JPH0297687A - Production of enameled substrate - Google Patents

Abstract

PURPOSE:To obtain an enameled substrate having high adhesive strength between the enamel coat and metal core by forming an oxide coating film on a metal core of an Fe-Ni-Cr alloy, immersing the core in a slurry contg. dispersed frit having a specified compsn., electro-depositing the frit and carrying out calcining. CONSTITUTION:An oxide coating film of 100Angstrom -5mum thickness is formed on a metal core consisting of Fe, 35-50wt.% Ni and 4-10wt.% Cr. The core is immersed in a slurry prepd. by dispersing frit contg. BaO, SiO2, MgO and B2O3 in an org. solvent and the frit is electro-deposited on the core by electrophoresis. Calcining is then carried out at a high temp. The resulting enamel coat bonds firmly to the surface of the metal core through the oxide coating film having satisfactory adhesion and an enameled substrate having superior adhesion and a low coefft. of thermal expansion is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a method of manufacturing a printed circuit board in which the surface of a metal substrate is enameled.

<Conventional technology> Enamel substrates are particularly easy to increase in size, are less expensive than ceramic substrates, are easier to process and mold, and have better heat dissipation than ordinary ceramic substrates (alumina). Since then, it has been used in various fields in recent years.

Conventional enamel substrates are made by coating the surface of a metal core such as iron, copper, or aluminum with crystalline glass or the like, and then printing and firing a metal glaze resistor to form a circuit pattern.

<Problems to be solved by the invention> However, when an IC package with a semiconductor element is mounted on the surface of such a conventional enamel substrate, or a bare IC chip is directly mounted, the metal core Because the coefficients of thermal expansion of the materials used, such as iron, aluminum, and copper, are large, the solder joints with the IC package and the IC chip itself may peel or crack due to thermal stress caused by heating and cooling. It was inevitable.

Therefore, in order to solve the problem caused by the difference in the coefficient of thermal expansion (α), IC packages or bare ICs are attached to the metal core.
Attempts have been made to use a FeNi-Cr alloy with a small α that matches the α of the chip.

However, since such Fe-Ni-Cr alloys have excellent high-temperature oxidation resistance, they have a problem in that strong adhesion between the enamel coating layer and the metal core cannot be obtained at the firing temperature.

Therefore, as a method to eliminate this drawback, attempts have been made to roughen the surface by pickling or blasting to improve adhesion. However, this method requires a lot of effort due to pickling and blasting, and also has the problem that the smoothness of the metal core is lost and that large substrates are prone to warping.

The present invention provides a method for manufacturing an enamel substrate that solves the problems of the conventional techniques.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the present inventors have conducted intensive research and found that F has excellent high-temperature oxidation resistance and has a small coefficient of thermal expansion.
A metal core of e-Nt-Cr alloy is coated with a metal core of 100 Å to 5 μ in advance.
An oxide film of m is provided, and it is coated with BaO.

5in2. A frit of crystallized glass containing MgO and B201 is immersed in a dispersed slurry, electrophoretically deposited using electrophoretic electrodeposition, and then fired at a high temperature. The present invention was completed based on the discovery that an enameled enamel substrate having strong adhesion between the two layers can be obtained.

Function> The metal core used in the present invention has excellent high-temperature oxidation properties, and
Fe-N1 (35 to 50
-Cr (4 to 10% by weight), and the method for forming the oxide film is hydrogen (H2
) and water vapor, but generally, methods that involve adjusting the atmosphere have the problem of high costs.
Usually, a method is preferably used in which the oxide film is formed in the atmosphere to a thickness of 100 Å to 5 μm.

Here, the reason why the thickness of the oxide film is limited to 100 Å to 5 μm is that if there are fewer than 100 people, the effect of improving adhesion will be weak;
This is because if it exceeds this, floating rust is likely to occur, and on the contrary, adhesion is reduced and peeling is likely to occur.

