CN112142974B

CN112142974B - Chain extender for improving elongation of photosensitive polyimide and formulation thereof

Info

Publication number: CN112142974B
Application number: CN202010596191.8A
Authority: CN
Inventors: A·R·迪克; J·D·韦克沃斯
Original assignee: Hutchinson Technology Inc
Current assignee: Hutchinson Technology Inc
Priority date: 2019-06-28
Filing date: 2020-06-28
Publication date: 2022-08-16
Anticipated expiration: 2040-06-28
Also published as: CN112142974A

Abstract

Photopolymer formulations, materials and uses of such materials are disclosed. Embodiments of the present disclosure provide photosensitive polyimide materials with chain extenders and formulations thereof that improve the elongation and formability of polyimide materials, as well as methods of making such polymeric materials.

Description

Chain extender for improving elongation of photosensitive polyimide and formulation thereof

Cross Reference to Related Applications

This application claims benefit and priority from U.S. provisional patent application serial No. 62/868,761 filed on 28.6.2019 and U.S. patent application serial No. 16/746,695 filed on 17.1.2020, the entire disclosures of which are incorporated herein by reference.

Technical Field

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 formulations thereof that improve the elongation and formability of the polyimide materials, as well as methods of making the same.

Background

Electronic circuits such as printed circuit boards are used in a wide range of components and generally include conductive and insulating layers. For example, in the disk drive industry, flexures (flextures) are structures that: which flexibly supports the read/write transducer near the rotating disk while also supporting a flexible circuit for conducting electrical signals to and from the transducer. In some structures, a stainless steel layer is included, sometimes as a base layer, with various insulating and conductive layers formed over the stainless steel layer.

In the manufacture of electronic circuits, polymeric materials are widely used as insulating layers coated on metal layers. To produce certain electronic components, conductive and insulating layers are patterned using photolithography and etching techniques, and therefore require a photopolymer material. Polyimide materials have found use as photopolymer materials in the manufacture of electronic components. Suitable polyimide materials must meet a number of parameters and properties both during the initial fabrication process and during subsequent processing and use.

In some cases, the manufacture of electronic components requires mechanical forming after the device is initially machined, and in such cases, the forming of a cured polymer layer coated on the metal part. Forming may include bending the polymer coated metal part up to an angle of about 90 degrees. As the footprint of the device decreases, a small forming radius is particularly desirable.

When the device is subjected to forming (e.g., bending of the device), the polymer coating is elongated in the forming region. The formation of polymeric coatings presents a number of challenges. The component or device typically includes a polymer layer coated on a metal layer, such as stainless steel. At initial fabrication, the metal layer in the device is in a neutral axis state, where the metal layer is neither in tension nor in compression. At this stage, the polymer layer will have cured. Next, the device is shaped or bent, which causes the polymer layer to elongate in the shaped area. As the radius of the shaped region continues to decrease, the polymer elongation in the shaped region continues to increase.

If the polymer limit strain is exceeded during the forming process, cracks in the polymer layer can occur and the polymer material will fail. This is a serious problem and severely limits the use of photopolymer materials in such molding apparatus applications. Common failure modes of the polymer layer after molding include complete fractures in the polymer layer and partial fractures in the polymer layer, both in the polymer layer formed over the metal layer and in the free-standing polymer layer, respectively. Such complete and partial fractures in the formed polymer layer are catastrophic and may render the device unusable.

This problem is prevalent in conventional polymeric materials. Very low molecular weight polymer formulations tend to crack severely during the solvent development step. On the other hand, higher molecular weight polymers are known to exhibit better elongation and formability after forming. However, when photosensitive materials are required, high molecular weight photopolymers are difficult or impractical to process. By way of example, but not limitation, high molecular weight polymers are generally considered to have an average molecular weight of about 40,000 and above. High molecular weight polymers exhibit properties that negatively impact initial manufacturing steps, particularly photolithographic processing steps. For example, high molecular weight photopolymers generally exhibit very high viscosity and/or low solids content. Filtration is very time consuming and expensive. The lithographic contrast and development speed are poor. Therefore, high molecular weight photopolymers are not suitable for use in the initial processing steps prior to the curing step.

