KR20210068129A - thermal substrate - Google Patents

Abstract

The thermal substrate includes a multilayer film, a first conductive layer attached to a first outer layer of the multilayer film, and a second conductive layer attached 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 in the range of 5 to 150 μm, wherein the first outer layer, the core layer, and the second outer layer each include a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness in the range of 250 to 3000 μm.

Description

thermal substrate

The field of the present disclosure is thermal substrates.

In the power electronics industry, an electrically insulating layer within a power electronics module is important to isolate circuitry from a thermal management layer. Thermal substrates in high power density power electronics packaging are rigid substrates on which semiconductor dies can be mounted. In addition to providing mechanical support, these substrates provide electrical isolation of circuits and dies, as well as provide a thermally efficient path for heat dissipation. BACKGROUND Power module devices, such as those found in automobiles, manipulate different types of currents and voltages to control equipment, and require large amounts of current flowing through their substrates and a high degree of electrical isolation. To achieve the competing requirements for both conduction and insulation, the thermal substrate comprises both conductive and insulating layers of different materials, such as metal (as conductor) and ceramic or polymer (as insulator), It takes the form of multiple layers, bonding them together in such a way that a path for flow can be spaced apart from the semiconductor die.

The most common structures used for thermal substrates are direct bonds formed through a high temperature bonding process between copper and a _{highly thermally conductive ceramic (eg, Al 2} O ₃ , AlN or Si ₃ N _{4 ).} copper: DBC) component. In a typical DBC structure, layers of metal and ceramic are bonded together in an environmentally controlled high temperature process to provide a thermally conductive and electrically insulating ceramic layer between the two layers of copper sheet. However, since these metal and ceramic layers have a large difference in coefficient of thermal expansion (CTE), the junction between them is subjected to a lot of thermomechanical stresses that cause degradation with high temperature gradients during power module operation. Also, the process used to bond the copper layer to the ceramic limits the thickness of the copper layer to less than 1000 μm. A typical DBC structure uses a 300 μm copper layer and a 380 μm ceramic layer.

In addition, organic-based insulating layers such as epoxies have recently been commercialized for relatively low power devices (ie, for operating temperatures below 150° C.). For these 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 filled with a thermally conductive filler to enable acceptable thermal conductivity, and is made into a thin film to provide thermal conductivity similar to that of the ceramic material. However, such thin-film epoxy deteriorates the electrical insulation properties of the thermal substrate.

Polyimide films are used in the manufacture of flexible printed circuit boards because of their excellent electrical insulating properties, mechanical strength, high temperature stability, and chemical resistance properties. Polyimide films are attached to thin metal foils to form metal-clad laminates, flexible printed connection boards for chip scale packages, die pad bonding of semiconductor devices or packaging materials, among other applications; For chip on flex, chip on lead, lead on chip, multichip module, ball grid array (or micro ball grid array), and/or tape automated bonding , the substrate is used.

US Pat. No. 7,285,321 describes a multilayer laminate having a low glass transition temperature (T _g ) polyimide layer, a high T _g polyimide layer, and a conductive layer. The high T _g polyimide layer is a thermoset polyimide and the low T _g 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 substrate film and two thermoplastic aromatic polyimide layers. The metal film and the release film are attached to opposite sides 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 through the addition of thermally conductive fillers. European Patent Application No. 0 659 553 A1 describes a method for providing a coextruded multilayer film which may comprise 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 may be added to either or both of the _{high and low T g polyimide layers.} . Fillers are typically added in the form of a slurry to a cast solution of the polymer. The solvent of the filler-based slurry may be the same or different from that used to prepare the polymer casting solution.

The thermal substrate includes a multilayer film, a first conductive layer attached to a first outer layer of the multilayer film, and a second conductive layer attached 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 in the range of 5 to 150 μm, wherein the first outer layer, the core layer, and the second outer layer each include a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness in the range of 250 to 3000 μm.

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

The thermal substrate includes a multilayer film, a first conductive layer attached to a first outer layer of the multilayer film, and a second conductive layer attached 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 in the range of 5 to 150 μm, wherein the first outer layer, the core layer, and the second outer layer each include a thermally conductive filler. The first conductive layer and the second conductive layer each have a thickness in the range of 250 to 3000 μm.

