JPH11168279A - Multilayer circuit board and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer circuit board which is high in flexibility and capable of propagating signals at a high speed. SOLUTION: Flexible resin sheets 1 each equipped with circuit patterns 2 and 4 and connecting electrode terminals are laminated into a multilayer circuit board as mutually and electrically connected together, wherein an air layer 8 is contained between the resin sheets 1 adjacent to each other in a vertical direction, through a manner where the air layer 8 is formed by removing a solvent-soluble filling material which is temporarily interposed between the resin sheets 1 adjacent to each other in a vertical direction for preliminarily bonding the resin sheets 1 together or keeping them in shape when the resin sheets 1 are laminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer circuit board and a method of manufacturing the same, and more particularly, to a multilayer circuit board having flexibility and capable of speeding up signal propagation and a method of manufacturing the same. The multilayer circuit board of the present invention can mount individual components such as semiconductor elements or chip capacitors / resistors. In the specification of the present application, “flexibility” is used to generally mean both properties of flexibility and flexibility.

[0002]

2. Description of the Related Art Higher performance of electronic equipment largely depends on higher speed and higher integration of semiconductor elements such as LSIs which can be called the heart. However, in order to make the most of the high speed of the elements, progress of a circuit board on which these elements are mounted at a high density cannot be overlooked. The circuit board has a multilayer structure in which fine conductor wiring is laid at high density at a narrow pitch, and furthermore, a number of conductor wiring layers are stacked.

[0003] Generally, conventional circuit boards are rigid and have little flexibility, as seen in printed wiring boards and ceramic circuit boards. However, there is a strong demand for miniaturization of electronic devices, particularly personal devices, and flexibility is required for circuit boards in order to fit the circuit boards in a limited space. As a circuit board on which a simple wiring is formed, a circuit board which satisfies the conditions of flexibility and flexibility, such as a flexible printed board, has been developed and put into practical use. A flexible printed board is formed by forming conductor wiring on one or both sides of a resin film such as polyimide. It has high flexibility, so it can be bent and used between conventional rigid boards (printed wiring boards and ceramic circuit boards). In many cases, it is used as a cable or used as a substitute for a connector, for example, for use in connection of a cable.

As a recent trend, circuit boards having the above-mentioned flexibility and flexibility have been used to improve the performance of electronic devices to be applied and to expand the range of application (for example, large-scale computers such as large computers). With application to systems, etc.), there is an increasing demand for multilayering. However, it is extremely difficult to stack a plurality of flexible sheets while positioning them and connect them to each other, and a technique for solving this is strongly desired.

[0005] Further, from the viewpoint of speeding up, a signal line is formed on one of two sheets vertically adjacent to each other at the time of lamination, a ground layer is formed on the opposing surface, and air is interposed between them. The structure has the following advantages. That is, since the speed of the pulse signal propagating through the signal line increases as the dielectric constant of the surrounding medium decreases, the propagation speed of the pulse signal is increased by interposing air having the lowest dielectric constant between the sheets. It becomes possible. Although the demands for circuit boards having such a configuration are increasing more and more, circuit boards that can sufficiently satisfy such demands have not yet been proposed or put to practical use.

[0006]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a multilayer circuit board having flexibility and capable of speeding up signal propagation.
Another object of the present invention is to provide a method of manufacturing a multilayer circuit board which can manufacture the multilayer circuit board according to the present invention by a simple method and with good yield.

[0007]

According to one aspect of the present invention, there is provided a multilayer circuit board in which a plurality of flexible resin sheets having circuit patterns and connection electrode terminals are laminated and electrically connected to each other. In the middle of the resin sheets vertically adjacent to each other, the temporary adhesion of the resin sheets at the time of lamination of those resin sheets, the removal of the solvent-soluble filler material that was temporarily interposed for shape retention, etc. A multilayer circuit board comprising an air layer.

