Multilayer printed circuit board with protection coat

FIELD: electronics; printed circuit boards.

SUBSTANCE: multilayer printed circuit board consisting of signal dielectric layers comprising topological patterns of the printed wiring and interchanging with screening layers having the form of a grid provided with printed conductors reflecting the topological pattern configuration of their nearest signal layer. Top layers of said printed circuit board are covered with a protection coat that consists of a mixture of ferrite powder and plastic binder based on protective varnishes or compounds and is applied by means of spreading, immersion or spraying.

EFFECT: enhancement of the quality of printed circuit board protection against effects of EMI.

 

The invention relates to techniques for electric printed wiring, in particular the designs of printed circuit boards for automation and computing.

When using printed circuit boards in high-speed digital devices printed conductors on the circuit Board to be sources of electromagnetic fields (EMF). Due to exposure to high-frequency EMFs may malfunction digital devices. The traditional solution in the design of printed circuit boards is the use of alternating shielding layers with the maximum possible area of the shielding. However, this does not provide protection from exposure to EMFs of the outer layers of the PCB, as external interference from a neighboring card devices, and internal noise generated by the elements of the printed wiring on the outer layers of the PCB will not be neutralized.

A known design of a multilayer Board, consisting of several glued together signal layers having topological pattern printed installation and set electric connection between the layers, and to provide controlled crosstalk multilayer printed circuit Board is provided with a continuous shielding layers, short United with a layer of earth AC [1].

The disadvantages of this design is tion are:

first, the sharp increase in the probability of failure with increasing dimensions of the card when using a continuous shielding layers due to delamination due to the different physical properties of dielectric and conductive layer;

secondly, the outer layers of multilayer printed circuit boards are not protected from the effects of both external and internal electromagnetic interference;

thirdly, the use of solid shielding layers leads to an increase in weight of the PCB.

Also known for the design of multilayer printed circuit boards, consisting of multiple signal layers with the topological figure of the printed installation, alternating with shielding layers made in the form of a grid, which allows to reduce the weight of the Board and improve its reliability due to less probability of its stratification [2].

The disadvantages of this design are:

first, low immunity and a strong influence of crosstalk in the presence of conductors with different cross-sections and configurations, which leads to its inapplicability when working at higher frequencies, at low rise and decline of the information signal and when using devices with high input impedance, and with the increase in the area of multilayer boards these drawbacks increase dramatically;

secondly, the outer layers of multi-stakeholder who eunuch printed circuit boards are not protected from the effects of external and internal electromagnetic interference.

Closest to the proposed technical solution is to design a multilayer printed circuit Board, which consists of a dielectric signal layers containing topological picture printed wiring and shielding layers, made in the form of a grid and provided with printed conductors, repeating configuration of conductors nearest the signal layer [3].

The disadvantage of this construction is that the outer layers of multilayer printed circuit boards are not protected from the effects of both external and internal electromagnetic interference.

The technical result of the invention is the improvement of quality protect printed circuit boards from exposure to EMFs.

The technical result is achieved by the fact that in the multilayer printed circuit Board comprising a signal dielectric signal layers containing the topological figure of PCB Assembly, alternating with shielding layers made in the form of a grid which is provided with printed conductors, repeating the topological configuration of the figure adjacent signal layers, the outer layers are covered with a protective coating consisting of a mixture of ferrite powder with polymer binder.

The proposed construction of a multilayer printed circuit boards will allow you to protect against printing the data conductors of the outer layers of the PCB from exposure to EMFs neighboring devices, to reduce the impact of the printed conductors on each other and reduce the amount of EMF PCB into the environment. This is due to the fact that the combined protective coating containing ferrite powder, absorbs the EMFs emitted from the printed conductors and the surrounding circuit Board devices.

The composition of the protective coating is obtained by adding a solution of a polymeric binder ferrite powder. As use ferrite, Mn - Zn, Ni - Zn, Ba - ferrite, and as the polymer binder used varnishes (PL-98, ETR-5, PFL-86 and others) or the compounds (EPC-1, EPC-4, etc-6 and others), are used in electronics for protection against aggressive environment. The concentration of the ferrite powder is 15-25%. Apply protective coating on the outer layers of the multilayer printed circuit Board by dipping in the solution, by spraying or smearing. The thickness of the protective coating is 0.4 to 0.7 mm

Thus, the use of this design of printed circuit boards in high-speed devices complex digital systems can improve quality protect printed circuit boards from EMF exposure, reduces the interaction between the printed conductors on the outer layers of the PCB reduces the EMF radiation into the surrounding space, which provides improved electromagnetic compatibility print p the ATA with other devices, as the polymer binder of the combined protective coating significantly reduces the aggressive effects of the environment.

Sources of information

1. Dolkart V.M., Novik GH Structural and electrical properties of multilayer printed circuit boards. M: Soviet radio, 1974. 88 C.

2. OST 4 g. 10.011. Edition 1-70 "printed circuit Board. Design". p.14, p. 6.25, 6.26.

3. SU, 1029434 A, 15.07.1983. Multilayer printed circuit Board (prototype).

Multilayer printed circuit Board with a protective coating consisting of a signal of dielectric layers with the topological figure of the printed installation, alternating with shielding layers made in the form of a grid, which is applied to the printed conductors, repeating the topological configuration of the figure adjacent signal layer, characterized in that the outer layers of the PCB is covered with a protective coating consisting of a mixture of ferrite powder with polymer binders based protective varnish or compounds.



 

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