EP0114000B1 - Charge thermoconductrice pour capsuler des composants électriques - Google Patents

Charge thermoconductrice pour capsuler des composants électriques Download PDF

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Publication number
EP0114000B1
EP0114000B1 EP83307923A EP83307923A EP0114000B1 EP 0114000 B1 EP0114000 B1 EP 0114000B1 EP 83307923 A EP83307923 A EP 83307923A EP 83307923 A EP83307923 A EP 83307923A EP 0114000 B1 EP0114000 B1 EP 0114000B1
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EP
European Patent Office
Prior art keywords
housing
filler
particles
slurry
volume
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP83307923A
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German (de)
English (en)
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EP0114000A1 (fr
Inventor
Charles Lien
Derek Wayne Whitehead
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ferranti International PLC
Original Assignee
Ferranti PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
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Application filed by Ferranti PLC filed Critical Ferranti PLC
Publication of EP0114000A1 publication Critical patent/EP0114000A1/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/46—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes silicones
    • H01B3/465—Silicone oils

Definitions

  • This invention relates to a novel fhermally conductive filler for insulating the interior of a housing containing electrical components and to a method of filling the housing and encapsulating the electrical components with the thermally conductive medium.
  • potting resins provide mechanical protection of the potted components but the thermal conductivity of such resins is relatively poor.
  • the thermal conductivity of typical potting material now used is of the order of 0.00021 kW/m.k (0.0005 cal/sec.cm.°C). Therefore, heat generated by the electrical components within the housing is not easily conducted to external surfaces of the housing.
  • thermally conductive particles can be added to polymerized potting resins in order to increase the thermal conductivity of the potting material.
  • These thermally conductive particles are generally electrically insulative ceramics which have good thermal conduction characteristics and typically may be beryllium oxide, aluminium oxide, boron nitride or some types of silicon carbide. These thermally conductive particles are normally stirred into the potting resin just before the resin is poured into the interior of a housing.
  • U.S. patent 4,265,775 describes the use of a number of these thermally conductive materials in particle or powder form, whilst U.S. patent 3,137,665 refers to the use of granular inorganic fillers of the same type.
  • British patent No. 874,801 describes the use of crystalline silicon carbide as a filler, though this is not an electrically-insulating material.
  • German patent 1,439,456 describes the use of a material which includes fine particles of, for example, quartz, metal, metal oxide or metal carbide to improve heat dispersal.
  • the thermal conductivity of the insulation medium with the added particles is usually only about twice that of the resin itself.
  • aluminium oxide for example, has a bulk thermal conductivity of 0.035 kW/m.K (0.084 cal/sec.cm °C) when particles of the ceramic consists of about 50% of the total volume of a conventional polymerized potting resin
  • the thermal conductivity of the ultimate material will be increased from about 0.00021 kW/m.K (0.0005 cal/sec.cm °C) to about 0.00042 kW/ m.K (0.001 cal/sec.cm °C).
  • the interior of an electrical housing filled with heat-generating devices is filled with and easily flowing slurry consisting of a mixture of more than 50% by volume and preferably more than 70% by volume of heat-conductive, electrically insulative particles, suspended in a dielectric fluid, together with a plurality of freely-suspended filler blocks of a material having the same properties as the mixture.
  • the dielectric fluid is preferably a liquid such as silicone oil.
  • the thermally conductive particles typically may be aluminium oxide particles or the like having a particle size which is preferably distributed about a mean diameter of about 150 micrometer. Beryllia can also be used, but it is more expensive than aluminum and is very toxic in powdered form.
  • the filler blocks may be of any required size and shape, since their purpose is simply to reduce the quantity of the slurry required to fill a space.
  • the term "freely-suspended" as used with reference to the filler blocks means that they are not attached to the housing or to any of the components contained therein and are substantially surrounded by the slurry.
