QFN Strip Etch Isolation for Leadframe Singulation
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Solution Overview
Problem
Current methods for electrically isolating leads in leadless plastic chip carrier packages are inefficient, either being slow, structurally weak, complex, and costly, or affecting positional accuracy, particularly during final electrical testing and singulation processes.
Innovation Solution
The use of chemical etching techniques to electrically isolate leads within the strip format of leadless plastic chip carrier packages, allowing for electrical testing before singulation, utilizing etch masks and plating to selectively remove leadframe material at dambar regions, thereby isolating individual units without the need for mechanical saw-cutting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical removal of the dambar using a circular saw is used, then electrical isolation of leads is achieved, but the operation is slow and creates a structurally weak array of IC components
Solution Approach 1:
The patent replaces the mechanical circular saw cutting system with a chemical etching system. The etching process uses chemical solutions to selectively remove the dambar material, achieving electrical isolation without mechanical contact. This substitution eliminates the structural weakness caused by mechanical cutting while maintaining isolation effectiveness.
Solution Approach 2:
The patent changes the physical state and properties of the dambar material through chemical etching. By controlling etching parameters such as solution concentration, temperature, and exposure time, the dambar is selectively removed to the required depth without affecting the structural integrity of the remaining IC component array.
2Measurement precision
If mounting on adhesive tape followed by mechanical singulation is used, then electrical isolation is achieved, but the structure becomes bulky and positional accuracy is affected
Solution Approach 1:
The patent extracts and removes the adhesive tape mounting step from the process. By performing etching directly on the leadframe strip in its original configuration, the method eliminates the need for secondary mounting operations, thereby reducing structural bulkiness and maintaining positional accuracy.
Solution Approach 2:
The patent performs the electrical isolation action before any mounting or singulation operations. The etching process is applied to the leadframe strip while it is still in its original state, establishing electrical isolation prior to any subsequent handling or mounting steps, thus preserving positional accuracy and simplifying the overall structure.
3Ease of manufacture
If mechanical singulation and transfer to shipping containers is used, then electrical isolation is achieved, but the process becomes complex, expensive and time-consuming
Solution Approach 1:
The patent merges the electrical isolation function with the existing leadframe strip structure. By etching the dambar regions directly on the strip, the method combines isolation with the original manufacturing flow, eliminating separate singulation and container transfer steps, thereby simplifying the process and reducing time loss.
Solution Approach 2:
The patent creates a universal etching process that can be applied to leadframe strips of various configurations without requiring unique tooling for each device body size and lead spacing. This multi-functional approach eliminates the need for specialized punch tooling and complex handling procedures, simplifying manufacturing across different product variants.
4Adaptability or versatility
If precision mechanical punch tool is used for isolation, then electrical isolation is achieved, but unique tooling is required for each device size and delamination risk increases
Solution Approach 1:
The patent replaces the mechanical punch tool system with a chemical etching system. The etching process uses chemical solutions that can be applied uniformly across different device sizes and configurations, eliminating the need for unique mechanical tooling for each device variant and reducing the complexity of tooling requirements.
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 method reduces indexing and testing times by enabling efficient electrical isolation within the strip format, improving mechanical stability and positional accuracy of individual units, and lowering process costs by eliminating the need for unique punch tooling and reducing delamination risks.
Implementation Method 1
The exposed leadframe material is etched using a etching solution to electrically isolate the leads and individual QFN units from one another
Implementation Method 2
a plating is formed on a bottom surface of the die attach pads, and a portion of the bottom surface of the leadframe where an etch mask is not formed
Data Source
AI summary
Various structures and fabrication methods for leadless plastic chip carrier (QFN) packages which utilize carriers in strip format, wherein the leads (or terminals) are formed to be electrically isolated from one another within each unit and in which the units are formed to be electrically isolated from one another within the strip using chemical etching techniques.