Thus, the problem is highly complex and the currently available polymeric materials are essentially unsuitable. Therefore, new developments are urgently required.

Disclosure of Invention

Broadly, embodiments of the present disclosure provide photopolymer formulations, materials and uses of the materials. More specifically, embodiments of the present disclosure provide photosensitive polyimide materials with latent chain extenders and formulations thereof that improve the elongation and formability of polyimide materials, as well as methods of making the polymeric materials.

The inventors have found that throughout the process, including the initial device manufacturing step, the means in which the polymer formulation undergoes the curing step and the subsequent shaping step, many complex factors must be understood and balanced against the chemistry and properties of the photopolymer formulation to address the above-mentioned problems.

As described in more detail below, polymers having lower molecular weights exhibit more desirable characteristics during initial manufacturing steps, particularly photolithographic processing steps. Whereas polymers with higher molecular weights exhibit better elongation or formability during subsequent forming steps. After extensive research and effort, the inventors have developed innovative polymer formulations and methods of preparation in which polymer formulations and chemistry are selectively manipulated to control the molecular weight of the polymer in order to achieve desired properties throughout the manufacturing, curing, and shaping steps. For example, in some embodiments, a method is provided that selectively controls the molecular weight of a poly (amic acid) in a photopolymer formulation to a relatively low weight average molecular weight range during an initial processing step and then increases the weight average molecular weight of a polyimide polymer during curing to form a polyimide insulation layer comprising a polyimide polymer having a high weight average molecular weight that exhibits improved elongation and formability during subsequent forming steps. Thus, in a broad sense, the molecular weight of the polyimide polymer is larger (increased) after curing.

In some embodiments, the weight average molecular weight of the polyimide polymer after curing is increased by at least two-fold compared to the weight average molecular weight of the base polymer in the initial polymer formulation prior to curing. In some embodiments, the weight average molecular weight of the polyimide polymer increases to about 60,000 after curing. In some embodiments, the weight average molecular weight of the polyimide polymer increases after curing to much greater than 60,000, for example 10,000,000. Although the weight average molecular weight of the cured polymer cannot be easily measured, it can be estimated based on comparison with known polymers having similar molding behavior.

For some embodiments, the photopolymer formulation can include a poly (amic acid) salt as a polyimide precursor and a tertiary amine salt of a tetracarboxylic acid as a potential chain extender.

For some embodiments, the poly (amic acid) salt comprises (i) a base polymer of a dianhydride and a diamine, and (ii) a crosslinking agent.

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

For some embodiments, the dianhydride is BPDA.

For some embodiments, the diamine is TFMB.

For some embodiments, the crosslinking agent is DEEM.

For some embodiments, the base polymer has a weight average molecular weight of about 40,000 and less.

For some embodiments, the base polymer has a weight average molecular weight of about 25,000-35,000.

For some embodiments, tertiary amine salts of tetracarboxylic acids are prepared as potential chain extenders by reacting a dianhydride with water and a tertiary amine at room temperature. For some embodiments, tertiary amine salts of tetracarboxylic acids are prepared as potential chain extenders by reacting the tetracarboxylic acids with tertiary amines.

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.

For some embodiments, the mole% of diamine is higher than the mole% of dianhydride.

For some embodiments, the mole% of dianhydride relative to the mole% of diamine is in the range of 0.900-0.999: 1.000.

For some embodiments, the ratio of mole% of dianhydride and potential chain extender to mole% of diamine is about 1.000: 1.000.

For some embodiments, the photopolymer formulation may further comprise a photoinitiator.

For some embodiments, the photopolymer formulation may further comprise a sensitizer.

For some embodiments, the photopolymer formulation may further comprise a dissolution accelerator.

For some embodiments, the photopolymer formulation may further comprise an adhesion promoter.

For some embodiments, a method of forming a polyimide polymer is provided, which may include: providing a photopolymer formulation according to some embodiments of the present disclosure; and curing the photopolymer formulation followed by activation of the latent chain extender and reformation of the dianhydride which reacts with the terminal amine groups to form new imide linkages to form the polyimide polymer.

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

For some embodiments, the method can further include controlling the ratio of mole% of dianhydride and potential chain extender to mole% of diamine to be about 1.000: 1.000.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain and illustrate the principles of the invention. The drawings are intended to show the major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are generally not drawn to scale.

