JP2532267B2 - Laminated circuit board - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a highly reliable laminated circuit board that ensures reliable insulation between circuit boards and has excellent mechanical strength and electrical characteristics.

[Prior art]

As one of the means for integrating the circuits on the circuit board, there is stacking the circuit boards. Conventionally, as a laminated circuit board, there are a laminated board in which the circuit forming surfaces do not face each other or a laminated board in which the circuit forming surfaces face each other. The laminated circuit boards that are laminated so that the circuit forming surfaces do not face each other have the following problems. That is, in order to make electrical connection between different circuit boards, through holes must be formed in at least one of the boards. When these through holes are connected by using a plating method, it is required that the process is long and that the circuit board is suitable for plating, chemical resistance, and wet processing are possible. Further, when solder is filled in the through holes to connect the circuits, a material having good solder wettability and adhesiveness must be used for the through holes and lands, and heat resistance is required for the entire circuit board. However, even if low-temperature solder is used, the workability and mechanical properties of the solder itself are inferior, so that there are drawbacks such as low electrical and mechanical reliability. Further, when the conductive paste or conductive adhesive is charged in the through holes to connect the circuits, the through holes become deeper because the board is interposed between the connected circuits, and therefore the thickness of the conductive paste or conductive adhesive is increased. Has a high conduction resistance, and the volume contraction during drying and curing causes cracks to easily cause a connection failure. In order to eliminate such a defect, the circuit boards may be laminated so that the circuit forming surfaces face each other. However, since the circuit forming surfaces face each other, insulation between circuit boards is required. That is, as a laminated circuit board having such a configuration,
An insulating layer is formed by screen printing, roll coating, dipping, etc. on the circuit formation surface of at least one circuit board, and then an adhesive layer is formed on top of it and the circuit boards are adhered and laminated, or insulation. There is one in which an adhesive layer having a function is formed and circuit boards are adhered and laminated. As a method for electrically connecting a predetermined portion of a circuit between such circuit boards, a through hole is provided in the insulating layer or the adhesive layer, and various conductive pastes or hot-melt type conductive sheets are provided in the through hole. A method of making electrical connection to each other by being present is used.

[Problems to be Solved by the Invention]

However, the laminated circuit board with the circuit forming surfaces facing each other has a risk that pinholes may be generated in the insulating layer or the adhesive layer due to mixing of dust or foreign matter, and the thickness of the adhesive layer having an insulating function is small. Therefore, the insulation reliability is low. In addition, electrical connection using a conductive paste or a hot-melt type conductive sheet has low adhesive strength depending on the material forming the circuit board, and is susceptible to change over time due to influences on temperature and humidity. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a highly reliable laminated circuit board in which insulation between circuit boards is reliable and which has excellent mechanical strength and electrical characteristics.

[Means for Solving the Problems]

