JP2000200973A - Low-temperature burning ceramic circuit substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electric inconveniences, such as a short-circuit due to an infiltration of moisture or humidity from a via conductor of a front layer of a low-temperature burning ceramic circuit substrate. SOLUTION: A via hole 12 formed in each low-temperature burning ceramic layer 11 is filled up with Ag-system via conductors 13, 14. The front part of the via conductor 13 located at a front layer of a substrate is formed into a minute layer 15 with higher minute density than the other parts. The minute layer 15 is increased in minute density by setting a mean particle size of a conductive particle included in Ag-system conductive paste forming the layer 15 to be 1 μm or less, more preferably 0.5 μm or less. In the via conductors 13, 14 other than the minute layer 15, in order to prevent the occurrence of cracks in the low-temperature burning ceramic layer 11 due to the difference in thermal expansion ratios between the via conductors 13, 14 and the low- temperature burning ceramic layer 11, a mean particle size of conductive particles is set to be several μm or more, thereby obtaining a relatively rough minuteness. After the substrate is burnt, a front layer conductive pattern 23 is formed on the surface of the substrate through a photolithographic method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-temperature fired ceramic circuit board having a surface conductor pattern formed on a substrate surface by a wet patterning method such as a photolithography method.

[0002]

2. Description of the Related Art A low-temperature fired ceramic circuit board fired at 800 to 1000 ° C. is a low-resistance, low-melting-point metal (Ag) used as an inner conductor and a via conductor that are fired simultaneously with ceramic.
System, an Au system, a Cu system, etc.), and has the advantage that the dielectric constant of the ceramic is low, and is known as a ceramic circuit board which can cope with recent high-speed signal processing. In order to meet the recent demand for high-density packaging and miniaturization, this low-temperature fired ceramic circuit board also incorporates a capacitor or resistor in the inner layer of the board, or forms a surface conductor pattern on the surface of the board by photolithography. Some have fine patterns.

[0003]

By the way, in order to prevent the ceramic layer from cracking due to the difference in the coefficient of thermal expansion between the via conductor and the ceramic layer, the via conductor has a relatively large gap between the conductive particles (density). The degree of thermal expansion is made coarse to absorb the difference in the coefficient of thermal expansion from the ceramic layer.

However, when the surface conductor pattern is formed by the photolithography method, the substrate surface is exposed to a developing solution in a development step after exposure. When water enters, the water penetrates into the built-in capacitor or the built-in resistor, and ions (Na ⁺ , K ^+, etc.) in the water are contained in the built-in capacitor or the built-in resistor. If post-baking is performed in this state, electrical defects such as short circuits may occur,
This has been one of the causes of lower yield and lower reliability.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to prevent an electrical defect such as a short circuit due to intrusion of moisture or moisture from via conductors on the surface of a substrate, thereby improving the yield. Another object of the present invention is to provide a low-temperature fired ceramic circuit board capable of improving reliability.

[0006]

In order to achieve the above object, in a low-temperature fired ceramic circuit board according to the present invention, at least a surface portion of an Ag-based via conductor located on a surface layer of a substrate is formed more densely than other portions. (Claim 1). As described above, when the denseness of at least the surface portion of the via conductor on the substrate surface is increased, the gap between the conductive particles in that portion is reduced, and even if the surface layer conductive pattern is formed by a wet patterning method such as a photolithography method, Moisture is less likely to penetrate into the via conductors on the surface layer of the substrate, preventing the penetration of moisture into the inner layer of the substrate. In this case, the via conductors on the entire substrate are not densified, but only the via conductors on the surface layer of the substrate or only the surface portion of the via conductors necessary for preventing the penetration of moisture are densified. Can be made relatively coarse and dense as in the prior art, and the gap between the conductive particles can be increased to some extent. This makes it possible to absorb the difference in the coefficient of thermal expansion between the via conductor and the ceramic layer, thereby preventing the low-temperature fired ceramic layer from being cracked around the via conductor.

As described above, in the low-temperature fired ceramic circuit board of the present invention, since it is difficult for moisture to penetrate into the via conductor on the surface of the board, at least one of the built-in capacitor and the built-in resistor is provided in the inner layer of the board. Is formed, the penetration of moisture into the built-in capacitor and the built-in resistor is prevented, and electrical problems such as short-circuit are prevented.

Here, as a method of densifying the via conductor, for example, an Ag-based conductor paste may be mixed with an additive to densify the via conductor, but the conductor contained in the Ag-based conductor paste may be densified. The via conductor may be densified by reducing the particle size of the particles. In this case, the fineness of the via conductor can be easily adjusted by adjusting the particle size of the conductive particles.

