High Power Ceramic on Copper Package Thermal Management
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Solution Overview
Problem
High power semiconductor packages face thermal conductivity degradation due to the use of metal matrix composite materials with lower thermal conductivity than copper, caused by CTE mismatches between copper heat sinks and ceramic lead frames, leading to stress-induced damage during brazing at high temperatures.
Innovation Solution
A high power package design featuring a copper heat sink with a thermal conductivity of at least 350 W/mK, attached to a ceramic lead frame using an epoxy instead of brazing, with a predetermined bow to counteract expansion mismatches, ensuring a planar interface and reliable attachment of a semiconductor chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-copper content heat sink is used, then thermal conductivity is improved, but CTE mismatch causes heat sink bowing and package damage during brazing
Solution Approach 1:
The patent changes the processing temperature parameter from conventional high-temperature brazing (800°C or higher) to low-temperature epoxy attachment (below 800°C). This parameter change allows the use of high-copper content heat sinks (thermal conductivity ≥350 W/mK) without causing CTE-mismatch-induced bowing and damage, as the lower processing temperature reduces thermal expansion stresses
Solution Approach 2:
The patent introduces an epoxy layer as an intermediary attachment material between the copper heat sink and the ceramic lead frame, replacing direct high-temperature brazing. The epoxy serves as a compliant intermediate layer that accommodates CTE differences between materials while providing reliable electrical and thermal connections at lower temperatures
2Stability of the object's composition
If metal matrix composite material is used for heat sink, then CTE mismatch is reduced, but thermal conductivity deteriorates
Solution Approach 1:
The patent changes the processing temperature parameter to enable the use of pure copper or high-copper content materials (thermal conductivity ≥350 W/mK) instead of metal matrix composites. By reducing the attachment temperature from conventional brazing (800°C+) to epoxy curing temperatures, the patent eliminates the need for CTE-matched composite materials while maintaining high thermal conductivity
Solution Approach 2:
The patent uses a composite attachment system consisting of epoxy material bonding the copper heat sink to the ceramic lead frame. This composite approach allows the heat sink itself to be made of pure copper or high-copper content material for optimal thermal conductivity, while the epoxy composite provides the necessary mechanical bonding and CTE accommodation
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 solution enhances thermal performance and reliability by maintaining high copper content while reducing stress-induced damage, ensuring efficient heat dissipation and operational integrity at extreme temperatures.
Implementation Method 1
an electrically insulating lead frame attached to the heat sink with an epoxy
Implementation Method 2
copper has a high thermal conductivity (385 W/mK). Such a heat sink would enable the package to efficiently dissipate large amounts of waste heat energy
Implementation Method 3
a semiconductor chip attached to the heat sink on the same side as the lead frame with an electrically conductive material having a melting point of 280° C. or greater
Implementation Method 4
copper has a CTE (coefficient of thermal expansion) of about 17 ppm and an alumina lead frame has a CTE of about 7 ppm. The CTE mismatch between a high-copper content heat sink and a ceramic lead frame would result in the heat sink expanding and contracting much more than the lead frame during the brazing process
Data Source
AI summary
According to an embodiment of a high power package, the package includes a heat sink containing enough copper to have a thermal conductivity of at least 350 W/mK, an electrically insulating attached to the heat sink with an epoxy and a semiconductor chip attached to the heat sink on the same side as the lead frame with an electrically conductive material having a melting point of 280° C. or greater.