JPH0595071U - Thick film circuit board - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a thick film circuit board in which the humidity resistance of the characteristic detecting electrode pad exposed to the outside is improved. [Structure] In a thick film circuit board in which a thick film wiring pattern 2 which forms a desired circuit, an output electrode pad 4, and a characteristic detection electrode pad 5 are formed on a ceramic insulating substrate 1, the characteristic detection electrode pad 5 comprises: The conductor layer 5a is formed by depositing a chemically inert conductor layer 5b on the conductor layer 5a.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a thick film circuit board in which a thick film conductor wiring pattern, a thick film resistor film, and various electrode pads are formed on a ceramic insulating substrate by using a thick film technique.

[0002]

[Prior Art]

 For thick film circuit boards, which are generally used in hybrid integrated circuits used in electronic devices, a ceramic substrate composed mainly of alumina is used from the viewpoint of electrical, mechanical strength and thermal conductivity. A silver-based thick film conductor such as silver or silver-palladium, or a copper-based silver thick film conductor such as copper was formed. Such a thick film circuit board has a great feature that a resistor film can be formed by using a thick film technique, and is smaller and thinner than a solid-state resistor. Will be possible.

However, when a thick film circuit board is applied to a field in which a desired circuit is required to have high density and high reliability, the chemical activity of the thick film wiring pattern becomes a big problem. come. When moisture or the like is generated on the densified thick film conductor, a short circuit phenomenon occurs between wiring patterns. In particular, when a wiring pattern is formed by a silver-based thick film conductor, the silver-based material has high activity, so that migration occurs and a short circuit between patterns occurs.

In order to prevent this moisture, a protective film such as glass has been formed over the entire surface after forming a wiring pattern.

However, when it is necessary to mount a resistor film or other electronic components such as a crystal oscillator on the thick film circuit board, the characteristics of the resistor film or the crystal oscillator are detected. However, it is necessary to trim the resistor film and adjust the surface area of the vibrating electrode of the crystal unit, and use the characteristic detection electrode pad that is connected to the measurement probe of the characteristic detection device that is not covered with the protective film. I had to set it up.

Generally, as a method of manufacturing a thick film circuit board having a resistor film, a wiring pattern, a characteristic detection electrode pad, an output electrode pad, and various electronic devices are formed on a ceramic substrate by using a silver-based thick film conductor material. The electrode pad on which the component is mounted is printed and dried, and then a resistor film is printed and dried between the prescribed wiring patterns using a thick film conductor material for antibodies, and the ceramic substrate is baked under prescribed firing conditions. , The wiring pattern, the characteristic detection electrode pad, the output electrode pad, and the electrode pad on which various electronic components are mounted are baked, and then a protective film is formed on the entire surface of the substrate so that the characteristic detection electrode pad and the output electrode pad are exposed. Had formed. After that, the resistance film was trimmed with a laser or the like while the measurement probe of the property detection device was in contact with the property detection electrode pad to adjust the resistance value of the resistance film to a predetermined value. After that, various electronic components were soldered to the mounting electrode pads and the lead terminals were soldered to the output electrode pads.

[0007]

[Problems of conventional technology]

 Here, the wiring pattern is covered with a protective film, and the mounting electrode pads and output electrode pads are covered with the solder layer of the solder joints. The above-mentioned migration does not occur in the electrode pads and output electrode pads, but the characteristic detection electrode pads are exposed to the outside, and even copper-based thick film conductors in which migration does not occur. Even if it is a material, the humidity resistance will drop significantly due to humidity.

The present invention has been devised in view of the above problems, and an object thereof is to provide a thick film circuit board in which the humidity resistance reliability of the characteristic detection electrode pad exposed to the outside is improved. It is a thing.

[0009]

[Means for solving problems]

 The present invention relates to a thick film circuit board formed by forming a thick film wiring pattern, an output electrode pad and a characteristic detection electrode pad forming a desired circuit on a ceramic insulating substrate, wherein the characteristic detection electrode pad is a base conductor. The thick film circuit board is characterized in that it is formed of a layer and a chemically inactive coated conductor layer.

