JP2003338668A - Circuit board, multilayer circuit board and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve stable electric connection between a conductive circuit and a conductive resin with low resistance, in a circuit board formed by provid ing the conductive circuits on both front and rear surfaces of an insulated substrate, and connecting the conductive circuits to each other with the conduc tive resin through a through hole formed in the insulated substrate. <P>SOLUTION: The conductive circuit provided to the insulated substrate comprises a groove. The groove and the through hole are filled with the conductive resin to increase an area of a contact surface between the conductive circuit and the conductive resin. Thereby the electrical connection of them is absolutely obtained and resistance is lowered. To form the groove to the conductive circuit, a resist pattern whose width is sufficiently smaller than the thickness of the conductive circuit is used for alkali-etching. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board or a package board on which electronic parts are mounted, and more particularly to a board structure for improving electric characteristics of a circuit formed on the board and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, the mounting area and wiring of printed circuit boards have become smaller and finer in association with the miniaturization of electronic equipment, the miniaturization of semiconductor chips and components, and the narrowing of terminal pitches. . At the same time, in information-related equipment, it is required to shorten the distance of the wiring that connects the parts in response to the widening of the signal frequency, and it is indispensable to multilayer the circuit board to achieve high density and high performance. It has become a technology. In this multi-layer circuit board, a key technology is to form a circuit for electrically connecting layers, which is not present in a conventional planar circuit. In the double-sided wiring board, which is the first step of the multilayer circuit board, through holes are formed in the insulating base material, and a conductor is plated along the wall surface of the hole to connect the front and back wirings. For example,
Also in the build-up multilayer board, a method of removing a part of the insulating layer between the circuit layers with a laser or the like and connecting by plating is used (see Fukuda: "First Electronics Packaging Technology" Industrial Research Group, p.71). The circuit wiring connection using plating has the advantage that minute circuits can be connected with a low and stable connection resistance, but the process is complicated and the number of steps is large, so the cost is high and it becomes a factor limiting the application of the multilayer substrate. Was there.

In recent years, a multilayer board using a conductive resin (conductive paste) has been put into practical use as an inexpensive interlayer connection method instead of plating, and the application of the multilayer board has begun to rapidly expand (for example, Shiraishi et al .: Matsushita Technical Journal, Vol.45, N
o.4, p. 401 (1999) or Fukuoka et al .: Electronic materials, Vo
l.34, No.16, p. 95 (1995)). With this technology,
A through hole (via hole) is opened using a laser using an insulating resin plate as a starting material, and then a conductive resin is filled in the through hole by a printing method to form a front and back connection circuit. An insulating base material having a connection portion made of a conductive resin provided at a desired position is sandwiched between copper foils and pressure-bonded repeatedly to form a multilayer connection conductive circuit.

FIG. 16 is a diagram showing the structure of a conventional multilayer circuit board, FIG. 16 (a) is a plan view, and FIG. 16 (b) is a sectional view taken along line DD ′. As shown in the figure, a conductive circuit 102 made of copper foil or the like is formed on an insulating substrate 101 made of a resin film.
A through hole 104 is provided in the insulating substrate 101 through 2. A conductive resin 105 is filled in the through hole 104. As shown in FIG. 16B, a plurality of such substrates are stacked with the through holes 104 aligned with each other to form a multilayer circuit board 100. As a result, the conductive circuit 102 and the conductive resin 105 are electrically connected via the conductive particles such as copper and silver contained in the conductive resin.

FIG. 17 shows an example of the manufacturing process of the conventional multilayer circuit board as described above. The insulating substrate 101 is used as a starting material (see step (a)), and a through hole 104 is formed at a predetermined position (see step (b)). Next, the through hole 104 is filled with a conductive resin 105 (see step (c)). Next, for example, copper foil 2a is attached to both surfaces of the substrate (see step (d)). Next, a photoresist film is formed on the surface of the copper foil, a predetermined circuit pattern is exposed and developed, and then chemical etching is performed using the photoresist film as a mask to form a predetermined conductive circuit 102. Circuit boards 110, 11 having a predetermined conductive circuit
The required number of 4 and the copper foil 102a are vertically stacked and thermocompression bonded (see step (f)). In this way, FIG.
The multilayer circuit board 100 shown in (g) was obtained.

FIG. 18 shows another example for obtaining the conventional multilayer circuit board 100. In this method, in steps (a) to (d), a circuit board 111 is manufactured in the same procedure as in FIG. 7 using a single-sided board having copper foil adhered on one side as a starting material. ) To step (h), a double-sided inverted-pasted substrate having copper foils 2a, 2a on both sides is used as a starting material, and the circuit board 1 is also processed in the same procedure as in FIG.
A plate 200 was obtained as shown in Fig. 18 (i).

In addition to this, a photosensitive resin is used as an insulating layer, and a through hole is formed by performing exposure and development, or chemical etching (Machida: Surface Mount Technology Vol.
17 No.1 p.31 (1997)) or a method of removing the resin by dry etching has also been proposed. Although the method using a conductive resin is inexpensive, there are some drawbacks such as high electrical resistance of the conductive resin portion and unstable contact resistance with a conductive circuit using a copper foil, but they also gradually Is being overcome by.

However, in a board on which a bare chip such as a multi-chip module is mounted, the thickness of a single-layer circuit board tends to decrease as the wiring density increases. Due to the reduction of the layer thickness, the insulating film used as a substrate is liable to be bent or wrinkled, which makes it difficult to secure dimensional stability. In a method for manufacturing a multilayer substrate using a conductive resin for interlayer connection, by using a copper foil-bonded film as a starting material, the rigidity of the film is increased and high dimensional accuracy can be easily maintained. The drawbacks remain.

In order to compensate for the above-mentioned drawbacks and to keep the contact resistance between the circuit conductor and the conductive resin stable and low, FIG.
After the conductive resin 105 is filled in the through hole 104 of the circuit board 111 as shown in (capping type), the conductive circuit 1 is formed.
02 and the through hole 104, a plating layer 114 is formed on the surface of the conductive resin 105 in the through hole 104 to form the conductive circuit 102 and the conductive resin 1.
The means for ensuring the contact area with 05 is proposed. By this means, the contact area between the circuit conductor and the conductive resin can be widened, so the contact resistance can be suppressed to a sufficiently low level, but the cost increase due to the plating treatment is unavoidable, and the interlayer connection method using the conductive resin is inevitable. The advantage of is lost.

In order to achieve a similar structure without using plating, when a through hole for front and back connecting circuits is formed in a substrate having a circuit conductor, the circuit conductor is left and only the substrate is penetrated.
A method of filling the formed through-hole with a cover with a conductive resin is considered. FIG. 21 (through-hole type with a lid) shows a cross-sectional view of the circuit board 112 obtained by this method. With this method, the electrical connection between the conductive resin 105 and the conductive circuit 102 is good, but there is a problem in filling the through hole with a lid with the conductive resin. In the case of a through hole, the filling of the conductive resin is easily achieved by printing and injecting the conductive resin from one side of the hole, but in the case of the through hole with a lid, the process of injecting the conductive resin is performed. The air remaining on the bottom of the hole is not discharged, and remains as bubbles, which tends to cause incomplete filling of the conductive resin. An apparatus that can fill the holes without leaving air bubbles by printing in vacuum has been developed, but the equipment cost and processing man-hours increase significantly, and the products to which this process is applied are limited. Can be used only in the field

On the other hand, by printing the conductive resin in a region including the surface of the circuit conductor and slightly larger than the opening of the through-hole, the contact area between the conductive resin and the circuit conductor is expanded to increase the contact resistance. Can be stabilized low. Figure 2
2 (land laminated type) shows a cross section of the circuit board 113 manufactured by this method. As shown in the figure, in this circuit board 113, a land 116 made of a conductive resin is formed on the conductive circuit 102 including the through hole 104,
Since the conductive circuit 102 and the conductive resin 105 are also in contact with each other on the surface of the conductive circuit 102, the contact area is shown in FIG.
The contact area is larger than that of the through-hole type. According to this method, when the through holes 104 formed in the insulating substrate 101 are filled with the conductive resin 105 by using the printing method, the lands 116 made of the conductive resin can be formed around the through holes at the same time, which results in low cost. The circuit board can be obtained with.

[0012]

However, in the above structure, there is a possibility that an obstacle may occur to the miniaturization of the circuit pitch and the thinning of the conductor for the purpose of further miniaturization and high density of the circuit board. is there. That is, the conductive resin 105 is overlaid on the conductive circuit 102 in the land portion around the through hole.
Since the printing is performed, the land thickness is extremely increased, which hinders the thinning of the substrate, and the flatness of the entire substrate after the multilayer lamination is easily impaired. Further, since it is necessary to align the center of the land with the position of the through hole during printing of the conductive resin, the dimension of the land cannot be made smaller than the alignment accuracy of the printing apparatus, and miniaturization of the circuit is restricted. Therefore, further improvement of the interlayer connection method is desired in order to use a conductive resin for the connection between the layers of the multilayer laminated substrate and to cope with high density while maintaining excellent electrical characteristics at low cost.

[0013]

In order to solve the above problems, a circuit board of the present invention has a through hole in an insulating substrate, and the through hole is filled with a conductive resin. A circuit board in which a resin and a conductive circuit formed on the surface of the insulating substrate are electrically connected, one end of which reaches a through hole on the conductor surface of the conductive circuit, and at least one of the other ends A circuit board having a groove whose portion does not penetrate to the back surface of the conductor of the conductive circuit is provided. In the present invention, the planar shape of the groove on the surface of the conductive circuit may be radial or star-shaped. Alternatively, the planar shape of the groove on the surface of the conductive circuit may be a combination of a radial shape or a star shape and a concentric circle of the through hole. By configuring the circuit board in this way, the contact area between the conductive circuit and the conductive resin is increased by a method that minimizes the increase in man-hours without using a special device, and the contact resistance is stabilized at a low level. A circuit board having good electrical characteristics can be obtained.

The multilayer circuit board of the present invention is a multilayer circuit board in which at least one circuit board of the present invention is laminated. Since the contact resistance between the conductive circuit of each circuit board and the conductive resin is low, the contact resistance is low as a whole even when laminated in multiple layers, and a multilayer circuit board having good electrical characteristics can be obtained.

Further, according to the method of manufacturing a circuit board of the present invention, a photoresist film is formed on a conductor film of an insulating substrate having a conductor film on at least one surface, and then a predetermined groove pattern is formed. The circuit pattern is exposed and developed, the substrate is immersed in an etchant by using the obtained photoresist film pattern as a mask to etch the conductor film, and then the obtained conductor pattern is used as a mask at a predetermined position on the substrate. After a through hole is provided in the through hole, a conductive resin is filled in the groove on the surface of the conductive pattern and the through hole to electrically connect the conductive resin and the conductive film.
In the method of the present invention, it is preferable that the width of the narrow groove pattern forming the photoresist film is 4 times or less the thickness of the photoresist film. According to the method of the present invention, since the depth of the groove varies due to the difference in etching rate, the increase in the number of steps is minimized without using a special device, and the contact between the conductive circuit and the conductive resin is inexpensive. It is possible to increase the area and obtain a circuit board having excellent electrical characteristics.

Further, the manufacturing method of the multilayer circuit board of the present invention employs a method of laminating and bonding at least one circuit board obtained by the manufacturing method of the present invention. According to this method, using a circuit board obtained at a low cost by minimizing the increase in man-hours without using a special device,
Since the layers are laminated by the usual method, a high-performance multilayer circuit board can be obtained at low cost.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the drawings. In the following figures, the scale is not necessarily accurate in order to make the structure easy to understand. (First Embodiment) FIG. 1 is a partial plan view showing a through hole portion of a circuit board of the present invention. 2 and 3 are line AA 'and line BB' of the circuit board shown in FIG. 1, respectively.
It is sectional drawing along. As shown in FIGS. 1 to 3,
In the circuit board 10 of the present invention, the through hole 4 is provided in the insulating substrate 1 made of resin or the like, and the conductive circuit 2 having a predetermined pattern made of copper foil or the like is provided on the surface of the insulating substrate 1. A groove 3 is formed on the surface of the conductive circuit 2. In this embodiment, the groove 3 is a linear groove 3a formed radially from the center of the through hole 4 and a groove 3 concentric with the through hole 4.
It consists of b. Inside the through hole 4 and inside the groove 3,
It is filled with a conductive resin 5 such as copper paste, and the conductive resin 5 and the conductive circuit 2 are electrically connected. Further, as shown in FIGS. 2 and 3, one end of the groove 3 reaches the through hole 4, and the other end is connected to the circular groove 3b. Further, the depth of the groove 3 of the conductive circuit 2 is thinner than the thickness of the conductive circuit 2, and the conductive resin 5 in the groove 3 is in contact with the conductive circuit 2 on the side surface and the bottom surface of the groove. Therefore, the contact area between the conductive circuit 2 and the conductive resin 5 is significantly increased as compared with the case of the conventional through-hole type circuit board shown in FIG.
The contact resistance between the conductive circuit 2 and the conductive resin 5 is low, and the circuit board exhibits stable electrical characteristics.

Next, an example of a method of manufacturing the circuit board of the present invention as shown in FIGS. 1 to 3 will be described. 4 and 5 are process cross-sectional views showing an example of the method for manufacturing a circuit board of the present invention. In this example, a single-sided copper-clad substrate (Copper Clad Laminate: CC) in which a copper foil 2a serving as a conductive circuit 2 is attached to one surface of an insulating substrate 1 made of a polyimide film
The laminated film 8 in which the adhesive 7 is bonded to L) 6 is used as a starting material (see FIG. 4A). The CCL is a type in which an insulating resin such as polyimide and a metal conductor foil are joined together with an adhesive, a type in which a polyimide precursor is applied on a copper foil and then heated and baked, and a metal film is vapor-deposited on a polyimide film. And a type in which copper is grown by plating with a vapor-deposited film as a seed layer. In the present invention, in addition to the laminating film in which an adhesive layer is present on the side opposite to the copper of these CCLs, all layers are made of thermoplastic polyimide. CCL consisting of can also be applied as a starting material. In addition, CCL using a liquid crystal polymer exhibiting thermoplastic behavior as an insulating layer
Is also applicable as a starting material.

Next, a photoresist film 35 is thermocompression-bonded to the surface of the laminated film 8 on the conductive circuit side using a roll laminator (see FIG. 4B). Next, a circuit pattern having a predetermined shape is exposed on the photoresist film 35 and developed to form a resist mask (FIG. 4).
(See (c)). At this time, a thin slit serving as the groove portion 31 connected to the through hole portion 41 is formed in the photoresist film around the through hole. The width of this narrow slit is made sufficiently thin with respect to the thickness of the photoresist film 35,
For example, the thickness is preferably four times or less the thickness of the photoresist film 35. The shape of the slit may be such that one end of the slit reaches the through hole portion, such as a shape that spreads radially from the through hole or a shape that surrounds the through hole in a substantially concentric shape.

Then, the substrate on which the resist mask is formed is immersed in an etchant containing ferric chloride as a main component and chemical etching is performed to remove unnecessary portions of the copper foil by etching (see FIG. 4 (d)). At this time, the etching rate of the slit portion having a width sufficiently smaller than the thickness of the photoresist film 35 becomes slow. It is known that, when etching is performed using a resist as a mask, if the resist opening distance approaches the resist thickness, the etching speed becomes slower as the opening distance becomes narrower (A. Kikuchie
t.al. "Etching Rate of Copper Foil for Printed Cir
cuit Boad ”Metallurgical Processes for Early Twe
nty-first Century, Edited by HYSohn, The Mineral
s, Metals & Materials Society, 1994). By utilizing this phenomenon, it is possible to form a through hole through the copper foil by chemical etching and simultaneously form a shallow groove on the surface of the copper foil.

The etching is stopped when the insulating substrate 1 is exposed by etching away the copper foil in the through hole portion 41 by chemical etching using an etchant containing ferric chloride as a main component. Then, the copper foil originally having the thickness t ₁ is etched away in the through hole portion 41, but the copper foil of the thin conductor circuit 2 having the thickness t ₂ still remains in the groove portion 31 (FIG. 4 (e)). )reference). An appropriate value for the thickness t ₂ of the conductor circuit 2 remaining in the groove 31 is about 5 μm. As an example of appropriate conditions for obtaining this level of residual copper foil, for example, CCL on which a copper foil with a thickness of 8 μm is pasted is used, and a photoresist film or liquid photoresist with a thickness of about 10 μm is pasted into the through hole. The diameter of 1
The width of the slit for the groove may be set to 00 μm or more and about 50 μm.

Next, after the remaining photoresist film is dissolved and removed, through holes 4 penetrating the insulating substrate 1 and the adhesive 7 are formed by using, for example, laser irradiation with the copper foil of the conductive circuit 2 as a mask. . The groove portion 31 in which the conductive circuit 2 serving as a mask remains by laser irradiation is not punched, but only the through hole portion 41 in which the conductive circuit 2 does not remain is punched to form the through hole 4 (FIG. f) and (g)). As a usable laser, a solid-state laser such as YAG or an excimer laser can be used in addition to a CO ₂ laser, but it is necessary to select energy so that the copper foil is not eroded but only the resin such as polyimide is eroded. There is. For the perforation of the resin-made insulating substrate, plasma etching or chemical etching using an appropriate chemical can be used instead of using laser irradiation. After the etching is completed, the inside of the through hole is cleaned by a chemical treatment, if necessary.

Finally, a conductive resin 5 is applied to the conductor circuit 2 side of the laminated film 8 having the groove 3 and the through hole 4 using a printing machine, and the surface of the conductor circuit 2 is directly contacted with a squeegee. To fill the groove 3 and the through hole 4 with the conductive resin 5 (see FIG. 4).
(See (h)). The conductive resin 5 is directly applied onto the metal foil without using a printing plate, and is filled with a squeegee, so that the conductive resin 5 remains only in the groove 3 and the through hole 4 which are the recesses. At this time, the conductive resin 5 in the groove 3 and the through hole 4 is continuous, and is integrated by subsequent firing. The conductive resin is a binder whose main component is an epoxy resin, and the average particle size is 5μ.
Viscosity of 50 to 150P, using metal particles of about m as filler
A heat-curable conductive paste of a · s is used. As the metal particles, silver particles or copper particles or copper particles as a filler,
Particles obtained by coating the surfaces of copper particles with silver can be used. Also,
The type of resin does not matter as long as the amount of solvent component is small and the volume reduction upon drying and curing is slight.

After drying the conductive resin, a photoresist film for a circuit pattern is formed again, the conductive circuit pattern is exposed and developed, and the copper foil is etched to form the conductive circuit 2 having a predetermined pattern. Thus, the circuit board 10 as shown in FIG. 5 (i) is obtained.

(Second Embodiment) In the case of manufacturing a multilayer circuit board, at least one circuit board 10 of the present invention obtained as described above is used, and a plurality of circuits having desired electric circuits are provided. It can be obtained by stacking circuit boards and connecting the layers by heating and pressure bonding, and at the same time curing the conductive resin to complete the electrical connection between the layers. For example, FIG. 6 (j) shows one circuit board 10 obtained in the first embodiment, another circuit board 20 having two through holes, and one copper foil 2a. By aligning one of the through-holes with each other and superimposing them by heat and pressure, a multilayer circuit board 50 having a three-layer conductive circuit as shown in FIG. FIG. 7 is a plan view of the multi-layer circuit board 50 thus obtained.
Radial grooves 3a, 3a and grooves 3b, 3b concentric with the through holes surrounding them are provided around the individual through holes 4, 4, and these grooves 3a and 3b are electrically integrated. It is joined. Here, FIG. 6K is a sectional view taken along the line CC ′ of FIG. 7.

(Third Embodiment) FIG. 8 is a partial plan view showing another embodiment of the groove 3 provided around the through hole 4. In this circuit board 21, the grooves 3 are provided radially around the through hole 4. Although there is no annular portion in this embodiment, since the contact area between the conductive circuit 2 and the conductive resin 5 is increased by forming the radial groove 3 in the same manner as in the first embodiment, both are not formed. It is possible to sufficiently lower the contact resistance of.

(Fourth Embodiment) FIG. 9 is a partial plan view showing still another embodiment of the groove 3 provided around the through hole 4. In this circuit board 22, the groove 3 is provided in a star shape centering on the through hole 4. This shape also increases the contact area between the conductive circuit 2 and the conductive resin 5, so that the contact resistance between the two can be made sufficiently low. When the groove 3 is formed in a star shape, since the groove width is different between the root portion and the tip portion of the groove, the etching rate is different and the depth of the groove formed by etching is also different. FIG. 10 is a diagram illustrating the depth of the groove. In the figure, 22 is a conductor circuit, 22a is the surface, and 22b is the through-hole surface. Reference numeral 23 is a groove provided in the conductor circuit 22. Here the groove depth of the base of the lower left direction of the star-shaped groove and d _1, if the groove depth of the tip of the star-shaped paper upper-right direction as d _2, the depth d ₁ of the tip Root depth d ₂
Deeper than. That is, d ₁ > d ₂ .

(Fifth Embodiment) FIG. 1 shows a method for forming a through hole 4 after forming a groove 3 on a copper foil to be a conductive circuit 2.
As shown in FIG. 1, it is also possible to use a method in which the conductive circuit 2, the resin-made insulating substrate 1 and the adhesive 7 are penetrated by machining by a drill 25 to form a hole at once. In this case, as shown in FIG. 11A, the conductive circuit 2 and the groove 3 are formed.
Is formed by utilizing chemical etching in the same manner as in the first embodiment, and then a drill 25 is used to form a hole. After forming the through hole 4 by penetrating the conductive circuit 2, the insulating substrate 1 and the adhesive material 7 as shown in FIG. 11B, the groove 3 and the through hole 4 are formed in the same manner as in the first embodiment. By filling the conductive resin 5, the circuit board 10 is obtained as shown in FIG.

(Sixth Embodiment) As a method of forming a through hole 4 on a copper foil which becomes a conductive circuit 2, a groove 3 is formed on the copper foil by laser irradiation as shown in FIG. It is also possible to use a method in which 4 is narrowed. As shown in FIG. 12A, the conductive circuit 2 and the adhesive 7 are formed on both surfaces of the insulating substrate 1.
Using the single-sided copper-clad laminated film 8 attached to FIG.
As shown in FIG. 2 (b), the groove 3 and the through hole 4 are irradiated with laser. At this time, a laser L ₁ for irradiating the position of the through hole 4
The scanning of the laser beam is controlled so that the energy of is larger than the amount of the laser L ₂ with which the position of the groove 3 is irradiated. In this way, the circuit board 10 shown in FIG. 12C is obtained.

(Seventh Embodiment) Next, a method of manufacturing a multilayer circuit board in which three circuit boards are laminated will be described. FIG.
Is a circuit board 31 having through-holes and grooves formed on a double-sided copper-clad board.
13 and two circuit boards 30 each having a through hole and a groove formed in a single-sided copper-clad board are stacked and thermocompressed as shown in FIG. 13 (a), as shown in FIG. 13 (b). The multi-layer circuit board 51 has three layers having the conductive circuits 2 on four sides. The groove 3 is formed in the conductive circuit on at least one surface of the circuit board 51, and the conductive resin 5 in the through hole 4 is formed.
Since the contact area with is large, a multilayer circuit board with low contact resistance can be obtained.

(Eighth Embodiment) Next, FIG. 14 shows one circuit board 31 having a through-hole and a groove formed in a double-sided copper-clad substrate and a circuit board having a through-hole and a groove formed in a single-sided copper-clad substrate. Three
Using two sheets of 0 and 32, they were superposed and thermocompressed as shown in FIG. 14 (a) to obtain a three-layered multilayer circuit board 52 having four-sided conductive circuits 2 as shown in FIG. 14 (b). It is a thing. As described above, the circuit boards to be stacked can have any structure as required, and the groove 3 is formed in at least one conductive circuit of the circuit board to be used and the conductive resin 5 is filled therein. In other words, since the contact area with the conductive resin 5 in the through hole 4 is large, the multilayer circuit board can have a low contact resistance.

(Ninth Embodiment) In addition, in the second embodiment shown in FIG. 6 (j), when the copper foil 2a is superposed on the lower side of the copper-clad circuit board 10, a diagram is shown instead of the copper foil. 15 (a)
As shown in FIG. 3, the conductive circuit 2 made of rough copper foil is formed on the surface of the release film 36, and the conductive circuit 2 is formed on the circuit board 3
Release film 3 after overlapping with 0 and 32 and thermocompression bonding
6 is peeled off and the multilayer circuit board 5 as shown in FIG.
A method of obtaining 3 can also be used.

[0033]

(Example) According to the manufacturing process of the first embodiment shown in FIGS. 4 to 6, a multi-layer circuit board 50 having a three-layer conductive circuit as shown in FIG. 6 (k) was manufactured. In this example, a polyimide film was used as the insulating substrate 1, and a single-sided copper-clad substrate using a copper foil having a thickness of 18 μm for the conductive circuit 2 was used as a starting material. A 15 μm thick photoresist film was thermocompression bonded onto the copper foil using a roll laminator. Then, the pattern was exposed and developed to form a resist mask pattern of a groove formed in the through hole portion and the peripheral portion of the through hole. The diameter of the through hole was 100 μm and the width of the groove was 50 μm.

Next, the copper foil was chemically etched using an etchant containing ferric chloride as a main component. Holes and slits were formed in the copper foil by etching, and CO ₂ laser was irradiated using this copper foil as a mask to penetrate the polyimide substrate and the adhesive. At this time, the copper foil still having a thickness of about 5 μm remained in the groove. Next, a silver paste was applied to the surface of the single-sided copper-clad substrate on which the through holes and grooves were formed, and the squeegee was directly contacted with the surface of the copper foil to fill the silver paste into the through holes and grooves.

After the filled silver paste was dried in an oven at 100 ° C., a resist film was pressed and the circuit pattern was exposed and developed. After etching the copper foil again using an etchant whose main component is ferric chloride solution,
The circuit board 1 having the structure shown in FIG.
Completed 0.

Next, a circuit board 20 having a structure as shown in FIG. 6 (j) is formed by the same method, and one circuit board 20, 99 circuit boards 10 and copper foil are formed as shown in FIG. 6 (j). As shown in the figure, they are piled up and heated to 150 to 250 ° C. while applying a pressure of 10 to 50 Kg / cm ² , and thermocompression bonded to them.
A multilayer circuit board 50 ′ having a structure in which 0 through holes were connected in series was created and the characteristics were evaluated.

(Comparative Example) In order to compare and evaluate the characteristics of the interlayer connection portion, 100 through holes were similarly connected in series to prepare a multilayer circuit board having a conventional through hole type structure shown in FIG. did.

When the electric resistances when a direct current was applied between the conductive circuits on the front surface and the conductive circuit on the bottom surface of the multi-layered substrates of the present example and the comparative example were compared, the multi-layered substrate of the present invention showed that the variation value of the electric resistance was It showed a constant value within a range of ± 20%. On the other hand, in the layered substrate having the conventional structure, the fluctuation value of the electric resistance reaches ± 200% and is unstable, and the absolute value of the electric resistance is 1.5 to 3 times that of the present invention. It was also expensive. Further, both substrates were subjected to a temperature cycle test of −20 ° C. to + 60 ° C. for 1000 cycles, and then the circuit resistance was measured again.
As a result, the resistance value of the multilayer circuit board of the present invention increased by 5 to 10%, whereas the resistance value of the multilayer circuit board of the conventional structure increased by 10 to 100%. From the above evaluation results, it was confirmed that the contact resistance between the conductive resin and the conductive circuit greatly affects the electric resistance of the entire circuit.

[0039]

The circuit board of the present invention is provided with a groove on the surface of the conductive circuit, and the conductive resin is filled in the groove to increase the contact area between the conductive circuit and the conductive resin in the through hole.
It has a low contact resistance.

[0040]

According to the circuit board of the present invention, it is not necessary to increase the conductor thickness even in a circuit board requiring a thin insulating layer thickness, and the interlayer connection circuit made of a conductive resin and the insulating board are provided. Since it can contact the conductive circuit in a wide area and achieve stable interlayer connection with low resistance, it is possible to reduce the board thickness even when a multilayer circuit board is configured, which contributes to the miniaturization of electronic parts. Will be able to.
Further, according to the method of manufacturing a circuit board of the present invention, it is possible to easily reduce the thickness of the circuit board by using a conventional material or a conventional apparatus without adding a large number of steps as compared with the conventional manufacturing process. Can be achieved. In addition, compared to the land laminated type in which conductive resin is printed on the conductor lands, the conductor thickness does not increase, the insulating layer can be made thin, and at the same time alignment work at the time of printing is not required. It has the advantage that it can be simplified.

[Brief description of drawings]

FIG. 1 is a partial plan view showing an example of a through hole portion of a circuit board of the present invention.

2 is a line AA ′ of the circuit board of the present invention shown in FIG.
It is sectional drawing along.

FIG. 3 is a line BB ′ of the circuit board of the present invention shown in FIG.
It is sectional drawing along.

FIG. 4 is a cross-sectional process diagram showing an example of a method for manufacturing a circuit board of the present invention.

FIG. 5 is a sectional process diagram following FIG. 4;

FIG. 6 is a cross-sectional process diagram of the method for manufacturing a multilayer circuit board of the present invention, which is subsequent to FIG. 5;

FIG. 7 is a partial plan view of the multilayer circuit board of the present invention shown in FIG.

FIG. 8 is a plan view showing an example of a through hole portion of another circuit board of the present invention.

FIG. 9 is a plan view showing an example of a through hole portion of still another circuit board of the present invention.

10 is a diagram illustrating the depth of the groove of the circuit board illustrated in FIG.

FIG. 11 is a diagram illustrating a method of processing a through hole in the method of manufacturing a circuit board according to the present invention.

FIG. 12 is a diagram illustrating another example of a method of processing a through hole in the method of manufacturing a circuit board according to the present invention.

FIG. 13 is a diagram showing an example of a method for manufacturing a multilayer circuit board according to the present invention.

FIG. 14 is a diagram showing another example of the method for manufacturing a multilayer circuit board according to the present invention.

FIG. 15 is a diagram showing still another example of the method for manufacturing a multilayer circuit board according to the present invention.

FIG. 16 is a diagram showing a structure of a conventional multilayer circuit board.

FIG. 17 is a sectional process diagram showing the method of manufacturing the conventional multilayer circuit board shown in FIG.

FIG. 18 is a sectional process view showing another conventional method for manufacturing a multilayer circuit board.

FIG. 19 is a diagram illustrating a structure of a through hole portion of a conventional circuit board.

FIG. 20 is a diagram illustrating another structure of the conventional circuit board.

FIG. 21 is a diagram illustrating another structure of the conventional circuit board.

FIG. 22 is a diagram illustrating still another structure of the conventional circuit board.

[Explanation of symbols]

1, 101 ... Insulating substrate, 2, 102 ... Conductive circuit, 3, 23 ... Groove, 4, 104 ... Through hole, 5 ...・
... Conductive resin, 6 ..., Single-sided copper-clad substrate, 7 ..., Adhesive, 8 ..., Laminated film, 10, 20, 21, 11
0, 111, 112 ... Circuit board, 25 ... Drill, 30, 31, 32 ... Circuit board, 35 ... Photoresist film, 36 ... ...... Release film, 50,
51, 52, 53 ... Multi-layer circuit board, 114 plating layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Okamoto             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office F term (reference) 5E317 AA04 BB03 BB12 CC25 GG03                       GG09 GG11 GG14 GG16                 5E338 AA12 AA16 CD05 EE11 EE23                       EE27 EE32                 5E346 AA15 AA43 CC02 CC10 CC32                       EE08 FF18 FF22 GG06 GG15                       GG22 GG28 HH07 HH24 HH32                       HH33

Claims (7)

[Claims] 1. An insulating substrate having a through hole, and the through hole is filled with a conductive resin. The conductive resin and a conductive circuit formed on the surface of the insulating substrate are electrically connected to each other. A circuit board formed by connecting to a conductor surface of the conductive circuit, one end of which reaches a through hole, and at least a part of the other end of which has a groove which does not penetrate to the back surface of the conductor of the conductive circuit. A circuit board characterized in that. 2. The planar shape of the groove on the surface of the conductive circuit is radial or star-shaped.
The circuit board according to. 3. The circuit according to claim 1, wherein the planar shape of the groove on the surface of the conductive circuit is a combination of a radial or star shape and a concentric circle of the through hole. substrate. 4. A laminated circuit board comprising at least one circuit board according to any one of claims 1 to 3, which is laminated. 5. A photoresist film is formed on a conductor film of an insulating substrate having a conductor film on at least one surface, and then a predetermined circuit pattern having a narrow groove pattern is exposed and developed. Using the obtained photoresist film pattern as a mask, the substrate is dipped in an etchant to etch the conductor film, and then the obtained conductor pattern is used as a mask to form through holes at predetermined positions of the substrate and the conductor surface. After providing a groove in the circuit board, a conductive resin is filled in the groove on the surface of the conductor pattern and in the through hole to electrically connect the conductive resin and the conductor film. Method. 6. The method for manufacturing a circuit board according to claim 5, wherein the width of the narrow groove pattern formed in the photoresist film is 4 times or less the thickness of the photoresist film. . 7. A method for manufacturing a multilayer circuit board, comprising laminating and bonding at least one circuit board obtained by the manufacturing method according to claim 5 or 6.