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

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

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% by weight, based on the weight of the dried first outer layer, and the thermally conductive filler of the core layer comprises: It is present in an amount of greater than 0 to 60% by weight, based on the weight of the core layer, and the thermally conductive filler of the second outer layer is present in an amount of greater than 0 to 50% by weight, based on the weight of the dried second outer layer.

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

In 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 BN, Al ₂ O ₃ , AlN, SiC, BeO, diamond, Si ₃ N ₄ , and their individually selected from the group consisting of mixtures.

In a further embodiment of the thermal substrate, the first thermoplastic polyimide is 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyl tetra aromatic polyanhydrides selected from the group consisting of carboxylic acid dianhydrides, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydrides, and mixtures thereof; and aromatic diamines selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene, 2,2-bis-(4-[4-aminophenoxy]phenyl)propane, and mixtures thereof.

In yet a further embodiment of the thermal substrate, the second thermoplastic polyimide is 4,4'-oxydiphthalic dianhydride, pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, an aromatic polyanhydride selected from the group consisting of hydrides, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydrides, and mixtures thereof; and aromatic diamines selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene, hexamethylene diamine, and mixtures thereof.

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

In yet a further embodiment of the thermal substrate, the polyimide of the core layer comprises: 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, pyromellitic acid Dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, bisphenol A dianhydride, 1,2,5,6-naphthalene tetracarboxylic acid dianhydride, 1,4,5,8 - an aromatic dianhydride selected from the group consisting of naphthalene tetracarboxylic acid dianhydride, and 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, and mixtures thereof; and p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)benzidine, m-phenylenediamine and 4 ,4'-diaminodiphenylmethane, and aromatic diamines selected from the group consisting of 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 of 150 to 320 °C.}

Many aspects and embodiments have been described above and are illustrative only and not restrictive. After reading this specification, those skilled in the art understand that other aspects and embodiments are possible without departing from the scope of the invention. Other features and advantages of the present invention will become apparent from the following detailed description and claims.

In one embodiment, the core layer for the multilayer film comprises a polyimide synthesized by a poly-condensation reaction comprising the reaction of 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 is 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, pyromellitic acid dianhydride, 3, 3',4,4'-benzophenone tetracarboxylic acid dianhydride, bisphenol A dianhydride, 1,2,5,6-naphthalene tetracarboxylic acid dianhydride, 1,4,5,8-naphthalene tetracarboxylic acid dianhydride lead, and 2,3,6,7-naphthalene tetracarboxylic acid dianhydride. In one embodiment, the aromatic diamine is p-phenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 2,2'-bis(trifluoro methyl) 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 thermosetting polyimide. In one embodiment, the core layer may comprise a polyimide having some thermoplastic properties.

In one embodiment, the first outer layer for the multilayer film comprises a first thermoplastic polyimide. In one embodiment, the first thermoplastic polyimide may be synthesized by a polycondensation reaction comprising a reaction of an aromatic dianhydride and an aromatic diamine. In one embodiment, the first thermoplastic polyimide may include 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 for the multilayer film comprises a second thermoplastic polyimide. In one embodiment, the second thermoplastic polyimide may be synthesized by a polycondensation reaction comprising a reaction of an aromatic dianhydride and an aromatic diamine. In one embodiment, the second thermoplastic polyimide may include 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 may include one or more aliphatic diamines, which may be useful to reduce the _{T g of the outer layer, if desired.} 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 g in the range of from about 150 to about 320 °C.}

As used herein, "aromatic diamine" refers to at least one ring, either alone (ie, substituted or unsubstituted, functionalized or unfunctionalized benzene or an aromatic ring of a similar type) or linked to another (aromatic or aliphatic) ring. It is intended to mean a diamine having an aromatic ring, which amine is to be considered aromatic, irrespective of any non-aromatic component that may be a component of the diamine. Thus, an aromatic diamine backbone chain moiety is intended to mean at least one aromatic component between two adjacent imide linkages. As used herein, “aliphatic diamine” is intended to mean any organic diamine that does not meet the definition of an aromatic diamine.

Depending on the context, “diamine” as used herein includes (i) the unreacted form (ie, the diamine monomer); (ii) a partially reactive form (ie, a portion or portions of an oligomer, or other polyimide precursor derived from or otherwise resulting from a diamine monomer); or (iii) a fully reactive form (a portion or portions of a polyimide derived from or otherwise attributable to a diamine monomer). The diamine may be functionalized with one or more components, depending on the specific embodiment selected in the practice of the present invention.

