Adhesion method and electronic component

Abstract: The present invention provides an adhesion method of improving the heat conduction in a fixed direction by using a heat conductive adhesive made by blending boron nitride powder and adhesive polymer and adhering by orienting boron nitride powder in the heat conductive adhesive to a fixed direction under the magnetic atmosphere. The invention also provides an electronic component for effectively dissipating heat generated from a semiconductor device (2), power source (4), light source or other components used for electric products, and an electronic component having excellent radiation.

Description: The present invention relates to an adhesion method of heat conductive adhesive requiring high heat conductivity, and to an electronic component. More particularly, it concerns an adhesion method of heat conductive adhesive for effectively dissipating heat generated from a semiconductor device, power source, light source or other components used for electric products, and an electronic component having excellent radiation properties. Conventionally, heat conductive adhesives having adhesive polymer as a matrix have been used for bonding a heat generating semiconductor device or electronic component with a heat radiating conductive member. Silver, copper, gold, aluminium, or other metals and alloys having a good heat conductivity, or aluminium oxide, magnesium oxide, silicon oxide, boron nitride, aluminium nitride, silicon nitride, silicon carbide or other ceramics, carbon black, graphite, diamond or various other heat conductive fillers are blended in these heat conductive adhesives, in order to enhance the heat conductivity. Among others, electric insulation heat conductive adhesives filled with boron nitride powder, having excellent heat conductivity and electric insulation are used largely. On the other hand, the Japanese Patent Laid-open No. SHO 62-194653 and Japanese Patent Laid-open No. SHO 63-62762 disclose adhesion methods for improving heat conductivity by orienting an adhesive including magnetic substance such as nickel in a magnetic field. However, boron nitride powder has a heat conductivity in a flake shape thickness direction smaller than a heat conductivity in the surface direction; therefore, an adhesive blending simply boron nitride powder in a polymer could not present a sufficient conductivity as its surface direction is charged in parallel to the thickness direction in the adhesive layer after adhesion. On the other hand none of the adhesion methods of the aforementioned Japanese Patent Laid-open No. SHO 62-194653 or the Japanese Patent Laid-open No. SHO 63-62762 could be applied to an application requiring electric insulation for blending electric conductive magnetic metal powder or the like. In other words, as an adhesion method having a good electric insulation and high heat conductivity has not been developed, and considerable heat generation from semiconductor devices or other electric components accelerates electro-chemical migration or corrosion of wiring or pad portions, and the generated heat stress provokes cracking or destruction of composing material, the interface of composing material junctions may peel off, or other problems occur in a way to shorten the life of electronic components. On the other hand, the heat conductive adhesive of the Japanese Patent Laid-open No. 2000-273426, by the Applicant, has diamagnetic filler of 20W/m·K or more in heat conductivity blended in the adhesive, but boron nitride powder was not taken into account as diamagnetic filler. For the purpose of solving the aforementioned problems, the present invention provides an adhesion method of heat conductive adhesive for effectively dissipating heat generated from a semiconductor device, power source, light source or other components used for electric products, and an electronic component having excellent radiation properties. For this effect, the present invention provides an adhesion method of improving the heat conduction in a fixed direction by using a heat conductive adhesive made by blending a particular boron nitride powder and adhesive polymer, and adhering by orienting boron nitride powder in the heat conductive adhesive to a fixed direction under a magnetic field atmosphere. The invention in one aspect provides an adhesion method of adhering objects to be adhered by interposing a heat conductive adhesive made by blending boron nitride powder that has an-isotropic magnetic susceptibility and adhesive polymer between said objects, and adhering by orienting boron nitride powder in the heat conductive adhesive to a fixed direction under a magnetic field atmosphere by the use of the an-isotropic magnetic susceptibility of the boron nitride powder. The invention in another aspect provides an electronic component characterized by its structure wherein a heat conductive adhesive made by blending boron nitride powder that has an-isotropic magnetic susceptibility and adhesive polymer is interposed between a heating device and a heat conductive member, and adhering with boron nitride powder oriented in the heat conductive adhesive to a fixed direction under a magnetic field atmosphere by the use of the an-isotropic magnetic susceptibility of the boron nitride powder. The invention will be further described with reference to the accompanying drawings, in which: Fig. 1 to Fig. 4 are examples of electronic components made by the adhesion method