5G is driving packaging innovation in the radio frequency front-end

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Smartphones use multi-chip SiP for the front-end module, filter set, and diversity receiving module in 4G LTE. SiP provides the required small size, shorter signal paths, and lower losses. The 4G LTE front-end module currently includes 10-15 chips, connected to organic substrates (up to 8 organic layers or 18 ceramic layers) using flip-chip ball bonding or copper pillars, while some power amplifiers still use wire bonding. 5G Sub-6GHz products are expected to utilize improved existing flip-chip SiP (such as double-sided FC packaging substrates) with a similar bill of materials to achieve incremental innovation. With the introduction of new architectures, 5G millimeter-wave frequencies have brought breakthrough packaging: fan-out wafer-level packaging (WLP) and glass substrate interposers, competing with advanced organic substrate flip-chip packaging with low-loss dielectrics.

Antenna technology and layout are one of the most critical challenges for 5G semiconductor systems. At millimeter-wave frequencies, the long path from the semiconductor packaging to the antenna represents high losses, making it desirable to integrate the antenna into the SiP. Higher frequencies require smaller antennas (measured in millimeters rather than centimeters), making them easier to integrate into SiP from a footprint perspective. However, a single antenna must currently operate with multiple frequency bands, making the antenna and additional circuitry more complex.

To integrate antenna elements with radio frequency components for 5G mobile communications, various packaging solutions with different architectures have been proposed. Due to cost and mature supply chains, flip-chip based on laminated substrates has been the first choice for antenna-in-package (AiP) packaging. Fan-out WLP/PLP packaging, benefiting from high signal performance, low losses, and reduced form factors, is a promising solution for AiP integration, but it requires double-sided redistribution layers (RDL). Apart from a few manufacturers, most OSATs are not yet ready to mass-produce using this technology.

Additionally, the circuits need to be shielded from antenna radiation while ensuring that the antenna is not blocked and can achieve clear reception/transmission. Just like laminated substrates, ceramics and glass have also become new choices for packaging substrate materials. The selection of 5G millimeter-wave packaging substrate materials must be balanced in terms of electrical characteristics, cost, processability, and supply chain readiness. Due to cost and material/component supply chain readiness, organic laminated substrates will be the first to be applied (along with limited ceramic applications), followed by ceramics and glass.