Nanoparticle Bonding Structures for Low-Temperature Flip-Chip Joints
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Solution Overview
Problem
The challenges in flip-chip packaging include the formation of uniform metal columns with small dimensions and the risk of brittle inter-metallic compounds due to reduced solder volume, which affects reliability and stand-off height, especially with high contact density and differential thermal expansion.
Innovation Solution
A method involving the formation of conductive nanoparticles with long dimensions smaller than 100 nanometers between juxtaposed conductive elements, followed by elevating the temperature to form metallurgical joints, accommodating non-coplanarity and using nanoparticles with melting point depression for lower-temperature bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If solder volume is reduced to accommodate high contact density, then contact density is improved, but reliability deteriorates due to formation of brittle inter-metallic compounds
Solution Approach 1:
The patent changes the material parameters by replacing traditional solder with nanoparticle-based conductive materials that have different melting points and bonding characteristics. This allows for smaller bond pads while maintaining joint reliability, as the nanoparticles can form strong metallurgical bonds with reduced volume compared to conventional solder joints.
Solution Approach 2:
The patent segments the bonding process into multiple stages: first forming metal columns on bond pads, then applying nanoparticle paste, and finally heating to form metallurgical joints. This segmentation allows for precise control of each bonding stage, ensuring reliable connections even with reduced material volume.
2Quantity of substance
If solder joint volume is reduced, then contact density is improved, but stand-off height is reduced
Solution Approach 1:
The patent changes the dimensional parameters by using nanoparticle materials that enable formation of tall, narrow metal columns rather than short, wide solder joints. This parameter change allows the stand-off height to be increased while the horizontal footprint is reduced, simultaneously improving contact density and maintaining mechanical clearance.
3Length of moving object
If metal column dimensions are reduced for high density, then contact pitch is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent performs preliminary actions by first forming uniform metal columns on the bond pads through electroplating or other deposition methods before applying the nanoparticle paste. This preliminary column formation establishes a uniform base structure that guides subsequent nanoparticle bonding, ensuring consistent column dimensions and positions even at high densities.
Solution Approach 2:
The nanoparticle paste acts as an intermediary material that facilitates uniform bonding across all contact points. The nanoparticles flow and distribute evenly during the heating process, filling gaps and ensuring consistent metallurgical bonds between the metal columns and substrate, thereby improving manufacturing precision.
4Temperature
If joining temperature is reduced using nanoparticles, then strain and warpage are reduced, but bonding temperature must be precisely controlled
Solution Approach 1:
The patent utilizes phase transitions of the nanoparticle materials, which have depressed melting points compared to bulk materials. The nanoparticles undergo controlled melting and sintering at lower temperatures, forming strong metallurgical bonds. This phase transition mechanism enables precise temperature control during bonding, as the narrow melting range of the nanoparticles provides a clear thermal signature for process monitoring.
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 approach enables reliable and efficient bonding at reduced temperatures, reducing strain and warpage, improving yield and efficiency, and facilitating larger substrate alignment.
Implementation Method 1
using nanoparticles with melting point depression for lower-temperature bonding
Implementation Method 2
elevating the temperature to form metallurgical joints
Data Source
AI summary
A method of making an assembly can include juxtaposing a top surface of a first electrically conductive element at a first surface of a first substrate with a top surface of a second electrically conductive element at a major surface of a second substrate. One of: the top surface of the first conductive element can be recessed below the first surface, or the top surface of the second conductive element can be recessed below the major surface. Electrically conductive nanoparticles can be disposed between the top surfaces of the first and second conductive elements. The conductive nanoparticles can have long dimensions smaller than 100 nanometers. The method can also include elevating a temperature at least at interfaces of the juxtaposed first and second conductive elements to a joining temperature at which the conductive nanoparticles can cause metallurgical joints to form between the juxtaposed first and second conductive elements.