of the present invention; and Fig. 5 and Fig. 6 are schematic views of the adhesion method and electronic component of the present invention. Boron nitride powder used in the present invention is not particularly specified as regards the kind of crystalline system, shape or size of powder particle, aggregation rate of powder particle, or their distribution. Concerning the crystalline system, boron nitride powder of hexagonal system, cubic system or other structures can be used. Particularly, highly crystalline boron nitride powder of hexagonal system or cubic system is preferable, because of its excellent heat conductivity. The particle form of boron nitride powder is not limited to flake form or flat form, but also various other forms of boron nitride powder, such as granular, massive, spherical, fiber, whisker form boron nitride powder, or ground product thereof can be used. The particle diameter of boron nitride powder is not specified; however, individual average primary particle diameter in the range of 0.01∼ 100µm, and more preferably in the range of 1∼50µm can be used. Under 0.01µm, it is difficult to charge in quantity, and boron nitride powder larger than 100µm is difficult to produce, and disadvantageous in terms of price. In addition, the adhesion layer becomes thick. As for the flake form boron nitride powder, it is practical to use within the range of 0.5∼50µm in its maximum diameter, because it can easily be blended with polymer and field oriented. Further, boron nitride powder having a structure where primary particles are aggregated is used. The quantity of boron nitride powder to be contained in adhesive polymer is preferably 10∼400 weight parts to 100 weight parts of polymer. Less than 10 weight parts, the improvement effect of heat conductivity is small, while a content more than 400 weight parts increases the composition viscosity and reduces the fluidity, making the handling difficult and bubble inclusion inevitable, so it is not appropriate. More preferably, boron nitride powder is added in 20∼300 weight parts, and still preferably 30 ∼ 200 weight parts. Higher concentrations may also be obtained by using boron nitride powders of different particle diameter, or by surface treatment. Preferable adhesive polymers for matrix include liquid or solid material made of epoxy base, polyimide base, acryl base, vinyl base such as polyvinyl acetate, urethane base, silicone base, olefin base, polyamide base, polyamideimide base, phenol base, amino base, polyimide silicone base, saturated and unsaturated polyester base, diallyl phthalate base, urea base, melamine base, alkyd base, benzo-cyclobutene base, polybutadiene or chloroprene rubber, nitrile rubber or other synthetic rubber base, styrene base thermoplastic elastomer or other publicly known resins or rubber. As for hardening system, adhesive polymer of all known all hardening systems, such as thermosetting, thermoplastic, ultraviolet or visible light curing, room temperature setting, moisture curing, or the like can be used. Among others, at least one selected from epoxy base, polyimide base, aryl base or silicone base adhesive polymers that present good adhesion with materials composing the electronic component such as various metals and ceramics, various plastics and rubbers, elastomers, is preferable. Besides, for the purpose of boron nitride powder surface treatment, it is possible to improve the wetness with adhesive polymer or chargeability by previously degreasing or cleaning the boron nitride powder surface, or through surface treatment with silane base, titanium base or aluminium base or other known coupling agent. It is also possible to add thixotropic agent, disperser, hardener, setting accelerator, delayer, tackifier, plasticizer, fire retardant, anti-oxidant, stabilizer, colourant or other known additives to the adhesive polymer used in the present invention. Moreover, it is also possible to use at the same time conveniently powder form metals and ceramics, to be more specific, silver, copper, gold, platinum, nickel, carbon, graphite, diamond, aluminium oxide, magnesium oxide, aluminium nitride, silicon oxide, silicon carbide, or the like, or fillers used for conventional heat conductive adhesives such as metal coating resin. However, as excellent electric insulation is one of the characteristics of the heat conductive adhesive used for the present invention, it is preferable, as far as possible, not to mix fillers of good electric conductivity such as metals. Moreover, in order to reduce the adhesive viscosity, it is effective to add volatile organic solvent or reactive plasticizer as they increase the workability. The adhesion method of the present invention is an adhesion method of adhering objects to be adhered by interposing a heat conductive adhesive made by blending particular boron nitride powder and adhesive polymer between said objects, and adhering by orienting boron nitride powder in the heat conductive adhesive to a fixed direction under the magnetic atmosphere. It is possible to improve the adhesive heat conductivity taking advantage of the high heat conductivity of oriented boron nitride powder, by orienting boron nitride powder in the adhesive along the magnetic line, under the magnetic atmosphere. In order to align flake or other form boron nitride powder in the gap direction of objects to be adhered, namely in the adhesive thickness direction, N pole and S pole of permanent magnet or electromagnet