JPH03190187A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To enable a soldering work to be easily made on the outermost layer and a wiring board to have a required circuit function at all times by a method wherein an inner circuit pattern and an interlaminar conductor are formed of metal powder containing conductive resin composition, and at least the soldered part of the outermost circuit pattern is formed of metal foil. CONSTITUTION:An inner circuit pattern 2 is formed of conductive paste which contains synthetic resin as a binder component and composed of many layers which are arranged in a heat resistant plastic resin layer 1 such as a polysulfone resin layer and electrically insulated from each other. An outermost circuit pattern layer 3 where required electronic components are mounted and their leads are soldered is provided with a soldering part such as a pad, where required electronic components are mounted and their leads are soldered, is formed of a metal foil through a selective etching. An interlaminar conductor 5 is formed of conductive paste which contains synthetic resin as a binder component and electrically connects the inner circuit patterns 2 together, the inner circuit pattern 2 with the outer circuit pattern 3, and the outer circuit patterns 3 together through through-holes or viaholes.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to multilayer printed wiring boards, and more particularly to improved multilayer printed wiring boards for packaged circuit devices.

(Prior art) For the purpose of downsizing wiring circuits or compacting circuit parts, mounted circuit devices have been widely put into practical use, with a multilayer printed wiring board as a base and required electronic components mounted and mounted on this board. It is provided.

As one type of multilayer printed wiring board for mounted circuits, there is a synthetic resin multilayer printed wiring board. That is, as a first method, an inner layer circuit pattern blank is formed with a desired circuit pattern by selective etching of a metal foil adhered to the surface of a resin-impregnated insulator layer made of insulating paper or glass cloth as a base material; A prepreg hardened layer that interposes on this inner layer circuit pattern blank plate and integrates them, and an outermost layer circuit pattern blank formed by selective etching of metal foil that is also integrated via the prepreg hardened layer. For example, a multilayer printed wiring board consisting of Second
Examples of the method include a multilayer printed wiring board in which the circuit patterns of the inner and outer layers are made of a conductive composition containing a metal powder such as silver, copper, gold, or nickel, and a synthetic resin as a binder. In the multilayer printed wiring board having the above structure, necessary electrical connections are made between inner layer circuit patterns, between inner layer circuit patterns and outer layer circuit patterns, or between outer layer circuit patterns using through holes, peer holes, or the like.

(Problems to be Solved by the Invention) However, the synthetic resin multilayer printed wiring board having the above structure has the following practical disadvantages. First, in the case of the first method, that is, in the case of a multilayer printed wiring board in which the circuit pattern of each layer is formed based on metal foil,
Because the electrical connection layer between the circuit pattern layers and the physical properties of the circuit pattern layer and the synthetic resin (insulator) forming the matrix, such as coefficient of thermal expansion, are significantly different, thermal history, stress action, or cooling/heating cycles may cause microscopic differences. There are problems with reliability, such as circuit patterns often being cut, and required circuit functions being impaired. Also, the second
In the case of the above method, that is, in the case of a multilayer printed wiring board in which the entire conductor area, including the outermost layer circuit pattern, is formed with a so-called conductive paste, the required electronic components are mounted and mounted on the surface on which the outermost layer circuit pattern is formed. Therefore, even if an attempt is made to solder, it is difficult to solder, and sometimes soldering is often impossible.

The present invention has been made in response to the above-mentioned circumstances, and aims to provide a highly reliable multilayer printed wiring board that can easily perform required soldering on the outermost layer and always maintains required circuit functions. .

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a multilayer circuit pattern that includes an outermost layer circuit pattern on which electronic components are mounted and soldered, an inner layer circuit pattern, and an interlayer conductor that electrically connects the circuit pattern layers. In the printed wiring board, the inner layer circuit pattern and the interlayer conductor are made of a conductive resin composition containing metal powder, and ``at least the part to be soldered of the outermost layer circuit pattern is made of metal foil. It is characterized by

(Function) According to the above configuration, the electrical connection layer between the circuit pattern layers and the physical properties of the circuit pattern layer and the synthetic resin system (insulator) forming the matrix are similar, such as the coefficient of thermal expansion, so that the thermal history is Breakage of minute circuit patterns due to temperature changes in the operating environment can also be completely avoided.

In addition, at least the part to be soldered of the outermost layer circuit pattern,
Since it is formed based on metal foil, the required soldering can be easily and reliably achieved.

(Example) The present invention will be described in detail below with reference to FIG. FIG. 1 shows a cross-sectional view of an example of the structure of a multilayer printed wiring board according to the present invention, in which 1 is a heat-resistant thermoplastic resin layer such as polysulfone resin, and 2 is a layer of heat-resistant thermoplastic resin in the heat-resistant thermoplastic resin layer 1. This is an inner circuit pattern layer made of a conductive paste containing a so-called synthetic resin as a binder component, which is arranged in multiple layers and electrically insulated from each other. Reference numeral 3 denotes an outermost layer (outermost surface) circuit pattern layer on which the required electronic components 4 are mounted and soldered; is formed by selective etching using metal foil as a base. 5 is a binder component of a so-called synthetic resin that makes necessary electrical connection between the inner circuit pattern layer 2, between the inner circuit pattern layer 2 and the outer circuit pattern layer 3, or between the outer circuit pattern layer 3 through through holes, peer holes, etc. This is an interlayer connection conductor made of conductive paste.

