Low-Temperature Pillar Pad Coupling via Conductive Paste
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Solution Overview
Problem
Conventional electric coupling methods in microelectronic devices, such as soldering and flip-chip interconnections, cause thermal stress due to differing thermal expansion coefficients, and require high temperatures, which can damage the substrate and semiconductor chip.
Innovation Solution
A method involving a convex-shaped pillar and pad with a suspension of carrier fluid, electrically conducting microparticles, and nanoparticles, where the carrier fluid evaporates to form percolation paths between the pillar and pad, followed by sintering to create metallic bonds without the need for high-temperature processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If soldering is used to electrically couple bond pads with contact pads, then robust electrical connections are achieved, but thermal stress is caused due to differing thermal expansion coefficients and high temperatures are required
Solution Approach 1:
The patent changes the temperature parameter by replacing conventional soldering (requiring temperatures above the melting point of solder) with a low-temperature process using conductive paste containing silver or gold particles. The paste is applied at room temperature or slightly elevated temperatures, and the binding agent is cured through UV irradiation or other low-energy methods, avoiding the high thermal stress of traditional soldering.
Solution Approach 2:
The patent substitutes the thermal-mechanical soldering process with a chemical-adhesive bonding process. Instead of melting and solidifying solder metal, the invention uses a binding agent that chemically adheres conductive particles to the substrate and bond pads, eliminating the need for high-temperature thermal cycles and associated thermal expansion stress.
2Strength
If soldering is used to electrically couple bond pads with contact pads, then robust electrical connections are achieved, but stress is caused to the substrate and semiconductor chip due to differing thermal expansion coefficients
Solution Approach 1:
The patent changes the temperature parameter by replacing conventional soldering (requiring temperatures above the melting point of solder) with a low-temperature process using conductive paste containing silver or gold particles. The paste is applied at room temperature or slightly elevated temperatures, and the binding agent is cured through UV irradiation or other low-energy methods, avoiding the high thermal stress of traditional soldering.
Solution Approach 2:
The patent substitutes the thermal-mechanical soldering process with a chemical-adhesive bonding process. Instead of melting and solidifying solder metal, the invention uses a binding agent that chemically adheres conductive particles to the substrate and bond pads, eliminating the need for high-temperature thermal cycles and associated thermal expansion stress.
3Strength
If conventional conductive pastes are compressed and sintered to form robust electrical connections, then strong electrical coupling is achieved, but high temperatures and complex processes are required
Solution Approach 1:
The patent substitutes the thermal-mechanical soldering process with a chemical-adhesive bonding process. Instead of melting and solidifying solder metal, the invention uses a binding agent that chemically adheres conductive particles to the substrate and bond pads, eliminating the need for high-temperature thermal cycles and associated thermal expansion stress.
Solution Approach 2:
The patent utilizes a phase transition approach by using UV-curable or chemically-curable binding agents that transition from a liquid or soft state to a hardened state through photochemical or chemical reactions. This allows the conductive paste to be applied in a workable state and then locked into place with strong adhesion through curing, replacing the need for high-temperature sintering.
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 method reduces thermal stress and achieves robust electrical connections with lower temperatures, maintaining mechanical integrity and flexibility against thermal expansion differences.
Implementation Method 1
evaporating the carrier fluid thereby confining the microparticles and the nanoparticles
Implementation Method 2
sintering the arranged nanoparticles for forming metallic bonds at least between the nanoparticles and/or between the nanoparticles and the front face of the pillar and the pad
Data Source
AI summary
A method for electrically coupling a pad and a front face of a pillar, including shaping the front face pillar, the front face having at least partially a convex surface, applying a suspension to the front face or to the pad, wherein the suspension includes a carrier fluid, electrically conducting microparticles and electrically conducting nanoparticles, arranging the front face of the pillar opposite to the pad at a distance such that the carrier fluid bridges at least partially a gap between the front face of the pillar and the pad, evaporating the carrier fluid thereby confining the microparticles and the nanoparticles, and thereby arranging the nanoparticles and the microparticles as percolation paths between the front face of the pillar and the pad, and sintering the arranged nanoparticles for forming metallic bonds at least between the nanoparticles and/or between the nanoparticles and the front face of the pillar or the pad.