HK1060722B - High thermal expansion glass and tape composition - Google Patents

Description

High thermal expansion glass and tape compositions

Technical Field

The present invention relates to high thermal expansion glass compositions for use in castable tape compositions that can be used to make multilayer circuits for Ball Grid Array (BGA) applications.

Background

Packaging techniques involving ceramic materials now require higher packing density, better performance and lower cost. Low temperature co-fired (co-fired) ceramic tape (LTCC) technology is considered a critical approach, which meets all of the above requirements. LTCC is a known technology used to combine highly conductive metallization (silver and gold) processes with reliable ceramic dielectric layers for IC circuit integration. Typically, LTCC substrates are composed of glass and ceramic. The use of glass allows low temperature sintering (sintering) of the dielectric layer to be carried out at temperatures below 900 deg.c, while ceramics (as fillers) have high mechanical strength and dimensional stability due to some interaction with glass. In most cases, the definition of glass is more important than the choice of ceramic material, especially when special functions are required. The choice of glass determines the compatibility of the resulting substrate with other contact materials (e.g., conductors) and passive devices.

LTCC materials have been carefully designed for BGA applications, now having 12-20ppm deg.C^-1PWB material with high TCE (temperature coefficient of expansion) is bonded to LTCC material by soldering. As in dissimilar materialsA potential method to obtain better integrity would be desirable to have a temperature greater than 9ppm DEG C^-1High TCE new ceramic substrates. A high TCE LTCC reduces thermal stress at the weld site, resulting in better thermal cycle resistance with substantially no cracking or electrical failure.

The present invention fills this need by providing new glass compositions of high thermal expansion. The resulting glass ceramic body exhibits good strength and silver compatibility after sintering. In addition, the new glass can be sintered at low temperature, namely below the melting point of silver, thereby expanding the working range of the current system.

Summary of The Invention

The invention relates to an alkali-containing magnesium borosilicate glass composition comprising, in mol%, 10-25% SiO₂、10-25％B₂O₃、5-10％BaO、40-65％MgO、0.5-3％ZrO₂、0.3-3％P₂O₅And 0.2-5% M₂O, wherein M is selected from alkali metal elements and mixtures thereof. Preferred alkali metal elements are Li, Na and K.

The invention also relates to a castable dielectric composition, which is a dispersion comprising fine solid particles, comprising, on a solids basis: (a)50-90 wt% of the above glass composition; (b)10-50 wt% ceramic filler; (a) and (b) dispersed in a solution of (c) an organic polymeric binder and (d) a volatile organic solvent.

The invention also relates to a castable dielectric composition for use in a process of casting (cast) a thin layer of the castable dielectric composition onto a soft substrate and then heating the cast layer to remove volatile organic solvents to form a high TCE LTCC green (green) tape.

In one embodiment of the invention, a silver conductor composition is deposited on the tape.

Detailed Description

The circuit materials constituting the glass and ceramic tapes of the present invention are free of elements such as Pb and Cd, which are present on the EPA hazardous waste list. The present invention is based on the discovery that ceramic tapes exhibiting high TCE can be made by mixing an alkali-containing magnesium borosilicate glass with a ceramic filler.

Glass

Disclosed herein is a novel magnesium borosilicate glass exhibiting a high TCE. The term "high TCE" is defined as a high coefficient of expansion of greater than 9 ppm/deg.C over the temperature range of 25-300 deg.C.

The alkali-containing magnesium borosilicate glasses of the invention are novel and differ from conventional borosilicate glasses in that the ceramics prepared with the glasses of the invention, with or without fillers, have high TCE values. The glass has a composition of 10-25% SiO in mol%₂、10-25％B₂O₃、5-10％BaO、40-65％MgO、0.5-3％ZrO₂、0.3-3％P₂O₅And 0.2 to 5% of alkali metal elements such as Li, Na and K. It is believed that the large amount of magnesium in the glass provides a high TCE value. The TCE value varies with the magnesium oxide content of the glass. In particular, the presence of alkali metal oxides increases the sensitivity of the glass to heating conditions by controlling the densification and crystallization behavior of the resulting ribbon. The important function of the alkali metal addition is to provide the desired flow and densification characteristics to the tape at the desired sintering temperature. The addition of lithium to the glass provides an effective means of causing the glass matrix to begin to sinter and complete crystallization under the desired heat treatment conditions. The addition of lithium has the effect of reducing the viscosity of the glass without affecting the desired physical and electrical properties of the tape. The magnesium borosilicate glass used in the castable dielectric composition of the present invention may contain some other oxide component, such as ZrO₂BaO and P₂O₅。

