JP2012114696A - High-frequency circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-frequency circuit board capable of suppressing passage loss of a high-frequency transmission line, such as a microstrip line for transmitting a high-frequency signal, and achieving high productivity, as well as low noise from a low-noise amplifier, high saturation power of an amplifier for transmission and low phase noise from a voltage variable oscillator.SOLUTION: The high-frequency circuit board includes: a transmission line formed from a metal conductor on a surface of an insulator substrate and a solder layer formed from reflow solder on a surface of a transmission line.

Description

The present invention relates to a low-loss high-frequency circuit board used in a high-frequency region.

A transmission line used in a high frequency region such as a microwave and a millimeter wave is formed on a flat substrate made of an insulator such as Teflon (registered trademark) or glass epoxy, and a microstrip line that is easy to manufacture is used. Although copper is mainly used as the surface conductor of the microstrip line, it is necessary to protect the copper surface because copper is likely to be oxidized and corroded and not conduct electricity.

For surface protection of copper, there are methods of tin plating, gold, and silver plating. However, tin plating has a problem of whiskers in which tin grows in an elongated bowl shape, and gold and silver plating have a problem of deterioration due to copper diffusion. It becomes.

Also, as a copper surface protection, a solder coat is used in which the substrate is immersed in molten solder and then air is blown to blow off excess solder attached to parts other than copper. Thermal deformation of the substrate due to passing through becomes a problem. In recent years, regulations such as the enforcement of restrictions on the use of specific hazardous substances in electrical and electronic equipment by the European Union (EU) have led to the need for electrical and electronic circuits that do not use lead, but lead-free solder containing tin, silver, and copper Since lead has a higher melting point than leaded solder, the lead-free solder coat is more susceptible to thermal deformation of the substrate.

For this reason, as shown in Patent Document 1, a method of performing gold plating after nickel plating is used to protect the copper surface of the lead-free high-frequency circuit board.

JP 2003-318611 A

  However, the thickness of the gold plating is as thin as about 0.1 μm, and the current mainly flows through the nickel plating. At high frequencies, the current concentrates on the surface of the conductor due to the skin effect, but since nickel has a shallow skin depth compared to tin, copper, etc., the portion through which the current flows is thin, so the resistance increases and the passage loss increases.

For this reason, in the communication device using the microstrip line substrate having the configuration shown in Patent Document 1, the transmission output amplifier has a reduced saturation output power due to an increase in the passage loss of the microstrip line after output. In addition, the low noise amplifier of the receiving system deteriorates the noise figure due to an increase in the passage loss of the microstrip line at the input section. Further, in a voltage controlled oscillator using a microstrip line as a resonator, the vibration increase coefficient is lowered due to an increase in passage loss of the microstrip line, and phase noise is deteriorated.

The present invention has been made to solve such a problem, and obtains a high-frequency circuit board with reduced productivity and high productivity of a high-frequency transmission line such as a microstrip line for transmitting a high-frequency signal. For the purpose. Furthermore, an object of the present invention is to reduce the noise of the amplifier using the microstrip line and to achieve a high saturation output, and to reduce the phase noise of the voltage variable oscillator.

  A high-frequency circuit board according to the present invention includes a transmission line formed of a metal conductor on the surface of an insulator substrate, and a solder layer formed of reflow solder on the surface of the transmission line.

  By implementing the present invention, the passage loss of the microstrip line is reduced, the amplifier is reduced in noise and output is high, and the voltage variable oscillator is reduced in phase noise.

It is a perspective view of the high frequency circuit board using the microstrip line in Embodiment 1 of this invention. It is sectional drawing of the microstrip line | wire of a prior art example. It is sectional drawing of the microstrip line in Embodiment 1 of this invention. It is an application process figure of the lead-free solder of the high frequency circuit board in Embodiment 1 of this invention. It is a manufacturing process and component mounting process diagram of a conventional printed wiring board. It is a structural example of a communication apparatus. It is a block diagram of the high frequency circuit board in Embodiment 2 of this invention. It is a block diagram of the high frequency circuit board in Embodiment 3 of this invention. It is a block diagram of the voltage controlled oscillator circuit in Embodiment 4 of this invention.

