JP2020174115A - Multilayer circuit board - Google Patents

Abstract

To provide a multilayer circuit board that can improve the productivity of a substrate including a high frequency circuit.SOLUTION: A multilayer circuit board 30 in which a first circuit board 10 including a high-frequency board and a second circuit board 20 joined to the first circuit board 10 are overlapped and joined in the thickness direction includes a connection portion 31 that electrically connects the first circuit board 10 and the second circuit board 20 via a solder layer or a conductive paste layer, and a heat conductor 33 that conducts heat from the second circuit board 20 to the first circuit board 10 between the first circuit board 10 and the second circuit board 20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a multilayer circuit board.

In a circuit board in which an antenna used in a high frequency band such as a millimeter wave band and a radio frequency (RF) integrated circuit (IC) are integrated, in order to facilitate the routing of signal lines and reduce the substrate area, generally multiple layers are used. A substrate is used. However, a special and expensive dielectric material having a low dielectric constant is used for a substrate corresponding to a high frequency band. Further, Patent Document 1 proposes a composite substrate using a general substrate material for a power supply circuit or the like and a substrate material corresponding to a high frequency band for a high frequency circuit portion.

JP-A-2016-40797

In Patent Document 1, through holes are used for electrical connection between a base substrate using a general substrate material and a high frequency substrate having excellent high frequency characteristics. For this reason, a drilling process is required through the base substrate and the high frequency substrate, and the productivity is low. Further, it is necessary to redundantly route the high frequency signal by providing the through hole, which may cause deterioration of the characteristics.

The present invention has been made in view of the above problems, and provides a multilayer circuit board capable of improving the productivity of a substrate including a high frequency circuit.

In order to solve the above problems, in the present invention, the first circuit board including the high frequency substrate and the second circuit board to be bonded to the first circuit board are laminated and bonded in the respective thickness directions. It is a circuit board, and between the first circuit board and the second circuit board, electrically between the first circuit board and the second circuit board via a solder layer or a conductive paste layer. Provided is a multilayer circuit board having a connecting portion to be connected and a heat conductor for conducting heat from the second circuit board to the first circuit board.

A radiator may be formed on the first circuit board.
The thermal conductor may include a piece of metal or a carbon material.
The conductive paste layer may be composed of silver paste, copper paste or carbon paste.
The high frequency substrate is a group consisting of liquid crystal polymer (LCP), polyphenylene ether (PPE) resin, fluororesin, cycloolefin resin, maleimide resin, polyimide resin, modified polyimide resin, polyphenylene sulfide (PPS) resin, quartz, ceramic, and sapphire. It may be composed of an insulating material having a dielectric loss of less than 0.01 selected from.

An antenna capable of transmitting or receiving or transmitting / receiving a high frequency signal may be formed on the first circuit board.
An integrated circuit (IC) that processes a high frequency signal may be mounted on the second circuit board.

According to the present invention, it is possible to provide a multilayer circuit board capable of improving the productivity of a substrate including a high frequency circuit.

It is sectional drawing which shows the multilayer circuit board of 1st Embodiment. It is sectional drawing which shows the 1st circuit board and the 2nd circuit board. It is sectional drawing which shows the multilayer circuit board of 2nd Embodiment. It is sectional drawing which shows the manufacturing process of the connection substrate in the order of (a)-(d).

Hereinafter, the present invention will be described with reference to the drawings based on the preferred embodiments.

The multilayer circuit board of the first embodiment will be described. FIG. 1 shows the multilayer circuit board 30 of the first embodiment, and FIG. 2 shows the first circuit board 10 and the second circuit board 20. The first circuit board 10 is configured by laminating a plurality of insulating substrates 11a, 11b, 11c. The second circuit board 20 is configured by laminating a plurality of insulating substrates 21a, 21b, 21c, 21d, 21e, and 21f. The number of layers of the insulating substrate included in the first circuit board 10 and the second circuit board 20 is not particularly limited, and may be one layer or two or more layers, respectively. Each insulating substrate can be composed of a film, a sheet, a prepreg, or the like. Although not particularly shown, a conductor layer can be provided on one side or both sides of the insulating substrate. Further, a through conductor may be provided by penetrating one layer or two or more layers of the insulating substrate.

