JP2001267746A - Multi-layered wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep insulating resistance by preventing the penetration of water, steam, etc., by densifying the top surface of a ceramic wiring board without spoiling debinding property, to reduce trouble accompanying wet type processing such as plating by improving washability by decreasing air pores present on the top surface, and to reduce trouble accompanying processing for coating the surface such thin-film formation. SOLUTION: Ceramic which is easier to densify than a green sheet forming a base material is made into paste at the highest temperature of a burning stage, and the paste is arranged on a green sheet forming a top surface and sintered to provide a ceramic multi-layered wiring board which have its surface air pores reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board for electronic equipment requiring high reliability, and more particularly to a ceramic wiring board.

[0002]

2. Description of the Related Art In addition to the length of a wiring, the dielectric constant around the wiring is related to the transmission delay, and transmission time is increased in proportion to the square of the relative dielectric constant. Therefore, to improve the signal transmission speed, the lower the permittivity around the wiring, the better.

As means for realizing a high wiring density, there is a multilayer wiring board. As a substrate to be a carrier for wiring,
Organic polymer materials or inorganic materials are used. The steps of manufacturing a multilayer wiring board using an inorganic material as a base include a step of slurrying an inorganic material powder with an organic binder and a solvent, a step of forming the slurry into a sheet, and forming a through hole (via hole) in the sheet. A step of embedding a wiring copper paste in the through-hole, a step of forming a predetermined wiring pattern on the sheet in which the wiring copper paste is embedded in the through-hole, using a wiring copper paste; It comprises a step of laminating and crimping the sheets, a step of heat-treating the laminated and crimped body, and the like. During the above heat treatment,
The organic binder in the laminated / compressed body and the organic matter in the copper paste decompose and disappear, and at the same time, the inorganic material and the copper paste which have been in powder form are sintered and densified. Further, the copper paste embedded in the above-described through holes serves as wiring between layers.

[0004] In the case of inorganic wiring boards, there is a tendency to change the base material from alumina to mullite and then to glass having a low relative dielectric constant. In addition to changing the material of the base material, an attempt to lower the sintering density by an additive to lower the dielectric constant has been reported (JP-A-7-329247).

[0005] There is an example in which plating is applied to the surface copper pattern of the substrate in order to ensure solder wettability and the like.
The copper pattern on the surface is a fine and electrically isolated pattern, and is often plated by an electroless plating method disclosed in Japanese Patent Application Laid-Open No. 4-157168.

[0006]

In the conventional thick film substrate, there has been a problem that the insulation resistance between the conductor patterns close to the surface is reduced. This phenomenon becomes remarkable when the substrate is washed with water or used in an environment with a large amount of water vapor, and causes a reduction in electrical reliability and weather resistance. Also,
When an organic thin film layer or the like is formed on the surface of the substrate, fine projections may be formed on the thin film, which may hinder the formation of fine wiring. Furthermore, when attempting to apply electroless plating to the metallization of the substrate surface, the treatment liquid etc. cannot be sufficiently washed, so that the plating is uneven and plating is deposited on ceramic parts other than metallization. Inconvenience may occur.

[0007] The above inconveniences seemed to be seemingly unrelated to each other, but it was found that the frequency of occurrence of defects was often the same when they were related to the sintering lot. That is, we have found that in a sintered lot in which one of the above defects, for example, insufficient insulation, has occurred, the other defects, thin film projections, and plating defects are more likely to occur. Because it is related to the firing lot,
The cause of the above failure is presumed to be in the sintered substrate, and as a result of a detailed study, the substrate that causes the failure has more elongated pores extending from the surface toward the inside than the non-defective substrate, and exists deeply. I scrutinized that. The diameter of the pores was about 3 to 5 μm and was distributed over several tens of μm in the depth direction. Its shape was complicated and irregular, with many constrictions and bends, as if it were an ant nest. Even in the case of a good substrate, the ant-nest-like pores are observed, though to a lesser extent, when observed in detail. However, the above-mentioned problem did not occur unless the density and the depth reached a certain level. The amount of pores that cause a problem depends on the structure of the board, the usage environment, quality control targets in the manufacturing process, and the like. When the depth of the pores was 60 μm or more in a visual field of 100 μm square and the pore depth was 30 μm or more, the probability of insufficient insulation tended to suddenly increase.

