Stepped UBM Pad Structure to Prevent Oxide Cracking
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Solution Overview
Problem
The existing semiconductor package manufacturing processes using semi-additive processes (SAP) face challenges with the reliability of under bump metallization (UBM) pads due to reactions with resin oxygen, leading to oxide film formation and potential cracking issues.
Innovation Solution
A semiconductor package design incorporating a seed layer with specific seed parts covering the UBM pad, including a stepped shape UBM pad configuration and a horizontal etching process to enhance reliability, and using materials like Ti, TiO2, CrN, or TiAlN for the seed layer to improve interconnect integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a seed layer is formed using semi-additive process (SAP) with photoresist coating and plating, then the UBM pad can be manufactured, but oxide film formation and cracking occur due to reactions with resin oxygen
Solution Approach 1:
The seed layer is divided into multiple discrete seed parts (first seed part, second seed part, third seed part) positioned at different locations. This segmentation allows selective coverage of critical areas while reducing overall resin oxygen exposure, preventing oxide film formation and cracking in the UBM pad region.
Solution Approach 2:
The patent introduces an encapsulation layer as an intermediary barrier between the resin oxygen and the seed layer/UBM pad. This encapsulation layer prevents direct contact between oxygen and the metallization structures, eliminating the chemical reactions that cause oxide film formation and subsequent cracking.
2Device complexity
If the UBM pad is formed with uniform thickness, then the manufacturing process is simpler, but cracking occurs due to stress distribution issues
Solution Approach 1:
The UBM pad is designed with asymmetric thickness distribution, being thicker at certain regions and thinner at others. This asymmetric structure optimizes stress distribution within the pad, preventing crack initiation and propagation while maintaining manufacturing feasibility through the segmented seed layer approach.
Solution Approach 2:
Different regions of the UBM pad are given different thickness characteristics tailored to their specific functional requirements. Critical areas experiencing higher stress are made thicker for enhanced durability, while less critical areas are made thinner to reduce material usage and manufacturing complexity.
3Area of stationary object
If the seed layer covers the entire UBM pad area, then complete coverage is achieved, but oxide film formation increases due to greater exposure to resin oxygen
Solution Approach 1:
Instead of forming a continuous seed layer covering the entire UBM pad, the patent uses segmented seed parts positioned only where needed. This reduces the total surface area exposed to resin oxygen, minimizing oxide film formation while still providing adequate electrical connection and structural support at critical locations.
Solution Approach 2:
The patent extracts or removes the seed layer material from areas where it is not critically needed, keeping only the essential seed parts. This selective retention reduces the overall interaction between the seed layer and resin oxygen, thereby reducing oxide film formation while maintaining necessary functionality.
Data Source
AI summary
A semiconductor package including a semiconductor chip; a lower redistribution layer on a lower surface of the semiconductor chip; a lower passivation layer on a lower surface of the lower redistribution layer; a UBM pad on the lower passivation layer and including an upper pad and a lower pad connected to the upper pad, the upper pad having a greater horizontal length at an upper surface thereof than a horizontal length at a lower surface thereof; a seed layer between the lower passivation layer and the UBM pad; and an external connecting terminal on a lower surface of the UBM pad, wherein the seed layer includes a first seed part covering a side surface of the upper pad, a second seed part covering a portion of the lower surface of the upper pad, and a third seed part covering a portion of a side surface of the lower pad.