Systems and methods for removing undesired metal within vias from printed circuit boards
A method is provided for modifying a via from a PCB including a plurality of subassemblies comprising a plurality of layers. The method may include drilling a via of the PCB to form a through-hole to remove an unwanted material in the via of the PCB. The method may also include depositing a carbon-based material over an inner wall of the through-hole. The method may further include back drilling a first portion of the through-hole by a drill from the top of the PCB to form a first blind via. The method may also include selectively plating a conductive material over the carbon-based material to form a plated through-hole.
1 . A drill for use in back drilling of a PCB, the drill comprising:
an inner core comprising a solid cylindrical body having an outer cylindrical surface and a closed planar end surface coupled to the outer cylindrical surface, the closed planar end surface being substantially perpendicular to a vertical central axis of the solid cylindrical body;
a continuous outer coating layer disposed over the outer cylindrical surface and the closed planar end surface of the inner core, the outer coating layer comprising a first cutting portion, a second cutting portion opposite to the first cutting portion, and an inner middle portion coupled between the first and second cutting portions, the first and second cutting portions comprising a conductive material and extending outwardly from the closed planar end surface of the inner core; and
a non-conductive coating disposed over the inner middle portion of the outer coating layer between the first and second cutting portions.
2 . The drill of claim 1 , wherein the inner middle portion of the outer coating layer between the first cutting portion and the second cutting portion is outside the closed planar end surface of the inner core.
3 . The drill of claim 1 , wherein the non-conductive coating comprises diamonds.
4 . The drill of claim 1 , wherein each of the first and second cutting portions comprises a tip extending outwardly from the closed planar end surface of the inner core.
5 . The drill of claim 1 , wherein the inner core comprises one of carbide, tungsten, or cobalt.
6 . The drill of claim 1 , wherein the first cutting portion has a shape substantially symmetric to the second cutting portion from the vertical central axis of the inner core.
7 . The drill of claim 1 , wherein each of the first and second cutting portions have a triangular shape with an outer edge substantially parallel to the vertical central axis and an inner edge in a cross-sectional view of the drill, the inner edge connecting to the outer edge at an end point and extending toward the closed planar end surface of the inner core at an angle θ less than 75° from the outer edge.
8 . The drill of claim 7 , wherein the first and second cutting portions have a depth defined by a distance between the closed planar end surface of the inner core and the end points of the first and second cutting portions, the depth ranging from 0.010 inches to 0.020 inches.
9 . The drill of claim 1 , wherein the drill is configured to back drilling a first portion of a through-hole from a top of a PCB to form a first blind via.
10 . The drill of claim 9 , wherein the drill stops drilling at an internal conductive trace of the PCB when the drill touches the internal conductive trace of the PCB, wherein the internal conductive trace is grounded during back drilling such that the drill accurately stops at the internal conductive trace that is grounded during back drilling.
11 . The drill of claim 9 , wherein the drill has a diameter larger than the through-hole of the PCB.
12 . The drill of claim 9 , wherein the drill is configured to back drilling a second portion of the PCB below the through-hole from a bottom of the PCB to form a second blind via.