Tuned MMIC Probe Pads for On-Wafer Impedance Matching
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Solution Overview
Problem
During on-wafer testing of microwave monolithic integrated circuits (MMICs), there is an impedance mismatch between the test probe and the MMIC due to the absence of bond wire inductance, causing improper tuning of the MMIC, which is designed to compensate for the anticipated bond wire inductance.
Innovation Solution
Incorporating a second reactive element on the MMIC chip connected to the test probe ground pad, providing an inductive impedance that resonates with the capacitive input impedance of the microwave circuitry to match the impedance of commercially available probes, ensuring non-reactive input impedance and maintaining the MMIC's functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the MMIC is designed with capacitive input and output impedance to compensate for bond wire inductance, then real 50 ohm input and output impedance is presented to the source and load when bonded to the circuit board, but during on-wafer testing before die separation, there is an impedance mismatch between the test probe and the MMIC because the bond wire inductance is absent
Solution Approach 1:
The invention separates the impedance compensation function into two distinct parts: the original capacitive compensation network designed for bond wire operation, and a new inductive compensation element specifically for probe testing. This segmentation allows each part to serve its specific function without interfering with the other, enabling both bond wire and probe testing compatibility
Solution Approach 2:
The inductive compensation element acts as an intermediary component that bridges the impedance mismatch between the test probe and the MMIC during on-wafer testing. This intermediate element provides the necessary inductance to cancel the capacitive reactance of the MMIC's input impedance, enabling proper 50 ohm matching during testing while leaving the original bond wire compensation intact
2Measurement precision
If the MMIC uses capacitive reactance to cancel bond wire inductance in the final application, then proper impedance matching is achieved, but during manufacturing testing the absent bond wire causes improper tuning and measurement inaccuracies
Solution Approach 1:
The invention performs preliminary impedance compensation by adding the inductive element during the on-wafer testing stage. This preliminary action ensures that the MMIC is properly tuned and measured before die separation, correcting the impedance mismatch that would otherwise exist during testing. The compensation is established in advance, allowing accurate measurements to be taken before the actual bonding operation
Solution Approach 2:
The invention changes the electrical parameters of the test setup by introducing an inductive element that modifies the overall input impedance of the MMIC during testing. This parameter change transforms the capacitive reactance-dominated impedance into a resistive 50 ohm impedance, enabling accurate measurements. The parameter modification is temporary and specific to the testing condition, not altering the final bonded configuration
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution ensures accurate on-wafer matching without perturbing the MMIC's functionality, improving the correlation between probe data and the final fixtured product, leading to a higher yield of functional MMICs.
Implementation Method 1
A second reactive element is on the chip connected to the test probe and in circuit with the first reactive input impedance of the microwave circuitry to provide a resonance with the first reactive input impedance of the microwave circuitry
Data Source
AI summary
A microwave integrated circuit chip having microwave transmission line coupled to an input of a microwave circuitry: The microwave transmission line comprises: a substrate; a strip conductor disposed on a first surface of the substrate, such strip conductor having an input signal pad at one end thereof, and a ground plane disposed on a second, opposite surface of the substrate. The microwave circuitry has capacitive input impedance. The chip includes a via passing from the first surface of the substrate, through the substrate, to the ground plane. A test probe ground pad is disposed on the first surface of the substrate and spaced from a portion of the via disposed on the first surface of the substrate. An electrical conductor is disposed on the first surface of the substrate extending from the portion of the via disposed on the first surface of the substrate via to the test probe ground pad, such electrical conductor providing an inductive impedance selected to provide a resonance with the capacitive input impedance of the microwave circuitry.