Laser Sintered Nano-Particle Micro Bumps for 3D-IC Packaging
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Solution Overview
Problem
Current 3D-IC packaging methods fail to produce micro bumps smaller than 10 μm with high strength and low resistivity, as existing techniques require higher temperatures and pressures, and often result in voids and increased stress, making them unsuitable for stacking logic and memory chips.
Innovation Solution
A method involving the formation of nano-particle layers with different absorption rates to a laser beam, where the first nano-particles are selectively heated and melted to form adhesion layers and filling material, reducing the horizontal size of micro bumps while maintaining bond strength and avoiding voids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional printing process is used to manufacture solder bumps, then manufacturing process is simple, but bump size cannot be reduced to 10 μm or smaller
Solution Approach 1:
The patent replaces the traditional mechanical printing process with a laser-based processing system. The laser beam precisely melts and sinter metal nanoparticles to form bumps of 10 μm or smaller, achieving the required manufacturing precision while maintaining ease of manufacture through automated laser scanning and processing.
2Manufacturing precision
If CuSn solder bonding is used to manufacture smaller bumps, then bump size is reduced, but bonding temperature must be higher than 250° C.
Solution Approach 1:
The patent changes the material parameters by using metal nanoparticles with specific properties (high laser absorption coefficient, low melting point) instead of traditional CuSn solder. This allows the bonding process to occur at lower temperatures while achieving the required small bump size, as the nanoparticle material responds differently to laser heating.
Solution Approach 2:
The patent utilizes controlled phase transitions of metal nanoparticles under laser irradiation. The laser beam induces rapid melting and subsequent solidification of the nanoparticles, forming dense bumps without requiring high bulk material temperatures. This localized phase transition enables small bump formation at lower overall processing temperatures.
3Strength
If thermocompression bonding method using copper bumps is used, then bonding strength is achieved, but high temperature (400° C.), high pressure (10 MPa), and vacuum environment are required
Solution Approach 1:
The patent replaces the thermocompression bonding method with a laser sintering process. The laser beam provides localized heating and melting of metal nanoparticles, eliminating the need for high temperature and pressure environments. This substitution achieves comparable or superior bonding strength while operating under ambient or near-ambient conditions.
Solution Approach 2:
The patent utilizes laser-induced phase transitions of metal nanoparticles to achieve bonding. The rapid heating and cooling cycle creates strong metallurgical bonds through controlled melting and solidification, replacing the need for high-temperature thermocompression while maintaining bonding strength.
4Strength
If thermocompression bonding method is used, then bonding is achieved, but large stresses are built up in chips causing cracks
Solution Approach 1:
The patent replaces mechanical compression bonding with laser-based sintering. The laser energy is absorbed by the metal nanoparticles, creating localized melting and bonding without applying large compressive forces to the chips. This eliminates the stress buildup that causes chip cracking while maintaining bonding strength.
5Temperature
If metal nanoparticles are directly bonded without melting, then low temperature processing is achieved, but voids form in bumps decreasing bond strength
Solution Approach 1:
The patent utilizes controlled phase transitions of metal nanoparticles under laser irradiation. The laser beam provides sufficient energy to melt the nanoparticles and fill voids, then rapid cooling solidifies the material to form dense, void-free bumps. This controlled melting and solidification process maintains low overall processing temperature while eliminating voids to ensure bond strength.
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
Enables the creation of micro bumps with sizes smaller than 10 μm, achieving high strength and low resistivity without the need for high temperatures or pressures, reducing stress and void formation, thus suitable for 3D-IC packaging.
Implementation Method 1
irradiating a laser beam onto the second nano-particle layer, the laser beam penetrating through the second nano-particle layer and being at least partially absorbed by at least some of the first nano particles to generate heat
Implementation Method 2
The first nano particles and the second nano particles have different absorption rates with respect to the laser beam
Implementation Method 3
The first nano particles are selectively heated and melted to form adhesion layers and filling material
Data Source
AI summary
A method for forming a micro bump includes forming a first nano-particle layer on a substrate and forming a second nano-particle layer on the first nano-particle layer. The first and second nano-particle layers include a plurality of first nano particles and a plurality of second nano particles, respectively. The method further includes irradiating a laser beam onto the second nano-particle layer, where the laser beam penetrates through the second nano-particle layer and is at least partially absorbed by at least some of the first nano particles to generate heat. The first nano particles and the second nano particles have different absorption rates with respect to the laser beam.