JP2006332246A - Circuit board, connection structure thereof and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board connection structure capable of establishing newly a part for mounting electronic components, connection structure of a circuit board, and electronic devices. <P>SOLUTION: A connection structure 30 of a circuit board comprises a first circuit board 31 where a surface circuit pattern 33 is formed in a surface 32A of a substrate 32, a second circuit board 35 where a circuit pattern 37 is formed in a surface 36A of a substrate 36, a first connection surface 34 of the surface circuit pattern 33 and a second connection surface 38 of the surface circuit pattern 37, an anisotropy conductive adhesive 40 interposed between the first and second connection surfaces 34 and 38, and a connection part 41 provided by thermocompression bonding of the first circuit board 31 and the second circuit board 35. In the first circuit board 31, the connection structure 30 of this circuit board forms a rear surface circuit pattern 43 in a rear surface 32B of the substrate 32, and carries out external exposure of a rear surface circuit pattern 43. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a circuit board in which a first circuit board and a second circuit board are connected by an anisotropic conductive adhesive, a circuit board connection structure, and an electronic apparatus using the circuit board connection structure.

Electronic devices such as mobile phones are required to be smaller, thinner, and lighter in the case, and as a circuit board accommodated in the case, a flexible substrate in which a circuit pattern is formed along a soft base material Is frequently used.
If the flexible substrates are connected to each other via a connector, the connector housing hinders miniaturization, thickness reduction, and weight reduction of the housing.

For this reason, each flexible substrate is laminated so that the connection surfaces provided in the mutual circuit patterns face each other, and an anisotropic conductive adhesive is interposed between the connection surfaces, so that each flexible substrate is arranged in the thickness direction. 2. Description of the Related Art A circuit board connection structure in which each flexible substrate is connected through a connecting portion by applying pressure and heating is frequently used (for example, Patent Document 1).
JP 2003-249734 A

In Patent Document 1, when connecting a pair of flexible substrates, a dummy pattern is provided in advance on the back surface corresponding to the connection surface of one flexible substrate, and deformation of each flexible substrate is prevented when pressurizing each connection portion. .
In such a circuit board connection structure, each flexible substrate is pressurized and heated in the thickness direction, so that no electronic component is mounted on the dummy pattern.

By the way, in recent years, since the demand for electronic devices is becoming more sophisticated, a circuit board that is smaller than conventional ones has been adopted.
That is, in recent circuit boards, since the area on which electronic components can be mounted is becoming smaller, there is a need to expand the area where electronic components can be mounted.

  An object of the present invention is to provide a circuit board, a circuit board connection structure, and an electronic apparatus in which a part where an electronic component can be mounted can be newly installed.

  The connection part of the circuit board of the present invention is provided in the first circuit board and the second circuit board in which the circuit pattern is formed on the surface of the substrate formed in a planar shape, and the surface circuit pattern of the first circuit board. A first connection surface and a second connection surface provided on the surface circuit pattern of the second circuit board; and an anisotropic conductive adhesive interposed between the first connection surface and the second connection surface. A circuit board connection structure provided with a connection portion provided by a connection step in which the first circuit board and the second circuit board are mutually pressurized in the thickness direction and heated. It has the back surface circuit pattern provided in the back surface, and the back surface circuit pattern is exposed outside.

A mounting area is expanded by having a back surface circuit pattern provided on the back surface of the first circuit board and exposing the back surface circuit pattern to the outside. And the back surface circuit pattern whose mounting area was expanded is utilized as a site | part which mounts an electronic component, or a site | part which connects a circuit board.
Thereby, an electronic component can be satisfactorily mounted on the back surface circuit pattern having an increased mounting area.
In addition, another circuit board can be connected to the back surface circuit pattern with an increased mounting area, and a plurality of circuit boards can be stacked in multiple layers.

  The circuit board connection structure of the present invention is characterized in that the front surface circuit pattern on the first connection surface corresponds to the back surface circuit pattern.

