JP2001007517A - Printed wiring board and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board which is highly dense and excellent in reliability and in which interlayer connection is applied by a conductive paste, as well as a method for producing such a printed wiring board efficiently. SOLUTION: This printed wiring board includes conductor layers which are connected with each other by a conductive paste generating no air bubbles and having a volatility of <3 wt.%. This method for producing the printed wiring board includes (a) a step for making a hole to a metallic foil from the side of an adhesive layer at a desired place of the metallic foil with the adhesive layer; (b) a step for filling the hole with a conductive paste and reducing the volatility of the conductive paste to <3 wt.%; (c) a step for overlapping the metallic foil with the adhesive layer in which the conductive paste is buried in the surface of an inner layer circuit board, in a manner that the metallic foil may be placed outside, and pressurizing/heating it for integration of laminated layered; and (d) a step for working the outer metallic foil to form a conductor pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a printed wiring board and a method of manufacturing the same.

[0002]

2. Description of the Related Art With the miniaturization, high performance, and multifunctionality of electronic devices, multilayer printed wiring boards have been required to have higher densities. In order to satisfy these requirements, thinning between layers, miniaturization of wiring, and reduction in the diameter of interlayer connection holes have been performed, and via holes that connect only conductors between adjacent layers have been used. The diameter is getting smaller. For multi-layer wiring,
Multiple circuit layers and insulating layers between the circuit layers are piled together,
Multi-layer wiring board that presses, heats, laminates and integrates and drills holes where necessary, forms a circuit, forms an interlayer insulating layer on top, forms a circuit on it, and drills holes And a build-up multilayer wiring board in which a circuit layer and an insulating layer are sequentially formed.

As one method of manufacturing this build-up multilayer wiring board, a hole formed in an adhesive layer is filled with a conductive paste, and an inner layer circuit board is pressed and heated to form an outer layer circuit formed in the adhesive layer. There is a method of electrically connecting. Thereafter, if necessary, the same steps as described above are repeated to form a required multilayer circuit.

With the recent increase in the density of multilayer printed wiring boards, it has been required that the diameter of the via hole be 0.2 mm or even 0.1 mm or less. When filling the paste, in order to prevent generation of voids due to volatilization of the solvent in the holes, it is common practice to use a conductive paste having no solvent or a volatilization amount of less than 3% by weight.

However, such a solvent-free or volatile amount is 3
If the conductive paste is used in an amount of less than 10% by weight, the viscosity of the conductive paste becomes high, and when the hole diameter is small, when the thickness of the adhesive layer is large, or when the non-through hole of the adhesive layer with metal foil is used, When filling the paste, there is a problem that it is difficult to fill the holes well.

As a method for solving this problem, for example,
As disclosed in Japanese Patent No. 26001128,
Fill the through hole of the non-compressible porous base material with a conductive paste with relatively low content of conductive material and excellent printability,
There has been proposed a method in which the binder component in the conductive paste permeates the pores of the non-compressible porous base material during the heating and pressurizing step, thereby increasing the composition ratio of the conductive material in the conductive paste.

[0007]

However, Patent No. 260
In the method disclosed in Japanese Patent No. 1128, a special material called an incompressible porous base material must be used, and the drilling conditions and handling are different from those of ordinary materials for printed wiring boards, so that production is efficient. However, there is a problem that a special adhesive must be used because it is porous and porous.

[0008] The present invention provides a printed wiring board having a high density and excellent reliability, in which layers are connected by a conductive paste,
An object of the present invention is to provide a method for efficiently manufacturing such a printed wiring board.

[0009]

The printed wiring board of the present invention is characterized in that the connection between the conductor layers is made by a conductive paste having a volatilization amount of less than 3% by weight and having no bubbles.

[0010] A method of manufacturing a printed wiring board according to the present invention is characterized by comprising the following steps. (A) a step of making a hole reaching the metal foil from the side of the adhesive layer at a desired position of the metal foil with an adhesive layer; (b) filling the hole with a conductive paste made of conductive particles, a resin and volatile components, 3% by weight
(C) a step of laminating a metal foil with an adhesive layer filled with a conductive paste on the surface of the inner circuit board so that the metal foil is on the outside, and pressing and heating to laminate and integrate (D) forming a conductor pattern by processing the outer metal foil;

