Power QFN Lead Frame With Segmented Die Pad
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Solution Overview
Problem
The existing resin-encapsulated semiconductor devices, particularly power QFN packages, face challenges in maintaining adhesion between the die pad and the resin encapsulant, leading to potential separation and reliability issues, especially when the semiconductor chip size exceeds that of the die pad, and are prone to stress-related failures due to resin encapsulation deformation.
Innovation Solution
A lead frame design with a die pad having a middle part formed at a higher level than the peripheral part, featuring a to-be-filled portion such as through holes or grooves in the thin part, enhances adhesion and stress distribution, allowing for semiconductor chips of various sizes to be mounted while preventing resin encapsulant separation and improving moisture resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the back face of the die pad is exposed to function as a heat-radiating plate, then heat radiation performance is improved, but adhesion between the die pad and resin encapsulant deteriorates due to separation
Solution Approach 1:
The die pad is segmented into a body portion and a thin part, creating a structured division that allows the resin encapsulant to mechanically interlock through through-holes formed in the thin part. This segmentation maintains the exposed back face for heat radiation while preventing separation through the anchoring effect of the through-holes.
Solution Approach 2:
Through-holes are formed in the thin part of the die pad, creating a porous structure that allows the resin encapsulant to penetrate and anchor into the die pad. This porous configuration enhances mechanical interlocking and adhesion while preserving the heat radiation function of the exposed back face.
2Productivity
If the size of the semiconductor chip is reduced to achieve higher assembly density, then productivity is improved, but heat radiation capability deteriorates due to smaller heat-generating components
Solution Approach 1:
The invention transitions from relying solely on chip size for heat radiation to utilizing the die pad's back face as a dedicated heat radiation surface. This dimensional shift allows small chips to be assembled at high density while the exposed die pad back face provides sufficient heat radiation area through its larger surface area relative to the chip.
3Reliability
If the outer edge portion of the die pad is formed with a thin part to allow resin encapsulant penetration, then adhesion is improved, but structural strength deteriorates
Solution Approach 1:
The thin part is created only at the outer edge portion of the die pad, applying the adhesion-enhancing thin structure locally where it is most needed for mechanical interlocking. The body portion of the die pad maintains its full thickness and structural integrity, while the localized thin part provides the necessary adhesion through resin penetration.
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 enhanced adhesion and stress distribution in the resin-encapsulated semiconductor device improve reliability and moisture resistance, enabling the use of semiconductor chips of different sizes without compromising package integrity, and effectively manage heat dissipation through the exposed die pad.
Implementation Method 1
an outer edge portion of the peripheral part is formed with a thin part which forms part of the upper part of the die pad projecting laterally beyond the lower part thereof and is formed with a to-be-filled portion
Implementation Method 2
Since the back face of the die pad 102 is exposed, this allows the die pad 102 to function as a heat-radiating plate. By bringing the die pad 102 into contact with a heat-radiating portion of a motherboard, heat emitted from a power semiconductor element consuming a lot of power is dissipated to outside
Data Source
AI summary
A power QFN package includes signal leads, a die pad, support leads, and an adhesive for die bonding. These elements are encapsulated with a resin encapsulant. The lower parts of the signal leads are exposed from the resin encapsulant to function as external electrodes. A middle part of the die pad is formed at a higher level than a peripheral part thereof. This permits the formation of through holes in a thin part of the die pad. This enhances the degree of flexibility in the size of a semiconductor chip and the moisture resistance thereof.