JP4005105B2 - Printed circuit board, radio wave receiving converter and antenna device - Google Patents

Description

  The present invention relates to a printed wiring board, a radio wave receiving converter, and an antenna device, and more particularly to a printed wiring board structure capable of reducing warpage after heat treatment for reflow and the like, and a radio wave receiving converter and antenna including the printed wiring board. Relates to the device.

  Conventionally, a printed wiring board in which a wiring pattern is formed on a substrate made of an insulator is widely known. An example of this printed wiring board is a high-frequency circuit board. A microstrip line or a coplanar line is often used as a line formed on the high-frequency circuit board.

  For example, a substrate portion on which a microstrip line is formed (hereinafter referred to as a “microstrip substrate”) includes a component surface (surface on the side where a transmission line is formed) and a ground surface.

  13 and 14 are schematic views of the microstrip substrate. As shown in these drawings, the microstrip substrate has a substrate 2 made of a dielectric, a strip line 1 formed on the surface of the substrate 2, and a ground pattern 3 formed on the back surface of the substrate 2. . The ground pattern 3 is usually composed of a metal layer that covers the entire ground surface of the microstrip substrate. In this specification, the ground pattern 3 is also referred to as a pattern including the entire metal layer. On the other hand, a coplanar circuit generally has a configuration in which a transmission line is surrounded by a ground pattern.

  For example, when the above-mentioned microstrip substrate is subjected to heat treatment for reflow or the like, the substrate 2 is warped due to the difference in the ratio of the area of the remaining metal on the front surface and the back surface of the substrate 2 (hereinafter referred to as “residual copper ratio”). To do. The greater the difference in the remaining copper ratio between the front surface and the back surface of the substrate 2, the greater the warp amount of the substrate 2.

  Normally, warping of a substrate due to heat treatment hardly occurs in a hard substrate, but warping appears significantly in a soft substrate such as a substrate made of polytetrafluoroethylene or a so-called flexible substrate, and the substrate performance and quality are large. Influence.

  Therefore, conventionally, in order to prevent warping, the substrate is massaged before reflow, low-temperature reflow is performed, or warpage calibration is performed in a separate process.

  However, even if the above-mentioned measures are taken, the board 2 is warped, and the parts are dropped or the parts are misaligned during reflow. In addition, chip cracks or the like may occur when the substrate 2 is incorporated in the housing, which may cause a serious quality problem. Further, there is a problem that a loss due to another process such as massage of the substrate 2 becomes very large.

  Accordingly, an object of the present invention is to devise the conductor pattern formed on the substrate, so that the performance of the printed wiring board after the heat treatment is maintained without deteriorating the performance of the product and reducing the loss due to another process. Is to make it smaller.

  Another object of the present invention is to provide a radio wave receiving converter and an antenna device that have high reliability and high performance by incorporating the printed wiring board.

The printed wiring board according to the present invention has a substrate having a through hole and a front surface and a back surface made of an insulator, a line pattern provided on the surface of the substrate , and on the surface of the substrate , separated from the line pattern, and a ground pattern provided around the through hole, Ru der metal surface ratio different from that in the front and back surfaces of the substrate. A first opening is provided between the ground pattern and the through hole so as to reach the surface of the substrate so as to surround the through hole so as to make the through hole independent of the ground pattern. A plurality of second openings reaching the surface of the substrate are provided in the pattern. The first opening and the second opening are openings for preventing warpage of the substrate after the heat treatment.

A conductor portion is generally formed in the through hole. During heat treatment such as reflow, heat is easily stored in the conductor, and this heat is transmitted to the conductor pattern formed on the substrate, which causes warpage of the substrate. Therefore, by providing an opening between the ground pattern and the through hole, the area of the path through which heat stored in the conductor portion in the through hole during heat treatment such as reflow is transmitted to the ground pattern can be reduced. Thereby, thermal diffusion from the through hole to the ground pattern during heat treatment can be suppressed, and warpage of the substrate due to such thermal diffusion can be suppressed.

The openings, Ru provided to surround the through hole. Thereby, it is possible to separate the through holes from the ground pattern, it is possible to effectively suppress the transfer of heat from the through hole to the ground pattern.

