JPH04106546A - Composition for liquid photograph developable by alkaline solution - Google Patents

Abstract

PURPOSE: To protect a metallic wire on a printed wiring board from corrosion by using a liquid image forming composition capable of using as a soldering mask and developing with an alkali solution. CONSTITUTION: The composition is concerned with a photopolymerizing composition developable with the alkali solution, is an acrylic copolymer composed substantially of a hydroxy-containing unit, a carboxyl-containing unit and a branched unsaturated double bond-containing unit, has the average molecular weight of 3000-100000 and >=30mgKOH/g acid value and is composed of 20-80wt.% acrylic copolymer consisting of 3-15mol% hydroxy-containing unit per the copolymer, 5-45mol% carboxyl-containing unit and 5-40mol% branched unsaturated double bond-containing unit, 5-40wt.% hydroxyl-containing photoreactive monomer containing >=2 double bonds, 5-30wt.% melamine compound and 0.5-12wt.% free radical photoinitiator.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention provides a permanent protective layer for printed wiring boards.
That is, it relates to an alkaline solution developable liquid imaging composition that can be used as a solder mask.

Solder masks are used as a covering layer on the surface of printed wiring boards to prevent short circuits during the soldering process, protect metal wires from corrosion, and maintain good electrical insulation. The performance of a solder mask is determined by its heat resistance, solvent resistance, and adhesive strength. These properties are measured as follows: - In boat fishing. That is, the test plate coated with the solder mask is immersed in molten tin-lead solder at 240-280° C. for 10 seconds and then in dichloromethane for 2 minutes. . Adhesive strength testing is then performed using No. 600 adhesive tape available from 3M Corporation, USA. Although delamination of the anti-solder layer may be observed, a suitable solder mask must show no signs of delamination under such testing.

Photographic coating solder masks have been developed to meet standards for finer and closer wire lines on printed wiring boards. Such solder masks are photopolymerizable compositions that can be polymerized using irradiation with light in a specific wavelength range. If the composition is covered by a mask, the non-irradiated areas of the composition will not be polymerized and will therefore be subsequently removed by dissolution using a solvent or alkaline solution. After that,
An image of the polymerized anti-solder layer is obtained.

This image is then further irradiated with ultraviolet light or about 1
It is heated to 50° C. and can therefore be classified with stronger protection. European Patent Application No. EP 01i5
No. 354 discloses a dry thin film type solder mask in which a photopolymerizable composition is inserted between a polyester thin film and a polyvinyl ester thin film. When the film is used, the polyvinyl film is removed and the remaining layer is pressed onto a printed wiring board. The disadvantage of this thin film is that it provides poor adhesion between wire lines. Even worse results are often obtained when the gap between wire lines is less than 8M.

In contrast, liquid photographic solder masks have superior adhesion strength due to their better flowability and wettability to printed wiring board substrates.

Photographic solder masks can be developed using solvents. However, the use of solvents poses environmental problems and further increases costs due to solvent recovery.

Aqueous alkaline solutions, such as a 1% aqueous Na 2 COa solution, have also been used to develop photographic solder masks. When such aqueous alkaline solutions are used in combination with photographic solder masks containing solids content higher than 70v+%, environmental pollution problems can be significantly reduced.

Conventionally, alkaline solution developable solder masks consist of a linear polymeric binder containing acid groups, a photosensitive or heat-sensitive crosslinking monomer, and a photoinitiator. Similar solder masks are available, for example in European Patent Application No. EP 011
No. 5354 and Japanese published patent application 1986-16044
It is disclosed in No. 0. The acidic binder does not participate in photo- or heat-sensitive crosslinking reactions and therefore, although it is possible for the composition to be developed using weakly alkaline solutions, the resultant product after calcination at high temperatures is The crosslinked thin films produced cannot withstand the attack of strong alkaline solutions such as 5% NaOH. Other properties such as solvent resistance (eg to CH2c!12), heat resistance and impact strength are also poor in such thin films. These property disadvantages are due to the high solubility of the acidic binder and the fragile cross-linked structure of the small molecular weight monomers.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an alkaline solution developable liquid imaging composition that can be used on printed wiring boards as a permanent protective layer.

Another object of the invention is to provide an alkaline solution developable liquid imaging composition used to protect metal wires on printed wiring boards from corrosion.

Yet another object of the invention is to provide a material having good electrical properties, durability to high temperatures and resistance to solvents.
An object of the present invention is to provide a liquid imaging composition that is developable with an alkaline solution.