[0010]

[Action]

 In the present invention, the characteristic detecting electrode pad exposed to the outside in the thick film circuit board is a chemically inactive conductor layer on the conductor layer, for example, the same oxide or silicide metal material as the resistor film, Alternatively, since the plating layer is deposited, the conductor layer below the characteristic detection electrode pad will not undergo any chemical change due to moisture such as corrosion.

Therefore, since the wiring pattern of the thick film circuit board, the conductor layers forming the various electrode pads, and the conductor material can be completely shielded from the outside, corrosion due to moisture can be prevented, and a thick film circuit with high humidity resistance and high reliability can be prevented. It becomes the substrate.

[0012]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial plan view of a thick film circuit board of the present invention, and FIG. 2 is a sectional view taken along line AA in FIG. For the sake of explanation, the electronic components mounted on the electronic component mounting electrode pads of the thick film circuit board and the lead terminals bonded to the output electrode pads are omitted.

In the figure, 1 is a ceramic substrate, 2 is a wiring pattern, 3 is an electronic component mounting electrode pad, 4 is an output electrode pad, 5 is a characteristic detecting electrode pad, 6 is a resistor film, and 7 is a protective film.

The ceramic substrate 1 is made of alumina ceramic or the like and has a rectangular shape.

The wiring pattern 2 is made of a silver-based conductor material such as silver or silver-palladium, or a copper-based conductor material such as copper, and is formed in a predetermined shape on the ceramic substrate 1 according to a desired circuit.

The electronic component mounting electrode pad 3, the output electrode pad 4, and the characteristic detecting electrode pad 5 are made of the same material as the wiring pattern 2 and are formed so as to be connected to the wiring pattern 2.

The resistor film 6 is formed on the substrate 1 by using a thick film resistor paste containing ruthenium oxide, lanthanum boride, lanthanum silicide, etc. as a main component of a conductive material. Both ends of the antibody film 6 are connected to the characteristic detecting electrode pads 5 via the pattern 2.

The protective film 7 is made of glass such as borosilicate glass and is formed on substantially the entire surface of the substrate 1 so as to expose the electronic component mounting electrode pads 3, the output electrode pads 4, and the characteristic detection electrode pads 5. Has been done. In addition, in FIG. 1, it is shown by a dotted line.

A feature of the thick film circuit board of the present invention is that the characteristic detecting electrode pad 5 exposed to the outside has a multi-layer structure of a base conductor layer 5a and a chemically inactive coating conductor layer 5b. .. In FIG. 1, the coated conductor layer 5b is shown by a chain line.

Each of the other electronic component mounting electrode pads 3 is covered with solder on the surface of the mounting electrode pad 3 by soldering when mounting the electronic component, and the output electrode pad 4 is a lead terminal. The surface of the output electrode pad 4 is covered with the solder due to the solder bonding at the time of bonding.

As a result, in the thick film circuit board on which the electronic components are mounted and the lead terminals are joined, the wiring pattern 2 is covered with the protective film 7, and the mounting electrode pad 3 and the output electrode pad 4 are Since the wiring pattern 2, the mounting electrode pad 3, and the output electrode pad 4 are covered with the solder, it is possible to suppress changes in characteristics of the wiring pattern 2, the mounting electrode pad 3, and the output electrode pad 4 due to migration or corrosion. Further, since the surface of the characteristic detecting electrode pad 5 is also covered with the chemically inactive coating conductor layer 5b, the characteristic change due to migration or corrosion can be suppressed, and as a result, high density Even if a circuit is formed, it will be a thick film circuit board that can prevent deterioration of reliability due to moisture as in the past.

Next, a method of manufacturing the thick film circuit board of the present invention will be described.

First, a ceramic substrate 1 having a predetermined shape is prepared.

Next, on the ceramic substrate 1, the wiring pattern 2, the mounting electrode pad 3, the output electrode pad 4, and the underlying conductor layer 5a of the characteristic detection electrode pad 5 are simultaneously printed and formed according to a predetermined circuit. To do. Specifically, a silver-based thick film conductor paste or a copper-based thick film conductor paste is screen-printed and dried. Here, the silver-based thick film conductor paste is prepared by mixing a predetermined amount of silver powder, silver-palladium powder or silver-platinum powder as a conductor material, an inorganic binder, and an organic vehicle. When the silver-based thick film conductor paste is used, it is desirable to fire it in an oxidizing atmosphere in the baking step described later.

