Taconic PCB

Based on the design experience of Viasion, when we design the circuit, we will focus on keeping the distance between the analog and digital circuits. It ensures we can walk on the surface when we route the RF circuit. Therefore, avoid cross-region of digital circuits and the analog signal line.

According to the above design rules, some design problems will also be encountered during the design. For example, when the RF line must contact the signal line, Viasion will solve it through two solutions. The best way is to arrange a new ground wire along the RF line and ensure it is connected to the primary ground wire to minimize signal interference.

For Viasion’s design experience, the layout of the PCB is divided into low-power areas and high-power areas, and when arranging high-power areas. Viasion will ensure no through holes on it. In principle, there should be at least one piece of land in the high power area on the PCB board, and it is better to have no through holes on it. Of course, the more copper foil, the better, and Viasion will make as much copper foil as possible, which is better for signal transmission.

In addition, Viasion will try its best to avoid generating free ground on each layer of the PCB during design, and we will try our best to concentrate the wiring and connect it to the main ground.

Viasion is familiar with this process, which is as follows.
RF line → baseband RF interface line → clock line → power supply part → digital baseband part → ground. Also, there is another important place. Viasion recommends coating the lower frequency single board microstrip line with a green solder mask. On the contrary, do not coat higher frequency single board microstrip lines. Because the solder mask will have a slight influence on the signal transmission, Viasion thinks this arrangement is the best.

PCB copper foil thickness refers to the thickness of the finished product, which should be marked on the drawing. RF board requires copper foil to be uniform and thin. The resistance temperature coefficient of uniform copper foil is consistent, and the signal transmission loss is minor.

The accuracy of characteristic impedance should be strictly controlled during the processing and manufacturing of Taconic printed circuit boards. The accuracy of the dielectric constant value is closely related to the uniformity of the resin content of the substrate material (prepreg). Each substrate material manufacturer formulates the technical index of resin content of the semi-cured sheet according to the PCB factory’s moulding and processing technology and the production level’s capacity.

Due to the different amounts of resin, there are differences in the melt viscosity of the semi-cured sheet and the lamination process. Viasion is very familiar with this process; These will lead to differences in PCB insulation thickness and accuracy. Furthermore, the multilayer boards produced by different manufacturers and semi-cured sheet materials with various resin content indicators show different levels and accuracy in their dielectric properties.

Based on Viasion’s experience, especially the dielectric constant value. Therefore, to improve the high-precision control of PCB characteristics, the substrate material manufacturer must cooperate reasonably with the PCB manufacturer regarding the index control of the resin quantity of the semi-cured sheet. In this regard, Viasion will strengthen communication and exchange with customers.

Based on the design experience of Viasion, when we design the circuit, we will focus on keeping the distance between the analog and digital circuits. It ensures we can walk on the surface when we route the RF circuit. Therefore, avoid cross-region of digital circuits and the analog signal line.

According to the above design rules, some design problems will also be encountered during the design. For example, when the RF line must contact the signal line, Viasion will solve it through two solutions. The best way is to arrange a new ground wire along the RF line and ensure it is connected to the primary ground wire to minimize signal interference.

For Viasion’s design experience, the layout of the PCB is divided into low-power areas and high-power areas, and when arranging high-power areas. Viasion will ensure no through holes on it. In principle, there should be at least one piece of land in the high power area on the PCB board, and it is better to have no through holes on it. Of course, the more copper foil, the better, and Viasion will make as much copper foil as possible, which is better for signal transmission.

In addition, Viasion will try its best to avoid generating free ground on each layer of the PCB during design, and we will try our best to concentrate the wiring and connect it to the main ground.

Viasion is familiar with this process, which is as follows. RF line → baseband RF interface line → clock line → power supply part → digital baseband part → ground. Also, there is another important place. Viasion recommends coating the lower frequency single board microstrip line with a green solder mask. On the contrary, do not coat higher frequency single board microstrip lines. Because the solder mask will have a slight influence on the signal transmission, Viasion thinks this arrangement is the best.

Based on the experience summarized by Viasion for many years, microstrip line structure is the most popular in the design of characteristic impedance of RF circuits, so it has been widely promoted and applied. According to Viasion’s year-round experience, four microstrip line structures are most commonly used: surface microstrip, embedded microstrip, stripline, and dual stripline. The model structure of the surface microstrip line is the most widely used among them.

The impedance of PCB signal routing is related to the dielectric constant of the plate, PCB structure, line width, etc. Generally, the RF signal wiring should be arranged on the surface layer as much as possible; in some cases, the inner layer can be used. The most common is the stripline on the third layer, with an impedance of 50Ω.

RF device is used in RF circuits to complete RF signal processing. It is generally made using shallow junction technology with high electrostatic sensitivity. According to Viasion’s year-round experience, generally, 100V~300V is very easy to ESD (electrostatic discharge) damage.

Due to the high operating frequency, wide frequency band and distributed parameters of RF devices, their unique manufacturing processes are determined, such as thin film technology, shallow PN junction, MOS process without ESD protection, GaAs materials, micro-packaging and other characteristics, which make RF devices, especially ICs, extremely sensitive to ESD, electrical surges, mechanical stress and other destructive factors, making their reliability far lower than common medium and low-frequency devices. According to Viasion’s year-round experience, ambient temperature and heat dissipation conditions also highly restrict the RF power amplifier. It is also susceptible to thermal stress. According to Viasion’s perennial design experience, These characteristics require that the RF materials have good process conditions such as ESD prevention, electrical surge prevention (overvoltage or overcurrent impact), mechanical stress prevention and thermal stress prevention in all links such as storage, transportation, processing and commissioning, and have strict production and commissioning process operation specifications and strict implementation, Only then can the reliability of RF devices be guaranteed.