Leadframe EMI Shielding Layer Grounded via Exposed Cut Ends

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Solution Overview

Problem

Existing leadframe-type semiconductor packages face challenges in effectively connecting EMI shielding structures to ground, especially when signal leads and ground leads are on the same side, leading to interference with encapsulant formation and reduced EMI shielding effectiveness due to limited space and unbalanced mold flows.

Innovation Solution

A leadframe-type semiconductor package design that includes an EMI shielding layer connected to the ground pin, where the EMI shielding layer electrically connects the die attach pad to the ground lead through cut ends exposed on the leadless sides of the encapsulant, ensuring proper grounding and EMI shielding without interfering with encapsulant formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If an internal type EMI shielding structure (first and second caps) is used to shield EMI, then EMI shielding effectiveness is improved, but the structure greatly interferes the formation of encapsulant and limits die sizes and leadframe layouts

Engineering Contradiction:

ImproveEMI shielding effectivenessVSAvoidencapsulant formation

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent extracts the EMI shielding function from internal caps and relocates it to an external EMI shielding structure formed by the leadframe's ground leads and ground tie bars. This external shielding structure does not interfere with encapsulant formation while maintaining EMI shielding effectiveness.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent transitions from internal EMI shielding (within the package cavity) to external EMI shielding (on the package exterior using leadframe components). This dimensional shift allows shielding without interfering with the encapsulant molding process.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Object-affected harmful factors

If a heat spreader is used as EMI shielding structure on top surface, then combined heat dissipation and EMI shielding is achieved, but unbalanced mold flows occur between top and bottom molds during encapsulant formation

Engineering Contradiction:

ImproveEMI shielding effectivenessVSAvoidmold flow balance

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The patent removes the heat spreader from its traditional position on the top surface and instead utilizes the leadframe's ground leads and ground tie bars as the EMI shielding structure. This extraction eliminates the interference with mold flow balance while maintaining EMI shielding functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If die attach pad is made small to save space, then leadframe layout flexibility is improved, but there is not enough wire bonding space for electrical connections between die attach pad and ground leads

Engineering Contradiction:

Improveleadframe layout flexibilityVSAvoidwire bonding space

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent merges the EMI shielding function with the ground lead structure by using the ground lead and ground tie bar as the shielding elements. This integration eliminates the need for additional space-consuming shielding components, allowing the die attach pad to remain small while providing sufficient space for wire bonding connections.

Inventive Principle:

Principle #5Merging (Combining)

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

This design achieves effective EMI shielding by ensuring the die attach pad is grounded externally, enhancing the EMI shielding effect while maintaining design flexibility and balancing mold flows during encapsulant formation.

Implementation Method 1

an EMI shielding layer (140) covering the first surface of the encapsulant and the leadless sides

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Implementation Method 2

Through the covering of the EMI shielding layer to electrically connect the first cut end with the second cut end, the die attach pad has ground potential through electrical connections from outside the encapsulant

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS8853834B2Leadframe-type semiconductor package having EMI shielding layer connected to ground

Publication Date: 2014.10.07 POWERTECH TECHNOLOGY INC

AI summary

Disclosed is a leadframe-type semiconductor package having an EMI shielding layer connected to ground, comprising a leadframe, a chip, an encapsulant, and an EMI shielding layer. The encapsulant has two lead-extending sides and two leadless sides. The EMI shielding layer covers at least one surface of the encapsulant and the leadless sides. A metal tie bar coupling to the die attach pad of the leadframe has a cut end aligned with and exposed on one of the leadless sides. A ground lead also has a cut end aligned with and exposed on one of the leadless sides Since the EMI shielding layer covers and electrically connects the cut ends of the metal tie bar and the ground lead, the die pad with its metal tie bar of the leadframe is connected to the ground lead through external electrical connection outside the encapsulant to allow the die pad having ground potential.