From the above measurement results, the mechanism by which the ant-like pores connected to the surface reduce the insulation resistance between the surface conductors was estimated as shown in FIG. In other words, in the defective substrate having a reduced insulation resistance, the open pores are dense on the surface, so it is easy to continue for a long time, and it connects the surface conductors. Moisture and the like did not easily escape, and the resistance between conductors decreased. On the other hand, it is presumed that a non-defective substrate having no problem in insulation resistance has a small number of pores and is not connected long enough to connect a plurality of conductors. It is assumed that the reason why the insulation resistance is lowered after washing with water or in a moist environment is that in such a state, moisture easily enters pores and hardly evaporates. Insulation resistance is low, that is, when a thin film layer is formed on a substrate having many pores on its surface, minute projections often occur because moisture and the like in the pores are formed while the varnish is not yet sufficiently cured during thin film formation. Is presumed to have been evaporated and the thin film layer was slightly swollen due to this pressure. It is presumed that the reason why the treatment liquid such as the electroless plating cannot be sufficiently washed away is that the treatment liquid permeated into the deep open pores.

In order to find out the cause of the open pores, which is the cause of the above-mentioned inconvenience, as a result of taking out and observing at several stages during the sintering, the inside of the laminated body becomes considerably densified when the sintering temperature is reached. There is almost complete densification at the end of the sintering temperature, whereas in the part of the surface at a depth of 80 to 50 μm, the densification is delayed compared to the inside and pores tend to remain, and during the sintering process, It turned out that it was not in the same state of densification. Furthermore, when the state of the pores after firing was observed at a high magnification with an electron microscope, the pores inside were spherical and the walls were covered with glass, and the pores on the surface were square. In addition, crystals added as fillers other than glass appeared on the wall surface.
The above state suggests that the surface has never been completely densified, and the pores on the surface are not due to the continuation of glass bubbles generated after densification, but enter the cooling process without densification, It was found that the glass was cured as it was. Since the open pores on the surface were caused by imperfect sintering as described above, we tried to increase the sintering temperature or lengthen the sintering time, and thought that it could be reduced to some extent. The rise in temperature often has an adverse effect on the copper used for wiring, and when the sintering temperature is set to 1035 ° C or higher, the probability of disconnection of the internal copper wiring increases, and the sintering time is prolonged. Also, the densification was practically saturated and had no remarkable effect. Further, since the above-mentioned open pores have an in-plane distribution which is considered to be related to the wiring density in the substrate, the thickness variation of the green sheet, and the like, the sintering temperature and the time, which act on the entire substrate during sintering, are not included. By adjusting the sintering conditions, it was not possible to achieve a uniform surface state.

A process has also been proposed in which the above open pores are removed by sintering after sintering or the like, and the newly formed internal voids are polished with glass or the like (Japanese Patent Laid-Open No. 6-112648). If it is attempted to completely remove the existing open pores by polishing, the metallization arranged on the surface for connection to the outside will be almost completely removed, and a step of forming a new connection pad after polishing is required. Costly. A method of partially removing and filling remaining pores with glaze glass or the like (Japanese Patent Laid-Open No.
-204337) requires considerable man-hours, such as application of the glass to the sintered surface, a heating step for the effect, and removal of the glaze glass remaining on the metallized surface, resulting in an increase in cost. It was virtually like firing twice.

It has been a problem to reduce the man-hour as much as possible and to take measures against insufficient insulation resistance due to open pores on the surface, minute projections when forming a thin film, and plating properties.

[0012]

In order to solve the above-mentioned problems, the present invention provides a ceramic paste which is more easily densified than a green sheet constituting a substrate at the highest temperature of a firing step. In the present specification, the ceramics that are easily densified are referred to as densifying agents. The degree of densification is measured by the relative density obtained by dividing the true specific gravity by the bulk specific gravity. That is, the densifying agent is a ceramic having a higher relative density than the green sheet constituting the base material at the highest temperature in the firing step.

