Flip-Chip Air Cavity Package for RF Capacitance Reduction

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

As semiconductor technology advances, the increasing capacitance in metal interconnects due to packaging materials hinders the performance of high-frequency RF circuits, necessitating a reduction in dielectric constant to match the faster switching times of IC devices.

Innovation Solution

Creating an air cavity around the IC die within the package, using a lead frame with selectively etched laminate material and photo-lithographic processes to define the air cavity, which reduces capacitance and enhances packaging for high-performance devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional packaging materials are used, then the IC device is well-protected and sealed, but the capacitance in metal interconnects increases significantly

Engineering Contradiction:

Improvedevice protection and sealingVSAvoidcapacitance in metal interconnects

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The packaging structure is segmented into distinct regions: a sealed cavity region that provides protection and an air cavity region that minimizes capacitance. The laminate material is selectively etched to create this segmented structure with both sealed and open (air-filled) portions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the packaging have different dielectric properties tailored to their specific functions. The sealed cavity uses traditional molding compound for protection, while the air cavity uses air (lowest possible dielectric constant) to minimize capacitance. This local differentiation optimizes both protection and electrical performance.

Inventive Principle:

Principle #3Local quality

2Speed

If the dielectric constant is reduced to match faster switching times, then high-frequency RF circuit performance improves, but traditional packaging materials cannot provide the required low-k dielectric property

Engineering Contradiction:

Improveswitching time and signal propagation speedVSAvoidpackaging material selection

Core Design Contradiction:

SpeedVSEase of manufacture

Solution Approach 1:

The dielectric constant parameter is changed from typical packaging materials (k=3-4) to air (k≈1) in the cavity region. This parameter change enables the packaging to support high-frequency RF circuits by matching the fast switching times of modern IC devices.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The packaging structure becomes a composite of different materials with different dielectric properties: molding compound for structural support and sealing, and air for low-k dielectric performance. This composite approach combines the advantages of both material types.

Inventive Principle:

Principle #40Composite materials

3Object-affected harmful factors

If an air cavity is created around the IC die, then capacitance is reduced and performance is enhanced, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvecapacitance reductionVSAvoidpackaging manufacturing process

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The air cavity structure is prepared in advance by selectively etching the laminate material before final assembly. This preliminary action creates the low-k dielectric region beforehand, simplifying the overall manufacturing process compared to attempting to create air cavities after assembly.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Traditional mechanical sealing methods are replaced with a selective etching process that creates the air cavity structure. This substitution enables precise control of the air cavity geometry and integration with the electrical interconnect structure.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 air cavity packaging significantly reduces capacitance in metal interconnects, improving the performance of high-frequency RF circuits and other applications requiring low-k dielectrics, such as bulk acoustic wave filters, by leveraging the properties of air for modem IC devices.

Implementation Method 1

the increasing capacitance in metal interconnects due to packaging materials hinders the performance of high-frequency RF circuits, necessitating a reduction in dielectric constant

Methodology Applied

Scientific EffectCapacitance reduction through air dielectric: Capacitance

Data Source

PatentEP1911080B1Flip-chip package with air cavity

Publication Date: 2013.02.06 NXP BV

Figure 1
Figure 2A~2D
Figure 2E~3

AI summary

According to an example embodiment, there is method (100) for manufacturing a semiconductor device in an air-cavity package. For a device die having an active surface, a lead frame is provided (5), the lead frame has a top-side surface and an under-side surface, the lead frame has predetermined pad landings on the top-side surface. A laminate material is applied (10) to the top-side surface of the lead frame. In the laminate material, an air- cavity region and contact regions are defined (15, 20, 25, 30, 35). The contact regions provide electrical connections to the predetermined pad landings on the lead frame. With the active circuit surface in an orientation toward the laminate material, the device die is mounted (40, 45). The bond pads of the active surface circuit are connected with ball bonds to the predetermined pad landings on the lead frame. An air-cavity is formed between the active surface of the device die and the top-side surface of the lead frame.