According to another aspect of the present invention, there is provided a method of manufacturing a multilayer circuit board according to the present invention, comprising the following steps: preparing a plurality of flexible resin sheets, A circuit pattern and connection electrode terminals necessary for completing the multilayer circuit board are formed at predetermined portions, and a solvent for temporarily bonding the resin sheet, maintaining the shape, and the like, on at least one surface of the resin sheet. A soluble filler material is applied to the entire surface at a thickness corresponding to the thickness of the air layer, the resin sheets are laminated in a predetermined order and electrically connected to each other, and the obtained resin sheet laminate is Dissolving and removing the solvent-soluble filler material.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A multilayer circuit board according to the present invention can be basically constructed in the same manner as a conventionally used multilayer circuit board. Therefore, a resin sheet having a circuit pattern and connection electrode terminals can be used. It can be manufactured by laminating a plurality of sheets and electrically connecting each other.

However, the resin sheet used in the multilayer circuit board of the present invention must be a flexible resin sheet, unlike the materials used in conventional printed wiring boards and ceramic circuit boards. Suitable resin sheets include, for example, polyester films and polyimide films. In these resin sheets, flexibility, that is,
Flexibility / flexibility is important, and the degree of flexibility varies greatly depending on factors such as the sheet resin used, the configuration of the circuit board, and how it is used. However, the state of bending when manufacturing or using the circuit board In this case, it is sufficient if it is flexible enough not to cause breakage or cracking.

Although each resin sheet can be used in various thicknesses depending on the number of laminated sheets and the use of the circuit board, it is usually about 20 to 500 μm.
Preferably it is about 50 to 200 μm. In addition, in one laminated circuit board, as necessary, resin sheets having different thicknesses may be used in combination. The application of the circuit pattern, the connection electrode terminals, and the like to the flexible resin sheet can be performed by using a technique generally used in the production of a multilayer circuit board. The terminals and the like can be arranged as desired. For example, in order to increase the speed, it is preferable to form a signal line on one of two adjacent resin sheets at the time of lamination and to form a ground layer on the opposing surface. In addition, about such a process,
This will be described in detail when manufacturing a multilayer circuit board.

After a circuit pattern and the like are applied to each resin sheet and necessary processing is performed, a desired number of resin sheets are laminated in a required order and are electrically connected to each other. Here, in the finally obtained multilayer circuit board, in the middle of the resin sheets vertically adjacent to each other, when the resin sheets were laminated, they were temporarily interposed for temporary adhesion of the resin sheets, shape retention, etc. It is important that the lamination and connection be performed such that an air layer from the removal of the solvent-soluble filler material is included. The solvent-soluble filling material used for temporary bonding of the resin sheet, shape retention, etc., is not particularly limited as long as it has a desired function without adversely affecting the already formed circuit pattern, electrode terminal, etc. From the viewpoint of ease of handling, waxes having a low softening point, such as polyethylene resin, polyester resin and higher fatty acid ester resin, are preferred. The solvent-soluble filler material, its use, and formation of an air layer by its removal will be described in detail below.

In the multilayer circuit board of the present invention, the air layer to be interposed between the resin sheets vertically adjacent to each other is dissolved and removed by a suitable solvent in the filling material filled in the middle of those sheets. This corresponds to the void formed by the above. Although the thickness of the air layer can be widely changed depending on the desired effect, etc., it is generally about 50 to 100 μm, and preferably 70 to 100 μm, for the purpose of increasing the speed and temporarily bonding the resin sheet.
９０90 μm. Although the number of resin sheets laminated for forming the air layer is not particularly limited, it is generally 2 to 8, preferably 2 to 4.

Although the construction of the multilayer circuit board of the present invention has been specifically described above, it will be more apparent from the following description of the manufacture of the multilayer circuit board.
According to the present invention, after a circuit pattern and connection electrode terminals are formed in a predetermined portion of a flexible resin sheet by a normal method, a solvent-soluble filler is applied to the entire surface of the sheet, and these are soldered. By electrically connecting to each other by conventional connection means such as conductive adhesive, and then removing the previously applied filler material,
A multilayer circuit board having flexibility and having a structure in which air is interposed between layers (sheets) can be manufactured.

