Miniaturized PCBs at the intersection of form and function
In recent years, we’ve seen a proliferation of new electronics applications requiring smaller packages, new form factors, lower power consumption and increased functionality including embedded signal processing, sensors, imaging interfaces and power management components – all integrated within tight dimensions and sometimes even flexible substrates. This trend is posing numerous challenges to conventional PCB technologies. Where previously flat-surface, rigid PCBs were the mainstay, the emergence of smart watches, IoT devices and other compact systems have spurred the development of advanced new miniaturized PCBs designed to fit the contours of ever-shrinking package sizes. This new generation of PCBs barely resembles the generation that preceded it, and designers have struggled to adapt.
These trends have influenced designers to stress production technologies to thinner conductions lines, high-speed signal transmission lines, difficult impedance controls and via-placement practices, as well as modified substrates and increased reliance on embedded devices. This imposes numerous constraints related to the design of the PCB, with significant implications for system reliability, functionality, power management and the overall success of the design project.
Myriad design challenges
Battery life is of course a critical consideration for the new generation of compact electronic devices, and this affects the PCB design in myriad ways. Designers need to be mindful of signal loss and propagation issues that will result in shortened battery life, and focus increased attention on signal integrity, power management, and EMI issues. Signal integrity issues can be particularly pronounced for flexible PCBs, where impedance control may be strained in instances where high-speed signals are skewed due to the flexing of the PCB.
Additional passive devices like resistors, capacitors, and inductors will be needed to counter the aforementioned signal and interference challenges, and the lack of available package space will typically require these devices to be embedded in the PCB. But embedding passive devices in PCBs is not a mature, developed capability, and can lead to functionality issues – perhaps the device won’t hold power, or reliability isn’t as hoped – and numerous restrictions are imposed on the design flow.
Increasing the functionality of compact electronic devices often entails employing near-field RF communications – yet another function that needs to be embedded in the PCB design. In conventional electronics, RF components are housed in rugged, rigid and higher-cost materials, with ample space to reside. Compact devices require the use of thinner and more flexible materials however, pressuring designers to stray outside mainstream PCB design principles. Copper traces need to be formed with much greater precision, and the distances between lines are much narrower. The placement of vias between PCB layers is also affected, impacting the size and positioning of these interconnects, and alternative materials may need to be substituted to strengthen these vias in instances where the surrounding PCB layers don’t employ the glass-fiber composition of conventional rigid PCBs.
Innovations in miniaturized PCB manufacturing
To meet the key challenges inherent to new generations of compact electronic devices, laser direct imaging (DI) systems are increasingly being employed by PCB manufacturers to form very thin conductors with 10-micron feature size. The ideal DI solution should provide a balance of high registration accuracy and optimal quality even at high production speeds. A suitably high depth of focus should ensure favorable results on PCB topography changes, with precision line uniformity. These systems provide a low-cost alternative to front-end lithography, and with continued innovation in solder mask positioning technology, the embedded electronics industry will soon be poised to achieve sub-10 micron lines.
Figure. Direct Imaging now allows mSAP and advanced HDI PCB with 10µm feature size. (Source: Orbotech)
In parallel, advanced UV laser drilling systems can be employed to drill small vias through a wide range of materials of varying thinness and strength, including ABF, polyimide, ceramic, resin, mold compounds, metal and solder resist, with no residue or damage to the bottom of the via and no undercut, with registration accuracy down to 6 microns.
Designed to streamline the manufacturing processes for today’s electronic devices as they become thinner, smaller, flexible and with higher functionality, these systems allow manufacturers of miniaturized PCBs to increase their manufacturing precision and quality, while improving their production throughput.
On the business side, investments in these production systems should ultimately improve PCB suppliers’ aggregate yield and therefore improve their profits. Many production shops have avoided producing high-functioning devices with miniaturized PCBs due to yield management concerns. The new generation of PCB inspection, imaging and laser drilling systems reduces yield risks considerably. At the same time, these systems accommodate smaller dimensions and newer PCB materials with repair capabilities that will keep yield at acceptable levels even under the stringent constraints imposed by continued PCB miniaturization.
Gil Tidhar is the Co-head of Orbotech’s Global Product Organization (GPO), where he is responsible for managing the unit’s overall activities as well as the development of the additive manufacturing products. Gil has over 25 years of experience as a technical leader and manager in various fields of electro-optics, physics and system engineering, where he has a proven track record in taking basic and applied scientific developments from concept to deployed systems, both in industry and start-up companies. Gil holds a number of patents in his fields of expertise and has published several papers. He also served as conference committee member and session chair for the SPIE DSS international annual symposium.