WO2002085962A1

WO2002085962A1 - Improved radiation curable composition

Info

Publication number: WO2002085962A1
Application number: PCT/EP2002/004456
Authority: WO
Inventors: Mohd Nor Azmi Alias; Kris Verschueren
Original assignee: UCB SA
Current assignee: UCB SA
Priority date: 2001-04-24
Filing date: 2002-04-23
Publication date: 2002-10-31
Anticipated expiration: 2003-10-24

Abstract

The present invention relates to a radiation curable composition for use as a UV etching resist formulation said composition comprising : a) an amido (meth)-acrylate in combination with b) a (meth)acrylate half ester. It relates also to compositions for UV solder mask formulation, the composition comprising: i) an epoxy (meth)acrylate and ii) an amido (meth)acrylate. Such compositions can provide adhesion to difficult metals like Cu, Ni, and Au.

Description

IMPROVED RADIATION CURABLE COMPOSITION

Field of Invention

The present invention relates to a radiation curable composition containing amide linkages and its utility in resistant inks for the fabrication of printed circuit boards. The present invention in its preferred embodiments has two aspects, the first aspect relating to a composition specific for UV etch resist composition and the second aspect relating to composition for UV solder mask application.

More specifically, a first aspect of the invention is directed to the use of radiation curable composition containing amido (NHCO) linkage for UV etch resist application to impart good hardness, and alkaline solubility in the alkaline stripping solution. The second aspect of the invention is directed to the use of radiation curable composition containing amido (NHCO) linkage for UV solder mask application to impart good adhesion to Cu, Ni and Au. The said composition also provides good chemical resistance to various fluxes used during the soldering processes in the printed circuit board fabrication.

The present invention is directed towards a radiation curable composition containing amido (NHCO) linkage the use for which includes:

1. adhesion to difficult metals like Cu, Ni, and Au;

2. maintaining adhesion to these metals while exposed to acidic or alkaline media or to high temperature in excess of 250°C;

3. maintaining good chemical and thermal resistance of the UV curable coating; and

4. providing high coating hardness

Background of the Invention

Use of adhesion promoters based on (meth)acrylated phosphoric acid is widely known in the formulation of UV solder masks. These adhesion promoters are highly acidic and can lead to detrimental effect to the properties of the solder mask such as poor resistance to chemicals used in printed circuit board processes. The applicant also founds that UV solder mask containing these type of adhesion promoters is susceptible to blistering or total delamination during the Sn/Pb soldering processes when water-based fluxes are used prior to the soldering processes. Due to increasing environmental concerns water-based fluxes are rapidly replacing solvent-based fluxes (or No- clean fluxes based containing solvent).

Flux is a component used in the soldering process of electronic product. It is known that there are many different types of fluxes in the market such as rosin-based flux, low volatile-organic-content flux, and water-based flux. These fluxes typically contains active ingredients such as halides, amines, and organic acids to help removing the oxides and contaminants on the metallic Cu surface prior to Sn/Pb soldering process. Typically ink supplier deigns the solder mask specific to a particular type of flux, and when the end-user requires using different types of fluxes, they'll encounter problems during the soldering process. Blisters or total delamination of the solder mask can be one of the dramatic problems due to flux and solder mask incompatibility. Therefore, an ink formulation that can be used with various types of fluxes would be an advantage to the end user. UV solder mask composition with good resistance to Sn/Pb soldering with different types of fluxes are disclosed in this invention.

In addition to achieve adhesion to different type of metals especially those difficult to adhere such as Ni and Au, different combinations of adhesion promoters and flexibilizers are required. The composition utilised in the UV solder mask of this invention is also useful when adhesion to these difficult metals are required.

A further aspect of the present invention is directed towards providing a UV etch resist composition with good surface hardness, excellent acid etching resistance and good alkaline solubility in the 3-5% NaOH stripping solution. Typical formulations of UV etch resist utilized acid functional monoacrylate to provide resistance to the acidic etching solution and solubility in the alkaline stripping solution. Use of monofunctional (meth)acrylate will lead to slow cure speed and the resultant UV curable resist could only achieve pencil hardness as high as H. This lead to sticking of the resist to the back of another board when many boards are stacked together after the UV curing step in waiting for the wet processes. Use of difunctional and sometime trifunctional (meth)acrylates can increase the pencil hardness of the resist but this lead to the resist to be insoluble in the stripping solution. The resist will strip in large flakes. In some PCB shops, alkaline soluble type of etch resist is preferred such that the user does not have to use filters to remove insoluble resists. Therefore, a formulation for UV etch resist that can provide high pencil hardness of greater than 2H, excellent etching resistance, and good alkaline solubility in the stripping solution is required.