Hereinafter, a method for manufacturing a multilayer circuit board according to the present invention will be described step by step. In the following description, a wax having a low softening point, which is a typical example, will be used as the solvent-soluble filler. (1) Formation of a flexible resin sheet and a circuit pattern, etc. A flexible resin sheet, that is, a film of polyester, polyimide, or the like is used as a base material, holes are formed in predetermined positions of the film, and electroless plating, vacuum deposition, A metal thin film layer is formed by a sputtering method or the like.
Electrolytic plating is further performed using the metal thin film layer as an electrode layer to form a film having a predetermined thickness. Alternatively, a film having a predetermined thickness can be formed only by the above-described electroless plating, vacuum deposition, sputtering, or the like.

In the process of forming a film in this manner, hole filling is also performed. Here, it is optional whether the inside of the hole is entirely buried or whether the film has a thickness enough to ensure electrical conduction on the inner surface of the hole. A method in which a film having a predetermined thickness is formed on the inner surface of the hole and the remaining portion is filled with a resin, for example, an epoxy resin or a polyimide resin can also be used.

Next, a desired circuit pattern and a pattern for connecting the films are formed by using a conventional general photolithography method. Here, the above-described pattern forming operation is usually performed on both sides of the film, and thus a circuit pattern is formed on both sides of the film. However, this operation may be omitted when unnecessary.

Further, the formation of the pattern for connecting the films described above is also a feature of the method of the present invention.
That is, usually, a part for connecting films to each other is included in the circuit pattern. However, since circuit patterns usually have density, patterns (dummy terminals) used only for connecting each film are provided in rough areas.
Is provided. This is effective in increasing the overall mechanical strength after connection and keeping the distance between connected films constant. (2) Lamination and Electrical Connection of Films After the formation of the circuit patterns and the like, a predetermined number of films are laminated in a predetermined order and electrically connected. For this electrical connection, for example, a method using soldering, a conductor (conductive) paste, an adhesive, or the like can be applied.

For example, various methods can be applied to the soldering method. For example, a solder bump (solid state) is formed in a predetermined place in advance, and a method of connecting by reflow or a method of applying a solder paste to a predetermined place is used. There is a method of applying the paste (paste state) and connecting by reflow. Here, as a method of forming the solder bump (solid state), various methods that have been used so far, such as a vacuum evaporation method and a transfer method, may be used. When a solder paste is used, a screen printing method, a dispenser method, or the like can be appropriately selected. Further, when the size of the film is small and the number of connection points is small, a method of placing solder balls can also be used.

In the following embodiments, as the solder material, a commonly used solder having a composition of Sn-37 wt% Pb is taken as an example. However, depending on the available temperature range, Sn- having a lower melting point than this solder is used. Bi-based or Sn-In-based solder,
Pb-5wt% S with higher melting point than Sn-37wt% Pb solder
All solders that are currently industrially available, such as n-composition solder and Sn-Ag solder, can be used.

Next, on a film on which solder bumps (for example, Sn-37 wt% Pb composition, melting point (eutectic point): 183 ° C.) are formed by, for example, a vacuum evaporation method or a transfer method, polyethylene having a low softening point is formed. For example, a predetermined amount of powder of “Mitsui High Wax 110P” (manufactured by Mitsui Chemicals, softening point: 113 ° C.) is scattered and placed on a hot plate.
Heat to ℃ to melt the polyethylene and flow over the film to form a polyethylene film. Thereafter, the polyethylene film is cooled to room temperature. At this time, the solder bumps may protrude from the polyethylene film or may be hidden in the film. Because, when connecting the film, the solder is heated to a temperature at which the solder melts, but at this time, the polyethylene is also in a fluid state, and is removed by the solder (when the polyethylene is in a fluid state, it is still in a solid state), This is because soldering is not hindered.
Since the thickness of the polyethylene film can be controlled by the amount of the polyethylene powder to be scattered, it is only necessary to measure a predetermined amount once in advance and then work under the same conditions.

Here, instead of polyethylene having a low softening point, polyester resins, for example, higher fatty acid ester resins such as polycaprolactone (“PLACCEL HIP” manufactured by Daicel Chemical Co., melting point: 60 ° C.) also have an appropriate melting point. If so, it can be used as well. After forming the polyethylene film, the film loses flexibility and does not deform under normal handling. (3) Screen Printing of Solder Paste Instead of forming the electrical connection using the solder bumps as described above, it is also possible to screen print and use the solder paste. Hereinafter, this case will be described.