The glass is prepared by conventional glass manufacturing techniques. The glass prepared was 500-1000 g. Typically, the ingredients are weighed and then mixed in the desired proportions and heated in a bottom-heating furnace to form a melt in a platinum alloy crucible. As is known in the art, heating is carried out to a maximum temperature (1400 ℃ C. and 1600 ℃ C.) for a time sufficient to render the melt completely a homogeneous liquid. The glass melt was then quench rolled in two counter-rotating stainless steel rolls to form a 10-20 mil thick glass sheet. The resulting glass plate is then ground to form a glass powder having a distribution set to have 50% by volume between 1 and 5 microns. The glass powder is then formulated with fillers and organic media as follows.

The glass powder is also compatible with co-sintered silver conductors. The glass does not flow excessively during sintering. This eliminates mixing with the silver and allows wetting of the solder. Solder wetting is a very important feature that enables ceramic circuits to be connected to external circuitry, such as printed circuit boards.

Blank tape composition

The green tape composition is a tape-forming castable dielectric composition. The above glass is one component of this composition. Upon firing of the composition, a crystalline phase is formed, thereby forming a glass-ceramic structure, resulting in high TCE and sufficient mechanical strength. However, ceramic oxide fillers (e.g. Al)₂O₃、ZrO₂、TiO₂、BaTiO₃And mixtures thereof) are typically added to the castable dielectric composition in an amount of 10 to 50 weight percent (on a solids basis). The filler controls the physical, thermal and electrical properties of the tape at a given temperature and frequency range.

Al₂O₃Is the ceramic filler chosen because it can partially react with the glass to form Al-containing crystalline phases or to modify the sintering behavior of the tape. Al (Al)₂O₃It is very effective in providing high mechanical strength and preventing harmful chemical reactions. Another function of the ceramic filler is to control the rheological properties of the system during sintering. Ceramic particles act as physical barriers that restrict the flow of the glass melt. It also inhibits sintering of the glass, thereby promoting better burn-off of the organics. Other fillers such as alpha-quartz, CaZrO may be used₃Mullite, cordierite, olives of magnesian originZirconia, CaTiO, stabilised with stone, zircon, zirconia, yttria or calcia₃、MgTiO₃、SiO₂And amorphous silica or mixtures thereof to modify the properties and characteristics of the tape.

The amount of glass relative to ceramic material is important in the formulation of the tape composition. Ceramic fillers in the range of 15-30% by weight on solids are considered preferred, allowing sufficient densification and conductor compatibility. Generally, if the filler concentration exceeds 50 wt%, the sintered structure is not dense enough and has too many pores. With the proper glass/filler ratio, it is clear that during sintering, the space between the fillers will be filled with liquid glass. In order to obtain higher densification after sintering the composition, it is important that the inorganic solid has a small particle size. In particular, substantially no particles exceed 15 microns, preferably no more than 10 microns. Due to these maximum particle size limitations, it is preferred that at least 50% of the particles (including glass and ceramic) be larger than 1 micron, preferably in the range of 2-5 microns.

In addition to fillers, colorants such as Cu may be added₂O、CuO、Fe₂O₃And CoO to improve the compatibility of the tape and the silver-based conductor. The addition of CuO to the glass prevents a significant amount of silver from diffusing from the printed conductor pattern into the tape. Cu⁺¹With Ag⁺¹Having the same ionic charge, is believed to act to prevent silver diffusion. It is advantageous to use both colorants in admixture. For example, the castable composition contains a small amount of Cu₂O、Fe₂O₃Or mixtures thereof, are very effective in reducing possible silver diffusion and darkening problems.

The organic medium in which the glass and ceramic inorganic powders are dispersed comprises a polymeric binder, which is soluble in volatile organic solvents, and optionally other dissolved materials such as plasticizers, mold release agents, dispersants, stripping agents, defoamers, and wetting agents.

