TO Package Grounding with Metal Block for Impedance Matching
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Solution Overview
Problem
Existing TO packages with glass-sealed signal pins face challenges in impedance matching due to the different permittivity of glass and air, leading to signal line impedance jumps, and have low tolerance for positional and shape tolerances, especially when connecting ground pins.
Innovation Solution
A TO package design featuring a metal header with a coaxially attached printed circuit board and a metal block providing mechanical and electrical grounding, along with a signal pin in a feedthrough, which includes an enlarged portion to compensate for impedance variations and positional tolerances, and uses a combination of glass and plastic insulating materials to minimize meniscus formation and impedance issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a glass feedthrough is used to hermetically seal the package, then hermetic sealing and temperature resistance are improved, but impedance jump in the signal line occurs due to different permittivity of glass and air
Solution Approach 1:
A metal block is introduced as an intermediary component between the glass feedthrough and the printed circuit board. This metal block serves multiple functions: it provides a transition zone that compensates for the impedance jump caused by the glass-air permittivity difference, establishes a reliable ground connection, and maintains the hermetic sealing integrity while enabling proper impedance matching for high-frequency signals.
Solution Approach 2:
The package structure employs a composite design combining glass feedthrough, metal block, and printed circuit board materials. Each material is selected for its specific properties: glass for hermetic sealing, metal for electrical conductivity and grounding, and the composite structure itself creates impedance transition zones that bridge the permittivity difference between glass and air, thereby maintaining signal integrity.
2Ease of manufacture
If a ground connection pin is connected in the same process step as signal pins, then assembly is simplified, but positional and shape tolerance compensation becomes difficult
Solution Approach 1:
The metal block performs multiple functions simultaneously: it provides the ground connection, serves as a mechanical support structure, compensates for impedance variations, and accommodates positional tolerances of both signal pins and ground connections. This multi-functional design simplifies the assembly process while maintaining manufacturing precision.
Solution Approach 2:
The metal block's physical parameters (size, shape, position) are designed to be adjustable within certain ranges to compensate for positional and shape tolerances. By allowing parameter variations in the metal block design, the system can accommodate manufacturing tolerances of glass-sealed pins while maintaining proper electrical connections and impedance matching.
3Ease of operation
If the printed circuit board is connected perpendicular to the signal pin, then connection is straightforward, but impedance uniformity and mechanical stability are reduced
Solution Approach 1:
The metal block is positioned asymmetrically relative to the signal pin, creating an optimized geometric relationship that maintains coaxial alignment for impedance uniformity while enabling the printed circuit board to be connected in a practical manner. This asymmetric configuration balances the competing requirements of connection ease and impedance control.
Data Source
AI summary
A transistor outline package is provided that includes a header having an upper surface, a lower surface, an inner surface, and a mounting area for an optoelectronic component in the inner surface. The header has a signal pin configured to connect an optoelectronic component. The signal pin is disposed in a feedthrough and protrudes from the lower surface. A printed circuit board attached on the signal pin substantially coaxially thereto. The printed circuit board is mechanically and electrically connected to the header by a metal block arranged adjacent to the feedthrough to provide grounding.