Method for dividing brittle-material substrate

1. A method for dividing a brittle-material substrate, the method comprising:

preparing a brittle-material substrate made of glass material and including a surface and having a thickness direction perpendicular to said surface, said surface being surrounded by a perimeter including first and second edges opposite to each other;

pressing a cutter edge against said surface of said brittle-material substrate, said cutter edge including a protruding portion and a side portion extending from said protruding portion and having a convex shape;

forming, by plastic deformation, a scribe line having a groove shape involving no vertical crack, said scribe line being formed between a first position closer to said first edge and a second position closer to said second edge on said surface of said brittle-material substrate by causing said cutter edge pressed in said pressing to slide on said surface of said brittle-material substrate;

after said forming the scribe line, forming a crack line by cracking said brittle-material substrate in said thickness direction, from said second position toward said first position along said scribe line;

dividing said brittle-material substrate along said crack line, wherein

said forming the scribe line is performed by forming the scribe line spaced away from said perimeter, and

the method further comprises forming an assist line by cracking said brittle-material substrate in said thickness direction, said assist line and said scribe line intersecting each other at said second position, wherein

said step of forming the crack line is commenced at said second position.

2. The method for dividing a brittle-material substrate according to claim 1 , wherein said forming the assist line is performed after said forming the scribe line.

3. The method for dividing a brittle-material substrate according to claim 1 , wherein said forming the assist line is performed before said forming the scribe line.

4. The method for dividing a brittle-material substrate according to claim 1 , wherein in said forming the scribe line, said cutter edge is pressed against said surface of said brittle-material substrate with a greater force at said second position than at said first position.

5. The method for dividing a brittle-material substrate according to claim 1 , wherein

said cutter edge includes first to third surfaces adjacent to each other, a vertex at which said first to third surfaces meet, and a ridge formed by said second and third surfaces, and

said protruding portion of said cutter edge comprises said vertex, and said side portion of said cutter edge comprises said ridge.

6. The method for dividing a brittle-material substrate according to claim 1 , wherein

said cutter edge has a shape of a cone including a vertex and a conical surface, and

said protruding portion of said cutter edge comprises said vertex, and said side portion of said cutter edge is formed along an imaginary line extending from said vertex on said conical surface.

7. The method for dividing a brittle-material substrate according to claim 1 , wherein said forming the scribe line comprises displacing said cutter edge from said first position to said second position.

8. The method for dividing a brittle-material substrate according to claim 1 , wherein said forming a scribe line comprises displacing said cutter edge from said second position to said first position.

9. A method for dividing a brittle-material substrate, the method comprising:

preparing a brittle-material substrate made of glass material and including a surface and having a thickness direction perpendicular to said surface, said surface being surrounded by a perimeter including first and second edges opposite to each other;

pressing a cutter edge against said surface of said brittle-material substrate, said cutter edge including a protruding portion and a side portion extending from said protruding portion and having a convex shape;

forming, by plastic deformation, a scribe line having a groove shape involving no vertical crack, said scribe line being formed between a first position closer to said first edge and a second position closer to said second edge on said surface of said brittle-material substrate by causing said cutter edge pressed in said pressing to slide on said surface of said brittle-material substrate;

said scribe line being spaced away from said perimeter, and

forming an assist line on said brittle-material substrate, said assist line and said scribe line intersecting each other at said second position, and applying a first stress to said assist line to cause cracking of said brittle-material substrate in said thickness direction along said assist line, wherein

forming a crack line along said scribe line is commenced by applying said first stress to said brittle-material substrate to separate said brittle-material substrate along said assist line, thereby initiating formation of said crack line from said second position for division of said brittle-material substrate along said crack line.

10. The method for dividing a brittle-material substrate according to claim 9 , wherein said forming said assist line comprises forming said assist line on another surface that is located opposite to said surface of said brittle-material substrate.

11. The method for dividing a brittle-material substrate according to claim 9 , wherein the division of said brittle-material substrate along said crack line is initiated by said first stress.

12. The method for dividing a brittle-material substrate according to claim 9 , further comprising applying a second stress to said crack line to initiate the division of said brittle-material substrate along said crack line.

13. The method for dividing a brittle-material substrate according to claim 9 , wherein said forming the assist line is performed after said forming the scribe line.

14. The method for dividing a brittle-material substrate according to claim 9 , wherein said forming the assist line is performed before said forming the scribe line.

15. The method for dividing a brittle-material substrate according to claim 9 , wherein in said forming the scribe line, said cutter edge is pressed against said surface of said brittle-material substrate with a greater force at said second position than at said first position.

16. The method for dividing a brittle-material substrate according to claim 9 , wherein

said cutter edge includes first to third surfaces adjacent to each other, a vertex at which said first to third surfaces meet, and a ridge formed by said second and third surfaces, and

said protruding portion of said cutter edge comprises said vertex, and said side portion of said cutter edge comprises said ridge.

17. The method for dividing a brittle-material substrate according to claim 9 , wherein

said cutter edge has a shape of a cone including a vertex and a conical surface, and

said protruding portion of said cutter edge comprises said vertex, and said side portion of said cutter edge is formed along an imaginary line extending from said vertex on said conical surface.

18. The method for dividing a brittle-material substrate according to claim 9 , wherein said forming the scribe line comprises displacing said cutter edge from said first position to said second position.

19. The method for dividing a brittle-material substrate according to claim 9 , wherein said forming a scribe line comprises displacing said cutter edge from said second position to said first position.