JPH05136565A - Thick-film multilayer ceramic board - Google Patents

Abstract

PURPOSE: To prevent the generation of unwanted conduction between lower inner conductive layers, even under a load of thermal stress on a thick film multilayer ceramic substrate by forming a solder layer with a screen printing glass ceramic C paste on the region which is surrounded by a film layer covering the conductive layer. CONSTITUTION: In a thick-film multilayer ceramic substrate in which a conductive layer 12 is provided on a surface dielectric layer 11, the conductive layer 12 and a functional part 15 are connected through a solder layer 14 formed on the conductive layer 12, a coated layer 13, consisting of unwettable by solder material covering the conductive layer 12 along a circumference 121 of the conductive layer, is provided, and a solder layer is formed in the region surrounded by the coated layer 13. It is preferable that the coated layer 13 cover the circumferential part 12 of the conductive layer, at least in a width of 20 μm from the circumference 121 of the conductive layer. Also, it is preferable that the conductive layer 12, which is covered by the coated layer 13, have at least a thickness of 5 μm. Consequently, there is no contact part between the solder layer 14 and the surface dielectric layer 11, so that the dielectric layer 11 is no longer destroyed, even when it is under the load of thermal stress.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick film multilayer ceramic substrate, and more particularly to a thick film multilayer ceramic substrate having an improved structure of a solder bonding conductor layer provided on the surface thereof.

[0002]

2. Description of the Related Art A thick film multilayer ceramic substrate is formed by sequentially printing and firing pastes of a thick film conductor layer and a thick film dielectric layer on a sintered ceramic substrate such as alumina. The thick film multilayer ceramic substrate has the advantages that it is easy to manufacture and that a low firing temperature can be used, so that a low resistance conductor such as silver, gold, or copper can be used. It has been pointed out that the strength is not sufficient because it is fragile. In particular, as shown in FIG. 2, the dielectric layer on the substrate surface
When the functional component 24 is mounted by the solder joint 23 through the solder joint conductor layer 22 provided on the 21, the stress is generated due to the difference in the thermal expansion coefficient between the solder and the conductor layer and the dielectric layer, and the cold heat is generated. There has been a problem that cracks or the like are generated in the dielectric layer when a thermal stress such as impact is applied, resulting in poor electrical insulation with the internal conductor 25. Although functional components are also joined with an organic conductive adhesive such as epoxy instead of solder, the organic conductive adhesive has drawbacks such as insufficient adhesive strength and high cost. For this reason, the thick film multilayer ceramic substrate on which the functional component is mounted is currently limited to applications in which thermal stress resistance is low.

[0003]

As described above,
In the conventional thick film multilayer ceramic substrate, there is a problem that the reliability of electrical insulation between the solder joint portion and the inner layer conductor existing below the solder joint portion is significantly deteriorated especially when a thermal stress is applied. Therefore, an object of the present invention is a thick-film multilayer ceramic substrate in which functional components are mounted on the surface of a multilayer structure by soldering, and unnecessary conduction with the lower inner-layer conductor is achieved even under a thermal stress load. Another object of the present invention is to provide a thick-film multilayer ceramic substrate that is more reliable and does not occur.

[0004]

[Means for Solving the Problems and Its Action] The object is to provide a conductor layer on a surface dielectric layer, and electrically connect the conductor layer and a functional component through a solder layer formed on the conductor layer. In the thick-film multilayer ceramic substrate, a coating layer made of a material that does not wet the solder is provided to cover the conductor layer along the periphery of the conductor layer, and the solder layer is formed in a region surrounded by the coating layer. To be achieved. It is preferable that the coating layer covers the peripheral portion of the conductor layer with a width of at least 20 μm from the peripheral edge of the conductor layer. Also,
The conductor layer covered by the coating layer preferably has a thickness of at least 5 μm.

A conductor layer for solder bonding is provided on the surface of the thick film dielectric layer, that is, the surface dielectric layer, farthest from the substrate of the thick film multilayer ceramic substrate of the present invention. In the present invention, the material forming the conductor layer on the surface dielectric layer is preferably silver, copper or a soft alloy containing these as the main components. In addition, gold, palladium, platinum and the like can be used. In addition, the conductor layer preferably has a thickness of 5 μm or more inside the peripheral edge portion covered with the coating layer of the present invention.

On the surface of the conductor layer, a coating layer is provided along the periphery of the conductor layer so as to cover the conductor layer with a predetermined width from the periphery. This coating layer is a layer made of a material that does not get wet with solder, such as glass ceramics. Examples of the material forming the coating layer include resins and metal oxides in addition to glass ceramics. The coating layer is at least 20 μm, more preferably 50 μm from the periphery along the periphery of the conductor layer.
It is preferable to cover the conductor layer with a width of. The width of the overlapping portion of the coating layer and the conductor layer is selected in consideration of the conductor material, the solder material, the usage conditions and the like.