The copper-based thick film conductor paste is prepared by mixing a predetermined amount of copper powder as a conductor material, an inorganic binder, and an organic vehicle to form a paste. When the copper-based thick-film conductor paste is used, it is desirable that the copper-based thick-film conductor paste be fired in a neutral or reducing atmosphere in the baking step described later.

Next, the resistor film 6 is printed between the wiring patterns 2 on the ceramic substrate 1. In addition, the same material as that of the resistor film 6 is used to simultaneously print the covering conductor layer 5b on the underlying conductor layer 5a of the characteristic detecting electrode pad 5 in the same printing process. Specifically, a thick film resistor paste is screen-printed and dried. Here, it is necessary to select a different material for the thick film resistor paste, depending on the material of the above-mentioned conductor paste. For example, when baking with a conductive paste in a neutral or oxidizing atmosphere, metal oxide powder such as ruthenium oxide, which does not change its characteristics even in an oxidizing atmosphere, an inorganic binder, and an organic vehicle are mixed in a specified amount to form a paste. .. When baking in a neutral or reducing oxidizing atmosphere, a predetermined amount of a metal boride powder such as lanthanum boride or a metal silicide powder such as tantalum silicide, an inorganic binder and an organic vehicle are mixed to form a paste. ..

Next, the printed conductor of the wiring pattern 2, the mounting electrode pad 3, the output electrode pad 4, the characteristic detection electrode pad 5, and the resistor film 6 formed on the ceramic substrate 1 is printed. Specifically, when the wiring pattern 2 and the like are formed of a silver-based thick film conductor paste and the resistor film 6 is formed of a resistor thick film paste of a metal oxide powder such as ruthenium oxide, the temperature of 800 to 800 Bake integrally at 900 ° C. When the wiring pattern 2 and the like are formed of a copper-based thick film conductor paste and the resistor film 6 is formed of a metal boride powder or a metal silicide powder thick film resistor paste, the temperature is 800 to 900 ° C. in a reducing atmosphere. Bake together.

In the above process, the wiring pattern 2 and the like are first printed and then the resistor film 6 is printed, but the reverse process may be performed. In the baking process, the wiring pattern 2 and the resistor film 6 are baked at the same time, but the wiring pattern 2 and the like may be baked first, and then the resistor film 6 may be baked, or vice versa. Absent.

Next, the protective film 7 is formed so as to cover the wiring pattern 2. Specifically, the protective film is printed using an inorganic insulating paste containing silica glass as a main component so that only the mounting electrode pad 3, the output electrode pad 4, and the characteristic detection electrode pad 5 are exposed. And is formed by firing at about 500 ° C. In addition to the inorganic insulating paste, a thermosetting resin such as epoxy or an ultraviolet curable resin may be used.

Next, the resistance film 6 is adjusted. Specifically, a laser beam is radiated through the protective film 7 so that the width of the resistor film 6 disappears to a predetermined resistance value. At this time, the measurement probe is brought into contact with the characteristic detection electrode pads 5 connected to both ends of the resistor film 6.

Next, various electronic components such as semiconductor elements and capacitors are soldered to the mounting electrode pad 3, and lead terminals are held on the output electrode pad 4 for soldering.

In the thick film circuit board thus formed, only the characteristic detecting electrode pad 5 is exposed to the outside, and the other part, that is, the wiring pattern 2 is covered with the protective film 7, and the mounting electrode pad 3 The output electrode pad 4 is covered with solder. However, since the surface of the characteristic detection electrode pad 5 is covered with the chemically inactive coating conductor layer 5b, migration or corrosion is less likely to occur due to moisture from the outside. As a result, even if the wiring pattern 2 of the desired circuit is formed with high density, the thick film circuit board has excellent moisture resistance.

In the above-mentioned embodiment, the covering conductor layer 5b of the characteristic detecting electrode pad 5 is formed of the same material as the resistor 6, but the sheet resistance of the resistor formed from the thick film resistor paste is 10 KΩ / When the material of □ is used and the film thickness of the coated conductor layer 5b is about 10 μm, the resistance value increases only by about 10 mΩ, which is not a practical problem.

