Patterned Seed Layer for RF Noise Isolation in IC Packages
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Solution Overview
Problem
5G RF mobile applications are susceptible to near field noise, such as electromagnetic near field noise, which negatively impacts design performance and can potentially destroy the application due to high frequency radiation noise between the die and package signal trace.
Innovation Solution
A repurposed seed layer electrostatic discharge (ESD) connection pattern is formed using a wafer level packaging process, which includes a patterned seed layer to act as an isolation layer or signal guard layer, reducing high frequency radiation noise between package balls and the processor die without increasing the Z-height of the RF mobile package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional packaging structure is used without additional noise isolation layers, then the device complexity and manufacturing cost are kept low, but electromagnetic near field noise between the die and package signal trace negatively impacts RF performance
Solution Approach 1:
The seed layer, traditionally serving only as a base for bump formation in wafer-level packaging, is repurposed to provide electromagnetic shielding and noise isolation functions. By patterning the seed layer to extend beyond bump regions and connect to ground planes, it simultaneously maintains its original bump-forming capability while adding RF noise isolation functionality, thus improving RF performance without adding separate dedicated shielding structures
Solution Approach 2:
The electrical properties of the seed layer are modified through selective patterning and grounding connections. By transforming the seed layer from an isolated conductive base to a grounded shielding network, its electrical parameters (grounding potential, field distribution) are changed to provide electromagnetic noise isolation, thereby improving RF signal integrity without requiring additional shielding materials or structures
2Reliability
If additional isolation layers or shielding structures are added to reduce electromagnetic noise, then RF performance improves, but the Z-height of the package increases
Solution Approach 1:
The seed layer performs multiple functions: it serves as the foundation for bump formation, provides electromagnetic shielding, and acts as a ground reference plane. By integrating these functions into a single existing layer rather than adding separate bump stops, shielding layers, and ground planes, the design achieves noise isolation without increasing package height
Solution Approach 2:
The noise isolation and grounding functions are merged into the seed layer itself rather than being implemented as separate structures. The patterned seed layer is directly connected to ground planes and forms an integrated shielding network that combines structural support, electrical grounding, and electromagnetic isolation in a single element, avoiding the need for additional Z-height
3Reliability
If the seed layer is repurposed to provide noise isolation by extending beyond bump regions, then electromagnetic shielding effectiveness improves, but the manufacturing process complexity increases
Solution Approach 1:
The seed layer is deposited and extended beyond the final bump regions during the initial packaging process, before bump formation occurs. This preliminary extension of the seed layer allows subsequent photolithography and etching steps to easily create the noise isolation pattern, as the extended seed layer already provides the necessary material coverage and grounding paths are pre-established
Solution Approach 2:
The seed layer is selectively patterned into different regions: areas under bumps that remain for bump formation, and extended areas that are ground-connected for shielding. This segmentation is achieved through photolithography masking and selective etching, dividing the seed layer into functional zones that provide both structural and electromagnetic isolation functions
Data Source
AI summary
An integrated circuit (IC) package is described. The IC package includes a die, having a pad layer structure on back-end-of-line layers on a substrate. The die also includes a metallization routing layer on the pad layer structure, and a first under bump metallization layer on the metallization routing layer. The IC package also includes a patterned seed layer on a surface of the die to contact the first under bump metallization layer. The IC package further includes a first package bump on the first under bump metallization layer.