By making the front surface circuit pattern on the first connection surface correspond to the back surface circuit pattern, the front surface circuit pattern can be reinforced with the back surface circuit pattern when the first circuit board and the second circuit board are mutually pressed in the thickness direction. .
As a result, the first circuit board and the second circuit board can be efficiently pressurized along the thickness direction.

  In the circuit board connection structure of the present invention, the overlapping area of the front surface circuit pattern and the back surface circuit pattern along the thickness direction of the first circuit board on the first connection surface is an area of the surface circuit pattern. It is characterized by being more than half.

By making the overlapping area of the front surface circuit pattern and the back surface circuit pattern more than half the area of the front surface circuit pattern, the back surface circuit pattern is used when the first circuit board and the second circuit board are mutually pressed in the thickness direction. The effect of reinforcing the surface circuit pattern can be increased.
Thereby, a 1st circuit board and the said 2nd circuit board can be pressurized much more efficiently along the thickness direction.

  The circuit board connection structure of the present invention is characterized in that the anisotropic conductive adhesive is based on a lead-free solderable thermosetting high heat resistant epoxy resin.

When using an anisotropic conductive adhesive based on lead-free solderable thermosetting high heat-resistant epoxy resin, when mounting electronic components and connecting circuit boards in the subsequent process In addition, high connection reliability can be maintained even when a thermal history is applied to the anisotropic conductive adhesive.
Thereby, an electronic component can be mounted on the back circuit pattern by a soldering process (reflow method or the like) in a state where the anisotropic conductive adhesive maintains high connection reliability.

  Further, the circuit board of the present invention includes a surface circuit pattern formed on the surface of the substrate formed in a planar shape, a back circuit pattern formed on the back surface of the substrate and exposed to the outside, and the surface circuit pattern And an anisotropic conductive adhesive disposed at a predetermined position.

By forming a back surface circuit pattern on the back surface of the substrate and exposing the back surface circuit pattern to the outside, the mounting area is expanded. And the back surface circuit pattern whose mounting area was expanded is utilized as a site | part which mounts an electronic component, or a site | part which connects a circuit board.
Thereby, an electronic component can be satisfactorily mounted on the back surface circuit pattern having an increased mounting area.
In addition, another circuit board can be connected to the back surface circuit pattern with an increased mounting area, and a plurality of circuit boards can be stacked in multiple layers.

  The electronic device of the present invention is characterized in that any one of the circuit board and the circuit board connection structure of the present invention is used.

  The circuit board and the circuit board connection structure of the present invention are compact. By using any one of the compact circuit board and the circuit board connection structure in an electronic device, the electronic device can be reduced in size, thickness, and weight.

  According to the present invention, by using the back circuit pattern with an increased mounting area as a part for mounting an electronic component or a part for connecting a circuit board, the electronic component can be favorably mounted on the back circuit pattern, or It has an effect that a plurality of circuit boards can be stacked in multiple layers by connecting other circuit boards.

  As shown in FIG. 1, the electronic device 10 according to the first embodiment includes an upper housing 11 and a lower housing 12, and a rotation shaft 13 disposed along a boundary line between the upper housing 11 and the lower housing 12. A connecting portion 14 that connects the upper housing 11 and the lower housing 12 so as to be rotatable relative to each other, and a circuit board connection structure 30 that is housed in the upper and lower housings and electrically connects each device. It is a mobile phone equipped with.

  The upper housing 11 includes a display unit 16 substantially at the center of the front surface 11A, a self-portrait camera 17 and a receiver 18 above the display unit 16, and a counter-photographing camera (not shown) on the back surface 11B.

The lower housing 12 includes a key 22 of the operation unit 21 at a substantially center of the surface 12A, and a microphone 23 below the operation unit 21.
The connecting portion 14 rotatably supports the lower end portion of the upper housing 11 and the upper end portion of the lower housing 12.

