Ag-Sn Bonding Structure for Heat-Resistant Semiconductor Joining
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Solution Overview
Problem
Conventional transient liquid phase diffusion bonding methods for semiconductor devices are insufficient in heat resistance due to the use of low-melting point metals like Sn, leading to potential softening and partial melting under high temperatures, which can compromise bonding strength and durability.
Innovation Solution
A bonding structure is developed using a compression-molded article of Ag powder and Sn powder, with a composition of 78.0% to 80.0% Ag and 20.0% to 22.0% Sn, forming a material texture with an island-like Ag phase and Ag3Sn phase, which provides enhanced heat resistance and bonding strength by incorporating a high-melting point Ag phase and a durable Ag3Sn intermetallic compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Sn is used as the main component of the bonding material, then bonding strength is achieved, but heat resistance deteriorates due to low melting point
Solution Approach 1:
The bonding material is designed as a composite system containing both Sn and Ag phases, where Sn provides bonding strength through intermetallic compound formation and Ag provides heat resistance through its high melting point. This composite structure allows the bonding portion to simultaneously achieve both bonding strength and heat resistance that neither material could provide alone.
Solution Approach 2:
The bonding material exhibits non-uniform composition with localized Sn-rich regions for bonding and Ag-rich regions for heat resistance. The Sn diffuses to form intermetallic compounds at the bonding interface while Ag remains as a high-melting-point matrix, creating different functional zones within the bonding material that address different requirements locally.
2Ease of manufacture
If conventional soldering method is used, then bonding process is simple, but bonding temperature must be high which reduces heat resistance
Solution Approach 1:
The bonding process utilizes the phase transition of Sn from solid to liquid at relatively low temperature (melting point 232°C). During bonding, Sn melts to form a liquid phase that facilitates diffusion and bonding, then solidifies to form the final bonding structure. This phase transition enables bonding at low temperature, preserving the heat resistance of the bonding material while maintaining process simplicity.
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 bonding structure achieves improved heat resistance and durability, maintaining bonding strength and preventing cracks under thermal stress, suitable for high-power density semiconductor devices.
Implementation Method 1
Sn, which is formed into a liquid phase, diffuses to the interface thereof with the materials to be bonded, for integration, and also diffuses to Ag to form an intermetallic compound (Ag3Sn) together with Ag
Implementation Method 2
melting of Sn with heating to a temperature (200 to 250° C.) around the melting point of Sn, as a bonding temperature
Implementation Method 3
a bonding method including placing a bonding material (insert metal) as a combination of predetermined two or more metals different in melting point, between materials to be bonded, and partially melting such an insert metal and the materials to be bonded, with heating to a temperature around a lower melting point of such an insert metal, to result in diffusion bonding
Data Source
AI summary
A bonding structure to be formed in bonding of a Si semiconductor or the like and a substrate, as materials to be bonded, with transient liquid phase diffusion bonding. The bonding structure includes a bonding portion presenting a specific material texture. A metal composition of the bonding portion includes 78.0% by mass or more and 80.0% by mass or less of Ag, 20.0% by mass or more and 22.0% by mass or less of Sn, and an inevitable impurity element. A characteristic material texture configured from an island-like Ag phase including 95% by mass or more of Ag and a Ag3Sn phase including a Ag3Sn intermetallic compound and surrounding the island-like Ag phase is presented in observation of any cross section of the bonding portion.