JP2540596B2 - Printed resistor built-in multilayer printed circuit board and method for manufacturing printed resistor mounted inner layer substrate used therefor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed circuit board with a built-in printed resistor and a method of manufacturing an inner layer substrate with a printed resistor used therein, more specifically, there is no deterioration in characteristics during the manufacturing process. The present invention relates to a method for manufacturing a multilayer printed circuit board containing a small number of printed resistors and an inner layer board on which the printed resistors are mounted.

(Prior Art) With the miniaturization and multi-functionalization of electronic devices, the circuit density of printed circuit boards is currently increasing.
For example, methods such as thinning of conductor circuits, multi-layering, multi-through holes including blind via holes, and mounting of fine chip components on the surface of a substrate have been adopted.

A printed resistor has been developed as one of the technologies for high-density mounting. This is between each terminal of the conductor circuit of the predetermined pattern formed on the surface of the insulating substrate,
It is formed by, for example, screen-printing a paste for a polymer thick film resistor and then thermosetting this paste.

This printed resistor has the advantage of higher density in that it can be applied to high-density component placement where it is difficult to individually mount resistor components on an insulating substrate, and as a resistor Since it has almost no thickness, it has the advantage that it can be formed under other parts or it can be three-dimensionally crossed with the conductor paste jumper wire with an insulating coating layer interposed. , Has been used for single-sided and double-sided circuit boards for consumer equipment.

By the way, with the increase in the density of the circuit and component mounting of the printed circuit board as described above, the multilayer printed circuit board has recently been used as a circuit board for consumer equipment. In the future, it is considered that even in this field, further densification will be advanced, centering on the technology of increasing the number of through holes and surface mounting of chip components.

Among these technologies, the surface mounting technology for chip components directly connects minute chip components to the circuit on the surface of the insulating substrate without using leads, thereby increasing the number of components that can be mounted within the same area. It was developed for the purpose of reducing the mounting density and enabling mounting of components on both the front and back surfaces of a wiring board.

However, even if the above technique is effective for increasing the density, it is not necessarily a good idea to apply this technique to a multilayer printed circuit board in the following points. That is, the area of the circuit board can be made sufficiently small by using multiple layers, but since the chip components can be mounted only on the two outermost layers of the circuit board, the minimum area required by the circuit board is After all, in many cases, it is limited by the number of chip components to be mounted. This problem can be solved by reducing the number of chip components to be mounted by attempting to make an individual circuit IC, but it is not easy to make an individual circuit IC, and the cost increases. Cause.

Generally, the number of resistors on a circuit board occupies 1/3 to 1/2 of the total number of components. Therefore, among the various chip components to be mounted, if only the resistor is thinned as the above-mentioned printed resistor and it can be combined with other substrates to be embedded in the multilayer printed circuit board, the problems as described above will be possible. Will be resolved. This measure can be applied not only to the resistors in the chip components to be mounted but also to the resistors of discrete components in which lead wires are connected through the component holes.

As a prior art proposed based on such an idea, an inner layer substrate on which a printed resistor formed by using a paste for a polymer thick film resistor is mounted is laminated with a prepreg or another wiring board. However, there is a multilayer printed circuit board that is integrally heated and pressed to integrate it (Japanese Patent Laid-Open No. 60-2634).
(See Japanese Patent No. 99). Then, at the time of this multi-layering, the surface of the printed resistor mounted on the inner layer substrate is covered with a protective coat which is a cured product of resin paste, and the printed resistor from the prepreg substrate located on the upper surface at the time of stacking. It is also practiced to suppress the adverse effects on the
(See Japanese Patent No. 0866).

