WE CLAIM:
1. A resin composition comprising:
a resin (a);
an antioxidizing agent (b); and
a crosslinking agent (d),
wherein
the resin (a) contains one or more resins selected from a polyimide precursor, a polyamide, a polyimide, polybenzoxazole, and copolymers thereof, and
the crosslinking agent (d) is a crosslinking agent having a phenolic hydroxyl group in one molecule thereof and having substituents each with a molecular weight of 4 0 or more at both ortho positions to the phenolic hydroxyl group.
2. The resin composition according to claim 1, wherein the resin (a) is an alkali-soluble resin having a phenolic hydroxyl group, and the resin composition further contains a naphthoquinonediazide compound (c).
3. The resin composition according to claim 1 or 2, wherein the crosslinking agent (d) is a crosslinking agent having three or more phenolic hydroxyl groups in one molecule.

4. The resin composition according to any one of claims 1 to 3, wherein the antioxidizing agent (b) is an antioxidizing agent having a hindered phenol structure.
5. The resin composition according to any one of claims 1 to 4, wherein the antioxidizing agent (b) contains a compound represented by a general formula' (1): [Chemical Formula 1] .
in the general formula (1), R1 represents a hydrogen atom or an alkyl group having 2 or more carbon atoms; R2 represents an alkylene group having 2 or more carbon atoms; A represents a monovalent to tetravalent organic group containing at least one of an alkylene group having 2 or more carbon atoms, an 0 atom, and an N atom; and k represents an integer of 1 to 4.
6. The resin composition according to any one of claims 1 to 5, wherein the resin (a) has a structural unit represented by a general formula (2): [Chemical Formula 2]

in the general formula (2), R3 to R6 each independently represent an alkylene group having 2 to 10 carbon atoms; a, b and c each represent an integer within ranges of 1 < a < 20, 0 < b < 20 and 0 < c < 20, and arrangement of repeating units may be either in a block manner or in a random manner; and in the general formula (2), * represents a chemical bond.
7. The resin composition according Lo any one of claims
1 to 6, wherein
the resin (a) contains at least a copolymer of a polyamide and a polyimide, and
the polyamide has a structural unit derived from a diamine having an aliphatic group, and a content of the structural unit derived from the diamine having an aliphatic group based on 100% by mole of structural units derived from diamines is in a range of 5 to 40% by mole.
8. The resin composition according to any one of claims
1 to 7, wherein
the resin (a) contains at least a copolymer of a polyamide and a polyimide, and
a content of a structural unit of the polyimide based

on 100% by mole of structural units of the polyamide and the polyimide in total is in a range of 2 to 50% by mole.
9. The resin composition according to any one of claims 1 to 8, further comprising a compound (e) represented by a general formula (3), wherein a content of the compound (e) represented by the general formula (3) based on 100 parts by mass of the resin (a) is in a range of 0.5 to 15 parts by mass, [Chemical Formula 3]
in the general formula (3), R7 to R9 each represent an 0 atom, an S atom, or an N atom, and at least one of R7 to R9 represents an S atom; 1 represents 0 or 1, and m and n represent an integer of 0 to 2; R10 to R12 each independently represent a hydrogen atom or an organic group having 1 to 2 0 carbon atoms.
10. The resin composition according to any one of claims 1 to 9, further comprising a heat-crosslinking agent (f) having a structural unit represented by a general formula (4) below:

[Chemical Formula 4]
in the general formula (4), R13 and R14 each independently represent a hydrogen atom or a methyl group; R15 is a divalent organic group having an alkylene group having 2 or more carbon atoms and may be any of linear, branched, and cyclic.
11. A resin sheet formed from the resin composition according to any one of claims 1 to 10.
12. A cured film obtained by curing the resin composition according to any one of claims 1 to 10.
13. A cured film obtained by curing the resin sheet according to claim 11.
14. The cured film according to claim 12 or 13, which has an elongation at break of 50% or more.
15. A method for producing a relief pattern of a cured film, comprising the steps of:
applying the resin composition according to any one

* - * r T
of claims 2 to 10 onto a substrate or laminating the resin sheet according to claim 11 onto a substrate, followed by drying to form a resin film; applying light via a mask;
eluting or removing an irradiated part with an alkaline solution to perform development; and
heat treating the resin film after the development.
16. The method for producing a relief pattern of a cured film according to claim 15, wherein the step of applying the resin composition onto a substrate, followed by drying to form a resin film includes a step of applying the resin composition onto the substrate using a slit nozzle.
17. A semiconductor electronic component or semiconductor device, comprising the cured film according to any one of claims 12 to 14 disposed as an interlayer insulating film between rewirings of copper metal.
18. The semiconductor electronic component or semiconductor device according to claim 17, wherein the rewirings are composed of oxidized copper metal wirings.
19. The semiconductor electronic component or semiconductor device according to claim 17 or 18, wherein the rewirings are copper metal wirings, and a line width of

'-.;.: * ■ >: * -
the copper metal wirings and an interval between adjacent wirings are 5 urn or less.
20. A semiconductor electronic component or semiconductor device, comprising the cured film according to any one of claims 12 to 14 disposed as an interlayer insulating film between rewirings on a sealing resin substrate on which a silicon chip is disposed.
21. The semiconductor electronic component or semiconductor device according to claims 17 Lo 20, wherein the rewirings are copper metal wirings, and a semiconductor chip and each of the copper metal wirings are further connected via a bump.
22. The semiconductor electronic component or semiconductor device according to claims 17 to 21, wherein a line width of metal wirings and an interval between adjacent wirings decrease as a rewiring layer recited in claim 17 approaches the semiconductor chip.
23. The semiconductor electronic component or semiconductor device according to claims 17 to 22, wherein the interlayer insulating film recited in claim 17 becomes thin in thickness as the interlayer insulating film

approaches the semiconductor chip.
24. An organic EL display device comprising the cured film according to any one .of claims 12 to 14.
25. A method for producing a semiconductor electronic component or semiconductor device, comprising the steps of
disposing the cured film according to any one of claims 12 to 14 as an interlayer insulating film between rewirings on a support substrate on which a temporary sticking material is disposed;
disposing a silicon chip and a sealing resin on the support substrate; and
, then peeling off the rewirings from the support substrate on which the temporary sticking material is disposed.