For better adhesion, it is preferred to use at least 5% by weight of the polymeric binder for 90% by weight of the solids (which solids comprise glass and ceramic filler) based on the total composition. However, it is particularly preferred to use no more than 20% by weight of the polymeric binder for 80% by weight solids based on the total composition. Within these limits, it is desirable to use as little binder as possible compared to the solid, to reduce the amount of organic matter (which must be removed by pyrolysis) and to obtain better particle packing, (which is required to reduce sintering shrinkage).

In the past, various polymeric materials have been used as binders for green tapes, such as poly (vinyl butyral), poly (vinyl acetate), poly (vinyl alcohol), cellulosic polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, methyl hydroxyethyl cellulose, atactic polypropylene, polyethylene, silicon polymers such as poly (methyl silane), poly (toluene silane), polystyrene, butadiene/styrene copolymers, poly (vinyl pyrrolidone), polyamides, high molecular weight polyethers, copolymers of ethylene oxide and propylene oxide, polyacrylamides and various acrylic polymers such as sodium polyacrylate, poly (lower alkyl acrylates), poly (lower alkyl methacrylates) and various copolymers and polymers of lower alkyl acrylates and lower alkyl methacrylates, copolymers of ethyl methacrylate and methyl acrylate and ethyl acrylate, The terpolymer of methyl methacrylate and methacrylic acid can be used as a binder for slip casting materials in advance.

U.S. patent 4536535, issued 8/20/1985 to Usala, discloses an organic binder which is 0-100% by weight methacrylic acid C_1-8Compatible polymers of alkyl esters, 100-0 wt.% of acrylic acid C_1-8A mixture of an alkyl ester and 0-5% by weight of an amine ethylenically unsaturated carboxylic acid. The use of such polymeric binders is preferred for the dielectric compositions of the present invention because such polymeric binders can be used in very small amounts, while large amounts of solids are used. The contents of the above-mentioned Usala application are hereby incorporated by reference.

Polymeric binders often also contain small amounts (relative to the binder polymer) of a plasticizer, which can be used to lower the glass transition temperature (Tg) of the binder polymer. The choice of plasticizer will, of course, depend primarily on the polymer to be modified. Plasticizers used in various adhesive systems are diethyl phthalate, dibutyl phthalate, dioctyl phthalate, butyl phthalate benzyl ester, alkyl phosphates, polyalkylene glycols, glycerol, poly (ethylene oxide), hydroxyethylated alkyl phenols, dialkyl dithiophosphates and poly (isobutylene). Among these, butyl phthalate benzyl ester is most commonly used in acrylic polymer systems because it can be effectively used at lower concentrations.

The solvent component for the cast slip is selected so that the polymer is completely dissolved and sufficiently volatile that the solvent can be evaporated from the dispersion with less heat applied at atmospheric pressure. In addition, the solvent must boil well at temperatures well below the boiling point and decomposition temperature of the other additives contained in the organic medium. Therefore, solvents with atmospheric boiling points below 150 ℃ are most commonly used. These solvents include acetone, xylene, methanol, ethanol, isopropanol, methyl ethyl ketone, ethyl acetate, 1-trichloroethane, tetrachloroethylene, amyl acetate, 2, 4-triethylpentanediol-1, 3-monobutyrate, toluene, dichloromethane, and fluorocarbons. It is believed that a solvent alone does not completely dissolve the binder polymer. And when mixed with other solvent components, they function well as solvents.

A particularly preferred solvent is ethyl acetate, since it avoids the use of chlorocarbon compounds which are harmful to the environment.

In addition to solvents and polymers, plasticizers may be used to improve processability when cutting the laminate. The preferred plasticizer is BENZOFLEX ® 400, which is polypropylene glycol dibenzoate.