  As shown in FIGS. 2 to 3A and 3B, the circuit board connection structure 30 of the first embodiment has a surface circuit pattern (circuit pattern) on a surface 32 </ b> A of a base material 32 formed in a planar shape. 33, a second circuit board 35 having a surface circuit pattern (circuit pattern) 37 formed on a surface 36A of a substrate 36 formed in a planar shape, and a first circuit board 31. The first connection surface 34 provided on the surface circuit pattern 33 and the second connection surface 38 provided on the surface circuit pattern 37 of the second circuit board 35 and the first connection surface 34 and the second connection surface 38 are interposed. And the connection part 41 provided by the connection process of mutually pressurizing and heating the first circuit board 31 and the second circuit board 35 along the thickness direction.

  The circuit board connection structure 30 has a back circuit pattern 43 provided on the back surface 32B of the base 32 in the first circuit board 31, and the back circuit pattern 43 is exposed to the outside.

  The first circuit board 31 is formed on a soft base material 32 formed in a planar shape, a surface circuit pattern 33 formed along the front surface 32A of the base material 32, and a back surface 32B of the base material 32 to be externally provided. This is a flexible substrate having an exposed back surface circuit pattern 43 and an anisotropic conductive adhesive 40 disposed at a predetermined position (that is, the first connection surface) 34 of the front surface circuit pattern 33.

In the first circuit board 31, the front surface circuit pattern 33 on the first connection surface 34 corresponds to the back surface circuit pattern 43.
That is, the first circuit board 31 is arranged in a state where the front surface circuit pattern 33 and the back surface circuit pattern 43 are parallel to each other and overlapped.

The overlapping area of the front surface circuit pattern 43 and the back surface circuit pattern 33 is a connection area where one pattern and one pattern are connected by the anisotropic conductive adhesive 40, that is, 50% or more of the first connection surface 34. .
The reason why the overlapping area of the front surface circuit pattern 43 and the back surface circuit pattern 33 is 50% or more of the first connection surface 34 will be described in detail with reference to FIGS.

The first circuit board 31 includes a connection area 45 connected to the second circuit board 35 using the anisotropic conductive adhesive 40 on the surface 32A side of the base material 32, and the connection area 45 on the back surface 32B side. Is provided with a back surface area 46 corresponding to. The connection area 45 and the back surface area 46 are not provided with a resist or coverlay 48.
That is, the first circuit board 31 has a resist or cover lay 48 formed so as to avoid the connection area 45 and the back surface area 46.

  The second circuit board 35 includes a soft base material 36 formed in a planar shape, a surface circuit pattern 37 formed along the front surface 36A of the base material 36, and a back surface formed on the back surface 36B of the base material 36. This is a flexible substrate having a circuit pattern 39.

The second circuit board 35 is arranged in a state where the front surface circuit pattern 37 and the back surface circuit pattern 39 are parallel to each other and overlapped.
The second circuit board 35 includes a connection area that is connected to the first circuit board 31 using the anisotropic conductive adhesive 40 on the surface 36 </ b> A side. No resist or coverlay is provided in this connection area.
That is, the second circuit board 35 is formed with a resist or a cover lay avoiding this connection area.

  The base materials 32 and 36 are formed of a film base material having a thickness of 10 to 100 μm based on an organic material such as epoxy, polyimide, liquid crystal polymer, bismaleimide triazine, or polyether ether ketone. Two layers, four layers, six layers, eight layers,...

An inner layer wiring (rolled or electrolytic Cu foil) having a thickness of 10 to 20 μm and an outer layer wiring having a thickness of 10 to 35 μm (similarly made of Cu based on Ni and Au plating) are formed on the base materials 32 and 26. Thus, the first circuit board is obtained.
The thickness of the first circuit board 31 and the second circuit board 35 is 20 to 500 μm.

