Offset Metal Pad Layout for Low-k Delamination Relief
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Solution Overview
Problem
Current integrated circuit chips face mechanical failure due to thermal-mechanical stresses from chip-package interactions, particularly in weaker low-k/ultra-low k films, leading to delamination or cracking, which is exacerbated by the mismatch in thermal expansion coefficients between silicon, lead-free C4 bumps, and organic flip-chip substrates.
Innovation Solution
The solution involves offsetting the metal pad towards the center axis of the base material and modifying its shape to reduce the aspect ratio, thereby alleviating tensile and peeling stresses. This is achieved by shifting the metal pad's radial alignment by an offset distance and making the smaller dimension parallel to the line from the metal pad's center to the base material's center, which reduces stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the metal pad is aligned concentrically with the metal pedestal, then the manufacturing process is simpler, but thermal-mechanical stresses cause delamination or cracking in low-k films
Solution Approach 1:
The patent applies asymmetry by intentionally misaligning the metal pad relative to the metal pedestal, creating an asymmetric configuration where the pad center is offset from the pedestal center. This asymmetric positioning redistributes thermal-mechanical stresses away from the vulnerable low-k film regions, preventing delamination and cracking while maintaining electrical functionality.
Solution Approach 2:
The patent applies local quality by modifying the stress distribution in specific local regions through pad offset. The asymmetric positioning creates favorable stress conditions in the low-k film regions that would otherwise be prone to failure, while maintaining acceptable stress levels across the entire structure.
2Reliability
If the metal pad has a large aspect ratio, then it provides better electrical connectivity, but it increases stress concentration leading to mechanical failure
Solution Approach 1:
The patent applies parameter changes by adjusting the geometric parameters of the metal pad, specifically its position (offset distance) and dimensions (length and width). By optimizing these parameters, the pad maintains sufficient electrical connectivity while reducing stress concentration in the underlying low-k films, thereby improving mechanical strength and reliability.
3Ease of manufacture
If conventional pad alignment is used, then manufacturing is easier, but thermal expansion mismatch exacerbates mechanical failures
Solution Approach 1:
The patent applies preliminary anti-action by pre-positioning the metal pad with an offset from the pedestal center before thermal cycling occurs. This preliminary asymmetric positioning creates a stress distribution pattern that counteracts the thermal expansion forces generated during operation, preventing mechanical failures that would otherwise occur with conventional concentric alignment.
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
This approach effectively reduces mechanical failures by mitigating thermal-mechanical stresses in the back-end-of-line (BEOL) regions, enhancing the reliability of integrated circuits by minimizing delamination and cracking in low-k/ultra-low k films.
Implementation Method 1
mechanical failure due to thermal-mechanical stresses from chip-package interactions
Implementation Method 2
reduces stress concentrations
Data Source
AI summary
The present invention provides a structure. In an exemplary embodiment, the structure includes a base material, at least one metal pad, where a first surface of the metal pad is in contact with the base material, and a metal pedestal, where the metal pedestal is in contact with the metal pad, where a radial alignment of the metal pad is shifted by an offset distance, with respect to the metal pedestal, such that the metal pad is shifted towards a center axis of the base material, where a first dimension of the metal pad is smaller than a second dimension of the metal pad, where the second dimension is orthogonal to a line running from a center of the metal pad to the center axis of the base material, where the first dimension is parallel to the line.