JPH02123795A - Multilayer circuit substrate - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding the structure of a multilayer circuit board in which a coaxial line for transmitting high-speed signals is embedded, an insulator is placed in the center of a cylindrical outer conductor with the aim of minimizing signal crosstalk. A coaxial line with a central conductor arranged therein is buried, and a ground layer is formed on the front and back surfaces so as to sandwich the coaxial line, and an insulating substrate is laminated in multiple layers. Configure to connect.

(Field of Industrial Application) The present invention relates to a multilayer circuit board in which a coaxial line for transmitting high-speed signals is buried, and a method for manufacturing the same.

In communication equipment, multilayer circuit boards that handle high-frequency bands of Gllz or higher are used to transmit high-speed signals using signal lines (strip lines), microstrip lines or strip lines in which a ground layer is placed parallel to the signal line (strip line) through an insulating layer. It is necessary to form a plate strip line to match impedance and prevent signal crosstalk as much as possible. Therefore, there is a demand for a multilayer circuit board that has good transmission characteristics with less signal crosstalk.

[Conventional technology]

A conventional line for transmitting high-speed signals is a triplate strip line in which a strip line (signal line) 12 is sandwiched between upper and lower ground layers 14b with an insulating layer 13 in between, as shown in the schematic diagram in Figure 4 (al). It has a structure called

In addition to the upper and lower ground layers 14b, the transmission characteristics of the triplate strip line are also influenced by the insulating layer 13, that is, the ground layer 14 that surrounds the strip wire 12 formed at both left and right ends of the insulating substrate. An experimental comparison of the cases of Fig. 4(b) and Fig. 4(c) in which the width W of The smaller the size shown in FIG. 4(C), the easier it is to match the impedance, suppressing cavity resonance within the substrate, and exhibiting good transmission characteristics.

The multilayer circuit board 11 having the actual structure of the schematic diagram in FIG. A wiring pattern 14 (including a land 14a for mounting and mounting components and a ground layer 14a) is formed between them, and these wiring patterns 14 are connected by a peer hole 14c, and the strip line 12 for transmitting high-speed signals is surrounded. A large number of pier holes 14c are arranged in parallel at intervals W to form the upper and lower earth layers 14.
It is connected to b and surrounded by a square.

[Problem to be solved by the invention]

However, according to the above-mentioned coaxial line structure,
Since the ground layer formed by the peer hole provides intermittent shielding, it is difficult to obtain sufficient electromagnetic shielding and it is difficult to obtain good transmission characteristics with little crosstalk.

In view of the above problems, an object of the present invention is to provide a multilayer circuit board that can reduce signal crosstalk as much as possible.

[Means to solve the problem]

In order to achieve the above object, in the multilayer circuit board of the present invention, a coaxial line is buried in an insulating substrate laminated in multiple layers, and ground layers are formed on the front and back surfaces so as to sandwich the coaxial line. The outer conductor of the ground layer is connected to the ground layer.

[Effect]

A signal line (strip line) is formed into a coaxial line, this coaxial line is buried in a multilayer circuit board, a ground layer is formed on the front and back sides of the coaxial line, and the outer conductor of the coaxial line and the ground layer are connected. By doing so, a multilayer circuit board having electromagnetically shielded signal lines can be obtained, and signal crosstalk within the multilayer circuit board can be reduced.

〔Example〕

The gist of the present invention will be explained in detail below based on embodiments shown in the drawings.

As shown in the perspective view and side sectional view of FIGS. 1(a) and fb), the multilayer circuit board includes lands 4a on which components are mounted and mounted on both outer layers, and a ground layer 4b that sandwiches a coaxial line 2 (described later) above and below. An insulating substrate 3 laminated in multiple layers with wiring patterns 4, wiring patterns 4 on each inner layer, and pier holes 4C for appropriately connecting the wiring patterns 4 on each inner layer depending on the circuit, and a cylindrical outer layer. It is composed of a coaxial line 2 in which a center conductor (signal line) 2a is disposed at the axis of a conductor 2b via an insulator 2c.

The coaxial line 2 is buried in a buried hole 3a provided in an insulating substrate 3, and the outer conductor 2b of the coaxial line 2 and the ground layer 4b formed on both outer layers are connected (or directly) through a peer hole 4C. Note that the coaxial line 2 is formed using an insulating material and a conductive material having the same composition as the insulating substrate 3 and the wiring pattern 4 to prevent thermal distortion from occurring during heating.

Next, a method for manufacturing the coaxial line 2 will be described using a perspective view showing the manufacturing process in FIG. That is, as shown in FIG.
(e.g. copper paste) 2a'.