Indeed, the term “diamine” is not intended to be limiting (or interpreted literally) as to the number of amine components in the diamine component. For example, (ii) and (iii) above include polymeric materials that may have two, one, or zero amine components. Alternatively, the diamine may be functionalized with an additional amine component (with the terminal amine component of the monomer reacting with the dianhydride to propagate the polymer chain). These additional amine components can be used to crosslink the polymer or provide other functionality to the polymer.

Similarly, the term "dianhydride," as used herein, refers to reacting (complementary thereto) with a diamine and combining to form an intermediate polyamic acid (which can then be cured to a polyimide). It is intended to mean a component capable of reacting so as to Depending on the context, “anhydride” as used herein may mean not only the anhydride component per se, but also a precursor of the anhydride component, e.g., (i) a pair of carboxylic acid groups (can be converted to anhydride by dehydration or similar types of reactions); or (ii) an acid halide (eg chloride) ester functionality that can be converted to an anhydride functionality (or any other functionality currently known or to be developed in the future).

Depending on the context, “dianhydride” refers to (i) a dianhydride in its unreacted form (i.e., whether the anhydride functionality is in the pure anhydride form or the precursor anhydride form, as described in the previous paragraph above. monomer); (ii) a partially reacted form (ie, a precursor polyimide composition reacted from or otherwise resulting from a portion or portions of an oligomer, or other partially reacted or dianhydride monomer); or (iii) a fully reactive form (a portion or portions of a polyimide derived from or otherwise attributed to a dianhydride monomer).

A dianhydride may be functionalized with one or more components, depending on the specific embodiment selected in the practice of the present invention. Indeed, the term "dianhydride" is not intended to be limiting (or interpreted literally) as to the number of anhydride components in the dianhydride component. For example, (i), (ii) and (iii) (in the paragraph above) are organic, which may have 2, 1 or 0 anhydride components, depending on whether the anhydride is in the precursor or reactive state. contains substances. Alternatively, the dianhydride component may be functionalized with an additional anhydride type component (along with an anhydride component that reacts with the diamine to give the polyimide). These additional anhydride components can be used to crosslink the polymer or provide other functionality 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 a range, preferred range, or list of upper preferred and lower preferred values, this means any upper range or preferred value of any pair and any upper range or preferred value of any pair, whether or not the ranges are separately disclosed. It is to be understood that any lower range or all ranges formed with preferred values are specifically disclosed. Unless otherwise specified, when a range of numerical values is recited herein, the range is intended to include its endpoints, 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 the range.

It should be understood that, when referring to specific polymers, applicants will sometimes refer to polymers by the monomers used to make them, or the amount of monomers used to make them. This description may not include specific names used to describe the final polymer, or may not include product-by-process terms, but any such reference to monomers and amounts is , such monomers or such amounts of monomers, and their corresponding polymers and compositions, should be construed to mean that the polymers are prepared.

The materials, methods, and examples herein are illustrative only and, except as specifically noted, are not intended to be limiting.

As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “having”, “having”, or its Any other ending changes are intended to cover non-exclusive inclusions. For example, a method, process, article, or apparatus comprising a list of elements is not necessarily limited to only those elements, but may include other elements not inherent in such method, process, article, or apparatus or not explicitly listed. may include Also, unless explicitly stated to the contrary, "or" means "inclusive or" and not "exclusive or". For example, condition A or B is satisfied by either: 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).

Also, the use of “a” or “an” is used to describe elements and components of the invention. This is done for convenience only and is intended to provide a general meaning of the present invention. This description is to be understood as including one or at least one, and the singular also includes the plural unless it is clear that it means otherwise.

organic solvent

A useful organic solvent for the synthesis of the polyimide of the present invention is preferably capable of dissolving the polyimide precursor material. Also, since these solvents should have a relatively low boiling point, such as less than 225° C., the polymer can be dried to a suitable (ie, simpler and less expensive) temperature. A boiling point of less than 210, 205, 200, 195, 190, or 180°C is preferred.

The solvents of the present invention may be used alone or in combination with other solvents (ie, co-solvents). Useful organic solvents include N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), N,N'-dimethyl-formamide (DMF), dimethyl sulfoxide (DMSO), tetramethyl urea (TMU), di Ethylene 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), gamma-butyrolactone, and bis-(2-methoxyethyl) ether , tetrahydrofuran. In one embodiment, preferred solvents include N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc).

