Optical Semiconductor Package Signal Lead Impedance Matching
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Solution Overview
Problem
In optical semiconductor device packages, the spatial restriction limits the reduction of lead wire diameter to match the characteristic impedance, making it difficult to achieve stable processing and effective signal transmission during high-speed communications.
Innovation Solution
The package design includes signal leads with a first portion, a second portion, and a third portion of varying diameters, with tapered portions between them, buried in sealing glass, to maintain mass productivity and improve reflection characteristics by reducing impedance mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wire diameter of the lead is reduced to match the characteristic impedance to 50Ω, then the impedance matching is improved, but the lead becomes easily bendable and stable processing becomes difficult
Solution Approach 1:
The lead is divided into multiple sections with different diameters: a first portion with larger diameter for stable processing and bonding, a second portion with reduced diameter for impedance matching, and a third portion with larger diameter again. This segmentation allows each section to serve its specific function while collectively resolving the contradiction between processing stability and impedance matching.
Solution Approach 2:
Different portions of the lead have different local qualities (diameters) optimized for different functions. The first and third portions have larger diameters for mechanical stability and bonding area, while the second portion has reduced diameter for electrical impedance matching. This local differentiation resolves the contradiction by applying the right quality in the right location.
2Manufacturing precision
If the wire diameter of the lead is reduced, then the characteristic impedance matching is improved, but the area for wire bonding becomes insufficient
Solution Approach 1:
The lead structure is segmented into different diameter portions, with the first and third portions providing sufficient bonding area for wire bonding operations, while the second portion provides the reduced diameter needed for impedance matching. This segmentation resolves the contradiction between bonding area requirements and impedance matching requirements.
Solution Approach 2:
Different local qualities (diameters) are applied to different portions of the lead: larger diameter at the bonding ends for sufficient bonding area, and reduced diameter in the intermediate portion for impedance matching. This local quality differentiation simultaneously satisfies both bonding area and impedance matching requirements.
3Manufacturing precision
If the hole for inserting the lead is enlarged to match the impedance, then the impedance matching is improved, but the spatial restriction of the package is violated
Solution Approach 1:
Instead of uniformly enlarging the lead diameter throughout, the invention applies local quality differentiation where only the intermediate portion (second portion) has reduced diameter for impedance matching, while the bonding portions maintain larger diameters. This allows impedance matching within the existing package spatial constraints without requiring hole enlargement.
4Area of stationary object
If the lead is processed into a nail lead shape with wider upper end, then the bonding area is increased, but the small wire diameter makes stable processing difficult
Solution Approach 1:
The lead is segmented into three portions where the first and third portions have larger diameters for stable processing and bonding, while the second portion has reduced diameter for impedance matching. This segmentation provides sufficient bonding area without compromising processing stability, unlike the nail lead shape where the entire lead has small diameter.
Data Source
AI summary
A package for an optical semiconductor device includes an eyelet, a signal lead inserted in a through hole formed in the eyelet, and sealing glass sealing the signal lead in the through hole. The signal lead includes a first portion, a second portion and a third portion that are greater in diameter than the first portion and on opposite sides of the first portion, a first tapered portion extending from the second portion to the first portion, and a second tapered portion extending from the third portion to the first portion. The first portion and the first and second tapered portions are buried in the sealing glass. The total length of a part of the second portion in the sealing glass and a part of the third portion in the sealing glass is 0.2 mm or less.