Therefore, the multilayer printed wiring board according to the present invention having the above structure can be easily manufactured as follows.

For example, a polysulfone resin film with a thickness of about 0.05 μl is punched with the required connection holes, and a conductive paste containing polysulfone resin as a binder and copper powder dispersed therein is applied to one or both sides of the film. An inner layer circuit pattern base plate is prepared on which the required inner layer circuit pattern layer 2 and interlayer connection conductor portion 5 are formed by a screen printing method.

On the other hand, in addition to drilling the required connection holes in a polysulfone resin film with a thickness of about 0.05 μl, selectively etching, for example, a copper foil attached to one side of the outermost layer, to form the required holes. An outer circuit pattern blank on which the outermost circuit pattern layer 3 is formed is prepared, and the conductive paste is filled into required connection holes to form interlayer connection conductor portions 5.

After that, the plurality of inner layer circuit pattern blank plates prepared above are aligned and stacked, and the outer layer circuit pattern blank plates are placed on at least one side of the inner layer circuit pattern blank plates, and the metal white base circuit pattern is placed as the outermost layer. After aligning and overlapping,
A desired multilayer print is produced by applying heat and pressure molding to weld and integrate the mutually opposing surfaces of the stacked polysulfone resin films, and by filling and integrating the corresponding interlayer connection conductor portions 5. A wiring board can be obtained.

A multilayer printed wiring board according to the present invention that can be constructed in this manner, for example, IOX Loam, has a thickness of 0.5 cm and has a four-layer circuit pattern structure, and has a structure in which the inner circuit pattern layers are interconnected and between the inner circuit pattern layer and the outer circuit pattern layer. A multilayer printed wiring board (embodiment) having 500 interlayer connection conductor parts and 100 through connection conductor parts, and the first conventional example
A thermal shock test and a bending test were conducted on a multilayer printed wiring board (comparative example) having the same structure in which the insulating layer was made of glass cloth and epoxy resin based on the above method, and the results were as follows.

For example.

Thermal shock test: No abnormality in the conductor layer forming the circuit. Bending test: No abnormality in the conductor layer forming the circuit. Comparative example.

Thermal shock test: The conductor layer that makes up the circuit has many opens and cannot be measured.Bending test: The conductor layer that makes up the circuit has an oven after one bend.Thermal shock test: -60"030 minutes, +125℃
This is the case where 500 cycles are repeated with 30 minutes as one cycle, and the bending test is performed at 10% with a bending rate of 20%.
This is a case of repeating 00 times.

Furthermore, when the multilayer printed wiring board according to the present invention having the above structure was evaluated for solderability of the outer layer circuit pattern to be soldered, it was found that soldering was easy and possible in each individual's manner.

In the above example, the insulating layer of the multilayer printed wiring board is made of polysulfone resin, but other thermoplastic resins such as polyphenylene sulfide resin, polyether resin, polyetherimide resin, polyether ether ketone resin, etc., or insulating paper or insulating cloth may be used. It may be based on.

Further, the formation of the electrical connection conductor portion between the circuit pattern layers and the inner circuit pattern layer is not limited to the above-mentioned conductive paste, but may be formed using another conductive paste using a synthetic resin as a binder.

[Effects of the Invention] According to the present invention, the electrical connection conductor between the circuit pattern layers and the physical properties of the circuit pattern layer and the synthetic resin system (insulator) forming the matrix are similar, so thermal history and Breakage of minute circuit patterns due to temperature changes in the usage environment is completely avoided, and the required circuit functions can be maintained at all times. Moreover, since at least the portion of the outermost layer circuit pattern to be soldered is formed based on metal foil, the required soldering can be easily and reliably achieved. Thus, it can be said that the multilayer printed wiring board according to the present invention is suitable for the construction of a functionally reliable mounted circuit device.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the structure of a multilayer printed wiring board according to the present invention. 1...Heat-resistant thermoplastic resin layer 2...Inner circuit pattern layer 3...Outermost circuit pattern layer 4...Electronic component

Claims (1)

[Claims] An outermost layer circuit pattern on which electronic components are mounted and soldered;
A multilayer printed wiring board comprising an inner layer circuit pattern and an interlayer conductor that electrically connects the circuit pattern layers, wherein the inner layer circuit pattern and the interlayer conductor are made of a conductive resin composition containing metal powder, and the outermost layer circuit pattern A multilayer printed wiring board, characterized in that at least the part to be soldered is made of metal foil.