JP2006236921A - Conductive paste, ceramic wiring board using it and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste for a via capable of providing long-term reliability without causing a defect such as a crack around a via conductor; and to provide a ceramic wiring board using it. <P>SOLUTION: This conductive paste contains at least metal powder, glass powder and an organic constituent. In the conductive paste, the glass powder is formed of glass having a wetting angle of 90-180° at 900°C with respect to a metal plate of the same kind of the metal powder. The ceramic board is formed of a low temperature-baked ceramic material capable of being baked at a temperature below 1,000°C. In glass constituting the via conductor, the wetting angle at 900°C of its glass powder with respect to a metal plate formed of a constituent metal of the via conductor is 90-180°. The via conductor comprises a metal continuous phase and a glass dispersion phase. A minute and discontinuous space is present in at least either of a boundary between the via conductor and the low temperature-baked ceramic board and a boundary the metal phase and the glass phase in the via conductor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a low-temperature fired ceramic sintered body, a conductor paste that can be suitably fired simultaneously, a ceramic wiring board having the conductor paste, and a method for manufacturing the same.

In general, a wiring board has a structure in which a metallized wiring layer is disposed on or inside an insulating substrate.
As a typical example using this wiring board, there is a semiconductor element housing package for housing a semiconductor element, particularly a semiconductor integrated circuit element such as an LSI (Large Scale Integrated Circuit element).

These semiconductor element storage packages generally use an electrically insulating material such as alumina ceramics, and a plurality of metallized wiring layers made of refractory metal powders such as W and Mo are formed on the surface and inside of the insulating substrate. Is done.
Further, a connection pad is formed on the lower surface of the insulating substrate, and an appropriate connection terminal is attached to the connection pad to be electrically connected to the external circuit board.
The semiconductor element mounted on the upper surface of the insulating substrate has a structure hermetically sealed by a lid.

  Also, recently, ceramic materials that can be fired at around 1000 ° C. that can use a low-resistance metal such as Cu or Ag for the metallized wiring layer in place of the alumina ceramics as the insulating substrate in the package for housing semiconductor elements. For example, an insulating material such as so-called glass ceramics, which is obtained by adding a ceramic filler powder to a glass powder and firing it, has been proposed.

  As a specific method for forming a metallized wiring layer containing copper as a main component on at least one of the surface and the inside of the insulating substrate made of glass ceramic, a slurry prepared by adding a solvent to a glass ceramic raw material powder and an organic binder Is formed into a sheet shape by a doctor blade method, etc., and through holes are punched into the obtained green sheet, and via hole conductors are formed by filling the through holes with a conductor paste mainly composed of copper. A conductive paste containing copper as a main component is printed on a wiring pattern by screen printing or the like, and a plurality of green sheets on which wiring patterns and via-hole conductors are formed are pressure-laminated and fired at 800 to 1000 ° C. It is produced by this.

In this case, it is important that the via conductor and the wiring layer formed by firing are sufficiently fused and fixed to the glass ceramic layer without causing inconveniences such as peeling and dropping from the substrate.
For this reason, for example, Patent Document 1 proposes a method in which a glass having good wettability such as a wetting angle with a metal of 30 degrees or less is added to the conductor paste to increase the adhesive strength with the substrate.

  However, when the conductor paste of this technique is applied to the conductor for the via hole, the adhesive strength between the via conductor and the substrate is too high, the mismatch of the firing shrinkage behavior with the ceramic material, and the stress due to the difference in thermal expansion coefficient cannot be relieved, There is a concern that cracks may occur in the ceramic or via conductor, or separation may occur at the interface between the ceramic and via conductor.

Examples of measures for preventing the occurrence of cracks and separation are as follows.
For example, Patent Document 2 discloses that a conductive metal oxide having a sintering temperature higher than that of a ceramic material is added as a method for matching the shrinkage behavior of a conductor material and a ceramic material. It solves the two problems of mismatch and increased conductor resistance.

Further, the influence of the via conductor diameter and the filling rate on the crack generation rate is accurately grasped. For example, when the via diameter is 0.2 mm, the crack generation is suppressed by setting the via filling rate to 90%. Proposals have also been made (Patent Document 3).
Furthermore, Patent Document 4 adds an inorganic pore forming agent made of W or an inorganic boron compound during via metallization, induces a foaming phenomenon during firing, introduces pores into the via conductor, and relieves thermal stress. It is disclosed that cracks can be suppressed.