The first circuit board 10 includes a high frequency board. The high frequency substrate is an insulating substrate that supports high frequencies. Examples of the high-frequency material constituting the high-frequency substrate include an insulating material having a dielectric loss of less than 0.01. In the present specification, the insulating material means an electrically insulating material (dielectric, non-conductive material), and does not need to be a heat insulating material (insulating material). Further, the measurement condition of the dielectric loss is defined as the dielectric loss tangent (tan δ) of JIS C 6781 (copper-clad laminate test method for printed wiring board), for example, the temperature is 20 ± 2 ° C. with respect to the measurement frequency of 1 MHz. , Relative humidity 60-70%. A high frequency substrate made of a high frequency material having a dielectric loss of 0.005 or less is more preferable. Specific examples of the high-frequency material constituting the high-frequency substrate include liquid crystal polymer (LCP), polyphenylene ether (PPE) resin, fluororesin, cycloolefin resin, maleimide resin, polyimide resin, modified polyimide resin, polyphenylene sulfide (PPS) resin, and the like. One or more selected from the group consisting of quartz, ceramic, and sapphire can be mentioned. The number of layers of the first circuit board 10 is not particularly limited, and examples thereof include 1 to 6 layers.

The first circuit board 10 may be a core substrate or a multilayer substrate composed of prepregs having a thickness of 100 μm or less in each layer, and a core substrate or prepreg having a thickness of more than 100 μm may be used as necessary for reducing loss. It may be included. In the first embodiment, the insulating substrates 11a, 11b, and 11c included in the first circuit board 10 are all composed of high frequency substrates, but the present invention is not limited to this. The insulating substrate included in the first circuit board 10 does not have to be all composed of a high frequency substrate.

An antenna 12 capable of transmitting, receiving, or transmitting and receiving a high frequency signal is formed on the first circuit board 10 of the first embodiment as an example of a high frequency element. For the purpose of securing a band, suppressing loss of high-frequency signals, for example, a substrate made of a high-frequency material may be bonded with an adhesive or a build-up layer made of a prepreg may be provided as a layer in contact with the antenna 12. .. In that case, at least a part of the layer other than the layer on which the antenna 12 of the first circuit board 10 is formed may not be composed of the high frequency material. The antenna 12 is not particularly limited as long as it has a structure that can be mounted or incorporated on a substrate, but for example, a flat antenna is preferable, and a patch antenna, a strip antenna, a slot antenna, and the like can be mentioned. A waveguide structure such as a post-wall waveguide (PWW) may be configured on the substrate, and an antenna may be configured by slots, openings, or the like of the waveguide. The antenna 12 may form an antenna array.

In the example shown in FIG. 1, the antenna 12 is formed on the insulating substrate 11a of the layer farthest from the second circuit board 20 in the thickness direction of the first circuit board 10. When the antenna 12 transmits a signal in the air or receives a signal from the air, the first circuit board so that the side opposite to the second circuit board 20 is the side in the air in the thickness direction of the first circuit board 10. 10 can be installed. Although not particularly shown, it is also possible to provide the antenna 12 on the other insulating substrates 11b and 11c of the first circuit board 10. The positions of the conductor layers or through conductors (not shown) provided on the insulating substrates 11a, 11b, and 11c are designed in consideration of the influence on the transmission or reception of the aerial signal in the antenna 12.

The second circuit board 20 may include a high frequency substrate at least in part, but the insulating material of the second circuit board 20 may be composed of only a general insulating material that is not compatible with high frequencies. The insulating substrate included in the second circuit board 20 can be made of a general insulating material having a higher dielectric loss than the high frequency material constituting the high frequency substrate. Examples of the insulating material that is not compatible with high frequencies include an insulating material having a dielectric loss of 0.01 or more. Specific examples of the insulating material constituting the insulating substrate include glass cloth base epoxy resin (FR-4, etc.), glass cloth / glass non-woven composite base epoxy resin, glass cloth / paper composite base epoxy resin, and synthetic fiber cloth. Examples thereof include a base material epoxy resin, a paper base material epoxy resin, a glass cloth base material polyimide resin, a glass cloth base material bismaleimide / triazine / epoxy resin, a paper base material phenol resin, and a flexible base material such as polyimide.