(Problems to be Solved by the Invention) However, when manufacturing a multilayer printed circuit board by incorporating an inner layer substrate on which a printed resistor is mounted, heating
The constituent resin of the printed resistor may soften during the process of pressurization, so that the resistance value of the printed resistor in the obtained multilayer printed circuit board may deviate significantly from the target set value. Many. Moreover, it is not possible to apply the usual trimming method to this resistance value which is once deviated from the set value, and it is impossible to adjust / restore the target set value again. For this reason, in order to manufacture a multilayer printed circuit board having a built-in printed resistor, it is necessary to solve the above-mentioned problem of characteristic deterioration of the printed resistor that occurs during the process of incorporating the printed resistor. . In other words, it is necessary to form a printed resistor on the substrate that does not cause characteristic deterioration in the process of incorporation.

Further, in the above heating / pressurizing process, heat generated when the paste is thermoset may cause thermal deterioration or discoloration of the inner layer substrate itself.

The present invention solves the above-mentioned problems by developing a printed resistor with less characteristic deterioration in the process of incorporation.
Therefore, it is equipped with a high-density and compact multilayer printed circuit board and the above-mentioned printed resistors, and it does not discolor even in the process of heating / pressurizing when it is built in the multilayer printed circuit board. An object of the present invention is to provide a method for producing a novel inner layer substrate that does not cause delamination in a produced multilayer laminated plate.

(Means and Actions for Solving the Problem) In order to achieve the above-mentioned objects, the present inventors have selected a kind of resin as a main component of a polymer thick film resistor or a protective coat,
As a result of intensive studies on the combination, the process for forming the printed resistor, the conditions in the process, etc., it is possible to obtain a printed resistor with little deterioration in characteristics when incorporated when satisfying the conditions described later. Based on this finding, the inventors have developed a method for manufacturing a multilayer printed circuit board with a built-in printed resistor of the present invention and an inner layer board incorporated therein.

That is, the multilayer printed circuit board with a built-in printed resistor of the present invention is a thermosetting resin that polymerizes by a reaction of a methylol group between the terminals of the conductor circuit formed on the substrate and the opening of the oxirane ring. A thermosetting resin polymerized by a reaction, or a polymer thick film resistor formed by bridging with a thermosetting product of a polymer thick film resistor paste containing a mixture of two types of resins as a resin main component, and the polymer thick film. An inner layer substrate on which a printed resistor having a protective coat made of a thermosetting material of a protective coat paste whose resin main component is the same as the resin main component is mounted on the surface of the resistor;
As a basic unit, a prepreg substrate that is adhered and integrated to at least the mounting surface of the printed resistor of the inner layer substrate; and a single-sided or double-sided printed circuit board that is adhered and integrated to the surface of the prepreg substrate. It is characterized by. In addition, the method of manufacturing the inner layer substrate used for it is a thermosetting resin that is polymerized by the reaction of the methylol group between the terminals of the conductor circuit formed on the substrate, and a thermosetting resin that is polymerized by the ring-opening reaction of the oxirane ring. Or a step of printing a polymer thick film resistor paste containing a mixture of the two kinds of resins as a resin main component, and then thermosetting the paste in a non-oxidizing gas to form a polymer thick film resistor; A step of printing a protective coating paste whose resin main component is the same as the resin main component on the surface of the polymer thick film resistor, and then thermosetting the paste in a non-oxidizing gas to form a protective coat. And a step of trimming the resistance value of the polymer thick film resistor to a predetermined value.

The multilayer printed circuit board of the present invention will be described in more detail with reference to the drawings. FIG. 1 shows a multilayer printed circuit board 1 according to the present invention.
It is a schematic side view which shows an example. In the figure, one surface or double-sided circuit boards 2a are laminated on both surfaces of an insulating substrate 1 on which a printed resistor described later is mounted, with an electrically insulating prepreg substrate 3a interposed therebetween. These substrates are adhered to each other and integrated as a whole. The above three-layer structure is the basic unit. The circuit board 2a is further laminated with the single-sided or double-sided circuit boards 2b, 2c via the prepreg boards 3b, 3c to form a multilayer printed circuit board. Through holes 4, via holes 5, and blind via holes 6 are formed in the multilayer printed circuit board according to the purpose.

