Low-Dielectric, Low-Profile IC Substrate Material Development for 5G Applications

Abstract

As 5G communication systems continue to be developed and deployed worldwide, the speed and processing performance of the semiconductors that form the foundation of this technology are increasing at a break-neck pace. Concurrently, 5G-enabled mobile devices, like smartphones and tablets, are undergoing significant changes in their form-factors. Customers are demanding ever thinner, smaller, and lighter devices with increased functionality.Enabling this transition is a reduction in the size of the semiconductor packages used for these devices. While package sizes continue to decrease, the processing speed and I/O count of the chips they encase continue to increase. These countervailing trends are driving the development of new semiconductor packaging materials and designs capable of delivering improved electrical properties, thinner insulation layers, and higher layer counts.In terms of materials, Polytetrafluoroethylene (PTFE) is an example of a semiconductor packaging polymer with excellent dielectric performance. This material exhibits low dielectric properties and excellent transmission performance, even for GHz signals. However, many leading-edge 5G packages employ multi-layer substrate designs which challenging to fabricate with PTFE-based materials.Other types of semiconductor package substrates laminates are constructed by combining, non-PTFE, low-dielectric polymers with glass cloth. One challenge with this composite approach is the higher dielectric characteristics of the reinforcing materials decrease the dielectric performance of the fabricated substrate. Additionally, there are limits to how thin the glass cloth can be manufactured. This, in-turn, makes it difficult to achieve the ultra-thin insulation layers required for 5G semiconductor package substrates.To address these technical challenges, a low dielectric resin-coated copper foil (RCC) approach was investigated as a new substrate material for 5G semiconductor packages. This RCC does not use glass-cloth reinforcement which improves the electrical performance while simultaneously reducing the substrate thickness. This new substrate material was constructed using a thermosetting polymer technology based on a modified polyphenylene ether (PPE) resin system.While possessing excellent dielectric properties, this RCC also exhibits the attractive characteristics of a thermosetting resin, such as better processability and heat resistance, required for fabricating high multilayer count semiconductor substrates. This substrate. It features excellent adhesion properties and supports fine-pitch interconnect designs. Additionally, because there is no glass cloth reinforcing material, the insulation layer can be ultra-thin, 10um or less.This paper reports the development process and electrical, mechanical, and physical testing data, as well as processing and multilayer formation testing for this new RCC material.