Phosphorus-Modified Copper Solder Paste for High-Temperature Reliability
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Solution Overview
Problem
Existing methods for firmly-bonding electronic components to substrates, such as those described in WO 2011/009597 A1, do not consistently produce reliable connections under high temperature conditions, particularly between 250 to 300°C, and lack improvements in connection stability.
Innovation Solution
A method using a solder paste with 10-30% by weight of copper particles or copper-rich alloys with phosphorus content >0 to ≤500 wt-ppm, 60-80% by weight of tin or tin-alloy particles, and 3-30% by weight solder flux, applied to create a ≥20 μm thick layer for bonding, which includes copper particles, copper/zinc, and copper/tin alloys with phosphorus fractions, ensuring mean particle diameters ≤15 μm for enhanced reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder paste without phosphorus-containing copper particles is used, then the soldering process is simple, but the connection reliability under high temperature conditions is insufficient
Solution Approach 1:
The invention changes the chemical composition parameters of the solder paste by incorporating copper particles with controlled phosphorus content (5-500 ppm). This parameter modification enables the formation of Cu3P intermetallic compounds during soldering, which significantly improves connection reliability under high temperature conditions while maintaining manageable process complexity
Solution Approach 2:
The invention uses composite material strategy by combining copper particles with specific phosphorus content, tin particles, and solder flux in defined proportions. This composite formulation creates synergistic effects where phosphorus-containing copper particles form protective Cu3P layers that enhance intermetallic compound structure and improve solder joint reliability at elevated temperatures
2Stability of the object's composition
If copper particles with high phosphorus content are used, then connection stability improves, but the risk of excessive phosphorus diffusion and harmful byproducts increases
Solution Approach 1:
The invention optimizes the phosphorus content parameter within a specific range (5-500 ppm) to achieve the desired balance. This controlled parameter setting ensures sufficient phosphorus is available to form stabilizing Cu3P intermetallic compounds while preventing excessive phosphorus diffusion that would create harmful byproducts and compromise joint integrity
Solution Approach 2:
The invention converts the potentially harmful effect of phosphorus diffusion into a beneficial outcome by controlling phosphorus content to form Cu3P intermetallic compounds. These compounds, which could be considered harmful if uncontrolled, actually serve as protective layers that stabilize the solder joint and improve connection reliability under thermal stress
3Ease of manufacture
If the mean particle diameter is reduced to ≤15 μm, then solder paste applicability and bonding quality improve, but manufacturing precision requirements increase
Solution Approach 1:
The invention sets the mean particle diameter parameter at ≤15 μm, which optimizes the balance between manufacturability and bonding quality. This particle size range ensures good flow characteristics and applicability of the solder paste while maintaining manageable manufacturing precision requirements for producing consistent, high-quality solder joints
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 method results in significantly improved and more reliable soldered connections, particularly at high temperatures, with increased shear strength at 200°C, as demonstrated by Inventive Examples 1 and 2, compared to Reference Examples 3 and 4, showcasing enhanced stability and performance.
Implementation Method 1
particles made of copper and/or of copper-rich copper/tin and/or copper/zinc alloys, which each have a phosphorus content >0 to ≤500 wt-ppm
Data Source
AI summary
A solder paste that contains or consists of (i) 10-30% by weight of at least one type of particles that each contain a phosphorus fraction of >0 to ≤500 wt-ppm and are selected from copper particles, copper-rich copper/zinc alloy particles, and copper-rich copper/tin alloy particles, (ii) 60-80% by weight of at least one type of particles selected from tin particles, tin-rich tin/copper alloy particles, tin-rich tin/silver alloy particles, and tin-rich tin/copper/silver alloy particles, and (iii) 3-30% by weight solder flux, in which the mean particle diameter of metallic particles (i) and (ii) is ≤15 μm.