Preformed Lead Frame Adhesion Layer
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Solution Overview
Problem
Conventional quad flat no-lead (QFN) lead frame devices experience poor adhesion strength between the polymeric encapsulating layer and the metallic die pad, affecting the reliability and performance of chip packaging devices.
Innovation Solution
A preformed lead frame device with an adhesion-strengthening layer, comprising a die pad sub-unit, lead sub-unit, and a polymeric molding layer, where the adhesion-strengthening layer is made of an oxide of the same metal material as the lead frame units, enhancing the adhesion between the molding layer and the die pad and leads, and the molding layer is designed to prevent solder overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the polymeric encapsulating layer is directly applied to the metallic die pad, then the packaging process is simple, but the adhesion strength between the encapsulating layer and die pad is poor
Solution Approach 1:
An adhesion-strengthening layer is introduced as an intermediary between the polymeric encapsulating layer and the metallic die pad. This intermediate layer acts as a mediator that chemically or physically bonds to both surfaces, significantly improving adhesion strength while maintaining a relatively simple overall structure.
Solution Approach 2:
The encapsulation structure employs composite materials by combining the polymeric encapsulating layer with an adhesion-strengthening layer of different material composition. This composite approach leverages the adhesive properties of one material and the protective properties of another to achieve superior bonding.
2Reliability
If the ratio of chip area to die pad area is reduced to minimize heterogeneous interfaces, then adhesion is improved, but the chip mounting flexibility and heat dissipation are compromised
Solution Approach 1:
The adhesion-strengthening layer serves as a universal intermediary that can accommodate various chip sizes and configurations on the die pad. This mediator enables strong bonding across different chip-die pad area ratios, providing both adhesion strength and mounting flexibility simultaneously.
Solution Approach 2:
The die pad structure is segmented into multiple regions with different functionalities: a central mounting area for the chip, peripheral adhesion regions with the strengthening layer, and edge regions for lead connections. This segmentation allows optimized performance for each function while working together as a unified structure.
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
Improves the adhesion strength between the molding layer and the lead frame units, enabling reliable chip packaging by preventing solder overflow and supporting chips of variable sizes, thus enhancing the overall performance and reliability of the chip packaging device.
Implementation Method 1
the adhesion-strengthening layer is made of an oxide of the same metal material as the lead frame units, enhancing the adhesion between the molding layer and the die pad and leads
Data Source
AI summary
A preformed lead frame device includes multiple spaced-apart longitudinal sections, multiple spaced-apart transverse sections intersecting the longitudinal sections, and multiple preformed lead frame units each surrounded by two adjacent ones of the longitudinal sections and two adjacent ones of the transverse sections. Each of the preformed lead frame units includes a die pad sub-unit including a die pad portion, multiple pillar portions, and a first gap formed among the die pad portion and the pillar portions, a lead sub-unit including leads and a second gap formed among the die pad sub-unit and the leads, an adhesion-strengthening layer disposed in the first and second gaps, and a molding layer filling the first and second gaps to cover the adhesion-strengthening layer.