Layered Solder Barrier for Intermetallic Control in Bonded Electrodes
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Solution Overview
Problem
When soldering electrodes made of different materials, fluidity issues occur during melting, leading to the formation of intermetallic compounds at the bonded interface, which deteriorates bonding strength and heat cycle resistance, especially in downsized electronic components, causing potential functional failures under impact loads.
Innovation Solution
A layered solder material is formed by rolling together a first layer of solder material, such as Sn-Ag-Cu or Sn-Sb, and a second layer of solder material, such as Sn-Ag-Cu-Ni or Sn-Pb, to create a solid-phase diffusion layer that acts as a barrier, preventing intermetallic compound formation between electrodes with different plating materials like Ni/Au or Ag-Pd and Cu.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If electrodes made of different materials are soldered together, then bonding between different plating materials is achieved, but intermetallic compounds form at the bonded interface causing deterioration of bonding strength and heat cycle resistance
Solution Approach 1:
A Cu-Sn intermetallic compound layer is formed as an intermediary between the Cu electrode and the SAC alloy solder. This intermediate layer acts as a buffer that prevents direct contact and excessive interaction between Cu and Sn, thereby controlling intermetallic compound formation while maintaining bonding compatibility between different plating materials.
Solution Approach 2:
The invention controls the thickness and composition parameters of the Cu-Sn intermetallic compound layer at the bonded interface. By optimizing these parameters (thickness control within specific ranges, composition ratio of Cu to Sn), the bonding strength and heat cycle resistance are maintained while preventing excessive intermetallic compound formation that would deteriorate reliability.
2Volume of moving object
If electrodes are downsized to meet miniaturization requirements, then electronic component size is reduced, but the electrodes become more susceptible to breaking under impact loads when intermetallic compounds are present
Solution Approach 1:
The invention precisely controls the thickness parameter of the Cu-Sn intermetallic compound layer to optimize the balance between bonding strength and impact resistance. By maintaining the intermetallic layer within specific thickness ranges, the electrode structure achieves sufficient strength for miniaturized components while resisting impact loads.
Solution Approach 2:
The bonded interface creates a composite structure consisting of multiple layers including the Cu electrode, SAC alloy solder, and controlled Cu-Sn intermetallic compound layer. This composite structure provides both the bonding functionality needed for miniaturization and the mechanical strength to resist impact loads.
3Adaptability or versatility
If multiple species of intermetallic compounds are formed in the bonded interface, then bonding between different materials is achieved, but the number of intermetallic compound species increases leading to deterioration of bonding strength and heat cycle resistant characteristics
Solution Approach 1:
The Cu-Sn intermetallic compound layer serves as a selective intermediary that facilitates bonding between Cu and SAC alloy while controlling the formation of other intermetallic compounds. This intermediate layer reduces the diversity of intermetallic compound species by providing a controlled reaction interface.
Solution Approach 2:
The invention creates a localized region with specific intermetallic compound characteristics at the bonded interface. By controlling the local composition and structure of the Cu-Sn intermetallic layer, the bonding interface achieves material compatibility while minimizing the variety of intermetallic compound species that would otherwise form.
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 ensures high bonding reliability between electrodes with different plating materials by restricting intermetallic compound formation, maintaining strength and resistance to heat cycles, even in small-sized electronic components.
Implementation Method 1
a solid-phase diffusion layer that acts as a barrier, preventing intermetallic compound formation between electrodes with different plating materials
Data Source
AI summary
When soldering a package having an electrode on which Ni/Au or Ag-Pd alloy is plated to a printed circuit board having a Cu electrode or an electrode on which Cu is plated, a solid-phase diffusion layer is formed within the inside of a layered solder material for bonding different species of electrodes by heating and cooling the layered solder material for bonding different species of electrodes. The layered solder material is composed of a solder material of Sn-Ag-Cu series or Sn-Sb series and a solder material of Sn-Ag-Cu-Ni series or Sn-Pb series. The electrode on which Ni/Au or Ag-Pd alloy is plated and the Cu electrode or the electrode on which Cu is plated are soldered with the solder material of Sn-Ag-Cu series or Sn-Sb series being attached to the Cu electrode and the solder material of Sn-Ag-Cu-Ni series or Sn-Cu series being attached to the electrode on which Ni/Au or Ag-Pd alloy is plated. This allows formation of intermetallic compounds to be restrained, thereby soldering them with high bonding reliability.