Fig. 1 illustrates an exemplary reaction to form a latent chain extender according to some embodiments of the present disclosure;

fig. 2 illustrates an exemplary reaction of forming a polymer having a higher weight average molecular weight from a polyimide precursor and a latent chain extender according to some embodiments of the present disclosure.

Detailed Description

To address the problems described in this summary, the inventors have expended considerable effort in studying parameters, characteristics, and variables that affect various properties of polymeric materials during different manufacturing process steps. For purposes of description, a manufacturing process step is broadly defined as: (1) including, but not limited to, initial device fabrication steps to coat an initial polymer formulation on a metal layer, and various photolithography steps such as patterned uv exposure and development; (2) curing the polymer formulation on the metal layer; and (3) a subsequent molding step. Those skilled in the art will recognize that other steps may be taken and in a different order, and that the invention disclosed herein is not so limited, but rather provides the above definitions for convenience and ease of description.

Polymer formulations including a polyimide precursor and a latent chain extender are provided. For certain embodiments, the polyimide precursor is a poly (amic acid) salt. Preferably, the polyimide precursor is a poly (amic acid) salt comprising (i) a polymer of a dianhydride and a diamine and (ii) a crosslinking agent. For some embodiments, the polyimide precursor is a tertiary amine salt of poly (amic acid). Polyimide precursors can be prepared by synthetic methods known in the art. For example, polyimide precursors can be prepared by a synthetic method in which a dianhydride and a diamine are polymerized in an organic solvent to produce a poly (amic acid) solution. Then, a crosslinking agent (e.g., a tertiary amine) is added to form a solution of a poly (amic acid) tertiary amine salt, as well as any other additives that are part of the light package.

Poly (amic acids), 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 invention are generally considered to have weight average molecular weights of about 40,000 and less, typically about 25,000 and 35,000. It should be noted that for the weight average molecular weight values disclosed in this disclosure, DMF with LiBr and phosphoric acid was used as the mobile phase and the values were determined using Gel Permeation Chromatography (GPC) based on PEO standards. It is also understood within the scope of the invention disclosed that for high weight average molecular weight polymers, the molecular weight required for elongation properties will vary with the polymer backbone.

The dianhydride of the polyimide precursor may include, but is not limited to, a monomer having an acid anhydride structure. Preferably, the dianhydride comprises a tetracarboxylic dianhydride structure. The dianhydride component used may be any suitable dianhydride used to form crosslinkable or crosslinked polyimide prepolymers, polymers or copolymers. For example, tetracarboxylic dianhydrides can be used singly or in combination as necessary.

For some embodiments, the dianhydride is an aromatic dianhydride. Illustrative examples of aromatic dianhydrides suitable for use in polyimide precursors 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) diphenyl sulfone 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) diphenyl sulfone 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 mixtures comprising one of the foregoing dianhydrides.

Preferred dianhydrides include the following dianhydride compounds and mixtures thereof.

3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) having the following formula:

3,4,3',4' -Benzophenone Tetracarboxylic Dianhydride (BTDA) having the formula:

2, 2-bis (3',4' -dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) having the formula:

pyromellitic dianhydride (PMDA) having the formula:

the diamine is a diamine compound having two amino groups in the molecular structure. Examples of the diamine compound include any aromatic diamine compound or aliphatic diamine compound, preferably aromatic diamine compounds.

