JPH069307B2 - Method for manufacturing composite circuit board - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board in a circuit module, a hybrid integrated circuit or the like used in various electronic devices, and in particular, a composite formed by stacking and compounding for high-density mounting. It relates to a circuit board.

2. Description of the Related Art In recent years, there have been remarkable advances in miniaturization and high-density mounting of electronic components, and in particular, multi-layering / multi-layering of circuit boards has been studied in various fields.

For example, regarding the CR built-in multilayer ceramic substrate by the green sheet method, Internepcon Japan / Semiconductor, 86ISHM, published by ISHM Japan Headquarters
P. of Special Seminar Proceedings 25-P. 32. In this case, in terms of high density, it is superior to the conventional circuit board and the like by the thick film printing method, but has the following drawbacks. First, since different materials such as electrode material, resistor material, insulating material, and dielectric material are co-sintered, it is necessary to strictly control the material selection and manufacturing process. Since it is bad, it is difficult to fire for a short time. For the above reasons, it has a drawback that the manufacturing cost is high.

Secondly, when a resistor is formed in the inner layer, it is difficult to modify the resistance value. This is because the insulating layer is interposed on the resistor, so that the laser beam or the like cannot be transmitted. Therefore, it is impossible to form a highly accurate resistance element in the inner layer.

As a method for overcoming the above-mentioned drawbacks of the green sheet method, a trial of a laminated hybrid IC in which a plurality of circuit boards on which circuits have been formed by using a sintered ceramic board is joined by soldering Can be raised. This is described in JP-A-62-43197. The above-mentioned solder joining method has the following features.

(1) Economical because electrical and mechanical joining can be performed simultaneously by reflow.

(2) Since the characteristics can be confirmed for each substrate, the yield can be improved.

(3) With respect to design changes, only a part of each board needs to be changed, which enables rapid development and trial production.

(4) Since the functions are divided for each substrate, such as resistance, capacitor, inductance, and component mounting, problems such as crosstalk in circuit design can be simplified.

(5) Since the resistors are laser-trimmed and then the substrates are joined together, a highly accurate resistive element can be obtained.

It was an object of the invention to provide a laminated composite circuit board with built-in RCL having the above features.

Problems to be Solved by the Invention However, the solder joining method for joining a sintered ceramic circuit board, which is disclosed in JP-A-62-43197, with solder has the following problems. The first problem is
This is a point that breakage easily occurs due to thermal fatigue due to temperature cycles and the like. In particular, when a thick film electrode such as Ag, AgPd, or Cu is used as the electrode material, there is a drawback in connection reliability that an alloy layer is formed due to Sn diffusion in the solder and mechanically becomes brittle.

Further, as a second problem, when mounting a component or an IC bare chip in a low backlash, there is a restriction on the operating temperature that it must be below the melting point of the solder used for joining. Actually, eutectic solder with Sn / Pb = 60/40 is usually used for component mounting, but the soldering temperature is 20
The solder dipping or reflow method at 0 ° C to 250 ° C is used. Moreover, even in the bonding of the IC bare chip, preheating at about 200 ° C. to 300 ° C. is required by the thermocompression bonding method using ultrasonic waves. Taking the above post-process heating conditions into consideration, only high-temperature solder having a high melting point can be used in the substrate joining method using solder. Specifically, a Pb content of 90% or more is required. Generally in the solder composition
When Pb is increased, the solder is easily oxidized and so-called "potato solder" is likely to be generated. This phenomenon easily causes deterioration of the bonding strength and has many problems in reliability. As described above, when the solder used for joining is eutectic solder, there is a temperature restriction on component mounting and normal soldering or bonding becomes impossible, or when high temperature solder is used for joining, Pb oxidation The problem remains that the bonding strength and its reliability will be problematic if a method of suppressing the above is not taken. To summarize these, the solder materials that can be used are very limited in consideration of the heating conditions for mounting components in the subsequent process. The above is the second problem.