  The first circuit board 31 and the second circuit board 35 use a thermosetting or photosensitive epoxy resin or urethane-modified epoxy resin in the form of an ink or a sheet as a solder resist, and polyimide as a coverlay. A film obtained by bonding a film with a thermosetting adhesive such as epoxy is used.

In the anisotropic conductive adhesive 40, the base resin component is a thermosetting epoxy resin, acrylic resin, imide resin, or silicone resin, and is used in a paste state or a B-stage state.
These resins are characterized by extremely low ion contamination (on the order of several ppm) and high heat resistance.
Specifically, it is sufficient that the glass transition temperature is higher than 125 ° C. which is the high temperature side of a normal thermal shock test, and it is desirable that the glass transition temperature is about 150 ° C.

This anisotropic conductive adhesive 40 contains a certain amount (5 to 20 wt%) of conductive particles in a dispersed state without agglomeration.
The conductive particles are metal powder or resin powder having the same hardness as or higher than the plating film of the circuit board pattern, and have a spherical shape or an indefinite shape of 2 to 10 μm.
The metal powder has a high melting point such as Cu, Ni, Ni / Au, Ag, or Ag / Pd. In the resin powder, the core is formed of resin, and the surface of the core is Ni / Au plated.

Furthermore, the anisotropic conductive adhesive 40 has an elastic modulus of about 1 to 2 GPa and a linear expansion coefficient of 20 to 60 ppm / ° C. at 40 to 100 ° C. as physical properties of the cured adhesive.
For the purpose of reducing the linear expansion coefficient, 10-50% of silica or the like is contained as an inorganic filler. The inorganic filler size is less than or equal to the conductive particle size.

Next, the first circuit board 31 will be described in detail based on FIGS. 4 (a) and 4 (b).
As shown in FIGS. 4A and 4B, the back circuit pattern 43 is provided in the back surface area 46 of the first circuit board 31, and the back circuit pattern 43 is exposed to the outside.
An electrode land 55 for soldering an electronic component (chip component) 56 (see FIG. 8) or the like is provided in a part of the exposed back surface circuit pattern 43.
The anisotropic conductive adhesive 40 is a thermosetting high heat resistance so that the anisotropic conductive adhesive 40 is not affected when this electronic component (chip component) 56 or the like is soldered lead-free. Based on epoxy resin.

Here, the exposed back surface circuit pattern 43 will be described. The exposed back surface circuit pattern 43 is wired in the same direction as the front surface circuit pattern 33 of the first circuit board 31.
Further, the back surface circuit pattern 43 overlaps the front surface circuit pattern 33 on the front surface 32A side.
Furthermore, the overlapping area of the back surface circuit pattern 43 and the front surface circuit pattern 33 is 50% or more (half or more) of the first connection surface 34.

The reason for this will be described below.
That is, in order to ensure the reliability of the anisotropic conductive adhesive 40, there is a minimum area required per terminal. For example, in the first circuit board 31 having a wiring width and a space between wirings of 1: 1 (each 50 μm) at a pitch of 100 μm, a connection width required for connection with the anisotropic conductive adhesive 40 is 1 mm or more. In some cases, the area per terminal is 50,000 square microns.

Therefore, when this anisotropic conductive adhesive 40 is used, if the first circuit board 31 has a line width and a space between wirings of 1: 1 (each 50 μm) at a pitch of 100 μm, the anisotropic conductive adhesive is used. And the width W of the connecting area 45, that is, the connection area 45 is set to 2.0 mm.
Then, by providing the back surface circuit patterns 43 and 55 that are 50% or more of the wiring area connected by the anisotropic conductive adhesive 40, a circuit pattern (wiring) that receives connection of each terminal is secured by 1 mm or more.
Since this portion is connected with the anisotropic conductive adhesive 40 on a flat surface, high connection reliability is ensured.

Next, a circuit board connection process will be described with reference to FIGS.
As shown in FIG. 5A, for the first circuit board 31, the surface circuit pattern 33 is formed on the surface 32 </ b> A of the base material 32, the resist 48 is formed so as to avoid the connection area 45, and the back surface of the base material 32. A back circuit pattern 43 is formed on 32B, and a resist 48 is formed so as to avoid the back surface area.

