CN112840747A

CN112840747A - Thermal substrate

Info

Publication number: CN112840747A
Application number: CN201980066443.1A
Authority: CN
Inventors: C·B·贝克斯; R·I·冈萨雷斯; T·D·兰特喆; R·特派西
Original assignee: DuPont Electronics Inc
Current assignee: DuPont Electronics Inc
Priority date: 2018-10-09
Filing date: 2019-10-08
Publication date: 2021-05-25
Also published as: TW202035142A; JP2022504391A; DE112019005062T5; WO2020076810A1; KR20210068129A

Abstract

The thermal substrate includes a multilayer film, a first electrically conductive layer adhered to a first outer layer of the multilayer film, and a second electrically conductive layer adhered to a 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 of 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 of 250 to 3000 μm.

Description

Thermal substrate

Technical Field

The field of the disclosure is thermal substrates.

Background

In the power electronics industry, electrically insulating layers within power electronics modules are critical to separating the circuitry from the thermal management layers. The thermal substrate in a high power density power electronics package is a hard board on which semiconductor die may be mounted. In addition to mechanical support, these substrates also provide electrical isolation of the circuits and die and a thermally efficient path for heat dissipation. Power module devices, such as those found in automobiles, handle different forms of current and voltage to control equipment and require a large amount of current and high electrical isolation through their substrates. To achieve the competing needs of both conduction and isolation, thermal substrates take the form of multiple layers of conductive and insulating layers comprising different materials, such as metals (such as conductors) and ceramics or polymers (such as insulators), and bond the layers together in a manner that forms a path for heat flow away from the semiconductor die.

The most common structures for thermal substrates are in copper and highly thermally conductive ceramics such as Al₂O₃AlN or Si₃N₄With a Directly Bonded Copper (DBC) component formed by a high temperature bonding process. In a typical DBC structure, a metal layer and a ceramic layer are bonded together in an environmentally controlled, high temperature process, providing a thermally conductive and electrically insulating ceramic layer between two copper sheet layers. However, these metal and ceramic layers have large differences in the Coefficients of Thermal Expansion (CTE), and therefore the bond between them experiences large thermo-mechanical stresses, resulting in damage at high temperature gradients during power module operation. In addition, the method for bonding a copper layer to a ceramic limits the thickness of the copper layer to less than 1000 μm. A typical DBC construction uses a 300 μm copper layer and a 380 μm ceramic layer.

Organic-based insulating layers, such as epoxy resins, have been commercialized in recent years for relatively low power devices (i.e., for operating temperatures below 150 ℃). For such thermal substrates, the temperature of the device is limited by the chemical and mechanical stability of the organic components. In addition, the organic material must be loaded with a thermally conductive filler to obtain acceptable thermal conductivity, and made into a thin film to provide thermal conductivity comparable to that of ceramic materials. However, these thin film epoxies compromise the electrical insulation properties of the thermal substrate.

Polyimide films are used in the manufacture of flexible printed circuit boards because they have good electrical insulation properties, mechanical strength, high temperature stability, and chemical resistance properties. Polyimide films are adhered to thin metal foils to form metal clad laminates and find wide use in die pad bonding and/or tape automated bonding of packaging materials for flexible printed circuit boards, semiconductor devices and chip scale packages, flexible chips, chip on lead (chip on lead), lead on chip (lead on chip), multichip modules, ball grid arrays (or micro ball grid arrays), and other applications.

U.S. Pat. No. 7,285,321 describes a glass transition temperature (T) of low_g) Polyimide layer, high T_gA multilayer laminate of a polyimide layer and a conductive layer. High T_gThe polyimide layer is a thermoset polyimide and has a low T_gThe polyimide layer is a thermoplastic polyimide. 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 film. The aromatic polyimide composite film is composed of an aromatic polyimide base sheet film and two thermoplastic aromatic polyimide layers. The metal film and release film were adhered to the opposite side of the aromatic polyimide laminate without the use of an additional adhesive layer with good adhesion between the polyimide laminate and the metal film.

Polyimide films can be made thermally conductive by adding thermally conductive fillers. European patent application No. 0659553 a1 describes a method for providing a coextruded multilayer film that may contain thermally conductive particles. Thermally conductive fillers such as BN, Al₂O₃AlN, BeO, ZnO and Si₃N₄Or mixtures thereof, may be added to the high T_gPolyimide layer and low T_gIn one or both of the polyimide layers. The filler is typically added to the polymer casting solution as a slurry. The solvent of the filler-based slurry may be the same or different from the solvent used to make the polymer casting solution.

Disclosure of Invention

The thermal substrate includes a multilayer film, a first electrically conductive layer adhered to a first outer layer of the multilayer film, and a second electrically conductive layer adhered to a 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 of 5 to 150 μm, and the first outer layer, the core layer, and the second outer layer each contain a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness of 250 to 3000 μm.

Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as defined in the appended claims.

Detailed Description

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

In another embodiment of the thermal substrate, T of the core layer_gT higher than the first outer layer_gAnd T of the second outer layer_gBoth of which are described below.

In another embodiment of the thermal substrate, the thermally conductive filler of the first outer layer is present in an amount of greater than 0 to 50 wt% based on the weight of the dry first outer layer, the thermally conductive filler of the core layer is present in an amount of greater 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 present in an amount of greater than 0 to 50 wt% based on the weight of the dry second outer layer.

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

In yet another embodiment of the thermal substrate, the thermally conductive filler of each of the first outer layer, the core layer, and the second outer layer is independently selected from the group consisting of: BN, Al₂O₃AlN, SiC, BeO, Diamond, Si₃N₄And mixtures thereof.

In another 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',4,4' -biphenyltetracarboxylic dianhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, and mixtures thereof; and an aromatic diamine selected from the group consisting of: 1, 3-bis (4-aminophenoxy) benzene, 2-bis- (4- [ 4-aminophenoxy ] phenyl) propane and mixtures thereof.

In yet another 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',4,4' -biphenyltetracarboxylic dianhydride, 3',4,4' -benzophenone tetracarboxylic 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',4,4' -benzophenone tetracarboxylic dianhydride, bisphenol a dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic dianhydride and 2,3,6, 7-naphthalene tetracarboxylic dianhydride, and mixtures thereof; and an aromatic diamine selected from the group consisting of: p-phenylenediamine, 4 '-diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 2 '-bis (trifluoromethyl) benzidine, m-phenylenediamine, and 4,4' -diaminodiphenylmethane, and mixtures thereof.

In another embodiment of the thermal substrate, the first thermoplastic polyimide and the second thermoplastic polyimide each have a T of 150 ℃ to 320 ℃_g。

Many aspects and embodiments have been described above and are merely exemplary and not limiting. Upon reading this specification, skilled artisans will appreciate that other aspects and embodiments are possible without departing from the scope of the invention. Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.

In one embodiment, the core layer of the multilayer film comprises a polyimide synthesized by a polycondensation reaction involving reacting a first aromatic dianhydride and a first aromatic diamine. In one embodiment, the polyimide may comprise 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, the aromatic dianhydride may be selected from the group consisting of: 3,3',4,4' -biphenyltetracarboxylic dianhydride, 4,4' -oxydiphthalic dianhydride, pyromellitic dianhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, bisphenol a dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic dianhydride, and 2,3,6, 7-naphthalene tetracarboxylic dianhydride. In one embodiment, the aromatic diamine may be selected from the group consisting of: p-phenylenediamine, 4 '-diaminodiphenyl ether (ODA), 3,4' -diaminodiphenyl ether, 2 '-bis (trifluoromethyl) benzidine (TFMB), m-phenylenediamine (MPD), and 4,4' -diaminodiphenylmethane (MDA). In one embodiment, the polyimide may comprise an aliphatic diamine. In one embodiment, the core layer may be a thermoset polyimide. In one embodiment, the core layer may comprise a polyimide having some thermoplastic properties.

In one embodiment, the first outer layer of the multilayer film comprises a first thermoplastic polyimide. In one embodiment, the first thermoplastic polyimide may be synthesized by a polycondensation reaction involving reacting an aromatic dianhydride with an aromatic diamine. In one embodiment, the first thermoplastic polyimide may 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 second outer layer of the multilayer film comprises a second thermoplastic polyimide. In one embodiment, the second thermoplastic polyimide may be synthesized by a polycondensation reaction involving reacting an aromatic dianhydride with an aromatic diamine. In one embodiment, the second thermoplastic polyimide may 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 outer layer and the second outer layer can comprise one or more aliphatic diamines, which can be useful for reducing the T of the outer layer when desired_g. In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide may be the same or different. In one embodiment, the first thermoplastic polyimide and the second thermoplastic polyimide each have a T of about 150 ℃ to about 320 ℃_g。

As used herein, "aromatic diamine" is intended to mean a diamine having at least one aromatic ring, either alone (i.e., substituted or unsubstituted, functionalized or unfunctionalized benzene or similar type of aromatic ring) or linked to another (aromatic or aliphatic) ring, and such amine is considered aromatic, whether or not there are any non-aromatic moieties that may also be components of the diamine. Thus, an aromatic diamine backbone segment is intended to mean at least one aromatic moiety between two adjacent imide linkages. As used herein, "aliphatic diamine" is intended to mean any organic diamine that does not meet the definition of aromatic diamine.

Depending on the context, "diamine" as used herein is intended to mean: (i) unreacted form (i.e., diamine monomer); (ii) (ii) partially reacted form (i.e., one or more portions of an oligomer or other polyimide precursor derived from or otherwise attributable to a diamine monomer) or (iii) fully reacted form (one or more portions of a polyimide derived from or otherwise attributable to a diamine monomer). According to particular embodiments selected in the practice of the present invention, the diamine may be functionalized with one or more moieties.

Indeed, the term "diamine" is not intended to be limiting (or literally interpreted) as the number of amine moieties in the diamine component. For example, the above (ii) and (iii) include polymeric materials that may have two, one, or zero amine moieties. Alternatively, the diamine may be functionalized with additional amine moieties (in addition to the amine moieties at the monomer ends that react with the dianhydride to extend the polymer chain). Such additional amine moieties may be used to crosslink the polymer or to provide other functional groups to the polymer.

Similarly, the term "dianhydride" as used herein is intended to mean a component that reacts with (or is complementary to) a diamine and combines to be able to react to form an intermediate polyamic acid that can then be cured to a polyimide. Depending on the context, "anhydride" as used herein may mean not only the anhydride moiety itself, but also precursors of the anhydride moiety, such as: (i) a pair of carboxylic acid groups (which can be converted to an anhydride by dehydration or similar type of reaction); or (ii) an acid halide (e.g., chloride) ester functionality (or any other functionality now known or developed in the future) capable of being converted to an anhydride functionality.

Depending on the context, "dianhydride" may mean: (i) unreacted form (i.e., dianhydride monomer, whether the anhydride functionality is in the true anhydride form or in the precursor anhydride form, as discussed in the paragraphs above); (ii) a partially reacted form (i.e., one or more portions of the polyimide composition reacted by or otherwise attributable to the oligomer or other portion of the dianhydride monomer or the precursor polyimide) or (iii) a fully reacted form (one or more portions of the polyimide derived from or otherwise attributable to the dianhydride monomer).

According to particular embodiments selected in the practice of the present invention, the dianhydride may be functionalized with one or more moieties. In fact, the term "dianhydride" is not intended to be limited (or literally interpreted) to the number of anhydride moieties in the dianhydride component. For example, (i), (ii), and (iii) (in the above paragraphs) include organic species that may have two, one, or zero anhydride moieties depending on whether the anhydride is in the precursor state or the reaction state. Alternatively, the dianhydride component may be functionalized with additional anhydride type moieties (in addition to the anhydride moieties that react with the diamine to provide the polyimide). Such additional anhydride moieties may be used to crosslink the polymer or to provide other functional groups to the polymer.

Although 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, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

In describing certain polymers, it should be understood that sometimes applicants refer to polymers by the monomers used to make them or the amounts of the monomers used to make them. Although this description may not include the specific nomenclature used to describe the final polymer or may not contain terms that define the article by way, any such reference to monomers and amounts should be construed to mean that the polymer is made from those monomers or that amount of monomers, as well as the corresponding polymer and compositions thereof.

The materials, methods, and examples herein are illustrative only and not intended to be limiting unless otherwise specified.

As used herein, the terms "comprising," "including," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, process, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such method, process, article, or apparatus. Furthermore, unless expressly stated to the contrary, "or" refers to an inclusive "or" and not to an exclusive "or". For example, condition a or B is satisfied by any one of the following: a is true (or present) and B is false (or not present), a is false (or not present) and B is true (or present), and both a and B are true (or present).

In addition, "a/an" is used to describe elements and components of the invention. This is done merely for convenience and to give a general sense of the invention. The description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Organic solvent

Useful organic solvents for synthesizing the polyimides of the present invention are preferably capable of dissolving the polyimide precursor material. Such solvents should also have a relatively low boiling point, such as less than 225 ℃, so that the polymer can be dried at moderate (i.e., more convenient and less costly) temperatures. Boiling points of less than 210 ℃, 205 ℃, 200 ℃, 195 ℃, 190 ℃, or 180 ℃ are preferred.

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

Co-solvents may typically be used in about 5 to 50 weight percent of the total solvent, and useful such co-solvents include xylene, toluene, benzene, "cellosolve" (ethylene glycol monoethyl ether), and "cellosolve acetate" (hydroxyethyl acetate ethylene glycol monoacetate).

Aromatic diamines

In one embodiment, any number of suitable aromatic diamines may be included in the core 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-bis- (4-aminophenyl) propane, 4 '-diaminobiphenyl, 4' -diaminobenzophenone, 4 '-diaminodiphenylmethane (MDA), 4' -diaminodiphenylsulfide, 4 '-diaminodiphenylsulfone, 3' -diaminodiphenylsulfone, bis- (4- (4-aminophenoxy) phenylsulfone (BAPS), 4,4' -bis- (aminophenoxy) biphenyl (BAPB), 4' -diaminodiphenyl ether (ODA), 3,4' -diaminodiphenyl ether, 4' -diaminobenzophenone, 4' -isopropylidenedianiline, 2' -bis- (3-aminophenyl) propane, N-bis- (4-aminophenyl) -N-butylamine, N-bis- (4-aminophenyl) methylamine, 1, 5-diaminonaphthalene, 3' -dimethyl-4, 4' -diaminobiphenyl, m-aminobenzoyl-p-aminobenzamide, 4-aminophenyl-3-aminobenzoate, N-bis- (4-aminophenyl) aniline, N-isopropylidenedianiline, N ' -isopropylidenedianiline, N-bis, 2, 4-diaminotoluene, 2, 5-diaminotoluene, 2, 6-diaminotoluene, 2, 4-diamine-5-chlorotoluene, 2, 4-diamine-6-chlorotoluene, 2, 4-bis- (β -amino-t-butyl) toluene, bis- (p- β -amino-t-butylphenyl) ether, p-bis-2- (2-methyl-4-aminopentyl) benzene, m-xylylenediamine, and p-xylylenediamine.

