Explain the PCB High Frequency Board Materials and Classification
High frequency board refers to the higher electromagnetic frequency of 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)
Category of PCB, copper-clad board in the microwave substrate on the manipulation of common rigid circuit board manufacturing methods of departmental processes or take special disposal methods and production of circuit boards. Generally speaking, high frequency board can be defined as the frequency of 1GHz or more circuit boards.
With the rapid growth of scientific technology, more and more equipment is envisioned in the microwave band (> 1GHZ) and even with millimeter-wave category (30GHZ) above the use, 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 must have a good motor energy, outstanding chemical invariance, with the increase in the frequency of power flags in the substrate loss requirements are very small, so the main high frequency plate came to the fore.
A. End Ceramic Additive Thermosetting Material
And epoxy resin / glass woven fabric (FR4) similar processing process, only the plate is more brittle, easy to break the plate, drilling and gong plate when the drilling nozzle and gong knife life to be cut by 20%.
B.PTFE (Polytetrafluoroethylene) Material
It is necessary to save the sheltering film to avoid scratches and indentation.
a) with a new drill nozzle (scale 130), a piece of one iteration for the best, pressure foot pressure of 40psi
b) Aluminum sheet for the cover, and then use 1mm dense amine pads, the PTFE plate grip
c) After drilling with a wind gun to blow out the dust in the hole
d) Use the most constant drilling machine, drilling parameters (basically, the smaller the hole, the faster the drilling speed, the smaller the Chip load, the lower the return speed)
C. Hole Disposal
Plasma disposal or sodium naphthalene activation disposal conducive to hole metallization
D. PTH Copper Sinking
a, After micro-etching (has been micro-etching rate of 20 micro inches of restraint), in PTH pulling from in addition to oil cylinder starting into the plate
b, If necessary, then the second PTH, only from the beginning of the estimated cylinder into the plate
E. Solder Resist
a, Pre-disposal: take acidic wash plate, not less than the machine grinding plate
b, Bake the board after pre-disposal (90 ℃, 30min), brush green oil curing
c, Three sections of the baking plate: a section of 80 ℃, 100 ℃, 150 ℃, when each 30min (if there is the invention of the substrate surface dumping oil, can be reworked: the green oil washed off, from the beginning of the activation of the disposal)
F. Gong Plate
White paper will be laid in the PTFE board line surface, high and low with a thickness of 1.0MM etched copper FR-4 substrate plate or phenolic base plate clamping:
In the selection of PCB used for high frequency circuits used in the substrate, to be out of the examination of the material DK, in the divergence of frequency under the transformation characteristics.
The requirements of the high speed transmission of biased flags, or characteristic impedance control requirements, focus on the examination of the DF and its frequency, temperature and humidity, and other prerequisites of the function.
Common substrate materials in the frequency shift under the premise of the DK, DF values show a larger shift in the discipline.
Especially in the frequency of l MHz to l GHz, their DK, DF value of the shift is doubly significant.
According to the coating online understanding, ordinary epoxy resin a glass fiber cloth-based substrate material (ordinary FR-4) in the l MHz frequency DK value of 4.7, while in the lGHz frequency, the DK value of 4.5.
The DK value at lGHz is 4.7, and the DK value at lGHz is 4.19. Above lGHz, the DK value tends to shift steeply.
The shift tends to follow the frequency increase, and become smaller (but the shift is not large), for example, in l0GHz, ordinary FR a 4 DK value of 4.15, with high-speed, high-frequency characteristics of the substrate material in the frequency shift of the environment, the DK value of the shift is small, since the l MHz to the lGHz shift in frequency, DK more than connected to the scale of the shift in the 0.02.
Its DK value in the low to high divergent frequency premise, a slight tendency to decline.
Common substrate material of the dielectric loss factor (DF), in the frequency shift (especially in the high-frequency scale of the shift) and the occurrence of the DF value of the shift than the DK is larger.
The shift in the discipline is tending to increase, so, in the evaluation of a substrate material of high frequency characteristics, the focus of its examination is its DF value shift environment.
With high-speed high frequency characteristics of the substrate material, in the high frequency shift characteristics, general-type substrate material there are two types of more significant differences between the two categories: a class is followed by the frequency shift, its (DF) value shift is very small.
Another class is in the transformation amplitude and common type substrate material only nearby, but its own (DF) value is lower.
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