TO Package Glass Feedthrough Impedance Control
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Solution Overview
Problem
Current TO packages with glass-sealed signal pins face challenges in maintaining high data transfer rates due to impedance jumps caused by glass insulation and volume variations of glass or glass ceramic potting compounds, which affect the signal path's impedance profile and lead to meniscus formation issues.
Innovation Solution
The TO package design includes a metal header with a signal pin feedthrough that is partially filled with glass or glass ceramic, leaving a recessed area to minimize volume variations and impedance changes, and uses a plastic potting compound to match permittivity, reducing meniscus formation and impedance jumps, while an enlarged portion on the signal pin further adjusts the impedance profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feedthrough is completely filled with glass or glass ceramic insulating material, then hermetic sealing and temperature resistance are provided, but volume variations cause meniscus formation that negatively impacts signal path impedance
Solution Approach 1:
The feedthrough is only partially filled with glass or glass ceramic insulating material, leaving a recessed area. This partial filling approach prevents complete meniscus formation while maintaining adequate hermetic sealing, thus resolving the contradiction between sealing reliability and impedance precision
Solution Approach 2:
The filling volume of the insulating material is changed from 100% to a partial volume, and the permittivity is adjusted by using plastic material with matched permittivity in the recessed area. This parameter change eliminates meniscus-related impedance variations while preserving sealing integrity
2Reliability
If glass insulating material is used in the feedthrough, then hermetic sealing is achieved, but impedance jump occurs due to different permittivity compared to air
Solution Approach 1:
The permittivity of the insulating material in the recessed area is changed by using plastic material with permittivity matched to the glass or glass ceramic. This parameter change compensates for the impedance jump caused by the glass-insulating material while maintaining hermetic sealing
Solution Approach 2:
A composite structure is created by combining glass or glass ceramic insulating material with plastic material in the feedthrough. This composite approach allows the glass to provide hermetic sealing while the plastic with matched permittivity reduces impedance discontinuities
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 significantly improves insertion and return loss, enabling higher bandwidth and data transfer rates by smoothing the impedance transition and reducing abrupt permittivity changes, thus enhancing the signal path's performance.
Implementation Method 1
the insulation made of glass which has a different permittivity than air. Such a jump in impedance
Implementation Method 2
uses a plastic potting compound to match permittivity, reducing meniscus formation and impedance jumps
Data Source
AI summary
A transistor outline package is provided that includes a header with a mounting area for an optoelectronic component. The header has a signal pin disposed in a feedthrough. The feedthrough is filled with an insulating material made of glass and/or glass ceramic. The feedthrough has a recessed area on at least one side that is not completely filled up with the insulating material. The recessed area defines a cavity at least partially around the signal pin and the signal pin has an enlarged portion in the recessed area.