KR19990062605A - An optical imaging composition comprising a photopolymerizable urethane oligomer and a binder polymer having a low glass transition temperature - Google Patents

Abstract

The present invention provides a negatively action photoimaging composition comprising an acid functional binder polymer having a glass transition temperature (T _g ) of about 60 to about 90 ° C., a photopolymerizable α, β-ethylenically unsaturated compound, and a photoinitiator, wherein the photopolymerizable compound is used. At least a portion of the is directed to the negatively acting optical imaging composition, characterized in that isocyanate trimers having a weight average molecular weight of at least about 1,000 and having tri-α, β-ethylenically unsaturated functionality.

Description

Photoimaging composition comprising a photopolymerizable urethane oligomer and a binder polymer having a low glass transition temperature

The present invention relates to a negative acting optical imaging composition such as used as a photoresist for forming a printed circuit board. The light imaging composition uses a binder polymer having a low glass transition temperature (T _g ) and includes a photopolymerizable urethane oligomer as at least part of the light imaging component.

The present invention relates to an intaglio photoimaging composition that is developable in an aqueous alkali solution. In particular, the present invention is applicable not only to primary light imaging resists, but also to compositions curable to form solder masks and the like.

Various such optical imaging compositions are disclosed. The basic components of a composition of the type related to the present invention are A) binder polymers, B) photopolymerizable α, β-ethylenically unsaturated compound (s) and C) photoinitiator chemical systems. The binder polymer A) has sufficient acid functionality, generally carboxylic acid functionality, and is soluble in aqueous alkali solution, thereby making the photoimaging composition developable in aqueous alkali solution.

The optical imaging composition of the present invention has certain advantages when applied to a dry film. Such dry coatings typically comprise relatively rigid support sheets such as polyethylene terephthalate, photoimaging composition layers and protective films such as polyethylene films. This dry coating film is supplied in roll form. When applied to a blank for a printed circuit board (typically a copper clad / fiberglass-epoxy substrate), the layer of photoimaging composition is applied to the blank under heating and pressure to subsequently peel off the support sheet.

A common problem with dry coating photoresist compositions is to balance the low temperature flow (edge fusion) of the rolled film when adhering the film to the support during processing. A conventional cure for prior art for improving adhesion is to combine low T _g polymers in a composition comprising a high content of multifunctional polymerizable monomer. Such compositions improve adhesion, but promote inadequate low temperature flow, tend to reduce the shelf life of dry coatings, and often have a shelf life of less than one month. Attempts to extend shelf life typically result in poor adhesion or reduced flexibility.

It is a general object of the present invention to provide an optical imaging composition suitable as a photoresist for producing printed circuit boards with good adhesion to substrates provided by low T _g polymers but with minimal low temperature flow, good shelf life and good flexibility. Is to provide.

The negative acting optical imaging composition has an A) glass transition temperature (T _g ) of about 60 to about 90 ° C., preferably about 80 to about 90 ° C., based on the total weight of A) + B) + C) From about 29 to about 69 weight percent of an organic polymer binder having sufficient acid functionality to develop the photoimaging composition in an aqueous alkaline solution;

B) about 30 to about 60 weight percent of an additional polymerizable component comprising a non-gaseous ethylenically unsaturated compound (s) capable of forming a polymer by free radical initiated chain extension addition polymerization; And

C) about 0.5 to about 15 weight percent of an organic radiation sensitive free radical generation system that is activatable by actinic radiation initiating the chain extension addition polymerization of the addition polymerizable material B). According to the present invention, component B) isocyanate trimers B ′ having about 2 to about 30% by weight of tri-α, β-ethylenically unsaturated functionality based on the total weight of A) + B) + C) ); B) The remainder of the content, ie up to 57% by weight, preferably at least about 5% by weight, based on the total weight of A) + B) + C), comprises other α, β-ethylenically unsaturated monomers. ). In addition, the composition according to the invention preferably comprises from about 1 to about 8% by weight of D) dibenzoate plasticizer, more preferably from about 2 to about 6, based on the total weight of A) + B) + C) It contains by weight.

Unless otherwise stated, all percentages are by weight. The total amounts of component A) (binder polymer), component B) [photoimaging composition (s)] and component C) (photoinitiator chemistry) are deemed to correspond to 100% by weight herein and other components, for example The plasticizer is calculated as parts based on 100 parts of A) + B) + C). Unless otherwise specified, the molecular weights of polymers and oligomers are weight average molecular weights (M _w ).