JP 2000-182435 A Japanese Patent Laid-Open No. 8-242049 JP-A-10-270854 JP 2002-176236 A

However, in the method of Patent Document 2, In ₂ O ₃ and SnO are adopted as conductive metal oxides, but these substances are soluble in alkali, so that it is difficult to perform plating treatment. At the same time, there is a concern about the deterioration of insulation resistance due to moisture intrusion.

Further, according to the methods of Patent Documents 3 and 4, for example, as shown in FIG. 3, there are numerous voids in a shape close to an infinite number of spheres in the via.
Although these voids are independent, due to the large number of them, moisture intrusion occurs due to a slight change in production conditions, and there is a concern that long-term reliability may be reduced.

  Accordingly, the present invention has been devised in view of the above problems, and its purpose is that cracks are generated around the via conductor due to the stress due to the difference in thermal expansion while being capable of plating and having low resistance. In addition, a via conductor paste capable of preventing the occurrence of separation that allows moisture to enter between the via conductor and the ceramic phase and realizing good long-term reliability, and a ceramic wiring board using the paste And a method of manufacturing the same.

    According to the present invention, a conductive paste comprising at least a metal powder, a glass powder, and an organic component, wherein the glass powder has a wetting angle at 900 ° C. between the metal powder and the same type of metal plate. A conductive paste is provided which is made of glass of 90 to 180 degrees.

  The metallization for via according to the present invention is a conductor paste containing a metal powder, a glass powder, and an organic component, and the glass powder has a wetting angle of 90 ° C. between the metal powder and the same kind of metal plate. It is characterized in that it is selected and used within a range of ~ 180 degrees.

Via conductors obtained by filling the conductor paste with the via holes in the ceramic layer and firing are at least a boundary portion between the via conductor and the ceramic layer and a boundary portion between the metal phase and the glass phase inside the via conductor. On the one hand, a fine and discontinuous gap-like gap is formed, which can relieve stress due to the difference in thermal expansion and prevent cracks around the via conductor, and further, between the via conductor and the ceramic phase. It is possible to prevent the occurrence of separation that allows moisture to penetrate into the water and achieve good long-term reliability.
That is, when the wetting angle is 90 degrees or more, wetting between the metal phase and the glass phase (inside the via conductor) or between the base ceramic and the metal phase and / or the glass phase (base / via conductor boundary) during sintering. A corner becomes large, the above voids can be effectively formed, stress due to a difference in thermal expansion can be relieved, and cracks can be prevented from occurring.

The conductor paste preferably has a glass powder content of 5 to 40% by volume per 100% by volume of the metal powder.
By making the content of the glass powder 5% by volume or more, the difference in shrinkage behavior between the metal powder and the ceramic can be alleviated.
In addition, the connection between the via conductor and the ceramic phase is strengthened, and the occurrence of separation is prevented, thereby improving long-term reliability.
By setting the content of the glass powder to 40% by volume or less, an increase in the resistance value of the via conductor can be prevented.
The content of the glass powder is particularly preferably 16 to 30% by volume.

Furthermore, it is preferable that the said glass powder consists of 2 or more types of glass powder in which the wetting angles with the said metal powder and the same kind of metal plate in 900 degreeC differ.
As a result, the function of effectively generating voids and the function of preventing the ingress of moisture can be expressed at the same time, so that both cracks and long-term reliability can be satisfied effectively.

  In particular, it is desirable that the two or more types of glass have a wetting angle of the first glass of 90 to 140 degrees and a wetting angle of the second glass of 130 to 180 degrees. By forming a continuous discontinuous minute gap, the stress due to the difference in thermal expansion can be relieved and the occurrence of cracks can be prevented.

Furthermore, it is preferable that the softening point of the glass powder is 700 to 900 ° C. By setting the softening point to 700 ° C. or higher, sintering of the metal powder can be suppressed and the shrinkage behavior with the ceramic substrate can be matched. As a result, separation can be prevented.
In addition, by setting the softening point to 900 ° C. or less, the glass in the via conductor is softened to block a large gap, prevent moisture from entering, and improve long-term reliability.

  The metal powder is preferably Cu or Ag. In any case, the resistance of the conductor can be reduced, and the firing temperature can be set to 1000 ° C. or lower, so that low cost can be achieved.

