Composite material and adhesive bonding material having the composite material

Abstract

A composite material is provided that includes at least one first material and particles. The particles have a negative coefficient of thermal expansion and the particles have a sphericity of at least 0.7. The composite material includes at least 30 vol % of the particles at a particle size of d.sub.501.0 m or at least 40 vol % of the composite material at a particle size d.sub.50>1.0 m.

Claims

1. A composite material, comprising: a first material; and particles having a negative coefficient of thermal expansion and a sphericity of at least 0.7, wherein the particles are present in at least 30 vol % of the composite material at a particle size of d.sub.501.0 m or are present in at least 40 vol % of the composite material at a particle size d.sub.50>1.0 m, wherein the particles comprise: i) a compound selected from a group consisting of ZrW.sub.2O.sub.8, Y.sub.2Mo.sub.3O.sub.12, LiAlSiO.sub.4, LiAlSi.sub.2O.sub.6, and ii) a phase system ZrO.sub.2-WO.sub.3-Al.sub.2O.sub.3-P.sub.2O.sub.5, or wherein the particle comprise Y.sub.2Mo.sub.3O.sub.12, LiAlSi.sub.2O.sub.6, or a combination of Y.sub.2Mo.sub.3O.sub.12 and LiAlSi.sub.2O.sub.6.

2. The composite material of claim 1, wherein the first material is selected from a group consisting of a polymer, a glass, and combinations thereof.

3. The composite material of claim 1, wherein the first material is selected from a group of consisting of epoxy resins, glass frits, glass solders, and combinations thereof.

4. The composite material of claim 1, wherein the negative coefficient of thermal expansion of the particles is in a range from 1.010.sup.6/K to 10010.sup.6/K in the temperature range from 50 C. to 200 C.

5. The composite material of claim 1, wherein the particles are spray calcination particles.

6. The composite material of claim 1, wherein the particles are pulsation reactor particles.

7. An adhesive bonding material, comprising a composite material including a first material and particles, the particles having a negative coefficient of thermal expansion and a sphericity of at least 0.7, wherein the particles are present in at least 30 vol % of the composite material at a particle size of d.sub.501.0 m or are present in at least 40 vol % of the composite material at a particle size d.sub.50>1.0 m, wherein the particles comprise: i) a compound selected from a group consisting of ZrW.sub.2O.sub.8, Y.sub.2M.sub.3O.sub.12, LiAlSiO.sub.4, LiAlSi.sub.2O.sub.6, and ii) a phase system ZrO.sub.2-WO.sub.3-Al.sub.2O.sub.3-P.sub.2O.sub.5, or wherein the particle comprise Y.sub.2Mo.sub.3O.sub.12, LiAlSi.sub.2O.sub.6, or a combination of Y.sub.2Mo.sub.3O.sub.12 and LiAlSi.sub.2O.sub.6.

8. The adhesive bonding of claim 7, wherein the first material is selected from a group consisting of a polymer, a glass, and combinations thereof.

9. The adhesive bonding material of claim 7, wherein the first material is selected from a group of consisting of epoxy resins, glass frits, glass solders, and combinations thereof.

10. The adhesive bonding material of claim 7, wherein the particles comprise a compound selected from a group consisting of ZrW.sub.2O.sub.8, Y.sub.2Mo.sub.3O.sub.12, LiAlSiO.sub.4, LiAlSi.sub.2O.sub.6, and a phase system ZrO.sub.2WO.sub.3Al.sub.2O.sub.3P.sub.2O.sub.5.

11. The adhesive bonding material of claim 7, wherein the negative coefficient of thermal expansion of the particles is in a range from 1.010.sup.6/K to 10010.sup.6/K in the temperature range from 50 C. to 200 C.

