Issue link: https://iconnect007.uberflip.com/i/1024460
22 PCB007 MAGAZINE I SEPTEMBER 2018 es, which in turn, requires a complete review of the PCB production process. This recent drive to reduce L/S can be linked to the release of the iPhone 7 in 2016. With the iPhone 7, Apple selected to abandon substrate-based application processor (AP) packages and opted for the new InFO (integrat- ed fanout) package from TSMC. With InFO, the typical IC substrate is re- placed with fine feature redistribution lay- ers (RDL) deposited directly onto the die and package mold surface. Collectively grouped as fan-out wafer level packages (FO-WLP), these package types can offer not only reduced thick- ness, but allow sub 5 mm L/S to be applied in the RDL, enabling an appreciable increase in I/O count, and with the associated reduction in pad pitch, this can occur without sacrific- ing real estate; more importantly, all of this is achieved while maximizing electrical and ther- mal performance which are critical in modern smartphone designs. PCB Technology Trends Outside of packaging, there are a number of other trends going on within PCB production, all of which impact critical steps of manufac- ture, and will affect HDI design going forward. Using established tool sets, the majority of to- day's microvias are formed by CO 2 lasers. One negative of the process is appreciable amounts of heat generated within the substrate, which leads to the formation of a heat-affected zone (HAZ) at each drill site, which impacts mini- mum via pitch as well as their size and quality. In order to resolve this, laser manufacturers are developing new tools with ultra-short pulse (USP) lasers, which replace the existing nano- Figure 2: Substrate-based AP package (left); substrate-less AP package using TSMC InFO (right). (Sources: Prismark Partners, left; Atotech, right) Figure 3: Impact of laser pulse duration on HAZ. (Source: IPG Photonics)