Tips for conserving space and enhancing functionality in small form factor devices.

At our company holiday party, there were several giveaways, including a 40" LCD TV, digital cameras and others. The most coveted prize was a brand new tablet. It prompted me to consider just how much functionality device manufacturers are able to fit into these smaller form factor tablets.

Indeed, tablets exemplify flex circuits’ potential to fit dozens of features into limited real estate. As a midpoint device between a smartphone and a laptop computer, tablets have become increasingly popular, with new models flooding the market. Some tablets are PCs with touch screens, while others are smartphone extensions, running enhanced mobile operating systems. Tablets, in all their forms, are rapidly advancing from generation to generation. As tablets have improved, so has flex assembly integration within these devices.

Several successful first-generation tablets used up to eight or nine flex assemblies each. Subsequent generations of devices added significantly more features in even thinner and lighter form factors, creating challenges to package the electronics. Second-generation tablets use almost double the number of flex assemblies to increase features, functionality and space for larger batteries. (Even with the additional functionality and use of more flex in the 2G tablet, the list price of the device and total hardware BoM cost was the same as the 1G model.)

Some tablets have not integrated flex assemblies. These versions reflect a PC laptop design mindset. The designs may have a few extra features, such as a physical keyboard, a stylus input device and multiple input and output ports. These features, coupled with a lack of flex assemblies, add considerable thickness and weight to the device (Figure 1).

I’d like to elaborate on techniques engineers can utilize to conserve space, the most basic of which is to integrate printed circuit boards and flexible flat cables/traditional cables into flex assemblies for components such as cameras, speakers, buttons, side keys, connectors and microphones. Standalone modules, like WiFi/BT/FM, 3G/WAN and touch screens, can be integrated on the main PCB or on a well-designed flex circuit. In some cases this eliminates additional wired connections and reduces overall device thickness.

Based on our analysis of the above devices, here are a few suggestions to consider for optimized PCB design to conserve space:

• Make the circuit board rectangular to improve the material utilization.
• Eliminate cut-outs to take advantage of the full perimeter of the device.
• Put components on one side of the board only.
• Use 3D flex circuit design techniques to place  components and modules in multiple planes to reduce the thickness in critical cross-section areas.

Other design options include placing components on flex circuits to reduce the expensive real estate on the main high-density interconnect PCB. These components include the LED flash, an ambient light sensor, headset jack or connectors. Replacing PCB peripheral modules containing PCB, connectors and flat cables with flex assemblies combines functionality to reduce device thickness. Integrating antennas and speakers is yet another example to reduce overall device thickness. Moving high data-rate components such as coax cables to flex circuits offers advantages in the area of signal integrity, while also reducing device thickness.

In the examples above, we observed two design strategies, one being a thinner tablet based on smartphone design methodology, the other being a thicker tablet based on PC laptop design methodology. The thinner tablet device uses flex circuits extensively, whereas the thicker tablet device does not incorporate flex circuits. This illustrates that fully utilizing the benefits of flex assemblies enables devices to be thinner and lighter. The concepts discussed can be applied to not only tablet devices, but to any electronic device. Another benefit of using flex assemblies is the creation of space for larger batteries. It also permits integration of components and sensors for more functionality.

Jay Desai is director of marketing at MFLEX (mflex.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .