DE112019005062T5 - Thermal substrates - Google Patents

Abstract

A thermal substrate comprises a multilayer film, a first conductive layer adhered to the first outer layer of the multilayer film, and a second conductive layer adhered to the second outer layer of the multilayer film. The multilayer film includes a first outer layer comprising a first thermoplastic polyimide, a core layer comprising a polyimide, and a second outer layer comprising a second thermoplastic polyimide. The multilayer film has a total thickness in a range from 5 to 150 µm, and the first outer layer, the core layer and the second outer layer each comprise a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness in a range from 250 to 3000 μm.

Description

FIELD OF REVELATION

The present disclosure is in the field of thermal substrates.

BACKGROUND OF THE REVELATION

In the power electronics industry, electrically insulating layers in a power electronics module are critical for separating circuits and thermal management layers. Thermal substrates in the assembly of power electronics with high power density are rigid plates on which semiconductor chips can be mounted. In addition to mechanical support, these substrates also provide electrical insulation for the circuit and the chip and provide a thermally efficient path for heat dissipation. Power module devices, such as those found in automobiles, manipulate various forms of currents and voltages to control devices and require large currents to flow through their substrates and a high degree of electrical isolation. To meet the competing needs of both conduction and insulation, thermal substrates take the form of multilayer structures that include both conductive and insulating layers of different materials such as metals (as conductors) and ceramics or polymers (as insulators), and connect them together in a way that allows a path for heat to flow away from the semiconductor chip.

The most common structures used for thermal substrates are DBC components (DBC = Direct Bond Copper), which are formed by a high-temperature bonding process between copper and a ceramic with high thermal conductivity, such as Al ₂ O ₃ , AlN or Si ₃ N ₄ become. In a typical DBC structure, layers of metal and ceramic are bonded together in a high temperature, controlled environment process, resulting in a thermally conductive and electrically insulating ceramic layer between two layers of copper foil. However, since these metal and ceramic layers have large differences in terms of the coefficient of thermal expansion (CTE), the bond between them is exposed to large thermomechanical stresses, which lead to deterioration under high temperature gradients during operation of the power module. In addition, in the processes used to connect copper layers to the ceramic, the thickness of the copper layers is limited to less than 1000 µm. Typical DBC constructions use 300 µm copper layers and a 380 µm ceramic layer.

In recent years, organic-based insulating layers such as epoxy resins have also been commercialized for relatively inferior powered devices (i.e., for operating temperatures below 150 ° C). For such thermal substrates, the temperature of the device is limited by the chemical and mechanical stability of the organic component. Organic materials must also be loaded with thermally conductive fillers to provide acceptable thermal conductivity and are manufactured as thin films to provide thermal conductivity comparable to ceramic materials. However, these thin film epoxy resins impair the electrical insulation properties of the thermal substrate.

Polyimide films are used in the manufacture of flexible printed circuit boards because of their good electrical insulation properties, mechanical strength, high temperature stability and chemical resistance. Polyimide films are adhesively applied to thin metal foils to form metal-coated laminates and are widely used, among other things, for chip-pad bonding of flexible connection circuit boards, semiconductor devices or packaging materials for chip-scale packages, chip-on-flex, chip-on -Lead, lead-on-chip, multi-chip module, ball grid array (or micro ball grid array) and / or tape automated bonding.

The U.S. Patent No. 7,285,321 describes a multilayer laminate comprising a layer of polyimide with low glass transition temperature (T _g ), a layer of polyimide with high T _g and a conductive layer. The high T _g polyimide layer is a thermosetting polyimide and the low T _g polyimide layer is a thermoplastic polyimide. The U.S. Patent No. 6,379,784 describes an aromatic polyimide laminate composed of an aromatic polyimide composite film, a metal film and a release sheet. The aromatic polyimide composite film is composed of an aromatic polyimide substrate film and two thermoplastic aromatic polyimide layers. The metal film and the release sheet are on opposite sides of the aromatic polyimide laminate without use of additional adhesive layers with good adhesion between the polyimide laminate and the metal film.

Polyimide films can be made thermally conductive by adding thermally conductive fillers. The European patent application No. 0 659 553 A1 describes a method for providing a coextruded multilayer film which can contain thermally conductive particles. Inorganic particles of thermally conductive fillers such as BN, Al ₂ O ₃ , AlN, BeO, ZnO and Si ₃ N ₄ or mixtures thereof can be added in one or both of the layers of polyimide with high and low T _g . Fillers are typically added to the casting solution of the polymer in the form of a slurry. The solvent of the filler-based slurry can be the same as or different from the solvent used to prepare the polymer casting solution.

SHORT REPRESENTATION

A thermal substrate comprises a multilayer film, a first conductive layer adhered to the first outer layer of the multilayer film, and a second conductive layer adhered to the second outer layer of the multilayer film. The multilayer film includes a first outer layer comprising a first thermoplastic polyimide, a core layer comprising a polyimide, and a second outer layer comprising a second thermoplastic polyimide. The multilayer film has a total thickness in a range from 5 to 150 µm, and the first outer layer, the core layer and the second outer layer each comprise a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness in a range from 250 to 3000 μm.

The above general description and the following detailed description are exemplary and explanatory only and are not intended to limit the invention as defined in the appended claims.

DETAILED DESCRIPTION

A thermal substrate comprises a multilayer film, a first conductive layer adhered to the first outer layer of the multilayer film, and a second conductive layer adhered to the second outer layer of the multilayer film. The multilayer film includes a first outer layer comprising a first thermoplastic polyimide, a core layer comprising a polyimide, and a second outer layer comprising a second thermoplastic polyimide. The multilayer film has a total thickness in a range from 5 to 150 µm, and the first outer layer, the core layer and the second outer layer each comprise a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness in a range from 250 to 3000 μm.

In one embodiment of the thermal substrate, the first outer layer has a thickness in a range from 1.5 to 20 μm, the core layer has a thickness in a range from 5 to 125 μm and the second outer layer has a thickness in a range from 1.5 to 20 µm.

In another embodiment of the thermal substrate, a T _{g of} the core layer is higher than both a T _{g of} the first outer layer and a T _{g of} the second outer layer.

