CONDUCTIVE PASTE COMPRISING LUBRICATING OILS AND SEMICONDUCTOR DEVICE

Abstract

The invention relates to a conductive paste, comprising from 50 to 97 wt % of electrically conductive particles, 3 to 50 wt % of an organic medium and 0 to 20 wt % of a glass frit, the organic medium comprising a solvent, wherein the organic medium additionally comprises 10 to 90 wt % of a hydrocarbon-based lubricating oil and 2 to 60 wt % of a polymeric component, each based on the total amount of the organic medium, the polymeric component having a solubility of at least 100 g/kg in the lubricating oil. The invention further relates to a semiconductor device comprising a semiconductor substrate with at least one surface onto which an electrically conductive pattern is printed by using the paste.

Claims

1. A conductive paste, comprising: from 50 to 97 wt % of electrically conductive particles, from 3 to 50 wt % of an organic medium, and from 0 to 20 wt % of a glass frit, wherein the organic medium comprises a solvent, from 10 to 90 wt % of a hydrocarbon-based lubricating oil, and from 2 to 60 wt % of a polymeric component, each based on a total amount of the organic medium, and the polymeric component has a solubility of at least 100 g/kg in the lubricating oil.

2. The conductive paste according to claim 1, wherein the polymeric component is a polyacrylate, a polymethacrylate, a copolymer of polyacrylate or polymethacrylate, or a mixture thereof.

3. The conductive paste according to claim 1, wherein the polymeric component is a polymethacrylate with a formula ##STR00003## in which n is a whole number and R is a linear or branched C.sub.1- to C.sub.22-alkyl.

4. The conductive paste according to claim 1, wherein the polymeric component has a relative weight average molecular weight ranging from 10,000 g/mol to 1,000,000 g/mol.

5. The conductive paste according to claim 1, wherein the hydrocarbon-based lubricating oil is at least one selected from the group consisting of a naphthenic oil, a paraffinic oil, an aromatic oil, and a natural oil.

6. The conductive paste according to claim 1, wherein the hydrocarbon-based lubricating oil has a viscosity ranging from 1 to 40 mm.sup.2/s at a temperature of 100 C.

7. The conductive paste according to claim 1, wherein the electrically conductive particles comprise carbon or silver, gold, aluminum, platinum, palladium, tin, nickel, cadmium, gallium, indium, copper, zinc, iron, bismuth, cobalt, manganese, molybdenum, chromium, vanadium, titanium, tungsten, or a mixture or an alloy thereof or are in a form of a core-shell structure thereof.

8. The conductive paste according to claim 1, wherein the electrically conductive particles are coated with an organic additive.

9. The conductive paste according to claim 1, wherein the solvent comprises at least one liquid organic component containing at least one oxygen atom.

10. The conductive paste according to claim 9, wherein the solvent additionally comprises 5 to 50 wt % of at least one dibasic ester.

11. The conductive paste according to claim 1, further comprising: from 0.1 to 20 wt % of at least one additive selected from the group consisting of a surfactant, a thixotropic agent, a plasticizer, a defoamer, a desiccant, a crosslinkers, a complexing agent, and a conductive polymer particle.

12. A semiconductor device, comprising a semiconductor substrate with at least one surface onto which an electrically conductive pattern is printed by using the paste according to claim 1.

13. The semiconductor device according to claim 12, wherein the semiconductor substrate is based on silicon.

14. The semiconductor device according to claim 12, wherein an anti-reflection layer is formed onto the semiconductor substrate and the electrically conductive pattern is printed onto the anti-reflection layer.

15. The semiconductor device according to claim 12, wherein the semiconductor device is a photovoltaic cell and the electrically conductive pattern has conductive gridlines.

Description

EXAMPLES

[0046] In the examples, paste compositions according to the following table have been used:

TABLE-US-00001 TABLE 1 Compositions of the pastes of the comparative example and the examples Comparative Examples 1-4 Example 5 Example 6 Weight % Weight % Weight % Weight % Ag powder 88.3 88.3 88.5 88.5 Glass frit 2.5 2.5 2.5 2.5 Surfactant 0.3 0.3 0.3 0.3 Thixotrope 0.1 0.1 0.1 0.1 Thickener 0.1 0.1 0.1 0.1 Ethyl cellulose 0.2 0.2 0.2 0.2 Solvent Type A 2.1 1.5 1.7 1.7 Solvent Type B 5.4 4.1 4.1 4.1 Hydrocarbon 1.9 2.1 2.1 oil with 20 to 50 carbon atoms Organic binders 1 polymeric 1 0.4 0.4 component in oil Sum 100 100 100 100

[0047] The silver powder used had a mean particle diameter of 0.5 m to 2.5 m. As glass frit, a leaded frit has been used. Solvent type A is a dibasic ester and Solvent type B is a mixture of a glycol, a glycol ether and a fatty acid ester.

[0048] The polymeric component is a polymethacrylate of the general formula

##STR00002##

[0049] In the examples copolymers of different polymethacrylates with different alkyls as group R have been used. In the following the polymethacrylates are described in the form CxMA, where Cx is the number of carbon atoms in the group R. C1MA for example is a polymethacrylate with methyl as R and C12MA is a poylmethacrylate with C.sub.12H.sub.25 as R. The amount of the different polymethacrylates in the polymeric component is in % by weight based on the total mass of the polymeric component. All other percentage data is based on the total mass of the paste.