A solder layer is formed in a region surrounded by the coating layer on the surface of the conductor layer, that is, in the central portion of the conductor layer. According to the present invention, the shape of the solder layer on the conductor layer is controlled by the presence of the coating layer, and the solder connection with the functional component is made only in the area surrounded by the coating layer on the surface of the conductor layer. Examples of the material forming the solder layer include alloys such as tin, lead, silver, bismuth and indium.

As described above, the thick-film multilayer ceramic substrate of the present invention is a multilayer circuit substrate formed of thick-film glass ceramic or the like, in which a coating layer of glass ceramic or the like is provided on the peripheral portion of the conductor layer on the surface, A conductor layer such as a soft metal under the solder layer end portion, preferably with a predetermined thickness,
The present invention is characterized in that the contact between the solder layer and the surface dielectric layer does not exist so as to exist. The operation of the present invention will be explained as follows.

The coefficient of thermal expansion of the glass-ceramic dielectric layer is generally in the range of 5 to 10 ppm / ° C., whereas the solder layer and the conductor layer are respectively 20 to 30 ppm / ° C. and 15 to 20 ppm.
ppm / ° C. Due to the difference in the coefficient of thermal expansion between the metal and the ceramic, stress is generated in the solder layer due to the temperature change, and shear stress is concentrated especially on the end portion of the solder layer. Therefore, in a situation where rapid temperature changes are repeated, the dielectric layer in contact with the solder layer end is broken by shear stress and cracks occur, resulting in poor insulation between the internal conductor and the solder bonding conductor layer. Cause a failure.

By covering the periphery of the solder-bonding conductor layer with glass ceramics or the like and limiting the shape of the solder layer to the central portion of the solder-bonding conductor layer, the position of this stress concentration can be set at the periphery of the conductor layer. It is possible to move inward from the outer end. Since the conductor layer under the solder end absorbs the stress, it becomes possible to endure severe thermal stress. In this case, the constituents of the conductor layer are silver,
If a soft metal such as copper is mainly used, the stress absorption capacity of the conductor layer is increased, so that the thick film multilayer ceramic substrate can withstand even more severe thermal stress. Functional components such as capacitors, resistors, transistors and lead wires can be mounted on the solder layer of the thick film multilayer ceramic substrate of the present invention. The thick film multilayer ceramic substrate of the present invention on which functional components are mounted can be used for various electric circuits and the like that require higher reliability.

[0011]

EXAMPLES The present invention will be described below with reference to examples and comparative examples. First, Table 1 shows the compositions of various thick film materials used in the examples and comparative examples, and Table 2 shows the contents of various functional parts used in the examples and comparative examples.

[0012]

[Table 1]

[0013]

[Table 2] Samples 1-8

A platinum / silver thick film conductor layer 1 layer and a glass ceramic A thick film dielectric layer 2 layer were sequentially laminated on a 96% alumina substrate by screen printing and firing. Then, a conductor layer having a thickness of 12 μm was formed on the thick film dielectric layer on the uppermost layer, that is, the surface dielectric layer, by using various materials shown in Table 3 by screen printing and firing. Next, a solder layer having a thickness of 200 μm was formed by screen printing using 63Sn / 37Pd solder paste, and the functional parts shown in Table 3 were attached. Then, according to a conventional method, reflow treatment is performed at a peak temperature of 230 ° C.,
Comparative samples 1, 3, 5 and 7 were prepared.

Next, samples 2, 4, 6 and 8 of the present invention were prepared. FIG. 1 is a schematic sectional view of Sample 2. First, in the same manner as in Sample 1, a thick film conductor layer and a thick film dielectric layer were sequentially laminated to form a conductor layer 12 having a thickness of 12 μm on the surface dielectric layer 11. The thickness of the conductor layer is 10 μm by screen printing and firing method using glass ceramics C paste on the periphery of the conductor layer.
m coating layer 13 was formed. This covering layer surrounds the conductor layer 12
It was formed so as to cover the surface dielectric layer with a width of 1 to 200 μm. Then, in the area surrounded by the coating layer, a solder layer 14 having a thickness of 200 μm was formed by screen printing using 63Sn / 37Pd solder paste, and the functional component 15 shown in Table 3 was attached thereon. Then, reflow treatment with a peak temperature of 230 ° C. was performed according to a conventional method to prepare samples 2, 4, 6 and 8.

The samples 1 to 8 were subjected to a thermal stress load test as follows. Prepare 10 samples for each,
The heat treatment of holding at 55 ° C. for 30 minutes and then at 125 ° C. for 30 minutes was set as one cycle, and this cycle was performed for 50 cycles to examine the number of samples in which insulation failure occurred. The number of insulation defects that occurred when the same heat treatment was repeated 100 cycles was also examined. The results of these tests are shown in Table 3. Table 3
From the results, it can be seen that the rate of occurrence of insulation failure can be reduced by forming the coating layer on the periphery of the conductor layer and controlling the shape of the solder layer.