Examples of the diamine compound include: aromatic diamines, such as 2,2' -bis (trifluoromethyl) benzidine (TFMB), p-phenylenediamine, m-phenylenediamine, 4' -diaminodiphenylmethane, 4' -diaminodiphenylethane, 4' -diaminodiphenylether, 4' -diaminodiphenylsulfide, 4' -diaminodiphenylsulfone, 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' -diaminobenzanilide, 3, 5-diamino-3 ' -trifluoromethylbenzanilide, p-phenylenediamine, m-phenylenediamine, 4' -diaminodiphenylethane, 4' -diaminodiphenylethane, 5-1- (4' -aminophenyl) -1,3, 3-trimethylindane, 6-4, 4' -diaminobenzinilide, p-phenylenediamine, p-phenylene, 3, 5-diamino-4 ' -trifluoromethylbenzanilide, 3,4' -diaminodiphenyl ether, 2, 7-diaminofluorene, 2-bis (4-aminophenyl) hexafluoropropane, 4' -methylene-bis (2-chloroaniline), 2',5,5' -tetrachloro-4, 4' -diaminobiphenyl, 2' -dichloro-4, 4' -diamino-5, 5' -dimethoxybiphenyl, 3' -dimethoxy-4, 4' -diaminobiphenyl, 4' -diamino-2, 2' -bis (trifluoromethyl) biphenyl, 2-bis [ (4- (4-aminophenoxy) phenyl) ] propane, 2, 2-bis [ (4- (4-aminophenoxy) phenyl) ] hexafluoropropane, 1, 4-bis (4-aminophenoxy) benzene, 4 '-bis (4-aminophenoxy) -biphenyl, 1,3' -bis (4-aminophenoxy) benzene, 9-bis (4-aminophenyl) fluorene, 4'- (p-phenyleneisopropyl) diphenylamine, 4' - (m-phenyleneisopropyl) diphenylamine, 2 '-bis [ (4- (4-amino-2-trifluoromethylphenoxy) phenyl) ] hexafluoropropane and 4,4' -bis [4- (4-amino-2-trifluoromethyl) phenoxy ] -octafluorobiphenyl; aromatic diamines having two amino groups bound to the aromatic ring and a heteroatom other than the nitrogen atom of the amino group, such as diaminotetraphenylthiophene; and aliphatic diamines and alicyclic diamines such as 1, 1-m-xylylenediamine, 1, 3-propylenediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4-diaminoheptamethylenediamine, 1, 4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4, 7-methyleneindanedimethylenediamine (hexahydro-4,7-methanoindanylene dimethylenediamine), tricyclo [6,2,1,02.7] -undecylenediamine and 4,4' -methylenebis (cyclohexylamine).

Among these, an aromatic diamine compound is preferable as the diamine compound. Specifically, for example, 2' -bis (trifluoromethyl) benzidine (TFMB), p-phenylenediamine, m-phenylenediamine, 4' -diaminodiphenylmethane, 4' -diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 4' -diaminodiphenyl sulfide and 4,4' -diaminodiphenyl sulfone are preferable, and 4,4' -diaminodiphenyl ether and p-phenylenediamine are particularly preferable. Most preferably, the diamine compound is TFMB. The diamine compound may be used alone, or two or more thereof may be used in combination.

The crosslinking agent that forms the poly (amic acid) salt may be any suitable crosslinking agent known in the art. For some embodiments, the cross-linking agent that forms the poly (amic acid) salt is a tertiary amine, thereby forming a poly (amic acid) tertiary amine salt as the polyimide precursor. Suitable crosslinking agents for use in the polymer formulation include, but are not limited to, 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).

These exemplary tertiary amines contain double bonds, which can serve as crosslinking agents. Other tertiary amines containing double bonds may also be used and they may also be used as crosslinking agents. The tertiary amine may also be an additive or part of an additive that affects other properties of the final resulting polyimide.

As described above, the polyimide precursor may be provided in a solvent. 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-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), hexamethylene phosphoramide (HMPA), N-methylcaprolactam, and N-acetyl-2-pyrrolidone.

The polymer formulation further includes a latent chain extender and a 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 the selected dianhydride with water and a tertiary amine crosslinker at room temperature. The dianhydride used to form the potential chain extender may be a dianhydride as described above. For purposes of this disclosure, the room temperature is about 20 to 24 □.

As an illustrative embodiment of a potential chain extender, a selected dianhydride (such as BPDA) is reacted with water and a tertiary amine crosslinking agent at room temperature to produce a tertiary amine salt of a tetracarboxylic acid, as shown by the reaction provided in figure 1. More specifically, in the exemplary reaction provided in fig. 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.

The tertiary amine may be a crosslinking agent, such as 2- (diethylamino) ethyl methacrylate (DEEM) or 2- (dimethylamino) ethyl methacrylate (DMAEMA). These exemplary tertiary amines contain double bonds, which can be used as crosslinkers. Other tertiary amines containing double bonds may also be used and they may also be used as crosslinking agents. The tertiary amine may also be an additive or part of an additive that affects other properties of the final resulting polyimide.