Other aromatic diamines that may be used 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-bis- (4- [ 4-aminophenoxy ] phenyl) propane (BAPP), 2,2 '-bis- (4-aminophenyl) -hexafluoropropane (6F diamine), 2' -bis- (4-phenoxyaniline) isopropylidene, 2,4, 6-trimethyl-1, 3-diaminobenzene, 4 '-diamino-2, 2' -trifluoromethyldiphenyloxy, 3 '-diamino-5, 5' -trifluoromethyldiphenyloxy, 4 '-trifluoromethyl-2, 2' -diaminobiphenyl, 2,4, 6-trimethyl-1, 3-diaminobenzene, 4 '-oxy-bis- [ 2-trifluoromethyl ] aniline ] (1,2,4-OBABTF), 4' -oxy-bis- [ 3-trifluoromethyl) aniline ] ], and mixtures thereof, 4,4' -thio-bis- [ (2-trifluoromethyl) aniline ], 4' -thio-bis [ (3-trifluoromethyl) aniline ], 4' -sulfinyl-bis- [ (2-trifluoromethyl) aniline, 4' -sulfinyl-bis- [ (3-trifluoromethyl) aniline ], and 4,4' -keto-bis- [ (2-trifluoromethyl) aniline ].

In one embodiment, useful aromatic diamines include isomers of bis-aminophenoxy benzene (APB), aminophenoxy phenyl propane (BAPP), dimethyl phenylene Diamine (DPX), bis aniline P, and combinations thereof, and the use of these particular aromatic diamines may reduce the lamination temperature of the polyimide and may increase the peel strength of the polyimide when adhered to other materials, particularly metals.

In one embodiment, the thermoplastic polyimide of the outer layer may comprise one or more of any 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 monomer for forming the core layer polyimide. The dianhydride may be used in its tetracarboxylic acid form (or as a monoester, diester, triester, or tetraester of the tetracarboxylic acid) or as its diester acid halide (chloride). However, in some embodiments, the dianhydride form may be preferred because it is generally more reactive than the acid or ester.

Examples of suitable aromatic dianhydrides include 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',3,3' -benzophenonetetracarboxylic dianhydride, 2,3,3',4' -benzophenonetetracarboxylic dianhydride, 3,3',4,4' -benzophenonetetracarboxylic 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' -thio-diphthalic anhydride, bis (3, 4-dicarboxyphenyl) sulfone dianhydride, bis (3, 4-Dicarboxyphenyl) Sulfoxide Dianhydride (DSDA), bis (3, 4-dicarboxyphenyl oxadiazole-1, 3,4) p-phenylene dianhydride, bis (3, 4-dicarboxyphenyl) 2, 5-oxadiazole 1,3, 4-dianhydride, bis 2,5- (3',4' -dicarboxydiphenyl ether) 1,3, 4-oxadiazole dianhydride, 4,4 '-oxydiphthalic anhydride (ODPA), bis (3, 4-dicarboxyphenyl) sulfide dianhydride, bisphenol A dianhydride (BPADA), bisphenol S dianhydride, 2, 2-bis- (3, 4-dicarboxyphenyl) 1,1,1,3,3,3, -hexafluoropropane dianhydride (6FDA), 5- [2,2,2] -trifluoro-1- (trifluoromethyl) ethylene, bis-1, 3-isobenzofurandione, 1, 4-bis (4, 4' -oxyphthalic anhydride) benzene, bis (3, 4-dicarboxyphenyl) methane dianhydride, cyclopentadienyltetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, vinyltetracarboxylic dianhydride, perylenetetracarboxylic dianhydride 3,4,9, 10-tetracarboxylic dianhydride, pyromellitic dianhydride (PMDA), Tetrahydrofuran tetracarboxylic dianhydride, 1, 3-bis- (4, 4' -oxydiphthalic anhydride) benzene, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2, 6-dichloronaphthalene-1, 4,5, 8-tetracarboxylic 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 layer may comprise one or more of any of the aromatic dianhydrides listed above for the core layer.

Heat conductive filler

In one embodiment, the thermally conductive filler, while thermally conductive, must also be electrically insulating to preserve the electrically insulating properties of the multilayer film. Examples of thermally conductive and electrically insulating fillers include BN, AlN, Al₂O₃、Si₃N₄、ZnO、MgCO₃MgO, BeO, diamond, SiC, many other oxide, nitride and carbide compounds and mixtures thereof. In one embodiment, the core-shell filler may comprise one of these filler materials coated by a coating of a second filler material. These thermally conductive fillers may be of any shape and size, and may have an average primary particle size (D) of about 0.001 to about 8 μm₅₀)。

Multilayer film

Polyimide film layers according to the present invention can be produced by combining diamines and dianhydrides (in the form of monomers or other polyimide precursors) with a solvent to form a polyamic acid (polyamic acid) (also known as polyamic acid) solution. The dianhydride and diamine may 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, the polyamic acid casting solution is derived from a polyamic acid solution. The polyamic acid casting solution preferably comprises a polyamic acid solution, optionally in combination with a conversion chemistry such as: i.) one or more dehydrating agents such as aliphatic anhydrides (acetic anhydride, etc.) and/or aromatic 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 typically used in a molar excess compared to the amount of amic acid groups in the polyamic acid. The amount of acetic anhydride used is typically about 2.0 to 4.0 moles per equivalent (repeat unit) of polyamic acid. Generally, a substantial amount of tertiary amine catalyst is used.

