Leadframe Thickness Layout for Stable Wire Bonding
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Solution Overview
Problem
In semiconductor device packaging, cantilever leads can deflect or become misaligned during wire bonding, leading to defects such as mold flash and unreliable surface mount solder joints, especially when not adequately supported.
Innovation Solution
A metal leadframe design with full thickness interior ends and partial thickness central portions, where the interior ends are supported during wire bonding, preventing deflection and misalignment, and allowing for reliable stitch bonding without additional mechanical supports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cantilever leads are used with thinner interior ends to increase mold compound adhesion, then adhesion is improved, but the leads become prone to deflection and misalignment during wire bonding
Solution Approach 1:
The lead is designed with varying thickness along its length: the interior end portion has reduced thickness to maximize mold compound adhesion, while the exterior end portion maintains full thickness to provide structural support and stability during wire bonding. This local variation in geometric property resolves the contradiction by optimizing each region for its specific function.
2Reliability
If custom heater blocks are used to support cantilever leads during wire bonding, then wire bonding reliability is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The leadframe structure itself provides support during wire bonding through its rigid connection to the die pad and its inherent structural integrity. The lead's attachment to the die pad and its geometric design allow it to maintain stability during the wire bonding process without requiring external support structures like custom heater blocks, thereby simplifying the packaging process.
3Reliability
If additional mechanical supports are added to prevent lead deflection, then wire bonding reliability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The leadframe is designed with a specific geometric configuration where the interior end portion of the lead has reduced thickness while the exterior end portion maintains full thickness. This local variation in structure provides the necessary support and rigidity during wire bonding without adding external mechanical supports, maintaining manufacturing simplicity.
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 design enhances the reliability of semiconductor device packages by preventing lead deflection and misalignment during wire bonding, reducing defects and ensuring consistent surface mount solder joints without requiring additional mechanical supports or changes to existing processes.
Implementation Method 1
the semiconductor die has bond pads that are used to form electrical connections to the leads using bond wires. Wire bonding is a well understood process long used in the semiconductor industry
Implementation Method 2
Mold compound covers the semiconductor die, the die pad, the wire bonds, the interior ends of the leads, the central portion of the leads, and portions of the exterior ends of the leads to form a semiconductor device package
Data Source
AI summary
An example apparatus includes: a metal leadframe including a die pad in a central portion and leads spaced from the die pad. The leads include: an interior end spaced from the die pad and having a full thickness of the metal leadframe; a central portion connected to the interior end and extending away from the die pad having a partial thickness less than the full thickness; and an exterior end having the full thickness extending from the central portion. A semiconductor die is mounted to the die pad by die attach material. Wire bonds couple bond pads of the semiconductor die to the interior ends of the leads. Mold compound covers the semiconductor die, the die pad, the wire bonds, the interior ends of the leads, the central portion of the leads, and portions of the exterior ends of the leads to form a semiconductor device package.