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-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), hexamethylene phosphoramide (HMPA), N-methylcaprolactam, and N-acetyl-2-pyrrolidone.

The chain extender is selected to be latent at room temperature, meaning that no reaction between the polyimide precursor and the chain extender will occur unless heated to a curing temperature (e.g., 250-. The polymer formulation with the latent chain extender is then used during the initial device fabrication (photolithography) step where a low molecular weight polymer is required. Once the photolithography step is complete, the polymer formulation is cured. After the polymer formulation is cured, the chain extender is activated, which means that the dianhydride is reformed, as shown in the exemplary reaction of figure 1. The resulting dianhydride reacts with the terminal amine groups to form new imide linkages, thereby forming a higher weight average molecular weight polymer. For exemplary purposes, fig. 2 provides an exemplary reaction of forming a polymer having a higher weight average molecular weight from a polyimide precursor and a latent chain extender. An exemplary polyimide precursor is BPDA-TFMB (amic acid) salt with 2- (diethylamino) ethyl methacrylate (DEEM).

In the polyimide precursor, the mole% of the diamine compound is preferably higher than that of the dianhydride. Regarding the ratio of mole% of dianhydride to mole% of diamine compound, the mole% of dianhydride relative to the mole% of diamine compound is preferably in the range of 0.900-0.999: 1.000, more preferably in the range of 0.950-0.990: 1.000.

In the polyimide precursor, the molar equivalents of diamine compound and the molar equivalents of dianhydride are measured by techniques known in the art. For example, the polyimide precursor resin may be subjected to hydrolysis treatment in an alkaline aqueous solution of sodium hydroxide and potassium hydroxide to decompose it into a diamine compound and a dianhydride. The obtained sample is analyzed by gas chromatography, liquid chromatography, or the like, and the ratio of dianhydride and diamine compounds constituting the polyimide precursor is determined.

For some embodiments, the polymer formulation includes a latent chain extender (forming a dianhydride at the curing temperature) in mole% such that the ratio of mole% of dianhydride and latent chain extender to mole% of diamine compound is about 1.000: 1.000.

To determine the mole% of potential chain extender (dianhydride formation at curing temperature), this can be predicted by the Carothers equation. That is, the diamine and dianhydride monomers are typically present in a ratio of about 1: 1 is added in a molar stoichiometric amount to maximize the average polymer chain length. The addition of diamine and dianhydride monomers in other ratios can change the average chain length of the resulting polymer. Typically, the method is used in a range of substantially 1: polymerization reactions carried out at a stoichiometry of monomers other than 1 molar ratio reduce the average polymer chain length predicted by the Carothers equation and are widely validated in practice. The Carothers equation is provided below.

M _n Number average molecular weight

M ₀ Molecular weight of repeating unit

X _n Degree of number average polymerization

The stoichiometric ratio of the monomers (r ≦ 1)

According to some embodiments of the present disclosure, the mole% of diamine compound in the polyimide precursor is preferably higher than the mole% of dianhydride as described above. By Carothers' equation, the mole% of potential chain extender (dianhydride formation at cure temperature) can be predicted such that the diamine and dianhydride monomers are typically present in a ratio of about 1: 1 was added in a molar stoichiometric amount. In other words, the ratio of mole% of dianhydride and latent chain extender to mole% of diamine compound is about 1.000: 1.000.

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

For some embodiments, the crosslinking agent used to form the poly (amic acid) salt (i.e., the polyimide precursor) may be included in the polymer formulation at about 0.1 to 10.0 moles per mole of dianhydride. For some embodiments, about 0.5 to 7.5 moles, 1.0 to 5.0 moles, or 1.0 to 3.0 moles of crosslinker per mole of dianhydride.

