Abstract: A method of detecting depth of a buried target disposed over an intermediate layer within a multi-layer substrate includes forming a test coupon on the intermediate layer during manufacture of the multi-layer substrate, the test coupon including a trace with probe sites at opposite ends; drilling a hole through the trace of the test coupon within the multi-layer substrate; monitoring electrical continuity of the test coupon during the drilling; and determining a depth of the buried target responsive to the monitoring. A hole may then be drilled based on the determined depth.