JPS62276437A - Evaluation of thick film material - Google Patents

Abstract

PURPOSE:To certainly evaluate adaptability, by a method wherein a thick film material is applied to a glass substrate having coefficient of heat expansion almost the same to that of a ceramic substrate and baked while the residual stress generated between the glass substrate and the baked thick film is measured according to a photoelastic method. CONSTITUTION:In place of a ceramic substrate to which a thick film material is adapted, a transparent glass substrate 8 having coefficient of heat expansion almost same to that of the ceramic substrate is used as a substrate. The thick film material 9 is applied to the glass substrate 8 and baked under the same condition as a case performing baking on the ceramic substrate and the residual stress generated between the glass substrate 8 and the baked thick film material 9 is measured according to a photoelectric method. That is, if there is residual stress in a specimen 6, internal strain is generated in glass and, as the result of the double refraction of light due to said internal strain, phase difference is generated and light is polarized and a part of light passes through an analyser to allow an interference fringe 7 to appear. The position of the interference fringe 7 is largely affected by the internal stress.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for evaluating the compatibility of thick film materials such as conductors, resistors, dielectrics, etc. with ceramic substrates.

[Conventional technology]

Thick film materials such as conductors, resistors, and dielectrics are used in hybrid integrated circuits and individual passive devices. These thick film materials are made by kneading powders of conductive materials, resistive materials, dielectric materials, etc. and glass powder with an organic vehicle to form a paste.The materials are applied onto a ceramic substrate by screen printing, transfer, etc. However, by firing at a temperature of 750 to 950°C, a conductive film, an abrasive film, and a dielectric film can be formed on the ceramic substrate.

The reason why glass powder is mixed into the above-mentioned thick film material is to fix the ceramic substrate and films such as conductors, resistors, dielectrics, etc. Therefore, this glass powder needs to be sufficiently softened at the firing temperature, and those having a softening point of about 430 to 600°C are selected for use.

The glass powder must also be compatible in coefficient of thermal expansion with the ceramic substrate to which it is applied.

This is because if the coefficient of thermal expansion is too different from that of the ceramic substrate, the fired film may peel off. Therefore, the glass powder used for thick film materials has a coefficient of thermal expansion of 60 to 80 x 1
A value of about 0-'/'c is selected.

However, even though the softening point and thermal expansion coefficient of the glass powder are selected in this way, the characteristics of the fired film may change over time. For example, if soldered onto a conductor film and left at around 150°C, the adhesion strength between the conductor film and the ceramic substrate may decrease, or the resistance film may be damaged by laser (L).
(ASER) cant, the resistance value may increase over time. The reason for this change in properties is that other additives of the thick film material mix into the glass interposed between the ceramic substrate and the fired film, changing the composition, increasing the difference in thermal expansion coefficients, and causing residual stress. This is thought to be due to an increase in This residual stress can be easily measured by some means.

[Problem that the invention seeks to solve]

The present invention was made in view of the above circumstances, and provides a method for evaluating the compatibility of a thick film material and a ceramic substrate to which the material is applied.

[Means for solving problems]

To achieve this objective, the method of the present invention uses a transparent glass substrate as a substrate, which has a coefficient of thermal expansion similar to that of the ceramic substrate, instead of a ceramic substrate to which a thick film material is applied, and A thick film material is applied to the ceramic substrate, and this is fired under the same conditions as when firing on a ceramic substrate.
The method is characterized in that the residual stress generated between the glass substrate and the fired thick film is measured by a photoelastic method.

In the method of the present invention, the coefficient of thermal expansion of the glass substrate only needs to be comparable to that of the ceramic substrate to which the thick film material is applied, and does not necessarily have to be the same.

This is because if there is a slight difference, the measurement results of residual stress can be corrected by extrapolation. However, the difference in thermal expansion coefficient between the glass substrate and the ceramic substrate is 10X 10-'/”C
It is desirable to keep it within the range. If the stress is larger than this, the residual stress may cause cracks in the glass substrate or fired thick film, making accurate stress measurement impossible. It goes without saying that the glass substrate needs to have a softening temperature higher than the firing temperature.

Such a glass composition is 5iOz, Al2O2, B
z03゜It can be easily obtained by changing the blending ratio of BaO, CaO, NazO, etc., but it is necessary to ensure that there are no non-uniform substances such as bubbles, striae, and undissolved substances in the glass, and that sufficient annealing (de-straining) is performed after solidification. ) is necessary.

This is because the presence of non-uniform objects and the presence of solidification strain affect the residual stress measurement results.

The appropriate thickness of the glass substrate is about 1 to 3 mm.