The third problem is that the space between the stacked substrates is 20 μm.
Since there is a gap of about 200 μm, it is impossible to prevent the ingress of moisture in high temperature and high humidity, which causes a problem in moisture resistance performance. Specifically, short circuits due to migration between wiring conductors, failures in built-in resistors, capacitors, inductance elements or mounted parts, and insulation failures due to moisture absorption are likely to occur.

As described above, the solder joining method disclosed in Japanese Patent Laid-Open No. 62-43197 can provide a high-density laminated composite circuit board that is inexpensive and can be embedded in the RCL, but its joining strength, joining reliability, and There are many problems in terms of moisture resistance,
It was poor in practicality.

The present invention has been made in view of the above points, and an object of the present invention is to provide an RCL built-in type laminated composite circuit board having excellent bonding strength and reliability, and also excellent moisture resistance.

Means for Solving the Problems In order to solve the above problems, the present invention provides a plurality of electrodes, resistance elements, or circuit wirings formed on an inorganic insulating substrate made of sintered ceramic or the like. It uses a circuit board. The process up to this point is the same as the solder joining method.
A connection conductor is applied and formed on a desired electrode of the circuit board, and sealing glass is applied and formed around each connection conductor, and then the connection conductors face each other and seal the periphery. It is a feature of the present invention that the connecting conductor and the sealing glass are sintered and adhered by baking at a baking temperature of 350 ° C. to 700 ° C. in a state where each circuit board is laminated so that the glass for sealing is sealed. . As the connecting conductor, any one of Ag, Pd, Pt, and Cu, or a mixture thereof, or a paste-like conductor composition containing the above metal as a main component and kneading with a glass frit, an organic binder, or the like. Are using. As the glass for sealing, a glass frit having a softening point of 300 ° C. to 700 ° C., or a paste-like insulator composition containing the above glass frit as a main component and kneading with an organic binder added is used.

Operation The present invention solves the above-mentioned problems of the conventional solder joining method using the sintered ceramics. In the present invention, any one metal of Ag, Pd, Pt, and Cu or a mixture thereof is used as the refractory metal other than solder. Desirably, a conductor composition in which glass frit and an organic binder are added to metal powder obtained by pulverizing these metals and kneaded into a paste can be used. This is highly practical because a screen printing method can be used when depositing the connecting conductor on the electrodes on the surface of the circuit board.

The above connecting conductor is diffused / alloyed with electrodes on the surface of the circuit board, for example, Ag, AgPd, Cu, etc., in the temperature range of 350 to 700 ° C. Alternatively, in the case of a paste-like conductor composition to which glass frit is added, the glass frit can obtain a bonding force by appropriately wetting the electrode on the surface of the circuit board. By controlling the shape, composition, firing atmosphere, and temperature of this connecting conductor, it is possible to obtain electrical connectivity, mechanical bonding strength, and reliability thereof.

Further, regarding the sealing glass provided around the connecting conductor, a composite frit having excellent moisture resistance is formed by selecting a glass frit composition that is sufficiently softened at 300 ° C. to 700 ° C. to form a sealed structure between the connecting conductors. Will be provided. In addition, even if only the connecting conductor is used, it has superior reliability compared to soldering, but since the bonding effect of the sealing glass reinforces the bonding between the substrates, Strength is greatly improved.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a method of manufacturing a composite circuit board according to an embodiment of the present invention. FIG. 1 (a) is a view showing a cross section of each circuit board used in the composite circuit board of the present invention. In FIG. 1 (a), 1 is a first circuit board and 2 is a second circuit board.
The circuit board of FIG. The first and second circuit boards 1,
Reference numeral 2 is an inorganic insulating substrate such as a sintered ceramic, and this time, alumina having a purity of 96% is used.
The electrode 3 is formed on the surface of the alumina. Although these circuit boards are omitted in the figure, circuit wiring formation, resistance element formation, capacitor element formation, inductance element formation, multilayering, etc. are thick film printing methods, green sheet methods, thin film methods, plating methods, etc. What was given by it may be used as needed. In this embodiment, the electrode 3 is Cu
An electrode is used, and a thick film Cu paste applied on an alumina substrate by screen printing is used at 850 ° C to 95 ° C.
It was obtained by firing in a nitrogen atmosphere at 0 ° C.