  The radio wave receiving converter of the present invention includes the printed wiring board described above. The antenna device of the present invention includes the radio wave receiving converter and a reflection parabola unit that reflects the received radio wave and guides it to the radio wave receiving converter.

  According to the present invention, it is possible to reduce the amount of warpage of the substrate after the heat treatment. When the present inventor provided heat treatment so that the copper ratio of the back surface grounding surface was 70 to 80% with respect to an actual high-frequency circuit board and performed heat treatment, the amount of warpage of the substrate after heat treatment was conventionally increased. It was possible to improve from 1/5 to 1/10. Since the amount of warping of the substrate can be reduced in this way, it is possible to reduce component dropout and displacement due to warping of the substrate, and to improve the reliability of the substrate. Further, the reliability after the product is incorporated into the housing can be improved. Furthermore, since the opening and the through hole of the present invention can be easily formed by a technique such as etching, a loss due to another process can be suppressed as compared with the case where the substrate is massaged.

  Since the radio wave receiving converter and the antenna device of the present invention are provided with the printed wiring board described above, they have high reliability and high performance.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
(Embodiment 1)
1 is a schematic cross-sectional view of a microstrip line portion in a printed wiring board according to a first embodiment of the present invention, and FIG. 2 is a back view of the printed wiring board shown in FIG.

  As shown in FIGS. 1 and 2, the printed wiring board includes a substrate (base material) 2 made of a dielectric (insulator), and a strip line (first conductor) formed on the surface of the substrate 2 and serving as a transmission line. Pattern) 1 and a ground metal layer (ground pattern) 3 formed to cover the entire back surface of the substrate 2.

  The substrate 2 is produced using, for example, glass fiber and polytetrafluoroethylene. The strip line 1 and the ground metal layer 3 are made of copper, for example. In order to prevent corrosion, the copper surface may be coated with gold plating, solder plating, organic resin, or the like.

  A plurality of openings 4 are provided in the ground metal layer 3. In the example shown in FIGS. 1 and 2, the openings 4 are formed substantially uniformly over the entire back surface of the substrate 2, and reach the surface of the substrate 2 or the coating layer formed on the surface of the substrate 2. Therefore, the surface of the substrate 2 or the coating layer formed on the surface of the substrate 2 is exposed at the bottom of the opening 4. The opening 4 can be formed by etching, for example.

  In microstrip lines, a transmission line is formed on one side of the board and a ground metal layer is formed on the other ground plane, so the metal plane ratio (remaining copper ratio) on each side may be extremely different. Many. Therefore, a large stress is generated between the metal layer having a different thermal expansion coefficient and the dielectric (substrate 2), and the substrate 2 is warped.

  In FIG. 5, relatively soft polytetrafluoroethylene is used as the material of the substrate 2, Cu layers 12 and 13 are formed on both surfaces of the substrate 2, and openings are formed in the Cu layer 13 on the ground surface (one surface). Data on the amount of warpage of the substrate 2 when the remaining copper ratio of the ground plane is formed and the heat treatment is performed at 200 degrees or more (for example, about 200 degrees to 230 degrees) is shown.

  As shown in FIG. 5, when the remaining copper ratio on the ground plane is 100%, there is no warpage of the substrate 2, but it can be seen that the warpage amount of the substrate 2 increases as the remaining copper ratio is lowered. In particular, the amount of warpage of the substrate 2 becomes the largest when the remaining copper ratio is around 0 to 25%.

  Next, FIG. 6 shows a warpage test result when the idea of the first embodiment is applied to an actual printed wiring board having a microstrip line.

  In this test, polytetrafluoroethylene was used, and a printed wiring board having a thickness of 110 mm and a size of 110 × 110 mm was adopted. Various wiring patterns and electronic components are mounted on the printed wiring board. A substrate in which an opening 4 is provided in the ground metal layer 3 of such a printed wiring board to adjust the remaining copper ratio of the ground plane, and a substrate having various remaining copper ratios is subjected to the same heat treatment as in FIG. The amount of warpage was measured.

