Flip-Chip Assembly Using Sinterable Paste for Stress Reduction
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Solution Overview
Problem
Conventional flip-chip interconnections face issues with thermomechanical stress-induced microcracks due to wide coefficient of thermal expansion differences between semiconductor chips and substrates, leading to potential electrical failures, and require expensive equipment for temperature and vacuum control, which is incompatible with the industry's need for rapid manufacturing and low costs.
Innovation Solution
The use of high-aspect ratio metallic columns with a sinterable paste composed of copper and tin/bismuth particles, which sinter into a metallic matrix embedded in a thermoset polymeric compound, allowing for a single cycle process at modestly elevated temperatures, reducing thermomechanical stress and eliminating the need for specialized equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder balls or gold bumps are used for flip-chip interconnection, then electrical connection is achieved, but thermomechanical stress causes microcracks due to CTE mismatch between chip and substrate
Solution Approach 1:
The patent uses a composite underfill material consisting of a polymeric matrix with embedded metallic particles (copper, aluminum, or their alloys). This composite structure combines the flexibility and stress-absorption capability of the polymer with the thermal conductivity and mechanical strength of metal particles, creating a material that can accommodate CTE mismatch while maintaining joint integrity and reducing thermomechanical stress concentrations.
Solution Approach 2:
The patent modifies the physical and chemical parameters of the underfill material by incorporating metallic particles with specific size distributions (0.1-10 micrometers), controlling the polymeric matrix composition, and optimizing the curing process parameters. These parameter changes enhance the underfill's ability to absorb stress, improve thermal management, and prevent microcrack formation at the joint interfaces.
2Manufacturing precision
If expensive equipment with temperature and vacuum control is used for underfilling, then underfilling quality is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs a simple, low-cost underfilling apparatus that does not require expensive temperature-controlled or vacuum-controlled equipment. The underfill material is applied using basic dispensing or dip techniques, and the process relies on the material's inherent capillary action and viscosity characteristics rather than complex environmental controls. This approach achieves satisfactory underfilling quality through material design rather than expensive equipment.
3Volume of moving object
If the gap between chip and substrate is small, then device profile is reduced, but underfilling process becomes more difficult
Solution Approach 1:
The patent carefully controls the viscosity parameters of the underfill material during the uncured state to enable effective capillary flow into narrow gaps. By optimizing the polymer matrix composition and adding appropriate solvents or plasticizers, the material achieves low enough viscosity to penetrate small gaps through capillary action, yet maintains sufficient body to avoid excessive leakage. The curing process parameters are also optimized to complete polymerization at appropriate times, ensuring proper fill of narrow gaps while maintaining device profile.
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 provides robust connections resistant to thermomechanical stress, reduces the risk of microcracks, and significantly lowers manufacturing costs by eliminating the need for expensive equipment and complex temperature control processes, while maintaining fine pitch center-to-center connections.
Implementation Method 1
a sinterable paste composed of copper and tin/bismuth particles, which sinter into a metallic matrix
Implementation Method 2
a polymeric compound, which forms a matrix in which the metal particles are embedded
Implementation Method 3
the precursor is distributed at the assembly edge and pulled by capillary force into the space between chip and substrate
Data Source
AI summary
A device including a first body (101) with terminals (102) on a surface (101a), each terminal having a metallic connector (110), which is shaped as a column substantially perpendicular to the surface. Preferably, the connectors have an aspect ratio of height to diameter of 2 to 1 or greater, and a fine pitch center-to-center. The connector end (110a) remote from the terminal is covered by a film (130) of a sintered paste including a metallic matrix embedded in a first polymeric compound. Further a second body (103) having metallic pads (140) facing the respective terminals (102). Each connector film (130) is in contact with the respective pad (140), whereby the first body (101) is spaced from the second body (103) with the connector columns (110) as standoff. A second polymeric compound (150) is filling the space of the standoff.