As shown in FIG. 5 (b), a gel-like anisotropic conductive adhesive 40 is applied to the connection area 45.
As for the application condition of the anisotropic conductive adhesive 40, in the case of a paste, the substrate is heated to about room temperature to 50 ° C. to improve the wetting and spreading (5-30 Pa · s in viscosity). In the case of a film (for example, a B-stage film), the film is heated to about 50 to 90 ° C. and transferred to the substrate 32 by a laminating method.

As shown in FIG. 5C, the second circuit board 35 is placed on the anisotropic conductive adhesive 40.
With respect to the second circuit board 35, a surface circuit pattern 37 is formed on the surface 36A of the base material 36, a resist is formed so as to avoid the connection area 45, and a back circuit pattern 39 and a resist 49 are formed on the back surface 36B of the base material 36. Has been.
The second connection surface 38 of the surface circuit pattern 37 is aligned with the first connection surface 34 of the surface circuit pattern 33.

As shown in FIG. 6A, the back circuit pattern 43 of the first circuit board 31 is received and placed on the stage 51. Next, a buffer sheet (for example, a silicone sheet) 52 is placed on the resist 49 formed on the back surface 36 </ b> B of the second circuit board 35, and the bonding heater head 53 is placed on the buffer sheet 51.
Next, by heating the bonding heater, the first circuit board 31 and the second circuit board 35 are mutually pressurized along the thickness direction and heated.

Here, the role of the buffer sheet 52 is mainly intended to maintain a uniform compressive force and prevent the anisotropic conductive adhesive 40 from adhering to the bonding heater 53.
Further, the receiving stage 51 is set to a size that fits in the back surface area 46. Therefore, the receiving stage 51 does not interfere with the resist or coverlay 48 formed on the back surface 32B of the first circuit board 31.
As a result, the back circuit pattern 43 of the first circuit board 31 receives an equal crimping force from the receiving stage 51.

In addition, since the receiving stage 51 does not interfere with the resist or cover lay 48, heat can be prevented from being radiated to the receiving stage 51 via the resist or cover lay 48. Therefore, it is not necessary to heat the heater head 53 more than necessary, and there is no possibility that the second circuit board 35 becomes high temperature.
This prevents the base material 36 of the second circuit board 35 from thermally expanding and impairing the dimensional stability, and further prevents peeling at the adhesive interface with the anisotropic conductive adhesive 40.
As an example, the thermocompression bonding conditions are 150 to 200 ° C. at the temperature of the anisotropic conductive adhesive 40, the crimping time is 3 to 20 sec, and the crimping load is 1 to 5 MPa with respect to the crimping area.

The reason why the resist or cover lay 48 is provided on the first circuit board 31 and the second circuit board 35 is as follows.
That is, in order to prevent the wiring of the first circuit board 31 and the second circuit board 35 from corroding due to moisture absorption or foreign matter adhesion, a resist or coverlay 48 is essential around the high-density wiring pattern.
Here, in order to improve the adhesion quality due to the heat radiation phenomenon at the time of thermocompression bonding, it can be easily understood that it can be solved by ending the application process of the resist 48, and will not be described here.

As shown in FIG. 6B, the first circuit board 31 and the second circuit board 35 are heated by the anisotropic conductive adhesive 40 in a state where the first connection surface 34 and the second connection surface 38 are connected. By being pressure-bonded, the connection portion 41 is obtained, and a circuit board connection structure 30, that is, a multilayer flexible substrate is obtained.
Thereby, the connection process of a circuit board is completed.

Next, a process of mounting the electronic component (chip component) 56 (see FIG. 8) on the circuit board connection structure 30 will be described with reference to FIGS.
The chip component 56 described here is a component that performs soldering. This electronic component includes a case where a CSP (chip size package) incorporating a semiconductor, an MCM (multichip module) in which a multichip module is formed on a circuit board, or a SIP (system in package) is soldered. Yes.