Embodiment 1 FIG.
1 is a perspective view of a high-frequency circuit board using a microstrip line according to Embodiment 1 of the present invention. In FIG. 1, 1 is a lead-free solder, 2 is gold plating, 3 is nickel plating, 4 is a copper substrate and a copper-plated conductor pattern, 5 is an insulator such as Teflon (registered trademark) or glass epoxy, 6 is It is a back surface ground pattern.

  FIG. 2 is a cross-sectional view of a conventional microstrip line. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 2, 7 is a high frequency current transmission region.

  FIG. 3 is a cross-sectional view of the microstrip line according to the first embodiment of the present invention. 3, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted.

  The high-frequency signal is transmitted as a high-frequency current through the surface conductor of the microstrip line formed on the surface of the high-frequency circuit board, and when this high-frequency current flows through the surface conductor, the current density of the high-frequency current in the cross-section of the surface conductor is There is a phenomenon that it is large on the surface and small when it is separated from the surface. This phenomenon is called the skin effect. The depth of the surface conductor in which the current is 1 / e (about 0.37) times the surface current is called the skin depth, and the skin depth is represented by √ (1 / (πσμf)) meters. Here, σ represents the conductivity of the conductor, μ represents the magnetic permeability of the conductor, and f represents the signal frequency of the high frequency signal.

Since nickel has a higher magnetic permeability than gold, silver, copper, etc., the skin depth is shallow, and the cross-sectional area of the surface conductor through which high-frequency current flows is narrow, so that high-frequency signal passage loss is large. By applying the lead-free solder 1 with a thickness of √ (1 / (πσμf)) or more on the nickel plating 3 and the gold plating 2, the high frequency current does not flow to the nickel plating 3, but the high frequency current due to the skin effect flows. A high-frequency current flows through the lead-free solder 1 having a wide cross-sectional area, and a high-frequency signal passing loss is reduced.

For example, when the high frequency signal is a signal frequency of 12 GHz, the skin depth of gold due to the skin effect is 0.72 μm. The thickness L2 of the gold plating 2 formed by plating on the surface of the copper pattern is about 0.1 μm, the thickness L3 of the nickel plating 3 is about 5 μm, and the thickness of the upper gold plating 2 is relative to the skin depth of the gold Therefore, most of the current flows through the nickel plating 3 as shown in FIG. However, since the skin depth of nickel is as shallow as 0.05 μm, the cross-sectional area through which the high-frequency current flows is narrow, so that the passage loss of the high-frequency signal increases.

The skin depth of lead-free solder 1 having a standard composition of tin: 96.5% / silver: 3% / copper: 0.5% is 1.53 μm, and lead-free solder 1 having a thickness L1 of 1.53 μm or more is used. By applying to the surface of the gold plating 2, as shown in FIG. 3, the high-frequency current flows through the lead-free solder 1 having a wider cross-sectional area than the nickel plating 3, so that the high-frequency signal passing loss is reduced.

  A method for forming the lead-free solder 1 will be described. FIG. 4 is a process diagram for applying lead-free solder to the high-frequency circuit board according to Embodiment 1 of the present invention. The lead-free solder 1 is applied in a solder printing process (S1) and a reflow process (S2).

In the solder printing step (S1), a solder printing mask having a hole formed in a portion of the conductor pattern 4 to which the nickel plating 3 and the gold plating 2 are applied is provided on the substrate, and paste is applied from above the printing mask. This is a step of printing the lead-free solder 1 on the conductor pattern 4 in the holed portion by applying the lead-free solder 1 in the shape of a hole. In the reflow step (S2), the high-frequency circuit board on which the lead-free solder 1 is printed in the solder printing step (S1) is conveyed in a reflow furnace having a furnace temperature of 245 ° C., and the printed lead-free solder 1 is melted. The lead-free solder 1 is brought into close contact with the conductor pattern 4.