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

In one embodiment, the thermally conductive filler is dispersed or suspended in a polar aprotic solvent such as DMAC or other solvent compatible with the polyamic acid. In one embodiment, the thermally conductive material may be dissolved in the organic solvent at a concentration of about 5 wt%, 10 wt%, or 15 wt% to about 20 wt%, 30 wt%, 40 wt%, 50 wt%, and 75 wt%. In one embodiment, the solvent used to disperse or suspend the thermally conductive filler is the same or different than 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 to achieve the desired filler loading of the final film. In one embodiment, the first outer layer may contain a thermally conductive filler in an amount greater than 0 wt% to about 50 wt% of the dried film. In one embodiment, the core layer may contain a thermally conductive filler in an amount greater than 0 wt% to about 60 wt% of the dry film. In one embodiment, the second outer layer may contain a thermally conductive filler in an amount greater than 0 wt% to about 50 wt% of the dried film. In one embodiment, the first outer layer, the core layer, and the second outer layer may each have the same or different amount of thermally conductive filler as the other layers in the multilayer film, in weight percent on a dry film basis. In one embodiment, the weight percentage of the thermally conductive filler in the core layer may be higher than the weight percentage of the thermally conductive filler in the first outer layer, the second outer layer, or both the first outer layer and the second outer layer. In another embodiment, the weight percentage of the thermally conductive filler in the core layer may be lower than the weight percentage of the thermally conductive filler in the first outer layer, the second outer layer, or both the first outer layer and the second outer layer.

The solvated mixture (polyamic acid casting solution with thermally conductive filler) can then be cast or applied onto a support such as an endless belt or drum to produce a film. The film containing the solvent may then be converted into a self-supporting film by heating at an appropriate temperature (thermal curing) with a conversion chemical reactant (chemical curing). The film can then be separated from the support and oriented with continued thermal and chemical curing, such as by tentering, to provide a polyimide film.

Useful methods for producing polyimide films according to the present invention can be found in U.S. patent nos. 5,166,308 and 5,298,331, which are incorporated by reference in this specification for all teachings therein. Many variations are possible, such as

(a.) A method in which a diamine component and a dianhydride component are preliminarily mixed together, and then the mixture is added in portions to a solvent while stirring.

(b.) A process wherein a solvent is added to a stirred mixture of diamine and dianhydride components. (contrary to the above (a))

(c.) A process wherein the diamine is dissolved exclusively in the solvent and then the dianhydride is added thereto, such as in a ratio that allows control of the reaction rate.

(d.) A process wherein the dianhydride component is dissolved exclusively in the solvent and then the amine component is added thereto, such as in a ratio that allows control of the reaction rate.

(e.) A method in which the diamine component and the dianhydride component are separately dissolved in a solvent, and then the solutions are mixed in a reactor.

(f.) A process wherein a polyamic acid having an excess of an amine component and another polyamic acid having an excess of a dianhydride component are initially formed and then reacted with each other in a reactor, particularly in a manner to form a non-random or block copolymer.

(g.) A process wherein a specified portion of the amine component and dianhydride component are first reacted and then the residual diamine component is reacted, or vice versa.

(h.) A process wherein a conversion chemical is mixed with a polyamic acid to form a polyamic acid casting solution, and then cast to form a gel film.

(i.) A process wherein the components are added partially or completely in any order to some or all of the solvent, and wherein some or all of any of the components may be added as a solution in some or all of the solvent.

(j.) A method of first reacting one of the dianhydride components with one of the diamine components to produce a first polyamic acid. Another dianhydride component is then reacted with another amine component to produce a second polyamic acid. The amic acids are then combined in any of a number of ways prior to film formation.

The thickness of each polyimide layer can be adjusted depending on the intended purpose of the film or end use specification. In one embodiment, the multilayer film has a total thickness of about 5 to about 150 μm, or about 15 to about 100 μm, or about 25 to about 75 μm. In one embodiment, the core layer has a thickness of about 5 to about 125 μm, or about 10 to about 100 μm, or about 15 to about 75 μm, or about 15 to about 40 μm. In one embodiment, the thickness of the outer layers is about 1.5 to about 20 μm, or about 3 to about 15 μm, or about 3 to about 12 μm for each outer layer, or about 3 to about 6 μm for each outer layer. The skilled person will appreciate that a minimum thickness of an outer layer with thermoplastic polyimide is required to provide sufficient adhesion to the metal layer to form a useful thermal substrate for power electronics applications. In addition, a minimum thickness of the core layer is required 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 may experience rapid temperature changes from room temperature to temperatures as high as 200 ℃. The actual drive cycle conditions of the power module in the automobile may require a rapid and repetitive pattern of rapid heat dissipation and high mechanical integrity to impose these temperature changes. Under these conditions, low T_gOrganic layers such as epoxy are prone to adhesion loss and delamination.