12. The adhesive bonding material of claim 7, wherein the particles are spray calcination particles.

13. The adhesive bonding material of claim 7, wherein the particles are pulsation reactor particles.

Description

DETAILED DESCRIPTION

(1) A feature common to all of the processes described to date in the prior art for producing the negative-expansion materials is that the raw material generated in the respective operation is obtained either monolithically or at least in an undefinedly coarse-grained structure and requires further comminution steps, generally operations of fine grinding, to bring it into an ultimate presentation form as a powder with defined particle size and particle-size distribution. The particle size to be obtained is frequently situated in the m or sub-m range. Further processing is possible only by such comminution. This further processing refers in particular to incorporation into organic compositions, as for example polymers or resin precursors thereof, which can be used as adhesives. Organic compounds, especially polymers, generally have very high thermal expansion. If such polymers are to be used for adhesive bonding, as for example for bonding inorganic materials, in the optical sector or in the chip industry, for example, there may be difficulties if the adhesive bond is exposed to substantial thermal fluctuations. Because of the very different expansion coefficients of the polymer and of the inorganic materials to be bonded, thermomechanical stresses are induced between the materials to be joined, and in the worst case may even lead to mechanical failure of the bonded component. Such failures can be avoided or at least significantly reduced by reducing the integral coefficient of thermal expansion, in other words the coefficient of expansion that results for the adhesive bonding material as a whole. This is brought about in a simple way through the addition of inorganic fillers with low thermal expansion. Known fillers employed nowadays for this purpose include SiO.sub.2, not only in crystalline form but also amorphously in the form of what is called silica or of quartz glass particles. These SiO.sub.2-based materials have a coefficient of thermal expansion which, while very small in amount, is nevertheless positive, with the value in the order of magnitude of approximately +110.sup.6/K.

(2) Via comminuting operations, such as said fine grinding operations, for example, as just mentioned for producing the negative-expansion powder materials having a particle size in the microscale or sub-microscale range, it is virtually impossible to produce spherical powder particles. Instead, fragmentary particles are formed in this case, featuring edges and angles. These particles, accordingly, have a sphericity of significantly less than 0.7.

(3) In many applications, non-spherical particles of a single material are much more difficult to process than their spherical counterparts, assuming the same particle size and particle-size distribution. This circumstance is manifested in particular on incorporation into thermoplastic matrices and liquid matrices (as in the case of liquid resin precursors for thermoset adhesives): for the same volume fill levels, the viscosity of the particle-filled formulation is significantly higher in the case where non-spherical particles are used than in the case where spherical particles of the same material are used, provided the latter possess a comparable particle size and/or particle-size distribution. Conversely, in the case of the spherical variant, such formulations can be provided with significantly higher fill levels than in the case of the non-spherical embodiment. The reason for this is that the internal friction in formulations filled with non-spherical particles is increased by the tendency of the particles to get caught up with one another when they move past one another within the formulation as a result of the action of external shearing forces. In the case of spherical particles, in contrast, they are better able to slide past one another.

(4) The capacity to achieve much higher volume fill levels under comparable conditions when using spherical particles in formulations filled therewith is of great relevance in practice: firstly, for example, for adhesive bonding materials which are to serve as encapsulating compositions (moulds, encapsulants), it is eventually possible after curing to realize composites having minimized coefficients of thermal expansion, without detriment to the pre-cure processing properties of the liquid adhesive precursors as a result of the introduction of the filler. Moreover, in adhesive materials which are employed for underfilling in the joining of semiconductor components (underfills), there is a limitation on the maximum particle size of fillers. In view of the increasing trend for minimalization, the limit here may be well within the sub-microscale range. Because of the particle-particle interactions, which become ever more effective as the particle size goes down, there is frequently a sharp rise in the viscosity of the precursors of such composites even at relatively low fill levels. A limit is quickly reached here at which the processability of the precursor is no longer ensured. Through the use of spherical filler particles it is possible to achieve a further marked increase in the maximum attainable fill level, relative to the value achievable in the case where non-spherical particles are used. In these cases, the adhesive precursor retains its processability even at higher fill levels. At the same time, the coefficient of thermal expansion of the adhesive material after curing is reduced significantly in accordance with the requirement.

(5) The particles with negative thermal expansion are of great importance for the adhesive industry: by addition as a filler to a polymer/multi-component adhesive, the inherent thermal expansion of the adhesive can be greatly minimized and therefore any discrepancy between the different expansion behaviours of the materials to be joined can be reduced. Mechanical stresses between the components to be joined are significantly reduced as a result, and the lifetime of the overall component is significantly prolonged or indeed made possible to a degree considerable for the application, particularly in the case of adhesive bonding in chip technology (moulding, potting, underfill), but also in the context of other technical bonding issues (e.g. automotive, lens construction in cameras).

(6) Working Examples

(7) Examples of production of particles having a negative coefficient of thermal expansion and a sphericity of at least 0.7:

(8) Production of spherical particles with ZrWO.sub.2O.sub.8 as main crystal phase of a glass-ceramic composed of the phase system ZrO.sub.2WO.sub.3Al.sub.2O.sub.3P.sub.2O.sub.5

(9) Shaping directly from the green glass melt

(10) A starting glass for an eventual negative-expansion glass-ceramic of the composition 24.2 wt % ZrO.sub.2, 68.6 wt % WO.sub.3, 1.4 wt % Al.sub.2O.sub.3 and 5.8 wt % P.sub.2O.sub.5 was melted in a discharge crucible at a temperature of 1650 C.

