Chain extenders and their formulations for elongation enhancement in photosensitive polyimides

Abstract

To provide photosensitive polyimide materials having chain extenders, and chain extenders that improve elongation and formability of the polyimide materials, and methods of making such polymer materials.SOLUTION: A photosensitive polymer formulation can comprise a poly(amic acid) salt as a polyimide precursor and a tertiary amine salt of a tetracarboxylic acid as a latent chain extender, and further can contain a cross-linking agent, so that it improves elongation and formability of the polyimide materials.SELECTED DRAWING: None

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 868,761, filed June 28, 2019, and U.S. Patent Application No. 16 / 746,695, filed January 17, 2020, the entire contents of which are incorporated herein by reference.

[0002] [Technical field] FIELD OF THE DISCLOSURE Embodiments of the present disclosure generally relate to photosensitive polyimide formulations, materials, and uses thereof. More particularly, embodiments of the present disclosure relate to photosensitive polyimide materials with chain extenders and their formulations that improve the elongation and moldability of the polyimide materials, and methods of making such polymeric materials. [Background technology]

[0003] Electronic circuits, such as printed circuit boards, are used in a wide variety of components and typically include conductive and insulating layers. For example, in the disk drive industry, flexures are structures that flexibly support read / write transducers in close proximity to the rotating disk, while also supporting flexible electrical circuitry for conducting electrical signals to and from the transducers. Some structures include a layer of stainless steel, sometimes as a base layer, on which various insulating and conductive layers are formed.

[0004] Polymer materials are widely used in the manufacture of electronic circuits as insulating layers coated on metal layers. For the manufacture of certain electronic components, conductive and insulating layers are patterned using photolithography and etching techniques, thus requiring photosensitive polymer materials. In the manufacture of electronic components, polyimide materials find use as photosensitive polymer materials. A suitable polyimide material must satisfy many parameters and characteristics, both during the initial manufacturing process and during subsequent processes and uses.

[0005] In some instances, mechanical forming is required for electronic component manufacturing after the device is initially fabricated, and in such instances, a cured polymer layer coated onto a metal part is subjected to forming, which involves bending the polymer-coated metal part through an angle of approximately 90 degrees. Small forming radii are particularly desirable in terms of reducing the device footprint.

[0006] When the device is subjected to forming (e.g., the device is bent), the polymer coating is stretched in the formed area. Forming a polymer coating presents many challenges. A part or device typically includes a polymer layer coated onto a metal layer, such as stainless steel. When initially fabricated, the metal layer in the device is in a neutral axis state, with no tension or compression. At this stage, the polymer layer will harden. The device is then formed or bent, which causes the polymer layer to stretch in the formed area. As the radius (extent) of the formed area continues to decrease, the stretch of the polymer in the formed area continues to increase.

[0007] If the polymer ultimate strain during the molding process is exceeded, cracks will occur in the polymer layer and the polymer material will fail. This is a significant challenge and has severely limited the practical utility of photopolymer materials in molded device applications. Common failure models for the polymer layer after molding include complete tearing in the polymer layer and partial tearing in the polymer layer, both in the polymer layer subjected to molding on top of the metal layer and in the independent polymer layer, respectively. Such complete and partial tearing in the molded polymer layer can be catastrophic and even disable the use of the device.

[0008] This problem is common across conventional polymeric materials. During the solvent development step, very low molecular weight polymer formulations tend to crack severely. On the other hand, higher molecular weight polymers are known to exhibit good elongation and moldability after molding. However, when photosensitive materials are required, high molecular weight photopolymers are difficult or impractical to process. By way of example and without limitation, high molecular weight polymers are generally considered to have average molecular weights in the range of about 40,000 or higher. High molecular weight polymers exhibit properties that negatively impact initial manufacturing steps, particularly photolithographic process steps. For example, high molecular weight photopolymers generally exhibit very high viscosity and / or low solids content. Filtration is very time consuming and expensive. Photolithographic contrast and development speed are poor. Thus, high molecular weight photopolymers are not suitable for the initial process steps prior to the curing step.

[0009] Thus, the problem is very complex and currently available polymeric materials are substantially inadequate, so new developments are greatly needed. Summary of the Invention

[0010] Generally, embodiments of the present disclosure provide photosensitive polymer formulations, materials, and uses of such materials. More specifically, embodiments of the present disclosure provide photosensitive polyimide materials with latent chain extenders and their formulations that improve the elongation and moldability of the polyimide materials, and methods of making such polymer materials.

[0011] The inventors have discovered that to solve the above problems, several complex factors must be understood and balanced regarding the chemical composition and properties of the photodefinable polymer formulation throughout the process, including during the initial device fabrication steps, the manner in which the polymer formulation is subjected to a curing step, and the subsequent molding step.