FIG. 1 (b) shows a state in which the connecting conductor 4 and the sealing glass 5 are applied onto the electrodes of the first and second circuit boards 1 and 2, respectively. Like the electrode 3, the connection conductor 4 is 30 μm thick by screen printing using a thick film Cu paste.
It is applied and dried in a film thickness of about 100 μm. The thick film Cu paste used for the connecting conductor 4 is Cu
80 to 98 wt% powder, 2 to 20 wt% glass frit, and 2 to 20 wt% organic binder were used. As for the Cu powder, a fine powder having a particle size of 1.5 μm or less was used so that the sinterability at 650 ° C. or less was easily obtained. Glass for seal 5
Is a glass frit having a softening point of 350 ° C. to 500 ° C. as a main component, a thick film glass paste added with an organic binder and kneaded, and applied by screen printing so as to have a film thickness equal to that of the connecting conductor 4. , Dried.

FIG. 1 (c) shows a structure in which the first circuit board 1 and the second circuit board 2 coated with the connecting conductor 4 and the sealing glass 5 are laminated so that the connecting conductors 4 face each other. FIG. 4 is a cross-sectional view of a composite circuit board joined and integrated by firing. Firing of the connecting conductor 4 and the sealing glass 5 is 50
The first circuit board 1 and the second circuit board 2 were joined and integrated by simultaneously performing them in a nitrogen atmosphere at 0 ° C to 650 ° C. For the purpose of improving the joint strength and its reliability, the conductor for connection and the glass for sealing are laminated in a semi-dried state, and 10 g / 10 kg
By applying a moderate load and reheating, a better bondability was confirmed. Alternatively, even if a load of about 10 g to 10 kg is applied at the time of firing, the bondability can be similarly improved.

The composite circuit board manufactured by the above structure and manufacturing method has excellent electrical bonding properties, and a conductor resistance of 50 mΩ or less was obtained in a bonding pad area of 0.5 mm × 0.5 mm. In addition, using two test circuit boards of 10 mm x 10 mm square, 40 bonding pads of 0.5 mm x 0.5 mm are arranged in all directions, and a sealing glass is arranged around the bonding pads and bonded to the sample. It was confirmed that an adhesive strength of 5 kg · f or more was obtained and the performance was sufficiently high in practical use.

In this embodiment, since the Cu film having a high melting temperature is used as the connecting conductor 4, the temperature range that can be used in the soldering of parts in the subsequent steps, the substrate preheating at the time of bonding the IC bare chip, etc. It is much wider than the conventional solder connection method.

Further, since the periphery of the connecting conductor and the gap are sealed with the sealing glass, a composite circuit board which prevents moisture from entering and has excellent moisture resistance is realized.

Another embodiment is shown in FIG. 2 as a more concrete application example.
FIG. 2 is a view showing an embodiment in which four circuit boards are laminated, a sectional structure is shown in FIG. 2 (a), and a perspective view is shown in FIG. 2 (b). In FIG. 2, 6 is an IC mounting substrate, 7 is a capacitor block substrate, 8 is an inductance block substrate, and 9 is a leadless chip carrier substrate with a built-in resistor.

Reference numerals 10, 10 ', 10 "and 10 indicate electrodes on the surface of each substrate. The leadless chip carrier substrate 9 at the bottom.
A resistance element 11 is formed on the top and soldered to the mother board by the end face electrodes 12. Reference numeral 13 is a through hole that electrically connects the front and back of each substrate, and a connection conductor 14 is applied on the electrode of the through hole portion. Further, a sealing glass 18 is applied to the periphery and the gap of the connecting conductor 14, and the respective substrates are laminated in the same manner as in the above-described embodiment, and then fired collectively to electrically and mechanically. An integrated RCL built-in composite circuit board is obtained. The IC bare chip 15 is fixed by die bonding on the IC mounting board 6 which is the uppermost stage of the composite circuit board integrated as described above, and is connected to the wiring on the IC mounting board by the bonding wire 16. There is. Reference numeral 17 indicates a resin for sealing the IC bare chip.

