Dual-Die IC Package with Exposed Back Surface for Thermal Dissipation

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Solution Overview

Problem

Conventional IC packaging methods do not effectively enhance thermal performance, particularly in power applications, where heat dissipation from the back surface of IC dice is crucial for device stability and performance.

Innovation Solution

An IC package design that includes two dice, where one die has an exposed metallic layer on its back surface for enhanced heat dissipation, and both dice are connected to a leadframe using solder joints, allowing for efficient thermal transfer to a printed circuit board and potentially incorporating a heat sink for further cooling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the back surface of the die is encapsulated with molding material, then the die is protected, but heat dissipation is reduced

Engineering Contradiction:

Improvedie protectionVSAvoidheat dissipation

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent applies local quality by selectively exposing the back surface of the die (specific region) while encapsulating other portions. The molding material is applied locally to protect the active surface and sides, while the back surface remains exposed for heat dissipation. This resolves the contradiction by providing protection where needed while maintaining thermal performance at the back surface.

Inventive Principle:

Principle #3Local quality

2Productivity

If a single leadframe is used to package two dice, then device density is doubled, but manufacturing complexity increases

Engineering Contradiction:

Improvesilicon densityVSAvoidpackaging structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent merges two separate die packaging operations into a single leadframe structure. Both dice are mounted on the same leadframe with their active surfaces facing opposite directions, and both are encapsulated together in a single molding operation. This combining approach doubles the silicon density while consolidating the manufacturing process rather than increasing complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent utilizes the third dimension by mounting dice on opposite sides of the leadframe, effectively using vertical space rather than expanding the horizontal footprint. This dimensional approach allows two complete IC packages to be integrated into what appears to be a single package footprint, doubling density without proportionally increasing overall package complexity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If molding material encapsulates the entire die, then protection is maximized, but thermal performance deteriorates

Engineering Contradiction:

Improvecomponent protectionVSAvoidthermal energy dissipation

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The molding material is applied selectively to specific regions of the die - covering the active surface, sides, and peripheral areas for protection, while deliberately leaving the back surface exposed. This local differentiation allows the structure to simultaneously achieve maximum protection where electrical components are located while maintaining optimal thermal dissipation through the exposed metallic back surface.

Inventive Principle:

Principle #3Local quality

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 significantly improves thermal performance by providing multiple pathways for heat dissipation, enabling increased device performance and stability in power applications while maintaining a conventional package size or doubling silicon density.

Implementation Method 1

the back surface of the first die is left uncovered by molding material and has an exposed metallic layer deposited thereon

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

A plurality of solder joints are arranged to physically and electrically connect I/O pads from the first or second die to associated adjacent solder pad surfaces on the leads

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 3

a heat sink may be soldered to the metallic layer on the back surface of the second die. The heat sink may also be soldered to a surface of the printed circuit board to further facilitate heat transfer out of the package

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS7619303B2Integrated circuit package

Publication Date: 2009.11.17 NAT SEMICON CORP

AI summary

An integrated circuit package is described that includes two dice. The active surface of each die includes a plurality of I/O pads. The active surface of the first die is positioned adjacent first surfaces of the leads of a lead frame such that I/O pads from the first die are arranged adjacent corresponding solder pad surfaces on the first surfaces. Similarly, the active surface of the second die is positioned adjacent second surfaces of the leads opposite the first surfaces such that I/O pads from the second die are arranged adjacent corresponding solder pad surfaces on the second surfaces. A plurality of solder joints are arranged to physically and electrically connect I/O pads from the first or second die to associated adjacent solder pad surfaces on the leads. In this way, a single lead frame can be utilized to package two dice, one on either side of the leads of the leadframe.