QFN Lead Trench Structure for Visible Wettable Flanks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Automotive electronic systems with quad flat no-leads package (QFN) face challenges in visual inspection due to obscured solderable leads, making it difficult to confirm successful soldering to a printed circuit board, and conventional wettable flank processes are hindered by copper burrs that affect soldering performance.
Innovation Solution
A package structure featuring discrete leads with a trench and lateral hole configuration, increasing the soldering space and visibility, and a method involving multiple sacrificial layers and metal layers to form the package structure, ensuring improved solder wettability and inspection ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wettable flank process is used to improve solderability, then wetting performance of side leads is improved, but copper burrs accumulate on the steps during cutting which affects soldering space
Solution Approach 1:
The patent extracts and removes the harmful copper burrs by forming a trench that extends through the lead body, allowing burrs to be separated from the main lead structure. The lateral hole further facilitates removal of burrs by providing an additional escape path, thus eliminating the harmful accumulation while preserving the wettable flank benefits.
Solution Approach 2:
The patent converts the potentially harmful copper burrs into beneficial soldering features by designing the trench and lateral hole to channel and concentrate solder material. The burrs, instead of blocking solder flow, become part of the solder pathway that enhances wetting area and visual inspection capability.
2Productivity
If QFN package is used for automotive electronics, then integration is improved, but visual inspection of soldered leads is obscured making inspection impossible
Solution Approach 1:
The patent utilizes optical contrast principles by creating a trench that exposes the internal structure of the lead. The lateral hole further enhances this effect by allowing light to interact with the solder material, creating visible reflections or color changes that indicate successful soldering. This enables automated visual inspection systems to detect solder presence without compromising QFN integration.
3Reliability
If trench is formed in lead to increase soldering space, then solder coverage is improved, but lead structure complexity increases
Solution Approach 1:
The patent segments the lead structure by introducing a trench that divides the lead into distinct regions. This segmentation creates the lateral surface for enhanced solder coverage while maintaining a systematic, modular structure that can be manufactured using standard semiconductor fabrication processes, thus managing complexity through structured division.
Solution Approach 2:
The patent adds a lateral dimension to the soldering interface by forming a lateral hole that connects to the trench. This creates a three-dimensional solder receptacle that increases solder coverage area without significantly increasing the overall lead footprint, effectively utilizing vertical and lateral spaces to enhance functionality while controlling structural complexity.
Data Source
AI summary
A package structure and a method are provided. The package structure includes: a die pad; a plurality of discrete leads disposed on either side of or around the die pad, wherein each of the leads includes an upper surface and a lower surface, a trench extending through a portion of the lower surface and a portion of an outer sidewall surface of a lead being formed in a region, away from the die pad, of the lead, a lateral hole being formed in the lead on a side surface of the trench, the lateral hole communicating with the trench to form a step; a first molding layer filling the gaps between the leads and the die pad; a semiconductor chip disposed on an upper surface of the die pad; and a second molding layer disposed on an upper surface of the first molding layer, the lead, and the die pad.