COMPARATIVE EXAMPLE

[0050] 1% to 3% of solvent type A and 3.5% to 6% of solvent type B are mixed first. 0.05% to 0.4% by weight ethyl cellulose is dissolved in this solvent mixture to form the ethyl cellulose medium, which is mixed further with 0.2% to 2% polyisobutyl methacrylate (organic binder), 0 to 2% surfactant, 0 to 1% thickner, 0 to 1% thixotrope have been added to form a uniform medium. All percentage values are wt % based on total amount of paste. The mixture has been homogenized by mechanical stirring and elevated temperature. Glass frit and metal powders are added to the medium in an incremental step to ensure that they are well dispersed in the medium. The powder-medium mixture is milled with triple-roll-mill to get a uniformly dispersed paste.

[0051] To compare Examples 1 to 6 with the Comparative Example, same silver powder, glass frit, surfactant, thickener, thixotrope and ethyl cellulose are used.

Example 1

[0052] The paste is prepared following the same procedures as in the Comparative Example, except that no organic binder is added, and instead, polymeric component with lubricating oil are added. The concentration of the mixture of solvents type A and type B is reduced accordingly to keep the same amount of organic liquid in the paste. In this example, the polymeric component is a copolymer of 25% C1MA+40% C12MA+35% C17MA, with a molecular weight M.sub.w of 127,000 g/mol and PDI=4.6.

Example 2

[0053] The paste is prepared following the same procedures as in the Comparative Example, except that no organic binder is added, and instead, polymeric component with petroleum oil are added. The concentration of the mixture of solvents type A and type B is reduced accordingly to keep the same amount of organic liquid in the paste. In this example, the polymeric component is a copolymer of 25% C1MA+75% C18MA with Mw of 57,100 g/mol, PDI=3.9.

Example 3

[0054] The paste is prepared following the same procedures as in the Comparative Example, except that no organic binder is added, and instead, polymeric component with petroleum oil are added. The concentration of the mixture of solvents type A and type B is reduced accordingly to keep the same amount of organic liquid in the paste. In this example, the polymeric component is a copolymer of 25% C1MA+75% C18MA with Mw of 28,000 g/mol, PDI=2.9.

Example 4

[0055] The paste is prepared following the same procedures as in the Comparative Example. In this example, the polymeric component is a copolymer of 25% C1MA+75% C18MA with Mw of 21,000 g/mol, PDI=2.7. The slightly difference of the polymeric component does not generate any measurable difference in printability when compared to Example 3.

Example 5

[0056] The paste is prepared following the same procedures as in the Comparative Example. In this example, the polymeric component is a copolymer of 25% C1MA+20% C17MA+55% C18MA with Mw of 529,000 g/mol, PDI=3.4. In this case, the polymeric component generates higher viscosity than the organic binder solution in the Comparative Example, therefore to the knowledge of a person skilled in the art, polymeric component concentration is adjusted slightly, but still in the range defined by Comparative Example. The printed result has less seepage than Comparative Example.

Example 6

[0057] The paste is prepared following the same procedures as in the Comparative Example. In this example, the polymeric component is 100% C18MA with Mw of 936,000 g/mol, PDI=7.1. In this case, the polymeric component generates higher viscosity than the organic binder solution in the Comparative Example, therefore to the knowledge of a person skilled in the art, polymeric component concentration is adjusted slightly, but still in the range defined by Comparative Example.

[0058] The pastes of the comparative example and examples 1 to 3 are screen printed onto solid substrates with the following printing conditions.

Printing Conditions:

[0059]

TABLE-US-00002 print speed flood speed pressure snap off [mm/s] [mm/s] [N] [mm] 180 300 100 2.0

Screen Parameters:

[0060] Comparative Example and Example 1 are printed with Screen A.

TABLE-US-00003 Mesh- Finger- Thread Fabric count opening EOM Tension Angle diameter thickness 325 37 m 12 m 24 N 30 16 m 28 m

[0061] Example 1-3 are printed with Screen B.

TABLE-US-00004 Mesh- Finger- Thread Fabric count opening EOM Tension Angle diameter thickness 325 30 m 12 m 24 N 30 16 m 28 m

[0062] The printed lines are examined under an optical 3D microscope for line dimension evaluations. The results are shown in FIGS. 1 to 5.

[0063] In the figures,

[0064] FIG. 1 shows the printed line of the comparative example with Screen A,

[0065] FIG. 2 shows the printed line of Example 1 with Screen A,

[0066] FIG. 3 shows the printed line of Example 1 with screen B

[0067] FIG. 4 shows the printed line of Example 2 with Screen B and

[0068] FIG. 5 shows the printed line of Example 3 with Screen B.

[0069] It can be seen in the figures, that the line printed with the paste according to the comparative example is wider than those printed with pastes according to the invention. Further, the seepage of the lines printed with pastes according to the invention are significantly reduced, thus a narrower line width. The line height variations are reduced as well. All the prints do not show line interruptions. Therefore, it is clearly demonstrated the Examples generating better printing results than the Comparative Example.