(11) In the melting assembly selected, the glass melt was held at a temperature of 1550 C. It was discharged from a nozzle with a diameter of 1 mm positioned on the base of the crucible. The glass jet thus produced was dropped onto a 53-toothed striking wheel 8 mm thick and with an outer diameter of 135 mm, this wheel rotating at a frequency of 5000 rpm about its own axis. In this way, the glass stream was filementized into individual pieces, and accelerated with an angle of inclination of between 20 to 30 as measured with respect to the horizontal. It was subsequently passed through a tubular furnace 3 m long, constructed in a curved shape and heated to 1550 C. with two gas burners, this furnace mimicking the flight path of the filamentized glass stream. As a result of the tendency to minimize the surface energy, the filaments in elongate form underwent a change in shape to spheres. Following emergence from the tubular furnace, the glass spheres were cooled by further flight in air until sufficient dimensional stability was achieved, and were finally captured in a collecting vessel.

(12) The cooled, very largely X-ray-amorphous green glass spheres produced by the hot shaping operation described were ceramicized and so converted into the eventual negative-expansion glass-ceramic in the course of a further temperature treatment at a maximum temperature of 650 C. and a hold time of 12 to 24 hours.

(13) Shaping by Rounding of Non-Spherical Green Glass Particles

(14) A starting glass for an eventual negative-expansion glass-ceramic of the composition 24.2 wt % ZrO.sub.2, 68.6 wt % WO.sub.3, 1.4 wt % Al.sub.2O.sub.3 and 5.8 wt % P.sub.2O.sub.5 was melted in a discharge crucible at a temperature of 1650 C.

(15) In the melting assembly selected, the glass melt was held at a temperature of 1550 C. It was discharged from a nozzle with a diameter of 1 mm, positioned on the base of the crucible, into a nip between two contra-rotating, water-cooled rolls, where it was quenched to form a green glass ribbon. The green glass ribbon was singularized into small splinters mechanically, using a hammer.

(16) The glass splinters were roughly comminuted by preliminary grinding in a bead mill, and the powder fraction having a particle size d.sub.100<100 m was removed by sieving from this roughly comminuted material. This green glass powder isolated by sieving was comminuted further in an additional downstream step of dry grinding in an opposed-jet mill to a particle size with a distribution of d.sub.10=0.8 m, d.sub.50=5.2 m, d.sub.90=12.4 m and d.sub.99=18.8 m.

(17) By introduction of the powder into an oxyhydrogen gas flame, the glass particles are melted again, and experience rounding in the process, owing to the tendency for minimization of the surface energy. On emergence from the flame, the particles are allowed to cool and are captured in a collecting vessel.

(18) The cooled, very largely X-ray-amorphous green glass spheres produced by the hot shaping operation described were ceramicized and so converted into the eventual negative-expansion glass-ceramic in the course of a further temperature treatment at a maximum temperature of 650 C. and a hold time of 12 to 24 hours.

(19) Filamentization of Salt Melts for Producing Spherical Y.sub.2Mo.sub.3O.sub.12 Particles

(20) 964 g of yttrium acetate tetrahydrate and 754 g of ammonium molybdate tetrahydrate were introduced into a ball mill, where they were ground for 4 hours to produce an ideally homogeneous powder mixture. The grinding balls used for this purpose were Al.sub.2O.sub.3 balls with a diameter of 40 mm.

(21) After sieving to remove the balls, the powder mixture was placed into a platinum discharge crucible, where it was cautiously brought to a temperature of 100 C., just above the melting point of ammonium molybdate tetrahydrate, which is at 90 C. A salt melt is formed, which was discharged via a nozzle having a diameter of 2 mm that was positioned on the base of the crucible. The jet generated in this way and consisting of the salt melt was dropped onto a 53-toothed striking wheel 8 mm thick with an outer diameter of 135 mm, this wheel rotating at a frequency of 5000 rpm about its own axis. In this way, the jet consisting of the salt melt was filamentized into individual pieces and accelerated with an angle of inclination of between 20 to 300 as measured with respect to the horizontal. It was subsequently passed through a tubular furnace 3 m long and of curved construction that mimicked the flight path of the filamentized jet consisting of the salt melt. The furnace was heated electrically so as to be maintained in the entry zone at moderate temperatures of 100-120 C., so that the salt melt was retained and the filaments, initially still of elongate form, underwent a change in shape, owing to the tendency for minimization of the surface energy, into spheres which are still liquid. In the downstream zones, the temperature selected was then significantly highertemperatures of around 900 C. were achieved here. Here, therefore, there was a first step of calcination of the liquid spheres, forming porous, pre-ceramic particles as an intermediate. Following emergence from the tubular furnace, these spheres were allowed to cool by further flight in air and were finally captured in a collecting vessel.