In one embodiment, the core layer and the outer layers of the multilayer film may be solution cast simultaneously by coextrusion. The polyimide may be in the form of a polyamic acid solution when cast. The casting solution forms an uncured polyamic acid film that subsequently cures to a polyimide. The adhesive strength of such laminates can be improved by employing various techniques for increasing the adhesive strength.

In some embodiments, the finished polyamic acid solution is filtered and pumped to a slot die where the streams are separated in a manner that forms the first and second outer layers of a three layer coextruded film. In some embodiments, the second stream of polyimide is filtered and then pumped to a casting die in a manner that forms the intermediate polyimide core layer of the three layer coextruded film. The solution flow rate can be adjusted to achieve the desired layer thickness.

In some embodiments, the multilayer film is prepared 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 or multi-cavity extrusion die. In another embodiment, the multilayer film is produced using a single cavity mold. If a single cavity mode is used, the laminar flow of the beam should have a sufficiently high viscosity to prevent mixing of the beam and provide uniform stratification. By using a coextrusion process, a multilayer film with good interlayer adhesion can be made without the use of an adhesive layer.

In one embodiment, the multilayer film may be formed by any conventional technique for forming polyimide films. In one embodiment, the outer layer may be applied to the core layer during an intermediate stage of manufacture to produce a polyimide film, such as a gel film or green film.

Thermal substrate

In one embodiment, the lamination process can be used to form a thermal substrate having a multilayer film adhered to a first electrically conductive layer and a second electrically conductive layer. In one embodiment, a first outer layer (comprising a first thermoplastic polyimide) of the multilayer film is between the first conductive layer and the core layer of the multilayer film, and a second outer layer (comprising a second thermoplastic polyimide) is on an opposite side of the core layer. In one embodiment, the second conductive layer is placed in contact with the second outer layer on the opposite side of the core layer. One advantage of this type of construction is that the lamination temperature of the multilayer film is reduced to the lamination temperature required for the thermoplastic polyimide of the outer layer to bond to the conductive layer or layers. In one embodiment, the conductive layer is a metal layer. In one embodiment, the metal layer is a metal sheet having a thickness of about 250 to about 3000 μm, or about 250 to about 2000 μm, or 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 onto the conductive layer. The pretreatment step may include heat treatment, corona treatment, plasma treatment at atmospheric pressure, plasma treatment at reduced pressure, treatment with coupling agents such as silanes and titanates, sand blasting, alkali treatment, acid treatment, and coating of polyamic acid. To improve the adhesion strength, various metal compounds may also be added, as is typical, such as U.S. Pat. nos. 4,742,099; 5,227,244, respectively; 5,218,034, respectively; and 5,543,222, which are hereby incorporated by reference.

In addition, the surface of the conductive layer (for the purpose of improving adhesion) may be treated with various organic and inorganic treatments. These treatments include the use of silanes, imidazoles, triazoles, oxides and reduced oxides treatments, tin oxide treatments, and surface cleaning/roughening (known as microetching) via acid or base agents.

As used herein, the term "conductive layer" means a metal layer (a composition having a conductivity of at least 50% higher copper). The metal layer need not be used as an element in pure form; they are also 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 pre-treat the metal layer prior to adhering the multilayer film. This pretreatment may include, but is not limited to, electrodeposition or immersion deposition of metals on thin layers of copper, zinc, chromium, tin, nickel, cobalt, other metals, and alloys of these metals. The pretreatment may consist of a chemical treatment or a mechanical roughening treatment.

In one embodiment, an Organic Direct Bonded Copper (ODBC) system may include a multilayer film and a first copper layer adhered to an outer surface of a first outer layer of the multilayer film. In one embodiment, the ODBC system may include a second copper layer adhered to the outer surface of the second outer layer of the multilayer film. In one embodiment, the first copper layer and the second copper layer have the same thickness. In a particular embodiment, the first and second copper layers have the same thickness and are about 300 μm to about 1000 μm thick. 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, the outer layer of the first copper layer includes micro-channels. These microchannels may provide improved heat dissipation to a thermal substrate.

In one embodiment, the copper layer may be laminated to the multilayer film using static pressure or an autoclave as is conventional for forming laminates of metal claddings with polyimide films for flexible circuit applications. ODBC structures using the multilayer films and conductive layers of the present invention maintain good adhesion strength due to the thermoplastic nature of the outer layers of the multilayer film and thus minimize the effects of CTE mismatch. This is in contrast to ceramic-metal bonding in DBC structures where the bond stiffness and CTE difference between ceramic and metal results in large thermo-mechanical stresses during power module operation. Thus, ODBC thermal substrates using the multilayer films and conductive layers of the present invention may be used for high power density power electronic packaging operating at temperatures up to 200 ℃.

