Lead-Free Soldering on Electroless Ni Plating
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Solution Overview
Problem
Lead-free soldering with electroless Ni plating results in decreased adhesive strength due to the formation of a brittle SnNi intermetallic compound and a P-enriched layer, leading to peeling issues under external impacts in electronic equipment.
Innovation Solution
Using a lead-free solder with 0.03-0.1 mass percent of P, such as Sn-P-Ag or Sn-P-Cu, to suppress the growth of the SnNi intermetallic compound and prevent Ni escape from the electroless Ni plating, thereby reducing the thickness of the brittle layers and enhancing bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroless Ni plating is used on Cu electrodes, then oxidation and sulfurization resistance is improved, but wettability by molten solder deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding specific amounts of P (0.01-0.06 mass%), Bi (0.1-2.0 mass%), and Sb (0.1-2.0 mass%). This parameter modification allows the solder to wet Ni-plated surfaces effectively while maintaining lead-free composition, resolving the wettability issue without sacrificing oxidation resistance.
Solution Approach 2:
The invention uses a composite solder alloy combining Sn, P, Bi, and Sb elements. This composite material approach creates synergistic effects where P enhances wetting on Ni, Bi lowers melting point, and Sb improves mechanical properties, collectively solving both the wettability and reliability problems.
2Temperature
If Pb-Sn solder with eutectic composition is used, then melting point is reduced to 183°C, but environmental harm increases due to Pb content
Solution Approach 1:
The invention replaces expensive and harmful Pb with a lead-free alloy system based on Sn, P, Bi, and Sb. This substitution eliminates environmental harm while maintaining suitable melting characteristics for soldering applications.
Solution Approach 2:
The invention modifies the solder composition parameters to create a lead-free alloy with controlled melting behavior. By adjusting the ratios of Sn, P, Bi, and Sb, the solder achieves appropriate melting and reflow characteristics without containing Pb, thus eliminating environmental harm.
3Object-affected harmful factors
If soldering is performed on electroless Ni plating with conventional lead-free solder, then Pb-containing solder is eliminated, but bonding strength decreases due to brittle SnNi intermetallic compound formation
Solution Approach 1:
The invention changes the chemical composition parameters of the solder by adding P (0.01-0.06 mass%), Bi (0.1-2.0 mass%), and Sb (0.1-2.0 mass%). These parameter modifications suppress the formation of brittle SnNi intermetallic compounds and promote the formation of more ductile intermetallic phases, thereby improving bonding strength while maintaining lead-free composition.
Solution Approach 2:
The invention uses a composite solder alloy system that combines multiple elements (Sn, P, Bi, Sb) to create a synergistic effect. This composite material approach controls intermetallic compound formation, reduces brittleness, and enhances bonding strength without requiring Pb.
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 significantly increases the bonding strength of solder joints, preventing peeling even under large external impacts, and ensures reliable soldered portions with improved impact resistance.
Implementation Method 1
the electroless plating method has the advantages that Ni plating of uniform thickness is formed over the entire surface of the material regardless of the type of material or its shape by simply immersing a material to be soldered in a plating solution without conduction of electricity
Implementation Method 2
A plating solution used for electroless Ni plating is a Ni—P plating solution containing a combination of nickel sulfate as a source of Ni and sodium hypophosphite as a reducing agent
Implementation Method 3
Cu is easily wet by molten solder, and it causes little occurrence of soldering defects such as unsoldered portions and voids when soldering is carried out
Implementation Method 4
the BGA substrate is heated in a reflow furnace to melt the solder balls
Data Source
AI summary
When electrodes of a BGA plated by electroless Ni plating are soldered with solder balls of a lead-free solder, peeling of soldered joints readily takes place under an external impact. When a BGA electrode plated by electroless Ni plating is soldered with a lead-free solder to which 0.03-0.1 mass percent of P is added, the growth of brittle SnNi intermetallic compounds formed on the portion being soldered and a P layer on the electroless Ni plating surface is suppressed, resulting in an increased bonding strength.