Paste and process for forming a solderable polyimide-based polymer thick film conductor

1. A polyimide-based polymer thick film paste composition for forming a solderable polyimide-based polymer thick film conductor, the paste composition comprising:

(a) 60-95 wt % of an electrically conductive metal powder;

(b) 2-6 wt % of a polyimide polymer;

(c) 0.10-0.35 wt % of an organosilicon compound and

(d) an organic solvent,

wherein the wt % are based on the total weight of the paste composition, and wherein the electrically conductive metal powder and the organosilicon compound are dispersed in the organic solvent, and the polyimide polymer is dissolved in the organic solvent and the ratio of the weight of the electrically conductive metal powder to the weight of the polyimide polymer is between 13 and 40.

2. The polyimide-based polymer thick film paste composition of claim 1 , said paste composition comprising: 75-90 wt % of an electrically conductive metal powder.

3. The polyimide-based polymer thick film paste composition of claim 1 , wherein said electrically conductive metal is selected from the group consisting of Ag, Cu, Au, Pd, Pt, Sn, Al, Ni, alloys of Ag, Cu, Au, Pd, Pt, Sn, Al, Ni, one of Ag, Cu, Au, Pd, Pt, Sn, Al, Ni coated with one of Ag, Cu, Au, Pd, Pt, Sn, Al, Ni and mixtures thereof.

4. The polyimide-based polymer thick film paste composition of claim 1 , wherein said electrically conductive metal is selected from the group consisting of Ag, Ag-coated Cu, Ag-coated-Ni and mixtures thereof.

5. The polyimide-based polymer thick film paste composition of claim 1 , wherein said polyimide polymer is represented by formula I:

wherein X is C(CH 3 ) 2 , O, S(O) 2 , C(CF 3 ) 2 , O-Ph-C(CH 3 ) 2 -Ph-O, O-Ph-O— or a mixture of two or more of C(CH 3 ) 2 , O, S(O) 2 , C(CF 3 ) 2 , O-Ph-C(CH 3 ) 2 -Ph-O, O-Ph-O—;

wherein Y is a diamine component or a mixture of diamine components selected from the group consisting of: m-phenylenediamine (MPD), 3,4′-diaminodiphenyl ether (3,4′-ODA), 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl (TFMB), 3,3′-diaminodiphenyl sulfone (3,3′-DDS), 4,4′-(Hexafluoroisopropylidene)bis(2-aminophenol) (6F-AP), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (FDA); 2,3,5,6-tetramethyl-1,4-phenylenediamine (DAM), 2,2-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2-bis[4-(4-aminophenoxyphenyl)] hexafluoropropane (HFBAPP), 1,3-bis(3-aminophenoxy)benzene (APB-133), 2,2-bis(3-aminophenyl)hexafluoropropane, 2,2-bis(4 aminophenyl)hexafluoropropane (bis-A-AF), 4,4′-bis(4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4′[1,3-phenylenebis(1-methyl-ethylidene)], and bisaniline (bisaniline-M) with the proviso that:

i. if X is O, then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS) and 3,4′-diaminodiphenyl ether (3,4′-ODA); BAPP, APB-133, or bisaniline-M;

ii. if X is S(O) 2 , then Y is not 3,3′-diaminodiphenyl sulfone (3,3′-DDS);

iii. if X is C(CF 3 ) 2 , then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (FDA), or 3,3′-diaminodiphenyl sulfone (3,3′-DDS); and

iv. if X is O-Ph-C(CH 3 ) 2 -Ph-O or O-Ph-O—, then Y is not m-phenylene diamine (MPD), FDA, 3,4′-ODA, DAM, BAPP, APB-133, or bisaniline-M.

6. The polyimide-based polymer thick film paste composition of claim 1 , wherein said organosilicon compound is polydimethylsiloxane.

7. The polyimide-based polymer thick film paste composition of claim 1 , wherein said organosilicon compound is a silsesquioxane or an alkoxysilane.

8. An electrical device containing a solderable polyimide-based polymer thick film conductor formed from the polyimide-based polymer thick film paste composition of claim 1 .

