Wafer Level Chip Size Package Redistribution Layers
Solution Overview
Problem
The complexity and increased manufacturing costs of wafer level chip size packages (WLCSPs) arise from the need for multiple redistribution layers and passivation layers to form complicated circuits, leading to electrical shorts and inefficiencies in circuit formation.
Innovation Solution
The formation of lands at the ends of redistribution layers, covered by a second dielectric layer, with a first under bump metallurgy (UBM) layer and a second UBM layer that serves as a ground or power plane, allowing for electrical connection between physically separated redistribution layers without shorts, and providing a shield against electromagnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two or more RDL layers are used to form complicated circuits, then circuit complexity is improved, but packaging complexity and manufacturing costs increase
Solution Approach 1:
The patent merges the functions of multiple RDL layers by allowing RDL traces to cross over each other in the same plane using bridge structures. This eliminates the need for multiple stacked RDL layers, reducing packaging complexity while maintaining the ability to form complicated circuits.
Solution Approach 2:
The patent transitions from a vertical stacking approach (multiple RDL layers in different planes) to a horizontal approach (multiple RDL traces crossing in the same plane). This dimensional change allows complex circuit routing without increasing packaging complexity.
2Adaptability or versatility
If two or more RDL layers are used to form complicated circuits, then circuit complexity is improved, but manufacturing costs increase
Solution Approach 1:
The patent combines multiple RDL routing functions into a single RDL layer, reducing the number of manufacturing steps required for depositing and patterning multiple layers. This simplification directly reduces manufacturing costs while maintaining circuit complexity capabilities.
3Adaptability or versatility
If multiple RDL layers are used, then circuit functionality is improved, but electrical shorts between layers increase
Solution Approach 1:
The patent eliminates the need for multiple RDL layers by enabling trace crossing in the same plane, thereby removing the interfaces between layers where electrical shorts could occur. This improves reliability while maintaining circuit functionality.
4Area of stationary object
If the second UBM layer is widely formed on the second dielectric layer, then ground plane area is improved, but material usage increases
Solution Approach 1:
The second UBM layer serves multiple functions simultaneously: it provides a large-area ground plane for signal reference, acts as an electromagnetic shield, and serves as a heat dissipation path. This multi-functionality justifies the material usage by delivering multiple benefits from a single structural element.
Solution Approach 2:
The patent converts what could be considered excess material usage into a beneficial electromagnetic shield and heat dissipation structure. The widely-formed second UBM layer, which might appear as material waste, actually provides protective and functional benefits that enhance overall device performance.
Data Source
AI summary
A wafer level chip size package (WLCSP) and a method of manufacturing the same are disclosed. Lands are formed at the ends of redistribution layers. The redistribution layers excluding the lands and a first dielectric layer are covered with a second dielectric layer. After forming a first under bump metallurgy (UBM) layer on the land, a solder ball is reflowed to the first UBM layer. A second UBM layer is widely formed on the entire second dielectric layer that is the outer circumference of the first UBM layer and is connected to the redistribution layer through a via-hole. Therefore, the second UBM layer having a large area can be used as a ground plane or a power plane. In addition, the second UBM layer can electrically connect the redistribution layers physically separated from each other. Therefore, the plurality of redistribution layers can cross each other without being electrically shorted with each other.