[0012] As will be explained in detail below, lower molecular weight polymers exhibit more desirable characteristics during the initial manufacturing steps, particularly the photolithography process steps, while higher molecular weight polymers exhibit better elongation or moldability during the subsequent molding steps. After considerable research and effort, the inventors have developed innovative polymer formulations and methods of making the same, where the polymer formulation and chemical composition are selectively manipulated throughout the manufacturing, curing, and molding steps to control the molecular weight of the polymer to achieve desired properties. For example, in some embodiments, a method is provided in which the molecular weight of the poly(amic acid) in the photopolymer formulation is selectively controlled to be in a relatively low weight average molecular weight range during the initial process steps, and then during curing, the weight average molecular weight of the polyimide polymer is increased to provide a polyimide insulating layer comprising a high weight average molecular weight polyimide polymer that exhibits improved elongation and moldability during the subsequent molding steps. Thus, the molecular weight of the polyimide polymer is broadly said to be higher (increased) after curing.

[0013] In some embodiments, the weight average molecular weight of the polyimide polymer increases at least twice after curing, compared to the weight average molecular weight of the base polymer in the initial polymer formulation before curing.In some embodiments, the weight average molecular weight of the polyimide polymer increases to about 60,000 after curing.For some embodiments, the weight average molecular weight of the polyimide polymer can increase to a value of more than 60,000, for example, up to 10,000,000 after curing.The weight average molecular weight of the cured polymer may not be easily measured, but may be estimated based on a comparison with known polymers of similar molding behavior.

[0014] For some embodiments, the photodefinable polymer formulation can include a poly(amic acid) salt as a polyimide precursor and a tertiary amine salt of a tetracarboxylic acid as a latent chain extender.

[0015] For some embodiments, the poly(amic acid) salt comprises (i) a base polymer of a dianhydride and a diamine, and (ii) a crosslinker.

[0016] For some embodiments, the poly(amic acid) salt is a poly(amic acid) tertiary amine salt.

[0017] In some embodiments, the dianhydride is BPDA.

[0018] In some embodiments, the diamine is TFMB.

[0019] In some embodiments, the cross-linking agent is DEEM.

[0020] For some embodiments, the weight average molecular weight of the base polymer is about 40,000 or less.

[0021] In some embodiments, the weight average molecular weight of the base polymer is about 25,000-35,000.

[0022] For some embodiments, the tertiary amine salt of a tetracarboxylic acid as the latent chain extender is prepared by reacting the dianhydride with water and a tertiary amine at room temperature. For some embodiments, the tertiary amine salt of a tetracarboxylic acid as the latent chain extender is prepared by reacting a tetracarboxylic acid with a tertiary amine.

[0023] For some embodiments, the latent chain extender is prepared by reacting BPDA with water and DEEM at room temperature to form a tertiary amine salt of a tetracarboxylic acid.

[0024] For some embodiments, the mol % of the diamine is higher than the mol % of the dianhydride.

[0025] For some embodiments, the mol % of the dianhydride to the mol % of the diamine is in the range of 0.900-0.999:1.000.

[0026] For some embodiments, the ratio of the mol % of the dianhydride and the latent chain extender to the mol % of the diamine is about 1.000:1.000.

[0027] For some embodiments, the photodefinable polymer formulation can further include a photoinitiator.

[0028] For some embodiments, the photodefinable polymer formulation can further include a sensitizer.

[0029] For some embodiments, the photodefinable polymer formulation can further include a solubility enhancer.

[0030] For some embodiments, the photodefinable polymer formulation can further include an adhesion promoter.

[0031] For some embodiments, a method of forming a polyimide polymer is provided that can include providing a photodefinable polymer formulation according to some embodiments of the present disclosure and curing the photodefinable polymer formulation to activate the latent chain extender and reform a dianhydride that reacts with the terminal amine groups to form new imide linkages to form a polyimide polymer.

[0032] For some embodiments, the poly(amic acid) salt comprises (i) a base polymer of a dianhydride and a diamine, and (ii) a crosslinker.

[0033] For some embodiments, the method can further include controlling the mol % of the diamine to be higher than the mol % of the dianhydride to control the weight average molecular weight of the base polymer of the poly(amic acid) salt in the photodefinable polymer formulation.

[0034] For some embodiments, the method can further include controlling the ratio of the mol % of the dianhydride and the latent chain extender to the mol % of the diamine to about 1.000:1.000. [Brief description of the drawings]

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the present invention and, together with the description, serve to explain and illustrate the principles of the invention. The drawings are intended to illustrate major features of representative embodiments in diagrammatic form. The drawings are not intended to illustrate every feature of an actual embodiment or the relative dimensions of the depicted components, and are not drawn to scale.