9. The electrical device of claim 8 , wherein said organosilicon compound is polydimethylsiloxane.

10. The electrical device of claim 8 , wherein said organosilicon compound is a silsesquioxane or an alkoxysilane.

11. A process for forming a solderable polyimide-based polymer thick film conductor, comprising the steps of:

(i) providing a substrate;

(ii) preparing a paste composition comprising:

(a) 60-95 wt % of an electrically conductive metal powder;

(b) 4-6 wt % of a polyimide polymer;

(c) 0.10-0.35 wt % of a organosilicon compound; and

(d) an organic solvent,

wherein the wt % are based on the total weight of the paste composition, and wherein the electrically conductive metal powder and the organosilicon compound are dispersed in the organic solvent, and the polyimide polymer is dissolved in the organic solvent and the ratio of the weight of the electrically conductive metal powder to the weight of the polyimide polymer is between 13 and 40,

(iii) applying said paste composition in the desired pattern onto said substrate; and

(iv) curing said paste composition applied in step (iii) by heating at a temperature of 320 to 380° C. for at least 30 minutes to form said solderable polyimide-based polymer thick film conductor.

12. The process of claim 11 , wherein after step (iii) but before step (iv) said paste composition applied in step (iii) is dried by heating at a temperature sufficient to remove said organic solvent.

13. The process of claim 12 , wherein said paste composition is cured by heating at a temperature of 330 to 380° C. for at least 1 h to form said solderable polyimide-based polymer thick film conductor.

14. The process of claim 11 , wherein said polyimide polymer is represented by formula I:

wherein X is C(CH 3 ) 2 , O, S(O) 2 , C(CF 3 ) 2 , O-Ph-C(CH 3 ) 2 -Ph-O, O-Ph-O— or a mixture of two or more of C(CH 3 ) 2 , O, S(O) 2 , C(CF 3 ) 2 , O-Ph-C(CH 3 ) 2 -Ph-O, O-Ph-O—;

wherein Y is a diamine component or a mixture of diamine components selected from the group consisting of: m-phenylenediamine (MPD), 3,4′-diaminodiphenyl ether (3,4′-ODA), 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl (TFMB), 3,3′-diaminodiphenyl sulfone (3,3′-DDS), 4,4′-(Hexafluoroisopropylidene)bis(2-aminophenol) (6F-AP), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (FDA); 2,3,5,6-tetramethyl-1,4-phenylenediamine (DAM), 2,2-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2-bis[4-(4-aminophenoxyphenyl)] hexafluoropropane (HFBAPP), 1,3-bis(3-aminophenoxy) benzene (APB-133), 2,2-bis(3-aminophenyl)hexafluoropropane, 2,2-bis(4 aminophenyl)hexafluoropropane (bis-A-AF), 4,4′-bis(4-amino-2-trifluoromethylphenoxy) biphenyl, 4,4′[1,3-phenylenebis(1-methyl-ethylidene)], and bisaniline (bisaniline-M) with the proviso that:

i. if X is O, then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS) and 3,4′-diaminodiphenyl ether (3,4′-ODA); BAPP, APB-133, or bisaniline-M;

ii. if X is S(O) 2 , then Y is not 3,3′-diaminodiphenyl sulfone (3,3′-DDS);

iii. if X is C(CF 3 ) 2 , then Y is not m-phenylenediamine (MPD), bis-(4-(4-aminophenoxy)phenyl)sulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (FDA), or 3,3′-diaminodiphenyl sulfone (3,3′-DDS); and

iv. if X is O-Ph-C(CH 3 ) 2 -Ph-O or O-Ph-O—, then Y is not m-phenylene diamine (MPD), FDA, 3,4′-ODA, DAM, BAPP, APB-133, or bisaniline-M.

15. The process of claim 11 , wherein the substrate is a polyimide, alumina or aluminum.

16. The process of claim 11 , wherein said paste composition is cured by heating at a temperature of 330 to 380° C. for at least I hour to form said solderable polyimide-based polymer thick film conductor.

17. An electrical device containing a solderable polyimide-based polymer thick film conductor formed using the process of claim 11 .