High Frequency PCB Knowledge

High Frequency PCB Knowledge

High-frequency PCB board applications

High frequency and induction heating technology is currently the highest heating metal materials, the fastest, and low consumption of environmental protection. It has been widely used in all walks of life of metal materials, thermal processing, heat treatment, thermal assembly and welding, melting and other processes. It can not only heat the workpiece as a whole, but also the targeted heating of the workpiece; can achieve deep penetration of the workpiece, but also only on its surface, the surface layer of heating; not only direct heating of metal materials can also be non-metallic Material for indirect heating. and many more. Therefore, the induction heating technology will be applied in all walks of life more and more widely. Its physical properties, accuracy, technical parameters are very high, commonly used in automotive anti-collision system, satellite systems, radio systems and other fields. High frequency of electronic equipment is the development trend.

 2 high-frequency PCB board selection

With a high dielectric constant, low-frequency loss of the material made into. At present, the high-frequency substrate used in the substrate is Fusi media substrate, such as PTFE, usually called Teflon, usually used in more than 5GHz. There are also FR-4 or PPO substrate, can be used between 1GHz ~ 10GHz products, the three high-frequency substrate properties are as follows.

At present, epoxy resin, PPO resin and fluorine resin are the three types of high-frequency substrate materials, the cost of epoxy resin is the cheapest, and fluorine resin is the most expensive; and dielectric constant, dielectric loss, water absorption And frequency characteristics, the best fluorine resin, epoxy resin is poor. When the frequency of application of the product is higher than 10GHz, only fluorine resin printed board can be applied. Obviously, fluorine resin high-frequency substrate performance is much higher than other substrates, but its shortcomings in addition to the high cost of rigidity is poor, and large thermal expansion coefficient. For polytetrafluoroethylene (PTFE), in order to improve performance with a large number of inorganic materials (such as silica SiO2) or glass cloth as reinforcing filler material to improve the rigidity of the substrate and reduce its thermal expansion. In addition, due to the molecular inertia of polytetrafluoroethylene resin itself, it is not easy to combine with copper foil, so it needs special surface treatment with copper foil. Treatment with PTFE or chemical etching on the surface of the plasma etching to increase the surface roughness or in the copper foil and PTFE resin layer between the adhesive layer to increase the adhesion, but may have on the media performance The development of the whole fluorine-based high-frequency circuit substrate requires cooperation of raw material suppliers, research units, equipment suppliers, PCB manufacturers and communication products manufacturers to keep up with the rapid development of high-frequency circuit boards in this field The need.

3 Basic characteristics of high-frequency substrate material requirements

(1) the dielectric constant (Dk) must be small and very stable, usually the smaller the better the signal transmission rate and the material is inversely proportional to the square root of the dielectric constant, high dielectric constant susceptible to signal transmission delay.

(2) Dielectric loss (Df) must be small, which mainly affects the quality of signal transmission, the smaller the dielectric loss so that the signal loss is also smaller.

(3) and copper foil thermal expansion coefficient as far as possible, because inconsistencies in the change in the cold and heat caused by copper foil separation.

(4) low water absorption, high water absorption will be affected in the damp when the dielectric constant and dielectric loss.

(5) Other heat resistance, chemical resistance, impact strength, peel strength, etc. must also be good.

4 FR4 PCB board board, how to distinguish between ordinary board and high-frequency board?

Normal fr4 PCB,Plain cotton fiber paper

High  frequency pcb, E - glass cloth

High frequency PCB is usually pressed with FR4 fiberglass board, and is the whole epoxy glass cloth to suppress, the color of the whole board is more uniform, bright. Density than the low-frequency board to be large, it is the weight of the focus.

Low-frequency board with a lot of low-end material from the pressure together, such as: paper substrate, composite substrate, epoxy board (also known as 3240 epoxy board, phenolic board), FR-4 fiberglass (composite board) And the composite substrate, the overall density is lower, the back of the same color, but careful to see easily see the substrate inside is basically no glass fiber cloth lines. The epoxy board and the FR4 glass fiber composite plate is the difference between the color of the substrate on the back of the shade, the epoxy board at the fracture, hand or other tools a scratch, it is easy to see a white powder, the color is white of. FR4 composite plate is more easy to read, because it is FR4 glass fiber cloth trimmed, the entire plate can be seen on the back of a strip of large stripes.

5 HIGH FREQUENCY PCB board performance when there will be any failure phenomenon

High-frequency board performance is mainly due to low dielectric constant value of high-frequency circuit stability. High-frequency effects of a special skin, the circuit board dielectric constant low leakage caused by high-frequency components, should have the signal weakened, frequency offset drift, serious will stop vibration. The overall electrical performance indicators decreased.

6 high frequency PCB board features

The high-frequency circuit board provided by the utility model is provided with a rib which can block the flow glue at the upper opening and the lower opening edge of the hollow groove of the core board, so that the core board is covered with the covering layer disposed on its upper and lower surfaces When the copper plate is bonded, the adhesive does not enter the hollow tank, that is, the high frequency circuit board can be finished by a second pressing process, and the high frequency circuit in the utility model The plate has the advantages of simple structure, low cost and easy manufacture.

7 high frequency PCB board production requirements

High-frequency board is one of the difficult plate, so we must try to meet the production requirements.

Drilling

1, the drilling speed is slow to 180 / S to use a new drill mouth, the upper and lower pad of aluminum, the best single PNL drilling, holes can not be water

2, over pore agent PTH hole template can be concentrated sulfuric acid (preferably not) 30Min

3, grinding copper plate and the same as the normal double-sided production

4, special attention: high-frequency board in addition to glue residue.

Anti-welding

1. High-frequency board If you need to green primer in the solder mask does not allow grinding before the cover in the MI red chapter.

2. If the substrate needs to be printed on the green oil to print green oil twice (to prevent the substrate green oil blistering), from the etching out and retreat tin can not be grinding plate before, only air-dry. The first primer, with 43T screen normal printing segment baking sheet: 50 degrees 50Min 75 degrees 50Min 95 degrees 50Min 120 degrees 50Min 135 degrees 50Min 150 50Min degrees, with line film exposure, after grinding can be developed, the second Times normal production. Need to note in the MI: the first base line with the film on the bit.

3. If some of the substrate needs to be printed on the green oil, part of the substrate is not printed on the green oil, the need for a "primer film", film backing only retain the substrate green oil, bottom baked plate and then the second Times normal production. The following picture is 018212 the need for a special "film backing."

Special attention to similar 018092 substrate is not printed on green oil can only be printed once green oil (see the figure, the blue Department of green oil window), to prevent the first green oil after the substrate green oil can not be developed .

Spray tin

Spray tin before adding 150 degrees 30Min can be sprayed tin

Line tolerances

Without the required line width tolerance ± 0.05mm required to produce according to customer requirements.