As shown in FIGS. 7A and 7B, an electrode land 55 for soldering an electronic component (chip component) 56 (see FIG. 8) of the multilayer flexible substrate is provided.
As shown in FIG. 8, solder 57 is applied on the electrode land 55. If the solder 57 is applied after the anisotropic conductive bonding step, it can also be applied by means such as a printing method or a dispensing method.

  Next, the chip component 56 is aligned face down on the electrode land 55, and a soldering process (overall reflow method, local reflow method, IR method, etc.) is performed, and the mounting process of the electronic component (chip component) 56 is performed. Complete.

Here, the thermocompression bonding conditions of the anisotropic conductive adhesive 40 will be described.
That is, in the normal circuit board connection step, as described in FIG. 6A, the temperature of the anisotropic conductive adhesive 40 is 150 to 200 ° C., the pressure bonding time is 3 to 20 seconds, and the pressure bonding load is the pressure bonding area. 1 to 5 MPa.
However, since there is a thermal history such as passing through the reflow furnace in the soldering process of the chip component 56, it is possible to increase the curing reaction rate of the anisotropic conductive adhesive 40 during the reflow process.

Therefore, the curing reaction rate in the thermocompression bonding process of the anisotropic conductive adhesive 40 is suppressed to 50 to 70%, and the curing reaction rate is set to 90% or more in the reflow process. For confirmation of the curing reaction rate, the cured product is subjected to thermal analysis (for example, differential scanning calorimetry).
By this method, in the thermocompression bonding step, the thermocompression bonding time can be shortened by about 30%, and the productivity is improved.

As described above, in the multilayer flexible substrate of the present invention, the anisotropic conductive adhesive 40 can be thermocompression bonded at a lower temperature than the conventional substrate configuration, and the anisotropic conductive adhesive 40 is used. Even if a thermal history is added in a later process, high connection reliability can be maintained.
In addition, since the curing rate can be increased by solder reflow, the thermocompression bonding time can be shortened and the productivity is improved.
Further, by removing the resist on the back surface, it has been given a role as a terminal for use as a circuit for joining other electronic components, so that high-density mounting is possible.

Next, the circuit board connection structure of the second embodiment will be described with reference to FIGS.
In addition, in 2nd Embodiment, the same code | symbol is attached | subjected about the same similar member as 1st Embodiment, and description is abbreviate | omitted.

As shown in FIG. 10B, the circuit board connection structure 60 of the second embodiment includes a multilayer flexible board 30 in which the first circuit board 31 and the second circuit board 35 are thermocompression bonded with an anisotropic conductive agent 40. The third circuit board 61 is thermocompression bonded with a thermocompression bonding material 62.
That is, the circuit board connection structure 60 of the second embodiment is obtained by thermocompression bonding the third circuit board 61 in place of the chip component (electronic component) 56 of the first embodiment, and the other configurations are the configurations of FIG. Is the same.

  The third circuit board 61 has the same configuration as that of the second circuit board 35, and includes a soft base 63 formed in a planar shape, and a surface circuit pattern 64 formed along the surface 63A of the base 63. A flexible substrate having a back surface circuit pattern 65 and a resist or coverlay 66 formed on the back surface 63B of the base 63.

Hereinafter, a connection process in which the third circuit board is thermocompression bonded with the anisotropic conductive agent 40 to the multilayer flexible board of the circuit board connection structure 60 will be described with reference to FIGS. 9 to 10.
First, as shown in FIG. 9A, a thermocompression bonding material 62 is applied to the back surface 32 </ b> A and the back circuit pattern 43 of the base material 32 that constitutes a part of the multilayer flexible substrate 30.
Since the application method of the thermocompression bonding material 62 is the same as that of the anisotropic conductive agent 40 of the first embodiment, the description thereof is omitted.