are opposed in the thickness direction, and disposed so that the magnetic line corresponds to the desired orientation direction of boron nitride powder. On the other hand, in order to enhance the heat conductivity in the adhesive plane inside direction, boron nitride powder can be oriented aligned in the plane inside direction by opposing the magnet N pole and S pole vertically to the thickness direction. Otherwise, boron nitride powder can also be aligned in the plane inside direction by opposing the magnet N pole and N pole, or S pole and S pole in the thickness direction. Besides, magnets need not to be opposed at both sides, but magnets disposed only on one side may also orient boron nitride powder in the adhesive. Magnetic field generation means use as exterior magnetic field may be a permanent magnet, electromagnet or coil, and a flux density range from 0.05 to 30 tesla can achieve a practical orientation of boron nitride powder. As the present invention uses a very weak an-isotropic magnetic susceptibility of boron nitride powder as magnetism, it is necessary to orient boron nitride powder sufficiently in a high magnetic field of 1 tesla or more, and to set matrix adhesive polymer by thermosetting reaction or cooling. The heat conductive adhesive used in the present invention can be produced by blending and evenly dispersing a predetermined amount of boron nitride powder in the adhesive polymer. For dispersion by mixing or kneading, it is preferable to add a known process for removing mixed bubbles by depression or pressurization. An electronic component of the present invention as shown in Fig. 1 to Fig. 4 can be manufactured by interposing a heat conductive adhesive made of particular boron nitride powder and adhesive polymer between a heating device and a heat conductive member, and adhering with boron nitride powder oriented in the heat conductive adhesive to a fixed direction under the magnetic atmosphere. Fig. 1 shows use for adhesion between a ball grid array type semiconductor package 2 and a radiator 4. Fig. 2 shows use for adhesion between a chip size type semiconductor package 2 and a printed circuit board 1; Fig. 3 shows use for adhesion between a pin grid array type semiconductor package 2 and a heat sink 5; and Fig. 4 shows use for adhesion between a semiconductor chip 8 and a die pad 7. Heat conductive adhesive can be interposed between objects to be adhered by screen printing, pad printing, dispenser application, potting, spray coating or other known methods. Heating devices include semiconductors, electric power sources or light sources, and heat conductive members include an ordinary radiator, cooler, heat sink, heat spreader, die pad, printed circuit board (PCB), cooling fan, heat pipe or casing. The heat conductive adhesive is denoted by reference numeral 3 in the drawings. Now, the present invention will be described more in detail based on examples. In the following examples and comparison examples, the heat conductivity was evaluated through the measurement of heat resistance value. Example 1 A heat conductive adhesive A is prepared by blending 40 weight parts of hexagonal crystalline system flake form boron nitride powder (made by Showa Denko K.K. UHP-S1 average particle diameter 1 to 2µm) treated with aminosilane base coupling agent and 100 weight parts of bisphenol F type epoxy resin containing amine base hardener as adhesive polymer, and degassing in a vacuum. The heat conductive adhesive A is applied with a dispenser to a ball grid array type semiconductor package 2 implemented on a PCB 1 shown in Fig. 5(1) (Fig. 5(2)). A radiator 4 is disposed and pressed on the upper portion of the heat conductive adhesive A as shown in Fig. 5(3), and an electronic component (Fig. 5(5)) is prepared by heat setting the heat conductive adhesive A in a magnetic field atmosphere where N pole and S pole of a permanent magnet 11 of flux density 0.6 tesla are opposed as shown in Fig. 5(4). The apparatus is turned on to measure the heat resistance after 6 minutes, obtaining 0.48°C/W. Comparison 1 A heat conductive adhesive A similar to the Example 1 is applied with a dispenser to a ball grid array type semiconductor package 2 implemented on a PCB 1 shown in Fig. 5(1) (Fig. 5(2)). A radiator 4 is disposed and pressed on the upper portion of the heat conductive adhesive A as shown in Fig. 5(3), and an electronic component (Fig. 5(5)) is prepared by heat setting the heat conductive adhesive A without impressing the magnetic field. The apparatus is turned on to measure the heat resistance after 6 minutes, obtaining 0.61°C/W. Example 2 A heat conductive adhesive B is prepared by blending 80 weight parts of hexagonal crystalline system flake form boron nitride powder (made by Showa Denko K.K. UHP-S1 average particle diameter 1 to 2µm) and 100 weight parts of added type liquid silicon rubber (made by GE Toshiba silicones, TSE3331) as adhesive polymer, and degassing in a vacuum. The heat conductive adhesive B is applied with a dispenser to a ball grid array type semiconductor package 2 implemented on a PCB 1 shown in Fig. 5(1) (Fig. 5(2)) as in the Example 1. A radiator 4 is disposed and pressed on the upper portion of the heat conductive adhesive B as shown in Fig. 5(3), and an electronic component (Fig. 5(5)) is prepared by heat setting the heat conductive adhesive B in a magnetic field atmosphere where N pole and S pole of an electromagnetic magnet 11 of flux density 2 tesla are opposed