This is because if the thickness is too large, the thick film material may crack during firing.

After coating and firing the thick film material on the glass substrate, cut the glass substrate across the fired film to a certain width, and mirror-polish the cut surface of the cut piece, or polish the cut surface to the same refractive index as the glass substrate. The sample is placed in an immersion solution and subjected to the photoelastic method. The thickness of this sample (cut width) may be about 0.5 to 1 mm.

Residual stress can be measured by the photoelastic method using an optical system as shown in FIG. This optical system consists of a light source 1, a monochromatic filter 2, a polarizer 3, a 174 wavelength plate (or sensitive color plate) 4, and an analyzer 5, and a sample 6 is placed between the polarizer 3 and the 1/4 wavelength plate 4. In this state, if the polarization planes of the polarizer 3 and analyzer 5 are made perpendicular to each other, if there is no residual stress in the sample 6, it will be taken out from the optical analyzer 5.
Even when looking at the sample 6 from the analyzer 5 side, it is a dark field.

However, if there is residual stress in the sample 6, internal strain will occur in the glass, and this internal strain will cause the light to become birefringent, resulting in a phase difference and polarization, with some of the light passing through the analyzer 5 as shown in Figure 2 ( Interference fringes 7 as shown in A) appear. The position of the interference fringes 7 depends on the magnitude of the internal distortion, and is convex on the dough with greater distortion. The maximum distance from the interface between the glass substrate 8 and the thick film 9 at the center of the interference fringes 7 is tarp John R [μm], and by setting this R to 4111, the photoelastic constant C (mu / can/ kg/
cut) and the wall thickness of sample 6 (i.e. optical path length) t (
The residual stress σ (kg/ant) can be calculated from the following equation:

R - □ □ t This retardation R can be measured by shining the light passing through the analyzer 5 onto a blank sheet of paper. It is easy to determine this from the rotation angle θ required to rotate the interference fringes and move them almost to the interface between the glass substrate 8 and the thick film 9 as shown in FIG. 2(B). In this case, the retardation R is proportional to the rotation angle θ, and can be calculated by R=k·θ. k varies depending on the wavelength of the light used, but
This is a constant that can be determined experimentally if the wavelength is determined in advance.

〔Example〕

5iOz 55.0, ^1z0314.5. Bz
(hl 1.5゜BaO8.4, Ca0 6.0 +N
A glass having a composition of 4.6% by weight az0 was used as a substitute for the alumina substrate.

The coefficient of thermal expansion of this glass is 65xlO-'/”c (5
0~300℃) and 71 x 10-' of alumina
/'c (40-400°C), which is very close to that. This glass was formed into a plate shape of 25 cm square and 2 cm thick. Ag-Pd thick film conductive paste was screen printed in a 7 square pattern on the center of the glass substrate, and after baking at 850°C, the glass The substrate was cut at intervals of 0.75 μl, and the cut surfaces were polished to prepare samples for the photoelastic method.

After immersing the thick film side of this sample in a Pb-Sn eutectic solder bath for 15 seconds and soldering, one piece was left as is, and the other pieces were soldered.
The samples were placed in a thermostat at 50°C and aged for 25, 50°, 75, and 100 hours, and how the residual stress changed was investigated using a photoelastic method. As a result, the weight was 35 kg/cnl at 0 hours of aging, but after 25 hours, 200.50 hours, and 300.75 hours, it was 1
70. After 100 hours, it was the same < 170 kg/cJ. This result suggests that it was. This result can well explain the phenomenon that when an Ag--Pd based thick-film conductive paste is coated on an alumina substrate, baked, and then soldered to a wing electrical film, the adhesion strength is significantly reduced due to aging.

This shows that the method of the present invention is an extremely effective means for evaluating the compatibility of thick film materials with ceramic substrates.

〔Effect of the invention〕

The method of the present invention has made it possible to reliably evaluate the compatibility of thick film materials with ceramic substrates, and has provided an effective means for developing and improving thick film materials.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical system for photoelasticity measurement, and FIG. 2 is a diagram showing interference fringes that occur when there is residual stress between a thick film and a glass substrate. 1... Light source, 2... Monochromatic filter, 3... Polarizer, 4... 174 wavelength plate (or sensitive color plate), 5...
・Analyzer, 6...sample. Patent applicant: Sumitomo Metal Mining Co., Ltd. Figure 1 (polarized light) Figure 2

Claims (1)

[Claims] A thick film material is coated and fired on a glass substrate having a coefficient of thermal expansion comparable to that of a ceramic substrate, and the residual stress generated between the glass substrate and the fired thick film is measured by a photoelastic method. Evaluation method for membrane materials.