Verification of trace length and trace impedance of fabricated load board using TDR

Abstract

In the realm of high speed semiconductor IC testing, the medium whereby the test signals passed has important role in order to ensure that the signal transmitted and received are the correct signals. One of the media that the signal passed in IC testing is the device interface board or load board in short. Load board is basically a printed circuit board with test socket(s) for inserting device under test (DUT) during the testing. It consists of numerous conductive traces connecting the DUT to the tester. They are carefully designed according to impedance design and control for the task they have to perform for the specific semiconductor devices. Once they are fabricated it is not possible to physically measure the trace length and impedance to validate their correctness since the traces are built internally. TDR has recently been used in the semiconductor industry for transmission line characterization and signal integrity analysis. TDR method was used successfully in this study to verify the trace length and impedance of the fabricated load board used for semiconductor's speed testing. The trace length of the evaluation load board was verified to within 8% accuracy. The trace impedance was measured to be 48 ohms which is very close to the theoretical value of 50 ohm. Thus the TDR method served as an useful tool for verification of the trace length and trace impedance of the load board.