Patent ID: 7331495

Claim:
A substrate ( 1 ) with a first ( 11 ) and a second side ( 12 ) and a thickness ( 20 ), which substrate ( 1 , 101 ) is provided at its first side ( 11 ) with: a first groove ( 4 ) having a depth ( 24 ) with respect to the first side ( 11 ); a second ( 5 ) and a third groove ( 6 ), each having a depth ( 24 ) with respect to the first side ( 11 ), wherein the first groove ( 4 ) intersects the second and the third groove ( 5 , 6 ) in a first and a second point of intersection ( 17 , 18 ), respectively; an initiation point ( 19 ) which lies between the first and the second point of intersection ( 17 , 18 ); wherein the first groove ( 4 ) comprises several protrusions ( 3 ) between the first and the second point of intersection ( 17 , 18 ); and wherein the second and third grooves ( 5 , 6 ) at the first and the second point of intersection ( 17 , 18 ) are deepened further down to a depression depth ( 22 ) greater than the depth of the first, the second or the third groove.