As a rule, co-solvents can be used at about 5 to 50 weight percent of the total solvent, and useful co-solvents include xylene, toluene, benzene, "Cellosolve" (glycol ethyl ether), and "cellosolve" solv acetate" (hydroxyethyl acetate glycol monoacetate).

aromatic diamines

In one embodiment, 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'-dia Minobiphenyl, 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-amino benzoyl-p-amino anilide, 4-aminophenyl-3-aminobenzoate, N,N-bis-(4-aminophenyl) Aniline, 2,4-diaminotoluene, 2,5-diaminotoluene, 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-butyl phenyl) ether, p-bis-2-(2-methyl-4-aminopentyl) benzene, m Any number of suitable aromatic diamines may be included in the core layer polyimide, including -xylylene diamine, and p-xylylene diamine.

Other useful aromatic diamines are 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) H) Benzene, 1,4-bis-(4-aminophenoxy) benzene, 1,4-bis-(3-aminophenoxy) benzene, 1-(4-aminophenoxy)-4-(3-amino Phenoxy) 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'-trifluoro Romethyl diphenyloxide, 3,3'-diamino-5,5'-trifluoromethyl diphenyloxide, 4,4'-trifluoromethyl-2,2'-diaminobiphenyl, 2,4 ,6-Trimethyl-1,3-diaminobenzene, 4,4'-oxy-bis-[2-trifluoromethyl)benzene amine] (1,2,4-OBABTF), 4,4'-oxy- Bis-[3-trifluoromethyl)benzene amine], 4,4'-thio-bis-[(2-trifluoromethyl)benzene-amine], 4,4'-thiobis[(3-trifluoro Romethyl)benzene amine], 4,4'-sulfoxyl-bis-[(2-trifluoromethyl)benzene amine, 4,4'-sulfoxyl-bis-[(3-trifluoromethyl)benzene amine ], and 4,4′-keto-bis-[(2-trifluoromethyl)benzene amine].

In one embodiment, useful aromatic diamines include isomers of bis-aminophenoxybenzene (APB), aminophenoxyphenylpropane (BAPP), dimethylphenylenediamine (DPX), bisaniline P, and combinations thereof. The use of this particular aromatic diamine can reduce the lamination temperature of the polyimide and increase the peel strength of the polyimide when attached to other materials (especially metals).

In one embodiment, the thermoplastic polyimide of the outer layer may include 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, may be used as the dianhydride monomer when forming the core layer polyimide. The dianhydrides may be used in their tetra-acid form (or mono, di, tri, or tetra esters of tetra acids), or as their diester acid halides (chlorides). 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'-biphenyl tetracarboxylic acid dianhydride (BPDA), 1,2,5,6-naphthalene tetracarboxylic acid dianhydride, 1,4, 5,8-naphthalene tetracarboxylic acid dianhydride, 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, 2-(3',4'-dicarboxyphenyl) 5,6-dicarboxybenzimidazole dianhydride Lead, 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'-biphenyl tetracarboxylic acid dianhydride, 2,3,3',4'-biphenyl tetracarboxylic acid dianhydride, bicyclo- [2,2,2]-octene-(7)-2,3,5,6-tetracarboxylic acid-2,3,5,6-dianhydride, 4,4'-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'-dicarboxy Diphenyl ether) 1,3,4-oxadiazole dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyphenyl) thioether dianhydride, bisphenol A dianhydride Lead (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′-oxy phthalic anhydride) benzene, bis (3,4-dicarboxyphenyl) methane dianhydride, cyclopentadienyl tetracarboxylic acid dianhydride, cyclopentane tetracarboxylic acid dianhydride, ethylene Tetracarboxylic acid dianhydride, perylene 3,4,9,10-tetracarboxylic acid dianhydride, pyromellitic acid dianhydride (PMDA), tetrahydrofuran tetracarboxylic acid dianhydride, 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 acid dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, phenanthrene- 1,8,9,10-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, benzene-1,2,3,4-tetracarboxylic acid dianhydride; and thiophene-2,3,4,5-tetracarboxylic acid dianhydride.