Further, the dense portion of the via conductor may be co-fired with the low-temperature fired ceramic layer together with the other portion of the via conductor. In this case, the number of firing steps does not increase, and the productivity does not decrease.

[0010] Alternatively, the dense portion of the via conductor may be post-fired by printing an Ag-based conductor paste on the previously fired via conductor. For example,
When printing a surface conductor or a surface resistor on the surface of the fired substrate and performing post-firing, in the step of post-firing the surface conductor or the like,
At the same time, the dense portion of the via conductor can be post-fired, so that the number of firing steps does not increase and the productivity does not decrease.

[0011]

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIG. The low-temperature fired ceramic layer 11 is made of CaO—Al ₂ O ₃ —SiO ₂ —
B ₂ O ₃ based glass powder: 50-65% by weight (preferably 60 wt%) and Al ₂ O ₃ powder: 50-35% by weight (preferably 40 wt%) is formed by a green sheet consisting of a mixture of I have. Low temperature co-fired ceramic, in addition to the above _{system, MgO-Al 2 O 3 -SiO} 2 -B 2 O 3
Mixture of Al-based powder and Al ₂ O ₃ powder, or S
A ceramic that can be fired at 800 to 1000 ° C., such as a mixture of iO ₂ —B ₂ O ₃ -based glass powder and Al ₂ O ₃ powder, may be used.

A via hole 12 is formed at a predetermined position of each low-temperature fired ceramic layer 11.
Are filled with Ag-based via conductors 13 and 14. The via conductors 13 and 14 of each layer are made of Ag, Ag / Pd, Ag / P
It is made of an Ag-based conductor paste mainly containing t, Ag / Au and the like.

The surface portion of the via conductor 13 located on the surface layer of the substrate becomes a dense layer 15 having a higher density than other portions.
g, Ag / Pd, Ag / Pt, Ag / Au, etc., and are formed of an Ag-based conductor paste. Dense layer 15
The density is increased by setting the average particle size of the conductive particles contained in the Ag-based conductive paste forming the conductive material to 1 μm or less, preferably 0.5 μm or less. In this case, if the shape of the conductive particles is made spherical, the gap between the conductive particles becomes smaller than in the case of irregular shaped conductive particles such as flakes, and the density can be further increased.

The via conductors 13 and 14 other than the dense layer 15 are
In order to prevent cracks from occurring in the low-temperature fired ceramic layer 11 due to a difference in the coefficient of thermal expansion between the low-temperature fired ceramic layer 11 and the low-temperature fired ceramic layer 11, the average particle diameter of the conductive particles of the Ag-based conductive paste used is set to several μm or more. The density is relatively coarse so that the gap between the conductive particles is increased to some extent. In this case, if the shape of the conductive particles is made irregular, such as a flake shape, the gap between the conductive particles becomes larger than that of the spherical conductive particles, and the denseness becomes coarse.

Before laminating the low-temperature fired ceramic layers 11 of each layer, an inner wiring pattern 16 is screened with an Ag-based conductor paste on the upper surface of each low-temperature fired ceramic layer 11 except for the uppermost low-temperature fired ceramic layer 11. Print. The lower electrode 18 of the capacitor 17 is screen-printed with an Ag-based conductor paste on the inner low-temperature fired ceramic layer 11 forming the built-in capacitor 17, and a Pb perovskite-based or BaTiO ₃ -based dielectric paste is applied on the upper surface thereof. The dielectric layer 19 is screen-printed, and the upper surface electrode 20 of the capacitor 17 is screen-printed on the upper surface with an Ag-based conductor paste. Further, the built-in resistor 21 is screen-printed on another low-temperature fired ceramic layer 11 with a RuO ₂ -based resistor paste.

After the printing step, the low-temperature fired ceramic layers 11 of each layer are laminated to form a green substrate.
At 150 ° C., 50 to 250 kgf / cm ² , they are heat-pressed and integrated. Further, alumina green sheets 22 (dummy green sheets) for firing under pressure are laminated on both surfaces of the green substrate, and are heat-pressed in the same manner as described above.

Thereafter, two alumina green sheets 2
The raw substrate sandwiched between the two is baked at 800 to 1000 ° C. (preferably 900 ° C.) while being pressed at a pressure in the range of ² to 20 kgf / cm ² , and has a low temperature having a built-in capacitor 17 and a built-in resistor 21. The fired ceramic circuit boards are fired simultaneously. In this case, since the alumina green sheets 22 laminated on both sides of the substrate do not sinter unless heated to 1550 to 1600 ° C., firing at 800 to 1000 ° C.
The alumina green sheet 22 is left unsintered.
However, during the firing process, the binder in the alumina green sheet 22 is scattered and remains as alumina powder.