  In the solder coating in which the molten lead-free solder is immersed, it is necessary to immerse the high-frequency substrate in the lead-free solder melted at a temperature of 250 ° C. for 8 seconds. Since lead-free solder is melted at a temperature of ° C., thermal deformation of the high-frequency substrate is mitigated as compared with the method using solder coating. Further, in the reflow process, the high frequency circuit board can be fixed to a metal fixing jig and conveyed in the reflow furnace, so that deformation of the high frequency circuit board can be suppressed.

  As shown in FIG. 5, the reflow process is a process in which lead-free solder is applied to the terminal mounting portion of the surface mount component and the surface mount component is mounted on the substrate. By applying the lead-free solder, there is an effect that the lead-free solder is applied without impairing the productivity.

  In the first embodiment of the present invention, a high frequency circuit board using a microstrip line has been described, but a coplanar line may be used.

Embodiment 2. FIG.
FIG. 6 is a configuration example of a communication apparatus. 9 is a communication antenna, 10 is a transmission / reception signal distributor / synthesizer, 11 is a transmission amplifier, 12 is a low-noise amplifier for reception, 13 is a band-pass filter, 14 is a mixer, 15 is a voltage-controlled oscillator, and 16 is a phase comparison. It is a vessel.

In the second embodiment of the present invention, the process shown in the first embodiment of the present invention is performed on the microstrip line between the transmission / reception signal distributor / combiner 10 and the low noise amplifier 12 for reception. FIG. 7 is a configuration diagram of a high-frequency circuit board according to Embodiment 2 of the present invention. Reference numeral 17 denotes an input section of a reception low noise amplifier that connects the transmission / reception signal distributor / combiner 10 and the reception low noise amplifier 12 using the microstrip line shown in the first embodiment of the present invention.

A method for manufacturing a high-frequency circuit board according to Embodiment 2 of the present invention will be described. The transmission / reception signal distributor / synthesizer 10 and the reception low noise amplifier 12 are surface-mounted components. FIG. 5 is a manufacturing process / component mounting process diagram of a conventional printed wiring board.

In FIG. 5, in the solder printing step (S11), a surface mounting component such as a transmission / reception signal distributor / synthesizer 10 or a receiving low noise amplifier 12 is mounted on a conductor pattern 4 on which nickel plating 3 and gold plating 2 are applied. This is a process of printing the lead-free solder 1 on the conductor pattern 4 in the holed portion by placing a solder print mask with a hole on the substrate and applying a paste-like lead-free solder 1 over the print mask. .

  In the component mounting step (S20), the surface mounting component is mounted so that the terminal of the surface mounting component is placed at a predetermined position of the applied lead-free solder 1.

In the reflow step (S30), the printed wiring board on which the surface mounting components are mounted in the component mounting step (S20) is transported in a reflow furnace having a furnace temperature of 245 ° C., and the printed lead-free solder 1 is melted. The terminal of the surface mount component is brought into close contact with the conductor pattern 4.

  In the lead-free solder application process diagram of the high-frequency circuit board according to the first embodiment of the present invention shown in FIG. 4 and the printed wiring board manufacturing process / component mounting process chart shown in FIG. 5, the solder printing process (S11) and the solder printing process (S1) is an operation of applying a paste-free lead-free solder on a printing mask placed on a substrate, and the reflow process (S30) and the reflow process (S3) are performed in a reflow furnace. These are melting operations, both of which are the same.

Therefore, by making a hole in a portion of the conductor pattern 4 on which the nickel plating 3 and the gold plating 2 are applied to the printing mask placed on the substrate in the solder printing step (S10), Since the lead-free soldering of the component to the conductor pattern 4 and the application of the lead-free solder 1 to a predetermined surface of the conductor pattern 4 are performed at the same time, the present invention is implemented in the conventional printed wiring board manufacturing process and component mounting process. The high-frequency circuit board of Mode 2 is manufactured, and there is an effect that productivity is not impaired.