In yet another embodiment of the thermal substrate, the thermally conductive filler of the first outer layer is present in an amount of more than 0 to 50% by weight, based on the weight of the dry first outer layer, the thermally conductive filler of the core layer is in a Amount of more than 0 to 60 wt .-%, based on the weight of the dry core layer, and the thermally conductive filler of the second outer layer is in an amount of more than 0 to 50 wt .-%, based on the weight of the dry second outer layer, before.

In another embodiment of the thermal substrate, a weight percentage of thermally conductive filler in the core layer is higher than that of the first outer layer, the second outer layer, or both the first and second outer layers, based on the dry weight of each layer.

In yet another embodiment of the thermal substrate, the thermally conductive filler of the first outer layer, the core layer and the second outer layer is each individually selected from the group consisting of BN, Al ₂ O ₃ , AlN, SiC, BeO, diamond, Si ₃ N ₄ and mixtures thereof.

In a further embodiment of the thermal substrate, the first thermoplastic polyimide comprises an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3, 3', 4, 4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof; and an aromatic diamine selected from the group consisting of 1,3-bis (4-aminophenoxy) benzene, 2,2-bis (4- [4-aminophenoxy] phenyl) propane, and mixtures thereof.

In a further embodiment of the thermal substrate, the second thermoplastic polyimide comprises an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3, 3', 4, 4'-benzophenone tetracarboxylic acid dianhydride and mixtures thereof; and an aromatic diamine selected from the group consisting of 1,3-bis (4-aminophenoxy) benzene, hexamethylenediamine, and mixtures thereof.

In yet another embodiment of the thermal substrate, the first thermoplastic polyimide and the second thermoplastic polyimide are the same.

In yet another embodiment of the thermal substrate, the polyimide of the core layer comprises an aromatic dianhydride selected from the group consisting of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3', 4 , 4'-benzophenonetetracarboxylic dianhydride, bisphenol A dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride, and mixtures thereof; and an aromatic diamine selected from the group consisting of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis (trifluoromethyl) benzidine, m-phenylenediamine and 4,4'-diaminodiphenylmethane and mixtures thereof.

In another further embodiment of the thermal substrate, the first thermoplastic polyimide and the second thermoplastic polyimide each have a T _g in the range from 150 to 320.degree.

Many aspects and embodiments have been described above, which are only exemplary and not restrictive. After reading this specification, those skilled in the art will recognize that still other aspects and embodiments are possible without departing from the scope of the invention. Further features and advantages of the invention will be apparent from the following detailed description and from the claims.

In one embodiment, a core layer for a multilayer film comprises a polyimide synthesized by a polycondensation reaction in which a first aromatic dianhydride is reacted with a first aromatic diamine. In one embodiment, the polyimide can be one or more additional aromatic Dianhydrides, one or more additional aromatic diamines, or both one or more additional aromatic dianhydrides and one or more additional aromatic diamines. In one embodiment, an aromatic dianhydride can be selected from the group consisting of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic dianhydride, bisphenol A dianhydride , 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-naphthalenetetracarboxylic dianhydride. In one embodiment, an aromatic diamine can be selected from the group consisting of p-phenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 2,2'-bis (trifluoromethyl) benzidine (TFMB), m-phenylenediamine (MPD) and 4,4'-diaminodiphenylmethane (MDA). In one embodiment, the polyimide can comprise an aliphatic diamine. In one embodiment, the core layer can be a thermoset polyimide. In one embodiment, the core layer can comprise a polyimide with some thermoplastic properties.

In one embodiment, a first outer layer for a multilayer film comprises a first thermoplastic polyimide. In one embodiment, the first thermoplastic polyimide can be synthesized by a polycondensation reaction in which an aromatic dianhydride and an aromatic diamine are reacted. In one embodiment, the first thermoplastic polyimide can comprise one or more additional aromatic dianhydrides, one or more additional aromatic diamines, or both additional aromatic dianhydrides and additional aromatic diamines. In one embodiment, a second outer layer for a multilayer film comprises a second thermoplastic polyimide. In one embodiment, the second thermoplastic polyimide can be synthesized by a polycondensation reaction in which an aromatic dianhydride and an aromatic diamine are reacted. In one embodiment, the second thermoplastic polyimide can comprise one or more additional aromatic dianhydrides, one or more additional aromatic diamines, or both additional aromatic dianhydrides and additional aromatic diamines. In one embodiment, the first outer layer, the second outer layer, or both the first and second _{outer layers can comprise one or more aliphatic diamines, which may be useful in lowering the T g of} the outer layers, if desired. In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide can be the same or different. In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide each have a T _g in the range of about 150 to about 320 ° C.

In the context of the present invention, an “aromatic diamine” is a diamine with at least one aromatic ring either alone (ie a substituted or unsubstituted, functionalized or unfunctionalized benzene ring or similar aromatic ring) or linked to another (aromatic or aliphatic ring) , and such amine is considered aromatic regardless of any non-aromatic moieties which might also be a component of the diamine. Thus, an aromatic diamine main chain segment is to be understood as meaning at least one aromatic grouping between two adjacent imide bonds. In the context of the present invention, an “aliphatic amine” is to be understood as any organic diamine that does not correspond to the definition of an aromatic diamine.

Depending on the context, "diamine" as used herein means: (i) the unreacted form (i.e. a diamine monomer); (ii) a partially reacted form (i.e. the part or parts of an oligomer or other polyimide precursor derived from the diamine monomer or otherwise ascribable to the diamine monomer), or (iii) a fully reacted form (the part or the Portions of the polyimide derived from or otherwise attributable to the diamine monomer). The diamine can be functionalized with one or more moieties, depending on the particular embodiment chosen in practicing the present invention.

The term "diamine" is in no way intended to be limiting (or interpreted literally) as to the number of amine moieties in the diamine component. For example, (ii) and (iii) above encompass polymeric materials that can have two, one, or zero amine moieties. Alternatively, the diamine can be functionalized with additional amine moieties (in addition to the amine moieties at the ends of the monomer which react with dianhydride to propagate a polymeric chain). Such additional amine moieties could be used to crosslink the polymer or to impart other functionality to the polymer.

