JPH02273986A - Thick film circuit board - Google Patents

Abstract

PURPOSE:To prevent the development of cracks when manufactured and obtain a thick film circuit board which does not destroy characteristics of a conductor by providing the 2nd conductor layer which is formed so that its layer and each part on the 1st conductor layer and a resistor layer overlap each other and is low in electrode effect. CONSTITUTION:A thick film circuit board 20 is composed of: the 1st conductor layer 22 that is formed on an insulating substrate 21; a resistor layer 23 that is formed so that its layer and the 1st conductor layer 22 does not overlap each other on the insulating substrate 21; the 2nd conductor 24 that is formed so that its layer and eachpart on the 1st conductor layer 22 and the resistor layer 23 overlap each other on the insulating substrate 21. As to materials for the 1st conductor layer, it is desirable to use the materials which are superior in conductor characteristics of solder wetability, solder corrosion resistance, and the like, e. g. an Ag-pd system high temperature baking paste. As to materials for the 2nd conductor layer, it is desirable to use the materials in such a way that a baking temperature is lower than the softening temperature of resistor glass and the above materials are low in glass and metallic oxides except Ag and further, there are enough sintering of Ag and a sheet resistance value is low. The circuit board in which no breakdown, i. e. cracks and the like develop when manufactured is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thick film circuit board having a thick film hybrid IC circuit.

(Prior art) Thick film circuit boards have been known in which conductive layers, resistor layers, insulator layers, etc. are formed on a ceramic substrate such as alumina by screen printing, and the structure of the thick film circuit board is , for example, as shown in FIG.

To explain the manufacturing method of this thick film circuit board, first,
An insulating substrate made of ceramic materials such as alumina!
For example, an Ag-based conductor paste is printed on the insulating substrate l by screen printing and baked in an oxidizing atmosphere at a temperature range of 800 to 900°C to form the conductor layer 2. For example, a ruthenium oxide resistor paste 1 is printed so as to overlap with the resistor layer 3, and baked in a temperature range of 800 to 900° C. to form the resistor layer 3. Usually, a protective glass paste is printed on the conductor layer 2 and the resistor layer 3.
A protective glass layer is often formed by baking at 450 to 600°C.

In this case, the resistance value R of the resistor layer 3 is adjusted to a designed value based on the sheet resistance of the resistor paste and the shape of the resistor. For example, as shown in FIG. 3, if the length of the resistor is W and the width of the resistor is W, then when forming a resistor with a resistance value R of Ω, for example, R=10, the sheet resistance is 10 with resistance paste of Ω/mouth, L=1 mm, W=
Print and bake to a size of 1 mm. Furthermore, if fine adjustment of the resistance value is required, the adjustment is performed using a laser trimming method or the like to reach the set value.

(Problems to be Solved by the Invention) However, in the conventional thick film circuit board using the alumina insulating substrate described above, there is a problem called the shape effect of the resistor. Here, the term "shape effect" refers to the fact that the sheet resistance value of a resistor obtained by printing and baking on a substrate differs depending on the shape of the resistor. Further, as shown in FIG. 4, for example, it is generally known that the relationship between the length of the resistor and the sheet resistance value has different shape effects depending on the combination of the conductor and the resistor.

For this reason, for commercially available resistors, the shape effect may be described in the catalog data, and in this case, the user can design a pattern based on the description in the catalog data. However, in reality, since the printing conditions differ for each user, the shape effect also differs slightly, so the user has to check the shape effect with a test pattern before designing the pattern, which makes pattern design complicated. It tends to happen.

In addition, as is well known, with the miniaturization and higher performance of electronic devices in recent years, materials for thick film circuit boards are required to have higher thermal conductivity, lower thermal expansion, and lower dielectricity than alumina.
Various aluminum nitride substrates and low-temperature fired substrates (LFC substrates) have been developed as substrate materials suitable for this purpose.

However, according to experiments conducted by the present inventor, when using commercially available conductors and commercially available resistors for aluminum nitride substrates or LFC substrates, cracks occur in the resistor at the boundary between the resistor and the conductor when the resistor is baked. It has also been found that cracks are less likely to occur in the resistor when only the resistor without the conductor is printed onto the substrate.

