Vertical Connection Bars in QFN Lead Frames
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Solution Overview
Problem
Conventional quad-flat no-leads (QFN) packages require additional processing steps such as half-cutting and selective plating after encapsulation to disconnect and separate multiple rows of leads, which is inefficient and costly.
Innovation Solution
A lead frame design with inner and outer rows of leads and bendable connection bars that connect inner row leads to outer row leads before encapsulation, allowing for vertical positioning of connection bars post-encapsulation to simplify the disconnection process and eliminate the need for additional cutting and plating steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional lead frame design with horizontal connection bars is used, then multiple rows of leads can be connected, but additional half-cutting and selective plating steps are required after encapsulation
Solution Approach 1:
The connection bars are repositioned from a horizontal configuration (in the plane of the lead frame) to a vertical configuration (perpendicular to the lead frame plane). This dimensional change allows the connection bars to extend through the molding compound, enabling electrical connection between inner and outer rows of leads without requiring post-encapsulation cutting or plating operations.
2Ease of manufacture
If conventional lead frame design is used, then assembly is simpler initially, but additional cutting and plating operations increase manufacturing complexity
Solution Approach 1:
The connection bars are pre-positioned in a vertical orientation before encapsulation with the molding compound. This preliminary positioning ensures that the electrical connections between lead rows are established in advance, eliminating the need for subsequent cutting and plating operations and streamlining the overall manufacturing process.
3Reliability
If connection bars remain horizontal after encapsulation, then lead connections are maintained, but disconnection of lead rows requires additional cutting steps
Solution Approach 1:
By extending the connection bars vertically through the molding compound, the patent enables a simple cutting operation at the top surface to disconnect lead rows. This vertical configuration provides accessible connection points that can be easily severed without requiring complex disassembly or additional processing steps.
Data Source
AI summary
A semiconductor device includes a lead frame having a die support area and a plurality of inner and outer row leads surrounding the die support area, and a semiconductor die mounted on the die support area and electrically connected to the leads with bond wires. A molding material encapsulates the semiconductor die, the bond wires, and the leads, and defines a package body. The semiconductor device further includes connection bars extending vertically from the leads to a top surface of the package body. The connection bars connect the inner row leads to respective ones of the outer row leads before the molding process is performed.