Lead Frame Triangular Cavities for Delamination Resistance

Solution Overview

Problem

Conventional semiconductor devices, such as QFN packages, experience delamination issues due to differences in thermal expansion rates between the molding compound and the lead frame, which can lead to stress on the adhesive bond and result in electrical connection loss and cracking, especially when contaminants or inherent weaknesses in the lead frame plating are present.

Innovation Solution

A lead frame configuration featuring a die paddle with substantially-linear metal connecting bars forming triangular cavities, which reduces the surface area exposed to the molding compound and enhances adhesion by trapping the compound within these cavities, thereby minimizing stress and delamination risks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the lead frame uses conventional flat surface configuration, then the molding compound can fully contact the lead frame surface, but the adhesive bond is weakened due to thermal expansion stress and contaminants causing delamination

Engineering Contradiction:

Improveadhesive bond strengthVSAvoidthermal expansion stress

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The die paddle surface is transformed from a uniform flat surface to a non-uniform surface with multiple cavities of varying sizes and shapes. These cavities create localized regions with different mechanical properties, allowing the molding compound to anchor within the cavities while the raised portions provide bonding surfaces, thereby improving adhesion resistance against thermal expansion stress.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The continuous flat surface of the die paddle is segmented into multiple discrete cavities and raised portions. This segmentation creates numerous small anchoring points for the molding compound throughout the die paddle surface, distributing the thermal expansion stress across multiple locations rather than concentrating it on a single flat surface.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the lead frame uses conventional flat surface configuration, then the structure is simple, but delamination occurs due to stress concentration on the large exposed surface area

Engineering Contradiction:

Improveresistance to delaminationVSAvoidlead frame structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The die paddle surface is transformed from a uniform flat surface to a non-uniform surface with multiple cavities of varying sizes and shapes. These cavities create localized regions with different mechanical properties, allowing the molding compound to anchor within the cavities while the raised portions provide bonding surfaces, thereby improving adhesion resistance against thermal expansion stress.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention converts the potential harm of a large exposed surface area (which concentrates stress and promotes delamination) into a benefit by creating multiple cavities. The cavities reduce the continuous exposed surface area while providing anchoring points that actively resist delamination forces, turning the surface area issue into an adhesion enhancement feature.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If contaminants are present on the lead frame surface, then the adhesive bond is weakened, but conventional flat surfaces trap contaminants more easily

Engineering Contradiction:

Improveadhesive bond strengthVSAvoidcontaminants

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The continuous flat surface of the die paddle is segmented into multiple discrete cavities and raised portions. This segmentation creates numerous small anchoring points for the molding compound throughout the die paddle surface, distributing the thermal expansion stress across multiple locations rather than concentrating it on a single flat surface.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention converts the potential harm of a large exposed surface area (which concentrates stress and promotes delamination) into a benefit by creating multiple cavities. The cavities reduce the continuous exposed surface area while providing anchoring points that actively resist delamination forces, turning the surface area issue into an adhesion enhancement feature.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 reduced surface area exposed to the molding compound significantly reduce the likelihood of delamination and cracking, ensuring a stronger bond and more reliable electrical connections in semiconductor devices.

Implementation Method 1

the adhesive bond between the molding compound and the lead frame

Methodology Applied

Scientific EffectAdhesive bonding: Adhesive

Implementation Method 2

differences between the coefficient of thermal expansion (CTE) of the molding compound and the lead frame

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS9293395B2Lead frame with mold lock structure

Publication Date: 2016.03.22 NXP USA INC

AI summary

A lead frame for a semiconductor device includes a die paddle and leads situated on a perimeter of the lead frame. The die paddle has a metal frame and a number of substantially linear metal connecting bars within the frame. The connecting bars interconnect different locations of the frame to form a multiple triangles, where a triangular-shaped cavity is formed within each triangle. An overall area of the cavities is greater than an overall area of the connecting bars.