Further, the method for manufacturing a printed wiring board according to the present invention is characterized by comprising the following steps. (A1) A step of making a hole penetrating the adhesive layer and the metal foil at a desired position of the metal foil with the adhesive layer. (B) Filling the hole with a conductive paste made of conductive particles, a resin and volatile components, 3% by weight
(C) a step of laminating a metal foil with an adhesive layer filled with a conductive paste on the surface of the inner circuit board so that the metal foil is on the outside, and pressing and heating to laminate and integrate (C1) a step of performing metal plating on the surface of the integrated substrate and electrically connecting the conductive paste and the metal foil; and (d) a step of processing the outer metal foil to form a conductor pattern.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive paste of the present invention contains conductive particles, a resin and volatile components as main components, and has a volatile content of 3% by weight or more. This volatilization amount preferably has a viscosity in the range of 10 to 100 Pa · s. If the volatilization amount is less than 3% by weight, the viscosity may increase and unfilled portions may remain as bubbles. When the viscosity is less than 10 Pa · s, the conductive paste flows too much and printing is difficult. In order to further reduce the viscosity to 100 Pa · s or less, the volatilization amount is more preferably 5% by weight or more.
Further, the volatilization amount is preferably 30% by weight or less. Volatility is 3
If the content exceeds 0% by weight, there is no change in the effect, but it is not economical because the volatilization time becomes long. Silver or copper, copper whose surface is coated with silver, or the like can be used as the conductive particles of the conductive paste. As the resin, an epoxy resin, a phenol resin, a polyimide resin, a polyamideimide resin, or the like can be used. Organic solvents such as ethyl lactate, ethyl carbitol, and butyl cellosolve acetate can be used for volatile components.

As the adhesive layer, those containing epoxy or polyimide as a component can be used, and an epoxy adhesive film containing a high molecular weight epoxy polymer having a molecular weight of 100,000 or more as a main component, an epoxy adhesive film containing modified rubber And polyimide-based adhesive films, and epoxy-based adhesive films in which a fibrous substance having a diameter of 1.0 μm to 6 μm and a length of 5 μm to 1 mm are dispersed in an epoxy resin.

(Steps a and a1) A drill and a laser can be used as a method of making a hole at a place where an electrical connection between layers is to be made. In step a, it is preferable to use a laser to make a hole reaching the metal foil, and an excimer laser or a carbon dioxide gas laser can be used as the laser, and a carbon dioxide gas laser is preferable in terms of processing speed and processing cost. is there. In step a1, it is preferable to use a drill because it is economical.

(Step b) Filling the hole with a conductive paste and reducing the volatilization amount of the conductive paste to less than 3% by weight can be performed by providing a heating step before the step c. it can. The heating conditions for reducing the volatilization amount to less than 3% by weight depend on the conductive paste and the filling amount thereof, and when the temperature is high, a short time is sufficient, but generally the temperature is 80 ° C. to 130 ° C. and the time is 5 minutes. It is preferable to set the range to 30 minutes. The higher the temperature and the longer the time, the lower the volatilization amount in the conductive paste can be.However, if the adhesive layer that is heated at the same time is hardened, the hardened shape is maintained, If there is, processing may be difficult in a subsequent step, and a condition that does not cure the adhesive layer is preferable. On the other hand, when the temperature is low, it takes too much time.

(Step c) To laminate a metal foil with an adhesive layer filled with a conductive paste on the surface of the inner layer circuit board so that the metal foil is on the outside and press and heat to laminate and integrate The laminating technique used for ordinary multilayer printed wiring boards can be used as it is. Generally, the temperature is 160-18
The conditions are 0 ° C., a pressure of 1 to 4 MPa, and a time of about 30 to 120 minutes.

(Step c1) In the step of performing metal plating on the surface of the laminated and integrated substrate in order to connect the conductive paste filled in the hole penetrating the metal foil and the adhesive layer with the outer metal foil. is there. Inexpensive metal plating such as copper plating and nickel plating can be used for metal plating.Electroless plating or electrolytic plating can be used for the plating method. It is preferably used.

(Step d) In order to form a conductor pattern by processing the outer metal foil, an etching resist is formed in the shape of a circuit, and a portion not covered with the etching resist is brought into contact with a chemical etching solution. Thereby, the metal foil can be selectively removed to form a circuit.

[0019]

EXAMPLES (Process of manufacturing inner circuit board) MCL-679 (Hitachi Chemical Co., Ltd.) is a glass cloth-epoxy resin impregnated double-sided copper-clad laminate having a base material thickness of 0.6 mm and a copper foil thickness of 18 μm. Drilling and electroless copper plating to form through-holes, remove unnecessary portions of copper foil by etching to form inner layer circuits, and then use silk-screen printing As a result, CCR-506 (Asahi Chemical Laboratory Co., Ltd.,
After filling the hole by applying (trade name) and curing by heating, the resin protruding from the hole was polished and removed to prepare an inner layer circuit board.

(Step a) MCF-3 having an epoxy adhesive layer having a thickness of 55 μm provided on one surface of a copper foil having a thickness of 18 μm.
000E (trade name, manufactured by Hitachi Chemical Co., Ltd.)
From the side of the adhesive layer of the metal foil with an adhesive layer in which a 15 μm-thick polyethylene terephthalate film was adhered to the surface of the adhesive layer with a roll laminator, a carbon dioxide gas impact laser drilling machine L-500 (manufactured by Sumitomo Heavy Industries, Ltd.
According to the product name), frequency = 150Hz, voltage = 20k
Under a condition of V, pulse energy = 85 mJ, and number of shots = 7 shots, a laser beam was irradiated to remove the resin at the portion for making interlayer connection, and a hole having a diameter of 0.15 mm reaching the copper foil was made.

