Backside RDL Protruding Bond Pads for PoP Crack Resistance
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Solution Overview
Problem
Integrated Fan-Out Package on Package (InFO PoP) devices are prone to electrical failures and poor reliability due to issues like crack propagation and ball fatigue if not appropriately formed, which can lead to poor performance and reliability in 3D IC packaging.
Innovation Solution
The use of protruding redistribution layer bond pads that cap metal vias and extend over the molding compound, forming a backside redistribution layer (RDL) to prevent cracks and enhance electrical coupling between packages, thereby improving the reliability and structural integrity of the PoP device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If InFO PoP devices are formed without appropriate backside RDL structure, then manufacturing process is simpler, but electrical reliability deteriorates due to crack propagation and ball fatigue
Solution Approach 1:
The patent segments the bonding interface into multiple functional zones: protruding bond pads that extend beyond via openings, via regions, and interconnect regions. This segmentation allows each zone to handle specific mechanical and electrical functions, distributing stress and preventing crack propagation across the entire structure.
Solution Approach 2:
The patent extends the bond pads protrudingly in the vertical dimension beyond the plane of the backside RDL. This dimensional extension creates an overlapping bonding area between packages, transforming a planar bonding interface into a three-dimensional structure that enhances mechanical interlocking and electrical connectivity while dissipating stress.
2Reliability
If bond pads are formed to protrude beyond via openings, then crack propagation is prevented, but manufacturing precision requirements increase
Solution Approach 1:
The protruding bond pads are formed in advance during the backside RDL fabrication process, before final package assembly. This preliminary formation establishes precise geometric references and alignment features that guide subsequent bonding operations, reducing the actual alignment precision required during assembly while maintaining crack resistance.
3Reliability
If backside RDL is formed with protruding bond pads, then electrical coupling is enhanced, but device complexity increases
Solution Approach 1:
The protruding bond pads serve multiple functions simultaneously: they provide electrical connectivity between packages, act as mechanical interlocking features, distribute mechanical stress, and define alignment references. This multi-functionality enhances electrical coupling while avoiding the need for separate dedicated structures for each function.
Data Source
AI summary
An embodiment package on package (PoP) device includes a molding compound having a metal via embedded therein, a passivation layer disposed over the molding compound, the passivation layer including a passivation layer recess vertically aligned with the metal via, and a redistribution layer bond pad capping the metal via, a portion of the redistribution layer bond pad within the passivation layer recess projecting above a top surface of the molding compound.