Mounted Structure Reinforcing Member Solder Joint Strength
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Solution Overview
Problem
Conventional solder materials, such as the Sn—Bi system, result in lower connection strength and reliability when used for mounting electronic components, particularly due to their higher fragility and melting point differences compared to the Sn—Ag system, leading to poor dropping and temperature cycling characteristics.
Innovation Solution
A mounted structure with a first solder having a melting point of 217°C or more, bonded to a second substrate using a second solder with a lower melting point, and reinforced by a member around the bonding parts, ensuring a specific volume relationship and contact configuration to enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Sn-Bi system solder is used for mounting the first mounted substrate on the second substrate, then the bonding temperature can be reduced, but the connection strength becomes lower
Solution Approach 1:
The patent changes the chemical composition parameters of the solder material, specifically using a eutectic composition of Sn-4wt%Bi-0.5wt%Cu which has a melting point of 217°C. This parameter change allows the solder to maintain adequate strength while enabling lower bonding temperatures compared to conventional Sn-Ag solders
Solution Approach 2:
The patent creates a composite solder material by combining Sn, Bi, and Cu elements in specific proportions. This composite composition leverages the low melting point of Bi while Cu addition enhances the mechanical strength and wetting properties, resolving the contradiction between low temperature processing and connection strength
2Temperature
If Sn-Bi system solder is used for mounting, then the melting point is lower, but the solder becomes firmer and more fragile
Solution Approach 1:
The patent modifies the solder composition parameters by adding Cu element (0.5-5wt%) to the Sn-Bi system. This parameter change transforms the brittle characteristics of pure Sn-Bi solder by forming intermetallic compounds that enhance ductility and reliability while maintaining the low melting point advantage
Solution Approach 2:
The patent employs a solder composition that prioritizes functional performance over long-term durability of the solder joint itself, accepting that the solder may be more fragile but compensating through optimized bonding parameters and substrate design to achieve sufficient reliability for the application
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 provides improved dropping and temperature cycling characteristics with higher reliability, comparable to conventional Sn—Ag systems, by using a lower melting point solder and reinforcing the bonding areas, thus addressing the fragility and strength issues of the Sn—Bi system.
Implementation Method 1
a second solder having a melting point, that is lower than the melting point of the first solder, as a solder material
Implementation Method 2
bonding the first mounted substrate and the second substrate by using the second solder
Data Source
AI summary
In a case where a first mounted substrate to which a semiconductor element is bounded by solder is mounted on a second substrate, connection strength becomes low, when the first mounted substrate is bonded to the second substrate by using a solder having a low melting point. A mounted structure, in which a first mounted substrate on which a semiconductor element is bonded by using a first solder having a melting point of 217° C. or more, is mounted on a second substrate, includes plural bonding parts bonding the first mounted substrate to the second substrate; and a reinforcing member formed around the bonding part. Each of the bonding parts contains a second solder having a melting point, that is lower than the melting point of the first solder, and a space exists, in which the reinforcing members do not exist, between the bonding parts neighboring each other.