Summary of the Invention

According to one aspect of the present invention there is provided a radiation curable composition, said composition including at least one amide (- NH(CO)-) linkage and at least one (meth)acrylate functionality. Preferably the amide linkage is contained within the internal structure of the (meth)acrylate.

According to a further aspect of the present invention there are provided methods for preparing a radiation curable composition containing at least one amide linkage and at least one (meth)acrylate linkage. One method for the production of said curable composition comprises:

(i) reacting gamma-butyrolactone with alkylamine, alkanolamine or alkyl diamine to produce an amido alcohol; and (ii) reacting said amido alcohol with methyl (meth)acrylate by transesterification to produce an amido(meth) acrylate and a mono alcohol (iii) removing said monoalcohol to provide a substantially pure solution of said amido(meth)acrylate The radiation curable composition so produced may in a preferred embodiment be further combined with a (meth)acrylate half ester.

The curable formulation of the present invention has particular application when secondary processes such as stripping of the temporary coating or resist is required such as in the etching resist application. This however does not compromise the adhesion of the said composition to the substrate to be protected, hardness of the coating containing the said composition, and chemical resistance in various chemicals.

A further application for the curable formulation of the present invention is for use in UV solder mask with good resistance to different fluxes used in the soldering processes.

Detailed Description of the Invention

The principal embodiment of the present invention relates to a radiation curable composition based on amide-containing (meth)acrylate which contains at least one amide, -NH(CO)-, linkage and at least one (meth)acrylate functionality. The amide linkage is preferred to be in the internal structure of the (meth)acrylate, as generally described below in I and II:

Monofunctional amido (meth)acrylate:

wherein R1 and R2 can be alkyl, aryl, arylalkyl or cycloalkyl.

Difunctional amido (meth)acrylate:

wherein R is alkyl,

Another example of difunctional amido (meth)acrylate (III) is as the following:

Difunctional amido (meth)acrylate

Examples of monofunctional amide-containing (meth)acrylate are those containing at least one amide linkage and at least one (meth)acrylate functionality. Preferred amido (meth)acrylates are those prepared from reaction of gamma-butyrolactone and alkylamine, alkanolamine or alkyl diamine to produce amido alcohols, and the amido alcohols are further reacted with methyl (meth)acrylate by transesterification to produce amido (meth)acrylate and a side product of mono alcohol which may be distilled under vacuum.

The second embodiment of the present invention relates to radiation curable composition with utility as a UV etching resist formulation. The said composition contains the amido (meth)acrylates I, or II or III, in combination with (meth)acrylate half ester generally described in IV:

(Meth)acrylate half ester

R = alkyl, alkene, cycloalkyl, aryl,

The (meth)acrylate half ester described in IV is based on partial esterification of acid anhydride with hydroxyl (meth)acrylates. Examples of acid anhydrides are succinic anhydride, maleic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 4-methylhexahydrophthalic anhydride but not limited to these only. Examples of hydroxyl (meth)acrylates are 2-hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate, but not limited to these only.

The UV etching resist formulation useful in the invention typically contains 60 wt% of (meth)acrylate oligomer, 30-40 wt% of inert fillers, 0.5-1% of phthalocyanin blue pigment, 1-5% of various additives such as slip agent, flow additives and thickening agent, and final 3-5% of photoinitiators. To provide good surface hardness, and alkaline solubility, the (meth)acrylate oligomer must contain both the (Meth)acrylate Half Ester IV, and Amido (meth)acrylate at a ratio of 1 :1 to 4:1. Inert fillers can be micronized talc which typically contains silica, alumina and magnesia, or barium sulfate or clay. Typical photoinitiators can be the type of benzophenone, benzyl dimethyl ketol, or ethyl anthraquinone and any mixture thereof but not limited to this.

A third embodiment of the present invention relates to a radiation curable composition for utility in the UV solder mask formulation. The UV solder mask composition useful in this invention contains Epoxy (meth)acrylate - V, and optionally, the amido (meth)acrylates or Urethane (meth)acrylate - VI .

