Extended Under Ball Metallization for Dielectric Stress Mitigation
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Solution Overview
Problem
Wafer-level packaging techniques face limitations in larger integrated circuit chips due to coefficient of thermal expansion (CTE) mismatch between chips and printed circuit boards, leading to stress and dielectric cracking during thermal cycling, drop tests, and cyclic bending.
Innovation Solution
Extended under ball metallization (UBM) is implemented, where the UBM area exceeds the contact area with the solder ball, providing structural support and reducing stress on dielectric layers, fabricated using conductive materials like copper, chromium, or silver, and configured in BOP or RDL structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wafer-level packaging is used for larger integrated circuit chips, then packaging density and integration are improved, but stress and dielectric cracking occur due to CTE mismatch during thermal cycling and mechanical testing
Solution Approach 1:
The under ball metallization is segmented into multiple layers (e.g., first UBM layer, second UBM layer) with different functions. The first layer provides electrical connection while the second layer extends beyond the solder ball contact area to provide stress distribution and structural support, resolving the contradiction between packaging density and stress resistance
Solution Approach 2:
The UBM structure transitions from a two-dimensional contact pad to a three-dimensional extended structure that protrudes beyond the solder ball contact area. This dimensional extension provides additional structural support and stress distribution capability while maintaining electrical connection functionality
2Ease of manufacture
If standard UBM size is used, then manufacturing simplicity is maintained, but dielectric cracking occurs due to insufficient stress distribution
Solution Approach 1:
The UBM structure implements local quality by having different regions serve different functions: the region under the solder ball provides electrical connection while the extended region beyond the contact area provides stress distribution. This localized functional differentiation prevents dielectric cracking without complicating the overall manufacturing process
Solution Approach 2:
The extended UBM structure is formed in advance during wafer fabrication before packaging. This preliminary action ensures that the stress-distributing structure is already in place to prevent dielectric cracking during subsequent thermal cycling and mechanical testing, eliminating the need for additional corrective measures
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 extended UBM reduces stress on dielectric layers by up to 42%, minimizing dielectric cracking during testing, and is effective in various applications including SOC, DRAM, and CPU devices.
Implementation Method 1
the under ball metallization extends beyond the contact area so that the area of the under ball metallization is greater than the contact area... configured to mitigate dielectric layer cracking due to stress
Implementation Method 2
The UBM typically provides a strong, stable, low resistance electrical connection between a contact pad... and a solder ball
Data Source
AI summary
Semiconductor devices are described that have an extended under ball metallization configured to mitigate dielectric layer cracking due to stress, particularly stress caused by CTE mismatch during thermal cycling tests, dynamic deformation during drop tests, or cyclic bending tests, and so on. In an implementation, the semiconductor package devices include an integrated circuit chip having a solder ball and under ball metallization, formed on the integrated circuit chip, which is configured to receive the solder ball so that the solder ball and the under ball metallization have a contact area there between, wherein the area of the under ball metallization is area greater than the contact area.