Alternating Leadframe Rows Prevent Solder Bridging in QFN Packages
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Solution Overview
Problem
Single-sided multi-row QFN semiconductor packages face issues such as solder bridging and lead-to-lead shorting during punch singulation, and lead shorting due to smearing during sawn singulation, which affect the quality and functionality of the device.
Innovation Solution
The design features a leadframe with alternating first and second rows of leads, where the outer ends of the first leads form a first row and the outer ends of the second leads form a second row, with an encapsulant covering at least a portion of the leads to prevent solder bridging and lead-to-lead shorting, and includes a flange to enhance package integrity and prevent moisture penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If punch singulation is used to separate semiconductor packages, then production efficiency is improved, but solder bridging and lead-to-lead shorting occur during the process
Solution Approach 1:
The patent applies preliminary action by removing portions of the leads (creating notches or gaps) before the singulation process. This pre-modification of the lead structure prevents solder bridging and lead-to-lead shorting during punch singulation, allowing high-speed production while maintaining package quality.
Solution Approach 2:
The patent extracts or removes specific portions of the leads (creating notches, gaps, or removing outer portions) to eliminate the problematic areas where solder bridging and shorting occur. This extraction of critical portions prevents defects while maintaining the overall lead functionality.
2Manufacturing precision
If sawn singulation is used to separate semiconductor packages, then manufacturing precision is improved, but lead smearing causes adjacent leads to short
Solution Approach 1:
The patent applies preliminary action by pre-modifying the lead structure (creating notches, gaps, or removing portions) before sawn singulation. This pre-modification prevents lead smearing from causing short circuits between adjacent leads during the cutting process, maintaining both precision and reliability.
Solution Approach 2:
The patent extracts or removes specific portions of the leads to eliminate the vulnerable areas where smearing occurs. By taking out these critical portions beforehand, the lead structure is protected from smearing-induced shorting during sawn singulation.
3Device complexity
If traditional leadframe structure is used, then device complexity is reduced, but moisture penetration and separation between mold cap and leadframe occur
Solution Approach 1:
The patent applies local quality by modifying specific portions of the leadframe structure (adding features such as notches, gaps, or enhanced bonding structures at critical locations) rather than redesigning the entire leadframe. This localized modification improves moisture resistance and bonding integrity while maintaining overall structural simplicity.
Data Source
AI summary
A semiconductor package includes a plurality of first leads, each with a top outer portion removed from the lead and an outer end, and a plurality of second leads, each with a bottom outer portion removed from the lead and an outer end. The first and second leads alternate with each other along an edge of the package. Also, the outer ends of the first leads form a first row along the edge of the package and the outer ends of the second leads form a second row along the edge of the package. In one embodiment, the first and second rows are parallel to each other and an encapsulant covers at least a portion of the first and second leads.