Similarly, the term “dianhydride” in the context of the present text is intended to denote the component that reacts with the diamine (is complementary to the diamine) and, in combination, is capable of reacting to form a polyamic acid intermediate (which then becomes a Polyimide can be cured). Depending on the context, “anhydride” within the meaning of the present text does not only need to denote an anhydride grouping itself, but can also denote a precursor of an anhydride grouping, such as, for example: (i) a pair of carboxylic acid groups (which are produced by a dehydration or similar reaction can be converted into anhydride); or (ii) an acid halide ester functionality (e.g., acid chloride ester functionality) (or any other functionality now known or to be developed in the future) that can be converted to an anhydride functionality.

Depending on the context, "dianhydride" may mean: (i) the unreacted form (i.e., a dianhydride monomer, whether the anhydride functionality is in a true anhydride form or in a precursor anhydride form, as discussed in the previous paragraph); (ii) a partially reacted form (that is, the part or parts of an oligomer or other partially reacted or precursor polyimide composition that has been reacted from a dianhydride monomer or is otherwise attributable to a dianhydride monomer), or (iii) a fully reacted form (that part or parts of the polyimide derived from the dianhydride monomer or otherwise attributable to the dianhydride monomer).

The dianhydride can be functionalized with one or more moieties, depending on the specific embodiment chosen in practicing the present invention. Indeed, the term "dianhydride" is not intended to be limiting (or interpreted literally) in any way with respect to the number of anhydride moieties in the dianhydride component. For example, (i), (ii) and (iii) (in the above paragraph) comprise organic substances which, depending on whether the anhydride is in a precursor state or a reacted state, may have two, one or zero anhydride groupings. Alternatively, the Dianhydride component can be functionalized with additional anhydride groups (in addition to the anhydride components which react with diamine to form a polyimide). Such additional anhydride moieties could be used to crosslink the polymer or to give the polymer some other functionality.

While methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

When an amount, a concentration or other value or parameter is given as either a range, preferred range or a list of upper and lower preferred values, it is to be understood that all ranges are expressly disclosed which arise from any pair of any upper range limit or any preferred value and any lower range limit or any preferred value, regardless of whether ranges are disclosed separately. If a range of numerical values is specified in this text, this range is intended to include its endpoints and all integers and fractions within the range, unless otherwise stated. It is not intended to limit the scope of the invention to the specific values mentioned in defining a range.

When describing certain polymers, it is understood that the polymers are sometimes referred to on the basis of the monomers used for their production or on the basis of the amounts of the monomers used for their production. While such description may not include the specific nomenclature used to describe the finished polymer or may not include product-by-process terminology, any such reference to monomers and amounts should be understood to mean that the polymer is made from those monomers or that amount of the monomers, and denotes the corresponding polymers and compositions thereof.

The materials, methods, and examples contained herein are for illustrative purposes only and are not intended to be limiting unless expressly stated. For the purposes of the present text, the terms “comprises”, “comprise”, “contains”, “contain”, “has”, “have” or any variation thereof are intended to encompass a non-exclusive inclusion. For example, a method, process, article, or device that includes a list of items is not necessarily limited to only those items, but may include other items not specifically listed or such a method , process, article, or device. Furthermore, unless expressly stated otherwise, “or” refers to an inclusive “or” rather than an exclusive “or”. For example, a condition A or B is met by one of the following: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

In addition, the use of “a” is used to describe elements and components of the invention. This is done for the sake of simplicity and to give a general idea of the invention. This description should be read to include one or at least one, and the singular includes the plural as well, unless it is obvious that something else is meant.

Organic solvents

Organic solvents useful for synthesizing the polyimides of the present invention are preferably capable of dissolving the polyimide precursor materials. Such a solvent should also have a relatively low boiling point, such as below 225 ° C, so that the polymer can be dried at moderate (i.e. more convenient and cheaper) temperatures. A boiling point of less than 210, 205, 200, 195, 190 or 180 ° C is preferred.

Solvents of the present invention can be used alone or in combination with other solvents (i.e., co-solvents). Useful organic solvents include: N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), N, N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetramethylurea (TMU), diethylene glycol diethyl ether, 1,2-dimethoxyethane (monoglyme), diethylene glycol (Diglyme), 1,2-bis- (2-methoxyethoxy) ethane (triglyme), bis- [2- (2-methoxyethoxy) ethyl] ether (tetraglyme), gamma-butyrolactone, bis- (2-methoxyethyl) ether, and tetrahydrofuran. In one embodiment, preferred solvents include N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc).

Cosolvents can generally be used at about 5 to 50 percent by weight of the total solvent, and useful such cosolvents include xylene, toluene, benzene, "Cellosolve" (glycol ethyl ether), and "Cellosolve Acetate" (hydroxyethyl acetate-glycol monoacetate).

Aromatic diamines

In one embodiment, any number of suitable aromatic diamines can be included in the core layer polyimide, including p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,5-dimethyl-1,4-diaminobenzene, trifluoromethyl-2,4-diaminobenzene , Trifluoromethyl-3,5-diaminobenzene, 2,5-dimethyl-1,4-phenylenediamine (DPX), 2,2-bis (4-aminophenyl) propane, 4,4'-diaminobiphenyl, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, bis (4- (4-aminophenoxy) phenyl sulfone (BAPS), 4,4'- Bis (aminophenoxy) biphenyl (BAPB), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-isopropylidenedianiline, 2,2'-bis (3-aminophenyl ) propane, N, N-bis (4-aminophenyl) -n-butylamine, N, N-bis (4-aminophenyl) methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, m-aminobenzoyl-p-aminoanilide, 4-aminophenyl-3-aminobenzoate, N, N-bis (4-aminophenyl) aniline, 2,4-diaminotoluene, 2,5-diaminotolu ol, 2,6-diaminotoluene, 2,4-diamine-5-chlorotoluene, 2,4-diamine-6-chlorotoluene, 2,4-bis (beta-amino-t-butyl) toluene, bis (p-beta- amino-t-butylphenyl) ether, p-bis-2- (2-methyl-4-aminopentyl) benzene, m-xylylenediamine and p-xylylenediamine.