  According to the present invention, there is also provided a wiring substrate comprising at least a ceramic substrate and a via conductor made of metal and glass, wherein the ceramic substrate is made of a low-temperature fired ceramic material that can be sintered at a temperature of 1000 ° C. or lower. The glass constituting the via conductor has a wetting angle of 90 ° to 180 ° at 900 ° C. between the glass powder and the metal plate made of the constituent metal of the via conductor, and The via conductor is composed of a metal continuous phase and a glass dispersed phase dispersed in the metal continuous phase, and the metal phase at the boundary between the via conductor and the low-temperature fired ceramic substrate or inside the via conductor; Provided is a ceramic wiring board characterized in that fine and discontinuous gap-like voids exist in at least one of the boundaries with the glass phase. That.

In the ceramic wiring board of the present invention, the via conductor is formed by using, for example, the above-described conductor paste of the present invention, and the boundary between the via conductor and the low-temperature fired ceramic substrate or via is formed. It is a prominent feature of the structure that fine and discontinuous gap-like voids exist at the boundary between the metal phase and the glass phase inside the conductor.
That is, the shape of the gap is not a sphere as shown in FIG. 3, but a gap as shown in FIG. 2, for example.
In addition, the gap is not necessarily formed in the vertical direction, and may have an inclination or a curved shape.

In the above-described ceramic wiring board of the present invention, it is preferable that the gap has a length in the parallel direction of the interface portion of the gap that is one tenth or less of the height of the via conductor.
When this length is one-tenth or less of the height of the via conductor, it is possible to prevent moisture from entering, and even when moisture enters, the penetration stops halfway and deterioration of insulation resistance can be prevented.

Moreover, it is preferable that the gap | interval thickness of the perpendicular direction of the interface part of the said gap | interval is 1/50 or less of the diameter of a via conductor.
When the thickness is 1/50 or less, cracks due to thermal stress can be suppressed, and moisture can be prevented from entering.
Further, even when moisture enters, the intrusion stops midway, and deterioration of the insulation resistance can be prevented.

  Furthermore, the present invention provides a step of forming a through hole in a green sheet containing at least a ceramic powder, a step of filling the through hole with the conductor paste according to any one of claims 1 to 7, and There is also provided a method for producing a ceramic wiring board, comprising a step of firing a green sheet having a via conductor.

The conductor paste for via conductor metallization according to the present invention has a large wetting angle between the metal phase and the glass phase during sintering. A discontinuous minute gap is formed at the boundary between the internal metal phase and the glass phase, and the generation of this gap relaxes the stress due to the difference in thermal expansion and prevents the generation of cracks.
Therefore, the obtained ceramic wiring board can be plated and has a low resistance, but can prevent cracks from being generated around the via conductor due to the stress due to the difference in thermal expansion. It is possible to prevent the occurrence of separation that allows moisture to enter, and to realize good long-term reliability.

Hereinafter, the contents of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of a wiring board according to the present invention, which is a basic structure of a so-called wiring board in which a metallized wiring layer is disposed on the surface or inside of an insulating substrate. It is a schematic sectional drawing of the package for a semiconductor element as an example.

1 includes an insulating substrate 1, a lid 2, a metallized wiring layer 3, a connection terminal 4, and a semiconductor element 5 accommodated inside the package. The insulating substrate 1 and the lid 2 are made of a semiconductor. A container 6 for accommodating the element 5 in an airtight manner is formed.
That is, the semiconductor element 5 is placed and accommodated on the upper surface of the insulating substrate 1, and the semiconductor element 5 is bonded and fixed to the insulating substrate 1 through an adhesive such as glass or resin.

  A plurality of metallized wiring layers 3 are deposited on the insulating substrate 1 from the periphery to the lower surface where the semiconductor element 5 is placed, and 3a (surface layer wiring), 3b (via conductor), 3c (inner layer wiring). ).

Further, a number of connection pads 4 a are provided on the lower surface of the insulating substrate 1 and are electrically connected to the metallized wiring layer 3.
A protruding terminal 4b made of a brazing material such as solder (tin-lead alloy) is attached to the surface of the connection pad 4a as a connection terminal to an external circuit board (not shown).
As a method for attaching the protruding terminals 4b, there are a method in which spherical or columnar brazing materials are arranged on the connection pads 4a and a method in which a brazing material is printed on the connection pads 4a by a screen printing method.
The metallized wiring layer 3 electrically connected to the connection pad 4a is electrically connected to each electrode of the semiconductor element 5 via a bonding wire, so that the electrode of the semiconductor element 5 is connected to the connection pad 4a. It will be electrically connected.