Such a multilayer printed circuit board is manufactured by stacking the substrates in an order according to the purpose, heating and pressurizing the substrates under predetermined conditions to integrate them, and then forming the holes.

The multilayer printed circuit board of the present invention has the greatest feature in the printed resistor mounted on the inner layer substrate 1 incorporated therein.

The printed resistor according to the present invention includes terminals of a conductor circuit formed on a substrate, a polymer thick film resistor bridging between the terminals, and a protective coat formed on the surface of the polymer thick film resistor. Composed of.

First, the insulating substrate on which the printed resistor is mounted may be any cured resin substrate reinforced with fibers and / or cloth that is commonly used as a substrate of a printed circuit board. Examples of the reinforcing material include paper non-woven fabric, glass fiber non-woven fabric, aramid fiber non-woven fabric, paper / aramid fiber non-woven fabric, glass fiber woven fabric, aramid fiber woven fabric, carbon fiber woven fabric or non-woven fabric, and Examples of the resin component forming the matrix include thermosetting resins such as phenol resin, epoxy resin, unsaturated polyester resin, and polyimide resin. Furthermore, it is also possible to use a circuit surface with copper foil or the like attached thereto.

A conductor circuit having a predetermined pattern is formed on the surface of this substrate. A polymer thick film resistor described later is bridged between the terminals. Therefore, the terminals are printed with a paste consisting of a certain amount of metal powder such as silver dispersed in a viscous resin in order to maintain stability of ohmic contact with the polymer thick film resistor to be formed. Or formed of, for example, a gold-plated copper foil or other metal foil.

The terminals of this conductor circuit are bridged by a polymer thick film resistor. This thick film resistor is a cured product of the paste (1) composed mainly of a resin described later.

This thick film resistor can be formed as follows. That is, first, the paste (1) is printed between the terminals of the conductor circuit.

The printing method in this case is not particularly limited as long as it is a conventionally applied method, and examples thereof include a screen printing method, a gravure printing method, an offset printing method, and a drawing method using a nozzle. . Among these methods, the screen printing method and the drawing method with a nozzle are preferable.

The paste (1) is prepared by using a resin component as a binder, and adding a predetermined amount of a solvent, a conductive filler and, if necessary, a non-conductive filler to the binder.

In the present invention, the resin used in the preparation of this paste (1) is a thermosetting resin that can be polymerized by the reaction of the methylol group (-CH ₂ OH) of the resin and converted into an infusible cured product. Resin (called resin A), oxirane ring Is a thermosetting resin (referred to as resin B) that is polymerized by the ring-opening reaction to change into an infusible cured product, or a mixture of the two types of resins.

The resin A is a resin composed of an aromatic ring compound or / and an aromatic ring compound having at least one methylol group in the molecule, and examples thereof include phenol-formaldehyde resin, urea-formaldehyde resin, melamine-formaldehyde resin, and phenol-modified resin. Examples thereof include xylene-formaldehyde resin, phenol-furfural resin, furfural-acetone resin, ketone-formaldehyde resin, benzoguanamine-formaldehyde resin, and aniline-formaldehyde resin. Of these resins, a phenolic resin is preferable because it has good adhesion to the substrate.

The resin B is a resin composed of a compound having a glycidyl group by the reaction of various compounds with epihalohydrin or by the oxidation of a double bond, and examples thereof include chrysidyl such as bisphenol type, phenol novolac type and cresol novolac type. Ether type epoxy resin; Glycidylamine type epoxy resin; Alicyclic epoxy resin;
Examples thereof include glycidyl ester type epoxy resins such as fatty acid ester type and aromatic carboxylic acid ester type. Of these resins, glycidyl ether type epoxy resins such as bisphenol type, phenol novolac type, and cresol novolac type are preferable because they have good adhesion to the substrate.

