Flexible, flame-retardant, aqueous-processable photoimageable composition for coating flexible printed circuits

• US 6,218,074 B1
• Filed: 07/21/1999
• Issued: 04/17/2001
• Est. Priority Date: 02/25/1997
• Status: Expired due to Term

• Current Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Dueber, Thomas Eugene, Lee, Yueh-Ling, Schadt, Frank Leonard III
• Primary Examiner(s): Hamilton, Cynthia
• Application Number:
  US09/358,212
• Time in Patent Office: 636 Days
• Field of Search: 430/907, 430/910, 430/284.1, 430/273.1, 522/92, 522/95, 522/75, 522/76, 522/79, 522/74
• US Class Current: 430/273.1
• CPC Class Codes: G03F 7/033 the binders being polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds, e.g. vinyl polymers
• CPC Class Codes: H05K 3/287 Photosensitive compositions
• CPC Class Codes: H05K 3/4676 Single layer compositions
• CPC Class Codes: Y10S 430/108 Polyolefin or halogen containing
• CPC Class Codes: Y10S 430/111 Polymer of unsaturated acid or ester

Abstract

A flexible, flame-retardant, aqueous processable, photoimageable resin composition for forming a permanent, protective coating film for printed circuitry and a multilayer photoimageable element containing a layer of the photoimageable resin composition in combination with a low tack photoimageable resin sublayer and a temporary support film are disclosed. The photoimageable resin composition has excellent aqueous developability and provides a cured coating film having good flexibility, adhesion, solvent resistance, surface hardness, thermal resistance, electrical insulating properties and flame retardancy.

Claims

1. A flexible, flame-retardant, aqueous-processable photoimageable resin composition suitable for forming a flexible permanent, protective coating on a flexible printed circuit board comprising:

(a) a brominated carboxylic copolymer binder formed from (i) a ring-brominated aromatic monomer, (ii) at least one of an alkyl acrylate, alkyl methacrylate or a non-brominated aromatic monomer, wherein alkyl contains from 1 to 20 carbon atoms, and (iii) an ethylenically unsaturated carboxylic acid monomer, said binder having a weight average molecular weight (M_W) of from 40,000 to 500,000 and containing from 3 to 40% bromine by weight;

(b) a non-brominated low molecular weight copolymer binder having a weight average molecular weight (M_W) of from 2,000 to 10,000, which is the reaction product of a primary amine with a copolymer formed from at least one ethylenically unsaturated dicarboxylic acid anhydride and at least one ethylenically unsaturated comonomer and containing at least one structural unit A and at least one additional structural unit selected from B₁, B₂, and combinations thereof containing carboxyl groups, wherein;

(i) 5 to 50 percent by weight of said low molecular weight copolymer binder is formed from at least one structural unit B₁, B₂ or combination thereof containing carboxyl groups;

(ii) 50 to 95 percent by weight of said low molecular weight copolymer binder is formed from structural unit A, wherein A is different from structural units B₁ and B₂; and

(iii) A, B₁ and B₂ have the structures;

wherein R₁ is H, alkyl or aryl;

R₂ is H, CH₃, aryl, —

COOR₇, —

CONR₈R₉ or —

CN;

R₃ and R₄ independently are H or al;

R₅ is alkyl aryl or aryl which is substituted with primary amino, secondary amino, tertiary amino, hydroxy or ether groups or mixtures thereof;

R₆ is —

OH or NHR₅; and

R₇, R₈ and R₉ independently are H, alkyl, aryl or aryl substituted with one or more hydroxy, ester, keto, ether or thioether groups;

wherein alkyl in any of the above R groups contains from 1 to 6 carbon atoms;

(c) an acrylated urethane monomeric component containing from 0 to 20% bromine by weight;

(d) a brominated acrylated monomer containing from 10 to 80% bromine by weight with the proviso that (d) is not a urethane monomeric component;

(e) a brominated additive containing from 10 to 85% bromine by weight with the proviso that (e) is not an acrylated monomeric component or a blocked polyisocyanate crosslinking agent;

(f) a photoinitiator or a photoinitiator system; and

(g) a blocked polyisocyanate crosslinking agent containing from 0 to 30% bromine by weight,

wherein the total content of bromine in the composition is in a range from 5 to 50% by weight, and further wherein when the composition is applied to a substrate with circuit lines, cured at a temperature greater than 100°

C. for one hour, the cured composition is capable of being bent and creased at an angle 90°

to the circuit lines without the formation of cracks or delaminations.