The metallized paste for vias according to the present invention is a conductor paste containing at least metal powder, glass and an organic component, and has a wetting angle of 90 to 90 ° C. between the metal powder and the same kind of metal plate at 900 ° C. It is characterized by 180 degrees.
For example, by setting the wetting angle with copper as the metallized metal to 90 ° or more, the above-described voids can be formed and cracks due to thermal stress can be prevented.
The wetting angle is preferably 100 to 170 degrees, more preferably 110 to 160 degrees.

The metal powder can be used without particular limitation as long as it is a conductive metal for metallization, but copper (Cu) and silver (Ag) powders are preferable from the viewpoint of low conductive resistance and stability. Used for.
The metal powder preferably has an average particle diameter of 1 to 5 μm, particularly 2 to 3 μm.

Examples of the glass include SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ and SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —alkaline earth oxides.
Examples of the alkaline earth oxide used for the glass include MgO, CaO, SrO, BaO and the like.

Moreover, it is preferable that this metallization for via | veer is 5-40 volume% of content of the said glass with respect to 100 volume% of said metal powder.
By making the amount of glass 5% by volume or more, shrinkage of via metallization can be suppressed, and separation due to a difference in shrinkage behavior from the ceramic substrate part can be prevented.
On the other hand, the resistance value of the via conductor can be lowered by setting the glass amount to 40% by volume or less.
The amount of glass added is more preferably 10 to 35% by volume, and most preferably 16 to 30% by volume.

  Further, the glass is more preferably composed of two or more kinds of glasses having different wetting angles, which makes it possible to sharpen the part that effectively generates voids and the part that prevents the ingress of moisture, both crack suppression and long-term reliability. Can be more suitably satisfied.

For example, as the first glass, the wetting angle with copper at 900 ° C. is preferably 90 to 140 degrees.
By setting the wetting angle to 90 degrees or more, the wetting angle between the metal phase and the glass phase during sintering is increased, and the above-described voids are formed to relieve stress due to the difference in thermal expansion and prevent the occurrence of cracks. .
In addition, by setting the wetting angle to 140 degrees or less, the size of the gap can be reduced, moisture intrusion can be prevented, and long-term reliability can be improved.
More preferably, it is 100 to 130 degrees, and more preferably 110 to 120 degrees.

The second glass preferably has a wetting angle with copper at 900 ° C. of 130 to 180 degrees.
By setting the wetting angle to 130 ° or more, the wetting angle between the metal phase and the glass phase is increased during sintering, and the voids as described above are easily formed, and the stress due to the difference in thermal expansion is relieved to reduce cracks. Occurrence can be prevented.
More preferably, it is 140 to 170 degrees, and most preferably 150 to 160 degrees.

The wetting angle can be controlled by the content of the alkaline earth metal in the glass. Generally, when the atomic number of the alkaline earth is low and the content is large, the wetting angle tends to be low.
Furthermore, the wetting angle can be lowered by adding a trace amount of an alkali metal such as Li, Na, or K, or a transition metal such as Ni, Co, Fe, Mn, Cr, Ti, or V.
On the contrary, in order to increase the wetting angle, the content of SiO ₂ , Al ₂ O ₃ or the like may be increased.

Moreover, it is preferable that the softening point of the said glass is 700-900 degreeC.
By setting the softening point to 700 ° C. or higher, sintering of the metal powder can be suppressed and the shrinkage behavior with the ceramic substrate can be matched, so that the occurrence of separation can be prevented.
In addition, by setting the softening point to 900 ° C. or less, the glass in the via conductor is softened to block a large gap, prevent moisture from entering, and improve long-term reliability.
The softening point is more preferably 750 to 850 ° C, and most preferably 770 to 830 ° C.

In the conductive paste, in addition to the above inorganic components, for example, an organic binder made of acrylic resin, epoxy resin, cellulose polymer, polyvinyl alcohol, α-terpineol, dibutyl phthalate, butyl carbitol, ethyl cellulose, ethylene glycol Organic components such as organic solvents such as diethylene glycol, toluene, xylene and mineral spirit are blended.
As for the compounding quantity of the said organic component, it is preferable that 2-5 mass parts and the organic solvent are 8-14 mass parts with respect to 100 mass parts of inorganic components, for example.

