Balanced Stress Semiconductor Assembly Using Silver Sintering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High power semiconductor packages face challenges with substrate warping and thermal resistance due to thick metallization, and lead frames are flimsy and costly when thickened for handling, leading to poor thermal and electrical conductivity.
Innovation Solution
A thin metallization layer (1-25 μm) is applied to one side of the substrate for low-temperature sintering, with copper or aluminum lead frames extending into the package for high current conduction, and the assembly is stress-balanced from the center, eliminating the need for stress-balancing metallization on both substrate sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick metallization is applied to the substrate to carry high current, then electrical conductivity is improved, but substrate warping increases and manufacturing cost increases
Solution Approach 1:
The substrate assembly is segmented into multiple functional layers: a first substrate with thin metallization for stress balance, a second substrate for electrical connection, and lead frames for current conduction. This segmentation allows each layer to perform its specific function without causing substrate warping, while collectively achieving high current carrying capability.
Solution Approach 2:
The solution transitions from a single-plane thick metallization approach to a multi-layer stacked configuration. By distributing the electrical conduction function across multiple dimensions (first substrate metallization layer, second substrate, lead frames), the system achieves high current capacity without requiring thick metallization on any single substrate, thereby preventing warping.
2Reliability
If thick metallization is applied to the substrate to carry high current, then electrical conductivity is improved, but manufacturing cost increases
Solution Approach 1:
The electrical conduction path is segmented across multiple components (thin metallization on first substrate, second substrate, lead frames) rather than requiring expensive thick metallization on a single substrate. This segmentation enables the use of thinner, less costly metallization layers while maintaining high current carrying capability through the distributed structure.
Solution Approach 2:
The lead frames serve multiple functions: providing electrical connection, carrying high current, and enabling mechanical assembly. This multi-functionality eliminates the need for separate thick metallization layers dedicated solely to current conduction, reducing overall manufacturing cost while maintaining electrical performance.
3Ease of operation
If the thickness of semiconductor devices is increased to match lead frame thickness for coplanar bonding, then ease of handling is improved, but thermal resistance and cost increase
Solution Approach 1:
The solution resolves the thickness mismatch issue by transitioning from a single-plane coplanar bonding requirement to a multi-layer stacked configuration. The lead frames extend beyond the semiconductor devices in the vertical dimension, allowing bonding at different heights and eliminating the need to increase semiconductor device thickness, thereby maintaining low thermal resistance.
Solution Approach 2:
The lead frames are designed with varying thicknesses and extensions at different locations to accommodate the semiconductor devices of standard thickness. The lead frames provide the necessary mechanical strength and handling capability through their extended structure, while the semiconductor devices maintain their optimal thin profile for low thermal resistance.
4Ease of operation
If lead frame thickness is increased for easier handling, then ease of operation is improved, but electrical conductivity and thermal conductivity worsen
Solution Approach 1:
The lead frames are constructed as composite structures, typically with a copper core for high electrical and thermal conductivity, plated with a harder material for improved handling and bonding. This composite construction allows the lead frames to maintain excellent conductivity while providing the mechanical strength needed for easy handling.
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 substrate warping, enhances thermal and electrical conductivity, and improves handling without increasing cost or thermal resistance, while maintaining stress balance across temperature changes.
Implementation Method 1
low temperature sintering
Data Source
AI summary
An assembly for packaging one or more electronic devices in die form. The assembly includes substrates on opposite sides of the assembly, with lead frames between the electronic devices and the substrates. The substrates, lead frames, and electronic devices are sintered together using silver-based sintering paste between each layer. The material and thicknesses of the substrates and lead frames are selected so stress experienced by the electronic devices caused by changes in temperature of the assembly are balanced from the center of the assembly, thereby eliminating the need for balancing stresses at a substrate level by applying substantially matching metal layers to both sides of the substrates.