2. The photoimageable resin composition of claim 1 comprising, based on the total weight of the composition, from 10 to 60% by weight of the brominated carboxylic copolymer binder (a);

from 2 to 15% by weight of the non-brominated copolymer binder (b);

from 5 to 30% by weight of the acrylated urethane monomeric component (c);

from 5 to 40% by weight of the brominated acrylated monomer (d);

from 1 to 40% by weight of the brominated additive (e);

from 0.01 to 10% by weight of the photoinitiator system (f); and

from 2 to 20% by weight of the blocked polyisocyanate crosslinking agent (g).

3. The photoimageable resin composition of claim 2 comprising, based on the total weight of the composition, from 25 to 45% by weight of the brominated carboxylic copolymer binder (a);

from 3 to 10% by weight of the non-brominated copolymer binder (b);

from 8 to 20% by weight of the acrylated urethane monomeric component (c);

from 10 to 30% by weight of the brominated acrylated monomer (d);

from 2 to 20% by weight of the brominated additive (e);

from 0.01 to 5% by weight of the photoinitiator system (f); and

from 5 to 15% by weight of the blocked polyisocyanate crosslinking agent (g).

4. The photoimageable resin composition of claim 1 wherein the brominated carboxylic copolymer binder (a) comprises, the polymerized reaction ii product of (i) from 5 to 55% by weight of a ring-brominated aromatic monomer, (ii) from 20 to 92% by weight of at least one of an alkyl acrylate, alkyl methacrylate or a non-brominated aromatic monomer, and (iii) from 3 to 25% by weight of an ethylenically unsaturated carboxylic acid monomer based on the total weight of the copolymer.

5. The photoimageable resin composition of claim 4 wherein the ring-brominated aromatic monomer (i) is selected from styrene, methylstyrene, alpha-methylstyrene, alpha-methyl methylstyrene, ethylstyrene, alpha-methyl ethylstyrene, and combinations thereof, said monomers having mono, di, tri, or tetra bromine substitution in the phenyl nucleus.

6. The photoimageable resin composition of claim 5 wherein the ring-brominated aromatic monomer (i) is dibromostyrene.

7. The photoimageable resin composition of claim 4 wherein the alkyl acrylate or alkyl methacrylate monomer (ii) is selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-heptyl (meth)acrylate, isoheptyl (meth)acrylate, n-methylheptyl (meth)acrylate, n-octyl (meth)acrylate, 6-methylheptyl (meth)acrylate, n-nonyl (meth)acrylate, 3,5,5-trimethyl (meth)acrylate, n-decyl (meth)acrylate and lauryl (meth)acrylate.

8. The photoimageable resin composition of claim 7 wherein the alkyl acrylate or alkyl methacrylate monomer (ii) is selected from ethyl acrylate, n-propyl acrylate, n-butyl acrylate and methyl methacrylate.

9. The photoimageable resin composition of claim 4 wherein the non-brominated aromatic monomer (ii) is selected from styrene, methyl styrene, alpha-methyl styrene, alpha-methyl methylstyrene, ethylstyrene, alpha-methyl ethylstyrene, benzylacrylate and benzyl methacrylate.

10. The photoimageable resin composition of claim 4 wherein the ethylenically unsaturated carboxylic acid monomer (iii) is selected from acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumuaric acid.

11. The photoimageable resin composition of claim 10 wherein the ethylenically unsaturated carboxylic acid monomer is selected from methacrylic acid and acrylic acid.

12. The photoimageable resin composition of claim 1 wherein the non-brominated low molecular weight copolymer binder (b) comprises the reaction product of a primary amine with a copolymer formed by polymerization of an ethylenically unsaturated dicarboxylic acid anhydride and an ethylenically unsaturated comonomer.