These and other objects, advantages, and features of the present invention will be more fully understood and appreciated by reference to the description herein.

A detailed description of the invention describes a permanent protective layer for printed wiring boards, namely:
An alkaline solution developable liquid imaging composition usable as a solder mask, the composition comprising: a) hydroxyl-containing units, carboxyl-containing units, and pendant unsaturated double bond-containing units; an acrylic copolymer consisting essentially of: wherein said copolymer has a number average molecular weight of 3. [lH~100.000, the acid value of the copolymer is 30 KOH/g or more, and the hydroxyl-containing unit is
15 mole percent of the copolymer, the carboxyl-containing units make up 5 to 45 mole percent of the copolymer, and the pendant unsaturated double bond-containing units make up 5 to 40 mole percent of the copolymer. 20-80% by weight of a polymer; b) 5-40% by weight of a hydroxyl-containing photoreactive monomer having two or more double bonds; C) 5-30% by weight of a melamine compound; and d) free radical light. Initiator 0.
5 to 12% by weight.

According to the present invention, the composition relates to a photopolymerizable composition developable in an alkaline solution, the composition comprising at least (1) hydroxy groups, carboxyl groups, and branched unsaturated carbon double bonds. It has a number average molecular weight of 3.000 to 10G, .000 and an acid value of 30.
an acrylic copolymer having KOH/g or more; (2)
It consists of a photoreactive monomer having a hydroxyl group in which the number of unsaturated carbon double bond functional groups is 2 or more, (3) a melamine compound, and (4) a free radical photoinitiator.

By applying the composition of this composition of the invention, it is possible to obtain a protective thin film having good electrical properties, good high temperature resistance and good solvent resistance,
This film is particularly suitable for use in printed wiring boards as a soldering inhibitor.

One of the characteristics of the compositions of the invention is the high number of crosslinking functional groups. Therefore, the degree of crosslinking of the coated thin film is very high, and therefore the composition has good heat resistance and solvent resistance.

The synthesis of copolymers with hydroxy groups, carboxyl groups and branched unsaturated carbon double bonds consists of two steps. The first step is the synthesis of a linear acrylic polymer and the second step is the addition of the branched unsaturated carbon double bonds to the polymer. In the polymerization of a linear acrylic polymer, the linear polymer contains the following monomers: (1) 0.05 to 0.3 mole fraction (mole percent);
(b) an acrylic monomer having a hydroxy group;
(e) 0.05 to 0.6 mole fraction of acrylic monomers having carboxyl groups; and (e) 0.2 to 0.6 mole fraction of acrylate monomers.

According to the invention, this polymerization is carried out in a suitable solvent and a reaction initiator is used to initiate the reaction. The molecular weight of the resulting polymer is approximately 3.0
00 to about 100. [100, and its acid value is 50■
Exceeds NOR/g. The structure of the resulting linear polymer is expressed as: C0OHC=OC=
0 ・o O OH In the previous formula, R=H, CH3, and when r=j ~ 18, R=CH, and n12 t 2++
1 m and p are integers.

(a) The acrylic monomer having a hydroxy group is selected from the group consisting of hydroxyethyl methacrylate, hydroxyethyl acrylate, and an acrylic monomer of the formula: HC=C-C-OR2-O
H In the above formula, R is H or CH3, R2 is axyl,
They are allysyl, polyethylene glycol, polypropylene glycol, and aryl group.

Said (b) acrylic monomer having a carboxyl group is selected from the group consisting of acrylic acid, methacrylic acid, and 2-methylenesuccinic acid.

The acrylic monomer (C) is selected from alkyl acrylate monomers and alkyl methacrylate monomers whose acrylic groups have 1 to 18 carbon atoms. Phenyl acrylate, 2-phenylethyl acrylate, 3-phenylpropyl acrylate, 2
- cyclohexylethyl acrylate, benzyl acrylate, benzyl methacrylate, phenyl methacrylate, 2-phenylethyl methacrylate,
3-phenylpropyl methacrylate, 2-cyclohexylethyl methacrylate, acrylonitrile,
Other acrylates such as styrene, methylstyrene, and the like can be used.

The grafting reaction between the branched unsaturated double bond and the linear acrylic polymer is one of the reactions shown below.

Substitution reaction between -OH on a linear copolymer.

and C0OH on the linear copolymer.

compound and -OH or -COO on the linear copolymer
Condensation reaction between H.