First, a screen for solder paste printing is placed in accordance with the position of the electrode for pattern circuit connection on the film, and a commercially available solder paste [solder composition is, for example, S
By using n-37 wt% Pb and a melting point (eutectic point: 183 ° C.), bumps or “bumps” of solder paste are formed on the electrodes. After drying this at room temperature, about 15
The paste is further dried at a temperature of 0 ° C. to disperse the solvent component of the paste and to solidify the paste.

Next, a predetermined amount of a powder of polyethylene having a low softening point (for example, “Mitsui High Wax 110P”, softening point: 113 ° C.) is sprinkled on the film and heated to 130 ° C. on a hot plate. The polyethylene is melted and flowed over the film to form a polyethylene film. Then, it cools to room temperature. At this time, the solder bumps are made to protrude from the polyethylene film. This is because, in the solder paste, when heated to a temperature at which the solder is melted, the resin component such as the flux is decomposed and scattered, so that the volume is reduced to about half that before melting. That is, as a result, a substantial amount of solder is insufficient, and when connecting the films, the possibility of poor connection increases.

When the solder paste is screen-printed and the solder is melted by reflow to form bumps, the situation is the same as that described in the previous section. (4) Use of conductive adhesive For the electrical connection of each film, a conductive adhesive can also be used as follows.

First, a stainless steel screen (only the electrode portion is opened) for applying a conductive adhesive is placed in accordance with the position of the pattern circuit connection electrode on the film, and a commercially available epoxy-based conductive adhesive is used. A bump or bump is formed on the electrode by using an agent. This is dried at room temperature, and further dried at a temperature of about 150 ° C. to disperse the solvent component of the conductive adhesive and solidify the conductive adhesive.

Next, a predetermined amount of a powder of polyethylene having a low softening point (for example, “Mitsui High Wax 110P”, softening point: 113 ° C.) is scattered on the film, and heated to 130 ° C. on a hot plate. The polyethylene is melted and flowed over the film to form a polyethylene film. Then, it cools to room temperature. At this time, the bumps of the conductive adhesive are made to protrude from the polyethylene film as in the case of using the solder paste. This is because, when the conductive adhesive is heated to a temperature at which the solder is melted, the resin component remaining after the drying treatment is decomposed and scattered, so that the volume is reduced. That is, as a result, when the respective films are connected to each other, the substantial amount of the adhesive is insufficient, and the possibility of poor connection is increased.

When a film of low softening point polyethylene or the like is formed, if the film forming material is in another form, for example, a liquid, the film is immersed in this liquid and then pulled up.
A film can also be formed. Furthermore, even if the low softening point polyethylene or the like is in a powder or solid state, if these materials are melted at an appropriate temperature, the film is immersed in this melt and then pulled up to form a film, as described above. You can also.

As described above, in the practice of the present invention, in addition to the characteristic temperature (melting point and softening point), the heat resistance of the film material used as the base material is not limited. The material may be appropriately selected in consideration of the properties, and is not limited to the materials described in the above description. (5) Connection of each film and completion of multilayer circuit board After completing necessary processing for electrical connection as described above, the connection electrode terminals of each film are connected to each other.
Or, position the dummy terminals. that time,
If only the original film is flexible, it is easily deformed because it is very flexible, so the work of positioning is very difficult and practically impossible. According to the above, as described above, for example, the film is not substantially deformed due to the presence of the polyethylene film having a low softening point. The same can be done. Although not described in the above description of the formation of the pattern wiring, it is preferable that the signal lines and the ground / power supply layer are formed on both sides of the film in such a manner that they face each other. Then, a ground / power supply layer is formed on the back surface. And when stacking each film,
The relationship is such that the signal line and the ground / power supply layer face each other on both sides of the film.

