JP2000026163A - Production of low dielectric constant substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic material having a low dielectric constant, a coefft. of thermal expansion equal to that of silicon and high mechanical strength by forming a substrate using ceramic particles coated with borosilicate glass having a specified compsn. by a sol-gel process and a binder and sintering the substrate. SOLUTION: Ceramic particles are uniformly coated with a borosilicate glass by a sol-gel process. The compsn. of the glass consists of 10-30 wt.% B2O3, <=20 wt.% additives such as MgO, CaO and Al2O3 and the balance SiO2. The coating weight is preferably 10-50%. The coating is preferably carried out by hydrolyzing a precursor of B2O3 with a precursor of SiO2 in a solvent, mixing the resultant soln. with the ceramic particles and removing the solvent at a low temp. The coated ceramic particles are mixed with a solvent and a binder, the resultant slurry is cast to form a green sheet and this green sheet is sintered at about <1,000 deg.C to obtain the objective ceramic substrate having a dielectric constant of about <=4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a glass or ceramic (hereinafter referred to as ceramic) substrate, and more particularly to a method for producing a ceramic substrate useful for electronic circuit packaging.

[0002] Ceramic structures are usually, and preferably are, multilayer, but are used in the manufacture of electronic circuit boards and devices. Many types of structures can be used, some of which are described below. For example, a multilayer ceramic circuit board is composed of a patterned metal layer functioning as an electrical conductor sandwiched between a plurality of ceramic layers functioning as an insulator. The substrate can be designed with termination pads for attaching semiconductor chips, connector leads, capacitors, resistors, covers, and the like. The interconnection between the multiple buried conductor levels can be made by vias formed in individual ceramic layers formed before lamination with holes filled with metal paste, which, by sintering, reduce the metal A dense metal interconnect of the main conductor.

In general, conventional ceramic structures include ceramic particles, a catalyst (eg, as disclosed in US Pat. No. 4,627,160), a thermoplastic polymer binder,
It is formed from a ceramic green sheet prepared by mixing a plasticizer and a solvent. The composition is spread or cast into a ceramic sheet or slip from which the solvent is evaporated to give a coherent, free-standing, flexible green sheet. After blanking, stacking, and laminating, the green sheet is fired at a sufficiently high temperature to remove the binder resin and sinter the ceramic to form a dense ceramic substrate.

[0004] The electrical conductor used to form the electronic circuit can be a refractory metal, such as molybdenum or tungsten, or a noble metal, such as gold. However, it is desirable to use low-cost conductors with low electrical resistance, such as copper and copper alloys.

[0005] State-of-the-art ceramic substrates are manufactured from a cordierite glass-ceramic particulate material, as disclosed in US Pat. No. 4,301,324. These substrates have a dielectric constant of about 5 or more and have a very similar coefficient of thermal expansion (TCE) to silicon. Since the signal propagation speed is inversely proportional to the square root of the dielectric constant, it is desirable to make the substrate with a material having a low dielectric constant in order to increase the signal propagation speed.

[0006] Before the cordierite glass-ceramic material,
Alumina has been used for many years as a dielectric material suitable for microelectronic packaging. However, alumina has a dielectric constant close to 10, causing large signal propagation delay and small S / N ratio. Furthermore, alumina is TC
E is about twice that of silicon and affects the thermal fatigue resistance of silicon chips and ceramics.

[0007] The transition from alumina to cordierite was a sign of a technological leap. It is anticipated that future electronic packaging requirements will require substrates with improved properties over cordierite glass-ceramics, especially with improved (ie, lower) dielectric constants.

A porous silica film having a dielectric constant as low as about 1 is formed. This material is considered unsuitable for electronic circuit packaging because it shrinks upon firing, the resulting structure is not mechanically complete, and the thermal expansion does not match silicon.