In addition, the polyimide film of the present invention generally has a low loss tangent. Loss tangent is typically measured at 10GHz and is used to measure dielectric material damage of nearby digital signals that are tracked through metal circuitry. There are different loss tangent values for different dielectric materials. The lower the loss tangent value of a given dielectric material, the higher the class of materials (the more) used in digital circuit applications. The polyimide of the present invention exhibits an excellent low loss tangent. In one embodiment, the polyimide layer has a loss tangent of less than 0.010, about 0.004 at 10 GHz. The polyimides of the present invention may also be used in applications ranging from 1 to 100GHz, with 1 to 20GHz being the most common.

The multilayer film of the present invention exhibits excellent damping action. The polyimides of the present invention may generally exhibit an attenuation value of about 0.3 measured in decibels per inch at 10GHz using a 50-ohm microstrip.

In one embodiment, the polyimide precursor of the core layer and the polyimide precursors of the first and second outer layers are simultaneously cast (using a multi-port die) to form a multilayer polyimide film (after curing of the polyamic acid layer). The multilayer film is then bonded to the metal layer using the thermoplastic polyimide of the outer layer as a bonding layer to the metal layer. Thus, the formed thermal substrate comprises a multilayer film and at least one conductive layer.

The advantageous characteristics of the invention can be observed by reference to the following examples which illustrate, but do not limit, the invention. All parts and percentages are by weight unless otherwise indicated.

Examples of the invention

The polyamic acid solution used to produce the core and outer layers is prepared solely by chemical reaction between the appropriate molar equivalents of monomers in a dimethylacetamide (DMAc) solvent. Typically, the diamine dissolved in DMAc is stirred under nitrogen and the dianhydride is added in solid form over a period of several minutes. Stirring was continued to obtain polyamic acid of maximum viscosity. The viscosity is adjusted by controlling the amount of dianhydride in the polyamic acid composition.

For the thermally conductive filler, a 25 wt% dispersion of BN in DMAc was made and then added to the polyamic acid solution such that the multilayer film had 50 wt% BN in the core layer and 25 wt% BN in the outer layers of the dried film.

The multilayer film was cast by coextrusion. Three separate streams of polyamic acid polymer were simultaneously extruded through a multi-lumen extrusion die onto a heated moving belt to form a coextruded trilayer polyimide film. The thickness of the polyimide core layer and the top and bottom thermoplastic polyimide outer layers were adjusted by varying the amount of polyamic acid fed to the extruder.

The extruded multilayer film is dried at an oven temperature of about 95 ℃ to about 150 ℃. The self-supporting film was peeled from the tape and heated with a radiant heater in a tenter oven at a temperature of about 110 ℃ to about 805 ℃ (radiant heater surface temperature) to completely dry and imidize the polymer.

The radiant heating set point temperature for curing the film was 805 ℃. The core layer polymer composition contains a polyimide derived from PMDA to ODA in an approximately 1:1 molar ratio.

The thermoplastic outer layer also contains a polyimide derived from a dianhydride to diamine in a molar ratio of about 1: 1. The dianhydride composition contained 20:80 mole ratios of monomers PMDA and ODPA, and the diamine composition was 100 mole% RODA monomer. The flow rate of the polyamic acid solution was adjusted to produce a three-layer film in which the thermoplastic outer layers were about 3 μm thick and the core layer was about 19 μm thick.

Cross-sectional Scanning Electron Microscope (SEM) images of the three-layer film were obtained to determine the thickness of the multilayer film and the individual core and outer layers. To obtain this image, a film sample was cut and mounted in epoxy and allowed to dry overnight. The samples were then polished using a Buehler variable speed grinder/polisher and placed in a desiccator for approximately two hours to ensure drying. Images were captured under variable pressure using a Hitachi S-3400SEM (Hitachi High Technologies America, Inc.), Schaumburg, Ill.). The total thickness of the multilayer film was about 25 μm.

A series of ODBC thermal substrates were prepared using the multilayer film. A 1000 μm copper sheet was laminated to both sides of the multilayer film using vacuum assisted hydrostatic pressure at a maximum temperature of 330 ℃. The thermal and reliability performance of the substrate was evaluated by periodic inspections during accelerated testing.

For thermal shock testing, several substrates were placed in a thermal shock chamber and cycled between temperature limits of-40 ℃ and 200 ℃. The substrate was inspected every 1000 cycles. After 5000 cycles, the ODBC substrates did not experience high potential (hipot) failure, but preliminary edge delamination was visually observed.

For thermal aging, a set of individual samples was placed in a hot chamber and subjected to an elevated temperature of 175 ℃. After 1100 hours, no hipot failure was observed, but edge delamination was again observed.