  In the metallized conductor paste for vias of the present invention, the organic component is dissipated or burned out by degreasing or baking, and the inside of the via conductor is a metal continuous phase formed by sintering the metal powder and the continuous phase. And a glass dispersed phase dispersed in the form of particles (see FIG. 2).

Next, the ceramic substrate of the present invention is a ceramic substrate that includes a via conductor and includes a low-temperature fired ceramic material that can be sintered at a temperature of 1000 ° C. or less, and includes a boundary portion between the via conductor and the ceramic, and a via Discontinuous gap-like microvoids exist in at least one of the boundaries between the metal phase and the glass phase inside the conductor.
Due to the discontinuous voids, it is possible to relieve thermal stress, suppress moisture intrusion, and obtain a ceramic substrate with excellent long-term reliability.

The shape of this gap is not a sphere as shown in FIG. 3 (reference numeral 29), but is a fine and discontinuous flat gap extending substantially along the boundary surface as shown in FIG. is there.
In FIG. 2, reference numerals 7 a, 7 b, and 7 c denote a gap at the interface portion between the metal phase 13 of the via conductor and the ceramic phase (substrate) 11, and 7 b denote a metal phase 13 and a glass phase inside the via conductor. Reference numeral 18 c denotes an air gap at the interface portion, and reference numeral 7 c denotes an air gap at the interface surrounded by the ceramic phase (substrate) 11, the via conductor metal phase 13, and the glass phase 18.
7d represents a void in the metal phase of the via conductor.

Moreover, it is preferable that the space | gap of the space | interval of the space | interval of the space | gap is 1/10 or less of the via conductor height in the parallel direction.
By making this length one-tenth or less of the height of the via conductor, intrusion of moisture can be prevented, and even if moisture infiltrates, the intrusion stops midway and deterioration of insulation resistance can be prevented.
More preferably, it is 1/15 or less, and further preferably 1/20 or less.

Moreover, it is preferable that the thickness in the vertical direction of the interface of the void is 1/50 or less of the via hole diameter.
By reducing the thickness to 1/50 or less, cracks due to thermal stress can be suppressed, and moisture can be prevented from entering.
Further, even when moisture enters, the intrusion stops midway, and deterioration of the insulation resistance can be prevented.
More preferably, it is 1/75 or less, more preferably 1/100 or less.

  Next, a method for manufacturing a ceramic wiring board according to the present invention is characterized in that, in the method for integrally firing a green sheet having through holes filled with a conductive paste, the conductive paste according to the present invention is used as the conductive paste. It is.

As a ceramic constituting the substrate, a fired glass ceramic composition containing glass and a ceramic filler such as alumina or quartz can be cited as a preferred example.
As the glass component in the glass ceramic used in the present invention, borosilicate glass, zinc borosilicate glass, lithium silicate glass, PbO glass, BaO glass, etc. are used. These glasses are amorphous. Alternatively, crystallized glass in which a crystal phase is precipitated by firing may be used.

As the ceramic filler, Al ₂ O ₃ , SiO ₂ (quartz, tridymite, cristobalite), mullite, cordierite, forsterite, petalite, nepheline, lithium silicate, carnegearite, garnite, zirconia and the like are used.
The glass and the filler are desirably those in which glass is mixed at a ratio of 30 to 90% by mass, particularly 40 to 70% by mass, and filler is 10 to 70% by mass, particularly 30 to 60% by mass.

  In order to produce the ceramic substrate, a mixture of the glass and filler is mixed with an appropriate molding organic resin binder, plasticizer and solvent to form a slurry, and then a desired molding means such as a doctor. After forming into an arbitrary shape into a sheet shape by a blade, a rolling method, a die press or the like, the organic resin binder component blended for molding is removed by heat treatment in an air atmosphere at around 700 ° C. (degreasing step).

  At this time, the shrinkage start temperature of the molded body is desirably about 700 to 850 ° C. If the shrinkage start temperature is lower than this, it is difficult to remove (degrease) the binder. It becomes difficult to control the characteristics, particularly the yield point, within a suitable range.

