise - much more sensitive than very high-speed digital signals. That means you`ll need to work to minimize noise, ringing and reflections while treating the whole system with care.
Impedance matching is important. As the RF and microwave frequencies move higher, tolerance becomes smaller. Often, your PCB driver will need to be fixed, such as at 50 ohms, and that means 50 ohms out from the driver, during transmission and sending to the receiver.
Product Categories : High Frequency PCB