UBM/RDL Routing Structure for Reliable PoP Interconnects
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Solution Overview
Problem
Existing semiconductor packaging technologies face challenges in achieving reliable and robust integration density, particularly in Package-on-Package (PoP) devices, due to issues such as electromigration, susceptibility to drop damage, and thermal cycling integrity in under bump metallurgy (UBM) and redistribution layer (RDL) routing structures.
Innovation Solution
The development of an improved UBM/RDL routing structure that includes a first conductive portion and a second conductive portion separated by insulating material, with a conductive UBM trace coupling them, and a UBM pad electrically connected to the second conductive portion, allowing for reliable electrical routing through underlying RDL portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional UBM/RDL routing structures are used in PoP devices, then manufacturing simplicity is maintained, but reliability deteriorates due to electromigration and susceptibility to drop damage
Solution Approach 1:
The UBM layer is segmented into multiple portions (first UBM portion, second UBM portion) that are electrically isolated from each other by insulating material. This segmentation allows independent routing paths through the RDL layer, preventing electromigration failures and improving reliability while maintaining manageable structural complexity through systematic division of the metallization layer.
Solution Approach 2:
The RDL metallization layer acts as an intermediary that electrically connects separated UBM portions. By introducing this intermediate conductive layer with insulating material between UBM portions, the structure achieves reliable electrical connectivity while protecting against direct failure modes, thus improving reliability without excessive complexity.
2Reliability
If direct UBM routing is used, then device complexity is minimized, but susceptibility to drop damage increases
Solution Approach 1:
The direct UBM routing is segmented into separate portions isolated by insulating material, creating discrete connection points. This segmentation distributes mechanical stress from drop impacts across multiple isolated points rather than a continuous structure, improving structural integrity while maintaining reasonable complexity through systematic isolation.
Solution Approach 2:
Insulating material is placed between UBM portions before final assembly, creating protective barriers that cushion against mechanical damage. This prior cushioning approach protects the metallization structure from drop damage and thermal cycling stresses, improving structural integrity without significantly increasing device complexity.
3Reliability
If conventional RDL routing is used, then manufacturing process simplicity is maintained, but thermal cycling integrity deteriorates
Solution Approach 1:
The metallization structure is segmented into UBM portions and RDL portions with insulating material between them, creating distinct thermal zones. This segmentation allows differential thermal expansion management, improving thermal cycling integrity while the segmentation follows standard fabrication sequences that maintain ease of manufacture.
Solution Approach 2:
The insulating material serves as a thermal intermediary between UBM and RDL portions, managing heat flow and thermal stress distribution. This intermediary layer protects the metallization structure from thermal cycling damage while the lamination process integrating this layer remains consistent with conventional manufacturing methods.
Data Source
AI summary
An under bump metallurgy (UBM) and redistribution layer (RDL) routing structure includes an RDL formed over a die. The RDL comprises a first conductive portion and a second conductive portion. The first conductive portion and the second conductive portion are at a same level in the RDL. The first conductive portion of the RDL is separated from the second conductive portion of the RDL by insulating material of the RDL. A UBM layer is formed over the RDL. The UBM layer includes a conductive UBM trace and a conductive UBM pad. The UBM trace electrically couples the first conductive portion of the RDL to the second conductive portion of the RDL. The UBM pad is electrically coupled to the second conductive portion of the RDL. A conductive connector is formed over and electrically coupled to the UBM pad.