PPI Bump Stop Structure for Solder Ball Placement Accuracy
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Solution Overview
Problem
The miniaturization of semiconductor packaging is limited by the lack of physical boundaries in traditional wafer level chip scale packaging (WLCSP) methods, leading to inaccurate solder ball placement and increased failure rates due to ball shift during the mounting process.
Innovation Solution
The introduction of a protrusion pattern in the post-passivation interconnect (PPI) structure, which acts as a wetting stop to constrain solder ball movement, ensuring accurate placement and improving reliability by creating a virtual boundary for solder ball placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional WLCSP method without UBM and protection layer is used to lower manufacturing cost, then manufacturing cost is reduced, but solder ball placement accuracy deteriorates due to lack of physical boundary
Solution Approach 1:
The PPI structure is segmented into functional zones: a bonding pad region for electrical connection and a protrusion pattern forming a bump stop structure that creates a physical boundary. This segmentation allows the solder ball to be constrained within a specific area while maintaining cost-effectiveness by eliminating the need for separate UBM and protection layers.
Solution Approach 2:
The protrusion pattern is strategically positioned around the bonding pad region to create localized physical boundaries. This local quality enhancement provides the necessary constraints for solder ball placement accuracy only where needed, without adding unnecessary structure across the entire device surface.
2Device complexity
If no protrusion pattern is provided in PPI structure, then device complexity is reduced, but solder ball reliability deteriorates due to ball shift during mounting
Solution Approach 1:
The protrusion pattern is pre-formed on the PPI structure before solder ball placement. This preliminary action creates the physical boundary in advance, guiding the solder ball to its correct position and preventing ball shift during the mounting process, thereby ensuring reliability without complicating the overall device design.
Solution Approach 2:
The protrusion pattern acts as an intermediary element between the bonding pad region and the solder ball. It provides the necessary physical boundary and wetting stop function, mediating the interaction between the solder ball and the PPI structure to prevent unwanted movement while maintaining simplicity in the overall device architecture.
3Device complexity
If solder ball is placed directly on bonding pad without physical boundary, then manufacturing process is simplified, but ball shift occurs leading to increased failure rate
Solution Approach 1:
The bump stop structure is merged with the PPI structure, integrating the boundary-forming function directly into the existing interconnect structure. This merging maintains manufacturing process simplicity by eliminating separate components while providing the necessary physical boundary to prevent ball shift and ensure reliability.
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 solution enhances ball drop accuracy and reliability by preventing undesired wetting and shifting of solder balls, thereby improving the overall performance and reliability of semiconductor devices without incurring additional manufacturing costs.
Implementation Method 1
The protrusion pattern of PPI structure acts as a wetting stop to constrain the ball movement
Data Source
AI summary
A method for manufacturing semiconductor devices is provided. A protection layer is conformally deposited over a passivation layer such that the protection layer has a protrusion pattern that protrudes from a top surface of the protection layer. Further, a post-passivation interconnect structure (PPI) is conformally formed on the protection layer such that the PPI structure includes a landing pad region, a protrusion pattern conformal to the protrusion pattern of the protection layer, and a connection line electrically connected to the conductive pad. A solder bump is then placed on the landing pad region in contact with the protrusion pattern of PPI structure. A semiconductor device with bump stop structure is also provided. The protrusion pattern of the PPI structure serves as a bump stop that constrains a ball shift in the placement of the solder bump over the landing pad.