Elongated Contact Pads for 3D IC Thermal Alignment
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Solution Overview
Problem
In three-dimensional (3D) and 2.5D integrated circuits, substrates with different coefficients of thermal expansion misalign due to thermal expansion mismatches, causing contact pads to misalign at elevated temperatures, which affects electrical connections.
Innovation Solution
The implementation of elongated contact pads that maintain alignment at both room temperature and elevated temperatures by varying their shape and size based on position and thermal expansion mismatch, ensuring continued electrical connectivity during thermal processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard contact pads are used on substrates with different coefficient of thermal expansion, then the pads align at room temperature, but they misalign at elevated temperatures due to thermal expansion mismatch
Solution Approach 1:
The contact pads are designed with non-uniform dimensions, specifically elongated in the radial direction from the substrate center. Pads farther from the center have greater elongation to compensate for their larger thermal expansion displacement. This local variation in pad geometry ensures that each pad maintains alignment with its corresponding bump across the temperature range, resolving the contradiction between room temperature alignment and elevated temperature reliability.
Solution Approach 2:
The patent modifies the geometric parameters of the contact pads by elongating them radially based on their distance from the substrate center. This parameter change compensates for the thermal expansion mismatch between the substrate and die, allowing the pads to maintain proper alignment with the bumps at both room temperature and elevated temperatures during solder reflow processes.
2Adaptability or versatility
If the substrate and die have different coefficients of thermal expansion, then the die can be manufactured with standard materials, but misalignment occurs during solder reflow at elevated temperatures
Solution Approach 1:
The contact pads exhibit local quality through their radially varying elongation. Pads at different radial positions have different elongation amounts, with outer pads being more elongated than inner pads. This local differentiation compensates for the cumulative thermal expansion mismatch that increases with distance from the substrate center, maintaining alignment precision across the entire die-substrate interface during temperature cycling.
Solution Approach 2:
The pad elongation is pre-designed and fabricated into the substrate before the actual bonding process. This preliminary geometric compensation ensures that when thermal expansion occurs during solder reflow, the elongated pads naturally accommodate the expansion differential and maintain alignment with the bumps, preventing misalignment issues without requiring additional adjustment steps.
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 elongated pads effectively maintain alignment and electrical contact between the die and substrate at elevated temperatures, such as during solder reflow, and return to alignment upon cooling, enhancing the reliability of 3D and 2.5D integrated circuits.
Implementation Method 1
Due to the difference in coefficient of thermal expansion, the substrates of the 3DICs may misalign. Furthermore, large monolithic dies with small contact bumps may also misalign from the contact pads of a substrate the monolithic die is connected to due to a mismatch om the coefficient of thermal expansion between the monolithic die and the substrate.
Data Source
AI summary
A 3DIC includes a die and a substrate. The die includes multiple bumps to provide electrical connection the substrate. The substrate includes multiple elongated contact pads. The elongated contact pads making electrical contact with the bumps and shaped to maintain alignment with the bumps over a temperature range.