(22) The porous, pre-ceramic particles were compacted in a further calcination step in an oven at 900 C. with a hold time of 7-8 hours to give the eventual spheres consisting of negative-expansion Y.sub.2Mo.sub.3O.sub.12 material.

(23) Production of Spherical ZRW.sub.2O.sub.8 Particles Via Spray Calcination Using the Pulsation Reactor Method

(24) 584.5 g (2.0 mol) of ethylenediaminetetraacetic acid (EDTA) were suspended in 6.0 L (333 mol) of water. In parallel to this, 560 g (4.0 mol) of 25% strength aqueous ammonium hydroxide solution were introduced into 3.6 L (200 mol) of water. The ammonium hydroxide solution was subsequently added dropwise with stirring to the EDTA solution. This partially neutralized EDTA solution was subsequently admixed with 644.5 g (2.0 mol) of zirconium oxydichloride octahydrate ZrOCl.sub.28 H.sub.2O. This resulted in production of a thick white precipitate which dissolved again when the solution was heated to 100 C. The solution was stirred at this temperature for 1 hour and then left to cool overnight. By partial precipitation of the colourless crystals of a Zr-EDTA complex, a turbid solution developed and was concentrated to dryness on a rotary evaporator. The solid residue of the mixture of Zr-EDTA complex and NH.sub.4Cl (weight ratio: 78%:22%) was subsequently dried at 110 C. for 24 h.

(25) 292.2 g (1.0 mol) of ethylenediaminetetraacetic acid were dissolved in 5.0 L (278 mol) of water and then admixed with 300 ml (2.0 mol) of 25% strength aqueous ammonium hydroxide solution. Dissolved therein were 463.7 g (1.7 mol WO.sub.3 equivalent) of ammonium metatungstate hydrate (NH.sub.4).sub.6H.sub.2W.sub.12O.sub.40n H.sub.2O (85 wt % WO.sub.3). Then 487.1 g of the Zr-EDTA complex/NH.sub.4Cl mixture (i.e. 1.0 mol of Zr-EDTA complex) were added and dissolved therein with gentle heating.

(26) The solution is conveyed with the aid of a peristaltic pump into a pulsation reactor at a volume flow rate of 3 kg/h, where via a 1.8 mm titanium nozzle it is finely atomized into the reactor interior, where it is subjected to thermal treatment. The temperature of the combustion chamber here is maintained at 1300 C., and that of the resonance tube at 1200 C. The ratio of the quantity of combustion air to the quantity of fuel (natural gas) was 10:1 (air.gas).

(27) The powder is introduced into a cuboidal alpha-alumina crucible and placed in a chamber kiln. The material for calcining is brought to a temperature of 1200 C. in the kiln, in an air atmosphere, for complete compaction of the spherical micro-scale particles consisting of ZrW.sub.2O.sub.8, and, after the temperature treatment, is quenched suddenly by being introduced into a stream of cold air, so that the mixed oxide which is meta-stable at room temperature had no opportunity to break back down into the individual components.

(28) Production of spherical ZrW.sub.2O.sub.8 particles via the droplet formation process

(29) 58.5 g (0.2 mol) of zirconium oxychloride octahydrate ZrOCl.sub.28 H.sub.2O were added to 500 mL (27.8 mol) of water and dissolved therein. Added to the mixture additionally were 252.2 g (1.2 mol) of citric acid monohydrate, and dissolution took place. The compound functioned as a complexing agent for stabilizing the Zr.sup.4+ ions, in order to prevent their premature precipitation in the course of further processing. In parallel, a separate solution was prepared from 90 g (0.33 mol of WO.sub.3 equivalent) of ammonium metatungstate (NH.sub.4).sub.6H.sub.2W.sub.12O.sub.40.xH.sub.2O (85% WO.sub.3) in 500 mL of water. The two solutions were then combined.

(30) By means of a droplet formation process via dies and/or cannulas, gel bodies with sizes of 0.3 to 2.5 mm were obtained in a dimensionally stable manner from the above-prepared parent solution by immersion and also reaction in an ammonia solution at a temperature of 60 C.