A preferred epoxy (meth)acrylate is based on reaction of 1 epoxy equivalent from bisphenol-A epoxy (or diglycidyl ether of bisphenol-A) with 0.90- 1.05 equivalent of acrylic or methacrylic acid and simultaneously with 0.01 - 0.10 equivalent of diacid from carboxyl terminated acrylonitrile butadiene (such as commercially available as Hycar CTBN1300Z13 from BF Goodrich). Example of this type of epoxy (meth)acrylate is Ebecryl 3604 from UCB Chemicals.

Another preferred epoxy (meth)acrylate is based on reaction of 1 epoxy equivalent from epoxy phenol novolac (commercially available as EPN1179 or EPN1180 from Ciba Specialty Chemicals or DEN431 or DEN438 from Dow Chemicals) with 0.90-1.05 equivalent of acrylic or methacrylic acid and simultaneously with 0.01 - 0.10 equivalent of diacid from carboxyl terminated acrylonitrile butadiene (such as commercially available as Hycar CTBN1300X13 from BF Goodrich). Epoxy cresol novolac such as ECN1280, and ECN1299 from Ciba Specialty Chemicals can be used to replace the epoxy phenol novolac partially or completely.

In some instances, mixture of 0.05-0.50 epoxy equivalent from diglycidyl ether of bisphenol-A and 0.50-0.95 epoxy equivalent from epoxy phenol novolac can be used in the preparation of the epoxy (meth)acrylate.

Preferred monofunctional amido (meth)acrylates are

Urethane (meth)acrylate useful in this invention contains at least one (meth)acrylate function. Example of monofunctional urethane (meth)acrylate is a reaction product of n-butyl isocyanate with hydroxyl functional (meth)acrylate like 2-HEA, HEMA, HPA or HPMA or mixture thereof. Example of multifunctional urethane methacrylate is those derived from reaction of polyester or polyether diols or triols with diisocyanates and/or triisocyanates, and later capped with hydroxyl functional (meth)acrylates containing 1 to 5 (meth)acrylate functions. Typical diisocyanates are toluene diisocyanates, isophorone diisocyanate, hexamethylene diisocyanates and many more but not limited to these.

Typical composition useful for UV solder mask contains 60-80 wt% epoxy (meth)acrylate, 5-20% amido (meth)acrylate, 5-20% of diluting (meth)acrylate monomers, 10-30 % of inert fillers, 1-2% of phthalocyanin green pigment, 1-5% of additives such as slip agent, flow additives and thickening additives, 0-3% adhesion promoter and 2-5% of photoinitiators. Optionally the amido (meth)acrylate can be replaced partially or completely with urethane (meth)acrylate of 1 -5 (meth)acrylate functionality per molecule of the urethane (meth)acrylate.

Throughout the description and claims of the specification the word

"comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps.

Examples

The utility of the current invention and its advantages are presented below by examples, but is not limited to these examples.

Example 1 : Amido acrylate I In a one litre flask 4.50 mole of Butyl-amine is dissolved in dioxane and the mixture heated 70 °C. At this temperature 4.54 mole of butyrolactone is added drop-wise during 2 hours. Stirring is continued for 9 hours at 110 °C. The reaction mixture is cooled to 80°C and the dioxane distilled under vacuum. At the end traces of dioxane and butyrolactone are removed by distillation under high vacuum.

In a 1 litre flask equipped with a rectifying column a mixture of 1 mole of amido alcohol, 2.5 mole methyl acrylate, polymerisation inhibitors (600 ppm), and 0.58 % dibutyltin oxide catalyst was heated to reflux while air was flushed through.

The column was topped by a varying reflux head to remove the methanol/methyl acrylate mixture. The reaction was considered to be complete when the refractive index of the distillate indicated it to be pure methyl acrylate.

The mixture was cooled to 80°C and the methyl acrylate distilled over under vacuum. (Amido acrylate 2 is prepared similar to Amido Acrylate 1 , but butylamine is replaced by cyclohexylamine).

Example 2: (Meth)acrylate Half Ester

(Meth)acrylate half ester I is prepared by charging 1 mole of hexahydrophthalic anhydride into a 3-neck glass vessel and heated to 60°C under agitation. 0.95 mole of 2-hydroethyl acrylate, 500 ppm hydroquinone, 500 ppm triphenyl stibene and 1000 ppm dilithium carbonate are added to the vessel. The mass is allowed to exotherm to 110°C, and once exotherm completed the mass is hold at this temperature for 2-4 hours. Then 0.05 mole of HEMA is added and the mixture is hold at 110°C for 2-4 hours until all the anhydride is completely opened. This is indicated when the acid value reached the theoretical value of 207 mg KOH/gm.