Other useful aromatic diamines include 2,2'-bis (trifluoromethyl) benzidine (TFMB), 1,2-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,2-bis (3 -aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1- (4-aminophenoxy) -3- (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,4- Bis (3-aminophenoxy) benzene, 1- (4-aminophenoxy) -4- (3-aminophenoxy) benzene, 2,2-bis (4- [4-aminophenoxy] phenyl) propane (BAPP), 2,2'- Bis (4-aminophenyl) hexafluoropropane (6F-diamine), 2,2'-bis (4-phenoxyaniline) isopropylidene, 2,4,6-trimethyl-1,3-diaminobenzene, 4,4'-diamino-2,2 '-trifluoromethyldiphenyloxide, 3,3'-diamino-5,5'-trifluoromethyldiphenyloxide, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, 2,4,6-trimethyl-1,3-diaminobenzene, 4,4' -Oxybis [2-trifluoromethyl) benzenamine] (1,2,4-OBABTF), 4,4'-oxybis [3-trifluoromethyl) benzenamine], 4,4'-thiobis [(2-trifluoromethyl) benzenamine], 4, 4'-thiobis [(3-trifluoromethyl) benzenamine], 4,4'-sulfoxylbis [(2-trifluoromethyl) benzenamine, 4,4'-sulfoxylbis [(3-trifluoromethyl) benzenamine] and 4,4 ' -Ketobis [(2-trifluoromethyl) benzene amine].

In one embodiment, useful aromatic diamines include the isomers of bisaminophenoxybenzenes (APB), aminophenoxyphenylpropane (BAPP), dimethylphenylenediamine (DPX), bisaniline P and combinations thereof, and the use of these particular aromatic diamines can lower the lamination temperature of the polyimide and the peel strength of the polyimide Increase adhesion to other materials, especially metals.

In one embodiment, the thermoplastic polyimide of the outer layers can comprise one or more of the aromatic diamines listed above for the core layer.

Aromatic dianhydrides

In one embodiment, any aromatic dianhydride or combination of aromatic dianhydrides can be used as the dianhydride monomers in forming the core layer polyimide. The dianhydrides can be used in their tetraacid form (or as mono-, di-, tri- or tetraesters of tetra-acid) or as their diester acid halides (chlorides). In some embodiments, however, the dianhydride form may be preferred because it is generally more reactive than the acid or ester.

Examples of suitable aromatic dianhydrides are 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride , 2- (3 ', 4'-dicarboxyphenyl) -5,6-dicarboxybenzimidazole dianhydride, 2- (3', 4'-dicarboxyphenyl) -5,6-dicarboxybenzoxazole dianhydride, 2- (3 ', 4'-dicarboxyphenyl) -5 , 6-dicarboxybenzothiazole dianhydride, 2,2 ', 3,3'-benzophenone tetracarboxylic acid dianhydride, 2,3,3', 4'-benzophenone tetracarboxylic acid dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA), 2,2', 3 , 3'-biphenyltetracarboxylic dianhydride, 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride, bicyclo [2,2,2] octene (7) -2,3,5,6-tetracarboxylic acid-2,3,5,6- dianhydride, 4,4'-thiodiphthalic anhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfoxide dianhydride (DSDA), bis (3,4-dicarboxyphenyloxadiazole-1,3,4) -p-phenylene dianhydride , Bis (3,4-dicarboxyphenyl) -2,5-oxadiazole-1,3,4-dianhydride, bis-2,5- (3 ', 4'-dicarboxydiphenylether) -1,3,4-oxadiazole dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyphenyl) thioether dianhydride, bisphenol A dianhydride (BPADA), bisphenol S dianhydride , 2,2-bis (3,4-dicarboxyphenyl) 1,1,1,3,3,3, hexafluoropropane dianhydride (6FDA), 5,5- [2,2,2] -trifluoro-1- (trifluoromethyl) ethylidene, bis-1,3-isobenzofurandione, 1,4- Bis (4,4'-oxyphthalsäureanhydrid) benzene, bis (3,4-dicarboxyphenyl) methane dianhydride, Cyclopentadienyltetracarbonsäuredianhydrid, Cyclopentantetracarbonsäu dianhydride, ethylenetetracarboxylic, perylene-3,4,9,10-tetracarboxylic dianhydride, pyromellitic dianhydride (PMDA), tetrahydrofurantetracarboxylic, 1, 3-bis (4,4'oxydiphthalic anhydride) benzene, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1, 4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, phenanthrene-1,8,9,10-tetracarboxylic dianhydride, pyrazine-2,3,5,6- tetracarboxylic dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride and thiophene-2,3,4,5-tetracarboxylic dianhydride.

In one embodiment, the thermoplastic polyimide of the outer layers can comprise one or more of the aromatic dianhydrides listed above for the core layer.

Thermally conductive filler

In one embodiment, thermally conductive fillers, although thermally conductive, must also be electrically insulating in order for the multilayer film to remain electrically insulating. Examples of fillers that are both thermally conductive and electrically insulating include BN, AlN, Al ₂ O ₃ , Si ₃ N ₄ , ZnO, MgCO ₃ , MgO, BeO, diamond, SiC, many other oxide, nitride and carbide compounds and mixtures thereof. In one embodiment, a core-shell type filler may comprise one of these fillers coated with a coating of a second filler. These thermally conductive fillers can have any shape or size and have an average primary particle size (D ₅₀ ) in a range from about 0.001 to about 8 μm.

Multilayer films

Polyimide film layers according to the present invention can be made by combining the diamine and dianhydride (monomer or other polyimide precursor form) together with a solvent to form a polyamic acid solution. The dianhydride and diamine can be combined in a molar ratio of about 0.90 to 1.10. The molecular weight of the polyamic acid formed therefrom can be adjusted by adjusting the molar ratio of dianhydride and diamine.

In one embodiment, a polyamic acid casting solution is derived from the polyamic acid solution. The polyamic acid casting solution, which preferably comprises the polyamic acid solution, can optionally be combined with conversion chemicals such as: i.) One or more dehydrating agents such as aliphatic acid anhydrides (acetic acid anhydride etc.) and / or aromatic acid anhydrides, and ii.) One or more catalysts, such as aliphatic tertiary amines (triethylamine, etc.), aromatic tertiary amines (dimethylaniline, etc.), and heterocyclic tertiary amines (pyridine, picoline, isoquinoline, etc.). The anhydride dehydrating material is often used in a molar excess compared to the amount of amic acid groups in the polyamic acid. The amount of acetic anhydride used is usually about 2.0 to 4.0 mol per equivalent (repeating unit) of polyamic acid. Generally a comparable amount of tertiary amine catalyst is used.