In the above reactions (i), (ii), (iii),
R is H or -CH3, and R2 must be a group that does not participate in the grafting reaction, e.g.
It can be selected from the group consisting of alkyl groups, alkoxy groups, aryl groups and aryl groups. The number of moles of monofunctional acrylate or methacrylate must be smaller than the number of moles of C0OH or -OH functional groups. At the end of the reaction, the 10H contained in the resulting grafted product
The number of moles of groups should, as a rule, account for 3 to 15% of the number of moles of repeating units in the polymer backbone, while the number of moles of -COOH groups should account for 3 to 15% of the number of moles of repeating units in said backbone. It must account for 5-40% of the moles of units. The amount of this graft polymer is about 20 to 20% of the composition.
80% by weight, preferably about 40-60% by weight.

In the above (100) reaction, the number of unsaturated carbon double bond functional groups in the photoreactive monomer having a hydroxy group is
Must be 2 or more. Photoreactive monomers that can be used include pentaerythritol (eridoride) triacrylate, dipentaerythritol hydroxypentaacrylate, bis(acryloxyethyl)hydroxyethyl isocyanurate, pentaerythritol diacrylate, and pentaerythritol dimethacrylate, and pentaerythritol trimethacrylate, in an amount of about 5-40% by weight of the composition.

In the compositions of the invention, suitable mela, amine compounds can, first of all, have their methoxy groups partially or completely substituted with hydroxy or alkoxy groups;
and hexa(methoxymethyl)-melamine whose alkoxy group can have 2 to 4 carbon atoms. The amount of melamine compound used is approximately 5% of the composition.
~30% by weight.

Free radical initiators suitable for the compositions of the invention include diphenylketone, dimethoxy-2-phenylacetophenone,
4.4'-dimethylamine diphenylketone, 2-chlorothioxanthone, and 2-hydroxy-2-methyl-
It is selected from the group consisting of 1-phenylpropane-1-one, 1-hydroxycyclohexylphenylketone, and the like. The amount of free radical initiator used is approximately 0
, 5 to 12% by weight.

Other free radical initiators can also be used in the compositions of the invention, such as derivatives of benzoin, benzoin alkyl ethers, benzyl ketals, and acetylbenzene.

In addition to the above ingredients, a solvent or plasticizer, a pigment, a filler, a thixotropic agent, a fire retardant, an antifoaming agent,
Additives such as wetting agents and wetting agents can also be added in suitable amounts. Non-reactive solvents such as ketones, ethers, esters, and alcohols can be used in this composition. Furthermore, hydrocarbons and halogenated hydrocarbons can also be used. Typically, the solvents used are acetone, butanone, cyclohexane, jetoxyethane, diethylene glycol diethylene ether, 1,4-dioxane, ethylene diacetate, isobutyl acetate, 2-ethoxy Ethyl acetate, 2-butoxyethyl acetate, ethoxyethoxyethyl acetate, 2-butoxyethyl acetate, ethoxyethoxyethanol, pentanol, cyclohexane, naphtha, toluene,
It can be selected from the group consisting of xylene, chlorobenzene, dichlorobenzene, and the like.

In the present invention, the antifoam agent is 31J Cotporiti
FC430 and FC431 commercially available from onUSA, or Mon5an+o Co, Mo commercially available from USA
Da! lov. In addition to this,
Commercially available from IIYK Co. [1YK-020] t
BYK-141 can also be added to the composition in any desired amount.

The coating method of the composition of the invention may be a net printing method, a roller printing method or a screen printing method, or it can also be coated using a scraper plate or a scraper knife.

The invention will be more clearly understood with reference to the following examples. All parts and percentages used in the following examples are by weight unless otherwise indicated.

Examples Example 1 Into a stirred 30-liter reactor vessel with a heating mantle, the temperature inside the vessel was adjusted to 70°C, and the following ingredients were added continuously over a period of 5 hours. I'm alive now.

Methacrylic acid Methyl ethyl hydroxyl methacrylate 22'-Azodi (Isobutyl acetate 2-butoxyshetanol Diacetate Glycol naphtha n-dodecanethiol 322 g 820 g Toro 24 g Rilonitrile) 4 g 200 g 200 g 00 g 2 Og The temperature is 4 It was maintained over time. As a result, a binder solution was obtained. Thereafter, the following ingredients were added to the binder solution and allowed to react for 7 hours.