13. The photoimageable resin composition of claim 12 wherein the ethylenically unsaturated dicarboxylic acid anhydride is selected from maleic acid anhydride, itaconic acid anhydride and citraconic acid anhydride.

14. The photoimageable resin composition of claim 12 wherein the primary amine is unsubstituted or substituted with a group selected from primary amino, secondary amino, tertiary amino, hydroxy, ester, keto, ether and thioether groups.

15. The photoimageable resin composition of claim 12 wherein the ethylenically unsaturated comonomer is selected from styrene, (meth)acrylic acid, (meth)acrylamides and (meth)acrylates.

16. The photoimageable resin composition of claim 12 wherein the non-brominated low molecular weight copolymer binder (b) comprises the reaction product of n-butyl amine with a copolymer of styrene, butyl meth-acrylate, butyl acrylate and itaconic acid anhydride.

17. The photoimageable resin composition of claim 12 wherein the non-brominated low molecular weight copolymer binder (b) has a weight average molecular weight (M_W) ranging from 3,000 to 6,000.

18. The photoimageable resin composition of claim 1 wherein the acrylated urethane monomeric component (c) is a urethane diacrylate comprising the reaction product of 2,6-toluene diisocyanate with a polyol with the end isocyanate groups end-capped with hydroxyethyl acrylate.

19. The photoimageable resin composition of claim 1 wherein the acrylated urethane monomeric component (c) is a brominated urethane diacrylate selected from the reaction product of dibromoneopentyl glycol with hexamethylene diisocyanate and end-capped with hydroxyethyl acrylate;

the reaction product of bis(2-hydroxyethylether) of tetrabromobisphenol-A with hexamethylene diisocyanate and end-capped with hydroxyethyl acrylate; and

the reaction product of dibromoneopentyl glycol and polyols with aliphatic or aromatic diisocyanates and end-capped with hydroxyethyl acrylate.

20. The photoimageable resin composition of claim 1 wherein the brominated acrylated monomer (d) contains at least one (meth)acryloyloxy group.

21. The photoimageable resin composition of claim 20 wherein the brominated acrylated monomer (d) is selected from bis-(3-methacryloyloxy-2-hydroxypropyl) ether of tetrabromobisphenol-A, bis3-acryloyloxy-2-hydroxypropyl) ether of tetrabromobis-phenol-A, bis-(2-methacryloyloxyethyl) ether of tetrabromobisphenol-A, bis-(2-acryloyloxyethyl) ether of tetrabromobisphenol-A, 2-tribromophenoxyethyl methacrylate, 2-(2-tribromophenoxyethoxy) ethyl acrylate, tribromophenyl acrylate, pentabromobenzyl acrylate, pentabromobenzyl methacrylate, tribromoneo-pentyl acrylate, and the reaction products of diepoxy oligomers of tetrabromobisphenol-A and epichlorohydrin with acrylic acid or methacrylic acid which are further reacted with succinic anhydride.

22. The photoimageable resin composition of claim 1 wherein the broniinated additive (e) is selected from mixed esters of 3,4,5,6-tetrabromo-1,2-benzene dicarboxylic acid with diethylene glycol and a glycol selected from propylene glycol and ethylene glycol;

bis-(2-hydroxyethyl) ether of tetrabromobisphenol-A;

2,2-bis-(bromomethyl)-3-bromo-1-propanol;

2,2-bis(bromomethyl)-1,3-propanediol;

di-(tribromophenolate) of tetrabromobisphenol-A diglycidyl ether and succinic esters thereof;

tetrabromobisphenol-A;

brominated poly(p-vinylphenol); and

poly(dibromophenylene oxide).

23. The photoimageable resin composition of claim 1 wherein the brominated additive (e) is selected from di-2-ethylhexyl tetrabromophthalate and tris-(dibromophenyl) phosphate.

24. The photoimageable resin composition of claim 1 wherein the brominated additive (e) comprises a flame-retardant, brominated filler compound.