After a predetermined number of films having a polyethylene film are stacked, when, for example, Sn-37 wt% Pb solder is used, the peak temperature is set to about 230 ° C. and heating is performed. At this time, if necessary, a load is applied. This is because no deformation occurs until the polyethylene film is softened. Also, even if polyethylene wax remains between the solder bumps formed on the electrode terminals, as described above, when the solder is melted and integrated with each other, it is removed out of the solder. The attachment is not disturbed. Further, another effect of the polyethylene wax is that the polyethylene wax also has an effect of blocking the atmosphere at the time of solder reflow, so that there is also an effect that the soldering is reliably performed. This is the case when the reflow condition is performed in the air, and is not obviously recognized in the reflow in a nitrogen atmosphere, as a matter of course.

After completion of the soldering, an organic solvent, for example,
The polyethylene wax is removed by heating and washing with acetone, methyl ethyl ketone, or the like. Then
Wash with ethyl alcohol. In this way, a multilayer circuit board having flexibility and having a configuration in which the signal line and the ground / power supply layer face each other via air is obtained.

[0032]

Next, the present invention will be described with reference to examples. It should be understood that the present invention is not limited to these examples. For example, although lamination is performed in a regular pattern in the illustrated example, lamination can be performed in a staggered pattern as needed. Example 1 A multilayer circuit board was manufactured by the process shown in FIG. 1 and FIG. 1. Preparation of Flexible Printed Board As shown in FIG. 1 (1A), a commercially available flexible print in which signal lines 2, connection electrode terminals 3, and ground / power supply layers 4 are formed on a polyimide film 1 as a base material. A board was prepared. Here, the diameter of the connection electrode terminal was 200 μm, and the pitch was 400 μm. Formation of Solder Bump As shown in FIG. 1 (1B), a solder bump 5 was formed on the connection electrode terminal 3 of the prepared flexible printed board. Here, the solder material is not particularly limited as long as it does not thermally affect the polyimide at the time of reflow. Therefore, ordinary Sn-37 wt% Pb eutectic solder was used. First, silicon (Si) without metal conductor pattern
Under a dimensional condition (diameter, pitch, etc.) corresponding to the connection electrode terminal, Sn-3 was formed on the substrate by vacuum evaporation.
A bump (height: 150 μm) of 7 wt% Pb eutectic solder was formed. Next, the solder bumps on the Si wafer were aligned with the connection electrode terminals of the flexible printed board, and heated to a peak temperature of about 230 ° C. Since there is no metal conductor pattern on the Si wafer, the solder melted by this heating migrates to the connection electrode terminals of the flexible printed board, and solder bumps are formed on the connection electrode terminals. Here, the solder reflow conditions (temperature, time, atmosphere, etc.) may be the same as the conventional soldering conditions, and are not particularly specified. In addition, the height of the solder bump after reflow was about 90-100 μm. After forming a solder bump on the connection electrode terminal using polyethylene wax,
As shown in (1C), a powder 6 of polyethylene wax (brazing material) having a softening point of about 80 ° C. was uniformly dispersed on a flexible printed board. Next, the flexible printed board with the polyethylene wax powder dispersed therein was placed on a hot plate or a thermostat heated to about 100 ° C., and the polyethylene wax was melted to form a uniform film on the flexible printed board [ See FIG. 1 (1D)]. In this case, the thickness of the polyethylene wax film solidified after melting was about 80 μm. In this example, the amount of the polyethylene wax powder to be scattered was measured in advance. By this method, the flexible printed board became inflexible and did not deform in normal handling. After the polyethylene wax film was formed on both sides of the flexible printed board, as shown in FIG. 2 (1E), the connection electrode terminals of each flexible printed board were aligned. At this time, if the original flexible printed board is rich in flexibility, it is easily deformed, so the alignment work is very difficult,
Although it was substantially impossible, in this example, the flexible printed board was not substantially deformed due to the presence of the polyethylene wax film. Actually, the positioning operation can be performed in substantially the same manner as the prepreg laminating step which is a conventional printed wiring board manufacturing step. Also, when stacking flexible printed boards,
As shown in the figure, the relationship was such that the signal line and the ground / power supply layer were opposed to each other. The laminate 9 was obtained. Formation of Electrical Connection (Soldering) After stacking a predetermined number of flexible printed boards having a polyethylene wax film to form a laminate 9, the laminate was heated to a peak temperature of about 230 ° C. Although not performed in this example, at this time, if necessary, a load can be applied. This is because no deformation occurs until the polyethylene wax film softens and melts. Also, even if polyethylene wax remains between the solder bumps formed on the electrode terminals, when the solder is melted and integrated with each other, it is excluded outside the solder, so that soldering is hindered. There was no. Furthermore, as another effect of the polyethylene wax, since the polyethylene wax also has an effect of blocking the atmosphere during solder reflow,
There was also an effect that the soldering was performed reliably. This is the case when the reflow condition is performed in the atmosphere,
