Redistribution Layer Openings for Thermal Crack Prevention
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Solution Overview
Problem
Existing redistribution layer (RDL) structures in integrated circuits (ICs) are prone to cracking due to thermal expansion mismatch between polymer and semiconductor materials, leading to increased resistance and potential open circuits, particularly when polymer layers are land-locked or confined by structures with smaller coefficients of thermal expansion (CTE).
Innovation Solution
Incorporation of stress release openings, such as over-via, via edge, and inter-via openings, in the RDL structure to dissipate thermal stress and prevent cracking, utilizing low-CTE substrates like silicon to direct thermal expansion away from the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polymer layers are used in RDL structure, then flexibility and ease of manufacture are improved, but thermal expansion mismatch causes cracking and reliability deteriorates
Solution Approach 1:
The patent segments the continuous polymer layer by introducing openings (via holes, trenches, or gaps) that divide the polymer into discrete segments. This segmentation allows differential thermal expansion in different regions, preventing stress accumulation and cracking while maintaining the overall structural integrity and ease of manufacture of the RDL structure.
Solution Approach 2:
The patent introduces a porous or open structure within the polymer layer by creating via holes, trenches, or gaps. This porous configuration reduces the effective thermal mass of the polymer, allows stress relief pathways, and accommodates thermal expansion without causing cracks, thereby improving reliability while maintaining manufacturability through standard fabrication processes.
2Stability of the object's composition
If polymer layers are confined by structures with smaller CTE, then structural stability is improved, but thermal stress increases and causes cracking
Solution Approach 1:
By segmenting the confined polymer layer through openings, the patent allows each segment to expand independently within the confined space. This prevents the accumulation of thermal stress that would otherwise lead to cracking, while the surrounding low-CTE structures continue to provide structural stability and positioning.
Solution Approach 2:
The openings act as intermediary spaces that mediate between the confined polymer and the surrounding low-CTE structures. These openings provide stress relief pathways and allow the polymer to accommodate thermal expansion without transmitting excessive stress to the metal layers, thereby reducing cracking while maintaining structural stability.
3Productivity
If multiple RDL layers are stacked, then functional density is improved, but thermal stress accumulation increases and causes metal layer damage
Solution Approach 1:
The patent applies segmentation to each polymer layer in the stacked RDL structure, introducing openings that allow each layer to independently accommodate thermal expansion. This prevents stress accumulation across multiple layers, protecting the metal layers from damage while maintaining the high functional density achieved through stacking.
Solution Approach 2:
The patent introduces a vertical dimension of stress management by creating openings that extend through the stacked polymer layers. This vertical stress relief pathway allows thermal expansion to be managed in the thickness direction, preventing stress accumulation that would otherwise damage the metal layers in horizontally stacked RDL structures.
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
Reduces the likelihood of cracks in metal features by effectively managing thermal stress, maintaining conductivity and preventing open circuits, thus ensuring reliable signal transmission.
Implementation Method 1
Because polymer layers have vastly different coefficients of thermal expansion (CTE) from those of semiconductor materials and metals, thermal cycles during fabrication processes and heat generated during high current usage may cause expansion of the polymer layers relative to surrounding features
Data Source
AI summary
The present disclosure provides methods and structures to prevent cracks in redistribution layers. A redistribution structure according to the present disclosure includes a first polymer layer disposed over a silicon substrate, a first contact via disposed in the first polymer layer, a second polymer layer disposed over the first contact via, a first redistribution layer including a first conductive pad disposed on the second polymer layer and a second contact via extending through the second polymer layer to physical contact the first contact via, a third polymer layer disposed over the first redistribution layer, a second redistribution layer including a second conductive pad disposed on the third polymer layer and a plurality of third contact vias extending through the third polymer layer to physically contact the first conductive pad. The first conductive pad has at least one opening and the second conductive pad has at least one opening.