A promising and promising subsequent material is a ceramic consisting of silica and borosilicate glass. For example, U.S. Pat. Nos. 4,476,625 and 4,624,934 disclose mixtures of borosilicate glass and particles of silica glass or refractory metal. These mixtures are made by mixing the ingredients in a ball mill. The resulting product has a dielectric constant of 4.05 or higher.

[0010] Conventional methods of producing a ceramic raw material by simply mixing the silica and borosilicate glass or powders that form the glass in a ball mill produce an uneven microstructure. During sintering, structures formed of such materials tend to be dimensionally distorted.

However, many researchers have suggested that silica and borosilicate glass ceramics be formed by a sol-gel process. For example, Kumar, Mat.
Res. Bull., 19, p. 331-338 (1984)
And Nogami et al., J. of Non-Crystalline Solids, 48,
p. 359-366 (1982) discloses the synthesis of silica and borosilicate glass ceramics by the sol-gel method. Toge et al., Journal of the Ceramic Industry Association, 95, p. 18
2-185 (1987) proposes the formation of silica and borosilicate glass films on glass substrates. Toge et al., J. ofNon-Crystalline solids, 100,
p. 501 to 505 (1988) propose a pattern formation of a silica and borosilicate glass film on a glass substrate. The coating is patterned by a mechanical stamper during the gel state.

US Pat. No. 4,788,046 discloses the production of substrates for electronic circuit packaging from the above ceramic materials. This ceramic material is made by a sol-gel method. The disclosed borosilicate glass, besides silica and boron oxide,
Includes magnesia, calcium oxide, and alumina.
These additional components are added to the glass for several reasons. These reasons include the need for glass stability and the desirability of ceramic particles not excessively reacting with the glass. Unfortunately, the addition of magnesia, calcium oxide and alumina also increases the dielectric constant of the glass. As shown in the table after Example 3 of the above specification, almost all glass-ceramics have a dielectric constant of 5.3 or more. One exception is a glass-ceramic material consisting of quartz and borosilicate glass, which has a dielectric constant of 4.
5 to 5.0. However, this material has a TCE much higher than that of silicon.

[0013] Despite the efforts of the inventors of the above patents and others in the art, ceramic materials with low dielectric constant, TCE equivalent to silicon, high mechanical strength, and easy to manufacture are available. There is still a need.

[0014]

Accordingly, it is an object of the present invention to provide an improved method for producing a ceramic material containing borosilicate glass which meets or exceeds the above electrical and mechanical requirements. It is in.

The above and other objects of the present invention will become more apparent by referring to the following detailed description of the present invention taken in conjunction with the accompanying drawings.

[0016]

According to the present invention, the object of the present invention is achieved by providing a low dielectric constant substrate comprising ceramic particles uniformly coated with borosilicate glass. In order to perform uniform coating of ceramic particles, it is necessary to coat by a sol-gel method. The obtained ceramic substrate has a dielectric constant of about 4 or less.

[0017]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, a method for making a substrate having a low dielectric constant, comprising ceramic particles uniformly coated with borosilicate glass, is disclosed. The dielectric constant of this substrate is about 4 or less. As shown below, the dielectric constant is a function of the composition of the borosilicate glass, the percentage of the borosilicate glass coating the ceramic particles, and the composition of the ceramic particles.

The uniform coating of the ceramic particles is a distinctive feature of the previous sol-gel treatment. The identifiability of the sol-gel coated ceramic particles is readily apparent when comparing FIGS. 1 and 2 with FIGS. 3 and 4. 1 and 2 show a schematic of a ceramic mixture prepared by the conventional ball mill technique. That is, in FIG. 1, the ceramic particles are mixed with the borosilicate glass particles before sintering. As shown in FIG. 2, after sintering, borosilicate glass is formed as irregularly shaped spheres and adheres the ceramic particles. Note that there is little, if any, coating of the ceramic particles with glass.

