Work pieces and methods of laser drilling through holes in substrates using an exit sacrificial cover layer

Abstract

Work pieces and methods of forming through holes in substrates are disclosed. In one embodiment, a method of forming a through hole in a substrate by drilling includes affixing an exit sacrificial cover layer to a laser beam exit surface of the substrate, positioning a laser beam in a predetermined location relative to the substrate and corresponding to a desired location for the through hole, and forming the through hole by repeatedly pulsing the laser beam into an entrance surface of the substrate and through a bulk of the substrate. The method further includes forming a hole in the exit sacrificial cover layer by repeatedly pulsing the laser beam into the through hole formed in the substrate such that the laser beam passes through the laser beam exit surface of the substrate and into the exit sacrificial cover layer.

1 .- 19 . (canceled) 
     
     
         20 . A work piece having through holes, the work piece comprising:
 a substrate having the through holes formed therein, wherein:
 the substrate comprises a laser beam entrance surface and a laser beam exit surface; 
 a longitudinal axis of each through hole extends from the laser beam entrance surface to the laser beam exit surface; 
 each through hole comprises an entrance diameter at the laser beam entrance surface of the substrate and an exit diameter at the laser beam exit surface; 
 the entrance diameter is less than about 40 μm; and 
 a ratio of the entrance diameter to the exit diameter is greater than about 0.7; and 
   an exit sacrificial cover layer detachably affixed to the laser beam exit surface of the substrate, wherein the exit sacrificial cover layer has a different composition than the substrate, and the exit sacrificial cover layer comprises holes, each hole having a longitudinal axis aligned with the longitudinal axis of a corresponding through hole;   wherein a thickness of the exit sacrificial cover layer is greater than about 100 μm.   
     
     
         21 . The work piece of  claim 20 , wherein:
 a thickness of the substrate is less than about 150 μm; and   a thickness of the exit sacrificial cover layer is greater than about 300 μm.   
     
     
         22 . The work piece of  claim 20 , wherein:
 the exit diameter defines an exit hole of the through hole having a circumference C; and   the laser beam exit surface of the substrate is free from one or more channels extending from the circumference C of the exit hole.   
     
     
         23 . The work piece of  claim 20 , wherein the substrate is glass. 
     
     
         24 . The work piece of  claim 20 , wherein a thickness of the substrate is less than about 300 μm. 
     
     
         25 . The work piece of  claim 20 , wherein the exit sacrificial cover layer is a polymer layer. 
     
     
         26 . The work piece of  claim 20 , wherein the exit sacrificial cover layer is a glass layer.