Solder Joint Intermetallic Growth via Temperature Gradient
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Solution Overview
Problem
In 3-D and 2.5-D packaging, solder joints face issues with stress and electromigration due to high current densities and shallow intermetallic compound thickness, while long-term high-temperature heating methods are problematic with pre-applied resins.
Innovation Solution
A method involving temperature difference heating with a predetermined temperature gradient to form an intermetallic compound in the solder joint between metal layers, allowing for rapid growth and maintaining constant thickness, which suppresses stress and enhances electromigration resistance, enabling the use of pre-applied resin techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long-term high-temperature heating is used to form intermetallic compound, then EM resistance is improved, but resin degradation occurs
Solution Approach 1:
The patent changes the heating parameters by introducing a temperature gradient (higher temperature at one substrate side, lower at the other) instead of uniform high-temperature heating. This allows the intermetallic compound to grow rapidly toward the lower-temperature side while keeping the overall heating time short, thus achieving good EM resistance without degrading the pre-applied resin
Solution Approach 2:
The patent uses a temperature gradient to accelerate the intermetallic compound growth rate, allowing the joint to reach sufficient thickness and EM resistance in a much shorter time period. This 'rushes through' the heating process, avoiding the long-term high-temperature exposure that would degrade the resin
2Device complexity
If shallow intermetallic compound thickness is used, then joint structure is simplified, but stress concentration occurs
Solution Approach 1:
The patent changes the growth direction and rate parameters by applying a temperature gradient. The intermetallic compound grows rapidly from the higher-temperature side toward the lower-temperature side, achieving sufficient thickness uniformly throughout the joint in short time, thereby reducing stress concentration while maintaining structural simplicity
3Device complexity
If uniform temperature heating is used, then heating process is simple, but intermetallic compound growth is slow
Solution Approach 1:
The patent applies asymmetric temperature distribution across the joint, with one substrate side heated to a higher temperature and the other to a lower temperature. This asymmetric heating creates a temperature gradient that drives rapid intermetallic compound growth from the hot side toward the cold side, significantly increasing productivity compared to uniform heating
Solution Approach 2:
The patent transitions from uniform temperature distribution (zero-dimensional) to temperature gradient distribution (one-dimensional variation across the joint thickness). This dimensional change in temperature field enables directional and accelerated intermetallic compound growth, improving productivity while adding controlled complexity to the heating process
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 method effectively forms an intermetallic compound in the solder joint in a shorter time, reducing stress and improving electromigration resistance while allowing for the use of pre-applied resins, resulting in a robust and reliable solder joint.
Implementation Method 1
maintaining a temperature gradient (temperature/unit thickness) between the two metal layers at a predetermined value or higher
Implementation Method 2
heating the structure to grow an intermetallic compound in a space between the two metal layers
Data Source
AI summary
Forming a solder joint between metal layers by preparing a structure having solder material placed between two metal layers and heating the structure to grow an intermetallic compound in a space between the two metal layers. Growing the intermetallic compound includes setting a first surface, in contact with the solder material between the two metal layers, to a first temperature, thereby enabling growth of the intermetallic compound; setting a second surface, in contact with the solder material between the two metal layers, to a second temperature, wherein the second temperature is higher than the first temperature; and maintaining a temperature gradient (temperature/unit thickness) between the two metal layers at a predetermined value or higher until the intermetallic compound substantially fills the space between the two metal layers.