For some embodiments, the polymer formulation optionally includes other additives, such as photoinitiators, sensitizers, dissolution accelerators, and adhesion promoters. The photoinitiator may be any suitable photoinitiator known in the art. For some embodiments, the photoinitiator generates free radicals upon UV exposure. Preferably, the photoinitiator absorption peak is located where the PI precursor absorption is minimal. For example, suitable photoinitiators for use in polymer formulations include, but are not limited to, 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-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone, and 2-methyl-4' - (methylthio) -2-morpholinopropiophenone; various benzoin-based initiators including benzoin, benzoin methyl ether, benzoin ethyl ether, 4 '-dimethoxybenzoin, 4' -dimethylbenzoyl; benzophenone-based initiators including benzophenone, 4' -bis (dimethylamino) benzophenone (Michler's ketone), 4' -bis (diethylamino) benzophenone (Michler's ethyl ketone), 4- (dimethylamino) benzophenone, 4- (diethylamino) benzophenone, 44 ' -dihydroxybenzophenone; and various hydroxybenzophenones and alkylbenzophenones, thioxanthones, including thioxanthen-9-one, isopropylthioxanthen-9-one, diethylthioxanthen-9-one, and chlorothioxanth-9-one. Preferably, the photoinitiator is OXE-01, OXE-02, diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide, phenyl bis (2,4, 6-trimethylbenzoyl) phosphine oxide, 4,4 '-bis (dimethylamino) benzophenone and 4,4' -bis (diethylamino) benzophenone. Most preferably, the photoinitiator is OXE-02.

For some embodiments, the photoinitiator may be included in the polymer formulation at about 0.1 to 10.0 parts by weight per 100 parts by weight of the 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 or 1.0 to 5.0 parts by weight per 100 parts by weight of poly (amic acid).

The sensitizer may be any suitable sensitizer known in the art. For some embodiments, the sensitizer is a tertiary amine containing an aryl group or a (meth) acrylate group to stabilize the radical ions formed in the photoreaction. Since a large amount of tertiary amine (meth) acrylate is already present in the formulation, a sensitizer may not be needed or optionally added in the formulation. 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 above-described crosslinking agents may also be considered sensitizers for polymer formulations.

For some embodiments, the sensitizer may be included in the polymer formulation at about 0.1 to 10.0 parts by weight per 100 parts by weight of the 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 or 1.0 to 5.0 parts by weight per 100 parts by weight of poly (amic acid).

The dissolution accelerator can be any suitable dissolution accelerator known in the art. For some embodiments, the dissolution accelerator is a small molecule with a sufficiently low volatility to remain in the cast film during the post-application bake. For example, suitable dissolution accelerators 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) acrylates of pentaerythritol, 2-and 3-nitrobenzaldehydes, dihydropyridine derivatives, and aromatic sulfonamides.

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

The adhesion promoter may be any suitable adhesion promoter known in the art. For some embodiments, the adhesion promoter is an alkoxysilane based on primary amine functional groups. For some embodiments, the adhesion promoter is a silicon-containing diamine because it will bind the entire PI backbone and not interfere with the chain extension mechanism. Examples of monofunctional amine adhesion promoters include 4-aminobutyltriethoxysilane, 4-amino-3, 3' -dimethylbutyltrimethoxysilane, 3- (m-aminophenoxy) propyltrimethoxysilane, m-aminophenyltrimethoxysilane, p-aminophenyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 11-aminoundecyltriethoxysilane, 3-aminopropylmethyldiethoxysilane. Exemplary silicon-containing diamines include 1, 3-bis (3-aminopropyl) tetramethyldisiloxane and its isomers (2-aminopropyl 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 thermal stability.

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

A method of 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. The polymer formulation includes a polyimide precursor and a latent chain extender as described above, where a low molecular weight polymer is required during the initial device fabrication (photolithography) step. Poly (amic acid), i.e., a polymer of dianhydride and diamine, is part of the polyimide precursor, having a relatively low weight average molecular weight. By way of example, and not limitation, low weight average molecular weight polymers according to the present invention are generally considered to have weight average molecular weights of about 40,000 and less, typically about 25,000 and 35,000.

To control the weight average molecular weight of the poly (amic acid) of the polyimide precursor, the mole percent of diamine compound is controlled such that it is higher than the mole percent of dianhydride in the initial polymer formulation. The mole% of the potential chain extender (dianhydride formation at curing temperature) is controlled by Carothers' equation so that the ratio is typically in the range of about 1: 1 molar stoichiometric amount of diamine and dianhydride monomers. In other words, the ratio of mole% of dianhydride and latent chain extender to mole% of diamine compound is about 1.000: 1.000.