  • the slurry is first mixed at room temperature by pouring the particles into the dielectric fluid and agitating this mixture. Slurry is then poured into a filler column which, in turn, is connected to the open top of the electrical housing. As the level of the slurry reaches large empty spaces in the housing solid filler blocks of appropriate size are fed into the housing, followed by more slurry. The filler column and housing are sealed to be air-tight so that the slurry cannot freely escape from the interior of the housing. The slurry is then subjected to vacuum to remove trapped air bubbles therefrom and the slurry is permitted to settle into the housing interior under the force of gravity. During the settling period, the assembly is tilted in different directions to eliminate Rankine slope effects. Oil appearing at the top of the column is decanted and replaced by additional slurry during the settling process. The volumetric packing density after settling for about 36 hours will often exceed 80% of particles by volume.
  • the slurry particles and filler blocks are then further compacted against one another to form a relatively non-flowable paste.
  • This further compacting can be carried out by a centrifugal process.
  • the entire housing is spun at moderate 'g" force for about two hours in a suitable fixture.
  • the insulation particles and filler blocks which are more dense than the suspending liquid, tend to compact in one direction relative to the housing due to centrifugal force effects and the particles form a paste-like consistency in which silicone oil fills the interstices between particles.
  • the paste now forms an almost solid continuous body which encapsulates the components and extends between the components and to the interior of the surrounding walls of the housing. It has been found that the final highly compacted mass has a thermal conductivity close to that of a solid block of the insulation material which is employed.
  • the filler column is then removed and the paste, which extends above the top of the open housing end, is sliced off to be flush with the housing top.
  • a housing lid is then sealed over the housing top to complete the enclosure.
  • the housing is made of conductive material to act as a heat sink to heat conducted form internal potted components through the encapsulant.
  • housing 10 which may be of a good thermal conductor, preferably of aluminium, and which may have any desired thickness.
  • Housing 10 has a top lid 11 attached and sealed thereto in any desired manner.
  • the housing 10 can typically have dimensions of 5 cm (2 inches) by 10 cm (4 inches) by 12.5 cm (5 inches) but it will be obvious that the invention can apply to any housing size which contains any type of component.
  • heat-generating electrical components are mounted within the housing and are schematically illustrated as the heat-generating components 12, 14, 16, 18, 20 and 22. These components can be of any desired nature.
  • component 12 could be a bridge-connected rectified circuit which might produce 4.8 watts during its operation.
  • Component 14 could be an inverter transformer which produces 25 watts during its operation.
  • Components 16 to 22 could be the elements of a bridge-connected rectifier which produces 1.2 watts.
  • Components 16 to 22 can be carried on a common circuit board with other components, not shown.
  • An electrical connector shown in the form of a multi-conductor ribbon 24 carries suitable wires from the interior electrical components of housing 10 to the exterior where the wires can be connected to other circuits. A suitable insulation seal can enclose and seal ribbon 24 as it passes through the wall of housing 10.
  • a multi-pin connector can be formed in the wall of housing 10 and individual wires from the components within housing 10 can be connected to the multi-pin connector.
  • the components can be thermally connected to the exterior walls of housing 10 by the noval heat conductive insulation of the invention which encapsulates the electrical components.
  • the housing 10 is provided with an open top (lid 11 is removed) and the electrical components to be mounted therein are fixed in place.
  • a filler column (not shown) which has a volume larger than that of housing 10, is sealed to the top of housing 10.
  • an insulation medium is prepared as a relatively non-viscous slurry of particles of a material having good thermal conductive properties but which are electrically insulative, suspended in an insulation fluid.