[0036] [Figure 1] FIG. 1 shows an exemplary reaction for forming a latent chain extender according to some embodiments of the present disclosure. [Diagram 2] FIG. 2 illustrates an exemplary reaction of a polyimide precursor and a latent chain extender to form a polymer having a higher weight average molecular weight, according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] In order to solve the problems described in the Summary of the Invention, the inventors have expended considerable effort in investigating the parameters, characteristics and variables that affect various properties of polymeric materials during different manufacturing process steps. For the purposes of this description, the manufacturing process steps are broadly defined as follows: (1) Initial device fabrication steps, including but not limited to coating an initial polymer formulation onto a metal layer, and various photolithography steps, such as patterned UV exposure and development. (2) Hardening of the polymer formulation on the metal layer (3) Subsequent molding process It will be appreciated by those skilled in the art that other steps may be employed and sequences may be altered, and that the invention disclosed herein is not limited in this respect, and the above definitions are provided for convenience and ease of exposition.

[0038] A polymer formulation is provided that includes a polyimide precursor and a latent chain extender. For some embodiments, the polyimide precursor is a poly(amic acid) salt. Preferably, the polyimide precursor is a poly(amic acid) salt that includes (i) a polymer of a dianhydride and a diamine and (ii) a crosslinker. For some embodiments, the polyimide precursor is a poly(amic acid) tertiary amine salt. The polyimide precursor can be prepared by a synthetic method known in the art. For example, the polyimide precursor can be prepared by the following synthetic method: a dianhydride and a diamine are polymerized in an organic solvent to prepare a poly(amic acid) solution; and a crosslinker, such as a tertiary amine, is added as well as any other additives that are part of the photopackage to prepare a poly(amic acid) tertiary amine salt solution.

[0039] Poly(amic acid), i.e., polymers of dianhydrides and diamines, have relatively low weight average molecular weights. By way of example and not limitation, low weight average molecular weight polymers according to the present disclosure are generally believed to have a weight average molecular weight in the range of about 40,000 or less, typically about 25,000 to 35,000. It should be noted that the weight average molecular weight values ​​in the present disclosure were determined by gel permeation chromatography (GPC) using LiBr and phosphoric acid as the mobile phase and DMF, based on PEO standards. It should also be understood within the scope of the disclosed invention that for high weight average molecular weight polymers, the molecular weight required for elongation performance will vary with the polymer backbone.

[0040] The dianhydride of the polyimide precursor may include, but is not limited to, a monomer having an anhydride structure. Preferably, the dianhydride includes a tetracarboxylic dianhydride structure. The dianhydride component used may be any dianhydride suitable for forming a crosslinkable or crosslinked polyimide prepolymer, polymer, or copolymer. For example, tetracarboxylic dianhydrides may be utilized alone or in combination as desired.

[0041] For some embodiments, the dianhydride is an aromatic dianhydride. Representative examples of aromatic dianhydrides suitable for use in the polyimide precursor include: 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)propane dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 2,2-bis(4-(2,3-dicarboxyphenoxy)phenyl)propane dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylsulfone dianhydride, 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl-2,2-propane dianhydride, 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride, 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)benzophenone dianhydride, and 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, and A mixture of one of the above dianhydrides Includes:

[0042] Preferred dianhydrides include the following dianhydride compounds: [ka] 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA), represented by the following formula: [ka] 3,4,3',4'-benzophenonetetracarboxylic dianhydride (BTDA), represented by the following formula: [ka] 2,2-bis(3',4'-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), represented by the following formula: [ka] and mixtures thereof.

[0043] The diamine is a diamine compound having two amino groups in the molecular structure. Examples of the diamine compound include aromatic diamine compounds and aliphatic diamine compounds, but aromatic diamine compounds are preferred.

[0044] Examples of diamine compounds include: 2,2'-bis(trifluoromethyl)benzidine (TFMB), p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide, 3,5-diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-methylene-bis(2-chloroaniline), 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 1,3'-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4'-(m-phenyleneisopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, and Aromatic diamines such as 4,4'-bis[4-(4-amino-2-trifluoromethyl)phenoxy]octafluorobiphenyl; Aromatic diamines having two amino groups bonded to an aromatic ring and to a heteroatom other than the nitrogen atom of the amino group, such as diaminotetraphenylthiophene; 1,1-meta-xylylenediamine, 1,3-propanediamine, Tetramethylenediamine, Pentamethylenediamine, Octamethylenediamine, Nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophorone diamine, tetrahydrodicyclopentadienylenediamine, Hexahydro-4,7-methanoindanylenediamine, Tricyclo[6,2,1,0 2,7 ]undecylenedimethyldiamine, and Aliphatic and alicyclic diamines such as 4,4'-methylenebis(cyclohexylamine) Includes:

[0045] Among these, aromatic diamine compounds are preferred as diamine compounds.For example, 2'-bis(trifluoromethyl)benzidine (TFMB), p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, 3,4'-diaminodiphenylether, 4,4'-diaminodiphenylsulfide, and 4,4'-diaminodiphenylsulfone are more preferred, and 4,4'-diaminodiphenylether and p-phenylenediamine are particularly preferred.The most preferred diamine compound is TFMB.The diamine compounds can be used alone or in combination of two or more.

