JPH05251837A - Circuit board - Google Patents

Abstract

PURPOSE:To prevent the generation of a crack and a cutaway in the peripheral edge of a glass insulating layer by a method wherein the crystalline glass layer is formed on the side more inner than the peripheral edge of an amorphous glass layer. CONSTITUTION:An amorphous glass layer 2 and a crystalline glass layer 3 are formed in order on the surface of a metal substrate 1. At this time, the layer 3 is formed in such a way that it is formed on the side more inner than the peripheral edge of the layer 2. By such a way, the generation of a crack and a cutaway in the peripheral edge part of the layer 3, which are caused by a heat history due to heating at the time of formation of the layer 3 on the layer 2 or heating and cooling in the forming process of a conductor layer subsequent to the formation of the layer 3, can be effectively prevented. Moreover, it is desirable that the distances (d and d') between the peripheral edge of the layer 2 and the peripheral edge of the layer 3 are apart by 50mum or above, preferably 100mum or above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel circuit board whose surface is covered with a glass insulating layer. Specifically, it is a circuit board having extremely high reliability with respect to crack resistance of the glass insulating layer formed on the surface of the metal substrate.

[0002]

2. Description of the Related Art Metallic substrates such as iron and aluminum are sometimes used for the purpose of improving the mechanical and physical strength of a circuit substrate using a ceramic substrate.

A circuit board using the above-mentioned metal substrate is generally provided with a glass insulating layer on the metal substrate in order to prevent a short circuit between the wiring patterns when forming a wiring pattern on the surface thereof. For example, Japanese Patent Publication No. 269396/1987 discloses a circuit board having a glass insulating layer formed on the surface of an iron alloy substrate containing aluminum.

However, in a conventional circuit board in which a glass insulating layer is formed on a metal substrate, for example, the insulating layer is made of SiO.
_When an amorphous glass containing ₂ as a main component is used, the glass layer is formed by heating a wiring pattern formed on the surface of the glass insulating layer and then laminating an insulating layer, a wiring pattern, etc. on the pattern. It is not suitable for high-density wiring because it melts easily. Further, the result of the beeling strength test method for evaluating the adhesiveness between the wiring pattern and the glass insulating layer has a drawback that the adhesive strength is weak.

The inventor of the present invention forms a surface of a glass insulating layer provided on a metal substrate in contact with the metal substrate with amorphous glass, and stacks the other surface of the amorphous glass layer with crystalline glass, We have proposed a circuit board with excellent crack resistance against temperature changes, adhesion of conductors, etc., and a highly reliable wiring pattern.

[0006]

However, in the above-mentioned circuit board, when the thickness of the crystalline glass formed on the upper portion of the amorphous glass layer is increased, when the crystalline glass layer is formed, The heating at the time of forming a wiring pattern or the like on the surface of the crystalline glass layer has a drawback that cracks or glass loss due to the cracks occurs at the peripheral edge of the insulating glass to be formed, and the wiring pattern is fatally damaged. That is,
The thickness of the glass insulating layer in the sense of insulating the metal from the conductor governs the insulating layer between the conductor layer such as the wiring pattern formed on the metal layer and the metal substrate, and in the above circuit board, is sufficient. In order to maintain the insulating property, it may be necessary to form the crystalline glass with a thickness of approximately 20 to 30 μm. However, when the crystalline glass layer having such a thickness is formed so as to completely cover the entire surface of the amorphous glass layer, cracks easily occur at the periphery of the formed glass insulating layer having a two-layer structure. I understood it. Also,
This phenomenon occurs even when exposed to a heating step from room temperature to high temperature (800 to 1000 ° C.) in forming the conductor and resistor after forming the glass insulating layer. Furthermore, in the production of a circuit board that requires two conductor layers, the crystalline glass layer needs to be made thicker, and cracks are inevitable at the peripheral edge thereof.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies to solve the above problems in a circuit board in which a metal substrate is covered with a glass insulating layer composed of an amorphous glass layer and a crystalline glass layer. It was As a result, it was found that by forming a crystalline glass layer laminated on the upper portion of the amorphous glass layer on the inner side of the peripheral edge of the amorphous glass layer, cracks / missing at the peripheral edge of the glass insulating layer can be prevented, and the present invention is achieved. It came to completion.

The present invention will be specifically described below with reference to the accompanying drawings, but the present invention is not limited to these drawings. FIG. 1 is a plan view showing a typical aspect of the circuit board of the present invention, and FIG. 2 is a side view thereof.

The circuit board of the present invention comprises an amorphous glass layer 2 and a crystalline glass layer 3 which are sequentially formed on the surface of a metal substrate 1, and the crystalline glass layer 3 is formed from the periphery of the amorphous glass layer 2. It is a circuit board characterized by being formed inside.

In the present invention, the material of the metal substrate 1 is not particularly limited, and known materials can be used without limitation. For example, iron, titanium, copper, nickel, chromium,
A metal such as aluminum or an alloy composed of these metals is preferably used. Among these materials, an iron alloy containing aluminum is generally used.

