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Methods for verifying correct counter-bore depth and precision on printed circuit boards

  • US 7,669,321 B1
  • Filed: 03/14/2006
  • Issued: 03/02/2010
  • Est. Priority Date: 07/13/2005
  • Status: Active Grant
First Claim
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1. A method of manufacturing a set of identical multiple-layer circuit boards, comprising:

  • incorporating a test site on each of the set of circuit boards, the test site having a set of test connections passing through a test via on respective test connection layers of each of the set of circuit boards, the set of test connections including a first test connection, a second test connection, and a third test connection, the test connection layers including (1) a first layer adjacent to a target layer, (2) a second layer spaced apart from the target layer with the first layer therebetween, and (3) a third layer spaced apart from the target layer with the first layer and second layer therebetween;

    wherein the first layer includes a first test connection point, the second layer includes a second test connection point, the third layer includes a third test connection point, and the first test connection layer, the second test connection layer, the third test connection layer are short circuited to a common test connection point,wherein the first test connection point, the second test connection point, the third test connection point, and a common test connection point surround the test via,wherein the first test connection is a first conductive pathway from the first test connection point, through the test via, to the common test connection point,wherein the second test connection is a second conductive pathway from the second test connection point, through the test via, to the common test connection point, andwherein the third test connection is a third conductive pathway from the third test connection point, through the test via, to the common test connection point;

    back-drilling, on a first circuit board of the set of circuit boards, with a back-drill the test via from the direction of the third layer to remove undesired via metallization, the back-drilling breaking the test connections of all the layers through which it passes;

    measuring, on the first circuit board, the continuity of the test connections to determine a pattern of broken and non-broken test connections resulting from the back-drilling; and

    examining, on the first circuit board, the pattern of broken and non-broken test connections to ascertain the actual depth of the back-drilling of the test via in relation to the target layer;

    wherein the method further comprising;

    in response to examining, on the first circuit board, the pattern of broken and non-broken test connections, adjusting the back-drill based on the ascertained actual depth of the back drilling of the test via in relation to the target layer, andback-drilling with the adjusted back-drill the test via of a second circuit board of the set of circuit boards;

    wherein back-drilling, on the first circuit board, with a back-drill the test via from the direction of the third layer to remove undesired via metallization breaks the third test connection of all the third layer, the second test connection of the second layer, and the first test connection of the first layer;

    wherein measuring, on the first circuit board, the continuity of the test connections to determine a pattern of broken and non-broken test connections resulting from the back-drilling determines that the third test connection, the second test connection, and the first test connection are broken;

    wherein examining, on the first circuit board, the pattern of broken and non-broken test connections to ascertain the actual depth of the back-drilling of the test via in relation to the target layer determines that undesired via metallization has been removed and that the target layer may have been nicked; and

    wherein adjusting the back-drill based on the ascertained actual depth of the back drilling of the test via in relation to the target layer includes adjusting the back-drill to drill shallower.

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