Applications of

The green tape is formed by casting a thin layer of a dispersion slurry of the above glass, filler, polymer binder and solvent onto a soft substrate, heating the cast layer to remove the volatile solvent, and separating the solvent-free layer from the substrate to form the green tape. The green tape is used primarily as a dielectric or insulating material for multilayer electronic circuits. The blank roll is die cut into tapes of a size slightly larger than the actual size of the circuit, with alignment holes at each corner. To connect the various layers of the multilayer circuit, through-holes are formed in the blank tape. This is typically formed by mechanical punching. However, a sharply focused laser may be used to form the holes in the blank strip. Typically, the through-hole size ranges from 0.006 "-0.25". The interconnections between the layers are formed by filling the vias with thick film conductive ink. Such inks are typically applied using standard screen printing techniques. Each layer of circuitry is completed using screen printed conductor tracks (tracks). Also, resistor inks or high dielectric capacitor inks may be printed on each layer to form resistive or capacitive circuit elements. Moreover, specially formulated high dielectric constant green tapes, similar to those used in the multilayer capacitor industry, can be incorporated as part of a multilayer circuit.

After each layer of circuitry is completed, the individual layers are stacked and laminated. A confining stamper is used to ensure precise alignment between the layers. The laminate was trimmed using a hot table cutter. Sintering is carried out in a standard thick film conveyor belt furnace or box furnace, which is equipped with process control, to form the sintered article.

As used herein, the term "sintering" refers to heating the article in an oxidizing atmosphere (e.g., air) to a temperature and for a time sufficient to volatilize (burn off) the organic materials in the layers, and to sinter the glass, metal, or dielectric material in the layers to densify the dielectric layer. For LTCC applications, sintering is typically carried out at temperatures below 900 ℃ with short heating times, less than 4 hours.

Those skilled in the art will recognize that in each lamination step, the layers must be precisely aligned so that the vias properly connect to the appropriate contact points of the adjacent functional layer.

The term "functional layer" refers to a layer printed on the green ceramic tape, which has a conductive, resistive or capacitive function. Thus, as described above, a typical green tape layer may have printed thereon one or more layers of resistive circuitry and/or capacitive and conductive circuitry.

The invention is described in further detail by means of the following examples. However, the scope of the present invention is not limited to these examples.

Examples

Examples 1 to 14

A series of alkali oxide-containing, high thermal expansion magnesium borosilicate glasses were prepared as shown in the glass compositions of table 1. Oxides and carbonates of each glass component can be used as raw materials. For all glasses, the raw materials were mixed and then melted in a platinum crucible at 1550 ℃. The melt was homogenized and then quenched in water. Dry milling is carried out in the presence of a small amount of isopropanol to prevent compaction of the powder, followed by drying with hot air. The resulting glass frit had a measured particle size of less than 6 microns.

In examples 9 to 12, Li in glass₂The O content was varied. Whether Li₂The content of O is high or low, and the glass melt is uniform. According to differential thermal analysis, different Li₂The addition of O can significantly alter the behavior of densification and crystallization. As shown in the following Table, high Li₂The O content lowers the crystallization temperature.

Glass #	Li in glass2O content (mol%)	Peak temperature of crystallization
			Example 1 example 10 example 11 example 12	0.51.62.73.8	776℃772℃765℃755℃

By Li₂The 0 content is useful in LTCC applications requiring rigid substrates below 900 c to control densification and crystallization.

Although Na was added in examples 13 and 14₂O and K₂O, influence on densification and crystallization without addition of Li₂O is significant, but the addition of alkali metal is considered to be an important factor in controlling the overall performance of the resulting high TCE ceramic substrate.

TABLE 1

Glass composition, mol%

Example #	1	2	3	4	5	6	7	8	9	10	11	12	13	14
															SiO2	15	22.2	13.5	14.5	17.7	17.7	13.5	11.8	14.4	14.5	14.0	13.5	15	14.5
B2O3	17	11.7	17	17	15.6	15.6	17	17	17	18.7	20.4	22.0	17	18.7
															BaO	6	6.7	6	10	6.9	6.9	6	6	6	5.8	5.6	5.4	6	5.8
MgO	57	52.5	62	57	54.3	54.3	59	61	58	55.1	53.1	51.2	57	55.1
															ZrO2	2.5	2.0	0.6	0.6	1.6	1.6	1.6	1.6	2.2	2.4	2.3	2.3	2.5	2.4
P2O5	2	0.4	0.4	0.4	0.4	0.4	2.4	2.1	2.1	1.9	1.9	1.8	2.0	1.9
															Li2O	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5	1.6	2.7	3.8	-	-
CaO	-	2.9	-	-	-	-	-	-	-	-	-	-	-	-
															CuO	-	1.1	-	-	-	-	-	-	-	-	-	-	-	-
ZnO	-	-	-	-	3.0	-	-	-	-	-	-	-	-	-
															SrO	-	-	-	-	-	3.0	-	-	-	-	-	-	-	-
Na2O	-	-	-	-	-	-	-	-	-	-	-	-	0.5	-
															K2O	-	-	-	-	-	-	-	-	-	-	-	-	-	1.6