Regarding the shape effect, the same effect was observed in the case of the aluminum nitride substrate and the LFC substrate as in the case of the alumina substrate.

Here, the two effects of the influence of the conductor on the resistor layer, such as the shape effect of the resistor and the occurrence of cracks in the resistor, are defined as "electrode effects."

The cause of the electrode effect is that when the resistor is baked, components diffuse from the conductor into the resistor, changing the quality of the resistor near the conductor and changing the electrical and thermal properties of that part. This is thought to be due to More specifically, the cause of the shape effect is A, which is the main component in the conductor.
This is thought to be due to the reaction between g and the resistor. On the other hand, the occurrence of cracks is thought to be caused by the reaction between the glass component in the conductor film and the resistor, but the conductor is
Since additives such as TiOs, glass, and transition metal oxides are essential, it is not possible to drastically reduce the amount of glass in the conductor film or to significantly change the composition.

The present invention was made in consideration of the above-mentioned circumstances, and by changing the structure of the thick film circuit board, it is possible to achieve a thickness that has almost no electrode effect, does not cause cracks during manufacturing, and does not impair the conductor properties. It is an object of the present invention to provide a film circuit board (means for solving the problem).A thick film circuit board of the present invention for solving the above problem has a first conductor formed on an insulating substrate. a resistor layer formed on the insulating substrate so as not to overlap the first conductor layer; and a resistor layer formed on the insulating substrate so as not to overlap with the first conductor layer; It is characterized by having a second conductor layer with a small electrode effect formed so as to partially overlap with the second conductor layer.

Here, the material suitable for the first conductor layer has solder wettability,
Materials with good conductor properties such as solder resistance and durable adhesive strength after soldering, such as Ag-Pd series, Ag-
It is desirable to use a high-temperature baking paste that is Pt-based and has a baking temperature of 800-B.

A material suitable for the second conductor layer has a baking temperature lower than the softening temperature of the resistor glass (for example, 650°C or lower), contains as little glass or metal oxides other than Ag as possible, and has a
It is desirable to use a material in which g and glass components are difficult to diffuse, Ag is sufficiently sintered, and the sheet resistance value is sufficiently low (for example, 20 mΩ/mouth or less).

Note that a protective glass paste is printed on the first conductor layer, second conductor layer, and resistor layer, and heated at 450 to 600°C.
Of course, the protective glass layer may also be formed by baking.

(Example) The present invention will be explained in detail below based on the drawings.

The basic structure of the thick film circuit board of the present invention is as shown in FIG. 1st to
The resistor layer 2 is formed so as not to overlap the conductor layer 22 of
3, and a second conductor layer 24 having a small electrode effect, which is formed on an insulating substrate 21 so as to overlap a part of the first conductor layer 22 and a part of the resistor layer 23.

A thick film circuit board with such a structure was tested in comparison with a conventional one. The materials used in the Examples and Comparative Examples of the present invention are common and are as shown below.

(2) The "insulating substrate" is a low-temperature fired substrate mainly composed of alumina, and its thermal expansion coefficient is 5.3x I O-6/''C in the temperature range from room temperature to about 500°C.

■The "first conductor" has a weight ratio of Ag:Pd=85=1
It is an Ag-Pd based conductor whose main components are Ag and Pd, and additives such as pbo-BzO, -S+O, ZnO-based glass, BitOs, ZnO3 and a trace amount of transition metal oxide are added to the metal in total. This material contains approximately 10 wt% of the components. By baking this material onto a substrate at 850° C., good conductor properties (solder wettability, solder breakage resistance, durable adhesive strength after soldering, 5 low wiring resistance) can be obtained.

■The "second conductor" is a commercially available Δg conductor with low-temperature baking specifications, and the baking temperature is 500 to 600℃ specified by the manufacturer.
The composition is a material in which approximately 7% lead borosilicate and BiaO+ are added to Ag l 00, and this material is
By baking at 600°C, the sheet resistance becomes 10 mΩ/hole. However, it is unsuitable for areas where solder is used, as it has a high solder resistance.

■The “resistor” is composed of conductive particles of P b* Ru20t-x (pyrochlore) and Ru Oa and pbo-si
Ox -B20s is a mixture of Aβgo3 glass, and the ratio of conductive particles to glass is 20=80 in terms of weight ratio. The baking temperature is 850°C.