25. The photoimageable resin composition of claim 24 wherein the flame-retardant, brominated filler compound is selected from ethylene bis-(tetrabromophthalimide), decabromodiphenyl oxide, bis-(tribromophenoxy) ethane and poly(pentabromobenzyl) acrylate.

26. The photoimageable resin composition of claim 1 wherein the blocked polyisocyanate crosslinking agent (g) is selected from aliphatic, cycloaliphatic, aromatic and arylaliphatic di, tri and tetraisocyanates, wherein the isocyanate groups are blocked by a compound selected from betacarbonyls, hydroxamates, triazoles, imidazoles, tetrahydropymmidines, lactams, ketoximes, oximes, low molecular weight alcohols, phenols, and thiophenols.

27. The photoimageable resin composition of claim 26 wherein the blocked polyisocyanate crosslinking agent (g) is selected from the trimer of 1,6-diisocyanatohexane blocked with methylethyl ketoxime;

isophorone diisocyanate blocked with methyl ethyl ketoxime; and

the reaction products of 1,6-diisocyanatohexane or trimer thereof with bis-(2-hydroxyethyl-ether) of tetrabromobisphenol-A blocked with methyl ethyl ketoxime.

28. The photoimageable resin composition of claim 1 comprising (a) from 25 to 45% by weight of a brominated carboxylic copolymer derived from the reaction of dibromostyrene, ethyl acrylate and acrylic acid and having a weight average molecular weight (M_W) of from 40,000 to 500,000 and containing from 5 to 30% bromine by weight;

(b) from 3 to 10% by weight of a non-brominated copolymer binder comprising a copolymer of itaconic anhydride, itaconic acid, butyl acrylate, butyl methacrylate and styrene reacted with n-butylamine having a M_W of 4,000;

(c) from 8 to 20% by weight of a urethane diacrylate derived from the reaction of 2,6-toluene diisocyanate and a polyol and end-capped with hydroxyethyl acrylate;

(d) from 10 to 30% by weight of a brominated diacrylate derived from the reaction of tetrabromobisphenol-A diglycidyl ether with acrylic acid and containing from 10 to 80% bromine by weight;

(e) from 2 to 20% by weight of a reactive mixed diester of 3,4,5,6tetrabromo-1,2-benzene dicarboxylic acid with diethylene glycol and propylene glycol containing from 10 to 85% bromine by weight;

(1) from 0.01 to 5% by weight of a photoinitiator system; and

(g) from 5 to 15% by weight of a methyl ethyl ketoxime blocked 1,6-diisocyanato-hexane trimer thermal crosslinking agent.

29. A flexible, flame-retardant, aqueous developable multilayer, photoimageable permanent coating element capable of adhering to a printed circuit board and withstanding molten solder after cure, comprising:

(1) a temporary support film;

(2) a first layer of a photoimageable permanent coating composition comprising;

(a′

) an amphoteric binder;

(b′

) a carboxyl group containing copolymer binder of the formula

wherein R₁₃ is H or C_1-4 alkyl;

R₁₄ is phenyl or —

CO₂R₁₅; and

R₁₅ is H or C_1-4 alkyl which can be substituted with one or more hydroxy groups;

(c′

) a monomer component containing at least two ethylenically unsaturated groups; and

(d′

) a photoinitiator or photoinitiator system;

(3) a second layer of a photoimageable permanent coating composition comprising;

(a) a brominated carboxylic copolymer binder formed from (i) a ring-brominated aromatic monomer, (ii) at least one of an alkyl acrylate, alkyl methacrylate or a non-brominated aromatic monomer, wherein alkyl contains from 1 to 20 carbon atoms, and (iii) an ethylenically unsaturated carboxylic acid monomer, said binder having a weight average molecular weight (M_W) of from 40,000 to 500,000 and containing from 3 to 40% bromine by weight;

(b) a non-brominated low molecular weight copolymer binder having a weight average molecular weight (M_W) of from 2,000 to 10,000, which is the reaction product of a primary amine with a copolymer formed from at least one ethylenically unsaturated dicarboxylic acid anhydride and at least one ethylenically unsaturated comonomer and containing at least one structural unit A and at least one additional structural unit selected from B₁, B₂, and mixtures thereof containing carboxyl groups, wherein;