The glass constituting the amorphous glass layer 2 is not particularly limited as long as it is amorphous and has an insulating layer, and a known composition is used without particular limitation.
Generally, insulating glass containing 30% by weight (wt%) or more, preferably 45% by weight or more of an amorphous component is preferably used. A typical composition is, for example, SiO ₂ as a main component and Al ₂ O ₃ , CaO, PbO, Ba.
O, silicate glass was formulated with ZnO or the like; PbO-B ₂ O
Lead borate glass containing ₃ as a main component and SiO ₂ , ZnO, CaO or the like mixed therein; Na ₂ O-CaO-SiO ₂
Is a main component, soda lime glass in which MgO, PbO and the like are mixed, Na ₂ O-B ₂ O ₃ -SiO ₂ as a main component, and PbO, ZnO, Al ₂ O _{3 and the} like in this borosilicate acid _{glass, CaO-MgO-Al 2 O} 3 -S
Examples include aluminosilicate glass containing iO ₂ as a main component and Na ₂ O or the like mixed therein. In the glass containing SiO ₂ as a main component among the above glass compositions,
The ratio of ₂ is preferably 30 wt% or more, particularly 40 to 70 wt%.

The glass constituting the crystalline glass layer 3 is not particularly limited as long as it exhibits crystallinity and has an insulating property, and a known composition can be used without limitation. Generally, the oxide frit is at least 25% by weight, preferably 3
Insulating glass containing 5 to 60 wt% is preferably used. As typical examples of the components, Al ₂ O ₃ , ZrO ₂ , CaO, PbO, Ti can be added to the above-mentioned amorphous glass.
A glass containing at least one oxide frit selected from O ₂ and BaO is preferable.

The greatest feature of the present invention is that the crystalline glass layer 3
Are formed inside the peripheral edge of the amorphous glass layer 2. That is, by adopting such a structure, the crystal due to the heat history due to the heating during the formation of the crystalline glass layer 3 on the amorphous glass layer 2 or the heating and cooling in the step of forming the conductor layer after the formation of the crystalline glass. It is possible to extremely effectively prevent the occurrence and cracking of cracks at the peripheral portion of the high quality glass layer.

In the present invention, if the crystalline glass layer 3 is formed inside the peripheral edge of the amorphous glass layer 2, the above effect is exhibited, but it is particularly preferable that the crystalline glass layer 3 extends from the peripheral edge of the amorphous glass layer. Distance (d, d ') to the periphery is 50 μm
As described above, it is desirable that they are separated by 100 μm or more.
The peripheral edge of the crystalline glass layer does not necessarily have to be parallel to the amorphous glass layer, and it is not necessary to have the same distance in all the portions. If the distance is shorter than 50 μm,
The formation thickness of the crystalline glass layer is a practical thickness, generally,
When the thickness is 20 μm or more, a crack is generated in the peripheral edge of the crystalline glass layer during the formation of the layer, the formation of the conductor layer in the next step, and the subsequent formation of the resistor, and the conductor pattern is damaged or missing. Tend.

The distance from the peripheral edge of the amorphous glass to the peripheral edge of the crystalline glass is determined in consideration of the adhesion between the amorphous glass and the metal, the difference in the coefficient of thermal expansion between the glass and the metal, and the conductor pattern. It is preferable to limit the amount to the minimum level that does not hinder the formation of

In the present invention, the amorphous glass layer has a difference in coefficient of thermal expansion of 6 × 10 ⁻⁶ / ° C. or less with respect to the metal substrate.
The crystalline glass layer is preferably used by adjusting its composition so that the difference in coefficient of thermal expansion from the amorphous glass layer is 4 × 10 ⁻⁶ / ° C. or less.

The adjustment of the coefficient of thermal expansion can be performed by adding an oxide of an alkali metal such as Na, K or Li to the glass composition.

The method of manufacturing the circuit board of the present invention is not particularly limited, but the following method can be mentioned as a representative manufacturing method.

That is, an amorphous glass paste is applied onto a metal substrate by a screen printing method, dried, and baked to form an amorphous glass layer, and then the crystalline glass paste is similarly amorphous. A method is preferred in which a crystalline glass layer is formed by printing and coating the inside of the periphery of the glass layer, and then drying and baking. Further, a method of forming an amorphous glass layer by the above method, then sprinkling the above oxide frit powder evenly on the surface of the layer, and then firing to form a crystalline glass layer on the surface is also adopted. it can. In this case, coating such as masking is applied so that the amorphous glass layer is exposed.

As the firing temperature, a temperature at which the crystalline glass having the above composition can be crystallized is adopted. Generally 700
A temperature of ˜1,100 ° C. is suitable. In addition, before forming the amorphous glass layer, it is preferable to activate the surface of the metal substrate in order to improve the adhesion of the glass layer to the metal substrate. As this activation treatment, a known treatment method is adopted without particular limitation. For example, an iron-based metal substrate is treated at 600 ° C. to 1,300 ° C. for 5 to 20 minutes in a decomposition gas of NH ₃ , or 600 ° C. to 1,200 ° C. in air or N ₂ gas. The treatment method is preferably such that an active layer is formed on the surface of the substrate by treating the substrate for 5 to 20 minutes.