As the second circuit board 20, a core substrate having a thickness of 100 μm or less or a multilayer substrate composed of a prepreg is preferable. As a result, the thickness of the substrate is thin and processing becomes easy. The number of layers of the second circuit board 20 is not particularly limited, but is typically 4 to 10 layers, and may exceed 10 layers.

In order to increase the gain of the antenna 12, it is preferable to increase the number of antennas 12 formed on the first circuit board 10. Therefore, in the first embodiment, the integrated circuit 22 that processes the high frequency signal is not mounted on the first circuit board 10, but the integrated circuit 22 that processes the high frequency signal is mounted on the second circuit board 20. The integrated circuit 22 is connected to the second circuit board 20 via a bump 23 made of a conductor such as solder. Examples of the integrated circuit 22 include integrated circuits (ICs) such as RFICs. In an antenna board that handles high-frequency signals, in order to suppress signal loss from the RFIC, the first circuit board on which the antenna is formed and the second circuit board on which the RFIC is mounted are integrated into the same multilayer circuit board. It is preferable that the configuration is as follows. As a result, the signal line can be easily routed and the substrate area can be suppressed. Since the substrate material for high frequency is expensive, the power supply circuit, the circuit for propagating the low frequency baseband signal, etc. are mounted on the second circuit board, and each insulating substrate constituting the second circuit board is not compatible with high frequency. , A general insulating material can be used. For example, if the signal is less than 10 GHz (about several GHz), it can be propagated by a coaxial cable or the like.

For example, when a high-frequency signal is generated by the integrated circuit 22, the high-frequency signal can be propagated inside the multilayer circuit board 30 to be supplied to the antenna 12 and radiated from the antenna 12 into the air. The wiring connecting the integrated circuit 22 and the antenna 12 preferably shortens the transmission distance in order to reduce the loss of high frequency signals. Therefore, the multilayer circuit board 30 has a configuration in which the first circuit board 10 and the second circuit board 20 are overlapped in their respective thickness directions and composited by joining. The total thickness of the multilayer circuit board 30 is, for example, 1 to 2 mm, specifically about 1.5 mm. The antenna 12 may have a non-feeding element, if necessary. For example, in a patch antenna, the characteristics can be improved by installing a non-feeding patch around the radiation patch.

When the integrated circuit 22 generates a high-frequency signal, at least the layer on which the integrated circuit 22 of the second circuit board 20 is mounted is used as the high-frequency board, and the wiring connected to the signal line and the ground layer of the mounted integrated circuit 22 is re-wired. It may be arranged.

The first circuit board 10 has a first joint surface 13 on one of the surfaces perpendicular to the thickness direction. Further, the second circuit board 20 has a second joint surface 24 on at least one of the surfaces perpendicular to the thickness direction. The first circuit board 10 and the second circuit board 20 are joined so that the first joining surface 13 and the second joining surface 24 face each other.

In order to realize the connection between the first circuit board 10 and the second circuit board 20 and the transmission of high frequency signals, the multilayer circuit board 30 is a first circuit between the first junction surface 13 and the second junction surface 24. It has a connecting portion 31 that electrically connects the substrate 10 and the second circuit board 20. The connection portion 31 is a connection portion between boards. As the connecting portion 31, a solder layer or a conductive paste layer is used. As a result, the transmission distance at the connection unit 31 can be shortened.

The solder constituting the solder layer can be appropriately selected from various types of solder such as solder balls and solder paste. In the product of the multilayer circuit board 30, the solder forming the solder layer after bonding may be layered by reflow.
Examples of the conductor used in the conductive paste layer include metal particles such as gold, silver and copper, and conductive carbon such as carbon black, graphite and carbon nanotubes. The conductive paste layer can be composed of various conductive pastes such as silver paste, copper paste, and conductive carbon paste. The conductive paste layer may be in the form of a paste having fluidity or deformability in the manufacturing process, and in the product of the multilayer circuit board 30, the conductive paste layer after bonding has fluidity or deformability due to firing, curing, or the like. You don't have to.