As described above, by using the composite circuit board with built-in RCL according to the present example, a high-density and surface-mountable laminated hybrid integrated circuit is formed.

Effects of the Invention As described above, according to the present invention, there are various effects listed below.

(1) The manufacturing method is simpler than the simultaneous sintering technology such as the green sheet method because the structure is such that each circuit board that uses an inorganic substrate such as sintered ceramics is individually manufactured and then joined with the connecting conductor. And the yield is improved. As a result, cost reduction can be realized. (2) In each board,
After forming the resistance element and correcting the resistance value in advance, when the bonding between the substrates is performed, the firing temperature is relatively low at 350 ℃ ~ 700 ℃, the resistance value change is very small, resulting in high An accurate resistance element can be built in the composite circuit board.

(3) The deterioration of the bonding strength due to Sn diffusion or the like, which is a problem of the conventional solder bonding method, is prevented, and the bonding reliability between the substrates is dramatically improved.

(4) Since a connecting conductor with a high melting temperature is used, it is possible to select an arbitrary temperature of 350 ° C or less as a temperature condition for graduating parts in the subsequent process, making the process design easier than the solder joining method. .

(5) Since the gap between the substrates is sealed with the sealing glass, the moisture resistance is improved and the bonding strength is also improved.

Since the above-described various effects are obtained, the method for manufacturing a composite circuit board according to the present invention has a great practical effect.

[Brief description of drawings]

1A to 1C are process diagrams showing a method for manufacturing a composite circuit board according to an embodiment of the present invention, and FIGS. 2A and 2B are a sectional view and a perspective view showing a concrete application example of the present invention. 1 ... First circuit board, 2 ... Second circuit board, 3 ...
Electrodes, 4 ... Connection conductor, 5 ... Sealing glass, 6 ...
... IC mounting board, 7 ... Capacitor block board, 8
...... Inductance block substrate, 9 ... Leadless chip carrier substrate with built-in resistor 10,10 ', 10 ", 1
0 ... Electrode, 11 ... Resistor, 12 ... End surface electrode, 13
...... Through hole, 14 ...... Connection conductor, 15 ...... IC
Bare chip, 16 ... Bonding wire, 17 ...
... Sealing resin, 18 ... Sealing glass.

Claims (4)

[Claims] 1. A plurality of circuit boards on which electrodes, resistance elements or circuit wirings are formed on an inorganic insulating substrate, and a connecting conductor is formed by coating on desired electrodes of the circuit board. In addition, after the sealing glass is applied and formed on the periphery and the gap of each connecting conductor, the connecting conductors face each other, and the circuit boards are laminated so that the sealing glass hermetically seals the periphery. A method for manufacturing a composite circuit board, characterized in that the connecting conductor and the sealing glass are sintered and adhered by firing to form an electrically and mechanically integrated body. 2. The conductor for connection is a paste-like conductor obtained by kneading a metal of any one of Ag, Pd, Pt and Cu, or a mixture thereof, or a glass frit, an organic binder or the like containing the metal as a main component. It is a composition, The manufacturing method of the composite circuit board of Claim 1 characterized by the above-mentioned. 3. The glass for sealing has a softening point of 300 ° C. to 700 ° C.
2. A method for producing a composite circuit board according to claim 1, which is a glass frit at 0.degree. C. or a paste-like insulator composition containing the glass frit as a main component and kneading with an organic binder added. . 4. An inorganic insulating substrate material comprising at least one of a low dielectric constant ceramic substrate such as alumina, a high dielectric constant ceramic substrate such as barium titanate, and a magnetic substrate such as ferrite. A method of manufacturing a composite circuit board according to claim 1.