In one embodiment, the polyamic acid solution and / or the polyamic acid casting solution are dissolved in an organic solvent at a concentration of from about 5.0 or 10% by weight to about 15, 20, 25, 30, 35 and 40% by weight.

In one embodiment, a thermally conductive filler is dispersed or suspended in a polar, aprotic solvent such as DMAC or another solvent compatible with polyamic acid. In one embodiment, the thermally conductive filler can be dispersed in an organic solvent in a concentration of from about 5, 10 or 15% by weight to about 20, 30, 40, 50 and 75% by weight. In one embodiment, the solvent used for dispersing or suspending the thermally conductive filler is identical to or different from the solvent used for the polyamic acid solution. The dispersion or suspension of thermally conductive filler can then be added to the polyamic acid casting solution in order to set the desired filler loading of the finished film. In one embodiment, the first outer layer can contain thermally conductive filler in an amount from greater than 0 to about 50 percent by weight of the dry film. In one embodiment, the core layer can contain thermally conductive filler in an amount from greater than 0 to about 60 percent by weight of the dry film. In one embodiment, the second outer layer can contain thermally conductive filler in an amount from greater than 0 to about 50 percent by weight of the dry film. In one embodiment, the first outer layer, the core layer, and the second outer layer can each have the same or a different amount of thermally conductive Filler than the other layers in the multilayer film, based on the weight percent of the dry film. In one embodiment, the weight percentage of thermally conductive filler in the core layer can be higher than that of the first outer layer, the second outer layer, or both the first and second outer layers. In another embodiment, the weight percentage of thermally conductive filler in the core layer can be less than that of the first outer layer, the second outer layer, or both the first and second outer layers.

The solvated mixture (the polyamic acid casting solution with thermally conductive filler) can then be cast or applied onto a support such as an endless belt or a rotating drum to obtain a film. Next, the solvent-based film can be converted into a self-supporting film by heating at a suitable temperature (thermal curing) together with conversion chemical reactants (chemical curing). The film can then be separated from the carrier and can be oriented, for example by tensioning, with the thermal and chemical curing being continued, in order to obtain a polyimide film.

1. (a.) Ein Verfahren, bei dem die Diamin- und Dianhydridkomponenten vorab miteinander vermischt werden und das Gemisch anschließend portionsweise unter Rühren zu einem Lösemittel gegeben wird.
2. (b.) Ein Verfahren, bei dem ein Lösemittel zu einer gerührten Mischung von Diamin- und Dianhydridkomponenten gegeben wird. (im Gegensatz zu (a) oben)
3. (c.) Ein Verfahren, bei dem Diamine ausschließlich in einem Lösemittel gelöst werden und dann Dianhydride in einem solchen Verhältnis zugegeben werden, dass die Reaktionsgeschwindigkeit gesteuert werden kann.
4. (d.) Ein Verfahren, bei dem die Dianhydridkomponenten ausschließlich in einem Lösemittel gelöst werden und dann Aminkomponenten in einem solchen Verhältnis zugegeben werden, dass die Reaktionsgeschwindigkeit gesteuert werden kann.
5. (e.) Ein Verfahren, bei dem die Diaminkomponenten und die Dianhydridkomponenten getrennt in Lösemitteln gelöst werden und dann diese Lösungen in einem Reaktor gemischt werden.
6. (f.) Ein Verfahren, bei dem die Polyamidsäure mit überschüssiger Aminkomponente und eine weitere Polyamidsäure mit überschüssiger Dianhydridkomponente vorab gebildet und dann in einem Reaktor miteinander umgesetzt werden, insbesondere in einer solchen Weise, dass ein nichtstatistisches oder Blockcopolymer entsteht.
7. (g.) Ein Verfahren, bei dem zuerst ein bestimmter Teil der Aminkomponenten und der Dianhydridkomponenten umgesetzt wird und dann die restlichen Diaminkomponenten umgesetzt werden oder umgekehrt.
8. (h.) Ein Verfahren, bei dem die Umwandlungschemikalien (Katalysatoren) mit der Polyamidsäure vermischt werden, um eine Polyamidsäure-Gießlösung zu bilden, und dann gegossen werden, um einen Gelfilm zu bilden.
9. (i.) Ein Verfahren, bei dem die Komponenten teilweise oder ganz in jeder beliebigen Reihenfolge entweder zu einem Teil des Lösemittels oder zu dem gesamten Lösemittel gegeben werden, wobei außerdem ein Teil oder die Gesamtheit einer beliebigen Komponente als Lösung in einem Teil des Lösemittels oder dem gesamten Lösemittel zugegeben werden kann.
10. (j.) Ein Verfahren, bei dem zunächst eine der Dianhydridkomponenten mit einer der Diaminkomponenten umgesetzt wird, wodurch eine erste Polyamidsäure entsteht. Dann wird die andere Dianhydridkomponente mit der anderen Aminkomponente umgesetzt, um eine zweite Polyamidsäure zu erhalten. Dann werden die Amidsäuren vor der Filmbildung auf eine von einer Reihe von Arten kombiniert.

Useful methods of making polyimide film in accordance with the present invention can be found in US Pat U.S. Patent No. 5,166,308 and 5,298,331 , which are hereby expressly incorporated by reference for all teachings therein. Numerous variations are also possible, such as:

1. (a.) A process in which the diamine and dianhydride components are mixed with one another beforehand and the mixture is then added in portions to a solvent with stirring.
2. (b.) A process in which a solvent is added to a stirred mixture of diamine and dianhydride components. (as opposed to (a) above)
3. (c.) A method in which diamines are only dissolved in a solvent and then dianhydrides are added in such a ratio that the reaction rate can be controlled.
4. (d.) A method in which the dianhydride components are exclusively dissolved in a solvent and then amine components are added in such a ratio that the reaction rate can be controlled.
5. (e.) A method in which the diamine components and the dianhydride components are separately dissolved in solvents, and then these solutions are mixed in a reactor.
6. (f.) A process in which the polyamic acid with excess amine component and a further polyamic acid with excess dianhydride component are formed in advance and then reacted with one another in a reactor, in particular in such a way that a non-random or block copolymer is formed.
7. (g.) A method in which a certain part of the amine components and the dianhydride components are first reacted and then the remaining diamine components are reacted, or vice versa.
8. (h.) A method in which the conversion chemicals (catalysts) are mixed with the polyamic acid to form a polyamic acid casting solution and then cast to form a gel film.
9. (i.) A method in which the components are added in part or in whole in any order either to part of the solvent or to all of the solvent, with part or all of any component being added as a solution in part of the solvent or can be added to the entire solvent.
10. (j.) A process in which one of the dianhydride components is first reacted with one of the diamine components to form a first polyamic acid. Then the other dianhydride component is reacted with the other amine component to obtain a second polyamic acid. The amic acids are then combined in one of a number of ways prior to film formation.

