Wettable Flank Lead Structure for Oxidation-Resistant Solder Inspection
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Solution Overview
Problem
Semiconductor packages with exposed copper terminations face challenges in solderability due to oxidation, making visual inspection of solder joint integrity difficult, especially in high-reliability applications like automotive, where full electrical testing is not feasible.
Innovation Solution
A packaged electronic device structure with an enhanced wettable flank surface, featuring a lead with a thick terminal portion and a thin terminal portion, where the outward-facing side surface is exposed and coated with a conductive layer for improved solderability and optical inspection, enhancing bond integrity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If exposed copper terminations are used on semiconductor packages, then manufacturing cost is reduced and structure is simplified, but solderability deteriorates due to copper oxidation and visual inspection capability is lost
Solution Approach 1:
The patent applies local quality by providing a wettable flank plating layer only on the flank surfaces (side surfaces) of the lead structure, while the top and bottom surfaces maintain their original copper termination structure. This localized plating approach improves solderability and visual inspection capability at the critical flank areas without requiring complete plating of all lead surfaces, thus balancing manufacturing cost with reliability enhancement.
Solution Approach 2:
The patent employs composite materials by combining copper (for electrical conductivity and cost-effectiveness) with a wettable flank plating layer (such as tin, nickel, or zinc coating) on the flank surfaces. This composite structure leverages the advantages of both materials: copper provides excellent electrical properties and low cost, while the plating layer provides enhanced solderability and oxidation resistance at the critical bonding interfaces.
2Reliability
If wettable flank plating is applied to improve solderability and visual inspection, then manufacturing complexity and cost increase
Solution Approach 1:
The wettable flank plating is applied locally only to the flank surfaces of the lead structure rather than the entire lead surface. This localized approach reduces the amount of plating material required and simplifies the plating process setup, thereby reducing manufacturing complexity and cost while still achieving the reliability benefits of improved solderability and visual inspection capability at the critical bonding areas.
3Ease of manufacture
If traditional flat lead terminations are used, then manufacturing is simpler, but optical inspection of solder joints is difficult or impossible
Solution Approach 1:
The patent introduces a dimensional change by creating a raised flank surface structure on the lead terminations. Instead of flat two-dimensional contact surfaces, the lead structure includes elevated flank surfaces that extend vertically. This three-dimensional configuration allows optical inspection systems to view the solder joints from the side at an angle, making the solder fillets visible and inspectable, thereby solving the optical inspection difficulty while maintaining manufacturing simplicity.
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 enhanced wettable flank surface facilitates stronger solder joints and allows for visual verification of solder fillet joints, improving reliability and manufacturing efficiency while being cost-effective and suitable for various electronic devices.
Implementation Method 1
Wettable flank plating is an additional process step that deposits a solderable conductive material, such as tin, with a normal conductive material thickness, on the semiconductor package underside terminals and on the exposed edge terminations or flanks.
Data Source
AI summary
A packaged electronic device includes a substrate having a lead. The lead includes an outward facing side surface having a first height, and an inward facing side surface having a second height that is less than the first height. An electronic device is electrically connected to the lead. A package body encapsulates the electronic device and portions of the lead. The outward facing side surface is exposed through a side surface of the package body, and the inward facing side surface is encapsulated by the package body. A conductive layer is disposed on the outward facing side surface to provide the packaged electronic device with an enhanced wettable flank. In one embodiment, the electronic device is electrically connected to a thick terminal portion having the outward facing side surface. In another embodiment, the electronic device is electrically connected to a thin terminal portion having the inward facing side surface.