Once the photolithography step is complete, the polymer formulation is cured. After curing of the polymer formulation, the chain extender is activated. The chain extender in turn forms a dianhydride that reacts with the terminal amine groups to form imide linkages to form a polymer of higher molecular weight than the poly (amic acid) of the polyimide precursor.

Additionally, a method of manufacturing a device using the above-described polymer formulation is provided. The device manufacturing method comprises coating, exposing, developing, curing, etching and mechanical forming. For some embodiments, coating comprises applying a polyimide coating on the substrate (superstrate). For some embodiments, the polyimide coating is a polymer formulation as discussed in detail above. Preferably, the substrate is a stainless steel substrate; however, other suitable substrates known in the art are also suitable. The polyimide coating may be applied using techniques including, but not limited to, liquid slot die coating, roll coating, spray coating, curtain coating, dry film lamination, and screen printing techniques. For some embodiments, the polyimide coating is applied by liquid slot die coating, then exposed to ultraviolet light, developed with a suitable solvent known in the art, and cured.

Curing of the polyimide coating (e.g., the polymer formulation described above) to form the polyimide insulating layer on the substrate can be carried out by any suitable technique known in the art, such as infrared curing. As shown by the exemplary reaction provided in fig. 2, during the curing step, DEEM and water are evolved and the chain extender is converted back to the dianhydride. The reformed dianhydride reacts with the terminal amine groups of the poly (amic acid) to form imide linkages, which increase the molecular weight of the polyimide polymer. Thus, the resulting polyimides exhibit relatively high molecular weights and improved elongation and formability properties that are desirable for subsequent forming steps.

For some embodiments, the method for fabricating a device further comprises applying a resist coating on the substrate. The resist coating is applied to the base material using techniques including, but not limited to, liquid slot die coating, roll coating, spray coating, curtain coating, dry film lamination, and screen printing techniques. The resist coating is then exposed to ultraviolet light, developed, etched (i.e., the substrate is etched in areas not protected by the resist pattern), and stripped using photolithography and etching techniques, including those known in the art. For some embodiments, the method includes mechanical shaping of the device. According to some embodiments, parts are formed at a 100 μm radius to test the formability of the parts.

Examples

The following is an exemplary procedure for preparing the polymer formulations of the present disclosure. In a 300mL reactor purged with nitrogen, NMP (100mL) was added. TFMB (28.80g) was measured in a beaker and then added to the reactor with vigorous stirring. Additional NMP (40mL) was added to the beaker to dissolve any TFMB that adhered to the beaker, which was then added to the reactor. After TFMB was completely dissolved, BPDA (25.20g) was slowly added to the reactor along with additional NMP (40mL) to ensure quantitative transfer of BPDA. The reactor temperature was set to 70 □ and the solution was stirred for 4 hours.

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

After the 300mL reactor was returned to room temperature, DEEM (31.90g) was added dropwise to the reactor over 30 minutes. Finally, the photopacking solution was added to the reactor and the solution was stirred at room temperature for 1 hour before degassing under vacuum, bottling and freezing.

The polymer formulations of examples 1-3 having the compositions shown in tables 1-2 were prepared by the above-described exemplary procedure. Comparative examples 1-13 were prepared in a similar manner, but did not include a latent chain extender in their composition. The compositions of comparative examples 1 to 13 are also shown in tables 1 to 2. All examples and comparative examples had about 18 weight percent poly (amic acid) in NMP solvent and about 28-29 weight percent poly (amic acid) DEEM salt solution after addition of the DEEM crosslinker.

TABLE 1

TABLE 2

The compositions of examples 1-3 and comparative examples 1-13 were used to prepare the devices. The devices were formed at a radius of 100 μm to test the formability of the devices. The polyimide solution was roll coated on a stainless steel plate, and then placed in a conveyor oven and dried. The resulting film is no longer tacky and is typically 20-24 μm thick. The film was then exposed to uv light through a photomask, post-exposure baked, and developed in an NMP based organic developer to form patterned features. The panels were then cured under nitrogen at 350 □ for 1 hour. The thickness of the cured film is 10-12 μm. The panel was then selectively etched by coating both sides of the panel with photoresist, patterning with ultraviolet light, developing in aqueous base, etching in ferric chloride and stripping the photoresist. A flat etched part is then mechanically formed using a fixed mandrel and a sliding impact punch with excess clearance. The auxiliary cam punch then completes the molded body. The internal diameter of the shaped body was about 100. mu.m.

