Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1995-04-03
1997-08-26
Ryan, Patrick
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
4283184, 4283193, 428327, 428365, 428375, 428480, 428902, 428913, 523222, 165 46, 165185, B32B 900
Patent
active
056609175
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal conductivity sheet (heat radiating sheet, or heat releasing sheet), and more particularly to a thermal conductivity sheet which is superior in a heat radiation, electrical insulation and pliability or flexibility, which has excellent close-contact property with respect to electronic equipment parts such as transistors, capacitors and LSI packages, and which can efficiently dissipate or transmit the heat produced by parts to the exterior.
BACKGROUND ART
Electric/electronic parts such as transistors, capacitors and LSI packages tend to shorten the service life and deteriorate the reliability with the heat generated during operation. As measures for preventing Such drawbacks, it has been proposed to interpose a thermal conductivity sheet, which is superior in thermal conductivity and close-contact, between electric/electronic parts and a heat sink (cooling means), such as a heat radiating fin, thermally connected to the electric/electronic parts for dissipating the generated heat to the exterior through the thermal conductivity sheet.
The thermal conductivity sheet is generally manufactured by dispersing a thermal conductivity filler in a matrix resin and shaping the mixture into the form of a sheet. Silicone rubber, for example, is employed as the matrix resin, while boron nitride in the form of particles, plates and needles, for example, is employed as the thermal conductivity filler.
More specifically, the thermal conductivity sheet is manufactured using the above-exemplified materials of a thermal conductivity filler and a matrix resin by any of three primary methods below.
In the first method, a matrix resin (e.g., silicone rubber) and a thermal conductivity filler (e.g., boron nitride (BN)) are combined and mixed with each other to prepare a material mixture. The material mixture is then shaped into the form of a sheet by using rolls, a calender, an extruder or the like as with usual rubber materials. The shaped sheet is pressed and vulcanized.
In the second method, a matrix resin (e.g., silicone rubber) and a thermal conductivity filler (e.g., boron nitride) are mixed and diluted in a solvent. A resulting mixture is then formed into a sheet by a doctor
The sheet is dried, pressed and then blade process. vulcanized.
In the third method, a matrix resin (e.g., silicone rubber) of 100 weight parts and a thermal conductivity filler (e.g., boron nitride) of 200 or more weight parts are combined together to prepare a compound material containing the thermal conductivity filler at a high ratio. The material is mixed by using a closed type kneading machine such as a kneader to form a powdery rubber material. A predetermined amount of the powdery rubber material is filled in a mold for shaping into a sheet, following which the molded sheet is pressed and vulcanized.
FIG. 41 is a sectional view showing a structure of the conventional thermal conductivity sheet fabricated by any of the prior art manufacture methods described above. In a prior art thermal conductivity sheet 10, thermal conductivity fillers 12 are combined and distributed in a matrix resin 11 in a condition where the long axes of the thermal conductivity fillers 12 are oriented in the direction of plane of the thermal conductivity sheet 10 (the longitudinal direction thereof).
The thermal conductivity fillers 12 are oriented so longitudinally of the sheet because the fillers 12 are aligned in the direction of rolling or extrusion when the material mixture is rolled or extruded for shaping into the sheet.
The inventors have found that the thermal conductivity sheet fabricated by any of the prior art manufacture methods has a problem below. Since the thermal conductivity fillers 12 are oriented in the direction of sheet plane, there is a tendency that the adjacent thermal conductivity fillers 12 are contacted with each other and the thermal conductivity fillers 12 as a whole are substantially continuously extended in the direction of plane of the thermal conductivity sheet 10 (the longitud
REFERENCES:
patent: 4256792 (1981-03-01), Koepke et al.
Endo Hiroshi
Fujimori Yoshinori
Hisano Katsumi
Iwasaki Hideo
Momma Jun
Bahta Abraham
Kabushiki Kaisha Toshiba
Ryan Patrick
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