The above-mentioned densifying agent is formed into a layer before firing on the surface of the green sheet used for the surface layer, and this densifying agent is also sintered during the firing step of the green sheet laminate as the base material.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One example according to the present invention will be described.
This example is a multi-layer wiring board developed for a computer.
In order to mount and mount I at high density with fine solder bumps, a glass ceramic g30 having a coefficient of thermal expansion close to that of Si was adopted as the base material of the wiring board. This glass ceramic g30
Is a borosilicate glass g0 having the sintering behavior shown in FIG. 2 and mullite crystals added as a filler at a volume ratio of 70:30 between the glass g0 and the filler.
The sintering behavior of 0 is as shown in FIG. The sintering behavior described above is obtained from the amount of shrinkage deformation of the green compact of each powder.

FIG. 3 shows the sintering behavior of the densifying agents d5, which are characteristic materials of the present invention, glass d0, which is the main component of d5, and the glass ceramic g30. The above glasses d0 and g0
Was as shown in Table 1. The densifying agent d5 is obtained by adding 5% by volume of mullite crystals to glass d0.

[0016]

[Table 1]

FIG. 4 explains the design concept of selecting the densifying agent d5 in relation to the sintering curve b of the densifying agent and the sintering curve a of the green sheet as the base material. The binder of the green sheet is thermally decomposed during firing, and the decomposition residue is graphitized and remains in the sintered body. However, in order to completely remove the graphite, it is necessary to introduce steam from the outside and burn it out. This burn-out reaction is described in JP-A-4-238858.
As mentioned in the above, it does not actually advance unless it is above 750 ° C. Since the densifying agent is applied to the surface of the green sheet as described later, if the densifying agent becomes more dense than the green sheet, the supply of water vapor into the laminate is hindered and the decarbonization reaction is insufficient. Since there is a possibility that a sintered body may be formed, the densifying agent needs to have a lower density at 750 ° C. than the green sheet in order to avoid the sintered body. In FIG. 4, at the temperature T1, the sintering curve b of the densifying agent has a lower relative density than the sintering curve a of the green sheet. At the stage where the green sheet is densified and the water vapor does not permeate into the inside, the decarbonization reaction does not occur, so that it is not necessary to consider this. It is difficult to specify the temperature at which the decarbonization reaction ends, but from the viewpoint of the sintering behavior, it is a temperature at which steam does not enter the interior. Experiments on glass-filler systems with several different softening temperatures showed that for materials with any softening temperature, when the relative density was greater than 80%, the decarbonization reaction described above was extremely slow and the carbon in the sintered couple was reduced by 10%.
If you try to reduce it to 0 ppm or less, several hundreds of
Since it was found that it was necessary to set the time, it was possible to use the relative density of 80% as a reference in practical use. Since it is not necessary to consider the flow of water vapor in the temperature range in which the green sheet is further densified, there is no need to suppress the relative density of the densifying agent to be lower than the relative density of the green sheet. However, in practice, at 750 ° C., most of the binder in the high-density agent is burned out, but since the high-density is hardly sintered, only the powder is solidified. If the relative density of the densifying agent at this point is less than 20%, the mass of the powder of the densifying agent often collapses and the thickness becomes thin, and at 750 ° C., the relative density is less than 20%. High densifiers were not practical. From the above, in the temperature range where the temperature is 750 ° C. or higher and the relative density of the green sheet is 80% or less, the high densification agent satisfies the condition that the relative density is smaller than the green sheet and the relative density is 20% or more. There is a need. This requires that in FIG. 4 the shrinkage curve of the densifying agent b must pass through region A in the temperature range from T1 to T2. Furthermore, the high densification layer needs to have a higher relative density than the green sheet constituting the base material at the highest temperature of the firing step, and therefore needs to pass through the region B.