  As shown in FIG. 6, in the above example, the optimum point of the remaining copper ratio is around 75%. However, when the remaining copper ratio is about 70 to 80%, the warpage amount of the substrate 2 is set to a small value. did it. That is, by providing the opening 4 according to the present invention in the ground metal layer 3, the amount of warpage of the substrate 2 can be reduced.

  The optimum remaining copper ratio varies depending on the type of substrate 2 and the coefficient of thermal expansion, the wiring pattern on the surface of the substrate 2, the hardness, thickness, size, etc. of the substrate 2. It is necessary to determine the remaining copper ratio individually.

  The characteristics of the microstrip line vary depending on the condition of the ground plane. Therefore, if the copper layer is arbitrarily removed, there may be a large characteristic deterioration. Therefore, when the present invention is applied to a high-frequency circuit board, the following special devices are required.

  That is, it is necessary to select the shape and size of the opening 4 according to the operating frequency. Specifically, the maximum width of the opening 4 is set to be equal to or less than the guide wavelength λg of the waveguide in which the microstrip line is installed. Thereby, characteristic deterioration of the microstrip line can be suppressed. In the example shown in FIG. 3, the shape of the opening 4 is circular. In this case, the diameter of the opening 4 is set to be equal to or less than the guide wavelength λg. The diameter of the opening 4 may be λg / 4 or less.

  Next, a method for designing the opening 4 will be described. Here, an example of a method for designing the circular opening 4 will be described.

  The diameter Rg (D in FIG. 3) of the opening 4 (circular hole) when the dielectric constant of the substrate 2 is ε and the wavelength in the tube is λg is expressed by the following formula (1).

Rg = λg / 4 (1)
Further, when the wavelength in the substrate 2 is λ, the formula (1) becomes the following formula (2).

Rg = (λ / 4) × (1 / √ε) (2)
By setting the diameter Rg of the opening 4 in accordance with the above formulas (1) and (2), the performance degradation of the microstrip line can be avoided.

Next, an example of a method for arranging the openings 4 will be described.
As shown in FIG. 3, after obtaining the diameter D of the opening 4 by the above formula (1), the arrangement of the opening 4 with respect to the remaining copper ratio is determined. For example, in the case of a remaining copper ratio of 75%, L1 × L2 = 2Rg√3.

(Embodiment 2)
Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 4 is a partial plan view of the printed wiring board according to the second embodiment.

  As shown in FIG. 4, the ground pattern 6 may be provided on the microstrip line surface of the substrate 2 on the side where the strip line 1 is formed, and the opening 4 may be provided in the ground pattern 6. Also in this case, the remaining copper ratio can be adjusted, and the warpage of the substrate 2 can be reduced. The shape and design method of the opening 4 are the same as those in the first embodiment.

(Embodiment 3)
Next, Embodiment 3 of the present invention will be described with reference to FIG. FIG. 7 is a partial cross-sectional view of the printed wiring board according to the third embodiment. In the third embodiment, the present invention is applied to a printed wiring board having a laminated substrate.

  As shown in FIG. 7, the printed wiring board includes substrates 7 and 9 made of different materials, an intermediate layer 8 formed between the substrates 7 and 9, and strip lines (transmission lines) on the surfaces of the substrates 7 and 9. ) 1.

  The substrate 7 is made of, for example, FR-4, and the substrate 9 is made of, for example, polytetrafluoroethylene. The intermediate layer 8 is composed of a metal layer such as copper.

  In the third embodiment, through holes 5 reaching the respective substrates 7 and 9 are formed in the intermediate layer 8. By providing the through holes 5 in this way, it is possible to suppress the generation of internal stress due to the difference in the thermal expansion coefficient of the foreign material during the heat treatment, and to contribute to the reduction of the warp of the substrate 2.

  The maximum width of the through hole 5 is also set to be equal to or less than the guide wavelength λg of the waveguide in which the transmission line is installed. Thereby, characteristic deterioration of the transmission line can be suppressed. Moreover, the opening shape of the through hole 5 may be circular, and in this case, the diameter of the opening of the through hole 5 is set to be equal to or less than the guide wavelength λg. The diameter of the opening may be λg / 4 or less.

