While 6G research progresses, the 5G millimeter wave market remains in its early stages, awaiting widespread adoption across various applications and user ecosystems. The advancement of Antenna-in-Package (AiP) technology is closely linked to the growth of both the 5G mmWave and 6G markets. Given that AiP is expected to become an integral part of all 5G millimeter wave base stations and 5G-enabled devices, such as smartphones, its continued development is crucial.
In the development of Antenna-in-Package (AiP) technology for high-frequency communication devices, cost-effectiveness is paramount, with the goal of achieving a price of $2 per 1x1 AiP module to enable widespread adoption. Achieving affordability involves overcoming the chicken-and-egg dilemma, where adoption must precede cost reduction through economies of scale. The use of cost-effective packaging materials and processes, along with miniaturization, is crucial, especially for integration into consumer devices such as smartphones. High performance is vital, requiring the fabrication and integration of high-gain, broadband mmWave antenna arrays, as well as addressing electromagnetic compatibility (EMC) and optimizing signal integrity (SI) and power integrity (PI). Reliability is ensured through efficient heat dissipation, while scalability allows the modules to meet diverse application needs. The IDTechEx report, "Antenna in Package (AiP) for 5G and 6G 2024-2034: Technologies, Trends, Markets," delves into key considerations such as antenna element selection, substrate technology, passive device integration, and supply chain maturity. This article will focus on substrate technology selection, as it has the greatest impact on all the aforementioned requirements.
Several factors must be considered when determining the appropriate substrate technology for AiP. These include the choice of core material, such as the coefficient of thermal expansion (CET), Young's modulus, moisture absorption, and thermal conductivity. The manufacturability of the chosen substrates is also crucial, including via size, number of metal layers, and line-to-space characteristics. Furthermore, the Dk and Df of the antenna layers, bumping technology, and embedding technology, among others, play an important role. For example, lower insertion loss correlates with a reduced number of metal layers in the routing, necessitating scaling up the dimensions of microvias (blind vias). Additionally, the high current densities of power amplifier ICs require numerous through-vias or plated through-holes (PTHs) in the package substrate, underscoring the importance of precise dimensions to support I/O density and signal integrity. Efficient power delivery requires specific aspect ratios with a pitch < 20 µm, highlighting the complexity of substrate design. The AiP substrate material requirements significantly influence antenna performance. A low dielectric constant (Dk) extends bandwidth and improves gain, while a high Dk allows for smaller AiP sizes. Low dielectric loss (Df) contributes to increased efficiency. A high Young's modulus ensures rigidity and reduces warping, while cores with a low coefficient of thermal expansion (CTE) are better suited to silicon. Zero moisture absorption is crucial for stability. Surface roughness is necessary to achieve low-loss interconnects. Integrating passive components requires thicker metallization, low dielectric losses, and flexibility in the metal layers.
Currently, four candidate substrates for AiP technology are being studied: HDI (High Density Interconnect) based on low-loss materials, LTCC (Low-Temperature Co-fired Ceramics), High-Density Fan-Out, and glass substrate technology. Among these options, HDI is currently the dominant technology for AiP. On the other hand, LTCC technology finds its main application in high-frequency communications sectors, particularly in the aerospace and defense industries, where cost considerations are less important.
Author: Dr. Yu-Han Chang, Principal Technology Analyst at IDTechEx