In this way, Fe-N1 (35-50% by weight) -C
r (4 to 10% by weight) on the surface of a metal core with a thickness of 100 Å.
The oxide film formed to a thickness of ~5 μm has excellent adhesion to the metal core of the base material.
, Stow, When crystallized glass containing MgO and B2O3 is immersed in a slurry dispersed in an organic solvent such as isopropanol and subjected to electrophoretic electrodeposition, it can be uniformly electrodeposited without causing any electrodeposition problems. .

In addition, by applying the conventional method to the coated object after electrodeposition, a strong bond can be obtained with the enamel coating layer through the highly adhesive oxide film formed on the surface of the metal core. , an enamel substrate with excellent adhesion and a small coefficient of thermal expansion can be obtained.

<Example> The content of the present invention will be specifically explained below with reference to Examples.

Using a metal core of Fe-Ni-Cr alloy having a small coefficient of thermal expansion and having the composition of Examples 1 to 4 shown in Table 1, it was heated to 900°C in the atmosphere to form an oxide film, which was assumed to be Fe2O. The surface was oxidized to a thickness of 200 Å to 3 μm.

Next, when electrodeposition was performed in a slurry in which BaO-Mg0-B, 0l-5iOz-based crystallized glass frits (maximum particle size 30 μm or less) were dispersed to a thickness of about 200 μm after firing, the surface was rough. A coating layer with a smooth surface free of cracks was obtained. Next, this was fired in a continuous furnace at a maximum temperature of 850°C, and an enameled substrate with a smooth surface without surface defects was obtained.

We conducted an electrodeposition test on these according to JIS R4301, and after mounting the IC package, we tested them at -15°C.
A thermal cycle test was conducted 1,000 times in a temperature range of ~150°C to check for cracks in the joints. Table 1 summarizes these results and the results of examining the thermal expansion coefficients before and after the formation of the enamel layer. Separately, for comparison, oxide films were formed on the metal cores of Comparative Examples 1 to 5 in Table 1 at a thickness of 100 Å or less and 10 μm or more, which are outside the appropriate range of the present invention, and electrodeposited and fired in the same manner as in the examples. The characteristics of the obtained substrate were evaluated in the same manner as in the examples. The results obtained are shown in Table 1.

As is clear from these results, in Examples 1 to 4 of the present invention, the metal core with a small coefficient of thermal expansion had a thickness of 200 Å to 3 μm.
An oxide film of BaO-MgO-820 is provided on the surface.
A substrate made by electrodepositing and firing 3-3i02 series crystallized glass lift has excellent adhesion and has a small overall coefficient of thermal expansion, so even when an IC package is mounted on it, the IC can be easily removed by heat cycles. It can be seen that there are no problems such as cracking or peeling at the solder joint with the package.

On the other hand, when the thickness of the oxide film is 100 Å or less as in Comparative Example 1.2, or when the appropriate thickness is 5 μ as in Comparative Example 3,
It can be seen that sufficient adhesion cannot be obtained when the oxide film is formed in a thickness greater than m.

<Effects of the Invention> As detailed above, according to the method of the present invention, a metal core having a low expansion coefficient and excellent high-temperature oxidation property can be produced using an extremely simple method without causing any electrodeposition problems.

MgO, B! Since it is possible to form a coating layer of crystallized glass containing SiO□ with excellent adhesion, it is possible to mount an IC package on a substrate or use it by directly mounting an IC chip. It has high utility value.

Agent Patent Attorney Mamoru Takeuchi

Claims (1)

[Claims] (1) Fe-Ni (35-50% by weight)-Cr (4-1
0% by weight) on the surface of a metal core with a thickness of 100 Å to 5 μ
After forming an oxide film of m, BaO, SiO_2, MgO
, B_2O_3 is immersed in a slurry in which a frit of crystallized glass containing B_2O_3 is dispersed, electrodeposited by electrophoretic electrodeposition, and fired.