RDL-BDL Coupled Inductor Layout for Higher Q in Die Interconnects
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Solution Overview
Problem
Existing integrated circuit (IC) package designs face challenges in improving the Q factor of inductors due to limited metallization layers and their thickness, leading to higher resistance and energy loss.
Innovation Solution
The integration of coupled coils in a redistribution layer (RDL) and an adjacent bump-level distribution layer (BDL) within the die interconnect structure, where the BDL is thicker than the RDL, forming an inductor with reduced resistance and enhanced conductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If inductors are formed in standard metallization layers within the die, then the inductor structure is simple to manufacture, but the metallization layer thickness is limited resulting in higher resistance and lower Q factor
Solution Approach 1:
The patent extends the inductor structure from the standard planar metallization layers into the vertical dimension by incorporating the bump-level distribution layer (BDL) which is located beneath the die. This vertical extension allows the inductor to utilize thicker conductive paths across multiple layers (RDL and BDL), thereby reducing resistance without significantly increasing lateral footprint or manufacturing complexity.
Solution Approach 2:
The inductor structure is nested within the existing interconnect architecture by utilizing both the redistribution layer (RDL) and the bump-level distribution layer (BDL) as concentric conductive elements. The RDL forms an outer coil while the BDL forms an inner coil, creating a nested configuration that reduces resistance through multiple conductive paths while maintaining compatibility with standard packaging processes.
2Reliability
If the number of metallization layers is increased to reduce resistance, then the Q factor improves, but the manufacturing process becomes more complex
Solution Approach 1:
The bump-level distribution layer (BDL) serves dual functions: it acts as an additional conductive layer for forming the inner coil of the inductor, and simultaneously maintains its standard function as an interconnect layer for signal and power distribution. This multi-functionality allows the inductor to benefit from extra conductive paths without requiring dedicated additional manufacturing steps beyond standard packaging processes.
Solution Approach 2:
The existing BDL structure, which is already present in the packaging architecture for its intended interconnect function, is utilized to form the inner coil of the inductor. This self-service approach allows the inductor to leverage existing thick conductive paths without requiring separate dedicated layers or complex additional fabrication processes, thereby improving Q factor while maintaining ease of manufacture.
3Loss of energy
If thicker metallization layers are used to reduce resistance, then the Q factor improves, but the available space for routing other interconnects is reduced
Solution Approach 1:
The patent resolves the space conflict by utilizing the vertical dimension and the previously unused BDL location beneath the die. The thick conductive paths are formed in the vertical stack (RDL and BDL) rather than expanding laterally, allowing the inductor to achieve low resistance through vertical integration without consuming additional lateral routing space for other interconnects.
Solution Approach 2:
The inductor is segmented into two separate coil structures formed in different layers: an outer coil in the RDL and an inner coil in the BDL. This segmentation allows each coil to be optimized independently and enables the inductor to achieve low resistance through the combined effect of multiple conductive paths without requiring any single layer to occupy excessive lateral space.
Data Source
AI summary
Aspects disclosed herein include a die interconnect structure with embedded inductor(s) including coupled coils formed in redistribution layer (RDL) and adjacent bump-level distribution layer (BDL) for improved Q factor. The die interconnect structure includes a metal pad and a first coil formed in the RDL. The die interconnect structure also includes the BDL which includes a secondary metal pad and a second coil. The die interconnect structure also includes a seed layer between the first coil and the second coil. The die interconnect structure includes an inductor comprising the first coil, the second coil, and a via coupling the first and second coils. In this manner, the additional second coil formed in the BDL has higher conductance, less resistance than a coil formed in metallization layers within the die and, thus, advantageously improving the Q factor of the inductor.