Grounded Conformal Shielding for Low-Profile WLCSP Packages
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Solution Overview
Problem
Wafer-level chip-scale packages (WLCSP) cannot implement conformal shielding due to the lack of a connection point to grounded metal layers in the redistribution layer, limiting effective electromagnetic interference (EMI) shielding.
Innovation Solution
Incorporating a conductive layer that extends to the edge of the package, allowing the conformal shield to be grounded, which eliminates the need for direct soldering to the PCB and reduces the Z-height, thus providing excellent EMI shielding without the space and volume penalties of traditional PCB metal cages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional PCB metal cage shields are used to reduce EMI, then EMI shielding effectiveness is improved, but PCB area and volume are increased due to thickness and soldering space requirements
Solution Approach 1:
The invention extracts the shielding function from the traditional thick PCB metal cage and relocates it to a conformal shield applied directly to the package sidewalls. This removes the need for large-area PCB metal cages while maintaining EMI protection, as the shielding function is now embedded in the package structure itself rather than requiring separate PCB real estate.
Solution Approach 2:
The conformal shield is nested within the package structure, conforming to the sidewalls and integrating with the existing package architecture. This nested approach allows the shielding function to be incorporated without adding external volume or requiring additional PCB space, as the shield becomes part of the package's own structure.
2Object-affected harmful factors
If thick metal cage shields are installed to reduce EMI, then EMI shielding effectiveness is improved, but manufacturing complexity and costs are increased due to additional steps
Solution Approach 1:
The invention merges the EMI shielding function with the existing conformal coating process used in semiconductor packaging. By applying the conductive shield material during the same manufacturing steps as the protective conformal coating, the shielding function is integrated into the existing manufacturing flow without requiring separate assembly steps for installing metal cages or attaching PCB ground metals.
Solution Approach 2:
The conformal shield structure serves multiple functions: it provides EMI shielding, acts as a protective coating, and integrates with the package's mechanical structure. This multi-functionality eliminates the need for separate shielding components and their associated assembly processes, reducing manufacturing complexity while maintaining shielding effectiveness.
3Area of stationary object
If conformal shield is applied to WLCSP structure, then PCB area is reduced, but the shield cannot be grounded because redistribution layer metals are confined within die area
Solution Approach 1:
The invention transitions the grounding connection from the traditional planar dimension (PCB ground metals) to a vertical dimension by extending conductive elements along the package sidewalls. The conformal shield is connected to ground metals that extend vertically along the package edges, creating a three-dimensional grounding path that bypasses the limitation of confined redistribution layer metals on the die surface.
Solution Approach 2:
The grounding structure is segmented into multiple conductive elements distributed along the package sidewalls and edges. Rather than requiring a single large ground connection, the grounding function is divided into multiple smaller connection points along the vertical edges, allowing the conformal shield to be grounded effectively without requiring redistribution layer metals to extend beyond the die area.
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
The grounded conformal shield effectively reduces EMI in WLCSP architectures while minimizing the increase in package thickness and avoiding the area and volume constraints associated with traditional metal cages, thereby enhancing EMI shielding without additional manufacturing complexities or costs.
Implementation Method 1
Proper countermeasures are required to reduce EMI. Standard methods rely on the installation of thick metal shields that encapsulate the entire RF portions of the system
Implementation Method 2
recent technology developments have enabled the realization of sputtered metal sheets on the four sidewalls and the top surface of electronic semiconductor packages
Data Source
AI summary
Embodiments disclosed herein include electronic packages with conformal shields and methods of forming such packages. In an embodiment, the electronic package comprises a die having a first surface, a second surface opposite the first surface, and sidewall surfaces. A redistribution layer is over the first surface of the die, and the redistribution layer comprises a first conductive layer. In an embodiment, an under ball metallization (UBM) layer is over the redistribution layer, and a conductive shield is over the sidewall surfaces of the die and the second surface of the die. In an embodiment, the conductive shield is electrically coupled to the UBM layer.