Closed loop backdrilling system

Abstract

A multilayer circuit board is provided with at least one signal layer, at least one feedback layer, and at least one dielectric layer positioned between the signal layer and the feedback layer. The signal layer is connected to at least one plated hole. The feedback layer has a contact pad, which is positioned adjacent to the plated hole, but is electrically isolated from the plated hole. The contact pad is connected to a measurement unit. The dielectric layer is positioned between the signal layer and the contact pad of the feedback layer. A portion of the plated hole forms a stub portion, which extends a distance away from the signal layer and typically extends a distance away from the contact pad of the feedback layer. To remove the stub portion, a hole is bored or routed into the multilayer circuit board until electrical feedback is received by the measurement unit upon contact of a portion of the boring device with the contact pad. Upon receipt of the electrical feedback by the measurement unit, the boring device is retracted from the hole, and the hole formed by the boring device is filled with an epoxy, or other filler material.

1 . A workpiece having a stub portion removed from a plated hole wherein the amount of the stub portion removed is determined from electrical feedback received from within the workpiece, the workpiece produced by a method comprising the steps of: 
 providing the workpiece with a feedback layer;    boring a hole into the workpiece with a boring device to remove at    least a portion of a plated hole until the boring device engages    the feedback layer; and receiving an electrical feedback signal from the boring device    indicating engagement with the feedback layer.    
   
   
       2 . The workpiece of  claim 1 , wherein the step of boring is defined further as the steps of moving the a cutting device of the boring device into the plated hole to remove a portion of the plated hole, stopping the movement of the cutting device and restarting the movement of the cutting device into the plated hole to remove more of the plated hole, and wherein the step of receiving feedback is defined further as receiving feedback responsive to the cuffing device engaging the feedback layer.  
   
   
       3 . The workpiece of  claim 1 , wherein the feedback layer is a ground layer.  
   
   
       4 . The workpiece of  claim 1 , wherein the feedback layer is a power layer.  
   
   
       5 . The workpiece of  claim 1 , wherein the feedback layer is a signal layer.  
   
   
       6 . The workpiece of  claim 1 , wherein the feedback layer is a separate network.  
   
   
       7 . A multilayer circuit board, comprising: 
 a signal layer;    a feedback layer having a contact pad;    a dielectric layer positioned between the signal layer and the feedback layer; and    a plated hole connected to the signal layer, and positioned adjacent to the contact pad, the contact pad being electrically isolated from the plated hole, a portion of the plated hole forming a stub portion, which extends a distance away from the signal layer and extends a distance away from the contact pad of the feedback layer.    
   
   
       8 . The multilayer circuit board of  claim 7 , wherein the feedback layer is a ground layer.  
   
   
       9 . The multilayer circuit board of  claim 7 , wherein the feedback layer is a power layer.  
   
   
       10 . The multilayer circuit board of  claim 7 , wherein the feedback layer is a power layer.  
   
   
       11 . The multilayer circuit board of  claim 7 , wherein the feedback layer is a separate network.  
   
   
       12 . The multilayer circuit board of  claim 7 , further comprising a second plated hole which is electrically connected to the contact pad.  
   
   
       13 . The multilayer circuit board of  claim 7 , wherein the contact pad substantially surrounds the plated hole.  
   
   
       14 . A method for backdrilling a stub portion of a plated hole in a multilayer circuit board, comprising the steps of: 
 moving a cutting device in a direction toward the plated hole such that the cutting device removes a portion of the plating adjacent the stub portion and disconnects a feedback layer from the plated hole; and    determining whether the feedback layer is disconnected from the plated hole.    
   
   
       15 . The method of  claim 14 , further comprising the step of retracting the cutting device away from the plated hole so that the conductivity of the cutting device will not interfere with the determination of whether the feedback layer is disconnected from the plated hole.