Step-Terminated SMD Fuse Structure for Contamination Control
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Solution Overview
Problem
Small footprint surface mount device (SMD) fuses face issues with contamination and plating residue trapped in their layers, compromising their operation, especially in miniaturized designs like 0603 SMDs, which affects their reliability and performance.
Innovation Solution
The design incorporates a stack of alternating structural and epoxy layers forming steps, with a flattened wire as the fusible element between these steps, and terminals with multiple surfaces to cover the steps, reducing the risk of trapped contamination and enhancing solderability by eliminating castellations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small footprint SMD fuses are produced using traditional wire-in-air manufacturing with alternating ceramic/FR4 and epoxy layers, then miniaturization is achieved, but contamination and plating residue are trapped within the layers affecting operation
Solution Approach 1:
The fuse structure is divided into distinct segments: a lower stack with larger layers, an upper stack with smaller layers, and a flattened wire fusible element positioned between them. This segmentation creates open interfaces between stacks that prevent contamination trapping while maintaining miniaturization benefits.
Solution Approach 2:
The design extracts and eliminates the problematic alternating layer structure that traps contamination. Instead, it uses a simplified construction with open interfaces between the lower and upper stacks, removing the source of contamination entrapment while preserving the small footprint advantage.
2Ease of manufacture
If traditional castellated terminations are used in small footprint fuses, then manufacturing is simplified, but solderability becomes inconsistent and bonding area is reduced
Solution Approach 1:
The terminal structure is designed with different surface qualities at different locations. The top surface provides a large planar bonding area for consistent soldering, while the side surfaces provide additional bonding area and mechanical support. This local differentiation of surface properties optimizes both manufacturability and solderability consistency.
Solution Approach 2:
The terminal extends in multiple dimensions with surfaces on multiple faces, transitioning from a simple planar castellated structure to a three-dimensional multi-surface structure. This dimensional expansion provides both large bonding area and consistent solderability across different manufacturing processes.
3Volume of moving object
If layers are made thinner to achieve smaller footprint, then miniaturization is improved, but contamination trapping within layers worsens
Solution Approach 1:
The design removes the problematic thin alternating layers that trap contamination. Instead of using multiple thin ceramic/FR4 and epoxy layers, it employs a simpler construction with open interfaces between lower and upper stacks, eliminating the contamination trapping mechanism while maintaining small size.
Solution Approach 2:
The structural parameters are changed from thin alternating layers to thicker, simpler stack structures with open interfaces. This parameter change reduces the number of interfaces where contamination can be trapped, while the overall footprint is maintained through optimized stacking arrangements.
Data Source
AI summary
A fuse includes a stack, a flattened wire, and a terminal. The stack has multiple layers arranged to form steps. The stack has an upper stack with layers of a first size and a lower stack with layers of a second, larger size. The flattened wire is located between the upper stack and the lower stack. The terminal is connected to the flattened wire and includes multiple surfaces to cover the steps at one end of the stack.