Further, a mixture obtained by mixing the above resin A and resin B in an arbitrary ratio can be used, and if necessary, a small amount of a thermoplastic resin or the like can be blended in addition to the above resin A and resin B. .

Since resin A and resin B are both thermosetting resins,
In the heating process described later, for example, in the case of resin A, the condensation polymerization reaction via a methylol group proceeds, and in the case of resin B, the polymerization reaction by the ring-opening reaction of the oxirane ring proceeds, and the curing of the three-dimensional network structure as a whole Change into a thing.

During this thermosetting process, these resins are converted into polymer thick film resistors by binding a conductive filler described below and a non-conductive filler as required. And at that time,
Since the above-mentioned filler is uniformly dispersed therein, the resistance value has a stable value with little variation even in a hot or / and humid environment, and the reproducibility is excellent. Furthermore, since the cured products of these resins have excellent heat resistance, they do not soften during heating / pressurization when they are built into a multilayer printed circuit board, and therefore before and after heating / pressurizing treatment. At, the characteristics of the printed resistors do not change significantly.

Further, since these resins have good affinity with other thermosetting resins utilized as resins for substrates such as maleimide resin, unsaturated polyester resin, epoxy resin, and phenol resin, these resins are When it is laminated with a resin substrate to form a multilayer, it adheres well to the substrate, and as a result, processing such as punching, cutting, punching or a thermal cycle,
No delamination occurs even when exposed to a high humidity environment.

As a solvent which is another component of the paste, a ketone-based solvent,
High boiling point solvents such as ester type, ether type and alcohol type are preferable, and examples thereof include butyl cellosolve acetate, butyl carbitol acetate, isophorone, and terpineol.

In addition, as the conductive filler mixed in the paste, carbon black such as furnace black, channel black, lamp black, thermal black, acetylene black, and Ketjen black; graphite powder such as artificial graphite powder and natural graphite powder Can be given. The latter powder is preferably a fine powder having an average particle size of several tens of μm or less. These carbon black and graphite powder may be used alone, or may be mixed and used in an appropriate ratio. Further, the non-conductive filler that is blended as necessary includes organic fillers and inorganic fillers. Each of these fillers has an average particle size of several tens.
It is preferably μm or less. Examples of the organic filler of the former include, for example, powder of a cured product of phenol resin, powder of a cured product of benzoguanamine resin, polymethylmethacrylate powder, polyethylene powder, and polystyrene powder, and examples of the inorganic filler include:
Examples thereof include colloidal silica powder, fused silica powder, alumina powder, talc, mica powder, iron oxide powder, calcium carbonate powder, magnesium carbonate powder, bentonite, dolomite, and kaolin.

The blending ratio of each of these components can be appropriately changed depending on the target resistance value of the resistor to be formed, the viscosity suitable for printing, and the like.

After printing the above-mentioned paste (1) between terminals, heating and thermosetting this paste, a polymer thick film resistor bridging between terminals is formed.

As the heating means at this time, for example, a hot-air stove, a far-infrared furnace, a near-infrared furnace, or a microwave heating furnace can be used each singly or in an appropriate combination. Of these, a hot stove is usually used.

Although other heating means have the advantage that heat curing can be achieved in a short time, on the other hand, there is a problem that the properties of the cured product after heat curing, that is, the polymer thick film resistor, become unstable. Is.

Generally, when the heat curing of the paste (1) progresses sufficiently during this treatment, the characteristics of the obtained polymer thick film resistor (for example, stability of resistance value, environment resistance) are improved, and variation in resistance value is small. Become. In consideration of this, in the case of the above-mentioned paste (1), it is preferable that the paste (1) is sufficiently cured and stabilized if it is heat-cured at a temperature of 150 ° C. or more for 60 minutes or more. .