For forming the wiring pattern on the circuit board of the present invention, known means can be adopted without particular limitation. For example, a wiring pattern forming method such as a transfer method, a vapor deposition method or a sputtering method is preferable in addition to the screen printing method which has been generally used conventionally.

[0022]

[Effect] As can be understood from the above description, the circuit board of the present invention has the characteristics of excellent moisture resistance and adhesion strength with a conductor, and has a practical thickness of a crystalline glass layer on a metal substrate. Even in the case of forming in a crack, it is possible to prevent cracks or damage / loss due to cracks. Therefore, the wiring pattern can be formed on the circuit board with extremely high reliability.

[0023]

EXAMPLES Examples will be shown below in order to more specifically describe the present invention, but the present invention is not limited thereto. In the examples and comparative examples, the crack resistance test, conductor adhesion strength test, and moisture resistance test were carried out by the following methods.

A) Crack resistance test A circuit board having 10 conductor patterns prepared by the same method is placed in a batch furnace stable at 800 ° C. for 30 minutes, and then placed in water left at room temperature. With this as one cycle, the appearance inspection after 10 cycles was carried out by a microscope to confirm whether or not cracks and peeling were generated at the periphery and inside of the crystalline glass layer, and the ratio was shown as normal.

B) Conductor Adhesive Strength Test 0.6φS on a 2 × 2 mm conductor pattern printed on the insulating glass layer of 10 circuit boards prepared by the same method.
After soldering the n-plated conductor, pull it in the direction of 90 degrees,
The peel strength was measured for each circuit board.

The conductor pattern is formed by depositing 80% silver and 2 palladium on the crystalline glass layer of the circuit board.
A thick film conductor pattern having a ratio of 0% was screen-printed, dried at 150 ° C. for 15 minutes, and then baked at 850 ° C. for 10 minutes in the air to be formed. The peel strength was measured after repeating firing at 850 ° C. for 10 minutes 5 times in order to simulate the firing substrate in a process similar to that of the actual circuit board.

C) High-temperature and high-humidity load test A circuit board on which a conductor pattern is formed is subjected to 85 ° C. and 85% R
Apply a bias of DC15V at high humidity of H, and
Insulation resistance was measured after being charged for 0 hours.

Example 1 A metal substrate made of heat-resistant steel containing aluminum was heat-treated in nitrogen at 900 ° C. for 10 minutes, and then an amorphous glass A having the composition shown in Table 1 was applied by screen printing.
After heating and drying at 850 ° C. for 15 minutes, it was baked in air at 850 ° C. for 10 minutes to form a 30 μm amorphous glass layer.

[0029]

[Table 1]

Next, a crystalline glass B having the composition shown in Table 2 is placed on the upper portion of the above-mentioned amorphous glass layer at a distance (d, d ': d = d') shown in Table 3 inside the peripheral edge of the glass A. After opening, printing, drying and firing were carried out under the same conditions as for glass A to form a crystalline glass layer having a thickness shown in Table 3 to obtain a circuit board. Table 3 shows various test results of the obtained circuit board. By forming the crystalline glass within 50 μm from the peripheral edge of the amorphous glass, cracks at the peripheral edge of the crystalline glass layer could be suppressed even when the thickness of the crystalline glass was increased.

Further, in Table 3, No. 2-8 circuit boards,
In the conductor adhesive strength test, no cracks were found in the peripheral portion and the central portion of the crystalline glass layer even after the heat history for forming the conductor pattern.

[0032]

[Table 2]

[0033]

[Table 3]

Example 2 A circuit board was obtained in the same manner as in Example 1 except that the amorphous glass A and the crystalline glass B used had the compositions shown in Tables 4 and 5, respectively.

[0035]

[Table 4]

[0036]

[Table 5]

Table 6 shows the results of various tests on the obtained circuit board.

[0038]

[Table 6]

Further, No. 1 in Table 6 above. In the circuit board Nos. 1 to 7, no cracks were observed in the peripheral edge portion and the central portion of the crystalline glass layer even after the heat history for forming the conductor pattern in the conductor adhesive strength test.

[Brief description of drawings]

FIG. 1 is a front view showing a typical embodiment of a circuit board of the present invention.

FIG. 2 is a side view of FIG.

[Explanation of symbols]

1 Metal Substrate 2 Amorphous Glass Layer 3 Crystalline Glass Layer d, d'Distance from Amorphous Glass Layer Edge to Crystalline Glass Layer Edge

Claims (1)

[Claims] A circuit board, characterized in that an amorphous glass layer and a crystalline glass layer are sequentially laminated on a surface of a metal substrate, and the crystalline glass layer is formed inside a peripheral edge of the amorphous glass layer.