Wafer-Level Package Seed Layer Reduction
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Solution Overview
Problem
The high manufacturing cost in wafer-level chip scale package structures is attributed to the use of multiple photo resists and seed layers, which are formed and partially removed during the formation of post-passivation interconnect (PPI) lines and pads.
Innovation Solution
The process involves forming a passivation layer over a metal pad, with a seed layer electrically coupled to it, and using a single photo resist stripping process to form PPI lines and pads, eliminating the need for a second polyimide layer and under bump metallurgy (UBM) seed layer, thereby reducing the number of photo resist and seed layer formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple photo resists and seed layers are formed during PPI structure fabrication, then the electrical connectivity and structural integrity are maintained, but the manufacturing cost increases
Solution Approach 1:
The patent combines the functions of multiple photo resists into a single photo resist layer and merges the seed layer formation process with the PPI structure fabrication. This consolidation maintains the necessary electrical connectivity while eliminating redundant manufacturing steps, thereby reducing material costs and process complexity without compromising reliability
Solution Approach 2:
The single photo resist layer performs multiple functions that traditionally required separate layers: it serves as both the patterning mask for PPI lines and the underlying mask for UBM formation. The seed layer is designed to be multi-functional, serving both as an adhesion layer and as a plating substrate for both PPI and UBM structures, thereby reducing the total number of formation steps and associated costs
2Reliability
If multiple photo resists and seed layers are formed during PPI structure fabrication, then the structural integrity is maintained, but the process complexity increases
Solution Approach 1:
The patent merges the PPI formation and UBM formation processes into a single integrated workflow using one photo resist and one seed layer. This consolidation maintains structural integrity through proper process sequencing while significantly reducing the number of discrete steps, masks, and material deposition cycles required, thereby lowering process complexity
Solution Approach 2:
The single photo resist layer is formed and patterned in advance to define both the PPI structure and the UBM location. The seed layer is deposited beforehand to provide a continuous plating substrate. These preliminary actions enable subsequent plating operations to proceed efficiently without requiring additional mask formation or seed layer deposition steps, thus simplifying the overall 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 reduces manufacturing costs by eliminating the need for additional photo resist and seed layer formations, while maintaining the electrical connectivity and structural integrity of the PPI structure.
Implementation Method 1
A seed layer is formed over the passivation layer. The seed layer is electrically coupled to the metal pad
Implementation Method 2
using a single photo resist stripping process to form PPI lines and pads
Data Source
AI summary
A method includes forming a passivation layer over a metal pad, which is overlying a semiconductor substrate. A first opening is formed in the passivation layer, with a portion of the metal pad exposed through the first opening. A seed layer is formed over the passivation layer and to electrically coupled to the metal pad. The seed layer further includes a portion over the passivation layer. A first mask is formed over the seed layer, wherein the first mask has a second opening directly over at least a portion of the metal pad. A PPI is formed over the seed layer and in the second opening. A second mask is formed over the first mask, with a third opening formed in the second mask. A portion of a metal bump is formed in the third opening. After the step of forming the portion of the metal bump, the first and the second masks are removed.