[0046] The crosslinking agent forming the poly(amic acid) salt can be any suitable crosslinking agent known in the art. For some embodiments, the crosslinking agent forming the poly(amic acid) salt is a tertiary amine, forming a poly(amic acid) tertiary amine salt as a polyimide precursor. Suitable crosslinking agents for the polymer formulation include: 2-(diethylamino)ethyl methacrylate (DEEM), 2-(Dimethylamino)ethyl methacrylate (DMAEMA), 2-(Dimethylamino)ethyl methacrylate (DMEM), 3-(Dimethylamino)propyl methacrylate (DMPM), 2-(Dimethylamino)ethyl acrylate (DMEA), 2-(Diethylamino)ethyl acrylate (DEEA), and 3-(Dimethylamino)propyl acrylate (DMPA) Preferably, the crosslinking agent is 2-(diethylamino)ethyl methacrylate (DEEM).

[0047] These representative tertiary amines contain double bonds and can act as crosslinkers. Other tertiary amines that contain double bonds can also be used and can act as crosslinkers. The tertiary amines can also be additives or part of additives that affect other properties of the final polyimide.

[0048] The polyimide precursor may be provided in a solvent as described above. Any suitable solvent known in the art may be used. For some embodiments, the solvent may be an organic solvent, including, but not limited to, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), hexanemethylene phosphoramide (HMPA), N-methylcaprolactam, and N-acetyl-2-pyrrolidone.

[0049] The polymer formulation further comprises a latent chain extender along with the polyimide precursor. For some embodiments, the latent chain extender is a tertiary amine salt of a tetracarboxylic acid. For some embodiments, the latent chain extender may be prepared by reacting a generally suitable dianhydride with water and a tertiary amine crosslinker at room temperature. The dianhydride used to prepare the latent chain extender may be a dianhydride as described above. In the present disclosure, room temperature is about 20-24°C.

[0050] As an exemplary embodiment of a latent chain extender, a commonly suitable dianhydride such as BPDA is reacted with water and a tertiary amine crosslinker at room temperature to produce a tertiary amine salt of a tetracarboxylic acid, as shown in the reaction of Figure 1. More specifically, in the representative reaction of Figure 1, a tertiary amine salt of a tetracarboxylic acid (chain extender) is prepared by reacting BPDA with water and 2-(diethylamino)ethyl methacrylate (DEEM) in a solvent such as NMP.

[0051] Tertiary amines such as 2-(diethylamino)ethyl methacrylate (DEEM) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) can be crosslinkers. These representative tertiary amines contain double bonds and can act as crosslinkers. Other tertiary amines containing double bonds can also be used and can act as crosslinkers. The tertiary amine can also be an additive or part of an additive that affects other properties of the final polyimide.

[0052] Any suitable solvent known in the art can be used. For some embodiments, the solvent can be an organic solvent, including, but not limited to, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), hexanemethylene phosphoramide (HMPA), N-methylcaprolactam, and N-acetyl-2-pyrrolidone.

[0053] The chain extender is selected such that it is latent at room temperature, meaning that no reaction occurs between the polyimide precursor and the chain extender unless heated to a curing temperature (e.g., 250-450°C). This polymer formulation with the latent chain extender is then used during the initial device fabrication (photolithography) step where a low weight molecular weight polymer is desired. Once the photolithography step is complete, the polymer formulation is cured. Once the polymer formulation is cured, the chain extender is activated, meaning that the dianhydride is reformed, as shown in the representative reaction in Figure 1. The reformed dianhydride reacts with the terminal amine groups to form new imide bonds. This results in the formation of a higher weight average molecular weight polymer. For illustrative purposes, a representative reaction to form a higher weight average molecular weight polymer from a polyimide precursor and a latent chain extender is shown in Figure 2. A representative polyimide precursor is comprised of BPDA-TFMB (amic acid) salt and 2-(diethylamino)ethyl methacrylate (DEEM).

[0054] In the polyimide precursor, the mol% of the diamine compound is preferably higher than the mol% of the dianhydride. The mol% ratio of the dianhydride to the diamine compound is preferably in the range of 0.900-0.999:1.000, more preferably 0.950-0.990:1.000.

[0055] In the polyimide precursor, the molar equivalent of the diamine compound and the molar equivalent of the dianhydride are measured by a method known in the art. For example, the polyimide precursor resin can be subjected to hydrolysis treatment in a basic aqueous solution of sodium hydroxide and potassium hydroxide so as to be decomposed into the diamine compound and the dianhydride. The obtained sample is analyzed by gas chromatography, liquid chromatography, etc., to determine the ratio of the dianhydride and the diamine compound constituting the polyimide precursor.

[0056] For some embodiments, the polymer formulation includes a latent chain extender (which forms a dianhydride at the cure temperature) in a mol % such that the ratio of mol % of dianhydride and latent chain extender to mol % of diamine is about 1.000:1.000.