In a reflow in a nitrogen atmosphere, as a matter of course, it is not clearly recognized. As shown in FIG. 2 (1F), the solder bumps 5 were integrated and an electrical connection was formed. After completion of the formation of the air layer and the soldering, the laminate was heated and washed with an organic solvent in order to dissolve and remove the polyethylene wax. Although acetone is used as the organic solvent in this example, methyl ethyl ketone and others may be used. Subsequently, after washing with ethyl alcohol, a multilayer circuit board 10 having an air layer 8 (corresponding to a void formed by removing polyethylene wax) between flexible printed boards was obtained as shown in FIG. 2 (1G). . This multilayer circuit board 10 is excellent in flexibility and flexibility,
The configuration was such that the signal line 2 and the ground / power supply layer 4 were opposed via the air layer 8. Example 2 A multilayer circuit board was manufactured by the process shown in FIG. 3 and FIG. Preparation of Flexible Printed Board As shown in FIG. 3 (2A), a commercially available flexible print in which signal lines 2, connection electrode terminals 3, and ground / power supply layers 4 are formed on a polyimide film 1 as a base material. A board was prepared. Here, the diameter of the connection electrode terminal was 200 μm, and the pitch was 400 μm. 3. Formation of Bump of Conductive Adhesive As shown in FIG. 3 (2B), the bump 15 of the conductive adhesive is formed on the connection electrode terminal 3 of the prepared flexible printed board using a normal screen printing method. Formed.
The shape of the bump 15 was a conical point. Here, as the conductive adhesive, a paste (paste) -like material obtained by kneading silver particles and an epoxy resin was used. The conductive adhesive bump 15 was heated to 100 ° C. in a nitrogen atmosphere to temporarily cure the conductive adhesive. No adverse effects were observed with atmospheric heating. Polyethylene Wax Application After forming a bump of conductive adhesive on the connection electrode terminal, as shown in FIG. 3 (2C), a polyethylene wax (wax) having a softening point of about 80 ° C. is placed on a flexible printed board. Material 6) was evenly scattered. Next, the flexible printed board with the polyethylene wax powder dispersed therein was placed on a hot plate or a thermostat heated to about 100 ° C., and the polyethylene wax was melted to form a uniform film on the flexible printed board [ See FIG. 3 (2D)]. In this case, the thickness of the polyethylene wax film solidified after melting is
It was about 80 μm. In this example, the amount of the polyethylene wax powder to be scattered was measured in advance.
By this method, the flexible printed board became inflexible and did not deform in normal handling. After the polyethylene wax films were formed on both sides of the flexible printed board, the connection electrode terminals of each flexible printed board were aligned as shown in FIG. 3 (2E). At this time, if the original flexible printed board is rich in flexibility, it is easily deformed, so the alignment work is very difficult,
Although it was substantially impossible, in this example, the flexible printed board was not substantially deformed due to the presence of the polyethylene wax film. Actually, the positioning operation can be performed in substantially the same manner as the prepreg laminating step which is a conventional printed wiring board manufacturing step. Also, when stacking flexible printed boards,
As shown in the figure, the relationship was such that the signal line and the ground / power supply layer were opposed to each other. The laminate 9 was obtained. Formation of Electrical Connection (Hardening of Conductive Adhesive) After laminating a predetermined number of flexible printed boards having a polyethylene wax film to form a laminate 9, the laminate was heated to a peak temperature of about 230 ° C. At this time, a load was applied so that when the polyethylene wax layer was softened, the tips of the conductive adhesive bumps penetrated each other. In this state, the conductive adhesive was heated to 150 ° C. in a nitrogen atmosphere to cure. In the case of this example, no adverse effect was observed even by heating in the air. Also, even if polyethylene wax remains between the bumps of the conductive adhesive formed on the electrode terminals, when the polyethylene wax softens and starts to flow, it is removed out of the bumps of the conductive adhesive, Contact between the bumps of the conductive adhesive was not hindered. further,
Another effect of polyethylene wax is that the polyethylene wax has the effect of blocking the atmosphere during heating, so the bumps of the conductive adhesive are joined (engaged).
There was also an effect that the operation was performed reliably. These effects are obtained when the heating is performed in the air, and are obviously not apparent in the heating in the nitrogen atmosphere, as a matter of course. As shown in FIG. 4 (2F), the conductive adhesive 15 was integrated, and an electrical connection was formed. Formation of Air Layer After the curing and joining of the conductive adhesive were completed, the laminate was heated and washed with an organic solvent to dissolve and remove the polyethylene wax. Although acetone is used as the organic solvent in this example, methyl ethyl ketone and others may be used. Subsequently, after washing with ethyl alcohol, a multilayer circuit board 10 having an air layer 8 (corresponding to a void formed by removing polyethylene wax) between flexible printed boards was obtained as shown in FIG. 4 (2G). . During the cleaning, the cured conductive adhesive did not dissolve. The multi-layer circuit board 10 has excellent flexibility and flexibility, and has a configuration in which the signal line 2 and the ground / power supply layer 4 face each other via the air layer 8.

