Ni-Sn Intermetallic Layer Structure for High-Temperature Chip Packaging
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Solution Overview
Problem
Current solder materials for power applications, such as PbSn and SAC solders, face reliability issues due to re-melting and fatigue at elevated temperatures, and lack a general-purpose replacement for high lead content solders, especially for thin dies and second-level mounting on PCBs, with alternatives being costly or thermally/electrically inferior.
Innovation Solution
A solder material comprising nickel and tin with a bimodal distribution of particle sizes, where small particles alloy with a tin-rich solder base to form a high-melting intermetallic phase, achieving a melting temperature above 270°C and enhanced mechanical stability through the formation of Ni3Sn4 or Ni3Sn2 phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If eutectic PbSn solder or SAC solder is used for second level mounting, then the soldering process is simple and cost-effective, but the board level interconnects re-melt during application and are prone to fatigue at elevated temperatures
Solution Approach 1:
The patent changes the melting temperature parameter by replacing conventional low-melting-point solders (PbSn eutectic at 180°C, SAC at 220°C) with a high-melting-point intermetallic phase-forming solder material. The solder material is designed to form Ni3Sn4 or Ni3Sn2 intermetallic phases with melting temperatures above 270°C, thereby resolving the contradiction between ease of manufacture and reliability at elevated temperatures.
Solution Approach 2:
The patent employs a composite solder material system consisting of nickel particles (with bimodal size distribution), tin-rich solder base material, and intermetallic phase-forming components. This composite structure enables the formation of stable intermetallic phases (Ni3Sn4/Ni3Sn2) that provide high-temperature stability while maintaining manufacturability through controlled particle distribution and phase formation kinetics.
2Reliability
If high lead content solder paste is used for die and clip attach, then the material provides good reliability, but it violates RoHS and ELV regulations requiring lead-free alternatives
Solution Approach 1:
The patent extracts and eliminates the harmful lead component from the solder material while retaining the desirable reliability characteristics. The invention replaces lead-based intermetallic phase formers with nickel and tin-based systems that form stable Ni3Sn4 or Ni3Sn2 phases, achieving lead-free compliance without sacrificing die and clip attach reliability.
Solution Approach 2:
The patent employs a cost-effective lead-free solder material composition using readily available nickel and tin powders with controlled particle size distributions. This approach provides an economical alternative to expensive specialty lead-free solders while achieving the required reliability performance for power semiconductor applications.
3Reliability
If AuSn is used as a replacement for Pb-soldering, then the material provides good high-temperature stability, but it significantly increases costs and imposes tighter design rules and geometric restrictions
Solution Approach 1:
The patent replaces expensive AuSn intermetallic phase-forming materials with cost-effective nickel and tin-based compositions. The use of common base metals (Ni, Sn) instead of precious metals (Au, Sn) dramatically reduces material costs while maintaining high-temperature stability through the formation of thermally stable Ni3Sn4/Ni3Sn2 intermetallic phases.
Solution Approach 2:
The patent employs a bimodal particle size distribution of nickel particles (first amount with size 1-20 μm, second amount with size 20-50 μm) to optimize local phase formation characteristics. This controlled particle distribution ensures uniform intermetallic phase formation throughout the solder joint, eliminating the need for tighter design rules and geometric restrictions associated with AuSn systems.
4Length of moving object
If thin dies are used with potential alternative solutions, then the design allows for thinner profiles, but solutions without melting materials or with low melting points create challenges for proper attachment and reliability
Solution Approach 1:
The patent changes the melting temperature parameter to above 270°C, which is sufficiently high to accommodate thin die profiles while ensuring reliable attachment. The high melting point of the intermetallic phases (Ni3Sn4/Ni3Sn2) provides adequate thermal margin during reflow soldering processes, enabling proper wetting and attachment of thin dies without the reliability issues associated with low-melting-point alternatives.
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 solder material provides a reliable, cost-effective drop-in replacement for high lead content solders, ensuring stability and performance in second-level soldering and mounting applications, with a melting temperature suitable for power applications and reduced further alloying during heat treatment.
Implementation Method 1
small particles alloy with a tin-rich solder base to form a high-melting intermetallic phase
Implementation Method 2
formation of Ni3Sn4 or Ni3Sn2 phases
Implementation Method 3
heating the layer structure to a melting temperature of the solder material until an intermetallic phase forms
Data Source
AI summary
A layer structure includes a first layer including at least one material selected from a first group consisting of nickel, copper, gold, silver, palladium, tin, zinc, platinum, and an alloy of any of these materials; a third layer including at least one material selected from a second group consisting of nickel, copper, gold, palladium, tin, silver, zinc, platinum, and an alloy of any of these materials; and a second layer between the first layer and the third layer. The second layer consists of or essentially consists of nickel and tin. The second layer includes an intermetallic phase of nickel and tin.