RU2713917C1 - Microwave switching board from high-resistance silicon on a metal base - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: present invention relates to the design of a microwave switching board made from high-resistance silicon on a metal base. On the front side of the silicon board there are at least two cavities-wells of different depth, on the front side there are strips of microstrip transmission lines made of metal with low electrical resistance of different thickness, on the reverse side of the silicon board there formed are air slots of different depth, which run parallel to the strips.

EFFECT: reduced ohmic losses when propagating UHF energy, enabling variation over a wider range of combined relative permittivity of the microstrip transmission line, eliminating overheating of UHF crystals and transmission lines formed on the board, ensuring preservation of structural strength of the silicon plate and possibility of making a circuit board using a group method.

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Description

The claimed invention relates to the design of a silicon patch circuit board with a resistivity of at least 10 kOhm · cm, located on a metal base and can be used in the manufacture of microwave power amplifiers used in remote sensing systems of the earth and high-frequency radio lines.

The prior art method for placement of microwave semiconductor components and integrated circuits (see US5063177A, publ. 05.11.1991). The invention relates to switching monolithic microwave integrated circuits and energy transfer at high frequencies. A silicon board is used as a passive element for transmitting energy at high frequencies. Silicon board has high thermal conductivity. By the method of anisotropic etching, indentations are formed in the circuit board for chip crystals and metallized holes. The recesses for the crystals are made with high accuracy.

Among the shortcomings, it should be noted the large losses in the conductive microstrips during the propagation of energy at high frequencies. Also, the design has insufficient strength due to the fragility of silicon.

From the prior art, the closest analogue to the proposed solution is known, revealing a microstrip line and a microstrip device containing it (see US6445345B1, published 03.09.2002).

The invention describes a microstrip line with low losses. The microstrip line is made in a dielectric substrate connected to a metal plate for grounding. In the metal plate in the places under the microstrips, air gaps are formed, which make it possible to reduce the energy loss in the conductor strips during the propagation of the microwave signal.

The disadvantages of the solution indicated as the closest analogue are:

- the air gap is formed in a metal plate, with a constant thickness of the dielectric plate. The design allows you to change the combined dielectric constant of the microstrip transmission line within narrow limits.

- the invention describes plates, the thermal conductivity of the material of which is hundreds of times less than the thermal conductivity of silicon.

The technical result of the claimed invention is to reduce ohmic losses in the propagation of microwave energy, the ability to vary within a wider range the combined relative dielectric constant of the microstrip transmission line, eliminating the overheating of microwave crystals and transmission lines formed on the board, ensuring the preservation of the structural strength of the silicon wafer and the possibility of manufacturing circuit board group method.

The technical result is achieved by creating a microwave switching board made of high-resistance silicon on a metal base, consisting of a single crystal silicon orientation board (100), with a resistivity of at least 10 kOhm · cm and a metal base, at least two well cavities are made on the front side of the silicon board of different depths, at the bottom of which electrically conductive holes are formed, on the front side are formed strips of microstrip metal transmission lines with low electrical resistance p of a certain thickness, on the reverse side of the silicon board, air grooves of different depths running parallel to the strips are formed by liquid anisotropic etching, the areas of grounded contacts on the front side are connected to the metal screen of the back side of the board using electrically conductive holes, the contacts for welding or soldering are outside the dimensions cavities-wells and grooves, on the back side of the silicon board everywhere, except grooves, a metal screen with a low electrical resistivity is made, t Ordering side silicon wafer entirely, except for the grooves is covered with solder, the metal base has a coating of a metal with low electric resistance and is connected to the silicon board by soldering.

The claimed invention is illustrated by the following figures:

Figure 1 - The front side of the silicon board;

Figure 2 - The back side of the silicon board;

Figure 3 - Section of a silicon board;

Figure 4 - A fragment of a section of a silicon board with a base.

The positions in the figures indicate the following:

1 - metal base;

2 - conductive coating;

3 - solder;

4 - a metal screen on the back of a silicon board;

5 - silicon board;

6 - strips of a microstrip transmission line;

7 - air cavity (groove);

8 - through metallized holes with contact pads;

9 - cavity-wells for crystals;

10 - through metallized holes in the cavities.

The claimed invention relates to the design of a silicon patch circuit board with a resistivity of at least 10 kOhm · cm, located on a metal base and can be used in the manufacture of onboard power amplifiers for space purposes in the frequency range from L to Ka.