[0033]

As described in detail above, according to the present invention, it is possible to provide a multilayer circuit board having excellent flexibility and flexibility. It can greatly contribute to the development. further,
In the multilayer circuit board of the present invention, since the air layer is interposed between the sheets constituting the multilayer circuit board, the propagation speed of the pulse signal can be further increased.

Further, according to the present invention, the excellent multilayer circuit board as described above can be easily manufactured with high reliability by an easy positioning operation.

[Brief description of the drawings]

FIG. 1 is a sectional view sequentially showing a preferred example (first half of a process) of a method of manufacturing a multilayer circuit board according to the present invention.

FIG. 2 is a sectional view sequentially showing a preferred example (second half of the process) of a method for manufacturing a multilayer circuit board according to the present invention.

FIG. 3 shows another method of manufacturing a multilayer circuit board according to the present invention.
FIG. 3 is a cross-sectional view showing one preferred example (first half of the process) in order.

FIG. 4 shows another method of manufacturing a multilayer circuit board according to the present invention.
FIG. 3 is a cross-sectional view showing one preferred example (the latter half of the process) in order.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Polyimide film (base material) 2 ... Signal line 3 ... Connection electrode terminal 4 ... Ground / power supply layer 5 ... Solder bump 6 ... Polyethylene wax powder 8 ... Air layer 9 ... Laminate 10 ... Multilayer circuit board

Claims (4)

[Claims] 1. A multilayer circuit board in which a plurality of flexible resin sheets each having a circuit pattern and connection electrode terminals are laminated and electrically connected to each other. A multilayer circuit comprising an air layer derived from the removal of a solvent-soluble filler material temporarily interposed for temporary adhesion of resin sheets, shape retention, etc. when laminating those resin sheets. substrate. 2. The method for manufacturing a multilayer circuit board according to claim 1, wherein: a plurality of flexible resin sheets are prepared, and the multilayer circuit board is provided on a predetermined portion of each resin sheet. Forming a circuit pattern and connection electrode terminals necessary to complete the substrate, on at least one surface of the resin sheet, a solvent-soluble filling material for temporary adhesion of the resin sheet, shape retention, etc. of the air layer Apply to the entire surface with a thickness corresponding to the thickness, laminate the resin sheets in a predetermined order and electrically connect to each other, and dissolve and remove the solvent-soluble filling material from the obtained resin sheet laminate. A method for manufacturing a multilayer circuit board, comprising: 3. The method according to claim 2, wherein the solvent-soluble filler is a wax having a low softening point. 4. The method according to claim 2, wherein the electrical connection of the electrode terminals is performed by soldering and / or applying a conductive adhesive.