That is, in the print mask, the portion where the transmission / reception signal distributor / combiner 10 and the reception low noise amplifier 12 are mounted and the conductor pattern 4 between the transmission / reception signal distributor / combiner 10 and the reception low noise amplifier 12 are arranged. By making holes in the entire surface, lead-free soldering of the transmission / reception signal distributor / synthesizer 10 and the receiving low-noise amplifier 12 and the input portion 17 coated with lead-free solder are formed simultaneously.

By using the microstrip line shown in the first embodiment of the present invention for the input unit 17 of the reception low noise amplifier 12, the passage loss is reduced and the noise figure of the communication device is reduced.

Embodiment 3 FIG.
FIG. 8 is a configuration diagram of a high-frequency circuit board according to Embodiment 3 of the present invention. 8, the same components as those in FIGS. 6 and 7 are denoted by the same reference numerals, and the description thereof is omitted. Reference numeral 21 denotes an output portion of a transmission amplifier for connecting the transmission amplifier 11 using the microstrip line shown in Embodiment 1 of the present invention and the transmission / reception signal distribution / synthesis unit 10.

The method for manufacturing a high-frequency circuit board according to Embodiment 3 of the present invention is the same as the method for manufacturing a high-frequency circuit board according to Embodiment 2 of the present invention. The print mask has holes in the portion where the transmission / reception signal distributor / combiner 10 and the transmission amplifier 11 are mounted and the entire surface of the conductor pattern 4 between the transmission amplifier 11 and the transmission / reception signal distributor / combiner 10. Open.

By using the microstrip line shown in the first embodiment for the output unit 21 of the transmission amplifier 11, the passage loss is reduced and the saturated output power of the communication device is increased.

Embodiment 4 FIG.
FIG. 9 is a configuration diagram of a voltage controlled oscillator circuit according to the fourth embodiment. 9, the same components as those in FIG. 6 are denoted by the same reference numerals, and the description thereof is omitted. 22 is a resonator formed of the microstrip line shown in the first embodiment of the present invention, 23 is an active element of a voltage controlled oscillator, 24 is a tuning element, and 25 is a resonator connecting the resonator 22 and the active element 23. This is a transmission line formed by the microstrip line shown in the first embodiment.

The method for manufacturing a high-frequency circuit board according to Embodiment 4 of the present invention is the same as the method for manufacturing a high-frequency circuit board according to Embodiment 2 of the present invention. The print mask has holes in the portion where the active element 23 and the tuning element 24 are mounted, the entire surface of the conductor pattern 4 of the resonator 22, and the entire surface of the conductor pattern 4 between the resonator 22 and the active element 23. Open.

If the loss of the resonator 22 of the voltage controlled oscillator 23 is large, the power dissipated from the system is increased, the vibration increasing coefficient is lowered, and the phase noise is deteriorated. By using the microstrip line shown in FIG. 2, the passage loss of the resonator 22 is reduced and the phase noise is reduced.

DESCRIPTION OF SYMBOLS 1 Lead-free solder 2 Gold plating 3 Nickel plating 4 Conductor pattern 5 Insulator 6 Back surface ground pattern 7 Range in which high-frequency current flows 9 Communication antenna 10 Transmission / reception signal distributor / synthesizer 11 Transmitter amplifier 12 Receiver low noise amplifier 13 Band pass filter DESCRIPTION OF SYMBOLS 14 Mixer 15 Voltage control transmitter 16 Phase comparator 17 Input part 21 Output part 22 Resonator 23 Active element 24 Tuning element 25 Transmission line

Claims (3)

A high-frequency circuit board comprising a transmission line formed of a metal conductor on a surface of an insulator substrate, and a solder layer formed of reflow solder on the surface of the transmission line. A transmission line formed of a metal conductor on the surface of the insulator substrate, a high-frequency electronic component having a terminal connected to the surface of the transmission line by electrical connection means, and the transmission line to which a terminal of the high-frequency electronic component is connected A high frequency circuit board having a solder layer formed by reflow soldering on the surface of the substrate. The high-frequency circuit board according to claim 1 or 2, wherein the solder is formed of a lead-free solder having a composition of tin: 96.5% / silver: 3% / copper: 0.5%.

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