  • Typical particles may be of aluminium oxide, beryllium oxide, boron nitride and certain types of known silicon carbides.
  • the particle size employed for these particles is not critical. Good results have been obtained with particles distributed about a mean diameter of less than about 300 micrometer which ensures uniform and homogeneous filling of the particles within housing 10 and into very small irregular crevices or the like, in the interior of housing 10.
  • the particles are loaded into a suitable dielectric fluid as silicone oil at room temperature an stirred to ensure thorough mixing and uniform distribution of the particles into the oil. There should be sufficient oil present in the mixture to ensure that the slurry will flow easily into the interior of housing 10. The particles should occupy more than one half by volume of the slurry.
  • a suitable dielectric fluid as silicone oil
  • aluminium oxide particles have a size distributed around a mean diameter of about 150 micrometer are stirred into a silicone oil carrier.
  • the powder and oil are in a ratio of about 70% to 30% respectively, by volume.
  • the slurry is very easily flowable in this condition.
  • Other stable dielectric fluids can be used in place of silicone oil.
  • the slurry is then poured into the filler column connected to container 10 of Figure 1 and 2.
  • the interior of the housing contains large voids solid filler blocks, such as blocks 34 and 36, are added, followed by further quantities of the slurry, and this is repeated until the container is full.
  • Further slurry is added to at least partially fill the filler column.
  • a vacuum is then applied to the filler column and housing to remove trapped air bubbles and the slurry is then permitted to settle into container 10 for a given settling period, for example, 36 hours.
  • the unit an column are tilted to different orientations to eliminate Rankine slope effects.
  • oil at the top of the column is decanted and is replaced with the 70% to 30% by volume slurry.
  • the alumina particles will reach a packing density in excess of 80% by volume of the slurry.
  • the assembly is then placed in a centrifugal apparatus and is rotated at a moderate "g" force to cause the aluminium oxide particles to compact further.
  • the compacted particles and filler blocks now form an almost solid past-like body which adheres to all exposed surfaces within housing 10 and which encapsulates all components within the housing.
  • a conductive lid 30 is then fastened to the top of housing 10.
  • a compressible synthetic rubber pad 31 is fixed to the interior of lid 31 to keep the paste under positive pressure within housing 10.
  • Paste compacted in this way and employing aluminium oxide particles had a thermal conductivity of the order of 0.0293 kW/m.K (0.07 cal/sec.cm °C) as compared with a thermal conductivity of 0.035 kW/m.K (0.084 cal/sec.cm °C) for the solid material.
  • the blocks can have any desired shape and reduce the volume of compacted particles needed to fill the housing interior.
  • the filler blocks 34 and 36 may be of the same ceramic material as the particles of the slurry and, in the preferred example, are of aluminium oxide.
  • the electrical components 12 through 22 were capable of having a working surface temperature of 220°C.
  • the mean free path distances from the surfaces of components 12 and 14 and of components 16,18,20 and 22 collectively was 25 mm (1 inch), 10 mm (0.375 inch) and 25 mm (1 inch) respectively, and their effective areas were 13 square cm (2 square inches), 255 square cm (8 square inches) and 26 square cm (4 square inches) repectively.
  • a magnetic/rectifier module of a 550 watt inverter working at 1 watt per cubic cm (16 watts per cubic inch) had an internal dissipation of the order of 30 watts.
  • the steady state temperature difference between the centre module and the outside walls was less than five centigrade degrees.
  • thermal conductivity for the encapsulating material with the proportion of filler. This is tabulated in the following table for two theoretical materials, one a thermally condutive powder and one a fluid. The thermal conductivities are shown for three alternative thermal conductivity ratios of the powder to fluid of 10:1, 100:1, 1000:1.
  • the table also shows that it would be valuable to achieve volumatic fill proportions of the more conductive material of greater than about 80%, and specifically in the range from 90% to 96%, and thereby obtain a significant proportion of the available benefits of the material with a ratio of 100:1.
  • the table also shows that the benefits of a 1000:1 material cannot be obtained until a loading of virtually 100% has been achieved.