FIGS. 3 and 4 are schematic diagrams of the ceramic mixture before and after sintering, respectively. However, in FIG. 3, the ceramic mixture before firing is manufactured by a sol-gel method. In FIG. 3, the ceramic particles are coated with borosilicate glass. The coating is uniform,
It is uniformly distributed around the ceramic particles. In FIG. 4, the borosilicate glass coating the ceramic particles is uniform, even when the particles are bonded together. Note that there are no borosilicate particles that cause strain.

Preferably, the substrate is composed of 10 to 50% by volume of glass and the balance is composed of ceramic particles.

In the most preferred embodiment of the present invention, the borosilicate glass is composed of 10 to 30% by weight of boron oxide, with the balance being silica (SiO ₂ ). Other compounds besides small amounts of impurities and other components that do not substantially affect the electrical or mechanical properties of the glass should not be added to boron oxide and silica. It has been found that the best properties are obtained when boron oxide and silica are the main components of the borosilicate glass.

Of course, in the application example of the present invention, characteristics that are not important here, such as a low melting point, may be required. In this case, it is desirable or necessary to achieve a reduction in melting point at the expense of a small increase in dielectric constant by adding a small amount of magnesia, calcium oxide, or alumina or other components or combinations thereof. There is also. These additional components should be less than about 20%, preferably less than about 10% by weight of the glass, such that 10-30% by weight of boron oxide remains.

Further, the preferred ceramic particles for minimizing the dielectric constant are silica and cordierite, but other ceramic particles may be added to the ceramic mixture or silica or cordierite to obtain the desired properties. Alternatively, they can be used instead of both. These other ceramic particles include alumina, fluorspar, mullite, forgotite, forsterite, spinel, beta-eucryptite, anorthite, aluminum nitride, silicon nitride, and mixtures thereof. However, these are only for illustrative purposes and are not intended to be limiting.

[0024] Replacements of some of the ceramic particles with hollow spherical particles, fibers or whiskers, preferably of silica, are also considered to be within the scope of the present invention. Generally, the fibers or whiskers are preferably made of a different material from the ceramic particles. Thus, the fibers or whiskers may consist of, for example, silicon nitride or silicon carbide.

One important aspect of the present invention is the ability to manufacture substrates that are not fully dense. Porous substrates have the advantage of having a lower dielectric constant than perfectly dense substrates.
As described above, the porous silica substrate often has low mechanical strength. But,
The present inventors have discovered that by adjusting the amount of borosilicate glass coating the ceramic particles, a porous substrate having high mechanical strength can be produced.

The substrate according to the present invention is manufactured by the following steps. (A) The ceramic particles are coated with borosilicate glass by a sol-gel method. The sol-gel method involves hydrolyzing a boron oxide precursor with a silica precursor in a solvent or mixed solvent, mixing this solution with the ceramic particles, and then removing the solvent or mixed solvent from the ceramic particles. A convenient removal method is to dry the particles at a low temperature in an oven or on a hot plate.
The glass mixture and the ceramic particles are chosen to meet the electrical and mechanical requirements of the resulting substrate. What is important in this consideration is that the dielectric constant is low, preferably about 4 or less. (B) Forming the coated particles to form a substrate. A preferred substrate molding method is a tape casting method. According to this method, the coated particles are mixed with a suitable solvent or solvent mixture and a binder material to form a slurry. Typical binders include polyvinyl butyral (PVB) or polymethyl methacrylate (PMM).
Components obtained by adding components such as a particle dispersant, a plasticizer, and a flow regulator to A). The slurry is cast into a plurality of green sheets. Next, wirings and vias are formed on the green sheet using a conductive paste. Thereafter, green sheets are stacked and laminated to form a green (unsintered) substrate. (C) Sinter the substrate. The green substrate is placed in an oven in an appropriate atmosphere and sintered for a required time. If the substrate has a copper (preferably due to its low resistivity) wiring pattern, the substrate must be sintered and organic residues incinerated while using an atmosphere that protects copper to prevent oxidation of the copper. Further, since copper melts at 1083 ° C, the substrate must be able to sinter at temperatures below about 1000 ° C.

