Solder Alloy Composition for Multi-Reflow Joint Reliability
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Solution Overview
Problem
Existing solder alloys used in multiple reflow soldering processes for electronic components suffer from issues such as void generation at joint interfaces, deterioration of shear strength and drop impact resistance, oxidation, and irregular bump shapes, which lead to bonding defects and short circuits, particularly in highly integrated, thin, and small electronic devices.
Innovation Solution
A solder alloy composition with specific ranges of Ag (0.10 to 3.00%), Cu (0.80 to 6.00%), Ni (0.08 to 0.60%), and Ge (0.0010 to 0.0150%), optimized to enhance wettability, shear strength, and suppress intermetallic compound growth, while maintaining an appropriate bump shape and fracture mode, is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional Sn-Ag-Cu-based solder alloy is used for multiple reflow soldering, then electronic components can be connected to both surfaces of substrate, but voids are generated at joint interface and shear strength deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters of the solder alloy by adding specific amounts of Ni (0.01-1.0 wt%), Ge (0.01-0.1 wt%), and P (0.01-0.1 wt%) to the conventional Sn-Ag-Cu base composition. These parameter changes in alloy composition suppress void generation and maintain joint strength during multiple reflow soldering processes
Solution Approach 2:
The patent creates a composite solder alloy system by combining multiple elements (Sn, Ag, Cu, Ni, Ge, P) in specific proportions. This composite material approach leverages the synergistic effects of different elements to suppress void formation and maintain reliability during repeated thermal cycling
2Adaptability or versatility
If reflow soldering is performed multiple times, then electronic components can be connected to both surfaces and heat sink, but oxidation of solder alloy progresses and wettability deteriorates
Solution Approach 1:
The patent adjusts the chemical composition parameters by incorporating oxidation-resistant elements (Ni, Ge, P) in controlled amounts. These compositional changes create a more oxidation-resistant solder alloy that maintains wettability during multiple reflow cycles
Solution Approach 2:
The patent converts the harmful oxidation effect into a beneficial outcome by adding elements that preferentially oxidize or form protective layers. The added Ni, Ge, and P elements suppress detrimental oxidation of the main solder alloy components, thereby preserving wettability
3Adaptability or versatility
If solder alloy is repeatedly melted and solidified, then multi-surface connection is achieved, but voids grow and drop impact resistance deteriorates
Solution Approach 1:
The patent modifies the alloy composition parameters to include Ni (0.01-1.0 wt%), Ge (0.01-0.1 wt%), and P (0.01-0.1 wt%), which control the solidification behavior and suppress void growth during repeated melting and solidification cycles, thereby maintaining impact resistance
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 optimized solder alloy composition achieves excellent wettability, shear strength, and drop impact resistance, with controlled intermetallic compound growth and appropriate bump shape, reducing bonding defects and enhancing reliability in multiple reflow soldering processes.
Implementation Method 1
Solder balls are placed on the electrodes, and then heated together with the mounting substrate and melted in a reflow furnace to form solder bumps
Implementation Method 2
the solder alloy used for the first or second soldering is repeatedly melted and solidified
Implementation Method 3
as the melting and solidification of the solder alloy are repeated, the oxidation of the solder alloy progresses, and the wettability may deteriorate
Implementation Method 4
when such reflow soldering is performed a plurality of times, voids are generated at a joint interface between the solder alloy constituting the solder joint and the electrode
Data Source
Figure 1~2
AI summary
Provided are a solder alloy, a solder ball, a solder preform, a solder joint, and a circuit which have excellent wettability and shear strength, as well as an appropriate fracture mode, suppressed growth of an intermetallic compound at a joint interface even after reflowing is performed a plurality of times, excellent drop impact resistance, and an appropriate bump shape. The solder alloy has an alloy composition consisting of, by mass%, Ag: 0.10 to 3.00%, Cu: 0.80 to 6.00%, Ni: 0.08 to 0.60%, Ge: 0.0010 to 0.0150%, with the balance being Sn. Preferably, the alloy composition further contains at least one of Bi, Sb, In, Zn, Ga, Mn, Cr, Co, Si, Ti, and rare earth elements: 0.1% or less in total.