The atmosphere at the time of heat curing needs to be a non-oxidizing gas atmosphere such as carbon dioxide gas, nitrogen gas, or argon. This is because when the paste (1) is subjected to thermosetting treatment in an oxidizing gas under the above-mentioned conditions, thermal degradation and discoloration of the substrate itself occur.

The polymer thick film resistor thus formed is coated with a protective coat. This protective coat is a cured product of the paste (2) containing a resin described below as a main component.

In forming the protective coat, first, the paste (2) is printed on the surface of the polymer thick film resistor. The printing method at this time may be the method applied to the printing of the paste (1). Further, the printing is preferably performed on the entire surface of the polymer thick film resistor including the overlapped portion of the polymer thick film resistor and the terminal, but even if it is not, most of the surface excluding the overlapped portion is printed. Needs to be done.

The resin main component of the paste (2) used must be of the same quality as the resin main component of the paste (1) used for forming the polymer thick film resistor. The homogenous resin main component as used herein means the same as the resin main component constituting the paste (1) or a resin containing 80% by weight or more of the resin main component of the paste (1). To do. Preferably, the same resin main component is used.

The paste (2) may be blended with a predetermined amount of various solvents and non-conductive fillers that have been blended when the paste (1) was prepared.

The printed paste (2) is subjected to thermosetting treatment under the same conditions as when the paste (1) is thermoset.
In this way, an electrically insulating protective coat is formed on the polymer thick film resistor.

This protective coat stably holds the resistance value of the printed resistor mounted on the inner layer substrate even in the process of heating and pressing when manufacturing the multilayer printed circuit board by incorporating the inner layer substrate according to the present invention. Function.

In this case, as described above, the resin main component of the paste (2) needs to have the same quality as that of the paste (1).

The reason is not necessarily clear, but when the surface of a polymer thick film resistor, which is a thermosetting product of the paste (1) already formed using a different resin paste (including solvent), is coated, Since there are innumerable micro voids and cracks on the surface of the thick film resistor, the above-mentioned paste (2) permeates into these places and is thermally cured at those places, but at that time, the paste (1 ) And paste (2) have different physical properties, so overall,
It is considered that the resistance value of the thick film resistor fluctuates. This is also a problem caused by the resin solution of the prepreg or other substrate that comes into contact with the thick film resistor when the protective coat is not formed or during the heating / pressurizing process. Therefore, if the resin main component of the paste for the protective coating is the same as that for the thick film resistor, the cured product becomes the same substance, and the resistance variation of the cured product as described above is suppressed. .

The polymer thick film resistor covered with the protective coat thus formed between the terminals is then trimmed to set a predetermined resistance value. A printed resistor is thus formed here.

Trimming at this time may be performed using a laser trimmer or an abrasive trimmer, as in the usual case.

Trimming in the present invention needs to be performed after forming the protective coat, and when performed before forming the protective coat, that is, at the time when the polymer thick film resistor is formed,
During the subsequent printing of the paste (2), its thermosetting process, and the heating / pressurizing process after it is laminated with another substrate such as a prepreg, a trift is added to the resistance value set by trimming, and multilayer printing is performed. This is inconvenient because the resistance value accuracy of the printed resistor when incorporated in the circuit board is reduced.

In this way, the inner layer substrate on which the printed resistor according to the present invention is mounted is obtained.

The multilayer printed circuit board of the present invention has a basic unit of three layers by laminating a single-sided or double-sided circuit board on at least the mounting surface of the printed resistor of the above-mentioned inner layer board via a prepreg board, and if necessary, A single-sided or double-sided circuit board is sequentially laminated on one or both sides of the basic unit via a prepreg board to form a multilayer structure, and then the whole is heated and pressed, and each board is manufactured as an integrated structure.

What is important in the present invention is that the surface of the printed resistor, that is, the side to be laminated with the prepreg substrate at the time of laminating the multilayer plate, is always provided with the protective coat layer formed by using the resin paste of the same quality as the polymer thick film resistor. Is.