Hydroquinone 2g Tetra-n-butyl-ammonium chloride 0g Glucidyl methacrylate 2988° Thereafter, a photopolymerizable copolymer was obtained. Its number average molecular weight is about 5600, and its acid value is about 8hg KO
It was R#.

Example 2 The following ingredients were added into a stirred 500 m reactor vessel while adjusting the vessel temperature to 45°C.

Toluene 2.4-diisocyanate 34.83 g stannic dibutyl dilaurate 0.331 g 2-(
2-Ethoxyethoxy)ethyl acetate 10° Then 27-3 g of ethyl hydroxyl methacrylate were stirred into the reaction mixture for 2 hours to obtain prepolymer (A).

The following ingredients were added sequentially over a period of 5 hours into 11 stirred reactor vessels.

Methacrylic acid 29.3 g Methyl methacrylate 25.0 g Butyl acrylate 37 g Ethyl hydroxyl methacrylate 156 g 2.2'-Azodi(
isobutylacrylonitrile)-butyrolacetone
94.7g methyl ethyl ketone
157gn-dodecanethiol
The reaction was then continued for 3 hours with 6
Continued at 6°C. Thereafter, 36.71 g of prepolymer (A) was added, and the reaction was continued for an additional 3 hours, resulting in a photopolymerized acrylic copolymer.

added. The reaction mixture was then stirred for an additional 2 hours Example 3 In this example, an alkaline liquid photographic composition was used. The composition has excellent heat resistance.

Binder solution of Example 1 215g dimethquine 2-phenylacetophenone 12g pentaerythritol triacrylate 36g hexamethoxymethylmelamine 15g antifoam agent
4g 2-butoxycetanol
12gNo. 7 Green pigment
4g After the above ingredients are mixed,
The mixture was milled using a 30 roller mill until all of the particles of the mixture were less than 10 microns. The composition was screen printed onto a 0.75 mm FR-4 base plate using a 110 mesh silk screen and then processed according to the following procedure.

(1) To remove the solvent from the plate so that the coated plate is non-stick, apply the mixture for 20 minutes.
Heat to 80°C for ~40 minutes.

(2) The circuit (wiring) base plate is brought into contact with a mask and exposed to light at 601]ml/crl. It should be noted that the radiation source used has a power of 3KW, 5KW or 7KW.

(3) Approximately 1% at liquid pressure of 1 to 2 kgv/a+f
An aqueous sodium carbonate solution of 60% was used for development.
Completes within ~120 seconds.

(4) Post-calcination at 140-150° C. for 40-60 minutes, thereby obtaining a permanent protective coating.

In the above composition, a 5 tou[er 21 scale photosensitive test film was used. This film is 60
It received an exposure of 0 m1/ai. After development, 10 greens
Sodo remained. This composition therefore has very high photosensitivity.

An FR-4 base plate coated with the composition of the invention was cut into 3 x 10 cm test specimens after being fired at high temperature. after,
The following tests were conducted on these specimens.

(i) Alkali resistance test specimens were immersed in a 5% Na0fl aqueous solution at 50°C.

The specimen was immersed in the solution for 5 minutes and then removed. The specimen was then washed with water and dried at ambient temperature. After that, 361 Co
No. 600 adhesive tape, commercially available from USA, was glued onto the specimen. No evidence of peeling was observed.

(jl) Dichloromethane solvent test For soldering, the specimen moistened with an auxiliary agent (solder-1id) is placed in a molten tin-lead bath at 260°C for 10 min.
It was soaked for seconds. The specimen is removed from the bath and the remaining solder is washed with water to remove the adjuvant.
40°C). After the specimen is dried,
It was soaked in dichloromethane for 2 minutes, then removed and dried again. No. 600 adhesive tape (commercially available from 3M Co., Ltd.) was adhered onto the specimen. No evidence of peeling was observed.

(iii) Thermal shock test specimens are baked at 120° C. for 10 minutes and immediately immersed in liquid nitrogen for 10 seconds;
It was then taken out. This procedure was repeated twice. The test specimen showed no evidence of peeling or other changes.

In conclusion, the composition according to the invention has excellent heat resistance and alkali resistance.

Example 4 Polymer solution of Example 2 200g Dimethoxy 2-phenylacetophenone 8g Dipentaerythritol pentaacrylate 40g Hexamethoxymethylmelamine 20g Barium sulfate 10g Methyl ethyl ketone 20g Green dye No. 7
The above ingredients were mixed to prepare a 4 g composition. The above composition was applied onto a 0.1 mm FR-4 base plate using a scraper. The coated film was about 30-. The procedure of Example 3 was used. Exposure was performed at 600 m1/ci. The alkali resistance test, solvent resistance test, and thermal shock resistance test of Example 3 were used. The electrical insulation resistance value exceeded 109 ohms, and the pencil hardness exceeded 4H.