The thickness of each polyimide layer can be adjusted depending on the intended use of the film or the specifications for the end use application. In one embodiment, the multilayer film has an overall thickness of from about 5 to about 150 μm, or from about 15 to about 100 μm, or from about 25 to about 75 μm. In one embodiment, the thickness of the core layer is in a range from about 5 to about 125 μm or from about 10 to about 100 μm or from about 15 to 75 μm or from about 15 to about 40 μm. In one embodiment, the thickness of the outer layer ranges from about 1.5 to about 20 µm for each of the outer layers, or from about 3 to about 15 µm, or from about 3 to about 12 µm, or from about 3 to about 6 µm for each of the outer layers. As will be apparent to those skilled in the art, a minimum thickness of the thermoplastic polyimide outer layers is necessary to provide sufficient adhesion to metal layers to form a useful thermal substrate for power electronics applications. In addition, a minimum thickness of the core layer is necessary to maintain the mechanical integrity of the multilayer film.

As a thermal substrate for high power density semiconductor devices (such as insulated gate bipolar transistors), the multilayer film can experience rapid temperature changes from room temperature to a temperature of up to 200 ° C. The actual drive cycle state of a power module in an automobile could exert these temperature changes in a rapid and repetitive pattern that requires rapid heat dissipation and high mechanical integrity. Under these conditions, an organic layer having a low T _g, such as an epoxy resin, against loss of adhesion and delamination prone.

In one embodiment, the core layer and the outer layers of the multilayer film can be solution cast simultaneously by coextrusion. At the time of casting, the polyimides can be in the form of a polyamic acid solution. The cast solutions form an uncured polyamic acid film which is later cured to a polyimide. The bond strength of such laminates can be improved by using various techniques to increase the bond strength.

In some embodiments, a finished polyamic acid solution is filtered and pumped to a slot die where the flow is split to form the first outer layer and the second outer layer of a three-layer coextruded film. In some embodiments, a second stream of polyimide is filtered and then pumped to a casting nozzle such that the central polyimide core layer of a three-layer coextruded film is formed. The flow rates of the solutions can be adjusted to achieve the desired layer thickness.

In some embodiments, the multilayer film is made by simultaneously extruding the first outer layer, the core layer, and the second outer layer. In some embodiments, the layers are extruded through a single cavity or multiple cavity extrusion die. In another embodiment, the multilayer film is made using a single cavity die. When using a nozzle with a single cavity, the laminar flow of the streams should have a viscosity high enough to prevent the flow from mixing and to provide uniform stratification. By using a coextrusion process, a multilayer film with good interlayer adhesion can be produced without the use of adhesive layers.

In one embodiment, the multilayer film can be formed by any conventional technique used in the formation of polyimide films. In one embodiment, the outer layers can be applied to the core layer during an intermediate manufacturing step in the manufacture of a polyimide film, for example to gel film or to green film.

Thermal substrates

A lamination process can be used in one embodiment to form a thermal substrate having a multilayer film adhered to first and second conductive layers. In one embodiment, a first outer layer of the multilayer film containing a first thermoplastic polyimide is between a first conductive layer and a core layer of the multilayer film and a second outer layer containing a second thermoplastic polyimide is on the opposite side of the core layer . In one embodiment, a second conductive layer is arranged in contact with the second outer layer on a side opposite the core layer. An advantage of this type of construction is that the lamination temperature of the multilayer film is reduced to the lamination temperature required to bond the thermoplastic polyimide of the outer layer to one or more conductive layers. In one embodiment, the conductive layer or layers are a metal layer or metal layers. In one embodiment, a metal layer is a metal sheet with a thickness in a range from about 250 to about 3000 μm or from about 250 to about 2000 μm or from about 300 to about 1000 μm.

In one embodiment, the polyimide film may be subjected to a pretreatment step prior to the step of applying the multilayer film of the present invention to a conductive layer become. Pretreatment steps can include heat treatment, corona treatment, plasma treatment under normal pressure, plasma treatment under reduced pressure, treatment with adhesion promoters such as silanes and titanates, sandblasting, alkali treatment, acid treatments and coating of polyamic acids. To improve the adhesive strength, it is generally also possible to add various metal compounds, as in the U.S. Patent No. 4,742,099 ; 5,227,244 ; 5,218,034 and 5,543,222 which are hereby incorporated by reference.

In addition, various organic and inorganic treatments can be applied to the surface of the conductive layer (to improve adhesion). These treatments include the use of silanes, imidazoles, triazoles, treatments with oxides and reduced oxides, tin oxide treatment, and surface cleaning / roughening (called microetching) with acidic or alkaline reagents.

In the context of the present invention, the term “conductive layers” means metal layers (compositions with at least 50% of the electrical conductivity of high-quality copper). Metal layers do not have to be used as elements in their pure form; they can also be used as metal alloys, such as copper alloys containing nickel, chromium, iron and other metals.

Particularly suitable metal layers are rolled, annealed copper or rolled, annealed copper alloys. In many cases it has proven advantageous to pretreat the metal layer before the adhesive application of the multilayer film. This pretreatment can include, but is not limited to, electrodeposition or dip deposition of a thin layer of copper, zinc, chromium, tin, nickel, cobalt, other metals, and alloys of these metals on the metal. The pretreatment may consist of a chemical treatment or a mechanical roughening treatment.