Methacrylate half ester II is prepared similar to the process above except that all the 1.00 mole of hexahydrophthalic anhydride is reacted to 1.00 mole of hydroxyethyl methacrylate.

Example 3: Application in UV etching resist

Blends of (meth)acrylate half ester and amido (meth)acrylate were evaluated for UV etching resist ink formulation as described in the table I below (all composition is described in parts per hundred resin).

The formulation is applied onto a clean Cu board using a 120T mesh screen with a circuit pattern. Thickness of the applied resist is approximately 10- 12 μm.

Then it is cured under UV light using a medium pressure Hg-lamp of 120 watts per cm power. The dosage applied for curing is approximately 750 mJ/cm². The pencil hardness is evaluated immediately after UV cure using pencils of HB to 9H. Coating hardness of minimum 2H is preferred.

Then the board with cured resist is etched in 35% FeCI₃ solution at 30°C for 5 minutes to etch the unprotected Cu. The resist must not be attacked by the acid solution during this process.

Finally the resist is stripped in 5% NaOH solution at 30°C. The resist must be stripped in at least 20 seconds. Resist that completely dissolved in the solution is preferred. Flakes that dissolved after few hours in the NaOH solution is also sometime preferred. Hard flakes that do not dissolved after few hours is less preferred.

Table 1 - UV Etching Resist Evaluation

Note : * Soft flakes are soluble after few hours in 5% NaOH solution. Example 4.

The amido acrylates are evaluated for solder mask application.

Cu laminated board is first prepared for the ink application by cleaning with dilute acid such as 5-10% HCI or H₂S0 , then rinsed with water and final cleaning with solvent such as acetone or isopropanol. The cleaned board is oven-dried to remove the residual solvent. A Ni-plated board is also prepared in a similar manner.

The prepared ink is applied onto the cleaned Cu or Ni-plated board using a patterned screen with 70-90T mesh at 45 degrees angle. This would typically gives a wet film of 20-30 microns.

The applied ink is cured under a medium pressure Hg vapor lamp with lamp power of 80 watts/cm at a conveyor speed of 3-4 m/minute. This would typically require 3-4 passes with a total UV dosage of 1500-2000 mJ/cm2.

The cured ink is tested for adhesion with a cross cut pattern, hardness with HB to 9H pencils, and soldering resistance.

Soldering resistance is tested by first spraying the flux onto the Cu board with UV solder mask, then board is baked at 170°C for 15 seconds to activate the flux. Then the board is dipped in molten Sn/Pb solder at 260°C for a maximum of 50 minutes. The solder mask is tested for cross cut adhesion. A

100% adhesion after soldering indicates good solder mask property.

Example 5.

The following example describes the utility of urethane (meth)acrylate for adhesion to Ni plated boards, and provide good soldering resistance using different fluxes.

Claims

1. A radiation curable composition for use as a UV etching resist formulation said composition comprising : a) an amido (meth)-acryate according to formula I, II or III : . Monofunctional amido (meth)acrylate :

wherein Ri and R₂ can be alkyl, arylalkyl or cycloalkyl.

Difunctional amido (meth)acrylate :

wherein R is alkyl,

Difunctional amido (meth)acrylate

in combination with : b) a (meth)acrylate half ester.

2. A radiation curable composition according to claim 1 said composition comprising: 30 to 70 wt% (meth)acrylate oligomer; 10 to 40 wt% inert filler; 0.5 to 1.0 wt% phthalocyanin blue pigment; 3 to 5 wt% photo initiators; and 1 to 5 wt% other additives.

3. A composition according to claim 1 or 2 wherein the (meth)acrylate oligomer contains both a (meth)acrylate half ester and an amido (meth)acrylate in a ratio of 1 :1 to 4:1.

4. A composition according to any preceding claim wherein the (meth)acrylate half ester comprises

(Meth)acrylate half ester

R = alkyl, alkene, cycloalkyl, aryl,

5. A radiation curable composition for use in a UV solder mask formulation said composition comprising : i) an epoxy (meth)acrylate and ii) an amido (meth)acrylate according to formula I, II or III:

. Monofunctional amido (meth)acrylate :

wherein Ri and R₂ can be alkyl, arylalkyl or cycloalkyl. Difunctional amido (meth)acrylate

wherein R is alkyl,

Difunctional amido (meth)acrylate

A composition according to claim 5 wherein said epoxy (meth)acrylate is derived from the reaction of diglycidyl ether of bisphenol-A (DGEBA) with (meth)acrylic acid.

