Sn-Sb Soldering with Ni Plating to Prevent Cu Elution
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Solution Overview
Problem
The existing solder materials, particularly Sn-Sb-based solder materials with high Sb content, exhibit a tendency to crack and deteriorate mechanical reliability due to high solidus temperatures, leading to poor wettability and void formation during surface-mount component soldering, and the use of Pb-based solder materials poses environmental and health concerns.
Innovation Solution
The use of Sn-Sb-based solder materials with limited Cu content (<0.005% by mass) as die-bonding solder and Sn-Ag-Cu-Bi or Sn-Ag-Cu-Bi-In-based solder materials with controlled composition ratios as mounting solder, where the Ni plating layer prevents Cu elution, ensuring a significant difference in solidus temperatures to prevent melting and enhance solderability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Sn-Sb-based solder material with high Sb content is used to achieve high solidus temperature, then the solder material resists melting during mounting, but the solder material cracks and deteriorates mechanical reliability
Solution Approach 1:
The invention changes the chemical composition parameters of the solder material by strictly limiting Cu content to 0.005% or less and controlling impurity levels (Fe≤0.003%, Ni≤0.003%, Zn≤0.003%). This parameter control maintains the high solidus temperature of Sn-Sb-based solder while preventing crack formation and improving mechanical reliability.
2Temperature
If Sn-Sb-based solder material is used to maintain high solidus temperature, then melting resistance is improved, but wettability deteriorates and voids form during soldering
Solution Approach 1:
The invention optimizes composition parameters by limiting Cu to 0.005% or less and controlling impurities (Fe≤0.003%, Ni≤0.003%, Zn≤0.003%), which maintains high solidus temperature while improving wettability and reducing void formation during soldering processes.
3Ease of manufacture
If Pb-based solder material is used to achieve low melting point, then soldering ease is improved, but environmental pollution and health risks increase
Solution Approach 1:
The invention extracts and eliminates Pb from the solder material composition, replacing it with Sn-Sb-based alloy. By strictly controlling Cu content (≤0.005%) and impurities, the invention achieves Pb-free soldering with maintained ease of manufacture while eliminating environmental and health hazards associated with Pb.
4Manufacturing precision
If Cu content is increased in Sn-Sb-based solder material, then soldering performance may improve, but solidus temperature decreases
Solution Approach 1:
The invention establishes an optimal parameter range by limiting Cu content to 0.005% or less, which prevents solidus temperature decrease while maintaining good soldering performance. This parameter control balances both soldering quality and temperature stability.
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 maintains the primary solidus temperature of Sn-Sb-based solder materials, reduces the minimum heating temperature in reflow furnaces, and improves bonding strength and mechanical reliability by preventing Cu elution and void formation, thus enhancing the reliability of surface-mount components.
Implementation Method 1
the die pad electrode portion (island portion) on which the circuit element is to be mounted is plated with Ni... any component which causes a solidus temperature to fall down is prevented from being eluted
Implementation Method 2
a solidus temperature... a heating temperature to be used in a reflow furnace... so that any soldering is performed under a condition such that any cracks occur
Data Source
Figure 1A~1E
Figure 2~3
Figure 4~5
AI summary
The melting of die-bonding solder material is prevented even when soldering a surface-mount component formed using the die-bonding solder material on a printed circuit board using a mounting solder material. The surface-mount component formed using (Sn-Sb)-based solder material having high melting point as the solder material 30 for die pad, the (Sn-Sb)-based solder material containing Cu not more than a predetermined quantity of Cu constituent and a main ingredient thereof being Sn, is soldered on a board terminal portion of a circuit board using (Sn-Ag-Cu-Bi)-based solder material as the mounting solder material 70 with the solder material being applied on the terminal portion. Since solidus temperature of the die-bonding solder material 30 is 243 degrees C. and liquidus temperature of the mounting solder material 70 is about 215 through 220 degrees C., the melting of die-bonding solder material 30 is prevented even at the heating temperature (240 degrees C. or less) of a reflow furnace.