In the case of the glass-filler system, the shrinkage behavior varies depending on the softening temperature, particle size, and filler amount of the glass. Therefore, these can be adjusted to obtain the desired sintering curve as described above. The temperature at which glass begins to sinter depends on the softening temperature, which is determined by the composition of the glass. The softening temperature of borosilicate glass is disclosed in JP-A-8-333.
157 is described in detail. Other than the composition, it is possible to increase the sintering start temperature by increasing the particle size of the glass. When the filler amount is increased, the sintering start temperature does not change much, but the whole sintering behavior becomes slow. It is possible to obtain a ceramic having a desired sintering degree by utilizing such characteristics. The temperatures at which densification began were 741 ° C. and 726 ° C., respectively, as determined from the measured sintering curves. Further, in the glass having the composition shown in Table 2, the temperature at which sintering was started was 825 ° C.
After sintering, g30
A denser and less voided surface was obtained. The reason why d0 was used as the glass for the densifying agent in the present residence was mainly from the viewpoint of the price and availability of the glass. Functionally, even the densifying agent using the glass having the composition shown in Table 2 was used. Please note that it was good. The average particle size of the glass d0 for the densifying agent d5 and the mullite crystals added thereto were all 2.5 μm.

[0019]

[Table 2]

Next, a specific manufacturing method of this embodiment will be described with reference to FIGS. Glass ceramic g30 powder 1
To 00 g, 16 g of water-soluble acrylic polymer, 68 g of water, and 16 g of isopropyl alcohol were added and mixed by a ball mill for 20 hours.
A μm green sheet 1 was prepared (5A). Among the green sheets 1, the high-densification agent 2 pasted to the green sheet 1 forming the surface of the multilayer substrate was formed by a screen printing method with a thickness of 20 μm (5B). The paste of the densifying agent was prepared by adding 62 g of a vehicle containing cellulose and 1.7 g of a dispersing agent to 100 g of the d5 powder of the densifying agent and stirring and mixing for about one hour. After forming a via hole 3 with a punch on the green sheet 1 on which the densifying agent 2 is printed (5C), copper paste is filled and printed in the via hole 3 as a conductor 4 for interlayer connection (5D), and further, terminals, LSIs and the like are connected. Similarly, a surface connection pad 5 for connection and an in-plane connection conductor 6 for obtaining in-plane conduction were similarly printed with copper paste (5E).

Green sheet 1 formed with high densifying agent 2
On the first layer, the green sheet 1 on which the densifying agent 2 is not formed is arranged on the second layer or lower, and a total of 48 layers are laminated,
A laminate was manufactured by heating at 130 ° C. and applying a pressure of 180 kgf / cm ² for 1 hour (FIG. 6). The surface connection pad 5 and the in-plane connection conductor 6 that have risen on the surface of the green sheet 1 in the process of the crimping sink inside.

The laminate was fired according to the temperature profile shown in FIG. The atmosphere during firing was nitrogen, and 200 ° C during the temperature rise.
To 950 ° C. at a partial pressure of 0.4 atm.

The substrate after the calcination had an insulation resistance of 2000 MΩ or more even after being exposed to an environment having a relative humidity of 80% for 24 hours, and 1000 MΩ or more even after washing with water. Disassemble the board
Upon inspection, the portion corresponding to the densifying agent 2 had a relative density of 99.5%, and the portion corresponding to the green sheet 1 had a relative density of 98%. Although it was slightly different from the relative density shown in FIG. 3 measured with the green compact, the portion corresponding to the densifying agent 2 was more densified than the portion corresponding to the green sheet 1. The number of pores appearing per 100 μm square on the surface was 30 or less in the portion corresponding to the densifying agent 2.

Further, the concentration of the carbon residue is 40 ppm and 45 ppm in the portion corresponding to the densifying agent 2 and the portion corresponding to the green sheet 1 in contact therewith, respectively.
The wiring board had no problem at all in terms of electrical and strength.