7. A composition according to claim 5 wherein said epoxy (meth)acrylate is derived from the reaction of epoxy novolac with (meth)acrylic acid.

8. A composition according to any of claims 5 to 7 wherein said epoxy (meth)acrylate also contains aliphatic diol or butadiene rubber.

9. A composition according to claim 5 wherein said urethane (meth)acrylate is derived from the reaction of n-butyl isocyanate with a hydroxyl functional (meth)acrylate.

10. A composition according to claim 9 wherein said hydroxyl functional (meth)acrylate is selected from the group comprising: 2-hydroxyethyl acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl acrylate, hydroxylpropyl (meth)acrylate.

11. A composition according to claim 5 wherein said composition comprises: 60 to 80 wt% epoxy (meth)acrylate; 5 to 20 wt% amido (meth)acrylate; 5 to 20 wt% (meth)acrylate monomers; 10 - 30 wt% inert fillers; 1 to 2 wt% phthalocyanin green pigment; 1 to 5 wt% other additives; 0 to 3 wt% adhesion promoters; and 2 to 5 wt% photoinitiators.

12. A method for the production of a radiation curable composition wherein said method comprises:

1. reacting gamma-butyrolactone with alkylamine, alkanolamine or alkyl diamine to produce an amido alcohol; and 2. reacting said amido alcohol with methyl (meth)acrylate by transesterification to produce an amido(meth) acrylate and a mono alcohol 3. removing said monoalcohol to provide a substantially pure solution of said amido(meth)acrylate

to produce a composition comprising an Amido (meth)acrylate according to formula I, II or . Monofunctional amido (meth)acrylate :

wherein R-i and R₂ can be alkyl, arylalkyl or cycloalkyl.

. Difunctional amido (meth)acrylate :

wherein R is alkyl,

Difunctional amido (meth)acrylate

13. A method according to claim 12 comprising the following steps:

(i) reacting γ-butyrolactone with alkylamine in dioxane at 110°C for 12-21 hours to produce amido alcohol:

+ H₂N — R H-,0-(CH₂)₃— (NHCO)-R

(ii) transesterification of the amido alcohol with excess of methyl acrylate at 80-100°C using a catalyst (such as dibutyltin dilaurate (DBTDL) or dibutyltin oxide (DBTO)):

(iii) removing alcohol to provide a substantially pure solution of monofunctional amido (meth) acrylate.

14. A method according to claim 12 said method comprising the steps: (i) reacting two moles of γ-butyrolactone for each mole of diamine to produce amido diol;

H₂N— R— NH₂ — »^► HO-(CH₂)₃— (NHCO)-R— (NHCO)(CH₂)₃— OH

(ii) esterification of the amido diol with (meth)acrylic acid and removing water of condensation to provide substantially pure solution of amido (meth)acrylate.

15. A method according to claim 12 said method comprising the steps:

(i) reacting two moles of γ-butyrolactone for each mole of diamine to produce amido diol;

H₂N— R— NH₂ ► HO-(CH₂)₃— (NHCO)-R— (NHCO)(CH₂)₃— OH

(ii) incorporating amido diol in urethane (meth)acrylate by reacting first with diisocyanate and capping with an OH-functional (meth)acrylate.

16. A method according to claim 6 said method comprising the steps :

(i) reacting γ-butyrolactone with alkanolamine to produce an amido diol

+ H₂N — R ► HO-(CH₂)₃— (NHCO)-ROH

17. A method according to claim 12 said method comprising the steps: (i) reacting γ-butyrolactone with alkanolamine to produce an amido diol

18. A method for preparing a curable composition according to claim 17 said method comprising partial esterification of an acid anhydride with an hydroxyl(meth)acrylate.

19. A method according to claim 18 wherein said acid anhydride is selected from succinic anhydride, maleic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride and 4- methylhexahydrophthalic anhydride.

20. A method according to claim 18 or claim 19 wherein said hydroxyl(meth)acrylate is selected from 2-hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate.

21. A method according to claim 12 wherin the alkylamine contains 5 or more than 5 carbon atoms.