(i) 5 to 50 percent by weight of said low molecular weight copolymer binder is formed from at least one structural unit B₁, B₂ or combination thereof containing carboxyl groups;

(ii) 50 to 95 percent by weight of said low molecular weight copolymer binder is formed from structural unit A, wherein A is different from structural units B₁ and B₂, and

(iii) A, B₁ and B₂ have the structures;

wherein R₁ is H, alkyl or aryl;

R₂ is H, CH₃, aryl, —

COOR₇, CONR₈R₉ or —

CN;

R₃ and R₄ independently are H or alkyl;

R₅ is alkyl, aryl or aryl which is substituted with primary amino, secondary amino, tertiary amino, hydroxy or ether groups or mixtures thereof;

R₆ is —

OH or NHR₅; and

R₇, R₈ and R₉ independently are H, alkyl, aryl or aryl substituted with one or more hydroxy, ester, keto, ether or thioether groups;

wherein alkyl in any of the above R groups contains from 1 to 6 carbon atoms;

(c) an acrylated urethane monomeric component containing from 0 to 20% bromine by weight;

(d) a brominated acrylated monomer containing from 10 to 80% bromine by weight with the proviso that (d) is not a urethane monomeric component;

(e) a brominated additive containing from 10 to 85% bromine by weight with the proviso that (e) is not an acrylated monomeric component or a blocked polyisocyanate crosslinking agent;

(f) a photoinitiator or a photoinitiator system; and

(g) a blocked polyisocyanate crosslinking agent containing from 0 to 30% bromine by weight,

wherein the total content of bromine in the second layer composition is in a range from 5 to 50% by weight, and further wherein when the composition is applied to a substrate with circuit lines, cured at a temperature greater than 100°

C. for one hour, the cured composition is capable of being bent and creased at an angle 900 to the circuit lines without the formation of cracks or delaminations.

30. The multilayer, photoimageable coating element of claim 29 wherein the first layer of photoimageable coating (2) is interposed between the temporary support film (1) and the second layer of photoimageable coating (3).

31. The multilayer, photoimageable coating element of claim 30 firer comprising a temporary support film on the surface of the second layer of photoimageable coating (3).

32. The multilayer, photoimageable coating element of claim 31 wherein the first layer of photoimageable coating (2) releases from the temporary support film (1) before the second layer of photoimageable coating (3) releases from the adjacent-temporary support film.

33. The multilayer, photoimageable coating element of claim 29 wherein the second layer of photoimageable coating (3) is interposed between the temporary support film (1) and the first layer of photoimageable coating (2).

34. The multilayer, photoimageable coating element of claim 33 further comprising a removable cover film on the surface of the first layer of photoimageable coating (2).

35. The multilayer, photoimageable coating element of claim 34 wherein the first layer of photoimageable coating (2) releases from the removable cover film before the second layer of photoimageable coating (3) releases from the temporary support film (1).

36. The multilayer, photoimageable coating element of claim 34 wherein the removable cover film is selected from polyester, silicone treated polyester, polyethylene and polypropylene.

37. The multilayer, photoimageable coating element of claim 36 wherein at least one surface of the removable cover film has a matte or an embossed finish.

38. The multilayer, photoimageable coating element of claim 37 wherein the removable cover film contains inorganic filler particles.

39. The multilayer, photoimageable coating element of claim 29 wherein the temporary support film (1) is selected from polyamides, polyolefins, polyesters, vinyl polymers and cellulose esters.

40. The multilayer, photoimageable coating element of claim 39 wherein the temporary support film (1) is polyethylene terephthalate having a thickness of from 6 to 200 microns.

41. The multilayer, photoimageable coating element of claim 39 wherein at least one surface of the temporary support film (1) has a matte or an embossed finish.

42. The multilayer, photoimageable coating element of claim 41 wherein the temporary support film (1) contains inorganic filler particles.