[0057] Determination of the mol% of latent chain extenders (which form dianhydrides at cure temperatures) can be predicted by the Carothers equation: diamine and dianhydride monomers are generally added in approximately a 1:1 molar stoichiometric ratio to maximize the average polymer chain length. Addition of diamine and dianhydride monomers in other ratios can alter the average chain length of the resulting polymer. As predicted by the Carothers equation and widely demonstrated in practice, polymerization reactions conducted with stoichiometric ratios of monomers that deviate from essentially 1:1 generally result in reduced average polymer chain length. The Carothers equation is:

number

[0058] According to some embodiments of the present disclosure, in the polyimide precursor, as described above, the mol% of the diamine compound is preferably higher than the mol% of the dianhydride. As the diamine and dianhydride monomers are generally added in a molar stoichiometric ratio of approximately 1:1, the mol% of the latent chain extender (which forms a dianhydride at the curing temperature) can be predicted through the Carothers equation. In other words, the ratio of the mol% of the dianhydride and latent chain extender to the mol% of the diamine compound is about 1.000:1.000.

[0059] For some embodiments, the polymer formulation includes the latent chain extender in an amount of 0.1 mol % to 10.0 mol %, such that the ratio of the mol % of the dianhydride and latent chain extender to the mol % of the diamine compound is about 1.000:1.000. For some embodiments, the polymer formulation includes the latent chain extender in an amount of 0.5 mol % to 5.0 mol %, or in an amount of 1.0 mol % to 3.0 mol %, such that the ratio of the mol % of the dianhydride and latent chain extender to the mol % of the diamine compound is about 1.000:1.000.

[0060] For some embodiments, the crosslinker for forming the poly(amic acid) salt, i.e., polyimide precursor, may be included in the polymer formulation in an amount of about 0.1 to 10.0 moles per mole of dianhydride. For some embodiments, the crosslinker is in an amount of about 0.5 to 7.5 moles, 1.0 to 5.0 moles, or 1.0 to 3.0 moles per mole of dianhydride.

[0061] For some embodiments, the polymer formulation optionally includes other additives, such as, for example, photoinitiators, sensitizers, solubility promoters, adhesion promoters, etc. The photoinitiator can be any suitable photoinitiator known in the art. For some embodiments, the photoinitiator generates radicals upon UV exposure. Preferably, the photoinitiator absorbance peak is located where the PI precursor absorbance is minimal. For example, suitable photoinitiators for the polymer formulation include: 1-[9-ethyl-6-(2-methylbenzyl)-9H-carbazol-3-yl]ethanone-1-(O-acetyloxime) (OXE-02) and 1,2-octanedione 1-[4-(phenylthio)phenyl]2-(O-benzoyloxime) (OXE-01); Various phosphine oxides such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; Various acetophenone-based initiators including 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone, and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone; Various benzoin initiators including benzoin, benzoin methyl ether, benzoin ethyl ether, 4,4'-dimethoxybenzoin, and 4,4'-dimethylbenzyl; Benzophenone-based initiators, including benzophenone, 4,4'-bis(dimethylamino)benzophenone (Michler's ketone), 4,4'-bis(diethylamino)benzophenone (Michler's ethyl ketone), 4-(dimethylamino)benzophenone, 4-(diethylamino)benzophenone, 4,4'-dihydroxybenzophenone, and various hydroxybenzophenones and alkylbenzophenones; Thioxanthones, including thioxanthen-9-one, isopropylthioxanthen-9-one, diethylthioxanthen-9-one, and chlorothioxanthen-9-one The photoinitiator includes, but is not limited to, OXE-01, OXE-02, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 4,4'-bis(dimethylamino)benzophenone, and 4,4'-bis(diethylamino)benzophenone. The photoinitiator is most preferably OXE-02.

[0062] For some embodiments, the photoinitiator may be included in the polymer formulation in an amount of about 0.1 to 10.0 parts by weight per 100 parts by weight of poly(amic acid). For some embodiments, the photoinitiator may be included in the polymer formulation in an amount of about 0.5 to 7.5 parts by weight, or 1.0 to 5.0 parts by weight per 100 parts by weight of poly(amic acid).

[0063] The sensitizer can be any suitable sensitizer known in the art. For some embodiments, the sensitizer is a tertiary amine containing an aromatic or (meth)acrylate group, which stabilizes the radical ion formed in the photoreaction. When the formulation is already rich in tertiary amine (meth)acrylates, the addition of a sensitizer to the formulation is not necessary and is optional. Suitable sensitizers for polymer formulations include, but are not limited to, N-phenyldiethanolamine (NPDEA), N-phenylglycine, Michler's ketone, Michler's ethyl ketone, and various alkyl 4-(dimethylamino)benzoates. For some embodiments, the crosslinker can also be considered a sensitizer for the polymer formulation.

[0064] For some embodiments, the sensitizer may be included in the polymer formulation in an amount of about 0.1 to 10.0 parts by weight per 100 parts by weight of poly(amic acid). For some embodiments, the sensitizer may be included in the polymer formulation in an amount of about 0.5 to 7.5 parts by weight, or 1.0 to 5.0 parts by weight per 100 parts by weight of poly(amic acid).