If the polymer thick film resistor and the prepreg substrate are brought into direct contact with each other at the time of stacking heating, the change in resistance value before and after the process becomes large, which is inconvenient.

The prepreg substrate used at this time preferably has the same resin as that of the above-mentioned inner layer substrate. In that case, the ratio of the thermosetting resin and the reinforcing material is preferably 80:20 to 40:60 by volume ratio, and the thermosetting resin is a semi-cured resin that retains heat fluidity under appropriate heating conditions. It is preferable to use the B stage.

The heating / pressurizing method after stacking the substrates is, for example, a press method such as a hot press or a vacuum hot press; a vacuum bag heating method in which pressure is applied at atmospheric pressure by vacuum operation; and an autoclave heating method in which gas can be pressed. I can give you. In this case, it should be noted that the pressurizing conditions are properly set in relation to the flow temperature of the prepreg substrate used so as to obtain a laminated and integrated state in which voids and delaminations do not occur. Of these methods, vacuum hot pressing is preferable because it is easy to operate and has high productivity.

Then, this multilayer laminate is subjected to perforation, through hole plating, and outer layer patterning treatment to obtain the multilayer printed circuit board of the present invention.

(Example of Invention) Example 1 (Production of Inner Layer Substrate) Phenol-formaldehyde resin (trade name, BLS-3
A paste a was prepared by sufficiently kneading 50 parts by weight of 135, Showa High Polymer Co., Ltd., 8 parts by weight of furnace black, 32 parts by weight of talc, and 80 parts by weight of butyl carbitol acetate.

Next, the substrate shown in Figure 2-A (length 54 mm, width 54 mm)
Prepared. That is, a single-sided copper-clad laminate having a copper foil thickness of 35 μm (glass epoxy substrate G-10 equivalent, thickness 1.
6mm) is etched by a conventional method to obtain 10 terminal pairs 7a to 7
A conductor circuit 7 having j was formed. Then, a polymer thick film silver paste C-100 (silver powder / modified phenol resin binder manufactured by Toagosei Kagaku Kogyo Co., Ltd.) was screen-printed on each terminal surface, dried and cured to secure ohmic contact and contact stability. .

After the paste a is screen-printed between the terminals so that the average thickness of the solid content is 20 ± 5 μm,
Oven with a nitrogen gas flow rate of 20 / min (95 capacity)
It was placed inside and heated at 180 ° C. for 60 minutes. The paste a was completely thermoset to form a polymer thick film resistor bridging between the terminals. The state is shown in FIG. In the figure, a polymer thick film resistor 14 having a width w and a distance between terminals is formed between a pair of terminals.

Then, paste b was screen-printed on the thick film resistor in the same pattern so that the solid content was 20 ± 5 μm. The paste b used is the paste a
It was prepared by kneading 70 parts by weight of the same resin as described above, 30 parts by weight of talc and 75 parts by weight of butyl carbitol acetate.

It was heated again at 180 ° C. for 30 minutes. Paste b was completely thermoset to form a protective coat covering the thick film resistor.

At this time, the dimensions of the total length l ′ of the polymer thick film resistor in each terminal pair 7a to 7j, the length of the bridging portion between the terminals (the portion which becomes the resistance excluding the overlapping portion with the terminals) l, and the width w are The results are shown in Table 1.

Then, perform laser trimming with a single cut to set resistance between each terminal (aspect ratio 1 / w = 1,
(Settings corresponding to Nos. 2 and 5) were determined, and an inner layer substrate on which the printed resistor according to the present invention was mounted was used.

