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  Closed loop backdrilling systemUSPTO Application #: 20060278429Title: 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. (end of abstract) Agent: Dunlap, Codding & Rogers P.C. - Oklahoma City, OK, US Inventors: Joseph A.A.M. Tourne, Patrick P.P. Lebens USPTO Applicaton #: 20060278429 - Class: 174266000 (USPTO) Related Patent Categories: Electricity: Conductors And Insulators, Conduits, Cables Or Conductors, Preformed Panel Circuit Arrangement (e.g., Printed Circuit), With Particular Conductive Connection (e.g., Crossover), Feedthrough, Hollow (e.g., Plated Cylindrical Hole) The Patent Description & Claims data below is from USPTO Patent Application 20060278429. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of Ser. No.10/944,583, filed on Sep. 17, 2004, which claims priority to the provisional patent application identified by U.S. Ser. No. 60/504,399, filed on Sep. 19, 2003, of which the entire content of which is hereby expressly incorporated by reference. BACKGROUND OF THE INVENTION [0002] Multilayer circuit boards and/or wiring boards are well known in the art. The multilayer circuit boards are formed with a number of signal layers (conductive layers) which are arranged in a predetermined pattern. The signal layers are insulated from each other by dielectric layers. Thus, the multilayer circuit board is formed from interleaved (e.g., alternating) signal layers and dielectric layers. [0003] Plated holes or "vias" are formed through the multilayer circuit board to connect one signal layer to another signal layer. The plated holes typically extend from one main side of the multilayer circuit board to an opposite side of the multilayer circuit board. In some instances, the plated holes or vias include a "stub portion" which extends away from the signal layer toward one of the sides of the multilayer circuit board. In some circumstances, it is desirable to remove the stub portion to enhance the signal to noise ratio in electronic systems that utilize high-speed signals. The smaller the stub portion the better the signal quality. [0004] In the past, the stub portion of the plated holes is removed in a process referred to as "back drilling". In the back drilling process, the stub portion of the plated hole is removed by drilling the stub portion to a predetermined depth. However, in practice the thicknesses of the various layers in the multilayer circuit boards are not uniform, and the depths of the signal layers within the multilayer circuit boards vary, which often changes the amount of the stub portion which needs to be removed. Drilling too deeply will disconnect the signal layer from the plated hole, or leave an unreliable connection; not drilling deep enough decreases the signal to noise ratio. [0005] The invention discussed herein uses a technique which overcomes the problems associated with the variance in thickness of the layers in the multilayer circuit board. SUMMARY OF THE INVENTION [0006] In general, the present invention relates to a multilayer circuit board, and a closed loop backdrilling system for backdrilling the multilayer circuit board. The 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 and is connected to a signal/electrical source, but is electrically isolated from the plated hole. 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. The feedback layer can be any layer within the multilayer circuit board, such as a separate network layer as shown in FIG. 2, or a ground layer, signal layer, or power layer. [0007] To remove the stub portion, a hole is bored or routed into the multilayer circuit board until electrical feedback is received from the feedback layer of the multilayer circuit board when a certain depth is reached. Typically, the electrical feedback is received from the multilayer circuit board upon contact of a portion of the boring device with the feedback layer. Upon receipt of the electrical feedback from the multilayer circuit board, the boring device is retracted from the hole, and the hole formed by the boring device can then be filled with an epoxy, or other filler material. [0008] In one preferred embodiment, the feedback layer is only used during the manufacturing process of the multilayer circuit board. In other words, in this embodiment, once the manufacturing process is complete, the feedback layer is not used to connect any components or signal layers or for any other electrical type of purpose. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING [0009] FIG. 1 is a diagrammatic view of a closed loop backdrilling system constructed in accordance with the present invention. [0010] FIG. 2 is a top plan view of one embodiment of a feedback layer formed in a multilayer circuit board wherein the feedback layer forms a separate network. [0011] FIG. 3 is a cross-sectional view of a portion of a multilayer circuit board constructed in accordance with the present invention. [0012] FIG. 4 is a top plan view of a contact pad of a feedback layer constructed in accordance with the present invention. [0013] FIG. 5 is a cross-sectional view of a portion of a multilayer circuit board constructed in accordance with an alternate embodiment of the present invention. [0014] FIG. 6 is a cross-sectional view of the portion of the multilayer circuit board constructed in accordance with an alternate embodiment of the present invention. [0015] FIG. 7 is a top plan view of an alternate embodiment of a contact pad constructed in accordance with the present invention. [0016] FIG. 8 is a diagrammatic view of an alternate embodiment of a closed loop backdrilling system constructed in accordance with the present invention. [0017] FIG. 9 is a diagrammatic view of yet another alternate embodiment of a closed loop backdrilling system constructed in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION [0018] Referring now to the drawings and in particular to FIG. 1, shown therein and designated by a reference numeral 10 is a closed loop backdrilling system constructed in accordance with the present invention. The closed loop backdrilling system 10 is used for depth drilling an already plated hole 12 formed in a workpiece 14 using electrical feedback from the workpiece 14 when a certain or predetermined depth is reached. The feedback during the drilling process makes it possible to yield much higher accuracy independent of the depth of a particular layer within the workpiece 14. In one preferred embodiment, the workpiece 14 is a multilayer printed circuit board 16. Although the workpiece 14 will be described herein as the multilayer circuit board 16, it should be understood that the workpiece 14 can be any apparatus, or device where it is desirable to drill to a certain or predetermined depth within the apparatus or device. [0019] The multilayer circuit board 16 is provided with at least one or more signal layer 20, at least one or more feedback layer 22, and at least one or more dielectric layer 24. The signal layer 20 is connected to the plated hole 12. The feedback layer 22 has a contact pad 26 (see FIG. 4). The contact pad 26 is spaced a distance away from the signal layer 20 and is electrically insulated from the plated hole 12. The dielectric layer 24 is positioned between the signal layer 20 and the contact pad 26 of the feedback layer 22 so as to electrically isolate the contact pad 26 from the signal layer 20. As will be discussed in more detail below, the contact pad 26 is contacted during the manufacturing process of the multilayer circuit board 16 to provide electrical feedback. Continue reading... Full patent description for Closed loop backdrilling system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Closed loop backdrilling system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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