In one embodiment, an organic DBC system (ODBC system) can comprise the multilayer film and a first copper layer adhered to an outer surface of the first outer layer of the multilayer film. In one embodiment, an ODBC system can comprise a second layer of copper adhered to an outer surface of the second outer layer of the multilayer film. In one embodiment, the first copper layer and the second copper layer are of the same thickness. In a specific embodiment, the first copper layer and the second copper layer are of the same thickness and are in a range of a thickness of approximately 300 μm to approximately 1000 μm. In one embodiment, the first copper layer is thicker than the second copper layer. In a specific embodiment, the first copper layer is 500 μm thick and the second copper layer is 2000 μm thick. In one embodiment, an outer layer of the first copper layer comprises microchannels. These microchannels can provide improved heat dissipation for the thermal substrate.

In one embodiment, the copper layers can be laminated to the multilayer film using a static press or an autoclave, such as is commonly used to form metal-clad laminates with polyimide films for flex circuit applications. An ODBC structure using the multilayer film and conductive layers of the present invention maintains good bond strength due to the thermoplastic nature of the outer layers of the multilayer film, thereby minimizing the effects of a CTE discrepancy. This is in contrast to the ceramic-to-metal bond in DBC structures, where the bond stiffness combined with the CTE difference between the ceramic and the metal results in large thermomechanical stresses during operation of the power module. As a result, thermal ODBC substrates with the multilayer film and conductive layers of the present invention can be used to package high power density power electronics with an operating temperature of up to 200 ° C.

In addition, the polyimide films of the present invention also generally have a low loss tangent value. The loss tangent is typically measured at 10 GHz and is used to measure the degradation of a nearby digital signal passing through a metal circuit trace by a dielectric material. There are different loss tangent values for different dielectric materials. The lower the loss tangent value for a given dielectric material, the (increasingly) better a material is for digital circuit applications. The polyimides of the present invention exhibit excellent, low loss tangent values. In one embodiment, the loss tangent value for the polyimide layers was less than 0.010, about 0.004, at 10 GHz. The polyimides of the present invention can also be used in applications in the 1 to 100 GHz range, with 1 to 20 GHz being the most common.

The multilayer films of the present invention show excellent attenuation. The polyimides of the present invention can often have an attenuation value measured in decibels per inch of about 0.3 at 10 GHz using a 50 ohm microstrip.

In one embodiment, a polyimide precursor for a core layer and polyimide precursors for the first and second outer layers are cast simultaneously (using a multi-aperture nozzle) to form a multilayer polyimide film (after the polyamic acid layers have cured). This multilayer film is then connected to one or more metal layers, the thermoplastic polyimide of the outer layer (s) being used as a connecting layer with the metal layer or layers. Thus, a formed thermal substrate includes the multilayer film and at least one conductive layer.

The advantageous properties of this invention can be observed from the following examples which illustrate but do not limit the invention. Unless otherwise stated, all parts and percentages are based on weight.

EXAMPLES

Polyamic acid solutions for making the core and outer layers were separately prepared by a chemical reaction between the appropriate molar equivalents of the monomers in dimethylacetamide (DMAc) solvent. Typically, the diamine dissolved in DMAc was stirred under nitrogen and the dianhydride added as a solid over a period of a few minutes. Stirring was continued to obtain the maximum viscosity of the polyamic acid. The viscosity was adjusted by controlling the amount of dianhydride in the polyamic acid composition.

For the thermally conductive filler, a 25% by weight dispersion of BN in DMAc was prepared and then added to the polyamic acid solutions so that the multilayer film had 50% by weight of BN in the core layer and 25% by weight of BN in the outer layers of the having dried film.

Multi-layer films were cast by coextrusion. Three separate polyamic acid polymer streams were simultaneously extruded through a multi-cavity extrusion die onto a heated moving belt to form a coextruded three-layer polyimide film. The thicknesses of the polyimide core layer and the upper and lower thermoplastic outer polyimide layers were adjusted by varying the amounts of polyamic acids fed to the extruder.

The extruded multilayer film was dried at an oven temperature in the range of about 95 to about 150 ° C. The self-supporting film was peeled off the tape and heated with radiant heaters in a tensioning furnace to a temperature of about 110 to about 805 ° C. (surface temperature of the radiant heater) in order to completely dry and imidize the polymers.

The target heater temperature used to cure the film was 805 ° C. The core layer polymer composition contained a polyimide derived from a molar ratio of PMDA to ODA of approximately 1: 1.

The thermoplastic skin layers also contained a polyimide derived from a dianhydride to diamine molar ratio of approximately 1: 1. The dianhydride composition contained the monomers PMDA and ODPA in a molar ratio of 20:80, and the diamine composition was 100 mol% RODA monomer. The flow rates of the polyamic acid solutions were adjusted to result in a three-layer film in which the thermoplastic outer layers were approximately 3 µm thick and the core layer was approximately 19 µm thick.

A cross-sectional scanning electron microscope (SEM) image of the three-layer film was obtained to determine the thicknesses of the multilayer film and the individual core and outer layers. For this purpose, a film sample was cut, mounted in an epoxy resin and left to dry overnight. The sample was then buffed using a Buehler variable speed grinder / polisher and placed in a desiccator for about two hours to ensure dryness. The image was taken using a Hitachi S-3400 SEM (Hitachi High Technologies America, Inc., Schaumburg, IL) under variable pressure. The total thickness of the multilayer film was approximately 25 µm.

The multilayer film was used to make a number of ODBC thermal substrates. 1000 µm copper sheet was laminated to both sides of the multilayer film using a vacuum assisted static press at temperatures with a maximum temperature of 330 ° C. The substrates were evaluated for their thermal and reliability performance by performing periodic inspections during accelerated testing.

For thermal shock tests, some substrates were placed in a thermal shock chamber and cycled between temperature extremes of -40 ° C and 200 ° C. The substrates were inspected every 1000 cycles. After 5000 cycles, the ODBC substrates showed no high potential (hipot) failure, but tentative edge peeling was visually observed.

For thermal aging, a separate set of samples was placed in a heating chamber and exposed to an elevated temperature of 175 ° C. No hipot failures were observed after 1100 hours, but edge peeling was observed again.