(Step b) On the metal foil with an adhesive layer having a hole,
A conductive paste MP-200V-5 (trade name, manufactured by Hitachi Chemical Co., Ltd.) was filled from above the surface of the polyethylene terephthalate film by a screen printing method. At this time, the volatile amount of the conductive paste was 5% by weight. The viscosity was 60 Pa · s. The metal foil with an adhesive layer filled with the conductive paste was heated at 110 ° C. for 15 minutes to reduce the volatilization amount of the conductive paste to 2% by weight. Further, the polyethylene terephthalate film was peeled off.

(Step c) A metal foil with an adhesive layer is laminated on both sides of the inner circuit board, and the pressure is 2.94 MPa, the temperature is 175 ° C., and the
The laminate was integrated under the conditions of minutes to obtain a laminate.

(Step d) An etching resist film HK-425 (trade name, manufactured by Hitachi Chemical Co., Ltd.) is laminated on both sides of the laminate, a photomask is overlaid, ultraviolet rays are irradiated and developed, and the etching resist is removed. Forming
Unnecessary copper was removed by etching to form an outer layer circuit, and a printed wiring board was manufactured.

The continuity resistance of the printed wiring board of this embodiment is as follows: 1. With 400 vias connected in series.
The via resistance obtained by subtracting the resistance of 2 Ω of the circuit portion on the surface from 5 Ω was 1.25 mΩ per via hole.
Further, when the sample is floated in a solder bath at 260 ° C. for 3 minutes or in a gas phase at −65 ° C. and 125 ° C.
The rate of change in resistance of the conductive paste when immersed 1000 times per minute was 5% or less.

Comparative Example (Process for Producing Inner-Layer Circuit Board)
An inner circuit board was produced. (Step a) A metal foil with an adhesive layer with holes was prepared in the same manner as in the example. (Step b) Except that CB100 (trade name, manufactured by DuPont) was used as the conductive paste, it was prepared in the same manner as in the example. At this time, the volatilization amount of the conductive paste was 2% by weight. The viscosity was 135 Pa · s. (Step c) A laminate was produced in the same manner as in the example. (Step d) An outer layer circuit was formed in the same manner as in the example, and a printed wiring board was manufactured. The conduction resistance of the printed wiring board of this comparative example was 1 MΩ or more when 400 vias were connected in series. In order to investigate the cause, casting with an acrylic resin and observing the cross section of the via hole portion revealed that the conductive paste was filled by entrapping voids in the holes.

[0026]

As described above, according to the present invention, a printed wiring board having a high-density and excellent reliability, in which layers are connected by a conductive paste, and a method for efficiently manufacturing such a printed wiring board. Can be provided.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/40 H05K 3/40 K (72) Inventor Kenji Takai 1500 Oji Ogawa, Shimodate City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Shimodate Research Institute, Inc. (72) Inventor Shigeharu Ariya 1500 Ogawa, Oji, Shimodate City, Ibaraki Prefecture F-term in Shimodate Research Laboratory, Hitachi Chemical Co., Ltd. AA43 CC08 CC31 DD23 EE13 EE18 FF13 FF18 GG08 GG09 GG15 GG17 GG28 HH31

Claims (4)

[Claims] 1. A printed wiring board wherein the connection between conductive layers is made by a conductive paste having a volatilization amount of less than 3% by weight and having no bubbles. 2. A method for manufacturing a printed wiring board, comprising the following steps. (A) a step of making a hole reaching the metal foil from the side of the adhesive layer at a desired position of the metal foil with an adhesive layer; (b) filling the hole with a conductive paste made of conductive particles, a resin and volatile components, 3% by weight
(C) a step of laminating a metal foil with an adhesive layer filled with a conductive paste on the surface of the inner circuit board so that the metal foil is on the outside, and pressing and heating to laminate and integrate (D) forming a conductor pattern by processing the outer metal foil; 3. A method for manufacturing a printed wiring board, comprising the following steps. (A1) A step of making a hole penetrating the adhesive layer and the metal foil at a desired position of the metal foil with the adhesive layer. (B) Filling the hole with a conductive paste made of conductive particles, a resin and volatile components, 3% by weight
(C) a step of laminating a metal foil with an adhesive layer filled with a conductive paste on the surface of the inner circuit board so that the metal foil is on the outside, and pressing and heating to laminate and integrate (C1) Step of performing metal plating on the surface of the laminated and integrated substrate to electrically connect the conductive paste and the metal foil (d) Step of processing the outer metal foil to form a conductor pattern 4. The method for producing a printed wiring board according to claim 2, wherein the printed wiring board prepared in the step (d) is used as an inner layer circuit board in the step (c).