Firing is performed in a non-oxidizing atmosphere at 850 ° C. to 1050 ° C., thereby densifying to a relative density of 90% or more.
If the firing temperature at this time is lower than 850 ° C., it cannot be densified, and if it exceeds 1050 ° C., the metallized layer is melted by simultaneous firing with the metallized wiring layer.

  In addition, in order to manufacture a wiring board in which a metallized wiring layer made of Cu or the like is disposed on the surface of the insulating board made of the glass ceramic, the raw material powder made of glass and filler as described above for forming the insulating board is used. A green sheet (raw sheet) is prepared by adding a suitable organic binder, a plasticizer, and a solvent to make a slurry, and using the doctor blade method or calendar roll method.

Then, for the metallized wiring layer and the connection pad, a Cu powder coated with a metal oxide on the surface, an organic binder, a plasticizer, and a solvent are added and mixed to prepare a metallized paste.
The coating layer can be formed on the surface of the Cu powder by a plating method, a sputtering method, or the like.
Then, this metallized paste is printed on the green sheet in a predetermined pattern by a well-known screen printing method.

In addition, a part of the green sheet is punched into the green sheet to form a through hole, and the hole is filled with the metallized paste of the present invention.
A plurality of these green sheets are laminated.

Thereafter, the laminate is heat-treated in a nitrogen atmosphere containing water vapor at 500 to 700 ° C. to remove the organic resin binder, and then fired in a non-oxidizing atmosphere such as nitrogen at 850 ° C. to 1050 ° C. for insulation. Baking until the substrate is densified to a relative density of 90% or higher.
Thereafter, the wiring board can be completed by forming a plating layer of Cu, Au, Ni or the like on the surface of the metallized wiring layer on the surface of the wiring board by an electrolytic plating method or an electroless plating method.

A crystalline glass of 40% SiO ₂ -32% Al ₂ O ₃ -7% MgO-10% ZnO-11% B ₂ O ₃ by weight ratio (average particle size 3 μm) was prepared.
This glass was mixed at a ratio of 75%, alumina at 20%, and cordierite at 5%. An acrylic resin was added to the mixture as an organic binder, and further pulverized with toluene as a solvent. A tape having a thickness of 100 μm was produced.
On the sheet, through holes having diameters of 50 μm, 100 μm, 200 μm, and 300 μm were formed by an NC processing machine, respectively.

Next, after adjusting each raw material so that it might become a composition shown in Table 1, and fuse | melting at 1500 degreeC, it cooled rapidly with the stainless steel water cooling roll, and obtained the glass cullet.
This was pulverized with a ball mill to obtain a glass powder having an average particle diameter of 3 μm.
Next, glass is added at a ratio as shown in Table 2 with respect to 100% by volume of copper or silver powder having an average particle size of 5 μm, 10% by volume of acrylic resin as an organic binder, and α-terpineol as an organic solvent. A paste for via conductor was prepared by adding 40% by volume and kneading.
Sample numbers 16, 17, and 18 in Table 2 contain two different types of glass.

  The paste thus obtained was filled in the through-holes of the glass ceramic green sheet by screen printing, and four layers were laminated under pressure. When the metal material was copper, 700 ° C. in a nitrogen atmosphere containing water vapor, After the binder removal treatment for 3 hours, it was fired at 900 ° C. for 1 hour, and in the case of silver, it was baked in the air at 500 ° C. for 3 hours and then at 900 ° C. for 1 hour.

<Crack / separation evaluation>
The cross section of the obtained sample was polished, and the presence or absence of cracks and separation was confirmed with a 20 × stereo microscope, a 200 × metal microscope, and a 1000 × electron microscope. Here, the crack represents a crack inside the ceramic layer or the via conductor, and the separation represents peeling of the via conductor and the ceramic layer.
Further, the shape of the void was measured with an electron microscope.

<Resistance evaluation>
The resistance value of the obtained sample was measured by the four-terminal method, and the specific resistance was determined from the cross-sectional area and height of the via conductor.
Note that 6 × 10 −8 Ωm or more was judged as NG.

<Reliability evaluation>
A reliability test was performed using the obtained sample.
A voltage of 5.5 V was applied to two adjacent via conductors, exposed to a temperature of 85 ° C. and a humidity of 85%, a high temperature and high humidity bias test was performed, and the insulation resistance was less than 1 × 10 9. The thing was judged NG.

