3-Sided Wettable Flank Leads for Mounting Stability and AOI
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Semiconductor devices with two or more leads exposed on one side have low package shear strength, leading to defects such as package tilt and instability during board surface mounting, and lack solder joint inspection capability by automated optical inspection tools.
Innovation Solution
A semiconductor device with a 3-sided wettable flank is developed, where the leads have three visible surfaces plated with Ni/Pd/Au alloy for enhanced wettability, increasing the electrical connection surface area and providing higher solder shear strength, better package mount coplanarity, and enabling automated optical inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If leads are connected by top surface and one side surface only, then manufacturing is simpler, but package shear strength is low and placement stability is poor
Solution Approach 1:
The patent transitions from a 2-sided connection (top surface and one side surface) to a 3-sided connection (top surface and two side surfaces forming a wettable flank). This dimensional expansion of the connection interface increases the bonding area and distributes mechanical stress more effectively, thereby enhancing package shear strength and placement stability without requiring fundamentally new manufacturing capabilities.
Solution Approach 2:
The lead structure is segmented into distinct wettable surfaces (top surface and two side surfaces) that are selectively plated. This segmentation allows each surface to contribute independently to the overall bonding strength, with the combined effect providing superior shear strength compared to a single continuous connection surface.
2Measurement precision
If leads have only top surface and one side surface connection, then device structure is simpler, but automated optical inspection capability is lost
Solution Approach 1:
The patent applies metallic plating (Ni/Pd/Au) to specific surfaces of the leads, creating distinct reflective characteristics that enhance visibility under automated optical inspection systems. The wettable flank configuration with its multiple plated surfaces provides sufficient geometric complexity and optical contrast for AOI tools to detect and measure solder joint quality accurately.
3Reliability
If leads are plated with Ni/Pd/Au alloy on three surfaces, then wettability and solder joint reliability improve, but manufacturing complexity increases
Solution Approach 1:
Instead of plating the entire lead structure uniformly, the patent applies Ni/Pd/Au alloy plating selectively to specific surfaces (top surface and two side surfaces forming the wettable flank). This localized plating approach concentrates the enhanced wettability and solder joint reliability where needed most, while reducing the overall material cost and manufacturing complexity compared to full-surface plating.
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 3-sided wettable flank design enhances package shear strength, reliability, and stability during mounting, reducing defects like tilt and rotation, while allowing for automated solder joint inspection and improved solder joint reliability.
Implementation Method 1
the leads have three visible surfaces plated with Ni/Pd/Au alloy for enhanced wettability
Data Source
AI summary
A semiconductor device has a substrate and leads formed on two or more sides of the substrate. An electrical component is disposed over the substrate and electrically connected to the lead with bumps or bond wires. The electrical component is encapsulated. A portion of the substrate is removed to form a wettable flank on at least three sides of the lead. The substrate has a molding compound and the lead is disposed within or adjacent to the molding compound. A portion of the molding compound can remain at corners of the substrate. The lead has a first surface or recessed surface on a first side of the lead, a second surface or recessed surface on a second side of the lead, and a third surface or recessed surface on a third side of the lead. A portion of a surface of the lead is plated.