Two-Layer Semiconductor Bump with Sintered Elastic Layer
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Solution Overview
Problem
The existing methods for forming bumps on semiconductor chips, such as plating and grinding, face challenges with uniformity and elasticity, leading to potential breakage due to heat cycles and equipment cost issues, while sintered bumps may cause lateral deformation affecting pitch and spacing.
Innovation Solution
A two-layer structure comprising a bulk metal layer for rigidity and a sintered metal layer for elasticity, where the sintered layer is formed from high-purity metal powder with a specific particle size range, allowing for deformation to compensate for height variations and ensuring stable bonding under low pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plating method is used to form bumps, then dense electrode with stable film thickness can be produced, but variations in bump height cause loose connection during mounting
Solution Approach 1:
The invention changes the material parameter from pure metal to sintered metal powder with specific characteristics (particle size 0.005-1.0 μm, purity ≥99.9 wt%). This material parameter change enables the bump to have elastic deformation capability, allowing it to compensate for height variations and achieve reliable connection without requiring excessive mounting pressure.
Solution Approach 2:
The invention uses sintered metal powder as a composite material that combines the benefits of metal density with the elasticity of porous structure. The sintered body maintains electrical conductivity while providing elastic deformation capability to accommodate bump height variations, resolving the contradiction between connection stability and height uniformity.
2Reliability
If excessive pressure is applied during mounting to compensate for bump height variations, then close contact can be achieved, but strain remains in bumps causing breakage due to heat cycles
Solution Approach 1:
The invention changes the mechanical parameter of the bump material by using sintered metal powder with controlled porosity and particle size. This creates a material that can deform elastically under mounting pressure, achieving close contact without remaining strain. The elastic deformation allows the bump to return to its original shape after mounting, preventing breakage during subsequent heat cycles.
3Manufacturing precision
If grinding and polishing is performed on plated bumps to eliminate height variations, then stable conductivity and low pressure mounting can be achieved, but ground fine powder may attach to neighboring bumps causing short-circuiting
Solution Approach 1:
The invention performs preliminary action by forming bumps with uniform height through sintering of metal powder with controlled particle size distribution before mounting. This eliminates the need for subsequent grinding and polishing operations, preventing the generation of fine powder that could cause short-circuiting between neighboring bumps.
4Manufacturing precision
If CMP polisher is used for planarization, then bump flatness can be improved, but equipment cost increases
Solution Approach 1:
The invention achieves bump flatness through preliminary action during the sintering process by controlling particle size and sintering conditions, eliminating the need for expensive CMP polishing equipment. The sintering process itself produces sufficiently flat bump surfaces for mounting applications.
5Manufacturing precision
If sintered body bumps are used to provide elasticity, then bonding at constant height is achieved, but lateral deformation occurs during mounting resulting in impaired spacing
Solution Approach 1:
The invention optimizes the particle size parameter of the metal powder to 0.005-1.0 μm and purity to ≥99.9 wt%, creating a sintered body with controlled porosity and mechanical properties. This parameter optimization balances the elasticity needed for height compensation with sufficient structural rigidity to prevent lateral deformation and maintain bump spacing during mounting.
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 solution enables bonding with excellent flatness and reduced strain, eliminating the need for excessive pressure and minimizing the risk of breakage, while also reducing substrate costs by using a combination of metals like gold and silver.
Implementation Method 1
The bump of a sintered body is more porous, relatively soft, and more elastic than that of the dense bulk metal formed by plating. The elasticity of the bumps enables bonding at a constant height even with variations in bump height, because contraction occurs corresponding to difference in height.
Implementation Method 2
the bumps are formed by sintering metal powder having a predetermined particle size and purity with an alternative composition
Data Source
AI summary
A two-layer structure bump including a first bump layer of a bulk body of a first conductive metal, which is any of gold, copper, and nickel, formed on a substrate and a second bump layer of a sintered body of a powder of a second conductive metal, which is any of gold and silver, formed on the first bump layer. The bulk body composing the first bump layer is formed through any of plating, sputtering, or CVD. The sintered body composing the second bump layer is formed by sintering the powder of the second conductive metal having a purity of not lower than 99.9 wt % and an average particle diameter of 0.005 μm to 1.0 μm. The second bump layer has a Young's modulus 0.1 to 0.4 times that of the first bump layer.