Low-Frequency and Low-Cost Test Methodology for Integrated RF Substrates

A low-cost test method is proposed for testing integrated radio-frequency (RF) substrates with embedded RF passive filters. The proposed method enables the testing of embedded high-frequency gigahertz filters by the analysis of low-frequency signal of the order of 100 MHz. In addition, the test method allows the testing without injecting external test stimulus into RF filters. Hence, significant reduction in the test cost is achieved by the proposed test method. As compared to the conventional test method which uses vector network analyzer (VNA), the proposed method reduces the test-setup cost by around 75%. The proposed test method relies on three core principles. First, the RF filter is made a part of the feedback network of an external RF amplifier circuit located on the probe card, thereby causing the amplifier to oscillate. Second, the output spectrum of the amplifier (GHz) is down-converted to a lower frequency (MHz) to facilitate test response measurement. Third, RF (GHz) specifications of the filters are predicted by the analysis of the low-frequency (MHz) test-setup output. Both parametric and catastrophic failures in the embedded high-frequency (GHz) passive filter can be detected at low-frequency (MHz) by monitoring the change in the oscillation frequency of the proposed test setup. The test method is demonstrated with both simulations and measurements.