The present invention relates to photoimaging compositions that are developable in aqueous alkali solutions and have substantially acidic functionality. Such photoimaging compositions typically comprise binder A) having an acid functionality, typically an acid value of at least about 80, preferably at least about 100, more preferably at least about 150, up to about 250. Acidic functionality is usually carboxylic acid functionality, but may also include, for example, sulfonic acid functionality or phosphoric acid functionality. The binder polymer for the photoimaging composition typically has a weight average molecular weight of about 40,000 to about 200,000, preferably at least about 80,000.

The polymer is typically derived from an acidic functional monomer and a non acidic functional monomer mixture. Some specific examples of such suitable acidic functional monomers include acrylic acid, methacrylic acid, maleic acid, fumaric acid, citraconic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-hydroxyethyl acryloyl phosphate , 2-hydroxypropyl acryloyl phosphate, 2-hydroxy-α-acryloyl phosphate and the like. Such one or more acidic functional monomers can be used to form the binder polymer.

Acidic functional monomers may be copolymerized with non-acidic functional monomers to provide the desired acid value, and examples of non-acidic functional monomers include esters of acrylic acid, such as methyl acrylate, methyl methacrylate, hydroxy ethyl acrylate, butyl Methacrylate, octyl acrylate, 2-ethoxy ethyl methacrylate, t-butyl acrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, n-hexyl acrylate, 1,5-pentanediol diacryl Latex, N, N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexane Diol diacrylate, 2,2-dimethylol propane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, gly Roll triacrylate, 2,2-di (p-hydroxyphenyl) propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl-2,2-di (p-hydroxyphenyl) propane dimethacryl Latex, triethylene glycol dimethacrylate, polyoxypropyltrimethylol propane triacrylate, ethylene glycol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2, 4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenylethylene-1,2-dimethacrylate Pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate, 1,5-pentanediol dimethacrylate and 1,4-benzenediol dimethacrylate; Styrene and substituted styrenes such as 2-methyl styrene and vinyl toluene and vinyl esters such as vinyl acrylate and vinyl methacrylate.

T _g of the acrylic polymer depends greatly on the monomer component. Generally, monomers that provide hydrocarbon chains with significant lengths on acrylate residues or esterified alcohol residues, such as n-butyl acrylate, n-hexyl acrylate and 2-ethyl hexyl acrylate, have a T _{g value} of There is a tendency to be low, and therefore, a given T _g can be obtained by appropriately selecting the monomer used to form the binder polymer.

Examples of such polymers and optical imaging compositions using such polymers are described in US Pat. Nos. 3,953,309, 4,003,877, 4,601,951, and 4,695,527, which are incorporated herein by reference.

In some cases, in some cases, the photoimageable acrylate functional isocyanate trimer B ′) (urethane oligomer) comprising all photopolymerizable component B) has the formula (1).

Wherein R is-(CH ₂ ) _p -NH-COO- (CHY-CHY-O) _m -CO-CX = CH ₂ , wherein X is H or CH ₃ , and Y is H, CH ₃ or C _2, and H _5, p is an integer of 1~36, m is an integer from 1 to 14. Such trimers are described in European Patent Application No. 0 738 927 A2. When used with low T _g polymers, the urethane oligomer should have a weight average molecular weight of at least about 1,000, up to about 10,000. Satisfactory low temperature and shelf life using a relatively high molecular weight photopolymerizable component with a low T _g binder polymer, ie urethane oligomers, without adversely affecting the adhesion and flexibility provided by the low T _g binder polymer Get Intuitively, since the monomer content is reduced as moles on a molar basis, a high molecular weight photopolymerizable component should be used to advantageously affect adhesion. Surprisingly, the urethane oligomers according to the present invention provide the advantage of using a low T _g binder polymer.

The remainder of the photopolymerizable component B) content used in the optical imaging composition of 0 to about 30% by weight, based on the total weight of A) + B) + C), is B), typically a monomer, dimer, or Ethylenic unsaturations, in particular short chain oligomers having α, β-ethylenic unsaturation, including monomer compounds having an α, β-ethylenically unsaturated functionality of at least two. Non-limiting examples of suitable photopolymerizable compounds include binder polymers, especially monomers as described above suitable for forming non-acidic functional compounds.

In order to initiate the polymerization of monomers upon exposure to actinic radiation, the photoimaging composition comprises a photoinitiator chemistry. Examples of suitable photoinitiators include 9-phenyl acridine, benzoin ether, benzyl ketal, acetophenone, benzophenone and related compounds with amines. In addition, suitable 9-phenyl acridine analogs, such as those described in US Pat. No. 5,217,845, incorporated herein by reference, are useful photoinitiators.