[0065] The dissolution promoter can be any suitable dissolution promoter known in the art. For some embodiments, the dissolution promoter is a small molecule with low enough volatility to remain in the cast film during the subsequent apply bake. For example, suitable dissolution promoters for polymer formulations include, but are not limited to, triethylene glycol dimethacrylate (TEGMA), benzotriazole (BTA), and trimethylolpropane trimethacrylate (PTMA). Other examples include, but are not limited to, tetraethylene glycol dimethacrylate, triethylene glycol triacrylate, tetraethylene glycol dimethacrylate, various tri- and tetra(meth)acrylate esters of pentaeryritol, 2-nitrobenzaldehyde and 3-nitrobenzaldehyde, dihydropyridine derivatives, and aromatic sulfonamides.

[0066] For some embodiments, the solubility enhancer may be included in the polymer formulation in an amount of about 0.1 to 20.0 parts by weight per 100 parts by weight of poly(amic acid). For some embodiments, the solubility enhancer may be included in the polymer formulation in an amount of about 0.5 to 15.0 parts by weight, or 1.0 to 10.0 parts by weight per 100 parts by weight of poly(amic acid).

[0067] The adhesion promoter can be any suitable adhesion promoter known in the art. For some embodiments, the adhesion promoter is an alkoxysilane based on a functional primary amine. For some embodiments, the adhesion promoter is a silicon-containing diamine that will bond through the PI backbone and will not interfere with the chain extension mechanism. Examples of monofunctional amine adhesion promoters include 4-aminobutyltriethoxysilane, 4-amino-3,3'-dimethylbutyltriethoxysilane, 3-(m-aminophenoxy)propyltrimethoxysilane, m-aminophenyltrimethoxysilane, p-aminophenyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 11-aminoundecyltriethoxysilane, 3-aminopropylmethyldiethoxysilane. Examples of representative silicon-containing diamines include 1,3-bis(3-aminopropyl)tetramethyldisiloxane and its isomers (the 2-aminopropyl group is a common impurity), as well as aminopropyl-terminated oligomers of polydimethylsiloxane. Most preferably, the adhesion promoter is isomerically pure 1,3-bis(3-aminopropyl)tetramethyldisiloxane due to its thermal stability.

[0068] For some embodiments, the adhesion promoter may be included in the polymer formulation in an amount of about 0.1 to 5.0 parts by weight per 100 parts by weight of poly(amic acid). For some embodiments, the adhesion promoter may be included in the polymer formulation in an amount of about 0.1 to 3.0 parts by weight, or 0.1 to 1.0 parts by weight per 100 parts by weight of poly(amic acid).

[0069] A method for controlling the molecular weight of a photosensitive polyimide formulation before and after curing is also provided. The method includes providing an initial polymer formulation as described above. As described above, the polymer formulation includes a polyimide precursor and a latent chain extender, and a low molecular weight polymer is required during the initial device fabrication (photolithography) step. Poly(amic acid), i.e., a polymer of a dianhydride and a diamine, is part of the polyimide precursor and has a relatively low weight average molecular weight. By way of example and not limitation, the low weight average molecular weight polymer according to the present disclosure is generally considered to have a weight average molecular weight in the range of about 40,000 or less, typically in the range of about 25,000 to 35,000.

[0070] In order to control the weight average molecular weight of the poly(amic acid) of the polyimide precursor, the mol% of the diamine compound is controlled to be higher than the mol% of the dianhydride in the initial polymer formulation. The mol% of the latent chain extender (which forms a dianhydride at the curing temperature) is controlled through the Carothers equation so that the diamine and dianhydride monomers are generally added in a molar stoichiometric ratio of approximately 1:1. In other words, the ratio of the mol% of the dianhydride and latent chain extender to the mol% of the diamine compound is about 1.000:1.000.

[0071] Once the photolithography process is complete, the polymer formulation is cured. Once the polymer formulation is cured, the chain extender is activated. The chain extender reacts with the terminal amine groups to reform the dianhydride that forms an imide bond, resulting in a polymer with a higher molecular weight than the poly(amic acid) of the polyimide precursor.

[0072] Further provided is a method of making a device using the polymer formulation. The method of making the device includes coating, exposing, developing, curing, etching, and mechanical molding. For some embodiments, coating includes applying a polyimide coating onto a substrate. For some embodiments, the polyimide coating is a polymer formulation as detailed above. Preferably, the substrate is a stainless steel substrate, but any suitable substrate known in the art is also suitable. The polyimide coating can be applied using techniques including, but not limited to, liquid slot die, roller coat, spray, curtain coat, dry film lamination, and screen printing techniques. For some embodiments, the polyimide coating is applied with a liquid slot die, exposed to UV light, developed with a suitable solvent known in the art, and cured.