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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
  • Organic Insulating Materials (AREA)

Claims (6)

1. Charge thermoconductrice pour capsuler des composants électriques contenus dans un boîtier, la charge comprenant un mélange de particules thermoconductrices électriquement isolantes et d'un fluide diélectrique formant une bouillie appropriée pour remplir complètement et de façon homogène tous les espaces à remplir dans ledit boîter, les particules constituant plus de 509 en volume de la bouillie avant d'être introduites dans le boîter et pouvant être ensuite comprimées pour former une pâte, dans laquelle les particules constituent plus de 80% en volume, caractérisée en ce que la charge comprend plusieurs blocs de charge en suspension libre d'une matière ayant les mêmes propriétés que ledit mélange, de manière à réduire le volume dudit mélange requis pour remplir le boiter.
2. Charge selon la revendication 1, caractérisée en ce que lesdites particules ont un diamètre moyen d'environ 150 micromètres.
3. Charge selon l'une quelconque des revendications 1 ou 2, caractérisée en ce que les particules sont formées d'une matière céramique.
4. Charge selon la revendication 3, caractérisée en ce que la matière céramique est choisi dans le groupe comprenant les oxydes métalliques, les nitrures métalliques et les carbures métalliques.
5. Charge selon l'une quelconque des revendications 1 à 4, caractérisée en ce que le fluide diélectrique est une huile de silicone.
6. Procédé de remplissage d'un boiter contenant des composants électriques à l'aide d'une charge telle que revendiquée dans l'une quelconque des revendications précédentes, caractérisé en ce que ledits blocs de charge sont introduits dans des espaces ménagés dans le boiter, avant le remplissage des espaces restants à l'aide de ladite bouillie.
EP83307923A 1983-01-11 1983-12-22 Charge thermoconductrice pour capsuler des composants électriques Expired EP0114000B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US45719983A 1983-01-11 1983-01-11
US457199 1983-01-11

Publications (2)

Publication Number Publication Date
EP0114000A1 EP0114000A1 (fr) 1984-07-25
EP0114000B1 true EP0114000B1 (fr) 1986-10-01

Family

ID=23815819

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Application Number Title Priority Date Filing Date
EP83307923A Expired EP0114000B1 (fr) 1983-01-11 1983-12-22 Charge thermoconductrice pour capsuler des composants électriques

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EP (1) EP0114000B1 (fr)
DE (1) DE3366648D1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2168855B (en) * 1984-12-20 1987-11-25 Stanley Electric Co Ltd Encapsulated electronic circuit
US5098609A (en) * 1989-11-03 1992-03-24 The Research Foundation Of State Univ. Of N.Y. Stable high solids, high thermal conductivity pastes
DE69709978T2 (de) * 1996-04-30 2002-11-21 Denki Kagaku Kogyo K.K., Tokio/Tokyo Wärmeableitende Abstandhalter für elektronische Einrichtungen
EP0951207B1 (fr) * 1998-03-23 2000-12-20 Di Boer Fabrizio & C. SNC Negesat Boítier de protection pour applications spatiales
TWI251320B (en) * 2003-07-04 2006-03-11 Fuji Polymer Ind Thermal conductive composition, a heat-dissipating putty sheet and heat-dissipating structure using the same

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE565347A (fr) * 1957-03-04
US3137665A (en) * 1960-11-28 1964-06-16 Dow Corning Highly filled vinyl polysiloxane potting composition
DE1439456A1 (de) * 1964-10-15 1969-05-29 Siemens Ag Halbleiterbauelement mit Gehaeuse
BE755079A (fr) * 1969-08-21 1971-02-22 Ciba Geigy Procédé et dispositif pour imprégner des articles ou pièces, notamment des bobinage électriques, au moyen de masses durcissables de résine coulée
US3885984A (en) * 1973-12-18 1975-05-27 Gen Electric Methyl alkyl silicone thermoconducting compositions
US4265775A (en) * 1979-08-16 1981-05-05 International Business Machines Corporation Non-bleeding thixotropic thermally conductive material

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
W. BATEL "Einführung in die Korngrössenmesstechnik", 2nd edition, 1964; SPRINGER, Berlin, Zur Praxis der Kennzeichnung einer Korngrö~enverteilung, pp. 21-23,56,57 *

Also Published As

Publication number Publication date
DE3366648D1 (en) 1986-11-06
EP0114000A1 (fr) 1984-07-25

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