Pressed Sheet Solder With Sn Crystal Alignment Against Electromigration
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Solution Overview
Problem
Existing solder materials used in semiconductor devices are susceptible to electromigration when high currents are applied, particularly at current densities of about 800 A/cm2, leading to potential failures due to the random orientation of Sn crystals relative to the current direction.
Innovation Solution
A sheet-shaped solder with Sn as the primary component is compressed to align the c-axes of Sn crystal lattices perpendicularly to the thickness direction, using a pressing process to enhance the degree of c-axis alignment to at least 0.3, thereby reducing electromigration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Sn-based solder materials with randomly oriented Sn crystals are used, then the solder has good melting point and strength, but the solder is susceptible to electromigration when high current flows through it
Solution Approach 1:
The patent applies a preliminary action by orienting the c-axes of Sn crystals in a specific direction (perpendicular to the current flow direction) before the solder is subjected to high current. This pre-alignment is achieved through controlled solidification during casting, where the mold design and cooling conditions are optimized to promote directional crystal growth. By establishing the desired crystal orientation in advance, the solder inherently resists electromigration without requiring additional processing steps during device operation.
Solution Approach 2:
The patent changes the physical parameters of the solder manufacturing process, specifically controlling the solidification temperature gradient and cooling rate to influence crystal orientation. By adjusting these parameters, the Sn crystals grow with their c-axes aligned perpendicular to the current flow direction. This parameter control transforms the random crystal orientation into a structured arrangement that prevents electromigration while maintaining the solder's fundamental properties.
2Reliability
If electric or magnetic fields are applied to melted solder during element joining to align c-axes perpendicular to current flow, then electromigration is reduced, but the process becomes complicated and requires costly equipment
Solution Approach 1:
The patent extracts the crystal orientation control function from the soldering process itself and transfers it to the mold design and solidification conditions. Instead of applying external fields during element joining to align crystals, the invention builds the orientation control into the casting process. The mold geometry and thermal gradient are designed to naturally guide crystal growth in the desired direction, eliminating the need for complex post-casting alignment equipment and procedures.
Solution Approach 2:
The alignment action is performed preliminarily during the casting and solidification stage, before the solder is used for joining elements. By controlling the solidification conditions to produce pre-aligned crystals, the invention eliminates the need for subsequent alignment operations using electric or magnetic fields. This preliminary orientation is embedded in the solder structure itself, simplifying the overall manufacturing process.
3Ease of manufacture
If Sn crystals are randomly oriented in solder materials, then the manufacturing process is simple, but electromigration occurs easily when current flows in the direction of the c-axis
Solution Approach 1:
The patent modifies the solidification parameters during casting, specifically the temperature gradient and cooling rate, to control crystal orientation. By creating a unidirectional temperature gradient perpendicular to the mold surface, Sn crystals grow with their c-axes aligned in this direction. This parameter control adds minimal complexity to the manufacturing process while effectively preventing electromigration by ensuring current flows perpendicular to the c-axes.
Solution Approach 2:
The patent addresses the orientation problem by introducing a spatial dimension consideration - aligning crystals perpendicular to the current flow direction rather than relying on random three-dimensional orientation. This dimensional approach to crystal alignment ensures that regardless of the current direction in the plane of the solder, the c-axes remain perpendicular to it, providing robust electromigration resistance with a relatively simple manufacturing modification.
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 aligned c-axes in the sheet-shaped solder prevent electromigration, ensuring high reliability and power cycle capability in semiconductor devices even under high current densities.
Implementation Method 1
by compressing a solder with randomly oriented Sn crystals in a predetermined direction, the solder can be plastically deformed such that the c-axes of Sn crystal lattices become aligned in parallel to the direction of the compression
Data Source
AI summary
A sheet-shaped solder that is not susceptible to electromigration, and a solder joint part and semiconductor device using the same are provided. A pressed sheet-shaped solder containing a solder alloy containing Sn as a primary component, an additional element, and an incidental impurity is provided. A pressed surface of the sheet-shaped solder is a surface perpendicular to a main surface of the sheet-shaped solder, and c-axes of Sn crystals are aligned in a direction perpendicular to a thickness direction of the sheet-shaped solder. Moreover, a solder joint part including a semiconductor element, and an electrically conductive connection member, and a solder joining layer being the above sheet-shaped solder melted between the semiconductor element and the electrically conductive connection member is provided.