QFN Package Corner Dummy Leads for Drop Impact Reliability

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Solution Overview

Problem

Quad flat no-lead (QFN) packages face reliability issues with drop and vibration due to increased stress at the package corners, leading to failures during board-level drop impact testing, especially as devices become thinner and more vulnerable.

Innovation Solution

Incorporating dummy leads in the corner regions of the QFN package, which are integral parts of the tie bars and have exposed surfaces, to redistribute stress and enhance corner reinforcement, along with a molding compound encapsulating the lead terminals and semiconductor die, improving the package's drop impact performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the package size increases, then the I/O lead terminals can accommodate more connections, but the maximum stress at package corners increases leading to drop impact failures

Engineering Contradiction:

Improvenumber of I/O connectionsVSAvoiddrop impact performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies local quality by adding dummy leads specifically at the corner regions where stress concentration occurs during drop impact. These dummy leads are not uniformly distributed but placed strategically at corners to provide localized reinforcement exactly where needed, allowing the package to maintain high I/O count while improving corner strength and drop reliability

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces asymmetry by adding dummy leads only at the corner regions rather than uniformly across all lead positions. This asymmetric configuration targets the specific weakness (corner stress concentration) without adding unnecessary leads elsewhere, optimizing the balance between connection count and drop impact resistance

Inventive Principle:

Principle #4Asymmetry

2Device complexity

If the package design maintains traditional lead configuration, then the structure is simple and manufacturing is easy, but corner regions experience maximum stress leading to failure

Engineering Contradiction:

Improvelead configuration structureVSAvoidboard level drop impact performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies preliminary action by incorporating dummy leads into the leadframe structure before the semiconductor die is mounted and before the package undergoes drop impact testing. The dummy leads are pre-positioned at corner regions to provide stress redistribution capability in advance, preventing failure before it occurs rather than addressing damage after the fact

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The dummy leads act as intermediary elements between the corner regions and the rest of the leadframe structure. During drop impact, these dummy leads serve as mediators that absorb and redistribute stress away from critical I/O leads and solder joints, protecting the functional connections while maintaining structural integrity

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11869831B2Semiconductor package with improved board level reliability

Publication Date: 2024.01.09 MEDIATEK INC

AI summary

A semiconductor package includes a die attach pad, a plurality of lead terminals positioned about the die attach pad and disposed along side edges of the semiconductor package, a semiconductor die mounted on the die attach pad, a molding compound encapsulating the plurality of lead terminals and the semiconductor die, and at least one dummy lead disposed in a corner region of the semiconductor package between the plurality of lead terminals.