Dual Surface Finish for IC Package Substrates
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Solution Overview
Problem
Current surface finish technologies for integrated circuit package substrates limit scalability due to lateral expansion, causing pad-to-pad bridging on the die side, while the same finish is applied to both die and land sides, neglecting unique connection requirements for each.
Innovation Solution
Implementing a dual surface finish configuration, where a first surface finish is applied to the land side and a second surface finish, often gold-based, is applied to the die side, allowing for closer spacing of die interconnect structures and increased input/output density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single surface finish is applied to both die side and land side of package substrate, then circuit board connection requirements are met, but lateral expansion causes pad-to-pad bridging on die side limiting scalability
Solution Approach 1:
The patent applies different surface finish compositions to different sides of the package substrate. The land side receives a first surface finish optimized for circuit board connection, while the die side receives a second surface finish with minimized lateral expansion properties. This local differentiation allows each side to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent segments the surface finish application into two distinct processes: applying a first surface finish to the land side and a second surface finish to the die side. This segmentation enables independent optimization of surface finish properties for each side, resolving the contradiction between connection reliability and pad spacing precision.
2Reliability
If surface finish thickness is increased to ensure coverage, then connection reliability improves, but lateral expansion increases causing pad bridging
Solution Approach 1:
The patent employs surface finish compositions with different lateral expansion characteristics for different sides. The die side surface finish is specifically selected or formulated to have minimized lateral expansion, ensuring that adequate thickness can be applied without causing pad-to-pad bridging, thus resolving the contradiction between coverage reliability and lateral area expansion.
3Productivity
If pad spacing is reduced to increase I/O density, then input/output density increases, but risk of pad-to-pad bridging increases
Solution Approach 1:
By applying a surface finish with minimized lateral expansion properties specifically to the die side, the patent enables reduced pad spacing without increasing the risk of bridging. The localized optimization of surface finish properties allows higher I/O density while maintaining reliable pad isolation.
4Ease of manufacture
If same surface finish composition is used on both sides, then manufacturing process is simplified, but unique connection requirements of die side cannot be optimized
Solution Approach 1:
The patent differentiates surface finish composition by side: the land side receives a finish optimized for circuit board connection, while the die side receives a finish with minimized lateral expansion for high-density pad arrangements. This local quality differentiation resolves the contradiction between manufacturing simplicity and connection requirement adaptability.
Solution Approach 2:
The patent segments the surface finish application into two distinct processes with different compositions, allowing each side to be optimized for its specific connection requirements while maintaining a systematic manufacturing approach.
Data Source
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AI summary
Embodiments of the present disclosure are directed towards techniques and configurations for dual surface finish package substrate assemblies. In one embodiment a method includes depositing a first lamination layer on a first side of a package substrate and a first surface finish on one or more electrical contacts disposed on a second side of the package substrate; removing the first lamination layer from the first side of the package substrate; depositing a second lamination layer on the second side of the package substrate and a second surface finish on the one or more electrical contacts disposed on the first side of the package substrate; and removing the second lamination layer from the second side of the package substrate. Other embodiments may be described and/or claimed.