■Step: Roll it up and dry it. The winding diameter is at least smaller than the thickness of the multilayer circuit board.

■Step: Apply a conductor paste 2b' that will become the outer conductor 2b to the outer peripheral surface and dry it.

Figure 2 (bl) cutting die/bonding method: ■Step: Ceramic insulation paste 2c'' which will become the insulator 2c is poured into the cutting die 5 having two semicircular semicircular hollows in cross section and dried. A conductor paste Ha' which will become the center conductor 2a is printed at the center and dried.

■Step: Pull out from the cutting die 5 and press both together.

■Step: Conductor paste that becomes external conductor 2b on the outer circumferential surface)
2b' is applied and dried.

In the cutting method shown in FIG. 2(C), Step 1: The mandrel 7 is erected on the axis of the cylindrical hole of the cutting die 6, and the ceramic insulating paste 20'' serving as the insulator 2c is poured in and dried.

■Step: Remove the mandrel 7, then the center conductor 2a
The conductor paste 2a' is filled.

■Step: Cut out from the cutting die 6, and put the outer conductor 2 on the outer circumferential surface.
A conductive paste 2b', which becomes b, is applied and dried.

Next, a method of manufacturing a multilayer circuit board using this coaxial line 2 will be explained with reference to the side sectional view of FIG.

■Step: Punching alignment holes (path shown), pier holes 4C, and embedded holes 3a for the coaxial line 2 on each ceramic green sheet 3 (the figure shows 6 sheets) forming the insulating substrate 3 of the multilayer circuit board. Open by. The size of the embedded hole 3a is made to match the outer dimensions of the coaxial line 2 at the stacked position.

■Step: Conductive paste 4C (for example, copper paste) in the peer hole 4C of each ceramic green sheet 3C
A conductive paste 4' is screen printed to form a predetermined wiring pattern 4 on the surface and dried.

■Step - Layer each ceramic green sheet 3'' while sandwiching the coaxial line 2 so as to embed it.

■Step: Heating the laminated ceramic green sheets 3゛ in a reducing atmosphere at a temperature of 900℃ to 1000℃,
Press and bake.

■Step 2 After screen printing and drying the conductive paste 4゛ (copper paste) that forms the outer layer wiring pattern 4 on the front and back sides (including the land 4a on which components are mounted and the ground layer 4b), the temperature is set at 750°C to 900°C. Heating, pressing and firing in a reducing atmosphere.

Through the above steps, a multilayer circuit board in which the coaxial line 2 is embedded can be manufactured.

In this way, a coaxial line in which a signal line and a cylindrical outer conductor are formed into a coaxial structure has a continuous conductor and a constant shape compared to a conventional discontinuous pier hole surrounded by a signal line. , it is possible to form a high-speed signal line with extremely low signal crosstalk and always having constant transmission characteristics.

Further, the coaxial line can be easily manufactured in advance in a single piece in a fixed shape by the above-mentioned winding method, die-cutting/bonding method, die-cutting method, or the like.

In addition, by forming the coaxial line using an insulating material and a conductive material that have the same composition or almost the same thermal shrinkage rate as the insulating substrate and wiring pattern, the thermal shrinkage rate becomes substantially the same, so that when the substrate is heated, pressed, and baked, Heat distortion can be eliminated.

〔Effect of the invention〕

As described in detail above, according to the present invention, a multilayer circuit board having a coaxial line exhibits an extremely useful effect in practice, such as being able to improve the transmission characteristics of high-speed signals with extremely low crosstalk.

[Brief explanation of the drawing]

1(al) and (b) are a perspective view and a side sectional view of one embodiment of the present invention, FIG. 2 is a perspective view showing the manufacturing process of the coaxial line of FIG. 1, and FIG. 3 is a view similar to that of FIG. 4(a), (bl), (C) are schematic diagrams showing strip lines, and FIG. 5(a), (tel is based on conventional technology. They are a perspective view and a side sectional view. In the figures, 1 is a multilayer circuit board, 2 is a coaxial line, 2a is a center conductor (signal line), 2b is an outer conductor, 2c is an insulator, 3 is an insulating substrate, and 4 is a In the wiring pattern, 4b indicates the ground layer.

Claims (1)

[Claims] A coaxial line (2) with a center conductor (2a) arranged through an insulator (2c) is buried in the center of a cylindrical outer conductor (2b), and ground is placed on the front and back sides so as to sandwich the coaxial line (2). layer(
4b) and is formed of an insulating substrate (3) laminated in multiple layers, and is characterized in that the outer conductor (2b) of the coaxial line (2) and the ground layer (4b) are connected. circuit board.