A microwave impedance circuit board made of high resistance silicon on a metal base contains:

- a metal base coated with high electrical conductivity;

- a silicon board soldered to the base with cavities formed by the method of anisotropic etching of different depths for crystals on the front side and air grooves on the back;

- metallized holes of different lengths with contact pads formed in the cavities and on the board;

- metal strips of different widths formed on the front side of the silicon wafer;

- a conductive screen formed on the back side of the silicon wafer everywhere except in places where grooves with an air gap are formed;

- solder connecting the silicon board to the base.

In a preferred embodiment, the base material is a carpet.

Losses in the microstrip transmission line must be minimized. It is known that transmission losses include losses in the dielectric material of which the board is made, ohmic losses of the strip conductor and radiation losses from the strip conductor. The dielectric loss of high-resistance silicon becomes noticeable at high frequencies. Radiation loss also becomes apparent at high frequencies.

Thus, in the frequency range up to 10 GHz, for ohmic transmission lines, ohmic losses in the strips are decisive.

The main effect, which allows to reduce ohmic losses during energy transfer, is achieved using dielectric substrate materials having a low relative permittivity. The use of such substrates allows us to make the strips wider and thereby reduce ohmic losses.

Creating a silicon wafer anisotropically etched grooves allows to reduce the thickness of a silicon wafer with a dielectric constant _k Ε = 11.67 and an air layer to increase the permittivity Ε = 1 _in the boundary between silicon and a conductive coating.

In this case, the combined dielectric layer can be represented as two series-connected capacitors. Based on this, the combined dielectric constant Ε _eff can be estimated from the formula:

Ε _eff = (d _k + d _in ) × Ε _k × Ε _in × (Ε _k × d _in + Ε _in × d _k ) ^-1 ;

Thus, substituting Ε _eff in the strip line calculation formulas, it is possible to increase the width of the stripes and thereby reduce the ohmic losses that occur during the propagation of the microwave signal.

For example, when the thickness of the silicon wafer is 0.38 mm, d _k = 0.05 mm, and d _in = 0.33 mm Ε _eff = 1.13.

Silicon has a thermal conductivity of 120 W / m · K, it is 5 times higher than polycoric ceramics and more than 200 times higher than the thermal conductivity of Rogers microwave laminates. This allows the use of silicon boards in power amplifiers for transmitters.

The metal base gives the product the necessary mechanical strength.

The withdrawal of contact pads beyond the thinned places of the plate allows the installation of conductors by traditional methods of soldering or welding.

The silicon circuit board is manufactured using standard technological equipment used in the manufacture of microchips using group technology.

As a result of work on the creation of a microwave switching board on high-resistance silicon, parameters were obtained that suggest that at frequencies up to 10 GHz this technology surpasses microwave technology in multi-layer printed circuit boards, namely Rogers RO4350. Losses in microwave lines in high-resistance silicon are less than losses in microwave laminate Rogers RO4350.

The thermal conductivity of high-resistance silicon is several times higher than the thermal conductivity of boards made of microwave laminates, LTCC and polycor, which can be widely used for power amplifiers. The technology allows creating crystals wells and transitional metallized holes in high-resistance silicon circuit boards.

Thus, the claimed invention provides:

- small ohmic losses in the propagation of microwave energy due to wide strips;

- changing the ratio of the thickness of the silicon board and the air gap allows you to vary within a wider range of the combined relative permittivity of the microstrip transmission line;

- high thermal conductivity of silicon, eliminates overheating of microwave crystals and transmission lines formed on the board;

- the structural strength of the silicon wafer during thinning does not deteriorate due to the formation of cavity-wells and grooves inside the wafer, and is connected to a metal base to increase the structural strength. To reduce mechanical stresses arising during soldering and welding, the contact points are moved outside the thinned spots of the silicon wafer.

- the possibility of manufacturing a patch board by group methods using standard technologies used in the technology of manufacturing microcircuits.

Claims (2)

1. Microwave switching board made of high-resistance silicon on a metal base, consisting of a single crystal silicon orientation board (100), with a resistivity of at least 10 kOhm · cm and a metal base, at least two cavity-wells of different depths are made on the front side of the silicon board, on the bottom of which electrically conductive holes are formed, on the front side there are formed strips of microstrip metal transmission lines with low electrical resistance of different thicknesses, on the back of the silicon Air grooves of different depths running parallel to the strips are used by liquid anisotropic etching, the areas of grounded contacts on the front side are connected to the metal screen of the back side of the board using electrically conductive holes, the contacts intended for welding or soldering are located outside the dimensions of the cavity-wells and grooves, on the back to the side of the silicon board everywhere, except for the grooves, a metal screen with a low electrical resistivity is made, the back side of the silicon board is completely, except for the grooves, covered with solder, the metal base has a coating of metal with low electrical resistance and is connected to the silicon plate by soldering. 2. The microwave switching board according to claim 1, characterized in that the base material is insidious.

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