Wafer Level Chip Scale Package RDL and UBM Process
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Solution Overview
Problem
Current Wafer Level Chip Scale Package (WLCSP) manufacturing techniques, such as sputtering and plating, face issues with weak interfacial bonding strength, corrosion, and complex processes, particularly due to the formation of copper intermetallic compounds and the need for repetitive seed layer sputtering and leakage descum processes.
Innovation Solution
The solution involves forming a Re-Distribution Layer (RDL) through sputtering and using it as a seed layer for electroplating the Under Bumped Metal (UBM), simplifying the process by combining sputtering and electroplating steps, allowing for uniform copper layer thickness and pure nickel UBM formation, which enhances bonding strength and reduces manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sputtering technique is used to form RDL and UBM, then the manufacturing process is simple, but interfacial bonding strength is weak and corrosion resistance is poor
Solution Approach 1:
The patent combines the RDL formation and UBM formation into a single sputtering process, where the RDL copper layer serves as both the redistribution layer and the seed layer for the UBM. This merging eliminates the need for separate seed layer deposition and reduces the number of process steps, while still achieving adequate bonding strength for the application.
Solution Approach 2:
The RDL copper layer is given multiple functions: it serves as the electrical redistribution layer, provides the seed layer for electroplating the UBM, and acts as the bonding interface for solder balls. This multi-functionality simplifies the overall structure and reduces the number of distinct layers required.
2Ease of manufacture
If sputtering technique is used to form RDL and UBM, then the manufacturing process is simple, but corrosion resistance is poor
Solution Approach 1:
The patent creates a composite structure where the UBM consists of multiple layers (Ni, Cu, or Ni/Cu alloy) deposited over the RDL copper layer. This composite material approach provides both the electrical conductivity needed for the UBM and the corrosion resistance required, as nickel and copper alloys offer superior corrosion resistance compared to pure copper.
3Reliability
If plating technique is used to form RDL and UBM, then reliability is improved, but manufacturing process becomes complicated
Solution Approach 1:
The patent performs the seed layer formation as a preliminary action during the RDL sputtering process itself. By depositing the copper layer with sufficient thickness and proper surface characteristics during the initial RDL formation, the substrate is prepared in advance for the subsequent electroplating of the UBM, eliminating the need for separate seed layer deposition steps.
Solution Approach 2:
The patent merges the RDL formation and UBM formation processes by using the same sputtering step to create both layers. The RDL copper layer is deposited first, then the same chamber or process is used to deposit the UBM layers directly over it, combining what would traditionally be separate fabrication steps into a single integrated process.
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 approach simplifies the manufacturing process, improves bonding strength, and enhances reliability by ensuring uniform UBM thickness and preventing copper corrosion, while maintaining superior electric conductivity and corrosion resistance.
Implementation Method 1
An RDL is formed on a semiconductor die through a sputtering process
Implementation Method 2
a UBM is formed on the RDL through an electroplating process by using the RDL as a seed layer
Data Source
AI summary
Disclosed are a wafer level chip scale package and a method for manufacturing the same. An RDL is formed on a semiconductor die through a sputtering process, and a UBM is formed on the RDL through an electroplating process by using the RDL as a seed layer. Thus, the RDL sputtering, UBM electroplating, RDL etching and leakage descum processes are carried out only one time, thereby simplifying the structure and manufacturing processes of the package. Since a copper layer of the RDL is formed with a relatively large thickness through the sputtering process, current density is uniformly distributed during the electroplating process, so it is possible to uniformly form the thickness of the UBM by using pure nickel.