■“Protection glass” is P bo Si Ox
B203-Aβ203 glass, baking temperature 60
It is 0°C.

The test results are as shown in Table 5.

(Hereinafter, blank spaces) Table 1 In Table 1, Comparative Examples 1 to 4 belong to the prior art, and Examples 1 and 2 belong to the present invention.

Philippines JLi special.”

As shown in FIG. 5, the structure of the thick film circuit board of Comparative Example 1 was such that a first conductor component was printed on a substrate 51 and baked at 850° C. to form a first conductor 52. Next, a resistor component was printed and baked in the same manner to form a resistor 53.

As a result of observing the obtained io thick film circuit boards, it was found that resistor 2
Cracks occurred in 3S out of 00 resistors.

As shown in FIG. 6, the structure of the thick film circuit board of Comparative Example 2 was such that a resistor component was printed on a substrate 61 and baked at 850° C. to form a resistor 62. . Next, the second conductor component is printed and baked at a low temperature of 600°C to form the second conductor 6.
3 was formed. Next, a protective glass component was printed so that a part of the second conductor 63 was exposed, and baked at 600° C. to form a protective glass 64.

When the obtained thick film circuit board was immersed in a solder bath at 235°C for about 5 seconds, the solder cracked significantly.

It turned out that it was not practical.

In the structure of the thick film circuit board of Comparative Example 3, as shown in FIG. Next, the first conductor component is printed and baked at 850°C.
A conductor 73 was formed.

As a result of observing the obtained 10 thick film circuit boards, it was found that resistor 2
Cracks had occurred in all of the 00 resistors.

1 School Plate-1 As shown in FIG. 8, the structure of the thick film circuit board of Comparative Example 4 was such that a resistor element 82 was formed by printing a resistor component on a substrate 81 and baking it at 850°C. . Next, the second conductor component is printed and baked at 850°C.
A conductor 83 was formed.

As a result of observing the obtained 10 thick film circuit boards, it was found that resistor 2
Cracks occurred in 41 out of 00 resistors.

The structure of the thick film circuit board of Example 1 is as shown in FIG. By doing so, the first conductor 9
2 and resistor 93 were formed at the same time. Next, a second conductor component was printed and a second conductor 94 was formed by low temperature baking at 600°C. Next, a protective glass component was printed so that a portion of the first conductor 92 was exposed, and a protective glass 95 was formed by baking at 600°C.

The characteristics of this thick film circuit board were good as shown in Table 1.

The structure of the thick film circuit board of Example 2 of Oiho Ri-Yu is as shown in FIG. In this way, the first conductor 92 and the resistor 93 were formed at the same time. Next, the second conductor component and the protective glass component were sequentially printed, and the second conductor 94 and the protective glass 95 were simultaneously formed by simultaneous baking at 600°C.

This property was good as shown in Table 1.

(Effects of the Invention) As explained above, according to the thick film circuit board of the present invention,
Since the circuit board structure has a configuration that does not impair conductor properties and does not cause shape effects, the resistance value can be designed without taking shape effects of the resistor into consideration, simplifying the design of the resistor pattern. Moreover, there is an effect that damage such as cracks does not occur in the resistor during manufacturing.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing the structure of a thick film circuit board according to an embodiment of the present invention, FIG. 2 is a schematic sectional view showing a thick film circuit board for explaining a conventional example, and FIGS. 3 and 4 5, 6, 7, and 8 are schematic cross-sectional views showing the structure of a thick film circuit board belonging to the prior art, and FIGS. 9 and 10 are diagrams for explaining a conventional example, respectively. 1 is a schematic cross-sectional view showing the structure of a thick film circuit board according to an embodiment of the present invention. 20... Thick film circuit board, 1... Insulating substrate, 22... First conductor layer, 23... Resistor layer, 24... Second conductor layer.

Claims (1)

[Claims] (1) A first conductor layer formed on an insulating substrate, a resistor layer formed on the insulating substrate so as not to overlap the first conductor layer, and a resistor layer formed on the insulating substrate so as not to overlap the first conductor layer. A thick film circuit board comprising a second conductor layer with a small electrode effect formed so as to overlap a part of the conductor layer and a part of the resistor layer.