Discontinuous Lead Frame Coating to Prevent Capacitor Delamination
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Solution Overview
Problem
Existing solid electrolytic capacitors face degradation due to delamination between the encasement and lead frame, primarily caused by thermal wicking of the surface coating, which allows ingress of environmental components and reduces their lifespan, especially in high-temperature applications.
Innovation Solution
A lead frame with a discontinuous surface coating is used, featuring a contact region and a discontinuous region to prevent thermal wicking and maintain case integrity, thereby enhancing the capacitor's resistance to thermal degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous surface coating is applied to the lead frame, then electrical conductivity and solderability are improved, but thermal wicking occurs causing delamination between encasement and lead frame
Solution Approach 1:
The surface coating is segmented into discontinuous regions rather than being continuous. This segmentation prevents the coating from acting as a continuous wick for thermal migration, thereby preventing delamination while maintaining electrical functionality through strategic placement of coating segments in contact regions.
Solution Approach 2:
The surface coating is applied selectively to specific contact regions where electrical conductivity is needed, rather than uniformly across the entire lead frame surface. This local quality approach ensures solderability and electrical contact where required while avoiding thermal wicking in non-contact areas.
2Ease of manufacture
If the lead frame is subjected to high temperature during surface mounting, then the capacitor is ready for operation, but the surface coating flows and wicks causing gap formation
Solution Approach 1:
The discontinuous surface coating is segmented into isolated contact regions that prevent continuous thermal wicking pathways. During high-temperature surface mounting, these segmented regions remain stable and do not flow continuously, maintaining encasement adhesion while allowing proper soldering operation.
Solution Approach 2:
The surface coating is pre-configured in a discontinuous pattern before the high-temperature surface mounting process. This preliminary configuration ensures that when thermal stress is applied during manufacturing, the coating structure is already optimized to resist wicking and maintain adhesion.
3Strength
If mechanical interlocking is enhanced through etching, then adhesion between encasement and lead frame is improved, but the surface coating still wicks under thermal stress
Solution Approach 1:
The surface coating is segmented into discontinuous regions that prevent thermal wicking pathways, addressing the thermal resistance issue. The mechanical interlocking through etching is maintained in the substrate while the coating segments prevent thermal migration, achieving both strong adhesion and thermal resistance.
Solution Approach 2:
The lead frame structure combines etched substrate material for mechanical interlocking with a discontinuous coating material for thermal resistance. This composite approach leverages the strengths of both materials: the etched surface provides mechanical bonding while the discontinuous coating prevents thermal wicking.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The discontinuous surface coating improves the thermal stability and longevity of the capacitor by preventing the formation of gaps between the encasement and lead frame, ensuring better resistance to thermal stress during reflow and normal use.
Implementation Method 1
the surface coating, 20, begins to flow, or wick, in the direction of the arrow thereby causing wicking of the surface coating from under the encasement, 22
Data Source
AI summary
Provided is a capacitor and method of forming the capacitor. The capacitor comprises a first capacitive couple comprising a first dielectric on a first anode and a first cathode on the first dielectric. The first anode and first cathode are connected to a lead frame comprising a discontinuous surface coating wherein the discontinuous surface coating comprises a contact region and a discontinuous region. At least one of the first anode or the first cathode is in electrical contact at the contact region. An encapsulant is in contact with the lead frame at the discontinuous region.