  As shown in FIG. 9B, the third circuit board 61 is placed on the thermocompression bonding material 62, and the connection surface of the front surface circuit pattern 64 is aligned with the connection surface of the back surface circuit pattern 43.

As shown in FIG. 10A, after alignment, the resist or coverlay 48 of the multilayer flexible substrate 30 is received and placed on the stage 51. Next, the buffer sheet 52 is placed on the resist or cover lay 66 of the third circuit board 61, and the bonding heater head 53 is placed on the buffer sheet 51.
Next, by heating the bonding heater, the third circuit board 61 and the multilayer flexible board 30 are mutually pressurized along the thickness direction and heated.

Here, the circuit board connection structure 60 does not receive any thermal history in the subsequent process because no more substrates are laminated.
Therefore, it is not necessary to use the anisotropic conductive adhesive 40 containing conductive particles as an adhesive for connecting the third circuit board 61 to the multilayer flexible substrate 30.

On the other hand, the multilayer flexible substrate 30 to which the first circuit substrate 31 and the second circuit substrate 35 are connected needs to be connected to the third circuit substrate 61 by thermocompression bonding in a subsequent process.
Therefore, the first circuit board 31 and the second circuit board 35 are connected using an anisotropic conductive adhesive 40 containing conductive particles. This is because the anisotropic conductive adhesive 40 containing conductive particles can maintain connection reliability even when it receives a thermal history of a subsequent process.

Since the thermocompression bonding material 62 having no conductive particles is used as an adhesive for connecting the third circuit board 61 to the multilayer flexible board 30, a wiring pattern narrower than the inner layer portion can be installed, and high-density mounting can be promoted.
However, in order to further improve the connection reliability of the circuit board connection structure 60, it is desirable to use the anisotropic conductive adhesive 40.

According to the circuit board connection structure 60 of the second embodiment, in the multilayer flexible substrate 30, the back surface circuit pattern 43 is used as a circuit for joining other circuit boards by removing the resist 48 on the back surface. A role as a terminal can be given.
Furthermore, by connecting the first circuit board 31 and the second circuit board 35 of the multilayer flexible substrate 30 with the anisotropic conductive adhesive 40, high connection reliability can be maintained even if a thermal history is applied in a subsequent process.

  In addition, when the third circuit board 61 is connected to the multilayer flexible substrate 30, the possibility of short-circuiting between terminals due to the conductive particles is eliminated by using the thermocompression bonding material 62 that does not contain conductive particles. In the portion, wiring formation at a narrower pitch than the inner layer can be realized, and high-density circuit formation is possible.

  In the above-described embodiment, the example in which the resist or cover lay 48 is formed on both sides of the connection area 45 and the back surface area 46 while avoiding the connection area 45 and the back surface area 46 of the first circuit board 31 has been described. However, the present invention is not limited to this, and the resist or coverlay 48 may not be formed on both sides of the connection area 45 and the back surface area 46.

  Moreover, in the said embodiment, although the 1st circuit board 31 and the 2nd circuit board 35 were illustrated as a flexible flexible board | substrate, it is not restricted to this, The 1st circuit board 31 and the 2nd circuit board 35 are made into a hard board | substrate. It is also possible to do.

  Furthermore, although the gel-like anisotropic conductive adhesive 40 is applied as an adhesive in the above-described embodiment, the film-like anisotropic conductive adhesive 40 can be attached.

In the above embodiment, an example has been described in which the end portion of the flexible substrate is a bonding portion, and the bonding portion is bonded with an adhesive. However, the present invention is not limited thereto, and the central portion of the flexible substrate may be the bonding portion. Is possible.
In each embodiment, the electronic component is mounted by lead-free soldering, but may be performed by a thermosetting conductive adhesive. In this case, it can be performed by a process of solidifying in a constant temperature bath together with the connection portion of the circuit board with the anisotropic conductive adhesive (usually at 100 to 150 ° C. for 10 minutes to 1 hour), and at the same time anisotropic conductive There is an effect of promoting the curing of the adhesive.
Further, the connection of the circuit board by the anisotropic conductive adhesive may be performed by another heat and pressure adhesive.

