Solder Dam Lead Frame for Capacitor Joint Integrity
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Solution Overview
Problem
Stacked multilayer capacitor assemblies face failures due to mechanical stress and thermal expansion mismatches between capacitors and circuit boards, leading to cracked solder joints and mechanical failure, particularly when high-temperature and low-temperature solders come into contact during the soldering process, resulting in a low-melting alloy that can fail at operating temperatures.
Innovation Solution
Incorporating solder dams with physical barriers or areas of reduced wettability on lead frames to prevent contact between high-temperature and low-temperature solders, thereby preventing the formation of a low-melting alloy that can cause joint failure, by acting as a barrier to solder flow and reducing the wettability of the solder on specific surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead frames are used to provide mechanical compliance between capacitors and circuit boards, then the durability against thermal expansion mismatch is improved, but the risk of solder joint failure due to mechanical stress remains
Solution Approach 1:
The lead frame structure is segmented into distinct functional zones: a compliance portion that absorbs thermal expansion stress and a solder joint portion that maintains strong electrical connection. This segmentation allows different parts of the lead frame to perform different functions simultaneously, resolving the contradiction between mechanical compliance and joint strength.
Solution Approach 2:
Different portions of the lead frame are given different local properties: the compliance portion has increased flexibility and lower modulus of elasticity to absorb stress, while the solder joint portion maintains high strength and rigidity for reliable electrical connection. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Reliability
If solder dams with physical barriers are added to prevent solder contact, then the reliability of solder joints is improved, but the device complexity increases
Solution Approach 1:
The solder dam function is merged into the lead frame structure itself rather than being a separate component. The lead frame is designed with integrated barriers and wettability variations that perform the solder containment function, eliminating the need for additional solder dam components and reducing overall device complexity.
Solution Approach 2:
Instead of adding physical barriers, the solution changes the surface parameters of the lead frame by creating areas of reduced wettability. This parameter change approach prevents solder bridging through chemical surface properties rather than mechanical barriers, simplifying the structure while maintaining reliability.
3Reliability
If areas of reduced wettability are created on lead frame surfaces, then the prevention of solder bridging is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The reduced wettability areas are created during the lead frame manufacturing process itself, before the capacitor assembly is formed. This preliminary action ensures that the wettability pattern is established early and remains consistent throughout subsequent manufacturing steps, reducing the need for additional precision adjustments later in the process.
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 solder dams effectively prevent contact between different solder compositions during mounting, reducing the frequency of joint failures and enhancing the durability and reliability of the capacitor assemblies by maintaining the integrity of the solder joints at operating temperatures.
Implementation Method 1
The first solder dam includes a area of reduced wettability to the solder than a wettability of surfaces on the remainder of the first lead frame
Data Source
AI summary
An electrical device for soldering to a circuit board with a solder includes a capacitor, a lead frame including a solder dam, and a solder joint electrically coupling the capacitor to the lead frame. The solder dam includes one of a physical barrier to flow or an area of reduced wettability to the solder. The solder dam is between the solder joint and the circuit board. The solder dam is on one or both of a lead portion and main portion of the lead frame. In one embodiment, the first solder dam extends substantially the full width of the first lead portion. The solder dam may be a barrier and/or include a metal oxide. A method of manufacturing the device includes soldering a lead frame to a capacitor with a solder and modifying a surface on the lead frame to include a physical barrier and/or an area of reduced wettability.