Optocoupler Terminal Structure for Lower Impedance at High Frequency
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Solution Overview
Problem
Semiconductor devices that transmit high frequency signals face challenges in improving frequency characteristics due to high impedance between output-side terminals, particularly in photo-relays with optically coupled light-emitting and light-receiving elements.
Innovation Solution
The semiconductor device is designed with a thin insulating member and balanced thicknesses of metal terminals and pads to reduce impedance, featuring an insulating resin sheet with specific thicknesses and metal layers to enhance high frequency signal passing characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional semiconductor device structure is used, then the device can be manufactured with standard processes, but the impedance between output-side terminals is high which degrades high frequency signal characteristics
Solution Approach 1:
The patent changes the physical parameters of the terminal structure by making the insulating member thickness (T1) less than the combined thickness of metal layers (T2+T3), and by designing the metal pad to extend from the front surface through the back surface. This parameter optimization reduces the impedance between terminals and improves high frequency signal characteristics.
Solution Approach 2:
The patent employs a composite structure combining insulating material (resin sheet) with metal layers (copper or aluminum) in a specific configuration. The metal pad extends through the insulating member, creating a composite structure that provides both electrical connectivity and mechanical support while reducing terminal impedance.
2Strength
If the insulating member thickness is increased for mechanical strength, then structural stability is improved, but the impedance between terminals increases which degrades high frequency characteristics
Solution Approach 1:
The patent optimizes the thickness parameter of the insulating member by setting it less than the combined thickness of the metal layers (T1 < T2+T3). This parameter change achieves the right balance between maintaining structural stability and reducing terminal impedance for improved high frequency characteristics.
Solution Approach 2:
The metal pad is designed to extend in the thickness direction (Z-direction) from the front surface through the back surface of the insulating member. This dimensional approach creates multiple electrical connection paths through the insulating member, effectively reducing impedance while maintaining structural integrity.
Data Source
AI summary
A semiconductor device includes an insulating member; a light-receiving element on a front surface of the insulating member; a light-emitting element on the light-receiving element; a first metal terminal electrically connected to the light-emitting element and provided on a back surface of the insulating member; a switching element mounted on the front surface via a metal pad, the switching element being electrically connected to the light-receiving element; and a second metal terminal provided on the back surface and electrically connected to the switching element via the metal pad. The insulating member has a first thickness in a first direction directed from the back surface toward the front surface. The metal pad has a second thickness in the first direction. The second metal terminal has a third thickness in the first direction. The first thickness is less than a combined thickness of the second and third thicknesses.