as shown in Fig. 5(4). The apparatus is turned on to measure the heat resistance after 6 minutes, obtaining 0.37°C/W. Comparison 2 A heat conductive adhesive B similar to the Example 2 is applied with a dispenser to a ball grid array type semiconductor package 2 implemented on a PCB 1 shown in Fig. 5(1) (Fig. 5(2)). A radiator 4 is disposed and pressed on the upper portion of the heat conductive adhesive B as shown in Fig. 5(3), and an electronic component (Fig. 5(5)) is prepared by heat setting the heat conductive adhesive B without impressing the magnetic field. The apparatus is turned on to measure the heat resistance after 6 minutes, obtaining 0.48°C/W. Example 3 A heat conductive adhesive C is prepared by blending 120 weight parts of hexagonal crystalline system fine particle form boron nitride powder (made by Denki Kagaku Kogyo K.K. SP-1 average particle diameter 0.6µm) and 100 weight parts of thermo-setting polyimide (made by Ube Industries, Ltd. Yupitite UPA-83), and degassing in a vacuum. The heat conductive adhesive C is screen printed on a die pad 7 of a lead frame 6 shown in Fig. 6(1) (Fig. 6(2)). A semiconductor chip 8 is disposed and pressed on the upper portion of the heat conductive adhesive C as shown in Fig. 6(2), and the heat conductive adhesive C is heat set in a magnetic field atmosphere where N pole and S pole of an electromagnetic magnet 11 of flux density 2 tesla are opposed as shown in Fig 6(3). An electronic component(Fig. 6(5)) is manufactured by connecting an electrode portion of the semiconductor chip 8 and a lead portion of the lead frame 6 by a bonding wire 9 (Fig. 6(4)) and by transfer molding with epoxy base sealant 10. The apparatus is turned on to measure the heat resistance after 6 minutes, obtaining 0.28°C/W. Comparison 3 A heat conductive adhesive C similar to Example 3 is screen printed on a die pad 7 of a lead frame 6 shown in Fig. 6(1) (Fig. 6(1)). A semiconductor chip 8 is disposed and pressed on the upper portion of the heat conductive adhesive C as shown in Fig. 6(2), and the heat conductive adhesive C is heat set without impressing the magnetic field. An electronic component (Fig. 6(5)) is manufactured by connecting the electrode portion of the semiconductor chip 8 and the lead portion of the lead frame 6 by a bonding wire 9 (Fig. 6(4)) and by transfer molding with epoxy base sealant 10. The apparatus is turned on to measure the heat resistance after 6 minutes, obtaining 0.40°C/W. Compared to Comparison 1∼Comparison 3, the electronic components made by the adhesion methods of Example 1∼Example 3 of the present invention are low in heat resistance value and excellent in heat conductivity because boron nitride powder is oriented by magnetic field in the heat conductive adhesive. Therefore, the adhesion method of the present invention can be applied largely to the adhesion of a semiconductor package of high heating value and a radiator such as a heat sink, or adhesion of a semiconductor chip of high heating value and a die pad portion, and supply a useful electronic component that is low in heat resistance and excellent in heat conductivity.

Claims: An adhesion method of adhering objects to be adhered by interposing a heat conductive adhesive made by blending boron nitride powder that has an-isotropic magnetic susceptibility and adhesive polymer between said objects, and adhering by orienting boron nitride powder in the heat conductive adhesive to a fixed direction under a magnetic field atmosphere by the use of the an-isotropic magnetic susceptibility of the boron nitride powder. An adhesion method as claimed in claim 1, characterized in that the heat conductive adhesive comprises 10 to 400 weight parts of boron nitride powder to 100 weight parts of adhesive polymer. An adhesion method as claimed in claim 1 or 2, characterized in that the adhesive polymer is at least one kind selected from epoxy base, polyimide base, acryl base, urethane base and silicon base adhesive polymer. An adhesion method as claimed in any of claims 1 to 3, characterized in that the boron nitride powder is of flake form and a maximum primary particle diameter of the boron nitride powder is in the range of 0.5 to 50 µm. An adhesion method as claimed in claims 1 to 4, characterized in that the heat conductive adhesive has electric insulating properties. An electronic component characterized by its structure wherein a heat conductive adhesive made by blending boron nitride powder that has an-isotropic magnetic susceptibility and adhesive polymer is interposed between a heating device and a heat conductive member, and adhering with boron nitride powder oriented in the heat conductive adhesive to a fixed direction under a magnetic field atmosphere by the use of the an-isotropic magnetic susceptibility of the boron nitride powder. An electronic component as claimed in claim 6, characterized in that the boron nitride powder is of flake form and a maximum primary particle diameter of the boron nitride powder is in the range of 0.5 to 50 µm. An electronic component as claimed in claim 6 or 7, characterized in that the heat conductive adhesive has electric insulating properties.

Inventors: KIMURA TSUNEHISA, TATEDA SHINYA, TOBITA MASAYUKI, YAMATO MASAHUMI, KIMURA, TSUNEHISA, TATEDA, SHINYA, TOBITA, MASAYUKI, YAMATO, MASAHUMI
Applicants: POLYMATECH CO LTD, POLYMATECH CO., LTD.
Application year: 2000
Main classification: C09J5
IPC codes: C09J5, H01L23, C01B21, C09J201, C09J9, H01L21, C09J11