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Redistribution Layer Technologies

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • The addition of a redistribution layer facilitates the reorganization of the electrical connection to suit the desired configuration. 

  • The redistribution layer enables efficient signal routing, power distribution, and high-level integration of the IC die.

  • With the fan-in approach, redistribution layer technology supports high-density integration and high yield. With the fan-out approach, thermal and electrical efficiency can be achieved. 

Redistribution layer

With the increasing need for more compact and efficient devices, the semiconductor industry has to constantly keep up with technological advancements to maintain this demand. The advancement in packaging technologies has been one way to meet miniaturization demands while also meeting device functionality, system performance, and power consumption requirements. Utilization of the redistribution layer has enabled efficient signal routing, power distribution, and high-level integration between the integrated circuit die and the external package. 

There are many IC packaging technologies where the need for a redistribution layer can be significant. In this article, we will talk about the various redistribution layer technologies and explore their applications. 

Redistribution Layer

Consider packing a microcontroller unit into a larger electronic system. The microcontroller unit uses a specific input/output (I/O) pad arrangement, which is used as an interface between the integrated circuit (IC) and the external system or component. These I/O pads facilitate the transmission of electrical signals, safeguard the IC against potential damage, and play an important role in the assembly and packaging of the IC. However, not all I/O pad arrangements match the desired interconnection scheme required by the system. This is where you need a redistribution layer.

A redistribution layer is an extra set of the metal layer, the addition of which facilitates the rearrangement of the electrical connection to suit the desired configuration. The redistribution layer bridges the gap between the I/O pads and the corresponding pads on the package substrate to allow for efficient and optimized routing of signals. Here are a few reasons why the redistribution layer may be utilized.

Advantages of the Redistribution Layer

Miniaturization

Allows higher pin count and finer pitch connections to enable miniaturization for IC packaging

Signal routing optimization

Ensures efficient signal routing, reduces signal delay, and improves signal integrity

Heterogeneous integration

Integrates different types of chips and components within a single package for system-level integration

Increased functionality

Supports integration of passive components such as resistors, capacitors, etc. to enhance the overall functionality

Improved electrical performance

Reduces parasite effect, impedance mismatch, and signal loss to enhance the electrical performance

Thermal management

Improves thermal dissipation within the package, optimizes heat transfer, and reduces overheating risk

Advanced packaging technologies

Support 3D integration, system-in-package (SiP), and wafer-level packaging (WLP) — the advanced packaging approaches

Types of Redistribution Layer Technologies

There are two types of redistribution layer technologies —  fan-in and fan-out. 

Fan-In Redistribution Layer Technology

Fan-in redistribution layer (FI-RDL) technology involves the redistribution of I/O signals from a larger die to a smaller package substrate. The technology is used in multi-chip modules and system-on-chip designs. The advantages of the FI-RDL approach are:

  1. Integration of multiple dies on a single, smaller substrate facilitates achieving compact package size while maintaining high functionality. 
  2. Each die is tested and validated before integration – this reduces the risk of packing-level defects and improves manufacturing yield.  

Fan-Out Redistribution Layer Technology

A fan-out redistribution layer (FO-RDL) involves the redistribution of I/O signals from a smaller die to a larger package substrate. This approach places the die face-down on the package substrate and RDL facilitates the redistribution of signal and power. The advantages of this approach include:

  1. By optimizing the die-to-package ratio to reduce the form factor of the package, a higher level of miniaturization can be achieved. 
  2. Shorter interconnect lengths reduce parasitic effects such as capacitance, inductance, and resistance, leading to faster signal propagation, reduced signal delays, and low power consumption, i.e., improved electrical performance. 
  3. The direct connection between the package substrate and die enables efficient heat transfer, reduces thermal resistance, and enhances the overall thermal management of the integrated circuit. 

Redistribution Layer Technologies for Advanced Packaging 

In modern semiconductor packaging, redistribution layer technologies have played a critical role in enabling efficient signal routing and power distribution within the IC. Through a suitable selection of RDL technologies, manufacturers are achieving higher performance and increased functional integration in semiconductor packaging.

The best package designer tool will allow you to efficiently accommodate the routing requirement of the redistribution layer and optimize signal integrity and thermal management. With 3D visualization, it is possible to visualize and validate the IC design, including the redistribution layer, to check for potential design issues, layer alignment, and integration of I/O pads.

The package-specific features offered by Cadence’s Allegro X, such as seamless integration and design capabilities, can improve the productivity and efficiency of your packaging workflow. To learn more about our industry’s leading IC package solution, contact us.