In one embodiment, the thermoplastic polyimide of the outer layer may include one or more of any of the aromatic dianhydrides listed above for the core layer.

thermally conductive filler

In one embodiment, the thermally conductive filler is thermally conductive, but 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, Al ₂ O ₃ , Si ₃ N ₄ , ZnO, MgCO ₃ , MgO, BeO, diamond, SiC, many other oxide, nitride and carbide compounds, and these contains a mixture of In one embodiment, the core-shell type filler may comprise one of these filler materials coated by a coating of a second filler material. This thermally conductive filler may be of any shape or size and may have an average primary particle size (D ₅₀ ) in the range of about 0.001 to about 8 μm.

multilayer film

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

In one embodiment, the polyamic acid casting solution is derived from a polyamic acid solution. Preferably, the polyamic acid casting solution comprising the polyamic acid solution comprises: i) at least one dehydrating agent, for example, an aliphatic acid anhydride (such as acetic anhydride) and/or an aromatic acid anhydride; and ii) one or more catalysts, for example, conversion chemistry, such as aliphatic tertiary amines (triethyl amine, etc.), aromatic tertiary amines (dimethyl aniline, etc.) and heterocyclic tertiary amines (pyridine, picoline, isoquinoline, etc.) It can be optionally combined with a substance. The anhydride dehydration material is often used in a molar excess relative 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 (repeating unit) of polyamic acid. In general, similar amounts of tertiary amine catalyst are used.

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

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 filler may be dispersed in the organic solvent at a concentration of from about 5, 10, or 15 weight percent to about 20, 30, 40, 50 and 75 weight percent. In one embodiment, the solvent used for the dispersion or suspension of the thermally conductive filler is the same as 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 to achieve the desired filler filling of the final film. In one embodiment, the first outer layer may include a thermally conductive filler in an amount from greater than 0 to about 50% by weight of the dried film. In one embodiment, the core layer may include a thermally conductive filler in an amount of greater than 0 to about 60 weight percent of the dried film. In one embodiment, the second outer layer may include a thermally conductive filler in an amount from greater than 0 to about 50% by weight 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 amounts of thermally conductive filler as the other layers of the multilayer film, based on the weight percentage of the dried film. In one embodiment, the weight percentage of thermally conductive filler in the core layer may be higher than the weight percentage of thermally conductive filler in the first outer layer, the second outer layer, or both the first and second outer layers. In other embodiments, the weight percentage of thermally conductive filler in the core layer may be lower than the weight percentage of thermally conductive filler in the first outer layer, the second outer layer, or both the first and second outer layers.

The solvation mixture (polyamic acid casting solution with thermally conductive filler) can then be cast or applied onto a support such as a seamless belt or rotary drum to obtain a film. The solvent-containing film can then be converted into a self-supporting film by heating with a conversion chemical reactant (chemical curing) to the appropriate temperature (thermal curing). The film can then be separated from the support and stretched through continuous thermal and chemical curing, for example by tentering, to provide a polyimide film.

Useful methods for making polyimide films according to the present invention can be found in US Pat. Nos. 5,166,308 and 5,298,331, which are incorporated herein by reference for all teachings therein. A number of variations are also possible, such as:

(a) A method in which the diamine component and the dianhydride component are mixed together in advance and then partially added to the solvent while the mixture is stirred.

(b) A method in which a solvent is added to a stirred mixture of the diamine and dianhydride components. (as opposed to (a) above)

(c) A method in which the diamine alone is dissolved in a solvent, and then a dianhydride is added thereto in such a proportion as to allow the reaction rate to be controlled.

(d) A method in which the dianhydride component alone is dissolved in a solvent, and then the amine component is added thereto in such a proportion as to make it possible to control the reaction rate.

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

(f) A process in which a polyamic acid having an excess amine component and another polyamic acid having an excess dianhydride component are preformed and then reacted with each other in a reactor, particularly in such a way as to produce a non-random or block copolymer.

(g) A method in which the amine component and a specific portion of the dianhydride component are reacted first, and then the residual diamine component is reacted, or vice versa.

(h) A method in which 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 method in which the components are partially or wholly added to some or all of the solvent in any order, and also some or all of the optional components can be added to some or all of the solvent as a solution.

(j) A method for obtaining a first polyamic acid by first reacting one of the dianhydride components with one of the diamine components. Then, another dianhydride component is reacted with another amine component to obtain a second polyamic acid. Then, prior to film formation, the amic acid is combined in any of a number of ways.

