Leadframe Wettable Flanks via Tie-Bar Electroplating
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Solution Overview
Problem
Semiconductor packages with leadframes face issues of reduced wettability and corrosion on exposed portions of leads due to lack of tin coating, leading to poor solder joints that cannot withstand extreme atmospheric conditions.
Innovation Solution
Implementing a leadframe design with half-etched gate and source leads directly coupled to tie bars, allowing for electroplating of flanks using only the tie bars, which replaces the need for electroless plating and reduces processing steps and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional leadframe design is used without half-etching, then manufacturing process is simpler, but wettability and corrosion resistance of leads deteriorate
Solution Approach 1:
The leadframe structure is segmented into distinct functional zones: half-etched leads with flanks for electroplating, tie bars for mechanical support, and unetched portions for structural integrity. This segmentation allows different regions to serve specialized functions, with the half-etched flanks providing enhanced wettability and corrosion resistance through electroplating while maintaining overall structural simplicity
Solution Approach 2:
The leadframe applies local quality by selectively etching only specific portions of the leads to create flanks, while leaving other portions unetched. This localized etching creates wettable surfaces exactly where needed for solder joints, without complicating the entire leadframe structure, thus improving reliability at the critical interface while maintaining manufacturing simplicity elsewhere
2Reliability
If electroless plating is used to coat lead flanks, then wettability improves, but manufacturing cost and processing steps increase
Solution Approach 1:
The invention replaces the chemical-based electroless plating system with an electroplating system. Instead of relying on autocatalytic chemical deposition, the patent uses electrical current delivered through tie bars to deposit solder alloy onto the lead flanks. This substitution enables better control over plating thickness and composition while simplifying the manufacturing process and reducing costs
Solution Approach 2:
The tie bars serve as intermediaries in the electroplating process, conducting electrical current from the power source to the lead flanks. This intermediary mechanism enables precise control of the electroplating deposition, ensuring uniform solder alloy coating on the wettable flanks while eliminating the need for complex electroless plating chemistry and processing steps
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 solution enhances the wettability and reliability of solder joints by enabling electroplating of lead flanks, eliminating the need for additional electroless plating processes and reducing costs, while maintaining corrosion resistance.
Implementation Method 1
The gate tie bar and the source tie bar may be configured to enable electroplating of a flank of the half-etched gate lead and the half-etched source lead
Data Source
AI summary
Implementations of a leadframe for a semiconductor package may include a half-etched gate lead directly coupled to a gate tie bar; a half-etched source lead directly coupled to a source tie bar; and a die flag directly coupled to at least two die flag tie bars. The gate tie bar and the source tie bar may be configured to enable electroplating of a flank of the half-etched gate lead and the half-etched source lead.