The present invention is configured as follows to achieve the above object. That is, the laminated circuit board of the present invention is a laminated circuit board in which two circuit boards on which circuits are formed are laminated so that the circuit forming surfaces face each other, and the electrical connection portion between the circuit boards has adhesiveness. The non-electrical connecting portion is connected through a conductive material, the non-electrical connecting portion is adhered through the double-sided adhesive sheet, and the electrical connecting portion is sealed on all sides by the presence of the double-sided adhesive sheet. Also, in a laminated circuit board in which two circuit boards on which circuits are formed are laminated so that the circuit forming surfaces face each other, the electrical connection portions between the circuit boards are connected via a conductive material having adhesiveness. The non-electrical connection part is adhered via a double-sided adhesive sheet, and the electric connection part is sealed by the presence of the double-sided adhesive sheet on the four sides and the remaining part by the presence of resin or rubber. It was done. The present invention will be described in more detail with reference to a laminated circuit board including a flexible printed circuit board (hereinafter, referred to as FPC) and a transparent conductive film (hereinafter, referred to as ITO) circuit board as an example. FIG. 1 is a sectional view showing an embodiment of the laminated circuit board of the present invention, and FIG. 2 is a plan view thereof. FIG. 3 is a sectional view showing another embodiment of the laminated circuit board of the present invention, and FIG. 4 is a plan view thereof. 1 is an ITO circuit board, 2 is an FPC, 3 is a double-sided adhesive sheet, 4 is a conductive material, 5 is a sealing material, 11 is a substrate, 12
Is an ITO circuit, 21 is a substrate, 22 is a printed circuit, 31 is a base material, 3
2 indicates the adhesive layers, respectively. The drawings are exaggerated for the sake of clarity, ignoring the relative dimensional relationships of the components. As the conductive material 4 having an adhesive property for connecting the electrical connection portion between the two circuit boards, a hot-melt type conductive paste or a conductive sheet can be used. In the case of this conductive paste, the electrical connection is completed by thermocompression bonding after being applied and dried at a predetermined position on one circuit board by a dispenser or a screen printing method. In the case of a hot-melt type conductive sheet, electrical connection is completed by temporary thermocompression bonding at a predetermined position on one circuit board and then main thermocompression bonding. In addition, if the circuit board has heat resistance, use a thermosetting conductive paste, and if the volatile components in the paste can be easily volatilized due to the shape and structure of the board around the paste application part, use an evaporative dry conductive paste. When the substrate and the paste film thickness are such that ultraviolet rays can be sufficiently transmitted, it is possible to use an ultraviolet curable conductive paste. Originally, the conductive material 4 of this kind is for ensuring continuity, and has a lower adhesive strength than that of an ordinary adhesive.
Therefore, by reinforcing / sealing the electrical connection portion with the double-sided adhesive sheet 3 or resin / rubber, it is possible to increase the mechanical strength and prevent deterioration of the electrical connection portion due to water vapor or ionic impurities. Double-sided adhesive sheet that insulates and bonds two circuit boards 3
In some cases, an adhesive layer 32 is provided on both sides of a base material 31 such as a plastic film or paper / cloth, and release paper is provided on each adhesive layer 32 as necessary. At the time of use, remove the release paper and attach it to the circuit formation surface of the circuit board. The material, thickness, shape, etc. of the double-sided adhesive sheet 3 are designed in accordance with the above-mentioned conductive material 4 used for the electrical connection portion and the required performance of the circuit board to be laminated. From the viewpoint of insulation reliability, it is preferable to use a plastic film of polyethylene terephthalate, polyimide, polysulfone, polyether sulfone, polyparabanic acid or the like as the material of the base material 31 of the double-sided adhesive sheet. When a material that requires heat drying or heat curing treatment is used as the conductive material 4, this plastic film may be selected in consideration of heat resistance according to the heat treatment temperature. When a material containing an organic solvent is used as the conductive material 4, it may be selected in consideration of the solvent resistance to them. Further, it may be selected in consideration of dimensional stability, mechanical strength, etc. according to the required function of the laminated circuit board. The material of the adhesive layer 32 of the double-sided adhesive sheet 3 is appropriately selected from rubber-based, acrylic-based, vinyl-based, epoxy-based, and silicon-based adhesive materials according to required heat resistance, solvent resistance, and the like. The thickness of the double-sided adhesive sheet 3 is designed in consideration of the layer thickness of the conductive material 4 formed in the electrical connection portion, insulation resistance, dimensional stability, and the like. The shape of the double-sided adhesive sheet 3 is appropriately designed according to the type of the conductive material 4 used for the electrical connection portion. For example,
When the conductive material 4 used is a hot-melt type conductive paste or conductive sheet, the inner size of the through-hole region of the double-sided adhesive sheet 3 may be larger than the outer size of the conductive paste or conductive sheet forming region ( (See FIGS. 5 and 6). This is because when the thermocompression bonding head 6 of the thermocompression bonding apparatus heats and presses the electrical connection portion of the two circuit boards, the area where the conductive paste or the conductive sheet is formed and the through-hole area of the double-sided adhesive sheet 3 come into contact with each other. If they are present, or if they are adjacent to each other with only a very small gap, the double-sided adhesive sheet 3 acts as a fulcrum on the pressing surface of the thermocompression bonding head 6, and the pressure on the conductive paste or the conductive sheet decreases in the vicinity thereof. As a result, uniform heat and pressure cannot be applied to the conductive paste or conductive sheet from the thermocompression bonding head (see FIGS. 7 and 8). When the conductive material 4 used is an ultraviolet-curable conductive paste, the outer size of the conductive paste forming region and the inner size of the through-hole region of the double-sided adhesive sheet 3 are opposite to the case of the hot-melt type. It is advisable to match and as much as possible to reduce the gap between them. This is for the following reason. That is, when connecting the electrical connection portions of the two circuit boards, it is necessary to apply the conductive paste, superpose the circuit boards in a fluid state, and irradiate the ultraviolet rays while further pressing. At this time, if the pressure is excessive, the conductive paste will bleed in the through holes, and the thickness of the conductive paste will vary. This unevenness in thickness causes unevenness in the degree of curing due to unevenness in ultraviolet light transmission, and also causes stress in the electrical connection due to bending of the circuit board.
As a result, the electrical characteristics and mechanical strength of the obtained laminated circuit board are adversely affected. As described above, by making the outer size of the conductive paste forming region and the inner size of the through-hole region of the double-sided adhesive sheet 3 match as much as possible, the double-sided adhesive sheet 3 acts as a spacer and the pressing force can be kept constant. It will be. Further, when the conductive material 4 to be used is an evaporative dry type conductive paste, it is preferable to provide the double-sided adhesive sheet 3 with a passage 7 that connects the electrical connection portion and the outside (see FIG. 9). This is to facilitate the volatilization of the solvent in the conductive paste. In this case, in order to protect the electrical connection portion from the external environment after the solvent is volatilized, the passage 7 between the electrical connection portion and the outside may be sealed with resin or rubber. The double-sided adhesive sheet 3 according to the present invention plays a role of reinforcing the electrical connection portion. For example, there is a possibility that the strength of the electrical connection portion may be reduced or the conduction resistance may be increased due to the change with time of the adhesive force due to the influence of environmental conditions such as temperature and humidity. Therefore, the substrate 11 is surrounded by the electrical connection.
・ If it is sealed with 21 and the double-sided adhesive sheet 3 (see FIGS. 1-2), the electrical connection is protected and reinforced, so that the mechanical strength and the electrical connectivity are prevented from being degraded. You can When the periphery of the electrical connection portion is not completely surrounded by the double-sided adhesive sheet 3, the remaining portion may be coated with the sealing material 5 such as resin or rubber, and dried or cured to seal (the third portion). (See FIG. 4). You can Further, when a solventless curable resin can be used as the adhesive layer 32 of the double-sided adhesive sheet 3, the electrical connection portion is pressed due to the volume contraction of the adhesive material at the time of curing, and the electrical connectivity is further improved. .