[0025]

According to the present invention, a ceramic wiring board having a high surface density and a sufficiently high insulating property of 1000 MΩ or more even after washing with water or under high humidity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of the vicinity of the surface of a substrate that does not become a substrate having insufficient insulation resistance.

FIG. 2 is a graph showing a sintering shrinkage curve of a glass ceramic or the like provided for the green sheet substrate of the present embodiment.

FIG. 3 is a sintering shrinkage curve diagram of the densifying agent of the present example.

FIG. 4 is a diagram showing a temperature-relative density region as a selection standard for a densifying agent.

FIGS. 5A and 5B are a perspective view and a cross-sectional view showing a change of the front surface green sheet in each step before pressure bonding of the present embodiment.

FIG. 6 is a perspective view and a cross-sectional view of a laminate of the present embodiment.

FIG. 7 is a diagram showing a firing temperature profile of the present embodiment.

[Explanation of symbols]

1 ・ ・ ・ Green sheet, 2 ・ ・ ・ High density agent, 3 ・ ・ ・ Via hole, 4 ・ ・ ・ Conductor for interlayer connection, 5 ・ ・ ・ Pad for surface connection,
6 ・ ・ ・ In-plane connection conductor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahide Okamoto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd. Production Technology Research Institute (72) Inventor Masato Nakamura 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Production Technology Research Laboratories (72) Inventor Bunichi Tagami 1 Horiyamashita, Hadano-shi, Kanagawa Prefecture Hitachi Computer Co., Ltd.General-purpose Computer Division (72) Inventor Norio Chiishi 1-Horiyamashita, Hadano-shi, Kanagawa Stock F-term (reference) in the general-purpose computer division of Hitachi Ltd. 5E346 AA12 AA55 CC17 CC18 EE29 HH08

Claims (5)

[Claims] 1. A surface having a metallization for connection to the outside and a ceramic portion in contact with the metallization disposed on the surface having a smaller number of pores than the inner ceramic portion, and the surface and the surface And a ceramic multilayer wiring board in which the ceramic portion in contact with the metallization disposed on the surface has the same composition. 2. The surface of the surface and the ceramic portion in contact with the metallization disposed on the surface and having a smaller number of pores than the inner ceramic portion, and the surface and the surface have a metallization for connection with the outside. Of the ceramic multilayer wiring board in which the ceramic portion in contact with the disposed metallization is the same composition, the ceramic on the surface is a composite of glass and inorganic crystal, and the amount of inorganic crystal contained in the internal ceramic is A ceramic multilayer wiring board, characterized in that the composition is a composition containing less inorganic crystals, and wherein the softening temperature of the glass constituting the ceramics on the surface is higher than the softening temperature of the glass constituting the internal ceramics. 3. A metallization for connection to the outside is formed, and the surface of the surface and the ceramic portion in contact with the metallization disposed on the surface have a smaller number of pores than the internal ceramic portion. Of the ceramic multilayer wiring board in which the ceramic portion in contact with the disposed metallization is the same composition, the ceramic on the surface is a composite of glass and inorganic crystal, and the amount of inorganic crystal contained in the internal ceramic is The sintering start temperature of the glass constituting the ceramics on the surface is higher than the sintering start temperature of the internal ceramics, and the thickness of the ceramics portion on the surface is reduced. A ceramic multilayer wiring board characterized by being smaller than the thickness of one green sheet. 4. A ceramic material having a relative density lower than that of a green sheet in a temperature range where a binder removal reaction is occurring and having a relative density higher than that of the green sheet at a maximum temperature of a substrate baking step is applied to the surface of the substrate. A ceramic multilayer wiring board that is arranged in a stage before via processing is performed on the green sheet to be composed. 5. A green sheet at a temperature of 750 ° C. in a temperature increasing step of a heat treatment step for manufacturing a substrate, which has a lower relative density than a green sheet at said temperature, and said green sheet at a maximum temperature of said heat treatment step at said maximum temperature. A ceramic multilayer wiring board in which a ceramic material having a relative density higher than that of a sheet is arranged at a stage before a via processing is performed on a green sheet constituting a surface of the substrate.