Another set of samples was attached to a cooling plate with Kapton® adhesive tape to test the performance change. Heating cartridges were attached to the top of the substrates with Kapton® tape, and thermocouples were placed in some locations on the package. The heating cartridges were switched on and off alternately so that the substrates could change between 40 ° C and 200 ° C. While the change between the maximum temperature and the minimum temperature for the power change test is smaller than that for the temperature change test, the heating cartridge and the cooling plate generate a thermal gradient within the samples that is not possible with passive temperature change. After 700 hours / 1300 test cycles, neither hipot failure nor edge delamination was observed.

Every change in the thermal output of the package was measured with a transient heat tester. A diode in a TO-247 package was attached to the top of the substrate under test with thermal paste. The substrate was also adhered to a cooling plate using the thermal paste. A transient power pulse was then applied to the package and the drop in temperature in the diode was monitored over time. This, together with a transient 1D line analysis, helps build the resistor-capacitance network for the package. The resistance measurements were monitored for changes between a new substrate and a substrate that had undergone an accelerated test. From thermal resistance measurements, as shown in Table 1, it can be seen that the ODBC substrates show good stability in all three of the accelerated tests. Table 1 Substrate condition Beginning Heat aging Change in performance Thermal shock Thermal resistance (K / W) 4.15 4.26 4.22 4.31 The acoustic image of the ODBC substrates shows that the connection area between the multilayer film and the copper sheets is uniform and free of defects, although a slight edge peeling is observed.

It should be noted that not all of the activities described above in the general description are required, that part of a particular activity may not be required, and that other activities may be carried out in addition to the activities described. In addition, the order in which each activity is listed does not necessarily correspond to the order in which it is performed. After reading this description, those skilled in the art will be able to determine which activities can be used for their specific needs or desires.

In the foregoing description, the invention has been described using specific embodiments. However, it will be apparent to those of ordinary skill in the art that various modifications and changes can be made without departing from the scope of the invention as set forth in the following claims. All of the features disclosed in this description can be replaced by alternative features that serve the same, equivalent, or similar purpose. Accordingly, the specification and figures are to be viewed in an illustrative rather than a restrictive sense, and all such modifications are intended to come within the scope of the invention.

Benefits, further advantages and solutions to problems have been described above in relation to specific embodiments. However, the benefits, advantages, solutions to problems and any elements that may result in benefits, benefits or solutions arising or becoming more pronounced are not to be understood as a critical, required or essential feature or element of any or all of the claims.

Where an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper and lower values, it is to be understood that expressly all ranges are disclosed that emerge from any pair of any upper range limit or any preferred value and any lower range limit or any preferred value, regardless of whether ranges are disclosed separately. If a range of numerical values is specified in this text, this range is intended to include its endpoints and all integers and fractions within the range, unless otherwise stated. It is not intended to limit the scope of the invention to the specific values mentioned in defining a range.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 7285321 [0006]
• US 6379784 [0006]
• EP 0659553 A1 [0007]
• US 5166308 [0051]
• US 5298331 [0051]
• US 4742099 [0059]
• US 5227244 [0059]
• US 5218034 [0059]
• US 5543222 [0059]

Claims (11)

Thermal substrate comprising: a multilayer film comprising: a first outer layer comprising a first thermoplastic polyimide, a core layer comprising a polyimide; and a second outer layer comprising a second thermoplastic polyimide, the multilayer film having a total thickness in a range of 5 to 150 µm, and the first outer layer, the core layer and the second outer layer each comprising a thermally conductive filler; a first conductive layer adhered to the first outer layer of the multilayer film; and a second conductive layer which is adhesively applied to the second outer layer of the multilayer film, the first conductive layer and the second conductive layer each having a thickness in a range from 250 to 3000 μm. Thermal substrate after Claim 1 wherein: the first outer layer has a thickness in a range from 1.5 to 20 µm; the core layer has a thickness in a range from 5 to 125 µm and the second outer layer has a thickness in a range from 1.5 to 20 µm. Thermal substrate after Claim 1 wherein a T _{g of} the core layer is higher than both a T _{g of} the first outer layer and a T _{g of} the second outer layer. Thermal substrate after Claim 1 wherein: the thermally conductive filler of the first outer layer is present in an amount of greater than 0 to 50 percent by weight based on the weight of the dry first outer layer; the thermally conductive filler of the core layer is present in an amount of more than 0 to 60% by weight, based on the weight of the dry core layer, and the thermally conductive filler of the second outer layer in an amount of more than 0 to 50% by weight, based on the weight of the dry second outer layer. Thermal substrate after Claim 1 wherein a weight percentage of thermally conductive filler in the core layer is greater than that of the first outer layer, the second outer layer, or both the first and second outer layers, based on the dry weight of each layer. Thermal substrate after Claim 1 wherein the thermally conductive filler of the first outer layer, the core layer and the second outer layer are each individually selected from the group consisting of BN, Al ₂ O ₃ , AlN, SiC, BeO, diamond, Si ₃ N ₄ and mixtures thereof. Thermal substrate after Claim 1 wherein the first thermoplastic polyimide comprises: an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'- Benzophenone tetracarboxylic acid dianhydride and mixtures thereof; and an aromatic diamine selected from the group consisting of 1,3-bis (4-aminophenoxy) benzene, 2,2-bis- (4- [4-aminophenoxy] phenyl) propane, and mixtures thereof. Thermal substrate after Claim 1 wherein the second thermoplastic polyimide comprises: an aromatic dianhydride selected from the group consisting of 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'- Benzophenone tetracarboxylic acid dianhydride and mixtures thereof; and an aromatic diamine selected from the group consisting of 1,3-bis (4-aminophenoxy) benzene, hexamethylenediamine, and mixtures thereof. Thermal substrate after Claim 1 wherein the first thermoplastic polyimide and the second thermoplastic polyimide are the same. Thermal substrate after Claim 1 wherein the polyimide of the core layer comprises: an aromatic dianhydride selected from the group consisting of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3', 4,4'- Benzophenone tetracarboxylic dianhydride, bisphenol A dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride, and mixtures thereof; and an aromatic diamine selected from the group consisting of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis (trifluoromethyl) benzidine, m-phenylenediamine and 4,4'-diaminodiphenylmethane and mixtures thereof. Thermal substrate after Claim 1 wherein the first thermoplastic polyimide and the second thermoplastic polyimide each have a T _g in the range of 150 to 320 ° C.