Package Substrate Trenches for Thermal Stress Isolation
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Solution Overview
Problem
The package substrate's higher coefficient of thermal expansion compared to the semiconductor substrate leads to stress-induced cracks in conductive bumps and the back-end-of-line (BEOL) of the semiconductor chip during packaging.
Innovation Solution
Incorporating trenches on the package substrate adjacent to upper pads to block stress generated by thermal expansion, thereby reducing the stress applied to conductive bumps and the BEOL, with trench depths ranging from 5% to 100% of the substrate's depth and widths greater than or equal to 10 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the package substrate has a higher coefficient of thermal expansion than the semiconductor substrate, then the package substrate can be manufactured with standard materials and processes, but stress-induced cracks occur in conductive bumps and BEOL during packaging
Solution Approach 1:
The package substrate is segmented by introducing trenches that divide the substrate into separate regions. These trenches act as stress isolation barriers that prevent stress from propagating across the entire substrate, thereby protecting the conductive bumps and BEOL from stress-induced cracks while maintaining the use of standard substrate materials with higher CTE
Solution Approach 2:
The trenches serve as intermediary structures between different regions of the package substrate. They mediate the stress distribution by providing a physical barrier that interrupts stress pathways, allowing the substrate to maintain its inherent high CTE properties while preventing stress transmission to sensitive components
2Stability of the object's composition
If the package substrate is expanded more than the semiconductor chip during packaging, then the package substrate accommodates thermal expansion, but stresses are applied to conductive bumps and BEOL causing cracks
Solution Approach 1:
By segmenting the substrate through trenches, the patent allows each segment to expand independently during thermal cycles. This segmentation prevents the accumulation of stress across the entire substrate, accommodating thermal expansion while protecting the strength of conductive bumps and BEOL structures
3Reliability
If trenches are provided in the insulation substrate to block stress, then stress spreading to upper pads is prevented, but the device structure becomes more complex
Solution Approach 1:
The trenches create a porous or discontinuous structure within the insulation substrate. This porous approach provides effective stress blocking capability by interrupting stress pathways, while the simple trench geometry minimizes the added structural complexity compared to more elaborate stress management designs
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
Prevents or reduces the generation of cracks in conductive bumps and the BEOL by mitigating thermal expansion-induced stress, enhancing the reliability of semiconductor packages.
Implementation Method 1
stress, which is generated by an expansion of the insulation substrate
Data Source
AI summary
Provided a package substrate including an insulation substrate, a conductive layer provided in the insulation substrate, upper pads provided on an upper surface of the insulation substrate and electrically connected to the conductive layer, lower pads provided on a lower surface of the insulation substrate and electrically connected to the conductive layer, and at least one trench provided at a portion of the insulation substrate adjacent to at least one of the upper pads and configured to block stress, which is generated by an expansion of the insulation substrate, from spreading to the at least one of the upper pads.