According to a preferred embodiment of the present invention, the flexibility is further improved by using a dibenzoate plasticizer together with an isocyanate trimer. This combination further improves the adhesion and fine strip properties of the fine lines. The dibenzoate plasticizer according to the present invention has the following formula (2).

C ₆ H ₅ -COO- [R] _n -R'-C ₆ H ₅

Wherein R is -CHX-CHX-O-, wherein one or both of X can be H or one X can be CH ₃ , the remaining X can be H, n is 1-10 , R 'is -CH ₂ -CH (CH ₃ ) -OOC-, -CH ₂ -CH ₂ -OOC- or -OC-. Non-limiting specific examples of suitable dibenzoates include dipropylene glycol dibenzoate, diethylene glycol dibenzoate, polypropylene glycol dibenzoate and polyethylene glycol dibenzoate and the like. The dibenzoate plasticizer D) is used in an amount of about 1 to about 8% by weight, typically about 2 to about 6% by weight, based on the total weight of A) + B) + C).

Compared to other plasticizers tested, dibenzoate significantly improves tent strength. The combination of dibenzoate plasticizer and isocyanate trimer with improved flexibility forms resist sidewalls of fine lines (less than 75 microns) that adhere better to the copper surface. It is known that the T _g of the formulation is lowered by adding dibenzoate. The lower the T _g , the better the flow during lamination and the better the conformation to the copper surface. This property is particularly important on copper surfaces with scratches or scratches. The larger area of the photoresist surface area is in better contact with the copper surface because the composition with dibenzoate is more compliant with copper. This increases the possibility of chemical bonding to the copper surface, thus improving the adhesion properties. Since dibenzoate cannot be incorporated into the backbone of the exposed acrylic monomer system, including the dibenzoate compound results in less shrinkage of the composition. This reduction in shrinkage probably contributes to improving the adhesion by reducing the stress on the copper / photoresist interface. Less shrinkage is observed especially when 9-phenyl acridine is used as the photoinitiator, because the crosslinking density is high by the initiator.

In addition, the photoimaging composition may contain various additional components as known in the art, including those that may be used to effect final hard cure of additional polymers such as solder masks, dyes, stabilizers, flexibilizers, fillers, and the like. It may include.

Processing of the optical imaging composition can be carried out by conventional methods. In a conventional method, a layer of photoimaging composition formed from a liquid composition or delivered as a layer from a dry coating is applied to a copper surface of a copper-clad substrate. The photoimaging composition layer is exposed to actinic radiation through a suitable plate. Exposure to actinic light causes the monomers at the light exposed sites to polymerize to produce crosslinked structures that are resistant to the developer. The composition is then developed in a dilute alkaline aqueous solution, for example 1% by weight sodium carbonate solution. The alkaline solution forms salts with the carboxyl groups of the binder polymer so that they are soluble and removable. After development, the caustic may be used to remove copper from the resist removed portion to form a printed circuit. Remove the resist using a suitable stripper.

The invention will be described in more detail by specific examples.

Example A (comparative) and Example B (included in the present invention)

Photoimaging compositions A and B were formulated as described in Table 1 below, each using an acrylic binder polymer having a T _g of 85 ° C.

Changes in Substrate Components and Monomers ingredient Formulation A Monomer Formulation B Oligomer Acrylic polymer (23% methacrylic acid, 66% methyl methacrylate, 11% butyl acrylate) 40.0 g 40.0 g Isocyanuric urethane trimethacrylate - 20.0 g Tetraethylene Glycol Diacrylate 10.0 g 10.0 g Ethoxylated (3 moles) trimethylolpropane triacrylate 20.0 g - 9-phenylacridine 0.2 g 0.2 g Dipropylene glycol dibenzoate 2.0 g 2.0 g Mikler ethyl ketone 0.09 g 0.09 g Nitrified Azo Dye (Furon Navy) 0.075 g 0.075 g Methyl hydroquinone 0.045 g 0.045 g Triphenyl Methane Dye (Flexoblue 680) 0.025 0.025 g

All compositions were prepared with 2-butanone: 2-propanol 7: 1 at about 50% solids. The solution was coated onto a biaxially oriented 80 gauge folatester film and dried to retain solvent up to about 1%. The coated mixture was laminated on a mechanically worn 1 oz / FR-4 / 1 oz clad copper composite using a hot roll laminator at a temperature of 110 ° C. at a pressure of 2 m / min and 3 bar.

