Wraparound Lead Package Minimizing Deflection in Microelectronic Packaging
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Solution Overview
Problem
Microelectronic packaging for high power semiconductor devices faces excessive thermal expansion mismatch between the heat spreader and insulator, leading to package deflection, mechanical stress, and reduced thermal dissipation due to inadequate thermal conductivity and contact area.
Innovation Solution
A wraparound lead package design with a symmetric three-layer structure, where the insulator is high-temperature-brazed between a wraparound lead layer and a buffer layer of the same material, minimizing deflection by counteracting thermal expansion differences, and then bonded to a heat spreader using a lower melt point braze, maintaining a flat surface for enhanced thermal dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a copper-moly/copper-copper laminate heat spreader is used to match CTE, then thermal expansion mismatch is reduced, but thermal conductivity becomes too low to effectively transfer thermal energy
Solution Approach 1:
The heat spreader uses a copper core (high thermal conductivity) sandwiched between two CTE-matched laminate layers (copper-moly/copper-copper). This composite structure allows the outer layers to provide CTE matching with the insulator while the inner copper core maintains high thermal conductivity for effective heat transfer, resolving the contradiction between CTE match and thermal energy transfer.
2Strength
If high-temperature brazing is performed between heat spreader and insulator, then strong mechanical bond is achieved, but excessive deflection occurs due to thermal expansion difference during cooling
Solution Approach 1:
The patent introduces an intermediate layer with specific thermal and mechanical properties between the heat spreader and insulator. This intermediate layer is designed with thermal expansion characteristics that bridge the gap between the heat spreader and insulator, reducing the thermal expansion difference during cooling and thereby minimizing package deflection while maintaining bond strength.
Solution Approach 2:
The intermediate layer acts as a mediator between the heat spreader and insulator, accommodating the thermal expansion mismatch during cooling. This intermediary layer prevents excessive deflection and camber by absorbing the differential thermal expansion, thereby maintaining package flatness while allowing strong brazing bonds to form.
3Ease of manufacture
If excessive package deflection occurs, then manufacturing is simplified, but mechanical stress increases causing insulator fractures and thermal pathways are reduced
Solution Approach 1:
The patent performs preliminary deflection control by designing the intermediate layer and lead structure to pre-compensate for thermal expansion differences before final brazing. This preliminary action ensures that when brazing occurs and cooling follows, the package maintains minimal deflection, preventing insulator fractures and preserving thermal pathway integrity without complicating the manufacturing process.
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 minimizes package deflection, reduces mechanical stress, and improves thermal dissipation by maintaining a flat heat spreader surface, ensuring effective heat transfer and increased reliability.
Implementation Method 1
an insulator that is high-temperature-brazed between a wraparound lead layer and a buffer layer
Implementation Method 2
the thermal expansion difference between the heat spreader and the insulator may cause excessive deflection
Implementation Method 3
thermal pathways extending from the high power semiconductor devices, through the heat spreader and into the second level assembly
Data Source
AI summary
Package deflection and mechanical stress of microelectronic packaging is minimized in a two step manufacturing process. In a first step, a ceramic insulator is high-temperature bonded between a wraparound lead layer and a buffer layer of a same material as the lead layer to provide a symmetrically balanced three-layer structure. In a second step, the three-layer structure is high temperature bonded, using a lower melt point braze, to a heat spreader. This package configuration minimizes package deflection, and thereby improves thermal dissipation and reliability of the package.