Further, as described above, the coating conductor layer 5b may be formed by a plating layer instead of being formed by the thick film resistor paste. At this time, a Ni layer of about 2 μm may be formed on the underlying conductor layer 5a of the characteristic detecting electrode pad 5 by electroless plating, and an Au layer of about 2 μm may be further formed by electroless plating.

In any case, since the coated conductor layer 5b formed of the thick film resistor paste and the coated conductor layer 5b formed of the plated layer are in an inactive state that does not change with respect to moisture, they are as described above. In addition, it greatly contributes to the improvement of the moisture resistance reliability.

Experimental Example 1 On the surface of a 5 mm square alumina ceramic substrate (A476 made by Kyocera), a copper-based thick film conductor paste (DP9153 made by DuPont) was used for the wiring pattern 2 and four 0.5 mm square electrode pads for characteristic detection. 5 was printed and fired. Then, a thick film resistor paste (DP6402 manufactured by DuPont) was printed and baked on the surface of the characteristic detection electrode pad 5. Then, printing and firing were performed using an inorganic insulating paste (QP507 manufactured by DuPont) so that only the characteristic detection electrode pad 5 was exposed.

On the thick film circuit board thus obtained, a phosphor bronze shield plate was attached so that the distance between the characteristic detection electrode pad 5 and the characteristic detection electrode pad 5 was 30 μm, and the environment was 120 ° C. and 100% relative humidity. It was left to stand below, a voltage of 5 V was applied between the electrode pad 5 and the shield plate, and a moisture resistance test was conducted for 500 hours. As a result, the insulation resistance before the test was 1000 MΩ or more, but the insulation resistance was not deteriorated even after the test.

Experimental Example 2 On the surface of a 5 mm square alumina ceramic substrate (A476 manufactured by Kyocera), a wiring pattern 2 and four characteristic detection electrode pads of 0.5 mm square were formed using a silver-based (silver-palladium) thick film conductor paste. 5 was printed and fired. After that, a protective film 7 is formed with an epoxy resin instead of the inorganic insulating paste, and after thermal curing, the surface of the characteristic detection electrode pad 5 is subjected to palladium activation, electroless Ni plating, and electroless Au plating, Moisture resistance and insulation resistance test were conducted.

As a result, the insulation resistance before the test was 1000 MΩ or more, but the insulation resistance was not deteriorated even after the test.

Comparative Example In the thick film circuit board of Experimental Example 1, a thick film circuit board in which the surface of the characteristic detecting electrode pad 5 is not covered with the thick film resistor paste is prepared, and the same moisture resistance and insulation resistance tests are performed. It was As a result, the insulation resistance before the test was 1000 MΩ or more, but after the test, the insulation resistance decreased to 12 MΩ.

In the above-mentioned embodiment, the characteristic detection electrode pad used for trimming the resistor film formed on the thick film circuit board has been described, but a crystal oscillator is mounted on the thick film circuit board. Alternatively, it can be widely used for a characteristic detection electrode pad, etc., which is mounted with a trimmer component and is brought into contact with the probe of a measuring device for adjusting the characteristic thereof.

[0042]

[Effect of the device]

 As described above, in the present invention, the surface of the resistor film that constitutes the circuit and the characteristic detection electrode pad that measures the characteristics of various electronic components are coated on the chemically inactive coated conductor layer. A thick film circuit board that does not cause migration even if the circuit has a high density and does not change its insulation resistance due to moisture and has excellent moisture resistance reliability.

[Brief description of drawings]

FIG. 1 is a partial plan view of a thick film circuit board according to the present invention.

FIG. 2 is a partial cross-sectional view taken along the line AA in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 ... Wiring pattern 3 ... Mounting electrode pad 4 ... Output electrode pad 5 ... Characteristic detection electrode pad 5a ... Base conductor layer 5b ... Coated conductor layer 6 ... Resistor film 7 ... Protective film

Claims (1)

[Scope of utility model registration request] 1. A thick film circuit board comprising a ceramic insulating substrate on which a thick film wiring pattern, an output electrode pad and a characteristic detecting electrode pad forming a desired circuit are formed, wherein the characteristic detecting electrode pad is a base layer. A thick film circuit board, comprising a conductor layer and a chemically inactive coated conductor layer.