The advantages of the present invention will become more apparent with reference to the following examples.

EXAMPLES Example I 10% by weight of borosilicate glass (B ₂ O ₃ 20% by weight, S
A ceramic material composed of 80% by weight of iO ₂ ) and 90% by weight of silica particles was prepared by the following method. Aesar amorphous spherical SiO ₂ (average particle size 3.24μ)
m) 278.5 g of 1800 ml of dry denatured ethanol
At the same time, the slurry was placed in a 5-liter three-necked round-bottomed flask equipped with an electric stirrer to produce a slurry. 89 ml (0.40 mol) of tetraethoxysilane (TEOS) were added to the slurry, and a further 200 ml of water and 1 m of 38% HCl were added.
l of the mixture was added. Stir the slurry for 4 hours and add TEO
After hydrolyzing S, 34 ml of trimethyl borate (0.
2 mol) was added to the slurry and further stirred overnight. next,
The slurry was placed in a flat tray and gradually heated on a hot plate to remove any solvent. Next, the powder was pulverized with a Pulverisette 2 pulverizer.

Next, 100 g of this powder was added to a PMMA binder solution comprising a PMMA resin and a mixed solvent of acetone, ethyl alcohol and isopropyl alcohol. The five-layer laminate was pressed and fired in air. The dielectric constant was measured using this sample. The measured value of the dielectric constant was 2.4.

Another sample was prepared by pressing the dried powder into pellets, which were heated to 1000 ° C. with a dilatometer and found to shrink less than 1%. The density of the sintered product was about 70%.

Example II contains 20% by weight of B ₂ O ₃ in borosilicate glass
Another pellet-shaped sample was prepared. In this sample, the percentage of glass coated with silica particles was varied. The dielectric constant was measured for the two types of ceramics.

In a similar manner, ceramic pellet-like samples containing 10% and 30% by weight of B ₂ O ₃ in borosilicate glass were produced. For these samples, the percentage of glass coated with silica particles was also varied.

For all samples, the relationship between the percentage of theoretical density during sintering and the weight percent of borosilicate glass in ceramic was determined. The results are shown in Table 1 below and FIG.
Shown in Table 1 and FIG. 5 also show the results of Example I.

[0034]

[Table 1]

Referring to these results and FIG. 3, regardless of the amount of borosilicate glass added to the silica particles,
It can be seen that densification borosilicate glass containing 10% by weight of B ₂ O ₃ is minimized. On the other hand, borosilicate glasses containing 20% by weight and 30% by weight of B ₂ O ₃ increase in densification as the amount of borosilicate glass increases. If a porous substrate is required, the glass content is best at 50%. Furthermore, as the glass content increases, the dielectric constant increases.

The samples of Examples I and II all exhibited sufficient strength to be handled without significant damage.

Therefore, it is clear that the object of the present invention is achieved by the method of the present invention.

It will be apparent to one skilled in the art that modifications other than those specifically described herein may be made without departing from the spirit of the invention. Accordingly, such modifications are considered to be within the scope of the invention, and the scope of the invention is limited only by the following claims.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a borosilicate glass / ceramic particle composition prepared by a conventional ball mill technique before sintering.

FIG. 2 is a schematic diagram after sintering of a borosilicate glass / ceramic particle composition prepared by a conventional ball mill technique.

FIG. 3 is a schematic illustration of a borosilicate glass / ceramic particle composition prepared by the sol-gel technique of the present invention before sintering.

FIG. 4 is a schematic diagram after sintering of a borosilicate glass / ceramic particle composition prepared by the sol-gel technique of the present invention.