(31) These gel bodies were subsequently shaped by calcining to form sintered spheres, by a sintering process. Sintering took place in an air atmosphere under atmospheric pressure. A first step involved heating to 700-800 C. and holding there for 12 hours, in order to burn the organic constituents out of the gel without residue. The temperature was subsequently raised to 1180 C. where it was held for a further 2 hours to produce the actual reactive sintering. In order to prevent the ZrW.sub.2O.sub.8, which is meta-stable at room temperature, breaking down into the individual oxides, the ceramic ZrW.sub.2O.sub.8 spheres formed were placed in a cold stream of air to cool.

(32) Examples relating to the production of composite materials of the invention (production of formulations filled with micro-scale and sub-micro-scale particles of high sphericity from a negative-expansion material).

(33) Production of an epoxy resin precursor filled with microscale, negative-expansion filler particles for use as mould/encapsulant adhesive material in packaging applications in the semiconductor field (IC packaging)

(34) 10.0 g of a bisphenol A diglycidyl ether-based epoxy resin (density: 1.16 g/cm) with a zero-shear viscosity of 0.6 Pa s were admixed with 69.4 g of glass-ceramic powder with ZrWO.sub.2O.sub.8 as main crystal phase of a glass-ceramic composed of the phase system ZrO.sub.ZWO.sub.3-A.sub.2O.sub.3P.sub.2O.sub.5 (coefficient of thermal expansion in the temperature range between 75 and 125 C.: 2.2 ppm/K; density: 5.37 g/cm) having a particle size distribution of d.sub.10=1.27 m, d.sub.50=8.56 m, d.sub.90=17.33 m and d.sub.99=26.14 m. The particles thereof possessed a sphericity of on average =0.93. For sufficient dispersal of the filler powder, the mixture was homogenized on a tumbler for an hour. The resulting adhesive precursor had a volume fill level of 60 vol % and shear-thinning flow behaviour, with the zero-shear viscosity being 114 Pa s. It could therefore still be processed in packaging applications in the semiconductor sector (IC packaging) in relation to the intended use as mould/encapsulant adhesive material.

(35) An attempt was made to use the same procedure to produce an adhesive precursor with a glass-ceramic powder consisting of non-spherical particles (=0.58) with ZrW.sub.2O.sub.8 as main crystal phase of a glass-ceramic composed of the phase system ZrO.sub.2WO.sub.3Al.sub.2O.sub.3P.sub.2O.sub.8, having a particle-size distribution with the following values: d.sub.10=1.08 m, d.sub.50=7.78 m, d.sub.90=15.26 m, d.sub.99=21.06 m. In these cases, however, all that was obtained was a kneadable composition which could no longer be handled using metering apparatus and metering methods that are commonly employed in the context of the target application.

(36) Production of an epoxy resin precursor, filled with sub-micro-scale, negative-expansion filler particles, for use as underfill adhesive material in packaging applications in the semiconductor field (IC packaging)

(37) 20.0 g of a bisphenol A diglycidyl ether-based epoxy resin (density: 1.16 g/cm.sup.3) with a zero-shear viscosity of 0.6 Pa s were admixed with 43.5 g of glass-ceramic powder with ZrW.sub.2O.sub.8 as main crystal phase of a glass-ceramic composed of the phase system ZrO.sub.ZWO.sub.3-A.sub.2O.sub.3P.sub.2O.sub.8 (coefficient of thermal expansion in the temperature range between 75 and 125 C.: 2.2 ppm/K; density: 5.37 g/cm) having a particle size distribution of d.sub.10=0.18 m, d.sub.50=0.56 m, d.sub.90=1.17 m and d.sub.99=1.82 m. The particles thereof possessed a sphericity of =0.91. For sufficient dispersal of the filler powder, the mixture was homogenized on a tumbler for an hour. The resulting adhesive precursor had a volume fill level of 32 vol % and Newtonian flow behaviour, with the viscosity being 13 Pa s. It could therefore still be processed in packaging applications in the semiconductor sector (IC packaging) in relation to the intended use as underfill adhesive material.

(38) An attempt was made to use the same procedure to produce an adhesive precursor with a glass-ceramic powder consisting of non-spherical particles (=0.58) with ZrW.sub.2O.sub.8 as main crystal phase of a glass-ceramic composed of the phase system ZrO.sub.2WO.sub.3Al.sub.2O.sub.3P.sub.2O.sub.5, having a particle-size distribution with the following values: d.sub.10=0.09 m, d.sub.50=0.36 m, d.sub.90=0.91 m, d.sub.99=1.55 m. In these cases, however, an adhesive precursor was obtained having a zero shear viscosity of 85 Pa s which could be handled only with great difficulty using metering apparatus and metering methods that are commonly employed in the context of the target application.