Low-Temperature Conductive Paste for Thermal Pathways
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Solution Overview
Problem
The electronics industry requires thermally conductive pastes that offer performance comparable to silver at a cost competitive with copper, while enabling low-temperature curing for applications like semiconductor chip packaging and solar cells.
Innovation Solution
A flowable composition comprising a blend of silver conductive flakes and spherical particles, with a resin binder and organic solvent, optimized for high packing density and low firing temperatures, allowing for excellent thermal and electrical conductivity and substrate adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional thermally conductive pastes are used, then thermal conductivity is achieved, but curing temperature is too high for temperature-sensitive substrates
Solution Approach 1:
The patent changes the chemical composition parameters of the paste, specifically using low-eutectic-temperature solder alloys (e.g., Pb-Sn-Bi, Pb-Sn-In, Pb-free eutectic alloys) that melt and form conductive pathways at temperatures below 200°C. This allows curing at low temperatures while maintaining reliable thermal and electrical conductivity through the formation of metallic intermetallic compounds and conductive networks.
Solution Approach 2:
The patent creates a composite material system combining solder particles (conductive phase) with flux and organic vehicle (binding phase). The solder particles provide thermal conductivity pathways, while the flux enables low-temperature activation and the organic vehicle provides adhesion. This composite structure achieves both low curing temperature and high thermal conductivity reliability.
2Reliability
If silver is used as the conductive material, then thermal and electrical conductivity is excellent, but cost is too high compared to copper
Solution Approach 1:
The patent replaces expensive silver with cost-effective solder alloys (Pb-Sn-Bi, Pb-Sn-In, or Pb-free eutectic alloys) that provide sufficient thermal and electrical conductivity for the application. These alternative materials achieve the required performance at a fraction of the cost of silver, making the conductive paste economically viable for mass production in power electronics and LED applications.
Solution Approach 2:
The patent changes the material composition from pure silver to multi-component solder alloys optimized for low melting points and good conductivity. By adjusting the alloy composition parameters (e.g., Pb:Sn:Bi ratios), the patent achieves a balance between cost, melting temperature, and thermal/electrical conductivity properties.
3Reliability
If high packing density of conductive particles is achieved, then thermal conductivity is improved, but paste viscosity increases making application difficult
Solution Approach 1:
The patent introduces flux and organic vehicle as intermediary substances that mediate between the conductive solder particles and the substrate. These intermediaries reduce particle aggregation, provide lubrication for particle movement during application, and enable screen printing or dispensing at high packing densities while maintaining paste flowability and printability.
Solution Approach 2:
The patent optimizes the particle size distribution parameters of the solder particles, using a mix of particle sizes that pack efficiently while maintaining fluidity. The organic vehicle composition parameters are also adjusted to provide appropriate viscosity and thixotropic properties, allowing the paste to flow during application but maintain structure during storage.
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
The composition provides reliable thermally conductive pathways with enhanced structural integrity and adhesion, achieving high thermal and electrical properties even after low-temperature firing, suitable for applications between semiconductor chips and their packaging.
Implementation Method 1
an organic solvent with a boiling point less than 200°C
Implementation Method 2
providing thermal conduction between a semiconductor chip and its associate semiconductor chip packaging
Data Source
Figure 1
AI summary
A flowable, (e.g., screen printable, stencil printable and/or dispensable) thermally conductive paste is disclosed and provide low temperature curing or firing. The pastes are useful in forming thermally conductive pathways for electronic type applications, such as, providing thermal conduction between a semiconductor chip and its associate semiconductor chip packaging (e.g. power electronic applications), which can be useful in power converters, electrical power steering modules, car head lights (LEDs), solar cells, printed circuit boards (PCBs), plasma display panels (PDPs), and the like. The pastes have a combination of conductive flakes and particles in a minimal amount of carrier fluid and carrier resin to provide advantageous deposition and heat melding properties.