QFN Package Lead Frame Design for Delamination Reduction

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Solution Overview

Problem

Quad flat no-leads (QFN) packages face issues with delamination and epoxy bleed-out due to temperature changes and mechanical stresses, and occupy excessive space on circuit boards, especially when accommodating different IC die sizes.

Innovation Solution

The design incorporates a second set of leads with internal ends extending inwardly to form a die pad area, reducing package size and eliminating the need for a top die paddle support, while maintaining the same lead count and die size, with first and second contact pads arranged in alternating or offset patterns for improved thermal management.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single row of contact pads is used in QFN packages, then the package structure is simple, but delamination and epoxy bleed-out occur due to temperature changes and mechanical stresses

Engineering Contradiction:

Improvepackage structureVSAvoiddelamination resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The single row of contact pads is segmented into two alternating rows, creating a more distributed support structure that reduces stress concentration and prevents delamination while maintaining structural simplicity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The alternating contact pad pattern is pre-designed to distribute thermal and mechanical stresses evenly before they can cause delamination or epoxy bleed-out, proactively preventing these reliability issues

Inventive Principle:

Principle #10Preliminary action

2Temperature

If a top die paddle support is used to provide thermal path, then thermal performance is improved, but package size increases occupying excessive space on circuit board

Engineering Contradiction:

Improvethermal performanceVSAvoidpackage footprint

Core Design Contradiction:

TemperatureVSArea of stationary object

Solution Approach 1:

The separate top die paddle support structure is removed entirely, with thermal management functions redistributed to the lead frame and alternating contact pads, eliminating the space-consuming component while maintaining thermal performance

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The lead frame and contact pads are designed to serve multiple functions simultaneously: electrical connection, mechanical support, and thermal management, eliminating the need for dedicated separate components and reducing overall package footprint

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of manufacture

If the IC die is small relative to the top die paddle support, then manufacturing is easier, but delamination occurs due to poor adhesion and stress concentration

Engineering Contradiction:

Improvedie attachmentVSAvoidadhesion stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The alternating contact pad pattern creates localized support zones distributed across the die pad area, providing optimal adhesion points that match the die size and prevent stress concentration, ensuring reliable attachment regardless of die dimensions

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS9324643B1Integrated circuit device having exposed contact pads and leads supporting the integrated circuit die and method of forming the device

Publication Date: 2016.04.26 STMICROELECTRONICS INT NV

AI summary

An integrated circuit (IC) device includes an IC die and encapsulation material surrounding the IC die. A first set of leads is coupled to the IC die and has first contact pads exposed on a bottom surface of the encapsulation material adjacent its periphery. A second set of leads is coupled to the IC die and has second contact pads exposed on the bottom surface of the encapsulation material adjacent its periphery. The second set of leads has internal ends extending laterally inwardly from respective ones of the second contact pads to define a die pad area supporting the IC die.