Capacitor Mounting Structure With Cu Layer for Heat-Stable Solder Bonds
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Solution Overview
Problem
The bonding strength of electronic components to a substrate decreases due to alloy formation between metal components exposed to high heat or time, particularly in multilayer ceramic capacitors with specific alloy types.
Innovation Solution
A mounting structure for electronic components using a substrate with a land, an electronic component with an external electrode, and solder containing Sn and Bi, where the external electrode and land include Ni and Au, and a Cu layer is added, forming an alloy of Sn, Cu, Au, and Ni in regions adjacent to the solder to enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soldering is used to join the external electrode to the land, then electrical connection is achieved, but bonding strength decreases due to alloy formation between metal components under high heat or time exposure
Solution Approach 1:
The patent introduces an intermediary Cu layer between the external electrode and the solder joint. This Cu layer acts as a barrier that prevents direct contact and alloying between the Ni components and Sn in the solder, thereby suppressing harmful alloy formation while maintaining electrical connection and bonding strength.
Solution Approach 2:
The patent employs a composite plating structure on the external electrode consisting of multiple layers (Ni, Cu, Ni, Au) with specific thickness ratios. This composite material approach creates a controlled metallurgical structure where the Cu layer specifically prevents unwanted alloying while allowing beneficial bonding, thus maintaining reliability under thermal stress.
2Ease of manufacture
If high heat exposure occurs during soldering, then soldering process is completed, but metal components alloy which reduces bonding strength
Solution Approach 1:
The Cu layer serves as a thermal and metallurgical intermediary that remains stable during the soldering heat process. It allows the soldering process to proceed normally while preventing excessive alloying between Ni and Sn that would occur without this intermediate layer, thus maintaining bonding strength after heat exposure.
Solution Approach 2:
The patent specifies precise thickness parameters for each plating layer (Ni: 0.1-1.0 μm, Cu: 0.01-0.5 μm, Ni: 0.1-1.0 μm, Au: 0.01-0.1 μm) to optimize the balance between soldering processability and resistance to heat-induced alloying. These parameter controls ensure the Cu layer is thin enough not to interfere with soldering but thick enough to prevent harmful alloy formation.
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 addition of a Cu layer in the external electrode suppresses the formation of brittle Ni-Sn and Ni-Sn-Au alloys, maintaining strong bonding between the capacitor component and the substrate even under high temperature conditions.
Implementation Method 1
The metal component included in the land of the board and the metal component included in the solder may be alloyed by exposure to high heat or elapse of time
Implementation Method 2
The external electrode is joined to the land by the solder
Data Source
AI summary
The mounting structure of an electronic component is exposed to a high temperature, which may cause a decrease in bonding strength of the electronic component to the land of the substrate. A mounting structure of an electronic component includes a substrate having a land, a capacitor component having a first external electrode stacked on an outer surface of a base body, and a solder including Sn and Bi. The first external electrode is bonded to the land with the solder. One or more selected from the land and the first external electrode contain Ni. One or more selected from the land, the first external electrode, and the solder contain Au, and one or more selected from the land, the first external electrode, and the solder contain Cu. An alloy portion including Sn, Cu, Au, and Ni is further included in a region adjacent to the solder.