(Manufacture of Multilayer Printed Circuit Board) As shown in FIG. 3, resin content of 58 volume was applied on both sides of the inner layer substrate 11 on which the printed resistor composed of the polymer thick film resistor 11a and the protective coat 11b covering the same was mounted. % Epoxy resin-glass cloth prepreg (thickness 0.1 mm) 12, 12 '
2 sheets each, and further, on both sides, single-sided copper clad laminates 13 and 13 'having the same conductor circuit pattern as in FIG. Was set in a hot press machine. Initial pressure 5kgf / cm ² , temperature 12
From the time that exceeds 0 ° C., from room temperature pressing conditions 35 kgf / cm ² 18
The temperature was raised to 0 ° C., and the temperature was maintained for 60 minutes. Then, it was left to cool while being pressed to obtain a three-layer multilayer board.

Forming copper-plated through holes with a diameter of 0.4 mm on the input side of the conductor circuit of the outer layer pattern of the obtained multilayer board,
A multilayer circuit board with a built-in printing resistor was used. The presence or absence of delamination was examined and the results are shown in Table 3.

(Characteristics of Printed Resistor) With respect to the obtained circuit board, the characteristics of the built-in printed resistor were measured based on the following specifications.

Lamination drift: The rate of change (%) of the resistance value with respect to the set resistance value when heating and pressurizing by laminating with another substrate.

TCR: Temperature coefficient of resistance value (ppm / ° C) L = 60 to 20 ° C, and H = 20 to 125 ° C.

Thermal aging: Rate of change in resistance value (%) when left in air at 120 ° C for 200 hours.

Short-time overload: The rated power per printing area is 40 mW / mm ^2, and the rated voltage corresponding to the rated power of each printing resistor is proportional to the effective resistance area (l × w in Fig. 4) 2.
The rate of change (%) of the resistance value measured 30 minutes after the voltage of 5 times the value was applied to each printing resistor for 5 seconds with respect to the set resistance value.

 The results are shown in Table 3.

Example 2, Comparative Examples 1 to 3 The components shown in Table 2 were kneaded at the indicated proportions (parts by weight) to prepare various pastes.

Using these pastes in combination as shown in Table 3, and in the same manner as in Example 1, an inner layer substrate mounting a printed resistor was manufactured. A multilayer circuit board was assembled by incorporating these boards in the same manner as in Example 1. The performance of the printed resistors of each of these circuit boards was measured in the same manner as in Example 1, and the results are collectively shown in Table 3.

Example 3 (Production of Inner Layer Substrate) The substrate (length 30 mm, width 50 mm) shown in FIG. 2-B was prepared. That is, a single-sided copper-clad laminate having a copper foil thickness of 35 μm (glass epoxy substrate G-10 equivalent product, thickness 1.6 mm) is etched by a conventional method to obtain a conductor circuit 8 having 12 terminal pairs 8a to 8l. Was formed. And each terminal surface has a thickness of 5
Electroless nickel plating with a thickness of 0.1 μm
Electroless gold plating was applied to ensure ohmic contact and contact stability.

The paste a prepared in Example 1 was screen-printed between these terminals so that the average thickness of the solid content was 20 ± 5 μm, and the whole was put in an oven (capacity 95) with a nitrogen gas flow rate of 20 / min. Heated at 180 ° C for 60 minutes. Paste a was completely thermoset to form a polymer thick film resistor bridging each terminal. The state is shown in FIG. In the figure, a polymer thick film resistor 14 having a width w and a terminal distance l is formed between a pair of terminals.

Then, the paste b prepared in Example 1 was applied on the thick film resistor in the same pattern with a solid content of 20 ±.
Screen printing was performed so that the thickness was 5 μm.

It was heated again at 180 ° C. for 30 minutes. Paste b was completely thermoset to form a protective coat over the polymer thick film resistor.

Thus, a thick film resistor having actual dimensions as shown in Table 4 was formed between the terminals 8a to 8l.

Finally, for each thick film resistor, its aspect ratio (l / w)
In accordance with the above, laser trimming was performed to adjust the respective set resistance values to obtain the printed resistor mounting inner layer substrate of the present invention.