TABLE 2

Glass composition, mol%

Example #	15	16	17
				SiO2	14.5	15	15
B2O3	16.5	17	17
				BaO	5.8	6	6
MgO	55.2	51	48
				ZrO2	2.5	2.5	2.5
P2O5	2	2	2
				Li2O	0.5	0.5	0.5
TiO2	3	6	9

TABLE 3

Ceramic tape composition, weight% (as solids)

Example #	18	19	20	21	22	23	24	25	26	27	28
												Glass example #	1	1	1	1	3	4	5	7	10	12	13
Glass	81.3	72.4	49.6	89.3	79.6	89.6	94.5	78.4	81.3	81.3	81.3
												Al2O3	17.9	26.8	49.6	9.9	19.9	9.9	5.0	19.6	17.9	17.9	17.9
Cu2O	0.5	0.5	0.5	0.5	0.5	0.5	0.5	1.5	0.5	0.5	0.5
												Fe2O3	0.3	0.3	0.3	0.3	-	-	-	0.5	0.3	0.3	0.3
Properties of the tape
												TCE(ppm/℃)	11.0	10.6	9.7	11.3	11.3	11.1	11.4	11.0	-	-	-
Dielectric constant	8.2	8.0	7.7	8.4	8.3	8.2	8.7	8.1	8.0	8.3	8.2
												Sintering x, y shrinkage (%)	14.3	13.6	7.4	14.5	15.7	-	22.3	-	15.9	15.4	14.6

Examples 15 to 17

As shown in Table 2, examples 15 to 17 show that the present invention particularly contains TiO₂The glass composition of (1), the glass being prepared by the same glass making method as the glass of Table 1. Adding TiO₂It is believed that a high dielectric constant can be achieved, which is useful for BGA devices operating at high frequencies. The high dielectric constant allows the size of the device or module to be reduced.

Examples 18 to 28

Table 3 illustrates some examples of tape compositions comprising the glasses of table 1. Tapes were prepared using various glass to alumina filler ratios to achieve full densification without excess glass to reasonably maintain high TCE over the temperature range of 25 ℃ to 300 ℃. These tapes are produced by dispersing glass powder and alumina powder in an ethyl acetate solvent containing methyl methacrylate, a methacrylic acid copolymer binder and a plasticizer. In addition, a coloring agent such as Fe is added₂O₃And/or Cu₂O into the tape slurry. Specifically, Cu₂O may act as a diffusion barrier to prevent silver from migrating out of the silver-based conductor.

The slurry was cast onto a mylar and then dried to form a tape. The tape was cut, laminated, printed with thick film silver and sintered at a conventional temperature schedule of 850 deg.c/10 minute hold. The ceramic was sintered very densely, the shrinkage in x, y direction was high, and the co-sintered silver showed no dark spots. Co-sintered silver and platinum-silver exhibit good wetting of conventional solder. The final tape also showed good dimensional stability without distortion or cracking along the co-sintered silver or palladium/silver pattern. This is a great advantage for stand-alone LTCC applications.

Table 3 also shows the properties of the tapes obtained after sintering in a conveyor-type furnace at 850 ℃ for 30 minutes. The coefficient of expansion depends on the glass composition and the content of alumina filler. For the given compositions in Table 3, the TCE values were all between 9 and 12 ppm/deg.C. Low frequency dielectric properties were tested using an impedance analyzer (Hewlett Packard4192A) in the frequency range of 1 khz to 13 mhz. The dielectric constants given in table 3 were measured at 1 mhz. No significant difference in dielectric constant was observed, although the value varied slightly depending on the glass composition and the content of alumina.

