System and method for curing conductive paste using induction heating

• US 10,115,856 B2
• Filed: 10/31/2016
• Issued: 10/30/2018
• Est. Priority Date: 10/31/2016
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Tesla Inc.
• Inventors: Zajac, Piotr
• Primary Examiner(s): Seven, Evren
• Application Number:
  US15/339,573
• Publication Number:
  US 20180122979A1
• Time in Patent Office: 729 Days
• Field of Search: None
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/043 Mechanically stacked PV cells
• CPC Class Codes: H01L 31/0504 specially adapted for series or parallel connection of solar cells in a module
• CPC Class Codes: H01L 31/188 Apparatus specially adapted for automatic interconnection of solar cells in a module
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

One embodiment can provide a system for curing conductive paste applied on photovoltaic structures using induction heating. The system can include a wafer carrier for carrying a plurality of photovoltaic structures and an induction heater. The wafer carrier can include a surface element that is in direct contact with the photovoltaic structures and is substantially thermally insulating. The induction heater can be positioned above the wafer carrier. The induction heater can include a heating coil and core that do not directly contact the photovoltaic structures.

Claims

1. A system for curing conductive paste applied on a plurality photovoltaic structures, comprising:

a wafer carrier for carrying the photovoltaic structures on a first side of the wafer carrier, wherein the wafer carrier includes a base and a strip carrier that is in direct contact with the photovoltaic structures; and

a heater positioned on the first side of the wafer carrier, wherein the heater includes an induction coil configured to operate near the photovoltaic structures, thereby providing localized induced heat for curing the conductive paste, and

two shields positioned on the first side of the wafer carrier and configured to shield a magnetic field caused by the induction coil from metallic parts of the photovoltaic structures other than the conductive paste, wherein a gap between the two shields allows the conductive paste to be exposed to the magnetic field produced by the induction coil.

2. The system of claim 1, wherein the strip carrier is made of polybenzimidazole (PBI) plastic.

3. The system of claim 1, wherein the strip carrier is patterned such that a fraction of a surface of the strip carrier is in contact with the photovoltaic structures.

4. The system of claim 1, wherein the strip carrier includes a number of components separated by air gaps to allow an individual component to expand when heated.

5. The system of claim 1, wherein the conductive paste has an induced temperature between 150 and 300°

C.

6. The system of claim 1, wherein the heater further includes a core housing element and a power supply providing an alternating current to the induction coil.

7. The system of claim 6, wherein the heater further includes a non-conductive, heat resistant, low magnetic permeability cooling enclosure enclosing the housing element and the induction coil.

8. The system of claim 6, wherein the induction coil is made of a material having a thermal conductivity between 350 and 450 W/(m·

k) and an electrical conductivity between 59 and 65×

10^6 S·

m.

9. The system of claim 6, wherein the core housing is made of a material having a magnetic permeability between 0.001 and 1.0 H/m.

10. The system of claim 1, wherein the induction heater is positioned approximately 0.1 to 4 millimeters from the conductive paste.

11. A method for curing conductive paste applied on photovoltaic structures, comprising:

placing a plurality of photovoltaic structures on a first side of a wafer carrier, wherein the wafer carrier includes a base and a strip carrier that is in direct contact with the photovoltaic structures;

positioning the wafer carrier near an induction heater;

positioning two shields on the first side of the wafer carrier; and

providing an alternating current to an induction coil of the induction heater, which by magnetic induction induces a current in the conductive paste applied to the photovoltaic structures, thereby producing heat in the conductive paste to cure the paste;

wherein the two shields are configured to shield a magnetic field caused by the induction coil from metallic parts of the photovoltaic structures other than the conductive paste, and wherein a gap between the two shields allows the conductive paste to be exposed to the magnetic field produced by the induction coil.

12. The method of claim 11, wherein the strip carrier is made of polybenzimidazole (PBI) plastic.

13. The method of claim 11, wherein the strip carrier includes a number of components separated by air gaps to allow an individual component to expand when heated.

14. The method of claim 11, wherein an induced temperature of the conductive paste is maintained at a predetermined temperature between 150 and 300°

C., and wherein the predetermined duration is between 2 and 6 seconds.

15. The method of claim 11, wherein the induction heater further includes a core housing element and a power supply for providing the alternating current to the induction coil.

16. The method of claim 15, wherein the induction heater further includes a non-conductive, heat resistant, low magnetic permeability cooling enclosure enclosing the housing element and the induction coil.

17. The method of claim 15, wherein the induction coil is made of a material having a thermal conductivity between 350 and 450 W/(m·

k) and an electrical conductivity between 59 and 65×

10^6 S·

m.

18. The method of claim 15, wherein the core housing is made of a material having a magnetic permeability between 0.001 and 1.0 H/m.

19. The method of claim 11, further comprising placing the wafer carrier such that the induction heater is positioned approximately 0.1 to 4 millimeters from the conductive paste.

20. A solar panel fabrication method, comprising:

obtaining a plurality of photovoltaic structures, wherein a photovoltaic structure includes a first edge busbar on a first edge of a first surface and a second edge busbar on an opposite edge of an opposite surface;

applying conductive paste on the first edge busbar of each photovoltaic structure;

aligning the photovoltaic structures on a wafer carrier in such a way that the first edge busbar of a first photovoltaic structure overlaps the second edge busbar of an adjacent photovoltaic structure with the conductive paste sandwiched in between;

positioning two shields on the first side of the wafer carrier; and

positioning the wafer carrier near an induction heater such that an induction coil of the induction heater induces current in the conductive paste, which produces heat in the conductive paste for a predetermined duration to cure the paste, thereby mechanically bond the photovoltaic structures to form a string;

wherein the two shields are configured to shield a magnetic field caused by the induction coil from metallic parts of the photovoltaic structures other than the conductive paste, and wherein a gap between the two shields allows the conductive paste to be exposed to the magnetic field produced by the induction coil.