The laminated material was imaged on a UV printer with appropriate optics with exposure adjusted to obtain a copper step of 7 as measured using a trademark Stouffer 21 step wedge (about 20 mJ / cm 2). 1% sodium carbonate monohydrate at 29 ° C. using a spray developer equipped with a conveyor belt at about 26 psi with controlled residence time (unless otherwise noted in certain examples) so that the break point occurs at 40-50% of the chamber length The exposed panels were developed in solution and rinsed with several sprays using tap water and deionized water.

Corrosion was carried out using a 2 N cupric chloride / hydrochloric acid solution at 48 ° C. in a caulter fitted with a number of spray nozzles and equipped with a conveyor belt. In a stripping unit equipped with a plurality of spray nozzles and a conveyor belt, phase formation, development, and corrosion treatment of the photoresist in a 3% sodium hydroxide solution at 54 ° C. was stripped from the corroded substrate.

The treatment reactions in the examples are cited at a number of time points through the procedure described above, which are set forth in Tables 2a and 2b below.

Results on monomer change, adhesion and flexibility in cold flow ingredient thickness Break Time ¹ Film adhesiveness Shade Adhesion ² Tent Robbery ³ Low temperature flow ⁴ Strip time ⁵ Fine Line Adhesion ⁶ Formulation A 38 μm 20 seconds moderation 75% intact 500 g Severe 55 seconds 45㎛ Formulation B 38 μm 19 seconds slightly 90% intact 750 g slightly 53 seconds 40 μm ¹ : Break time is recorded when the resist is completely dissolved in 1% Na ₂ CO ₃ at 30 ° C.

² : The developed photoresist was cut several times in a direction other than 90 ° from the previous cut using a razor blade device. This test measures brittleness and adhesion. Results are reported as% of resist remaining intact after all blade cuts (100% is maximum). Exposure to Stouffer 21 Copper Step 7 at break in 25% development chamber. Developer is 1% Na ₂ CO ₃ at 30 ℃ ³ : Laminate 0.25 inch holes on both sides using photoresist. The resist is then exposed and developed (exposed to Stouffer 21 Copper Step 7 at 25% breaking point in the development chamber). The flexibility of the resist for the tented hole is measured by force gauge by pressing the resist with a round probe. Record the force in grams needed to break the tent ⁴ : Low temperature flow is measured by resist strain (orange peeling) measured after 14 days at room temperature. ⁵ : Exposed resist to Stouffer 21 copper step 7 at 30 ° C. 1% Na ₂ CO ₃ developing solution at break in 25% developing chamber. The resist is then corroded in cupric chloride at 130 ° C. After corrosion, the photoresist is stripped in 3% NaOH at 130 ° C. and time is recorded in seconds ⁶ : The fine line adhesion is measured after development. This is the smallest line bonded to a 400 micron space. Exposure to Stouffer 21 Copper Step 7 at break in 25% development chamber. Developing solution is 1% of the _{30 ℃ Na 2 CO 3 · H} 2 O being

The optical imaging composition of the present invention has good adhesion to the substrate and is suitable for producing printed circuit boards with minimal low temperature flow, good shelf life and good flexibility.

Claims (5)

Based on the total weight of A) + B) + C) A) about 29 to about 69 weight percent of an organic polymer binder having a glass transition temperature (T _g ) of about 60 to about 90 ° C. and having sufficient acid functionality to develop the photoimaging composition in an aqueous alkaline solution; B) about 2 to about 30% by weight of isocyanate trimers having a weight average molecular weight of at least about 1,000 and having tri-α, β-ethylenically unsaturated functionality and B) 0 to other α, β-ethylenically unsaturated compounds From about 30 to about 60 weight percent of an additional polymerization component comprising an α, β-ethylenically unsaturated compound, including about 57 weight percent; And C) about 0.5 to about 15 weight percent organic radiation sensitive free radical generation system. The optical imaging composition of claim 1, wherein B) is present in an amount of at least about 5% by weight based on the total weight of A) + B) + C). The optical imaging composition of claim 1, wherein the free radical generating system C) comprises 9-phenyl acridine. The optical imaging composition of claim 1 further comprising about 1 to about 8 weight percent of D) a dibenzoate plasticizer based on the total weight of A) + B) + C). The optical imaging composition of claim 1, wherein the binder polymer has a T _g of about 80 to about 90 ° C. 3.