External Electrode Alloy Layer for Soldering Reliability
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Solution Overview
Problem
Existing electronic parts with external electrodes face issues of deteriorated strength at high temperatures and soldering defects due to oxidation and poor wettability when using Pb-free solder, especially in high-temperature environments and during repeated reflow processes.
Innovation Solution
Incorporating a Cu-Ni or Cu-Mn alloy layer with an antioxidant film, such as a Sn-containing or noble metal film, on the external electrode to prevent oxidation and ensure rapid diffusion with Sn, forming intermetallic compounds with high melting points for enhanced heat resistance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional external electrode structure with Ag-Pd metal powder and glass frit is used, then soldering property is improved, but strength at high temperature deteriorates causing electronic part detachment
Solution Approach 1:
The external electrode is segmented into multiple functional layers: a base layer (Ag-Pd alloy) for soldering property, and additional layers (oxidation-resistant metal layer and glass layer) for high-temperature strength. Each layer performs a specific function, resolving the contradiction between soldering property and high-temperature strength.
Solution Approach 2:
The external electrode uses composite material structure combining Ag-Pd alloy powder with oxidation-resistant metals (Ni, Pd, Pt) and glass frit. This composite structure provides both good soldering wettability from the Ag-Pd base and high-temperature stability from the oxidation-resistant components, preventing electronic part detachment.
2Reliability
If Pb-free solder is used for mounting, then environmental compatibility is improved, but oxidation of external electrode occurs causing soldering defects
Solution Approach 1:
An oxidation-resistant metal layer (Ni, Pd, or Pt) is applied over the Ag-Pd alloy base layer before soldering. This preliminary protective layer prevents oxidation of the underlying solderable surface during the Pb-free soldering process, eliminating soldering defects while maintaining environmental compatibility.
Solution Approach 2:
The oxidation-resistant metal layer creates an inert protective environment over the Ag-Pd alloy surface, preventing direct contact between oxygen and the solderable metal surface during high-temperature Pb-free soldering, thus preventing oxidation and soldering defects.
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 solution effectively prevents soldering defects, maintains high solder wettability, and ensures strong, reliable joints at elevated temperatures, preventing electronic part detachment even under multiple reflow cycles or in high-temperature conditions.
Implementation Method 1
the alloy layer is reacted with Sn contained in the joining material to produce an intermetallic compound
Implementation Method 2
the alloy layer of the external electrode is reacted with Sn contained in the joining material to produce an intermetallic compound in the heat treatment step
Implementation Method 3
an antioxidant film which is formed on an outer side of the alloy layer
Implementation Method 4
the alloy layer is reacted with Sn contained in the joining material to produce an intermetallic compound in the heat treatment step
Data Source
Figure 1
Figure 2
AI summary
Disclosed is an electronic part which has excellent heat resistance of a soldered portion in mounting the electronic part by soldering, has good solder wettability of the external electrode, and can perform highly reliable mounting, and a method for forming a joint structure having high joint reliability and high heat resistance. In an electronic part A1 including an electronic part main body (ceramic laminate) 1 and an external electrode 5 formed on the surface of the electronic part main body 1, the external electrode includes at least one alloy layer 10 selected from among a Cu-Ni alloy layer and a Cu-Mn alloy layer, and an antioxidant film 20 which is formed on the outer side of the alloy layer. The antioxidant film includes a Sn-containing film containing Sn. The antioxidant film includes a noble metal film made of a noble metal. The antioxidant film includes an organic substance film made of an organic substance.