(Manufacture of Multilayer Printed Circuit Board) In order to verify the performance of the inner layer substrate described above, Example 1
Following the same procedure as above, a multilayer printed circuit board was manufactured and its performance was investigated.

 The above results are shown in Table 5.

Example 4, Comparative Examples 4 to 7 The components shown in Table 2 were kneaded at the indicated ratios (parts by weight) to prepare various pastes.

Using these pastes in combination as shown in Table 5, and under the conditions shown in Table 5, an inner layer substrate having a printed resistor mounted thereon was manufactured. A multilayer printed circuit board was assembled by incorporating these substrates in the same manner as in Example 3. The performance of the printed resistors of each of these printed circuit boards was measured in the same manner as in Example 3, and the results are collectively shown in Table 5.

(Effects of the Invention) As is clear from the above description, the multilayer printed circuit board of the present invention has little deterioration in the characteristics of the printed resistors incorporated therein. Therefore, since the multilayer printed circuit board of the present invention can accommodate the resistors that occupy 1/3 to 1/2 of the number of mounted components as a thin built-in circuit, the area required for mounting the components becomes small and high density is achieved. Compact and lightweight, it is extremely useful as a circuit board for various electronic devices.

[Brief description of drawings]

FIG. 1 is a schematic side view showing an example of the multilayer printed circuit board of the present invention, FIGS. 2-A and 2-B are plan views of a substrate for forming a printed resistor, and FIG. 3 is a book. FIG. 4 is a view showing a laminated state when an inner layer substrate according to the invention is incorporated to manufacture a multilayer printed circuit board, and FIG. 4 is a thickness bridging between terminals of the substrate of FIGS. 2-A and 2-B. It is a top view of a membrane resistor. 1 ... Insulating board, 3a, 3b, 3c, 12, 12 '... Prepreg board, 2a, 2b, 13, 13' ... Single-sided or double-sided circuit board, 4 ...
Through hole, 5 ... Biaper hole, 6 ... Blind via hole, 7,8 ... Conductor circuit, 7a to 7j, 8a to 8l ... Terminal pair, 11a, 14 ... Polymer thick film resistor, 11b ... … A protective coat.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiro Miki 1-14-1, Nishi-Shimbashi, Minato-ku, Tokyo Within Toago Synthetic Chemical Industry Co., Ltd. No. 15 Inside Nago Electronics Co., Ltd.

Claims (2)

(57) [Claims] 1. A thermosetting resin which is polymerized by a reaction of a methylol group, a thermosetting resin which is polymerized by a ring-opening reaction of an oxirane ring, or a terminal of a conductor circuit formed on a substrate, and between the terminals. A polymer thick film resistor formed by bridging a thermosetting material of a polymer thick film resistor paste containing a mixture of the above two resins as a resin main component, and the resin main component on the surface of the polymer thick film resistor. An inner layer substrate on which a printed resistor having a protective coat made of a thermosetting paste of the same protective resin paste as that of the resin main component is mounted; and an adhesive on at least the mounting face of the printed resistor of the inner layer substrate. A printing resistor having as a basic unit a prepreg substrate that is integrated by being integrated; and a single-sided or double-sided printed circuit board that is adhered and integrated on the surface of the prepreg substrate. Built-in multi-layer printed circuit board. 2. A thermosetting resin which is polymerized by a reaction of a methylol group, a thermosetting resin which is polymerized by a ring-opening reaction of an oxirane ring, or the above two kinds, between terminals of a conductor circuit formed on a substrate. Printing a polymer thick film resistor paste containing the resin mixture as a resin main component and then thermosetting the paste in a non-oxidizing gas to form a polymer thick film resistor; A step of printing a protective coating paste whose resin main component is the same as the resin main component on the surface of, and then thermosetting the paste in a non-oxidizing gas to form a protective coat; And a step of trimming the resistance value of the thick film resistor to a predetermined value.