[0017]

[Table 3] Samples 11-18

A platinum / silver thick film conductor layer and a glass ceramic B thick film dielectric layer were sequentially laminated on a 96% alumina substrate. Then, a conductor layer having a thickness of 12 μm was formed on the uppermost surface dielectric layer by using a platinum / silver paste by screen printing and a firing method.
Next, using 63Sn / 37Pd solder paste, screen printing was performed to obtain 200 μm or 300 μm as shown in Table 4.
A solder layer having a thickness of m was formed and the functional parts shown in Table 4 were attached. Then, according to a conventional method, a reflow treatment with a peak temperature of 230 ° C. was performed to prepare samples 11 to 13.

Then, in the same manner as in Samples 11 to 13, a thick film conductor layer and a thick film dielectric layer were laminated on the substrate to form a conductor layer on the surface dielectric layer. A coating layer having a thickness of 10 μm was formed on the periphery of the conductor layer by screen-printing and firing the glass ceramics C paste. This coating layer was formed so as to cover the conductor layer with a width of 100 μm or 200 μm from the periphery as shown in Table 4. Further, it was formed so as to also cover the surface dielectric layer. Then, 63Sn / 37Pd solder paste was screen-printed on the inside of the coating layer to obtain 200 μm or 300 μm as shown in Table 4.
A solder layer having a thickness of m was formed, and functional parts as shown in Table 4 were attached thereon. Then, according to the usual method, peak temperature 2
Reflow treatment was performed at 30 ° C. to prepare Samples 14 to 18. The samples 11 to 18 were subjected to the same thermal stress load test as described above, and the number of occurrences of insulation failure out of 10 samples was measured.

[0020]

[Table 4] Samples 21-28

Sample 21 was prepared in the same manner as samples 11 to 18 except that the material of the dielectric layer was changed to glass ceramics A.
28 were prepared and a heat stress stress test was conducted. The results are shown in Table 5.

[0022]

[Table 5] Samples 31-38

Samples 31 to 38 were prepared in the same manner as samples 11 to 18 except that the material of the surface conductor layer was changed to silver and the material of the dielectric layer was changed to glass ceramics A, and a heat stress load test was conducted. It was The results are shown in Table 6.

[0024]

[Table 6]

From the results of Tables 3 to 6, even if the material of the dielectric layer, the material of the conductor layer, the type of the functional component to be mounted, and the width of the coating layer are changed, the shape of the solder layer is controlled to prevent insulation failure. It can be seen that the occurrence of Samples 1 to 38
With the thickness of the solder layer described in the description of the manufacturing method of
The film thickness before mounting the functional component, that is, the film thickness after screen printing. Samples 41-48

Two thick film dielectric layers of glass ceramics A were sequentially laminated on a 96% alumina substrate. Then, as shown in Table 7, silver, palladium / silver, and copper paste were used on the thick film dielectric layer (surface dielectric layer), which is the uppermost layer, by screen printing and firing to obtain Table 7. A thick film conductor layer of 2 × 2 mm size having the thickness shown was formed. A coating layer having a thickness of 10 μm was formed on the peripheral edge of the conductor layer by screen printing and firing (curing for resin A) using glass ceramics C and D and resin A. This coating layer was formed so as to cover the conductor layer with a width of 100 μm or 200 μm from the periphery as shown in Table 7. In addition, the surface of the dielectric layer is surrounded by 400
It was made to cover with a width of μm. Then, 6 inside the coating layer
Samples 41 to 48 were prepared by using 3Sn / 37Pd solder (2 mmφ ball) to perform a reflow treatment at a peak temperature of 230 ° C. to form a hemispherical solder layer, on which a 0.8 mmφ copper wire was attached. The samples 41 to 48 were subjected to the same heat stress stress load test as described above. The results are shown in Table 7. From the results in Table 7, it can be seen that the occurrence of insulation failure can be reduced by controlling the shape of the solder layer even if the material of the dielectric layer and the film thickness of the conductor layer are changed.

[0027]

[Table 7]

[0028]

As described above, in the thick film multilayer ceramic substrate according to the present invention, the coating layer is provided along the periphery of the conductor layer on the surface dielectric layer, and within the area surrounded by the coating layer. Since the solder layer is formed on the surface, there is no contact between the solder layer and the surface dielectric layer, and as a result, the dielectric layer is not destroyed even under thermal stress load. It is a substrate.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a thick film multilayer ceramic substrate according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a conventional thick film multilayer ceramic substrate.

[Explanation of symbols]

11 ... Surface dielectric layer, 12 ... Conductor layer, 121 ... Conductor layer periphery, 13
… Covering layer, 14… Solder layer, 15… Functional parts.

Claims (2)

[Claims] 1. A thick film multilayer ceramic substrate in which a conductor layer is provided on a surface dielectric layer and the conductor layer and the functional component are electrically connected via a solder layer formed on the conductor layer, wherein the conductor layer A thick film multi-layer ceramics substrate, characterized in that a coating layer made of a material that does not wet the solder is provided to cover the conductor layer along the periphery of the solder layer, and the solder layer is formed in a region surrounded by the coating layer. 2. The thick-film multilayer ceramic substrate according to claim 1, wherein the coating layer covers the conductor layer with a width of at least 20 μm from the peripheral edge of the conductor layer.