The thickness of each polyimide layer can be adjusted according to the intended purpose of the film or end application specification. In one embodiment, the multilayer film has a total 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 ranges from about 5 to about 125 μm, or from about 10 to about 100 μm, or from about 15 to about 75 μm, or from about 15 to about 40 μm. In one embodiment, the thickness of the outer layer is from about 1.5 to about 20 μm for each outer layer, or from about 3 to about 15 μm for each outer layer, or from about 3 to about 12 μm, or from about 3 to about 6 μm in the range of μm. Those skilled in the art will understand that a minimum thickness of the outer layer with the thermoplastic polyimide is required to provide sufficient adhesion to the metal layer to form a useful thermal substrate for power electronics applications. Also, in order to maintain the mechanical integrity of the multilayer film, a minimum thickness of the core layer is required.

As thermal substrates for high power density semiconductor devices (eg, insulated gate bipolar transistors), multilayer films can undergo rapid temperature changes from room temperature to as high as 200°C. The actual driving cycle conditions of an automobile's power module can affect these temperature changes in a fast and repeatable pattern, requiring rapid heat dissipation and high mechanical integrity. Under these conditions, low T _g organic layers, such as epoxy, are susceptible to adhesion loss and peeling.

In one embodiment, the core layer and the outer layer of the multilayer film may be solution cast simultaneously by coextrusion. Upon casting, the polyimide may be in the form of a polyamic acid solution. The casting solution forms an uncured polyamic acid film, which is then cured to polyimide. The adhesive strength of these laminates can be improved by using various techniques to increase the adhesive strength.

In some embodiments, the finished polyamic acid solution is filtered and pumped to a slot die, and the flow is split in such a way as to form a first outer layer and a second outer layer of the trilayer coextrusion film. In some embodiments, a second stream of polyimide is filtered and then pumped to a casting die in such a way as to form an intermediate polyimide core layer of a three-layer coextrusion film. The flow rate of the solution 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 layer is extruded through a single or multi-cavity extrusion die. In another embodiment, the multilayer film is made using a single-cavity die. If a single-cavity die is used, the laminar flow should be of high enough viscosity to prevent comingling of the flow and to provide uniform stratification. By using the co-extrusion process, a multilayer film having excellent interlayer adhesion can be produced without the use of an adhesive layer.

In one embodiment, the multilayer film may be formed by any conventional technique used to form polyimide films. In one embodiment, an outer layer may be applied to the core layer during an intermediate manufacturing step of making a polyimide film, such as a gel film or a green film.

thermal substrate

In one embodiment, a lamination process may be used to form a thermal substrate having a multilayer film attached to the first and second conductive layers. In one embodiment, the first outer layer of the multilayer film comprising a first thermoplastic polyimide is between the core layer of the multilayer film and the first conductive layer, the second outer layer comprising a second thermoplastic polyimide is the core layer is on the opposite side of In one embodiment, the second conductive layer is disposed in contact with the second outer layer on the opposite side of the core layer. One advantage of this type of structure 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 be bonded to the conductive layer(s). In one embodiment, the conductive layer(s) are metal layer(s). In one embodiment, the metal layer is a metal sheet having a thickness ranging 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, before the step of applying the multilayer film of the present invention on the conductive layer, the polyimide film may be subjected to a pretreatment step. Pretreatment steps include heat treatment, corona treatment, plasma treatment under atmospheric pressure, plasma treatment under reduced pressure, treatment with coupling agents such as silane and titanate, sandblasting, alkali treatment, acid treatment, and coating of polyamic acid can do. In general, for improving adhesive strength, see U.S. Patent Nos. 4,742,099; 5,227,244; 5,218,034; and 5,543,222, it is also possible to add various metal compounds.

In addition, the conductive layer surface (for the purpose of improving adhesion) can be treated through various organic and inorganic treatments. These treatments include silane, imidazole, triazole, oxide and reduced oxide treatments, tin oxide treatments, and surface cleaning/roughening (also referred to as micro-etching) using acidic or alkaline reagents. includes steps.

As used herein, the term “conductive layer” means a metal layer (a composition having at least 50% of the electrical conductivity of high-grade copper). The metal layer need not be used as a component in its pure form; They may also be used as metal alloys, such as copper alloys containing nickel, chromium, iron, and other metals.

A particularly suitable metal layer is rolled, annealed copper, or rolled, annealed copper alloy. It has proven advantageous in most cases to pretreat the metal layer prior to attaching the multilayer film. Such pretreatment may include, but is not limited to, electrodeposition or dip-deposition on the metal of thin layers of copper, zinc, chromium, tin, nickel, cobalt, other metals, and alloys of these metals. The pretreatment may be a chemical treatment or a mechanical roughening treatment.