  Furthermore, in the said embodiment, although the mobile telephone was illustrated as the electronic device 10, the electronic device 10 is not limited to this.

  The present invention is suitable for application to a circuit board in which a first circuit board and a second circuit board are connected by an anisotropic conductive adhesive, a circuit board connection structure, and an electronic apparatus using the circuit board connection structure. is there.

It is a perspective view which shows the electronic device of 1st Embodiment which concerns on this invention. It is a perspective view which shows the connection structure of the circuit board and circuit board which concern on 1st Embodiment. (A) is sectional drawing which shows the connection structure of the circuit board which concerns on 1st Embodiment, (B) is a perspective view which shows the 1st circuit board which concerns on 1st Embodiment. (A) is a bottom view showing the first circuit board according to the first embodiment, (B) is a cross-sectional view taken along line AA of (A). It is a figure explaining the example which interposes an anisotropic conductive adhesive between the 1st circuit board concerning a 1st embodiment, and the 2nd circuit board. It is a figure explaining the example which carried out the thermocompression bonding of the 1st circuit board and 2nd circuit board which concern on 1st Embodiment. It is a figure explaining the example which solders an electronic component to the connection structure of the circuit board which concerns on 1st Embodiment. It is sectional drawing which shows the example which mounted the electronic component in the connection structure of the circuit board which concerns on 1st Embodiment. It is a figure explaining the example which overlaps the connection structure of the circuit board of 2nd Embodiment which concerns on this invention. It is a figure explaining the example which carries out the thermocompression bonding of the connection structure of the circuit board which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electronic device 30,60 Connection structure of a circuit board 31 1st circuit board (circuit board)
32, 36 base material 32A, 36A base material surface 32B, 36B back surface of base material 33, 37 surface circuit pattern (circuit pattern)
34 1st connection surface (predetermined position of surface circuit pattern)
35 Second circuit board (circuit board)
38 Second connection surface 40 Anisotropic conductive adhesive 41 Connection portion 43 Back surface circuit pattern (circuit pattern)
56 Electronic parts (chip parts)
61 1st circuit board 62 Thermocompression bonding material

Claims (6)

A first circuit board and a second circuit board in which a circuit pattern is formed on the surface of a substrate formed in a planar shape;
A first connection surface provided in a surface circuit pattern of the first circuit board and a second connection surface provided in a surface circuit pattern of the second circuit board;
An anisotropic conductive adhesive interposed between the first connection surface and the second connection surface;
A circuit board connection structure comprising a connection portion provided by a connection step in which the first circuit board and the second circuit board are mutually pressurized along the thickness direction and heated.
A back surface circuit pattern provided on the back surface of the first circuit board;
A circuit board connection structure, wherein the back circuit pattern is exposed to the outside.   2. The circuit board connection structure according to claim 1, wherein the front surface circuit pattern on the first connection surface corresponds to the back surface circuit pattern.   The overlapping area of the front surface circuit pattern and the back surface circuit pattern along the thickness direction of the first circuit board on the first connection surface is at least half of the area of the front surface circuit pattern. Alternatively, the circuit board connection structure according to claim 2.   The circuit board according to any one of claims 1 to 3, wherein the anisotropic conductive adhesive is based on a lead-free solderable thermosetting high heat resistant resin. Connection structure. A surface circuit pattern formed on the surface of the substrate formed into a planar shape;
A back surface circuit pattern formed on the back surface of the substrate and exposed to the outside;
A circuit board comprising: an anisotropic conductive adhesive disposed at a predetermined position of the surface circuit pattern.   Any one of Claims 1 thru | or 4 is used, The electronic device characterized by the above-mentioned.

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