After firing, the alumina powder (alumina green sheet 22) remaining on both surfaces of the substrate is removed by polishing or the like, and then a surface conductor pattern 23 is formed on the surface of the substrate by photolithography as follows. First, a photosensitive conductor paste is applied to the surface of the substrate and dried. Thereafter, the photosensitive conductive paste film is exposed by an exposure device, and this is exposed to NaCO3. (1%) aqueous solution to remove unnecessary portions of the photosensitive conductive paste film to form a surface conductive pattern 23. After this, the surface conductor pattern 23
Is fired at 850 ° C. for 10 minutes.

In the manufacturing method described above, the via conductor 13 located on the surface of the substrate and the dense layer 15 on the surface thereof are simultaneously fired with the low-temperature fired ceramic layer 11. Low temperature firing ceramic layer 1
After firing simultaneously with the step 1, the Ag-based conductor paste may be printed on the via conductor 13 to post-fire the dense layer 15.

[Embodiment (2)] In the embodiment (1), only the surface portion of the via conductor 13 located on the surface layer of the substrate is the dense layer 15, but the embodiment (2) of the present invention shown in FIG.
Here, the entire via conductor 25 located on the surface of the substrate is a dense layer. In this case, the via conductor 2 located on the substrate surface layer
5 (dense layer) may be fired simultaneously with the low-temperature fired ceramic layer 11 together with the via conductors 14 of the other layers.

[0021]

EXAMPLES The present inventor conducted a test for evaluating the reliability when the entire via conductor located on the surface layer of the substrate or the surface portion thereof was a dense layer, and the test results are shown in Table 1 below.

[0022]

[Table 1]

In each of the embodiment and the comparative example, a low-temperature-fired ceramic of CaO-Al ₂ O ₃ -SiO ₂ -B ₂ O ₃ system was used, a via conductor was formed with an Ag paste, and a dielectric of a built-in capacitor was used. The body layer is formed of a Pb perovskite-based or BaTiO ₃ -based paste, and the built-in resistor is formed of a RuO ₂ -based resistor paste.

In the embodiment, the via conductor structure shown in FIG. 1 is adopted, and only the surface portion of the via conductor on the surface layer of the substrate is a dense layer. The dense layer used had an average particle diameter of Ag particles of 0.2 μm and a spherical particle shape. The parts other than the dense layer
Ag particles having an average particle size of 5 μm and a particle shape of flake were used.

In the embodiment, the via conductor structure shown in FIG. 2 is adopted, and the entire via conductor on the surface layer of the substrate is a dense layer. The dense layer used had an average particle diameter of Ag particles of 0.2 μm and a spherical particle shape. Except for the dense layer, those having an average particle size of Ag particles of 5 μm and a particle shape of flake were used.

The comparative example corresponds to the conventional example, in which all the via conductors were formed in a porous form from a flake-shaped Ag paste having an average particle diameter of Ag particles of 5 μm. In the comparative example, all the via conductors had an average particle diameter of Ag particles of 0.2.
The particles were densely formed with a silver paste having a particle size of μm.

In the reliability evaluation test, 85 ° C., 85% RH
The number of short-circuit occurrences of 10 ⁵ Ω or less per 10 samples was measured for the example and the comparative example under the conditions of an applied voltage of 50 V (DC) and 1000 hours under the humidity environment of, and the vicinity of the via conductor. Was observed for cracks.

In the comparative example corresponding to the conventional example, since all of the via conductors are coarse and porous, the via conductor absorbs moisture from the fine voids between the conductor particles of the via conductor exposed on the substrate surface. Short-circuits of 10 ⁵ Ω or less occurred in all samples, and the short-circuit occurrence rate became 100%.

In the comparative example, all the via conductors are formed densely and the gap between the conductor particles is small.
Moisture absorption from the via conductor on the substrate surface was suppressed, and no short circuit occurred in all samples.However, if all via conductors were formed densely, the difference in coefficient of thermal expansion with the ceramic layer could not be absorbed by the via conductor. As a result, cracks occurred around the via conductor in the ceramic layer.

On the other hand, in the embodiment, only the surface portion of the via conductor on the surface layer of the substrate or the entire via conductor on the surface layer of the substrate is densely formed, and the gap between the conductive particles is reduced. , The moisture absorption from the via conductor was suppressed, and no short circuit occurred in all the samples. In addition, unlike the comparative example, the embodiment and the comparative example do not densify the via conductor of the entire substrate, but only densify the minimum via conductor of the surface layer of the substrate or its surface portion necessary for preventing moisture absorption. Therefore, the via conductors of the other layers have a relatively coarse density, and the difference in the coefficient of thermal expansion with the ceramic layer can be absorbed by the via conductors. Therefore, in the example, no crack occurred around the via conductor of the ceramic layer.

