Multi-layer Preform Sheet for Kirkendall Void Suppression
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Solution Overview
Problem
Conventional bonding members fail to provide high bonding strength and heat resistance over long durations, especially in devices experiencing large temperature changes, due to issues like Kirkendall void formation and damage to substrates, and existing solutions either require high temperatures or consume bonding metals, leading to incomplete bonding.
Innovation Solution
A multi-layer preform sheet with a first layer containing an intermetallic compound and a second layer of metals with a melting point above 300°C, where the metals form an intermetallic compound, acting as a barrier to suppress metal diffusion and void growth, and a metal matrix to enhance toughness and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the content of refractory metal or intermetallic compound is increased to enhance heat resistance and bonding strength, then bonding strength and heat resistance are improved, but higher bonding temperatures are required which may cause damages to substrates and electronic parts
Solution Approach 1:
The bonding member is divided into multiple layers with different functions: a first layer containing Sn and Cu for bonding, and a second layer containing refractory metal or intermetallic compound for heat resistance. This segmentation allows each layer to perform its specific function without requiring the entire bonding member to withstand high temperatures during bonding, thus improving bonding strength and heat resistance while avoiding substrate damage.
Solution Approach 2:
The bonding member uses a composite structure combining Sn-Cu alloy in the first layer with refractory metal or intermetallic compound in the second layer. This composite material approach enables the bonding member to achieve both low bonding temperature (from Sn-Cu) and high heat resistance (from refractory metal/intermetallic compound) simultaneously, resolving the contradiction between bonding strength and bonding temperature.
2Temperature
If the amount of intermetallic compound is increased to enhance heat resistance, then heat resistance is improved, but bonding metals are consumed to form intermetallic compound which may make bonding incomplete
Solution Approach 1:
The bonding member is segmented into a first layer for bonding (Sn-Cu alloy) and a second layer for heat resistance (refractory metal or intermetallic compound). This segmentation ensures that the Sn and Cu metals in the first layer are available for complete bonding without being consumed by intermetallic compound formation, while the second layer provides the required heat resistance.
Solution Approach 2:
The first layer containing Sn and Cu acts as an intermediary between the bonding interface and the second layer containing refractory metal or intermetallic compound. This intermediary layer ensures complete bonding at the bonding interface while the second layer provides heat resistance, preventing the consumption of bonding metals for intermetallic compound formation.
3Device complexity
If conventional bonding members are used, then bonding process is simple, but Kirkendall voids form due to unbalanced mutual diffusion of metals which reduces mechanical strength
Solution Approach 1:
The bonding member uses a composite structure with a first layer of Sn-Cu alloy and a second layer of refractory metal or intermetallic compound. This composite structure controls the diffusion process during bonding, preventing unbalanced mutual diffusion of metals and the formation of Kirkendall voids, thereby maintaining high mechanical strength while keeping the bonding process relatively simple.
Solution Approach 2:
The invention changes the compositional parameters of the bonding member by incorporating specific ratios of Sn, Cu, and refractory metal or intermetallic compound in distinct layers. This parameter change controls the diffusion kinetics during bonding, preventing Kirkendall void formation and maintaining mechanical strength without significantly increasing process complexity.
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 multi-layer preform sheet forms a highly reliable, heat-resistant, and mechanically strong bonding portion that maintains performance over long durations and harsh environments without damaging substrates, effectively preventing Kirkendall voids and ensuring high bonding strength and flexibility.
Implementation Method 1
a first layer which is a bonding member containing an intermetallic compound... acting as a barrier to suppress metal diffusion
Implementation Method 2
a second layer containing a first metal and a second metal... where the metals form an intermetallic compound
Data Source
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AI summary
Aiming at providing a multi-layer preform sheet capable of forming a highly reliable and high-quality electric interconnect, an electro-conductive bonding portion and so forth that are less likely to produce the Kirkendall void, this invention discloses a multi-layer preform sheet having at least a first layer and a second layer, the first layer being composed of a solder material that contains an intermetallic compound, and the second layer containing a first metal having a melting point of 300°C or above, and a second metal capable of forming an intermetallic compound with the first metal.