Millimeter Wave Connector Interposer Impedance Matching
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Solution Overview
Problem
Existing methods for integrating millimeter wave connectors with integrated circuits face challenges in scalability and impedance matching, particularly at high frequencies, due to limitations in surface mount technology and wire-bonded alumina substrates, which result in performance degradation and unwanted parasitic inductances.
Innovation Solution
The use of a multilayer printed circuit board (PCB) interposer with a pin landing pad and transition portion, conductively coupled to a signal pin, and a transmission line that matches the characteristic impedance of the integrated circuit's I/O pads, allowing for improved impedance matching and increased integration density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If surface mount technology (SMT) with coaxial connectors on PCB is used, then manufacturing cost is reduced and assembly speed is improved, but frequency performance deteriorates above 20 GHz due to large pads and feature sizes
Solution Approach 1:
The system is divided into separate functional modules: a PCB assembly with coaxial connectors operating at lower frequencies, and a ceramic package with planar transmission lines operating at millimeter wave frequencies. This segmentation allows each module to be optimized for its specific frequency range, resolving the contradiction between assembly efficiency and high-frequency performance.
Solution Approach 2:
A ceramic package serves as an intermediary component between the PCB coaxial connector and the integrated circuit. The ceramic package contains planar transmission lines and bonding structures that are optimized for millimeter wave frequencies, acting as a mediator that transitions signals from the lower-frequency PCB environment to the high-frequency IC environment.
2Reliability
If wire-bonded alumina substrates are used for millimeter wave connector integration, then impedance matching is improved, but parasitic inductance increases and integration density decreases
Solution Approach 1:
The wire-bonding process and associated parasitic inductances are eliminated by using a hybrid approach. The PCB assembly uses SMT with direct solder connections, extracting the problematic wire-bonding step from the overall system. The ceramic package then provides direct planar transmission line connections to the IC, avoiding the need for wire bonds entirely.
Solution Approach 2:
The mechanical wire-bonding system is replaced with an integrated planar transmission line system fabricated on the ceramic substrate. This substitution eliminates the mechanical wire bonds that introduce parasitic inductance, replacing them with controlled impedance traces that maintain signal integrity at millimeter wave frequencies.
3Volume of moving object
If chip-on-board (COB) technique is used, then size is reduced and density is improved, but return loss increases due to pad size mismatches
Solution Approach 1:
The ceramic package incorporates local impedance matching structures and transition features at critical interfaces. The pad geometries and transmission line characteristics are locally optimized at each bonding interface to match impedances between the IC, ceramic substrate, and PCB, minimizing reflections and return loss while maintaining compact packaging.
Data Source
AI summary
An apparatus for connecting a millimeter wave signal to an integrated circuit includes a connector to receive the millimeter wave signal. The connector includes a signal pin. A pin landing pad is conductively coupled to the signal pin. The pin landing pad includes a transition portion. A transmission line is configured to couple the pin landing pad to an input/output (I/O) pad of an integrated circuit. The apparatus further includes an interposer including the pin landing pad, the transmission line, and the I/O pad of the integrated circuit.