Stacked Dice Buck Converter Package with Conductive Die Attach Pad

Solution Overview

Problem

Conventional buck converters have a large footprint, require extensive wirebonding, and exhibit complex electrical paths leading to higher parasitic capacitances and inductances, which result in inefficient performance and larger size, making them unsuitable for portable applications.

Innovation Solution

A flip-leaded molded package with stacked dice configuration where the high side die's source and low side die's drain share a conductive die attach pad within a molding compound, reducing parasitic capacitances and inductances, and allowing for improved heat dissipation and higher switching frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If conventional wirebonding and separate die mounting are used, then electrical connections can be established, but the footprint increases and parasitic capacitances and inductances increase

Engineering Contradiction:

Core Design Contradiction:

Area of stationary objectVSDevice complexity

Solution Approach 1:

The patent merges the die attach pad and wirebond function into a single integrated structure. The conductive die attach pad serves dual purposes: mechanically supporting the low side die and providing electrical connection to the drain, eliminating the need for separate wirebonds and reducing overall device complexity and footprint.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The conductive die attach pad performs multiple functions simultaneously: it provides mechanical support for the low side die, establishes electrical connection to the drain, and serves as a heat dissipation path. This multi-functionality reduces the number of separate components needed, thereby reducing footprint and complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If extensive wirebonding is used, then electrical connections are established, but parasitic capacitances and inductances increase

Engineering Contradiction:

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and eliminates the wirebonding step from the electrical connection process. By using direct die-to-pad contact through the conductive die attach pad, the harmful parasitic elements inherent in wirebonding (capacitances and inductances) are removed, improving electrical performance.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The conductive die attach pad acts as an intermediary structure that provides direct electrical contact between the low side die drain and the external circuit. This intermediary eliminates the need for wirebonds and their associated parasitic elements, while still providing reliable electrical connection.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Area of stationary object

If the high side die is mounted with limited heat dissipation area, then the footprint is reduced, but heat dissipation capability is insufficient

Engineering Contradiction:

Core Design Contradiction:

Area of stationary objectVSTemperature

Solution Approach 1:

The patent utilizes the vertical dimension (z-axis) for heat dissipation by exposing the high side die drain to the external environment. This allows heat to be dissipated from the top surface of the package rather than requiring additional lateral heat sink area, maintaining small footprint while improving thermal performance.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The high side die drain structure serves its own heat dissipation needs by being directly exposed to the external environment. The drain structure itself acts as the heat dissipation element, eliminating the need for separate heat sink components and maintaining compact form factor.

Inventive Principle:

Principle #25Self-service

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 configuration reduces the device footprint, enhances heat dissipation, decreases switching losses, and improves power-conversion efficiency by minimizing parasitic capacitances and inductances, enabling higher switching frequencies and better electrical performance.

Implementation Method 1

A low side die contacts one surface of the die attach pad such that the low side drain makes an electrical contact with the die attach pad. A high side die mounted on the opposite surface of the die attach pad such that the high side source makes an electrical contact with the die attach pad.

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

The source of the high side die is electrically connected to the drain of the low side die through a conductive die attach pad

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS8063472B2Semiconductor package with stacked dice for a buck converter

Publication Date: 2011.11.22

AI summary

Disclosed in this specification is a buck converter package with stacked dice and a process for forming a buck converter. The package includes a die attach pad with a low side die mounted on one surface and a high side die mounted on the opposing surface. The die attach pad is conductive, such that the drain of the low side die is connected to the source of the high side die through the pad. A controller die controls the gates of the high and low side dies. A plurality of leads extends outside of the package to permit electrical connections to the inside of the package. The high side drain is exposed to one of the surfaces of the package.