In one embodiment, an organic direct bonded copper (ODBC) system can include a multilayer film and a first copper layer attached 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 are the same thickness. In a specific embodiment, the first copper layer and the second copper layer are the same thickness and range from 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 comprises microchannels. Such microchannels can provide improved heat dissipation for thermal substrates.

In one embodiment, using a static press or autoclave, as commonly used to form metal-clad laminates with polyimide films for flexible circuit applications, the copper The layers may be laminated to the multilayer film. ODBC structures using the multilayer film and conductive layer of the present invention maintain excellent adhesive strength due to the thermoplastic nature of the outer layer of the multilayer film, thus minimizing the impact of CTE mismatch. This is in contrast to the ceramic-metal bonding of DBC structures where the bonding stiffness combined with the CTE difference between the ceramic and the metal causes large thermomechanical stresses during power module operation. Consequently, ODBC thermal substrates using the multilayer film and conductive layer of the present invention can be used for high power density power electronics packaging, operating at temperatures up to 200°C.

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

The multilayer film of the present invention exhibits good attenuation. Often the polyimides of the present invention can exhibit attenuation values (measured in decibels per inch) of about 0.3 at 10 GHz using 50 ohm microstrips.

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

Advantageous properties of the invention may be understood by reference to the following examples which illustrate but not limit the invention. All ratios and percentages are by weight unless otherwise specified.

Example

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

For thermally conductive fillers, by preparing a 25 wt % dispersion of BN in DMAc and then adding to the polyamic acid solution, the multilayer film was obtained by providing 50 wt % BN in the core layer and 25 wt % BN in the outer layer of the dried film. has

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

The extruded multilayer film was dried at an oven temperature ranging from about 95 to about 150°C. The free-standing film was peeled from the belt and heated through a radiant heater in a tenter oven to a temperature of about 110 to about 805° C. (radiation heater surface temperature) to completely dry the polymer and imidize it.

The radiant heating setpoint temperature used to cure the film was 805°C. The core layer polymer composition contained a polyimide derived from PMDA to ODA in a molar ratio of about 1:1.

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

To determine the thickness of the multilayer film and the individual core and outer layers, cross-sectional scanning electron microscopy (SEM) images of the trilayer film were acquired. To acquire these images, film samples were cut, fixed with epoxy, and allowed to dry overnight. The samples were then ground using a Buehler variable speed grinder/grinder and placed in the dryer for about 2 hours to ensure drying. Images were captured using a Hitachi S-3400 SEM (Hitachi High Technologies America, Inc., Schaumburg, IL) under variable pressure. The total thickness of the multilayer film was about 25 μm.

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

For thermal shock testing, multiple substrates were placed in a thermal shock chamber and cycled between temperature extremes of -40°C and 200°C. The substrate was inspected every 1000 cycles. After 5000 cycles, the ODBC substrate did not suffer from hipot failure, but pre-edge delamination was visually observed.

For thermal aging, a separate set of samples was placed in a thermal chamber and an elevated temperature of 175° C. was applied. After 1100 h, no hipot failure was observed, but edge delamination was observed again.

To test the power cycle, another set of samples was attached to the cold plate with Kapton® tape. A heater cartridge was attached to the top of the substrate with Kapton® tape, and thermocouples were placed at multiple locations through the package. The heater cartridge was alternated between an on state and an off state to allow the substrate to be cycled between 40°C and 200°C. Compared to the thermal cycle test, in the power cycle test, there is less variation between the maximum and minimum temperature, but the heater cartridge and cold plate create a thermal gradient in the sample that is not possible through manual thermal cycling. After testing of 700 hours/1300 cycles, no hipot failure or edge delamination was observed.

Any change in the thermal performance of the package was measured by a transient thermal tester. The diodes in the TO-247 package were attached to the top of the board under test using thermal grease. The thermal grease also adhered the substrate to the cooling plate. A transient power pulse was applied to the package and the decay in temperature at the diode was monitored over time. This, combined with transient 1D conduction analysis, helps establish a resistance-capacitance network for the package. Resistance measurements were monitored for any changes between the substrate that had completed the accelerated test and the new substrate. The thermal resistance measurements as shown in Table 1 demonstrate that the ODBC substrate shows good stability in all three accelerated tests.

Table 1

Acoustic imaging of the ODBC substrate showed that the bonded area between the multilayer film and the copper sheet was uniform and defect-free, but slight edge delamination was observed.