In the low-temperature fired ceramic circuit board of the present invention, the surface conductor pattern 23 may be formed by a wet patterning method other than a photolithography method such as a plating method.
In the configuration examples of FIGS. 1 and 2, the surface conductor pattern 23 is also formed on the lower surface of the substrate. However, the structure may be such that the surface conductor pattern is not formed on the lower surface of the substrate.

In the above-described embodiment, the pressure firing method in which the raw substrate is fired while pressing in the firing step is employed, but firing may be performed without pressing. Further, in the above embodiment, the dielectric layer of the built-in capacitor is formed by printing a dielectric paste, but a dielectric green sheet may be laminated on the inner layer of the substrate.

The ratio of the dense layer to the via conductor on the surface of the substrate is, for example, １ ／, ３, ／, ４,
In other words, at least the surface portion of the via conductor on the surface layer of the substrate may be a dense layer. Further, a configuration in which at least one of the built-in capacitor and the built-in resistor is not formed may be adopted.

[0034]

As is apparent from the above description, in the first aspect of the present invention, at least the surface of the Ag-based via conductor located on the surface of the substrate is formed more densely than other portions. Of water or moisture from the via conductor can be prevented, and electrical problems such as short circuit can be prevented. Moreover, since the via conductors in the portions other than the dense layer can be made denser, the difference in the coefficient of thermal expansion from the ceramic layer can be absorbed, and cracks are prevented around the via conductor in the low-temperature fired ceramic layer. It is possible to realize an improvement in yield and an increase in reliability in combination with the above-described waterproof / moisture-proof effect.

According to the present invention, at least one of the built-in capacitor and the built-in resistor is formed in the inner layer of the substrate.
This can contribute to high-density mounting and miniaturization of low-temperature fired ceramic circuit boards.

In the third aspect, the via conductor is densified by reducing the particle size of the conductive particles contained in the Ag-based conductive paste. Can be easily adjusted.

In the fourth aspect, the dense portion of the via conductor is co-fired with the low-temperature fired ceramic layer together with the other portions of the via conductor.
No loss of productivity.

According to the fifth aspect of the present invention, the dense portion of the via conductor is printed on the previously fired via conductor with an Ag-based conductor paste and post-fired. It is possible to independently set the firing conditions for various parts, and to expand the range of choice of conductor paste.

[Brief description of the drawings]

FIG. 1 shows an embodiment (1) of the present invention, in which (a)
Is a vertical cross-sectional view illustrating a pressure firing step, and (b) is a vertical cross-sectional view of a low-temperature fired ceramic circuit board on which a surface conductor pattern is formed.

FIG. 2 is a longitudinal sectional view of a low-temperature fired ceramic circuit board showing an embodiment (2) of the present invention.

[Explanation of symbols]

11: low temperature firing ceramic layer, 12: via hole, 1
3, 14: Via conductor, 15: Dense layer, 16: Inner layer wiring pattern, 17: Built-in capacitor, 18: Lower electrode, 19
... dielectric layer, 20 ... top electrode, 21 ... built-in resistor, 22
... Alumina green sheet, 23 ... Surface conductor pattern,
25 ... via conductor (dense layer).

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5E317 AA24 BB04 BB14 CC17 CC22 CD01 CD21 GG05 GG11 GG17 5E346 AA12 AA14 AA15 AA43 BB20 CC18 CC39 DD34 EE24 EE27 FF18 FF45 GG02 GG06 GG09 HH08 HH21 HH33

Claims (5)

[Claims] Claims: 1. A plurality of low-temperature fired ceramic layers are laminated,
In a low-temperature fired ceramic circuit board in which each layer is electrically connected with an Ag-based via conductor and a surface layer conductor pattern is formed on the substrate surface by a wet patterning method such as a photolithography method, an Ag-based via conductor located on the substrate surface layer A low-temperature fired ceramic circuit board, characterized in that at least the surface portion of the ceramic circuit board is formed more densely than other portions. 2. The semiconductor device according to claim 1, wherein at least one of a built-in capacitor and a built-in resistor is formed in an inner layer of the substrate.
A low-temperature fired ceramic circuit board according to item 1. 3. The dense portion of the via conductor is densified by reducing the particle size of conductive particles contained in an Ag-based conductive paste forming the via portion. A low-temperature fired ceramic circuit board as described. 4. The low-temperature firing according to claim 1, wherein the dense portion of the via conductor is co-fired with the low-temperature firing ceramic layer together with another portion of the via conductor. Ceramic circuit board. 5. The method according to claim 1, wherein the dense portion of the via conductor is printed after an Ag-based conductor paste is printed on the previously fired via conductor and then fired. A low-temperature fired ceramic circuit board as described.