The connecting portion 31 may be two or more types of a solder layer or a conductive paste layer. Although not particularly shown, a conductor layer made of a metal foil, a metal plating layer, or the like may be formed in a region of the first joint surface 13 or the second joint surface 24 where the connection portion 31 is provided. A connection portion 31 connected to the ground and grounded may be arranged around the connection portion 31 that transmits a high frequency signal.

It is preferable to form a sealing layer 32 made of an insulating resin or the like in the region where the connecting portion 31 is not formed between the first joint surface 13 and the second joint surface 24. Examples of the material constituting the sealing layer 32 include a non-conductive film (NCF), a non-conductive paste (NCP), an underfill material, and the like. In order to strengthen the mechanical bonding, an epoxy resin or the like is used. It is preferable to use a curable resin. When the connecting portion 31 is a solder layer, it is easy to control the range in which the solder layer is formed. Therefore, instead of covering the periphery of the connecting portion 31, the sealing layer 32 is located at a position away from the solder layer, for example, the first. It may be formed at the end or corner of the joint surface 13 or the second joint surface 24.

In the multilayer circuit board 30 of the first embodiment, the thermal conductivity of the solder layer or the conductive paste layer serving as the connecting portion 31 is low. Therefore, a heat conductor 33 that conducts heat from the second circuit board 20 to the first circuit board 10 is provided between the first circuit board 10 and the second circuit board 20. As a result, as shown by the arrow H1, the first circuit board 10 and the second circuit board 20 can be connected to each other without providing heat-dissipating vias penetrating all the layers of the first circuit board 10 and the second circuit board 20. The thermal conductivity between them can be improved. Even when the second circuit board 20 on which the integrated circuit 22 is mounted is close to the housing (not shown) and the heat dissipation from the second circuit board 20 is not sufficient, it occurs on the second circuit board 20 side. The generated heat can be dissipated from the side of the first circuit board 10. The thermal conductor 33 may contain a metal piece such as copper or silver, or a carbon material such as carbon nanotube or graphite as a material having excellent thermal conductivity. The number of heat conductors 33 provided between the first circuit board 10 and the second circuit board 20 is not particularly limited, and may be one, two, or three or more. In order to improve the contact property between the first circuit board 10 and the second circuit board 20 of the thermal conductor 33, a resin paste such as a silicone resin, solder, an adhesive sheet or the like may be used.

Since the first circuit board 10 on which the antenna 12 is formed transmits or receives or transmits / receives an aerial signal via the antenna 12, it is easy to secure a large space for heat dissipation from the first circuit board 10. By providing the heat radiating body 14 on the first circuit board 10, the heat radiating property from the first circuit board 10 can be further improved as shown by the arrow H2. Examples of the heat radiating body 14 provided on the first circuit board 10 include a heat sink, a cooling fan, heat radiating fins, a heat radiating plate, a metal plate, and a heat radiating via. The number of heat radiating bodies 14 provided on the first circuit board 10 is not particularly limited, and may be one, two, or three or more.

As a method of manufacturing the multilayer circuit board 30 of the first embodiment, a step of manufacturing a first circuit board 10 in which an antenna 12 and a radiator 14 are arranged, and a second circuit board 20 on which an integrated circuit 22 is mounted are manufactured. The step of arranging the heat conductor 33 between the first circuit board 10 and the second circuit board 20 and connecting by the connecting portion 31, the step of connecting the connection portion 31 and the periphery of the heat conductor 33 with a sealing layer 32. Examples thereof include a manufacturing method having a step of sealing with. After preparing the first circuit board 10 and the second circuit board 20 as separate circuit boards, the first circuit board 10 and the second circuit board 20 are connected to each other via the connecting portion 31 to form the first circuit. Signals can be exchanged between the substrate 10 and the second circuit board 20.

