Vertically Stacked FEM Circulator for Low-Profile Signal Isolation

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Solution Overview

Problem

Traditional circulators are challenging to integrate into modern front-end modules (FEMs) due to incompatible assembly processes and large dimensions, which are not suitable for ultra-high frequency applications, especially in portable communication devices where low-profile designs are required.

Innovation Solution

A front-end module design that vertically stacks a thinned flip-chip die with a circulator, comprising a metal layer, a ferrimagnetic portion, and a permanent magnetic portion, aligned and encapsulated within mold compounds to form a compact circulator structure compatible with existing FEM processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional circulators are integrated into FEMs, then signal isolation in ultra-high frequency applications is achieved, but the assembly process compatibility with existing FEM processes is lost and the height increases

Engineering Contradiction:

Improvesignal isolationVSAvoidassembly process compatibility

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The circulator is reconfigured from a traditional planar structure to a vertically stacked three-dimensional structure. The metal layer, ferrimagnetic portion, and permanent magnetic portion are arranged in vertical layers, transforming the circulator into a compact z-axis configuration that integrates seamlessly with the flip-chip die's vertical interconnect structure, thereby achieving both signal isolation and process compatibility

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The circulator components are nested within the mold compound structure. The metal layer is formed within the mold compound, and the ferrimagnetic and permanent magnetic portions are positioned within openings defined by the mold compound, creating a nested configuration where the circulator is embedded within the existing FEM package structure rather than being assembled separately

Inventive Principle:

Principle #7Nested doll (Nesting)

2Reliability

If traditional circulators are used, then signal isolation is provided, but the height and footprint increase beyond low-profile requirements

Engineering Contradiction:

Improvesignal isolationVSAvoidheight

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The circulator design transitions from a horizontal expansion layout to a vertical stacking architecture. By arranging the metal layer, ferrimagnetic portion, and permanent magnetic portion in vertical layers along the z-axis, the circulator achieves its electromagnetic isolation function within a compact height profile that meets low-profile device requirements

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The mold compound serves as a thin encapsulating structure that defines the circulator geometry. The mold compound forms vertical walls that confine the circulator components, creating a thin-profile package that maintains the circulator's electromagnetic functionality while minimizing overall height

Inventive Principle:

Principle #30Flexible shells and thin films

3Reliability

If traditional circulators are integrated, then signal isolation is achieved, but the manufacturing complexity increases due to incompatible assembly processes

Engineering Contradiction:

Improvesignal isolationVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The circulator manufacturing process is merged with the existing FEM mold compound formation process. The metal layer is formed during the same manufacturing stage as the mold compound, and the ferrimagnetic and permanent magnetic portions are integrated within the same package structure, eliminating separate circulator assembly steps and reducing overall manufacturing complexity

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 enables efficient signal isolation in ultra-high frequency applications while maintaining a low profile, compatible with current manufacturing processes, and enhances the integration of circulators in portable communication devices.

Implementation Method 1

a permanent magnetic portion resides over the ferrimagnetic portion and within the opening

Methodology Applied

Scientific EffectMagnetism: Magnetism

Implementation Method 2

A ferrimagnetic portion resides over the top surface of the thinned flip-chip die and within the opening

Methodology Applied

Scientific EffectFerrimagnetism:

Data Source

PatentUS20230387042A1Front-end module with vertically stacked die and circulator

Publication Date: 2023.11.30 QORVO US INC

AI summary

The present disclosure describes a front-end module (FEM) and a process for making the same. In the disclosed FEM, a thinned flip-chip die, which includes a device region with a metal layer, resides over a module carrier. A mold compound resides over the module carrier, surrounds the thinned flip-chip die, and extends beyond a top surface of the thinned flip-chip die to define an opening over the top surface of the thinned flip-chip die and within the mold compound. A ferrimagnetic portion resides over the top surface of the thinned flip-chip die and within the opening, and a permanent magnetic portion resides over the ferrimagnetic portion and within the opening. Herein, the permanent magnetic portion, the ferrimagnetic portion, and the metal layer of the device region are vertically aligned, and form a circulator vertically stacked with the thinned flip-chip die.