43. The multilayer, photoimageable coating element of claim 29 wherein the composition of the fist layer of photoimageable permanent coating comprises (a′

) from 5 to 25% by weight of amphoteric binder;

(b′

) from 30 to 80% by weight of carboxylic copolymer binder;

(c′

) from 5 to 30% by weight of an ethylenically unsaturated monomer; and

(d′

) from 0.50 to 10% by weight of a photoinitiator or photoinitiator system.

44. The multilayer, photoimageable coating element of claim 43 wherein the amphoteric binder comprises a copolymer derived from the copolymerization of (i) from 30 to 60% by weight of an N—

C_1-12 alkyl acrylamide or methacrylamide or a C_1-4 alkyl aminoalkyl acrylate or methacrylate;

(ii) from 10 to 20% by weight of an acidic comonomer selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid and the C_1-4 alkyl half esters of maleic and fumaric acid; and

(iii) from 20 to 55% by weight of a comonomer selected from the group consisting of C_1-12 alkyl(meth)-acrylates, C_2-4 hydroxyalkyl(meth)acrylates and hydroxystearyl-(meth)acrylates, based on the total weight of the copolymer.

45. The multilayer, photoimageable coating element of claim 44 wherein the amphoteric binder comprises a copolymer of from 35 to 45% by weight of N-tertiary octyl acrylamide, from 12 to 18% by weight of acrylic or methacrylic acid, from 32 to 38% by weight of methyl methacrylate, from 2 to 10% by weight of hydroxypropyl acrylate and from 2 to 10% by weight of C _1-4 alkyl aminoalkyl(meth)-acrylate, based on the total weight of the copolymer.

46. The multilayer, photoimageable coating element of claim 43 wherein the ethylenically unsaturated monomer component is selected from hexamethylene glycol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, polyoxyethylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, bisphenol A diacrylate, di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di(3-acryloxy-2-hydroxypropyl) ether of tetrabromobisphenol-A, aliphatic urethane diacrylate and aromatic urethane diacrylate.

47. The multilayer, photoimageable coating element of claim 29 wherein the composition of the second layer of photoimageable permanent coating comprises, based on the total weight of the composition, from 10 to 60% by weight of the brominated carboxylic copolymer binder (a);

from 2 to 15% by weight of the non-brominated copolymer binder (b);

from 5 to 30% by weight of the acrylated urethane monomeric component (c);

from 5 to 40% by weight of the brominated acrylated monomer (d);

from 1 to 40% by weight of the brominated additive (e);

from 0.01 to 10% by weight of the photoinitiator system (f); and

from 2 to 20% by weight of the blocked polyisocyanate crosslinking agent (g).

48. The multilayer, photoimageable coating element of claim 47 wherein the composition of the second layer of photoimageable permanent coating comprises (a) from 25 to 45% by weight of a brominated carboxylic copolymer derived from the reaction of dibromostyrene, ethyl acrylate and acrylic acid and having a weight average molecular weight (M_W) of from 40,000 to 500,000 and containing from 5 to 30% bromine by weight;

(b) from 3 to 10% by weight of a non-brominated copolymer binder comprising a copolymer of itaconic anhydride, itaconic acid, butyl acrylate, butyl methacrylate and styrene reacted with n-butylamine having a M_W of 4,000;

(c) from 8 to 20% by weight of a urethane diacrylate derived from the reaction of 2,6-toluene diisocyanate and a polyol and end-capped with hydroxyethyl acrylate;

(d) from 10 to 30% by weight of a brominated diacrylate derived from the reaction of tetrabromobisphenol-A diglycidyl ether with acrylic acid and containing from 10 to 80% bromine by weight;

(e) from 2 to 20% by weight of a reactive mixed ester of 3,4,5,6-tetrabromo-1,2-benzene dicarboxylic acid with diethylene glycol and propylene glycol containing from 10 to 85% bromine by weight;

(f) from 0.01 to 5% by weight of a photoinitiator system; and

(g) from 5 to 15% by weight of a methyl ethyl ketoxime blocked 1,6-diisocyanato-hexane trimer thermal crosslinking agent.