Optoelectronic Module ESD Protection via Lead Frame Segmentation
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Solution Overview
Problem
Existing optoelectronic modules for computer mice lack effective protection against electrostatic discharges (ESD), which can damage the light source circuit, necessitating additional components like overvoltage protection diodes, increasing manufacturing costs and complexity.
Innovation Solution
The method involves cutting conductive tracks connected to the light source circuit through openings in the molding, isolating them from external conductive tracks, and decoupling electrical power supply and drive between the light source and photoreceptor circuits, allowing for protection without additional components and facilitating module assembly and mechanical reinforcement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional overvoltage protection diodes are mounted to protect the light source circuit from ESD, then the light source circuit is protected, but the manufacturing cost and device complexity increase
Solution Approach 1:
The patent extracts the light source circuit from the common ground potential by providing a dedicated ground connection through the lead frame. The light source circuit is electrically isolated from the housing and other circuits by assigning it a separate ground path, thereby protecting it from ESD without requiring additional protection diodes.
Solution Approach 2:
The lead frame acts as an intermediary element that provides a dedicated ground connection for the light source circuit. This intermediary ground path isolates the light source circuit from ESD affecting other parts of the module, eliminating the need for additional protection components.
2Ease of manufacture
If conductive tracks are left accessible through the molding for external connections, then ease of manufacture and assembly is improved, but the light source circuit becomes vulnerable to ESD from external handling
Solution Approach 1:
The patent segments the ground connections by providing a dedicated ground track for the light source circuit that is electrically isolated from other ground paths. This segmentation ensures that external handling of other conductive tracks does not affect the light source circuit's ground potential, protecting it from ESD while maintaining assembly ease.
3Ease of operation
If the light source circuit is connected to external conductive tracks for power supply and control, then ease of operation is improved, but vulnerability to electrostatic discharges increases
Solution Approach 1:
The patent extracts the light source circuit's ground connection from the common ground network and provides it with a dedicated ground path through the lead frame. This extraction isolates the light source circuit from ESD affecting external conductive tracks, while maintaining ease of operation through proper electrical connections.
4Ease of manufacture
If no additional protection components are used, then manufacturing cost is reduced, but the light source circuit lacks protection from ESD
Solution Approach 1:
The patent implements self-service protection by designing the lead frame to provide a dedicated ground connection for the light source circuit. The module's own structure (lead frame) serves as the protection mechanism, eliminating the need for additional protection components and reducing manufacturing costs while ensuring reliability.
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
The process enables the fabrication of an optoelectronic module (10, 20), which comprises a first light source circuit (5) and a second photoreceptor circuit (6) for capturing light reflected from the first light source circuit onto an external surface. A first molding (20) with an encapsulating material is made on a portion of a connection grid (10) having several conductive tracks (12) and an outer frame (11) connecting all the conductive tracks. A first light source circuit (5) is placed on a portion of a first conductive track (13) of the connection grid not covered by the first molding. A second photoreceptor circuit (6) is placed on a portion of a second conductive track (14) of the connection grid not covered by the first molding.A through-hole (21) is also made in the first molding (20) between the outer frame (11) and the location of the first light source circuit (5) to provide access to the first connection track (13) and a third connection track (15) for the first light source circuit. The contact areas of the first and second circuits (5, 6) are connected by metal wires (25) to corresponding exposed areas of certain conductive tracks (12) of the connection grid (10). The first and third connection tracks (13, 15) are then cut through the through-hole (21) of the first molding (20) to electrically isolate the first light source circuit (5) from the external parts. The light source circuit is thus protected from electrostatic discharge.A second molding can still be made on the first molding (20) to close the through opening and obtain first and second openings on the first and second circuits (5, 6) for the passage of light.