Ni-Sn Intermediate Layer Prevents Solder Splash on Cu PCB
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Solution Overview
Problem
The use of lead-free solder in electronic component mounting can result in solder splash during reflow soldering due to its low melting point, leading to potential short circuits between the circuit board and mold resin.
Innovation Solution
An electronic component mounting structure is developed with a circuit board having a Cu electrode and an electronic component featuring a Ni-plated Sn electrode, where an intermediate bonding layer with a Cu-Sn alloy and Sn regions is formed between the electrodes, increasing the melting point and reducing solder splash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder is used for mounting electronic components, then environmental safety and human health are improved, but the melting point decreases leading to solder splash during reflow soldering
Solution Approach 1:
An intermediate bonding layer is introduced between the Cu electrode and the Sn plating. This intermediate layer acts as a mediator that prevents direct contact between Cu and Sn, thereby preventing the formation of low-melting-point Cu-Sn intermetallic compounds. The intermediate layer consists of a Ni plating layer that remains stable at reflow soldering temperatures, thus maintaining high melting point characteristics while still enabling reliable bonding.
Solution Approach 2:
The electrode structure is designed as a composite multi-layer system: Cu electrode + intermediate bonding layer (Ni) + Sn plating. This composite structure combines the advantages of each material: Cu provides excellent electrical conductivity and bonding, Ni provides high temperature stability and acts as a diffusion barrier, and Sn provides good solderability. The composite structure prevents the formation of brittle Cu-Sn intermetallic compounds while maintaining low-melting-point solderability.
2Object-affected harmful factors
If lead-free solder is used, then environmental concerns are reduced, but solder splash occurs during reflow soldering causing short circuits
Solution Approach 1:
The intermediate bonding layer serves as a physical barrier that prevents molten solder from penetrating into the interface between the Cu electrode and mold resin during reflow soldering. By blocking the capillary action pathways, the intermediate layer eliminates the solder splash phenomenon that would otherwise cause short circuits, while still allowing the lead-free solder to function properly for environmental safety.
3Ease of manufacture
If Sn plating is applied directly on Cu electrode, then solderability is improved, but low-melting-point eutectic structure forms causing solder splash
Solution Approach 1:
The Ni intermediate bonding layer is positioned between the Cu electrode and Sn plating to prevent direct Cu-Sn contact. This eliminates the formation of the Cu6Sn5 eutectic structure with its low melting point of 48°C. The Sn plating still maintains excellent solderability by directly contacting the Ni layer, which has high temperature stability and does not form low-melting-point eutectics with Sn.
Solution Approach 2:
The invention changes the chemical composition parameters of the bonding interface by replacing direct Cu-Sn contact with Ni-Sn contact. The Ni-Sn system does not form low-melting-point eutectic compounds like Cu-Sn does. This parameter change in the intermediate layer composition raises the effective melting point of the bonding structure while preserving solderability.
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 elevated melting point of the intermediate bonding layer effectively prevents solder splash during motherboard mounting, ensuring reliable bonding and reducing the risk of short circuits.
Implementation Method 1
the lead-free solder included in the module is remelted by the heat of reflow soldering, and flows into the interface between the circuit board and the mold resin due to a capillary action
Data Source
AI summary
The present disclosure is directed to an electronic component mounting structure including: a circuit board provided on a surface thereof with a first electrode containing Cu as a main component; and an electronic component mounted on the circuit board, the electronic component including a second electrode on a surface thereof; wherein the second electrode includes a first plating containing Ni as a main component and a second plating containing Sn as a main component formed on a surface of the first plating, and an intermediate bonding layer is provided between the first plating and the first electrode, and the intermediate bonding layer includes a first region containing an alloy of Cu and Sn as a main component and a second region containing Sn as a main component.