Laminated Cu-Mo Heat Sink Structure for Low-Warpage Packages

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Solution Overview

Problem

Conventional packages with heat sinks face challenges in securing reliability of junction and heat dissipation performance due to warpage caused by thermal expansion differences between the heat sink and ceramic frame, leading to potential hermeticity loss and insufficient heat dissipation.

Innovation Solution

A package design with a ceramic frame and a heat sink having a specific laminated structure of copper and molybdenum layers, where the thickness ratios of these layers are optimized to balance thermal expansion and prevent excessive warpage, ensuring reliable junctions and efficient heat dissipation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the heat dissipating substrate includes layers of metal with low coefficient of thermal expansion (such as molybdenum) at a volume ratio of more than 10%, then the coefficient of thermal expansion of the heat dissipating substrate decreases to match the ceramic substrate, but the heat dissipating substrate becomes warped after cooling due to thermal deformation of the ceramic substrate during brazing

Engineering Contradiction:

Improvereliability of junction between heat dissipating substrate and ceramic substrateVSAvoidwarpage of heat dissipating substrate

Core Design Contradiction:

ReliabilityVSShape

Solution Approach 1:

The patent applies asymmetry by making the Cu layer near the ceramic substrate thicker than the Cu layer near the opposite surface. This asymmetric thickness distribution creates differential thermal expansion that compensates for the warpage caused by brazing, allowing the heat dissipating substrate to maintain proper alignment with the ceramic substrate while preventing excessive warping after cooling

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes the thickness parameters of the Cu and Mo layers to achieve the desired balance. Specifically, the Cu layer near the ceramic substrate is designed with greater thickness than the Cu layer near the opposite surface, and the Mo layers are positioned and sized to provide appropriate thermal expansion characteristics. These parameter adjustments enable the heat dissipating substrate to have a coefficient of thermal expansion close to the ceramic substrate while minimizing warpage

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the heat dissipating substrate has a high coefficient of thermal expansion (8 ppm/°C or more) to match the ceramic frame, then thermal expansion compatibility is improved, but heat dissipation performance may be compromised due to material composition constraints

Engineering Contradiction:

Improvehermeticity of package in heating cycleVSAvoidheat dissipation efficiency

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent uses composite materials by combining Cu layers and Mo layers in a specific configuration. The Cu layers provide high thermal conductivity for efficient heat dissipation, while the Mo layers provide low thermal expansion to match the ceramic substrate. This composite structure achieves both thermal expansion compatibility (8 ppm/°C or more) and maintains excellent heat dissipation performance

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies local quality by having different material compositions in different regions of the heat dissipating substrate. The Cu layers are positioned to maximize heat dissipation pathways, while Mo layers are strategically placed to control thermal expansion. The asymmetric thickness distribution further optimizes local properties to balance thermal expansion compatibility and heat dissipation efficiency

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

The optimized package design effectively suppresses warpage and maintains hermeticity while ensuring sufficient heat dissipation performance across a wide temperature range, enhancing the reliability and efficiency of the package.

Implementation Method 1

Heat from the electronic component is efficiently discharged out of the package (typically to the support member) through the heat sink

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

The heat dissipating substrate (heat sink) having such a configuration has a lower coefficient of thermal expansion than the ceramic substrate. The ceramic substrate is thus thermally deformed more at a heating temperature (e.g., 800° C.) at brazing during assembly, so that the heat dissipating substrate is warped after cooling

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS11854934B2Package with heat dissipating substrate

Publication Date: 2023.12.26 NGK ELECTRONICS DEVICES INC

AI summary

A heat sink includes first to fifth layers. The first layer supports a frame made of ceramics, is made of copper, and has a thickness t1. The second layer is laminated to the first layer, is made of molybdenum, and has a thickness t2. The third layer is laminated to the second layer, is made of copper, and has a thickness t3. The fourth layer is laminated to the third layer, is made of molybdenum, and has a thickness t4. The fifth layer is laminated to the fourth layer, is made of copper, and has a thickness t5. A formula 3≤t1/t5≤5 is satisfied. A formula 3≤t3/t5≤5 is satisfied.