Note that not all of the foregoing operations are required in the general description, some of specific operations may not be required, and additional operations may be performed in addition to those described. Still further, the order in which each task is listed is not necessarily the order in which they are performed. After reading this specification, those skilled in the art will be able to determine which operation may be used for their specific needs or goals.

In the foregoing specification, the present invention has been described with reference to specific embodiments. However, it will be understood by those skilled in the art that various modifications and changes may be made therein without departing from the scope of the invention as set forth in the claims below. All features disclosed herein may be replaced with alternative features serving the same, equivalent or similar purpose.

Accordingly, the specification and drawings 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 the present invention.

With respect to specific embodiments, advantages, other advantages, and solutions to problems have been described above. However, an advantage, advantage, solution to a problem, and any element(s) that may cause any advantage, advantage, or solution to occur or become more pronounced are important, necessary, or It should not be construed as an essential feature or element.

When an amount, concentration, or other value or parameter is given as a range, preferred range, or list of upper and lower values, it means any pair of upper and lower ranges or preferred values and any of the upper and lower ranges, regardless of whether the ranges are individually disclosed. It is to be understood that all ranges formed by the lower ranges or preferred values of are specifically disclosed. Unless otherwise specified, when a range of numerical values is recited herein, the range is intended to include its endpoints, 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 the range.

Claims (11)

As a thermal substrate,
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 in the range of 5 to 150 μm, the first outer layer, the core layer, and the second outer layer each comprising a thermally conductive filler;
a first conductive layer attached to the first outer layer of the multilayer film; and
a second conductive layer attached to the second outer layer of the multilayer film;
The first conductive layer and the second conductive layer each have a thickness in the range of 250 to 3000 μm,
thermal substrate. According to claim 1,
The first outer layer has a thickness in the range of 1.5 to 20 ㎛,
The core layer has a thickness in the range of 5 to 125 μm,
wherein the second outer layer has a thickness in the range of 1.5 to 20 μm. According to claim 1,
T _g of the core layer is higher, the thermal substrate than both the T _g of the first outer layer 1 T _g and the second outer layer. According to claim 1,
the thermally conductive filler of the first outer layer is present in an amount of greater than 0 to 50% by weight based on the weight of the dried first outer layer;
The thermally conductive filler of the core layer is present in an amount of greater than 0 to 60% by weight based on the weight of the dried core layer,
wherein the thermally conductive filler of the second outer layer is present in an amount of greater than 0 to 50% by weight based on the weight of the dried second outer layer. According to claim 1,
The weight percentage of thermally conductive filler in the core layer is, based on the dry weight of each layer, the weight percentage of thermally conductive filler in the first outer layer, the second outer layer, or both the first and second outer layers. Higher than that, the thermal substrate. According to claim 1,
The thermally conductive filler of each of the first outer layer, the core layer, and the second outer layer is selected from the group consisting of BN, Al ₂ O ₃ , AlN, SiC, BeO, diamond, Si ₃ N ₄ , and mixtures thereof. individually selected thermal substrates. According to claim 1,
The first thermoplastic polyimide,
4,4'-oxydiphthalic acid dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetra aromatic dianhydrides selected from the group consisting of carboxylic acid dianhydrides, and mixtures thereof; and
heat comprising 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. Board. According to claim 1,
The second thermoplastic polyimide,
4,4'-oxydiphthalic acid dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetra aromatic dianhydrides selected from the group consisting of carboxylic acid dianhydrides, and mixtures thereof; and
A thermal substrate comprising an aromatic diamine selected from the group consisting of 1,3-bis(4-aminophenoxy)benzene, hexamethylene diamine, and mixtures thereof. According to claim 1,
wherein the first thermoplastic polyimide and the second thermoplastic polyimide are the same. According to claim 1,
The polyimide of the core layer,
3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-benzophenone tetra Carboxylic acid dianhydride, bisphenol A dianhydride, 1,2,5,6-naphthalene tetracarboxylic acid dianhydride, 1,4,5,8-naphthalene tetracarboxylic acid dianhydride, and 2,3,6,7- aromatic dianhydrides selected from the group consisting of naphthalene tetracarboxylic acid dianhydrides, and mixtures thereof; and
p-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)benzidine, m-phenylenediamine and 4, A thermal substrate comprising an aromatic diamine selected from the group consisting of 4'-diaminodiphenylmethane, and mixtures thereof. According to 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.}