Comparison Examples B, F, Carbo of Goodrich Co.
+et XL 27 was used as the binder in this comparative example. The copolymer was an acrylate copolymer. Its acid value was approximately 80 mg KOI (/g) and its molecular weight was 40.000.

Ca+boset XL 27
100 g dimethoxy 2-phenylacetophenone
10g Pentaerythritol triacrylate 36g
Hexamethoxymethyl melamine 15g Methiethyl ketone 50g Green dye No.
, 74 g The above ingredients were mixed to prepare the composition. The above composition was applied onto a 0.1 mm FR-4 base plate using a scraper. The coating film was about 30 IJIm. The specimen was processed according to the procedure of Example 3. The test was performed after the specimen was fired at high temperature. It was found that there was evidence of significant delamination in the alkali resistance test and the solvent resistance test, and significant cracking was found in the thermal shock resistance test.

The invention being thus described, it will be obvious that the compositions of the invention may be varied in many ways. Such modifications should not be considered a departure from the spirit and scope of the invention, and all such modifications are to be included within the scope of the claims of the invention.

Claims (6)

[Claims] (1) A photopolymerizable composition developable with an aqueous alkaline solution after imagewise exposure, comprising: a) a hydroxyl-containing unit, a carboxyl-containing unit, and a pendant unsaturated double bond; a linear acrylic copolymer consisting essentially of containing units, the copolymer having a number average molecular weight of 3,000 to 100,000.
and the acid value of the copolymer is 30 mg KOH/g or more, the hydroxyl-containing units constitute 3 to 15 mole percent of the copolymer, and the carboxyl-containing units constitute 5 to 45 mole percent of the copolymer, and 20 to 80% by weight of an acrylic copolymer in which the side chain unsaturated double bond-containing units constitute 5 to 40 mole percent of the copolymer; b) a hydroxyl-containing photoreactive monomer 5 having two or more double bonds; c) 5-30% by weight of a melamine compound, and d) 0.5-12% by weight of a free radical photoinitiator. (2) The hydroxyl-containing photoreactive monomer includes pentaerythrite triacrylate, dipentaerythrite hydroxypentaacrylate, pentaerythrite diacrylate, quaternary pentaerythrite dimethacrylate, pentaerythrite The photopolymerizable composition according to claim 1, which is selected from the group consisting of light trimethyl acrylate, bis(acryloxyethyl)hydroxyethyl isocyanurate, and mixtures thereof. (3) The melamine compound has 2 to 4 methoxy groups.
2. Photopolymerizable composition according to claim 1, which is hexamethoxymethylmelamine, which contains 1 carbon atom and can be partially or completely substituted by hydroxyl or alkoxyl groups. 4. The photopolymerizable composition of claim 1, wherein the photoinitiator is selected from the group consisting of derivatives of benzoin, benzoin alkyl ethers, benzyl ketals, and acetophenones. (5) The linear acrylic copolymer contains (a) 0.05 to 0.3 mole fraction of an acrylic monomer having a hydroxy group, and (b) 0.05 to 0.6 mole fraction of a carboxyl monomer. and (c) 0.2 to 0.6 mole fraction of an acrylate monomer, wherein said copolymer is polymerized using said photoinitiator in a solvent. A reaction is initiated, and as a result, a linear polymer with the following structure ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [In the formula, R_1 = H, CH_3, and when r = 1 to 18, R_2 = C_rH_2_r_+_1, and n, m, and p are integers. (6) The grafting reaction between the branched unsaturated double bond and the linear acrylic copolymer is the reaction shown below: , a substitution reaction between -OH on the linear copolymer; (i
i) Condensation reaction between a compound having the formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ and -COOH on the linear copolymer; and (iii) Condensation reaction between a compound having the formula ▲ There are mathematical formulas, chemical formulas, tables, etc. and -OH or -COO on the linear copolymer.
a condensation reaction with H, in which R_1 is H or -CH_3, and
The photopolymerizable composition according to claim 1, wherein R_2 is a group that does not participate in a graft reaction and is selected from the group consisting of an alkyl group, an alkoxy group, an aryl group, and an aryl group.