  The same design method as in the first embodiment can also be adopted for the above-described through hole 5, but when calculating the diameter of the opening of the through hole 5, the dielectric constant ε of the substrates 7 and 9. It is necessary to decide the diameter by adopting the larger one. Also, when handling two or more frequencies, it is necessary to calculate based on the higher frequency.

(Embodiment 4)
Next, Embodiment 4 of the present invention will be described with reference to FIG. FIG. 8 is a partial cross-sectional perspective view of the printed wiring board according to the fourth embodiment.

  In the fourth embodiment, the present invention is applied to a coplanar line portion in a printed wiring board.

  As shown in FIG. 8, the printed wiring board according to the fourth embodiment includes a line pattern (signal line) 17 and a ground pattern 18 on the same surface of the board 2. Then, an opening 4 is provided in the ground pattern 18. Thereby, the remaining copper ratio in the track | line surface of the board | substrate 2 can be adjusted, and the curvature amount of the board | substrate 2 after heat processing can be reduced.

(Embodiment 5)
Next, Embodiment 5 of the present invention and its modification will be described with reference to FIGS. FIG. 9 is a partial plan view of the printed wiring board according to the fifth embodiment. In the fifth embodiment, the present invention is applied to a printed wiring board having a through hole.

  Usually, in the high frequency circuit, the through hole 10 is used to electrically ground the transmission surface and the ground surface on the back surface. Since the inner surface of the through hole 10 is covered with a metal layer (conductor portion) 16 formed by plating or the like, the thermal conductivity of the through hole 10 is larger than that of the surrounding dielectric. Therefore, the heat distribution of the entire substrate 2 is disturbed, and the substrate 2 in the area where the through holes 10 are concentrated is likely to be warped.

  Therefore, an opening 15 is provided between the ground pattern (conductor pattern) 6 around the through hole 10 and the through hole 10. Thereby, the area of the path through which heat stored in the metal layer 16 in the through hole 10 during heat treatment such as reflow is transmitted to the ground pattern 6 can be reduced. Thereby, thermal diffusion from the through hole 10 to the ground pattern 6 can be suppressed during heat treatment, and warpage of the substrate 2 due to the thermal diffusion can be suppressed.

  In particular, as shown in FIG. 9, by providing the opening 15 so as to surround the through hole 10, the through hole 10 can be made independent from the ground pattern 6. That is, the through hole 10 can be made independent of the conductor pattern on the substrate surface. Thereby, the diffusion of heat from the through hole 10 to the substrate surface can be eased, and the warpage of the substrate 2 due to local heat concentration can be reduced.

  When it is necessary to electrically connect the through hole 10 to the ground pattern 6, as shown in FIG. 10, the metal layer 16 in the through hole 10 and the ground pattern 6 are connected by the narrow connection pattern 11 having a small heat capacity. To do. Thereby, the area of the path when heat is transferred from the through hole 10 to the ground pattern 6 can be reduced, and the heat conduction from the through hole 10 to the substrate surface can be reduced.

  Said connection pattern 11 can be comprised by metal patterns, such as copper, for example. In the example shown in FIG. 10, four connection patterns 11 are provided, but the number of connection patterns 11 may be singular or plural.

  In the example shown in FIG. 10, the connection pattern 11 is provided so as to bridge over the opening 15. As a result, it appears that a plurality of openings are provided around the through-hole 10 in appearance.

  Furthermore, it is conceivable that the ground pattern 6 is patterned by etching or the like to provide a plurality of openings around the through hole 10. Also in this case, the heat conduction from the through hole 10 to the substrate surface can be reduced as in the above case.

  In the above embodiment, the case where the present invention is applied to a high-frequency circuit board has been described, but the present invention can also be applied to other printed wiring boards. That is, any conductive pattern formed on the substrate surface in order to prevent warpage of the substrate after the heat treatment is within the scope of the present invention.

  When the present invention is applied to a high-frequency circuit board, since the electrical influence due to the shape and size of the opening and the like is large as described above, it is necessary to select the shape and size of the opening and the like according to the design method described above. . However, when the present invention is applied to other than the high-frequency circuit board, there is no restriction as in the case of the high-frequency circuit board. Therefore, the conductor pattern may be selectively removed to provide an arbitrarily shaped opening, a through hole, a slit, a notch, or the like as long as the circuit characteristics are not deteriorated.

