Leadframe Die Pad Anchoring Structure Against QFN Delamination
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Solution Overview
Problem
Quad flat no-lead (QFN) packages are susceptible to cracking due to differential thermal expansion between the leadframe and molding compound, leading to package failure, as the leadframe delaminates from the molding compound, especially at the edges of the die pad where stress is highest.
Innovation Solution
A leadframe design with angled flanges or anchoring posts around the die pad, which increases the contact surface area with the molding compound, providing a stronger bond and reducing the likelihood of delamination, by incorporating flanges that extend from the die pad's edge and are bent towards its center, or using anchoring posts with varying thicknesses to enhance the bonding with the molding compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a recess is etched under the edges of the die pad to form a seal between the molding compound and leadframe, then the package is protected from contaminants, but the differential thermal expansion between the metal leadframe and molding compound causes delamination and cracking at the outer edges
Solution Approach 1:
The patent transitions from a two-dimensional recess seal to a three-dimensional angled flange structure. The flanges extend outward from the die pad edges and are positioned at an angle (e.g., 45 degrees) relative to the die pad surface, creating a立体 sealing interface that increases contact area with the molding compound and distributes thermal stress more effectively.
Solution Approach 2:
The patent modifies the geometric parameters of the sealing structure by introducing angled flanges with specific dimensions and orientations. The flanges have defined widths, lengths, and angles that optimize both the sealing effectiveness and stress distribution, changing the physical parameters of the interface between leadframe and molding compound.
2Ease of manufacture
If the leadframe structure is simplified for easier manufacturing, then production efficiency increases, but the package becomes more susceptible to cracking due to insufficient stress distribution
Solution Approach 1:
The patent segments the die pad structure by adding discrete flange elements at the edges rather than creating a complex overall structure. Each flange is a separate, simple geometric feature that can be easily fabricated using standard PCB or leadframe manufacturing processes, while collectively providing enhanced stress distribution.
Solution Approach 2:
The patent applies structural modifications only at critical locations (the edges of the die pad) where stress concentration occurs during thermal cycling. The flanges are positioned specifically at the outer edges to provide localized reinforcement and sealing where it is most needed, while leaving the rest of the leadframe structure simple and easy to manufacture.
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
The increased surface area contact between the leadframe and molding compound prevents delamination and cracking, enhancing the reliability of integrated circuit packages by maintaining a strong bond despite thermal expansion and contraction cycles, and allowing for smaller package sizes with reduced failure risks.
Implementation Method 1
The flange is also bent towards a center of the die pad, such that a plane defined by a second, or top, surface of the flange is positioned at an angle with respect to the first surface of the die pad... The molding compound completely surrounds the flange, thus providing a strong bond between the molding compound and the leadframe
Implementation Method 2
the coefficients of thermal expansion, or the rate at which a size of an object changes in relationship to temperature, are different for the metal of the leadframe and the molding compound. As such, when the package endures repeated heating and cooling cycles during use, the metal that comprises the leadframe will expand and contract much more quickly than the surrounding molding compound
Data Source
AI summary
A leadframe having extensions around an outer edge of a die pad are disclosed. More specifically, leadframes are created with a flange formed at the outer edge of the die pad and extending away from the die pad. The flange is bent, such that it is positioned at an angle with respect to the die pad. Leadframes are also created with anchoring posts formed adjacent the outer edge of the die pad and extending away from the die pad. The anchoring posts have a central thickness that is less than a thickness of first and second portions opposite the central portion. When the leadframe is incorporated into a package, molding compound completely surrounds each flange or anchoring post, which increases the bond strength between the leadframe and the molding compound due to increased contact area. The net result is a reduced possibility of delamination at edges of the die pad.