Semiconductor Lead Wettable Flanks via Temporary Conductive Bridging
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Solution Overview
Problem
Existing semiconductor packages face challenges in achieving sufficient thickness and variety of wettable materials on lead flanks due to the physical disconnection of leads from the leadframe post-cutting, limiting solder wetting and bondability with the motherboard.
Innovation Solution
The method involves applying an electrically conductive layer to establish an electrical connection between cut leads and the leadframe, enabling electroplating of lead flanks to achieve thicknesses greater than 2 microns, using either an electrically conductive tape or a jig with pogo pins to facilitate electroplating, and subsequently removing the layer to form wettable flanks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If leads are cut from the leadframe to form individual packages, then package independence and singulation are achieved, but electrical connection between leads and leadframe is lost, preventing electroplating of flanks
Solution Approach 1:
The patent applies preliminary action by establishing electrical connection through conductive tape before the electroplating process. The conductive tape is applied to the leadframe and leads in advance, creating a temporary electrical pathway that enables electroplating of the flanks even after cutting. This preliminary setup resolves the contradiction by ensuring electrical connection is established before the cutting operation that would otherwise break it.
2Reliability
If electroplating is applied to achieve thick wettable material (>2 microns), then solder wetting capability is improved, but process complexity increases due to need for conductive layer application and removal
Solution Approach 1:
The conductive tape serves as an intermediary element that enables the electroplating process. It is applied to the leadframe and leads, providing the necessary electrical connection for electroplating to occur. After electroplating deposits the thick wettable material on the flanks, the tape is removed. This intermediary approach resolves the contradiction by simplifying the overall process compared to alternative methods, while achieving the desired thick plating for solder wetting.
3Reliability
If conductive tape is applied over entire leadframe, then electrical connection is ensured for all leads, but material usage and processing time increase
Solution Approach 1:
The patent applies local quality by positioning the conductive tape specifically where electrical connection is needed - on the leadframe and leads that require electroplating. Rather than uniformly covering the entire leadframe, the tape is applied locally to the relevant surfaces. This resolves the contradiction by using the minimum necessary material to achieve reliable electrical connection for the electroplating process.
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 approach enhances the solder wetting capability and bondability of the leads to the motherboard, improving the reliability and efficiency of semiconductor package connections.
Implementation Method 1
electroplating the flank of the at least one lead to render the flank wettable
Data Source
AI summary
Implementations of a method of providing wettable flanks on leads of a semiconductor package may include applying mold compound around a plurality of leads included in a leadframe; electroplating exposed portions of the plurality of leads; cutting at least one lead of the plurality of leads to expose a flank of the least one lead; applying an electrically conductive layer over the plurality of leads; electroplating the flank of the at least one lead to render the flank wettable; removing the electrically conductive layer from the plurality of leads; and singulating to form a semiconductor package.