Prior to the step of aligning the first circuit board 10 and the second circuit board 20 and connecting them by the connecting portion 31, either the connecting portion 31 is connected to the first circuit board 10 or the second circuit board 20. It may be provided in. For example, in the step of manufacturing the first circuit board 10, the connecting portion 31 may be provided on the first joint surface 13. Further, in the step of manufacturing the second circuit board 20, the connecting portion 31 may be provided on the second joint surface 24. When a solder ball is used as the connecting portion 31, flux, solder paste, or the like may be used to mount the solder ball on the first circuit board 10 or the second circuit board 20.

As described in Patent Document 1, when through holes are formed over all layers of a multilayer circuit board, the length of the through holes becomes long, which makes manufacturing difficult. Increasing the diameter of the through hole facilitates manufacturing, but reduces area efficiency.

According to the multilayer circuit board 30 of the first embodiment, a high frequency signal can be transmitted via the connection portion 31, so that even when an interlayer through hole is provided in the first circuit board 10 or the second circuit board 20. The maximum length of the through hole is the thickness of the first circuit board 10 or the second circuit board 20. Therefore, productivity can be improved. Further, since the diameter of the through hole can be reduced, the area efficiency of the substrate can be improved. Further, by arranging the heat conductor 33 between the first circuit board 10 and the second circuit board 20, the heat generated on the second circuit board 20 side on which the integrated circuit 22 is mounted can be efficiently generated. It can be transmitted to the 1 circuit board 10 side and dissipate heat from the 1st circuit board 10 side. Further, by providing the heat radiating body 14 on the first circuit board 10, a further heat radiating effect can be obtained.

Next, the multilayer circuit board of the second embodiment will be described. FIG. 3 shows the multilayer circuit board 40 of the second embodiment. FIG. 4 shows the manufacturing process of the connection substrate in the order of (a) to (d). Since the configurations of the first circuit board 10 and the second circuit board 20 can be the same as those of the first embodiment including the configurations of the antenna 12, the radiator 14, the integrated circuit 22, and the like, overlapping description is omitted. To do.

The connection substrate 47 includes an insulating base material 41 and a connection portion 42. It is preferable that both sides of the insulating base material 41 have adhesiveness. The connecting portion 42 is a conductor that penetrates the insulating base material 41. The conductive material constituting the connecting portion 42 can be selected in the same manner as the connecting portion 31 of the first embodiment. Further, the heat conductive material constituting the heat conductor 43 can be selected in the same manner as the heat conductor 33 of the first embodiment. In the connection board 47 before joining the first circuit board 10 and the second circuit board 20, it is preferable that the connection portion 42 protrudes from both sides of the insulating base material 41.

As a method for producing the connection substrate 47, for example, a step of preparing an insulating base material 41 having films 44 formed on both sides as shown in FIG. 4A, and an insulating base material as shown in FIG. 4B. In the step of forming the vias 45 and 46 penetrating the 41 and the film 44, as shown in FIG. 4C, the via 45 is filled with a conductive material to form a connecting portion 42, and the thermal conductor 43 is arranged in the via 46. As shown in FIG. 4D, there is a method of removing the film 44 from the insulating base material 41 and projecting the connecting portion 42 from both sides of the insulating base material 41.

When the insulating base material 41 is adhesive, the film 44 may be a protective sheet. When the insulating base material 41 is adhesive, the film 44 may be a temporary bonding material. When the connecting portion 42 is formed from solder balls, solder balls corresponding to the dimensions of the via 45 may be prepared. By sandwiching the connection board 47 between the first joint surface 13 and the second joint surface 24, the first circuit board 10 and the second circuit board 20 can be connected. Further, if necessary, heating or pressure pressing may be performed when connecting the first circuit board 10 and the second circuit board 20.

In the multilayer circuit board 40 of the second embodiment, the connection portion 42 can electrically connect the first circuit board 10 and the second circuit board 20. Further, the heat conductor 43 can conduct heat from the second circuit board 20 to the first circuit board 10. The multilayer circuit board 40 of the second embodiment has effects such as heat conduction and heat dissipation generated on the second circuit board 20 side, and also improves productivity, which is an effect of the multilayer circuit board 30 of the first embodiment. Be prepared.