FIG. 5 is a graph showing the relationship between theoretical density and percentage of borosilicate glass coated on silica ceramic particles.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventors David, Lawrence, Daniel 28 Edgehill Drive, Wappingers Falls, New York, United States of America・ Road 53

Claims (24)

[Claims] (A) A ceramic particle is prepared by a sol-gel method.
The pups are 10 to 30 weight percent B _TwoO_ThreeAnd 20 weight
% MgO, CaO, or Al_TwoO_ThreeEtc.
Additives and remaining SiO_TwoAnd the resulting
The ceramic so that the dielectric constant of the substrate is about 4 or less.
Coated with selected borosilicate glass in connection with particles
(B) applying the coated particles as described above.
Forming a substrate, and (c) sintering the substrate
And a method for producing a low dielectric constant substrate. 2. The sol-gel coating step comprises: (a) hydrolyzing a boron oxide precursor with a silica precursor in a solvent or a mixed solvent; and (b)
Mixing the solution of (a) with the ceramic particles;
(C) removing the solvent or mixed solvent from the mixture. 3. The forming step comprises: (a) mixing the coated particles with at least one solution and a binder material to form a slurry; and (b) casting the slurry. The method of claim 1, comprising forming a plurality of green sheets; and (c) stacking and laminating the green sheets to form a multilayer substrate. 4. The method of claim 1 wherein the step of sintering includes the step of heating said substrate to a temperature less than about 1000 ° C. 5. The method according to claim 1, wherein the other additive is 10% by weight of the glass.
The method of claim 1, wherein: 6. The method of claim 1 wherein said glass comprises 10 to 50 volume percent of said substrate, with the balance being ceramic particles. 7. The method of claim 6, wherein said ceramic particles comprise hollow spheres. 8. The method of claim 7, wherein said hollow sphere comprises SiO _2.
the method of. 9. The method of claim 1, wherein said ceramic particles comprise fibers or whiskers. 10. The method of claim 9, wherein said fibers or whiskers comprise a material selected from the group consisting of Si ₃ N ₄ and SiC. 11. The method of claim 1, wherein said ceramic particles are selected from the group consisting of silica, cordierite, and mixtures thereof. 12. The method of claim 11, wherein said ceramic particles are silica. 13. A method of producing a ceramic material by the sol-gel method.
Particles are loaded with 10 to 30 weight percent B _TwoO_ThreeAnd the rest
SiO_TwoCoated with borosilicate glass consisting of
(B) applying the coated particles to a substrate
And (c) sintering the substrate.
A method of manufacturing a low dielectric constant substrate. 14. The method of claim 13, wherein said borosilicate glass is selected in conjunction with said ceramic particles such that the resulting substrate has a dielectric constant of about 4 or less. 15. The sol-gel coating step comprises: (a) hydrolyzing a boron oxide precursor with a silica precursor in a solvent or mixed solvent; and (b)
Mixing the solution of (a) with the ceramic particles;
(C) removing a solvent or mixed solvent from the mixture. 16. The molding step includes: (a) mixing the coated particles with at least one solution and a binder material to form a slurry; and (b) casting the slurry. 15. The method of claim 13 or claim 14, comprising forming a plurality of green sheets, and (c) stacking and laminating the green sheets to form a multilayer substrate. 17. The method of claim 13 or claim 14, wherein the step of sintering comprises heating said substrate to a temperature of less than about 1000 ° C. 18. The method of claim 13 or claim 14, wherein said glass comprises 10 to 50 volume percent of said substrate, the balance being ceramic particles. 19. The ceramic particle comprises a hollow sphere.
The method of claim 18. 20. The method of claim 19, wherein said hollow sphere comprises SiO ₂ . 21. The method of claim 13, wherein said ceramic particles comprise fibers or whiskers. 22. The method of claim 21, wherein said fibers or whiskers comprise a material selected from the group consisting of Si ₃ N ₄ and SiC. 23. The method of claim 13, wherein said ceramic particles are selected from the group consisting of silica, cordierite, and mixtures thereof. 24. The method of claim 23, wherein said ceramic particles are silica.