Coax-to-PCB Interface Using Capacitive Ground Coupling for Low PIM
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Solution Overview
Problem
Existing coaxial-to-PCB interfaces face challenges with passive intermodulation (PIM) interference due to galvanic contact requirements, which are costly, difficult to assemble, and can lead to unreliable connections.
Innovation Solution
A coaxial-to-PCB interface that uses capacitive coupling between the connector ground and PCB ground, eliminating the need for soldering and incorporating a metallic cylinder for capacitive coupling, along with a solder mask or thin dielectric material for isolation, allowing for thermal expansion mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic contact is used between connector ground pins and PCB ground, then reliable electrical connection is achieved, but passive intermodulation (PIM) interference increases and assembly complexity increases
Solution Approach 1:
The patent replaces the mechanical galvanic contact system with a capacitive coupling system. The ground connection is achieved through electric field coupling between the connector ground shield and PCB ground plane, separated by a dielectric barrier (solder mask or air gap), eliminating direct metal-to-metal contact that causes PIM while maintaining electrical connectivity through capacitance.
Solution Approach 2:
The patent introduces a dielectric intermediary (solder mask or air gap) between the connector ground shield and PCB ground plane. This intermediary layer prevents direct galvanic contact that generates PIM while allowing capacitive coupling to maintain the ground reference, thus resolving the contradiction between reliable connection and PIM reduction.
2Reliability
If soldering is used to connect connector ground pins to PCB ground, then electrical connection is achieved, but manufacturing complexity and assembly difficulty increase
Solution Approach 1:
The patent replaces the soldering process with a capacitive coupling mechanism. The ground connection is formed by the electric field between the connector ground shield and PCB ground plane through the dielectric barrier, eliminating the need for thermal soldering processes, specialized equipment, and complex assembly procedures while maintaining reliable electrical connectivity.
3Object-generated harmful factors
If good low PIM connectors are used, then PIM interference is reduced, but cost increases and device size increases
Solution Approach 1:
The patent extracts the ground connection function from the mechanical connector structure and implements it separately through capacitive coupling between the connector ground shield and PCB ground plane. This separation allows the use of simpler, less expensive connectors while achieving low PIM performance through the capacitive ground coupling mechanism.
Solution Approach 2:
The patent introduces a dielectric intermediary layer that enables capacitive coupling between the connector ground shield and PCB ground plane. This intermediary structure reduces PIM interference by preventing direct galvanic contact while using standard, cost-effective materials and simple geometry, avoiding the need for complex specialized connectors.
4Reliability
If soldered ground connections are made, then electrical connection is achieved, but thermal conductivity causes soldering difficulties and cold joints increase PIM
Solution Approach 1:
The patent replaces the thermal soldering process with a capacitive coupling system. The ground connection is established through electric field coupling between the connector ground shield and PCB ground plane separated by a dielectric barrier, eliminating the need for high-temperature soldering that is difficult due to the high thermal conductivity of ground materials and that can result in cold joints increasing PIM.
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 design achieves low PIM, simplifies assembly, and reduces energy leakage, making it suitable for 4G and 5G radio systems with improved reliability and reduced insertion loss.
Implementation Method 1
a ground contact between the connector and PCB is disclosed as being replaced by a capacitive coupling method. In some embodiments, the ground of the connector has a capacitive or metallic ring or cylinder (a large area typically in the shape of a ring, or less typically, another shape) that is placed in close proximity to the PCB ground
Data Source
AI summary
A low passive intermodulation (PIM) coaxial-to-printed circuit board (PCB) interface and method of constructing the same. According to one aspect, a coaxial-to-PCB interface couples signals between an electrical conductor trace in the PCB and an inner conductor of a coaxial structure having an insulator surrounded by an outer conductor. A metallic cylinder is inserted over the outer conductor of the coaxial structure and positioning the coaxial structure with respect to the PCB so that the outer conductor and insulator of the coaxial structure lie below a lower surface of the PCB. The inner conductor of the coaxial structure is inserted into a via extending from the lower surface of the PCB to an upper surface of the PCB. Solder is deposited in the via to provide an electrically conductive path between the electrical conductor trace of the PCB and the inner conductor of the coaxial structure.