Optical Module Underfill Placement for High-Frequency Signal Integrity
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Solution Overview
Problem
Miniaturizing optical semiconductor chips while maintaining good high-frequency characteristics is difficult due to the decrease in solder ball pitch and diameter, which leads to reduced connection reliability and impedance mismatch caused by the permittivity of resin underfill, resulting in decreased high-frequency characteristics.
Innovation Solution
The optical module design includes a specific arrangement of conductive materials and underfill resin, where the underfill is only provided on the conductive material side that connects lower-speed signal components, avoiding the high-speed signal path and maintaining the characteristic impedance, thus preventing a decrease in high-frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the optical semiconductor chip is miniaturized, then the size is reduced, but the high-frequency characteristics deteriorate due to impedance mismatch caused by resin underfill
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different signal lines. High-speed signal lines are excluded from underfill application, while low-speed signal lines receive underfill. This localized differentiation allows the chip to be miniaturized with underfill for structural support while preserving high-frequency characteristics on critical signal paths by avoiding the permittivity effect of resin.
2Volume of moving object
If the solder ball pitch and diameter are decreased for miniaturization, then the chip size is reduced, but the connection reliability decreases
Solution Approach 1:
The patent applies local quality by providing resin underfill specifically in regions where solder balls connect low-speed signal lines, while excluding regions with high-speed signal lines. This localized support compensates for the reduced mechanical strength from smaller solder balls on non-critical connections, maintaining overall connection reliability while enabling chip miniaturization.
Data Source
AI summary
An optical module includes an optical semiconductor chip including a first electrode pad, a second electrode pad, and a third electrode pad arranged between the first electrode pad and the second electrode pad, a wiring substrate on which the optical semiconductor chip is flip-chip mounted, including a fourth electrode pad, a fifth electrode pad, and a sixth electrode pad arranged between the fourth electrode pad and the fifth electrode pad, a first conductive material connecting the first electrode pad with the fourth electrode pad, a second conductive material connecting the second electrode pad with the fifth electrode pad, a third conductive material arranged between the first conductive material and the second conductive material, connecting the third electrode pad with the sixth electrode pad, and a resin provided in an area on the second conductive material side of the third conductive material between the optical semiconductor chip and the wiring substrate.