【Example】

An example in which a laminated circuit board is obtained from an FPC and an ITO circuit board is shown below. First, silver paste (LS-500 made by Osaka Asahi Chemical Co., Ltd.) was screen-printed on a 125 μm thick polyimide film in a predetermined circuit pattern, dried at 50 ° C. for 10 minutes, and then at 80 ° C.
FPC was prepared by heating for 30 minutes to heat cure. Also 1.1
A resist with a predetermined circuit pattern is formed by screen printing on ITO formed by vapor deposition on mm thick soda glass, and the ITO is patterned by etching.
A TO circuit board was produced. Next, a 25 μm thick double-sided adhesive sheet (manufactured by Nitto Denko)
Retaining the insulating part of the FPC and ITO circuit glass substrate and the predetermined peripheral shape, each electrical connection part was punched out in a size of 6 mm square, the release paper on one side was peeled off, and it was adhered to the predetermined position on the circuit forming surface of the FPC. . Next, hot-melt type isotropic conductive paste (manufactured by Nippon Graphite Co., Ltd.) is applied to each of the 4 mm square terminals, which are electrical connections with the FPC circuit in the circuit of the ITO circuit board, by 5 mm by screen printing. It was formed into a square size and dried at 110 ° C. for 3 minutes. The other release paper of the double-sided adhesive sheet adhered to the FPC was peeled off and adhered to a predetermined position on the ITO circuit board. Next, the electrical connection portion on which the isotropic conductive paste was formed was removed from the base film surface side of the FPC by a thermocompression bonding head 1
After thermocompression bonding at 40 ° C. for 10 seconds, the FPC circuit and the ITO circuit board circuit were electrically connected. Further, an epoxy thermosetting resin was applied to the peripheral portion of the electrical connection portion and heated at 130 ° C. for 2 minutes to seal the electrical connection portion.

【The invention's effect】

In the laminated circuit board of the present invention, the non-electrical connection portion between the circuit boards is laminated via the double-sided adhesive sheet, and the electrical connection portion is laminated via the conductive material having adhesiveness. Since there is certain insulation between circuit boards,
It is a highly reliable laminated circuit board having excellent mechanical strength and electrical characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the laminated circuit board of the present invention, and FIG. 2 is a plan view thereof. FIG. 3 is a sectional view showing another embodiment of the laminated circuit board of the present invention, and FIG. 4 is a plan view thereof. 5 to 9 are sectional views showing the electrical connection portion, FIG. 5 is an AA sectional view of FIG. 6, and FIG. 7 is an AA sectional view of FIG. 1 ... ITO circuit board, 2 ... FPC, 3 ... double-sided adhesive sheet, 4 ... conductive material, 5 ... encapsulating material, 11 ... substrate, 12
…… ITO circuit, 21 …… Substrate, 22 …… Printed circuit, 31…
… Base material, 32… adhesive layer.

Claims (2)

(57) [Claims] 1. In a laminated circuit board in which two circuit boards on which circuits are formed are laminated so that their circuit forming surfaces face each other, the electrically connecting portion between the circuit boards has a conductive material (4) having an adhesive property. ), The non-electrical connection portion is adhered via the double-sided adhesive sheet (3), and the electrical connection portion is sealed on all sides by the presence of the double-sided adhesive sheet (3). Laminated circuit board. 2. In a laminated circuit board in which two circuit boards on which circuits are formed are laminated so that the circuit forming surfaces face each other, the electrically connecting portion between the circuit boards has a conductive material (4) having an adhesive property. ), The non-electrical connection part is adhered via the double-sided adhesive sheet (3), and the electric connection part has a remaining part by resin due to the presence of the double-sided adhesive sheet (3). A laminated circuit board characterized by being sealed by the presence of rubber.