<Wetting angle evaluation>
The wetting angle of the glass used for the conductive paste with respect to the metal material was measured as follows.
The measurement is performed using a copper plate when the conductive material is copper, and a silver plate when the conductive material is silver. On these plates, a glass powder press-processed with a diameter of 5 mm and a height of 5 mm is placed and fired under the firing conditions described above. After that, cross-sectional observation was performed and the wetting angle was measured.
In the measurement under the above conditions, there was no substantial difference in the wetting angle between the copper plate and the silver plate.

  As is clear from Table 2, in Sample Nos. 1 and 26, the wetting angle was less than 90 degrees, so that the adhesive strength with the ceramic layer became too strong and cracks occurred.

In Sample No. 9, the glass content was considerably less than 2% and 5%, so that there was a difference in shrinkage behavior between via metallization and ceramic, and separation occurred.
This separation has a length of 20 μm in the axial direction and a length of 3 μm in the radial direction, and the insulation resistance after reliability is reduced due to the penetration of moisture.
In Document No. 15, the glass content exceeds 45% and 40%, and the insulation resistance after the reliability test is 10 9, but the specific resistance is as high as 6 × 10 −8.

In Material No. 19, since the softening point of the glass was lower than 650 ° C. and 700 ° C., there was a difference in shrinkage behavior between via metallization and ceramic, and separation occurred.
This separation was as long as 24 μm in the axial direction and 2 μm in the radial direction, and the insulation resistance after reliability decreased due to the ingress of moisture.
In the material number 25, since the softening point of glass was as high as 950 ° C., the insulation resistance after the reliability test deteriorated.

It is a schematic sectional drawing of the package for semiconductor element accommodation which is a typical example of the wiring board of this invention. It is a cross-sectional schematic diagram of a conventional via conductor. 2 is a schematic cross-sectional view of a via conductor of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Cover body 3 Metallized wiring layer 4 Connection terminal 5 Semiconductor element 6 Container 7 Air gap (the present invention)
11, 21 Ceramic (substrate)
13 Metal phase 18 Glass phase 23 Substrate / via conductor interface 29 Air gap (prior art)

Claims (11)

  A conductive paste comprising at least a metal powder, a glass powder, and an organic component, wherein the glass powder has a wetting angle of 90 to 180 degrees at 900 ° C. between the metal powder and the same type of metal plate. A conductive paste characterized by comprising:   The conductor paste according to claim 1, wherein the content of the glass powder is 5 to 40% by volume per 100% by volume of the metal powder.   The conductor paste according to claim 2, wherein the content of the glass powder is 16 to 30% by volume per 100% by volume of the metal powder.   The conductive paste according to any one of claims 1 to 3, wherein the glass powder is composed of two or more kinds of glass powders having different wetting angles between the metal powder and the same type of metal plate at 900 ° C.   The conductor paste according to claim 4, wherein the wetting angle of the first glass is 90 to 140 degrees and the wetting angle of the second glass is 130 to 180 degrees.   The conductive paste according to any one of claims 1 to 5, wherein the glass powder has a softening point of 700 to 900 ° C.   The conductor paste according to claim 1, wherein the metal powder is Cu or Ag. A wiring board comprising at least a ceramic substrate and a via conductor made of metal and glass,
The ceramic substrate is a low-temperature fired ceramic substrate made of a low-temperature fired ceramic material that can be sintered at a temperature of 1000 ° C. or less, and the glass constituting the via conductor is a metal plate made of the glass powder and the constituent metal of the via conductor And the via conductor is composed of a continuous metal phase and a glass dispersed phase dispersed in the continuous metal phase, and the via conductor and the via conductor at 900 ° C. At least one of the boundary between the low-temperature fired ceramic substrate and the boundary between the metal phase and the glass phase inside the via conductor has a fine and discontinuous gap-like gap. Ceramic wiring board.   9. The ceramic wiring board according to claim 8, wherein the gap has a length in a parallel direction of an interface portion of the gap that is not more than one-tenth of the height of the via conductor.   10. The ceramic wiring board according to claim 8, wherein the gap has a gap thickness in the vertical direction at an interface portion of the gap that is not more than 1/50 of the diameter of the via conductor.   A step of forming a through hole in a green sheet containing at least a ceramic powder, a step of filling the through hole with the conductor paste according to any one of claims 1 to 7, and a via conductor thus obtained A method for producing a ceramic wiring board comprising the step of firing a green sheet.

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