Recess Lead for Surface Mount Package Wettable Flank
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Solution Overview
Problem
The existing QFN surface mount packaging technology faces challenges with dimensional and inspection limitations due to the design of the wettable flank lead, which can result in reliability issues and copper burrs during the singulation process, and there is a need for improved electrical isolation between adjacent leads.
Innovation Solution
The design includes a lead with a central segment and extensions on either side, featuring a recess for solder inspection and a wider copper area to reduce etch time and prevent copper burrs, with angular edges and a step-style shape to enhance solder wettability and integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a wettable flank lead design is used to enable visual solder inspection, then solder wettability and inspection capability are improved, but dimensional limitations and electrical isolation between adjacent leads deteriorate
Solution Approach 1:
The lead is divided into distinct segments: a body portion and an extended portion that protrudes beyond the encapsulant. This segmentation allows the extended portion to serve as a dedicated wettable flank for solder inspection while the body portion maintains proper electrical isolation. The physical separation between adjacent leads is preserved through this segmented structure, preventing electrical interference while enabling visual solder joint verification.
Solution Approach 2:
The lead structure extends into a third dimension by having the extended portion protrude beyond the encapsulant surface. This dimensional extension creates a wettable flank that is accessible for visual inspection without compromising the planar electrical isolation between adjacent leads. The extended portion provides an additional dimension for solder wettability while maintaining the original two-dimensional electrical isolation geometry.
2Ease of manufacture
If traditional etching process is used to create wettable feature, then manufacturing simplicity is maintained, but copper burrs are produced during singulation
Solution Approach 1:
The etching parameters are modified by adjusting the etch depth to create a stepped profile rather than a uniform recess. The etch depth is controlled to stop at the boundary between the lead and the encapsulant, preventing over-etching that would generate copper burrs. This parameter change maintains the simplicity of the etching process while eliminating the harmful copper burr formation during subsequent singulation operations.
3Reliability
If plating process is used to create wettable feature, then solder wettability is improved, but curved edge and insufficient step cut dimensions are produced
Solution Approach 1:
The lead structure incorporates a localized extended portion with specific geometric characteristics optimized for solder wettability. This extended portion has increased surface area and appropriate geometry to enhance solder attachment, while the rest of the lead maintains its original dimensions. The local quality enhancement is concentrated where needed for soldering without affecting the overall manufacturing precision of the leadframe structure.
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
This design improves the reliability and manufacturability of the wettable flank by reducing the concave crescent shape, increasing electrical isolation, and minimizing copper burrs, while maintaining sufficient solder wettability and inspection capabilities.
Implementation Method 1
The recess is sized and configured to accommodate reflowing solder therein to enable a visual solder inspection
Implementation Method 2
the solder to wick up the edge of the package for visual inspection
Data Source
AI summary
A lead for a surface mount package for a semiconductor device, and the surface mount package employing the same. In one example, the lead includes a central segment with a first side and a second side, a first extension from a portion of the first side, and a second extension from a portion of the second side. The lead also includes a recess extending through a portion of the central segment, the first extension and the second extension.