(Embodiment 6)
Next, a radio wave receiving converter (LNB: Low Noise Block down Converter) and an antenna apparatus incorporating a high frequency circuit board to which the present invention is applied will be described with reference to FIGS.

  As shown in FIG. 11, radio waves (signals) from satellites are reflected and concentrated by the reflecting parabolic unit 21, and are guided to and taken in by the radio wave receiving converter 20. The reflection parabolic unit 21 and the radio wave receiving converter 20 constitute an antenna device.

  Radio waves from the satellite are circularly polarized waves, including right-handed circularly polarized waves and left-handed circularly polarized waves. The radio wave receiving converter 20 separates these two components, amplifies each of the components, and converts the radio waves in the several tens GHz band into signals in the 1 GHz band. The converted signal is sent to a television 23 via an indoor receiving device such as a satellite receiver 22 via a cable.

  As shown in FIG. 12, the radio wave receiving converter 20 includes a metal chassis 24 having an output terminal (F-type connector) 25, a high-frequency circuit board 26, and a metal frame 27 assembled to the chassis 24. Is provided. The printed wiring board of the present invention is used as the high-frequency circuit board 26 incorporated in the radio wave receiving converter 20.

  The frame 27 is fixed to the chassis 24 with screws, and the chassis of the radio wave receiving converter 20 is formed by the chassis 24 and the frame 27. The high-frequency circuit board 26 of the present invention is incorporated in this housing.

  Although the embodiment of the present invention has been described as described above, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and includes meanings equivalent to the terms of the claims and all modifications within the scope.

It is a cross-sectional schematic diagram of the microstrip line part in the printed wiring board of Embodiment 1 of this invention. It is a reverse view of the printed wiring board shown in FIG. FIG. 3 is a partially enlarged view of the opening shown in FIG. 2. It is a fragmentary top view of the printed wiring board in this Embodiment 2. It is a figure which shows the relationship between the remaining copper rate of a ground surface, and the curvature amount of a board | substrate. It is a figure which shows the relationship between the remaining copper rate of the ground plane at the time of forming an actual pattern, and the curvature amount of a board | substrate. It is a fragmentary sectional view of the printed wiring board of Embodiment 3 of the present invention. It is a fragmentary perspective view of the printed wiring board of Embodiment 4 of the present invention. It is a fragmentary top view of the printed wiring board of Embodiment 5 of the present invention. FIG. 10 is a partial plan view of a modification of the example shown in FIG. 9. It is a conceptual diagram which shows the converter for radio waves and antenna apparatus of this invention. It is a disassembled perspective view of the converter for radio wave reception of the present invention. It is a perspective view of the board | substrate which has the conventional microstrip line. It is sectional drawing of the board | substrate shown in FIG.

Explanation of symbols

  1 Strip line, 2, 7, 9 Substrate, 3 Ground metal layer, 4, 14, 15 Opening, 5 Through hole, 6, 18 Ground pattern, 8 Intermediate layer, 10 Through hole, 11 Connection pattern, 12, 13 Cu layer , 16 Metal layer, 17 Line pattern, 20 Radio wave receiving converter, 21 Reflection parabolic part, 22 Satellite receiver, 23 Television, 24 Chassis, 25 Output terminal, 26 High frequency circuit board, 27 Frame.

Claims (3)

A substrate having through holes and having a front surface and a back surface made of an insulator;
A line pattern provided on the surface of the substrate;
On the surface of the substrate, provided with a ground pattern spaced apart from the line pattern and provided around the through hole,
In the front surface and the back surface of the substrate, a printed wiring board having a different metal surface ratio,
A first opening is provided between the ground pattern and the through hole so as to reach the surface of the substrate while surrounding the through hole so as to make the through hole independent of the ground pattern. A plurality of second openings reaching the surface of the substrate in the ground pattern located around
The first opening and the second opening are openings for preventing warping of the substrate after heat treatment . A radio wave receiving converter comprising the printed wiring board according to claim 1 . An antenna device comprising: the radio wave receiving converter according to claim 2; and a reflection parabolic unit that reflects the received radio wave and guides it to the radio wave receiving converter.

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