[0073] Curing of the polyimide coating (e.g., the polymer formulation) to form a polyimide insulating layer on a substrate can be carried out by any suitable technique known in the art, such as infrared curing. During the curing process, DEEM and water are released and the chain extender reverts to a dianhydride, as shown in the representative reaction in Figure 2. The reformed dianhydride reacts with the terminal amine groups of the poly(amic acid) to form imide bonds, thereby increasing the molecular weight of the polyimide polymer. Thus, the resulting polyimide exhibits relatively high molecular weight and properties such as improved elongation and moldability required for the subsequent molding process.

[0074] For some embodiments, the method of making the device further includes applying a resist coating onto the substrate. The resist coating can be applied onto the substrate using techniques including, but not limited to, liquid slot die, roller coat, spray, curtain coat, dry film lamination, and screen printing techniques. The resist coating is then exposed to UV light, developed, etched (i.e., the substrate is etched where not protected by the resist pattern) and removed using photolithography and etching techniques known in the art. For some embodiments, the method includes mechanical molding of the device. According to some embodiments, parts are molded with a diameter of 100 μm to test their moldability. EXAMPLES

[0075] The following is a representative procedure for preparing a polymer formulation of the present disclosure: NMP (100 mL) was added to a nitrogen-purged 300 mL reactor. TFMB (28.80 g) was weighed into a beaker and added to the reactor with vigorous stirring. Additional NMP (40 mL) was added to the beaker to dissolve the TFMB adhering to the beaker, which was then added to the reactor. After the TFMB was completely dissolved, BPDA (25.20 g) was slowly added to the reactor along with additional NMP (40 mL) to ensure quantitative transfer of BPDA. The reactor temperature was set to 70° C. and the solution was stirred for 4 hours.

[0076] In a separate flask under nitrogen, BPDA (1.27 g) was suspended in NMP (30 mL). DEEM (3.22 g) and water (0.156 g) were added and the contents were stirred at room temperature for 4 hours until everything was dissolved. OXE-02 (1.62 g) was then added and stirred until dissolved to form the photopackage solution.

[0077] After the 300 mL reactor was cooled to room temperature, DEEM (31.90 g) was added dropwise to the reactor over 30 min. Finally, the photopackaging solution was added to the reactor and the solution was stirred at room temperature for 1 h before being degassed under vacuum, bottled, and frozen.

[0078] The polymer formulations of Examples 1-3 having the compositions shown in Tables 1-2 are prepared according to the representative procedures described above. Comparative Examples 1-13 are prepared in a similar manner, but without the latent chain extender. The compositions of Comparative Examples 1-13 are also shown in Tables 1-2. In both the Examples and Comparative Examples, the poly(amic acid) solution in NMP solvent is about 18% by weight, and the poly(amic acid) DEEM salt solution after addition of the DEEM crosslinker is about 28-29% by weight.

[0079] [Table 1]

[0080] [Table 2]

[0081] The compositions of Examples 1-3 and Comparative Examples 1-13 are used to fabricate devices. Devices were molded at 100 μm diameter to test the moldability of the parts. The polyimide solution was roller coated onto a stainless steel panel and placed in a conveyor oven to dry. The resulting film was no longer tacky and was typically 20-24 μm thick. The film was exposed to UV light through a photomask, baked after exposure, and developed in an NMP-based organic developer solution to form a patterned structure. The panel was then cured at 350° C. for 1 hour under nitrogen atmosphere. The cured film had a thickness of 10-12 μm. The panel was then selectively etched by coating both sides with photoresist, patterning with UV, developing with an aqueous base, etching with ferric chloride, and stripping the photoresist. The flat etched parts were then mechanically molded with excess clearance using a fixed core and a sliding wipe punch. A second cam punch followed to complete the molding. The inner diameter of the molded product is approximately 100 μm.

[0082] The molded parts were then observed under an optical microscope at 20x zoom in the mold area. Between 40 and 100 parts were observed for each example and comparative example. Parts with polyimide edges having several tears at the form line or parts with complete tears in the polyimide layer were considered to have cracks. Parts with defects outside the mold area but no cracks within the mold area were excluded from testing.

[0083] As shown in Table 2, the devices of Examples 1-3, which contained a latent chain extender in their polymer formulation, had excellent moldability. That is, the devices of Examples 1-2 did not have any cracks in their polyimide insulating layer. Example 3 showed that the polyimide insulating layer formed from the polymer formulation of the present disclosure had only 10% cracks.

[0084] On the other hand, the devices of Comparative Examples 2-13 had poor moldability, with polyimide insulating layers formed from polymer formulations without latent chain extenders having at least 58% cracking. Comparative Example 1 showed excellent moldability with only 3% cracking. However, Comparative Example 1 has a very high weight average molecular weight of 59.8K. As mentioned above, high weight average molecular weight polymers exhibit properties that negatively impact initial manufacturing steps, especially photolithography process steps. Thus, Comparative Example 1 is not suitable for the initial process steps prior to the curing step to mold the device.