The shrinkage values of the sintered tapes in table 3 characterize the sinterability of a given tape composition. Sufficient densification is required for better mechanical strength and tightness. Excess alumina filler was found to be detrimental to the densification of the final tape. The alumina filler may not exceed 30 wt.% in order to avoid sufficient densification.

Examples 29 to 31

In examples 29 to 31, the ceramic green tape was prepared by mixing the glass of example 1 with other fillers (e.g., TiO)₂And ZrO₂) Mixing to prepare the product. All belts were sintered in the same 850 ℃ conveyor furnace. All belt compositions show good solderability and co-sintered palladium-Compatibility of silver conductors. Dielectric constant dependent on TiO₂Increased in content, and ZrO₂An increase in the filler content does not substantially increase the dielectric constant. Dielectric constant dependent on TiO₂The improvement is due to TiO₂Inherently having a high dielectric constant.

Example #	29	30	31
				Glass example #	1	1	1
Glass	81.4	81.4	77.4
				Al2O3	14.9	8.9	17.9
TiO2	3.0	8.9	-
				ZrO2	-	-	4.0
Cu2O	0.4	0.5	0.4
				Fe2O3	0.3	0.3	0.3
TCE(ppm/℃)	11.1	10.9	10.7
				Dielectric constant	9.3	10.7	8.4
Sintering x, y shrinkage (%)	14.0	11.4	14.9

Examples 32 to 34

Use of the composition containing TiO in Table 2₂The glass and ceramic filler of (2) to prepare the tape. The tape was sintered at 850 ℃. The results show that it is possible to display,adding TiO into glass₂The dielectric constant of the tape can be increased. The increased x, y shrinkage values also indicate that the inclusion of Ti in the glass aids in densification. It is proposed to add TiO to the glass₂Instead of adding TiO to the belt composition₂As a filler, densification can be more effectively produced at a sintering temperature of 850 ℃.

Example #	32	33	34
				Glass example #	15	16	17
Glass	81.4	81.4	81.4
				Al2O3	17.8	17.8	17.8
Cu2O	0.5	0.5	0.5
				Fe2O3	0.3	0.3	0.3
TCE(ppm/℃)	10.6	10.7	10.9
				Dielectric constantNumber of	8.8	9.2	9.9
Sintering x, y shrinkage (%)	15.6	15.2	15.1

Claims (11)

1. A glass composition comprising, in mole percent, 10-25% SiO₂、1 0-25％B₂O₃、5-10％BaO、40-65％MgO、0.5-3％ZrO₂、0.3-3％P₂O₅And 0.2-5% M₂O, wherein M is selected from alkali metal elements and mixtures thereof.

2. The glass composition according to claim 1, wherein the alkali metal element is selected from the group consisting of Li, Na and K.

3. The glass composition of claim 1, wherein the glass composition has a TCE greater than 9ppm/° c over the range of 25 ℃ to 300 ℃.

4. A castable dielectric composition comprising a dispersion of fine solid particles, said dispersion comprising, on a solids basis:

(a)50-90 wt% of the glass composition of claim 1;

(b)10-50 wt% ceramic filler;

said (a) and (b) being dispersed in a solution of (c) an organic polymeric binder and (d) a volatile organic solvent.

5. A castable dielectric composition according to claim 4, wherein said ceramic filler is selected from the group consisting of Al₂O₃、ZrO₂、TiO₂、BaTiO₃And mixtures thereof.

6. A castable dielectric composition according to claim 4, wherein at least 50% of said particles of glass and ceramic filler are greater than 1 micron.

7. A castable dielectric composition as claimed in claim 4, further comprising a colorant.

8. A castable dielectric composition according to claim 7, wherein said colorant constitutes from 0.2% to 3% by weight of the composition.

9. A castable dielectric composition according to claim 7, wherein said colorant is selected from the group consisting of Cu₂O、Fe₂O₃And mixtures thereof.

10. A tape made by casting a thin layer of the castable dielectric composition of claim 4 onto a soft substrate, heating the cast layer to remove the volatile organic solvent, and separating the solvent-removed layer from the substrate.

11. The tape of claim 10, wherein a silver conductor composition is deposited on the tape.