Issue link: https://iconnect007.uberflip.com/i/1221561
46 PCB007 MAGAZINE I MARCH 2020 were to follow—relied heavily on the use of flexible PCBs. They delivered the functional- ity required by the market and provided it in a wearable and portable form factor. Around that same time, Apple released the latest flagship smartphone: the iPhone 6. It was equipped with an LCD display, a single-lens camera, and had 4G connectivity. The most common FPCB material for consumer electron- ics at that time was double-sided copper-clad flex laminate with 12-µm copper foil and 25- µm polyimide dielectric films, with over 80% of flex circuits in typical devices using this ma- terial construction. Today, Apple's iPhone 11 utilizes an OLED screen, face recognition technology, multiple cameras, wireless charging, and limited 5G an- tennas. The flex drilling applications for con- sumer electronics have expanded to increase a much wider range of constructions and more challenging materials. This broadening of ma- terial sets has allowed PCB manufacturers to create FPCBs with significantly smaller traces and vias to accommodate more compact cir- cuit designs. It has also enabled new func- tionalities requiring thicker conductive layers, such as high-current wireless charging. A lot has changed in the last five years. As the demands for smaller scale and greater functionality continue to dominate the hand- held device market, designs for flex PCBs are getting more complex and more challenging for flex PCB manufacturers to deal with effective- ly. They are increasingly forced to focus on in- novation related to the processes they use, the materials they can process, and the technology they deploy. The need to pack more features into less space means that flex PCB designs have necessarily become more complex. De- signs with higher via counts and smaller via sizes continue to push the limits of what can be packed into the same—or less—space and thinner material stackups are becoming the norm. The continued movement to smaller, more densely-packed devices has put pressure on PCB manufacturers. Maintaining high yields in this environment requires them to implement more precise and advanced processing tech- niques and controls while they maximize pro- duction throughput and minimize production costs. 5G: A Case Study in Material Processing Challenges The application of 5G technology is a good example of how the market for new feature- rich devices presents new challenges for PCB manufacturers, especially as it relates to incor- porating new and difficult materials sets into production. Manufacturing previous genera- tions of handheld devices leveraged established techniques and technologies for working with miniature coaxial cables and relatively easy-to- process dielectric materials, such as polyimide. That's not the case when processing many of the materials necessary to enable the 5G capa- bilities and ever more-compressed packaging on a state-of-the-art smartphone today. The trade-off for using LCP and other low- K dielectrics, such as polytetrafluoroethyl- ene (PTFE) and modified or fluorinated poly- imides, is that many of the approaches used to lower their "k" value also can cause the ma- terials to be difficult to work within produc- tion—especially high-volume production. As one example, the thermal properties of many of the newer dielectrics create unique process- ing challenges. Throughput can be hampered when the heat applied by the laser interacts ex- cessively with the dielectric. Limiting that ef- fect—minimizing that heat-affected zone—can be accomplished by implementing heat mitiga- tion techniques, such as increasing the laser beam velocity to space the laser pulses farther The flex drilling applications for consumer electronics have expanded to increase a much wider range of constructions and more challenging materials.