[0085] Various modifications and additions may be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the above embodiments refer to particular features, the scope of the present invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to include all such alternatives, modifications, and alterations that fall within the scope of the claims, together with all equivalents.

Claims

1. a poly(amic acid) salt as a polyimide precursor; Tertiary amine salts of tetracarboxylic acids as latent chain extenders A photosensitive polymer formulation comprising: The poly(amic acid) salt is (i) a base polymer of a dianhydride and a diamine; (ii) a tertiary amine containing a double bond as a crosslinker; Including, the mol % of the dianhydride to the mol % of the diamine in the photopolymer formulation is in the range of 0.900-0.999:1.000; in said photopolymer formulation, the ratio of the mol % of said dianhydride and said latent chain extender to the mol % of said diamine is 1.000:1.000; The tertiary amine constituting the tertiary amine salt of tetracarboxylic acid as the latent chain extender contains a double bond, The latent chain extender is a tertiary amine salt of 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA), and the tertiary amine constituting the tertiary amine salt is 2-(diethylamino)ethyl methacrylate (DEEM); A photosensitive polymer formulation before curing, wherein the tertiary amine containing a double bond as the crosslinking agent is one selected from 2-(dimethylamino)ethyl methacrylate (DMAEMA), 3-(dimethylamino)propyl methacrylate (DMPM), 2-(dimethylamino)ethyl acrylate (DMEA), 2-(diethylamino)ethyl acrylate (DEEA), and 3-(dimethylamino)propyl acrylate (DMPA).

2. 2. The photodefinable polymer formulation of claim 1, wherein the poly(amic acid) salt is a poly(amic acid) tertiary amine salt.

3. 2. The photosensitive polymer formulation of claim 1, wherein the dianhydride is 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA).

4. 2. The photopolymer formulation of claim 1, wherein the diamine is 2,2'-bis(trifluoromethyl)benzidine (TFMB).

5. The photosensitive polymer formulation of claim 1 , wherein the weight average molecular weight of the base polymer is 40,000 or less.

6. 2. The photosensitive polymer formulation according to claim 1, wherein the weight average molecular weight of the base polymer is 25,000 to 35,000.

7. The photosensitive polymer formulation of claim 1 further comprising a photoinitiator.

8. The photodefinable polymer formulation of claim 1 further comprising a sensitizer.

9. The photodefinable polymer formulation of claim 1 further comprising a solubility enhancer.

10. The photodefinable polymer formulation of claim 1 further comprising an adhesion promoter.

11. Providing a photosensitive polymer formulation according to claim 1; and curing the photosensitive polymer formulation to activate the latent chain extender and reform the dianhydride which reacts with the terminal amine groups to form new imide linkages to form a polyimide polymer.

1. A method for forming a polyimide polymer comprising:

12. 12. The method of claim 11, further comprising controlling the mol % of the diamine to be higher than the mol % of the dianhydride to control the weight average molecular weight of the base polymer of the poly(amic acid) salt in the photodefinable polymer formulation.

13. A metal layer; a polyimide polymer formed on the metal layer; A device comprising: The polyimide polymer is a cured product of a photosensitive polymer formulation; The photosensitive polymer formulation comprises: a poly(amic acid) salt as a polyimide precursor; Tertiary amine salts of tetracarboxylic acids as latent chain extenders Including, The poly(amic acid) salt is (i) a base polymer of a dianhydride and a diamine; (ii) a tertiary amine containing a double bond as a crosslinker; Including, the mol % of the dianhydride to the mol % of the diamine in the photopolymer formulation is in the range of 0.900-0.999:1.000; in said photopolymer formulation, the ratio of the mol % of said dianhydride and said latent chain extender to the mol % of said diamine is 1.000:1.000; The tertiary amine constituting the tertiary amine salt of tetracarboxylic acid as the latent chain extender contains a double bond, The latent chain extender is a tertiary amine salt of 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA), and the tertiary amine constituting the tertiary amine salt is 2-(diethylamino)ethyl methacrylate (DEEM); The tertiary amine containing a double bond as the crosslinking agent includes one selected from 2-(dimethylamino)ethyl methacrylate (DMAEMA), 3-(dimethylamino)propyl methacrylate (DMPM), 2-(dimethylamino)ethyl acrylate (DMEA), 2-(diethylamino)ethyl acrylate (DEEA), and 3-(dimethylamino)propyl acrylate (DMPA).

14. The device of claim 13 , wherein the poly(amic acid) salt is a poly(amic acid) tertiary amine salt.

15. The device of claim 13, wherein the dianhydride is 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA).

16. The device of claim 13, wherein the diamine is 2,2'-bis(trifluoromethyl)benzidine (TFMB).

17. The device of claim 13, wherein the weight average molecular weight of the base polymer is 25,000 to 35,000.

18. The device of claim 13 , wherein the photopolymer formulation further comprises at least one of a photoinitiator, a sensitizer, a solubility promoter, and an adhesion promoter.

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