The molded part was then inspected by an optical microscope at 20 x zoom in the molding area. Each of the examples and comparative examples was examined for 40-100 parts. Parts with polyimide edges having cracks at the molding line or parts with complete breaks in the polyimide layer are considered to have cracks. Parts with defects outside the forming area but no cracks in the forming area were excluded from the test.

As shown in table 2, the devices of examples 1-3, which included a latent chain extender in their polymer formulations, had excellent formability. That is, the device of example 1-2 did not have any cracks in its polyimide insulating layer. Example 3 demonstrates only 10% cracking in its polyimide insulation layer formed from the polymer formulation of the present disclosure.

On the other hand, the devices of comparative examples 2-13 showed poor formability and at least 58% cracks in their polyimide insulation layers formed from polymer formulations without latent chain extenders. Comparative example 1 showed excellent formability and had only 3% cracks. However, comparative example 1 has a very high weight average molecular weight of 59.8K. As mentioned above, the weight average molecular weight polymer exhibits properties that negatively impact the initial manufacturing steps, particularly the photolithographic processing steps. Therefore, comparative example 1 is not suitable for an initial processing step prior to a curing step for molding a device.

Various modifications and additions may be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, although the embodiments described above 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 embrace all such alternatives, modifications and variations as fall within the scope of the appended claims and all equivalents thereof.

Claims

1. A photopolymer formulation prior to curing comprising:

poly (amic acid) salts as polyimide precursors; and

a tertiary amine salt of a tetracarboxylic acid as a potential chain extender, wherein the poly (amic acid) salt comprises (i) a base polymer of a dianhydride and a diamine, and (ii) a tertiary amine as a crosslinker,

the mole% of the dianhydride relative to the mole% of the diamine in the photopolymer formulation is in the range of 0.900-0.999: 1.000, wherein the poly (amic acid) salt provides the mole% of the dianhydride and the mole% of the diamine in the photopolymer formulation, and

the ratio of mole% of the dianhydride and the latent chain extender to mole% of the diamine in the photopolymer formulation is 1.000: 1.000.

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

3. The photopolymer formulation of claim 1, wherein the dianhydride is BPDA.

4. The photopolymer formulation of claim 1, wherein the diamine is TFMB.

5. The photopolymer formulation of claim 1, wherein the cross-linking agent is DEEM.

6. The photopolymer formulation of claim 1, wherein the base polymer has a weight average molecular weight of 40,000 and less.

7. The photopolymer formulation of claim 1, wherein the base polymer has a weight average molecular weight of 25,000-35,000.

8. The photopolymer formulation of claim 1, wherein a tertiary amine salt of a tetracarboxylic acid is prepared as the latent chain extender by reacting a dianhydride with water and a tertiary amine at room temperature.

9. The photopolymer formulation of claim 1, wherein 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.

10. The photopolymer formulation of claim 1, further comprising a photoinitiator.

11. The photopolymer formulation of claim 1, further comprising a sensitizer.

12. The photopolymer formulation of claim 1 further comprising a dissolution accelerator.

13. The photopolymer formulation of claim 1, further comprising an adhesion promoter.

14. A method of forming a polyimide polymer, comprising:

providing the photopolymer formulation of claim 1; and

curing the photopolymer formulation followed by activating the latent chain extender and reforming the dianhydride which reacts with the terminal amine groups to form new imide linkages forming the polyimide polymer.

15. The method of claim 14, further comprising controlling a mole% of the diamine above a mole% of the dianhydride to control a weight average molecular weight of the base polymer of the poly (amic acid) salt in the photopolymer formulation.

16. The method of claim 14, further comprising controlling a ratio of mole% of the dianhydride and the latent chain extender to mole% of the diamine to be 1.000: 1.000.