As a method of manufacturing the multilayer circuit board 40 of the second embodiment, a step of manufacturing the first circuit board 10 in which the antenna 12 and the radiator 14 are arranged, and the second circuit board 20 on which the integrated circuit 22 is mounted are manufactured. A manufacturing method including a step of connecting the first circuit board 10 and the second circuit board 20 by a connecting board 47 can be mentioned. After preparing the first circuit board 10 and the second circuit board 20 as separate circuit boards, the first circuit board 10 and the second circuit board 20 are connected to each other via the connection board 47 to form the first circuit. Signals can be exchanged between the substrate 10 and the second circuit board 20.

When a solder ball is used as the connecting portion 42, flux, solder paste, or the like may be used at a position corresponding to the connecting portion 42 on at least one of the first joint surface 13 and the second joint surface 24. As a result, when the connection board 47 is sandwiched between the first circuit board 10 and the second circuit board 20, the solder balls of the connection portion 42 are connected to the first circuit board 10 and the second circuit board 20. Can be facilitated.

Although not particularly shown, a dielectric layer may be formed on the surface of the first circuit board 10 on which the antenna 12 is formed. The method for forming the dielectric layer is not particularly limited, and examples thereof include a method of attaching and coating the dielectric layer on the antenna 12. In the dielectric layer, the substance that the radiation patch or the non-feeding patch comes into contact with is changed from air (dielectric constant 1.0) to a dielectric, so that the antenna 12 avoids the influence on the transmission or reception of the aerial signal. , A conductor layer, an insulating layer having no conductor such as a through conductor. Further, the antenna 12 can be protected by the dielectric layer. When the antenna 12 has a radiating element and a non-feeding element, a dielectric layer can be formed on both the radiating element and the non-feeding element.

Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. Modifications include addition, replacement, omission, and other changes of components in each embodiment. It is also possible to appropriately combine the components used in the two or more embodiments.

The frequency of the high frequency signal is not particularly limited, and examples thereof include 30 to 300 GHz and 60 to 80 GHz. Examples of high-frequency elements applicable to high-frequency circuits include antennas, waveguides, filters, diplexers, directional couplers, distributors, photoelectric conversion elements, and the like.

10 ... 1st circuit board, 11a, 11b, 11c ... Insulated board, 12 ... Antenna, 13 ... 1st junction surface, 14 ... Heat radiator, 20 ... 2nd circuit board, 21a, 21b, 21c, 21d, 21e, 21f ... Insulated substrate, 22 ... Integrated circuit, 23 ... Bump, 24 ... Second junction surface, 30, 40 ... Multilayer circuit board, 31, 42 ... Connections, 33, 43 ... Thermal conductor, 32 ... Sealing layer, 41 ... Insulating substrate, 44 ... Film, 45, 46 ... Via, 47 ... Connecting substrate.

Claims (7)

A multilayer circuit board in which a first circuit board including a high-frequency board and a second circuit board joined to the first circuit board are overlapped and joined in the respective thickness directions.
Between the first circuit board and the second circuit board, there is a connection portion that electrically connects the first circuit board and the second circuit board via a solder layer or a conductive paste layer. A multilayer circuit board characterized by having a heat conductor that conducts heat from the second circuit board to the first circuit board. The multilayer circuit board according to claim 1, wherein a radiator is formed on the first circuit board. The multilayer circuit board according to claim 1 or 2, wherein the heat conductor contains a metal piece or a carbon material. The multilayer circuit board according to any one of claims 1 to 3, wherein the conductive paste layer is composed of silver paste, copper paste or carbon paste. The high frequency substrate is a group consisting of liquid crystal polymer (LCP), polyphenylene ether (PPE) resin, fluororesin, cycloolefin resin, maleimide resin, polyimide resin, modified polyimide resin, polyphenylene sulfide (PPS) resin, quartz, ceramic, and sapphire. The multilayer circuit board according to any one of claims 1 to 4, which is selected from the above, comprising an insulating material having a dielectric loss of less than 0.01. The multilayer circuit board according to any one of claims 1 to 5, wherein an antenna capable of transmitting, receiving, or transmitting and receiving a high frequency signal is formed on the first circuit board. The multilayer circuit board according to any one of claims 1 to 6, wherein an integrated circuit (IC) for processing a high frequency signal is mounted on the second circuit board.

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