The semiconductor industry and the business of packaging and assembly is undergoing a major change. Heterogeneous integration is an economic solution that addresses the end of silicon scaling as historically documented by Gordon Moore.
One idea is to design in the most advanced semiconductor node the functions that are absolutely required to be in that node, and use this chip in combination with others in a package that provides the desired function in a more cost effective manner. Die function portions that can be fabricated in older nodes at lower cost can be combined in a single package. IP reuse reduces cost. Heterogeneous integration also allows functions that could not be fabricated on the same die to be placed in a package together to achieve the required performance.
There are many package solutions that can achieve the goal of heterogeneous integration. A roadmap is useful as a guide to trends that ultimately determine the most appropriate package for a specific application. The roadmap helps to determine the trends in density (i.e., IO/mm, which refers to the number of wires/IO that can escape along the die perimeter and IO/mm2), bump pitch, minimum trace widths, and spacing (lines/ spaces), minim via and lad pad dimensions, etc
The roadmap also provides a better understanding of available package options. For the closest proximity of the die, the silicon interposer allows the chips to be placed in close proximity and communication takes place using the traces formed with copper and polymer on the passive interposer. An alternative that can provide similar desired density has been introduced by Intel in the form of its embedded multi-die interconnection bridge (EMIB), where a high density silicon is embedded in the laminate substrate to achieve the required density for die-to-die communication where required. Another alternative is the use of fan-out wafer level packaging on a substrate.
The roadmap can also be useful in indicating when an emerging technology such as a glass interposer might be an option or if an organic interposer meets the density requirements.
Roadmaps also provide indications of areas that require increased industry attention and problems that need to be solved. Performance metrics, including state of the art metrics and manufacturing metrics, can also be provided. These metrics may be helpful to industry participants in developing new materials and processes.
Roadmaps can also help guide the use of terminology that can provide common nomenclature that the supply chain can use to better communicate. For example, the current nomenclature (2.1D, 2.3D, 2.45D and 2.5D architectures) is not always rooted in the same assumptions and a roadmap will help provide clarity on physics-based nomenclatures.
For example, the latest version of the heterogeneous roadmap proposed that 2D means side-by-side. An organic substrate would be a 2DO, while a passive silicon interposer would be a 2DS. 3D refers to active silicon where the interconnection is done without use of the package (a direct path is used). Adoption of terms that provide clarity improve the understanding of the available options and trends.
— E. Jan Vardaman is the founder and president of TechSearch International Inc., a consulting company in the field of advanced semiconductor packaging technology.