Use of

The tape attached another set of samples to the cold plate to test the power cycle. Use of

The tape attaches the heater cartridge to the top of the substrate and places the thermocouples in several locations of the package. The heater cartridge alternates between an on state and an off state to allow the substrate to cycle between 40 ℃ and 200 ℃. Although the variation between the maximum temperature and the minimum temperature of the power cycle test is smaller compared to the thermal cycle test, the heater cartridge and the cold plate form a thermal gradient within the sample where passive thermal cycling may not be used. At 700 hours/1300 test cyclesThereafter, no hipot failure or edge delamination was observed.

Any change in the thermal properties of the package is measured by the transient thermal tester. The diodes in the TO-247 package were attached TO the top of the substrate under testing using thermal grease. Thermal grease also adheres the substrate to the cold plate. A transient power pulse was applied to the package and the decay of the temperature in the diode was monitored over time. This, together with the instantaneous 1D conduction analysis, helps to build up the resistive-capacitive network of the package. Any changes in the resistance measurements between the new substrate and the substrate on which the accelerated test has been completed are monitored. Thermal resistance measurements as shown in table 1 indicate that the ODBC substrates showed good stability in all three acceleration tests.

TABLE 1

Condition of substrate	Initial	Thermal ageing	Power cycle	Thermal shock
					Thermal resistance (K/W)	4.15	4.26	4.22	4.31

The acoustic image of the ODBC substrate showed that the bonding area between the multilayer film and the copper sheet was uniform and free of defects, although slight edge delamination was observed.

It should be noted that not all of the activities described above in the general description are required, that a portion of a specific activity may not be required, and that other activities may be performed in addition to those described. Furthermore, the order in which each activity is listed need not be the order in which they are performed. After reading this specification, skilled artisans will be able to determine which activities are available for their specific needs or desires.

In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. All the features disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose.

Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all the claims.

When an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper and lower values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

Claims

1. A thermal substrate, comprising:

a multilayer film, comprising:

a first outer layer comprising a first thermoplastic polyimide;

a core layer comprising polyimide; and

a second outer layer comprising a second thermoplastic polyimide,

wherein the multilayer film has a total thickness of 5 to 150 μ ι η, and the first outer layer, the core layer, and the second outer layer each comprise a thermally conductive filler;

a first electrically conductive layer adhered to the first outer layer of the multilayer film; and

a second electrically conductive layer adhered to the second outer layer of the multilayer film, wherein the first and second electrically conductive layers each have a thickness of 250 to 3000 μ ι η.

2. The thermal substrate of claim 1, wherein:

the first outer layer has a thickness of 1.5 to 20 μm;

the core layer has a thickness of 5 to 125 μm; and is

The second outer layer has a thickness of 1.5 to 20 μm.

3. The thermal substrate of claim 1, wherein the T of the core layer_gT higher than the first outer layer_gAnd T of said second outer layer_gBoth of which are described below.

4. The thermal substrate of claim 1, wherein:

the thermally conductive filler of the first outer layer is present in an amount of greater than 0 to 50 wt% based on the weight of the dry first outer layer;

the thermally conductive filler of the core layer is present in an amount of greater than 0 to 60 wt%, based on the weight of the dry core layer; and is

The thermally conductive filler of the second outer layer is present in an amount of greater than 0 to 50 wt% based on the weight of the dry second outer layer.

5. The thermal substrate of claim 1, wherein the weight percent of thermally conductive filler in the core layer is higher than the weight percent of thermally conductive filler in the first outer layer, the second outer layer, or both the first outer layer and the second outer layer, based on the dry weight of each layer.

6. The thermal substrate of claim 1, wherein the thermally conductive filler of each of the first outer layer, the core layer, and the second outer layer is individually selected from the group consisting of: BN, Al₂O₃AlN, SiC, BeO, Diamond, Si₃N₄And mixtures thereof.

7. The thermal substrate of claim 1 wherein the first thermoplastic polyimide comprises:

an aromatic dianhydride selected from the group consisting of: 4,4' -oxydiphthalic dianhydride, pyromellitic dianhydride, 3',4,4' -biphenyltetracarboxylic dianhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, and mixtures thereof; and

an aromatic diamine selected from the group consisting of: 1, 3-bis (4-aminophenoxy) benzene, 2-bis- (4- [ 4-aminophenoxy ] phenyl) propane and mixtures thereof.

8. The thermal substrate of claim 1 wherein the second thermoplastic polyimide comprises:

an aromatic diamine selected from the group consisting of: 1, 3-bis (4-aminophenoxy) benzene, hexamethylenediamine, and mixtures thereof.

9. The thermal substrate of claim 1 wherein the first and second thermoplastic polyimides are the same.

10. The thermal substrate of 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',4,4' -benzophenone tetracarboxylic dianhydride, bisphenol a dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic dianhydride and 2,3,6, 7-naphthalene tetracarboxylic dianhydride, and mixtures thereof; and

an aromatic diamine selected from the group consisting of: p-phenylenediamine, 4 '-diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 2 '-bis (trifluoromethyl) benzidine, m-phenylenediamine, and 4,4' -diaminodiphenylmethane, and mixtures thereof.

11. The thermal substrate of claim 1, wherein the first thermoplastic polyimide and the second thermoplastic polyimide each have a T of 150 ℃ to 320 ℃_g。