Designing Miniature Printed Circuit Boards

As the electronics sector demands ever smaller components, Jan Pederson looks at how this is affecting the design of printed circuit boards

Today's electronics industry is characterised by a strong miniaturisation trend. Components are getting smaller and smaller, which also places new demands of the design of the printed circuit boards (PCBs) they are mounted on. NCAB Group is committed to global standards association IPC's work to develop standards for ultra-dense Ultra HDI PCBs, and will be in a position to deliver them to customers this year.

At present, there are several emerging innovations and technologies within the design and manufacture of PCBs. The first is High-Density interconnect (HDI) technology, which allows for higher component density and improved performance in smaller form factors. Another area of innovation is flexible PCBs used in flexible and wearable electronics, where improved durability and form factor are matters of interest.

Additionally, microvias - used as the interconnects between layers in HDIs and PCBs - are gaining interest in the sector, with smaller vias allowing for higher component density and improved signal integrity. The use of special materials like ceramics, composites and nanomaterials to improve the performance and reliability of PCBs is also gathering pace, as is 3D-IC stacking which involves stacking multiple layers of integrated circuits to increase component density and improve performance.

To implement these technologies, we know that manufacturers must invest in updated equipment and processes, as well as develop a skilled workforce trained in the use of these new technologies. In addition, proper design and simulation tools must be used to ensure the PCB design is optimised for these new technologies and can be manufactured reliably.

We are seeing a spread of innovative products that are driving the need for HDI, such as in wearables where PCBs are being integrated into wearable devices like smartwatches, fitness trackers and clothing. In this instance, PCBs are being manufactured with flexible materials that allow for a more versatile design and package. The thriving Internet of Things (IoT), artificial intelligence (AI), and 5G technology are a few of the industries that are accelerating manufacturing to a new level. These technologies must be integrated, so implementation involves careful consideration during the design phase to ensure optimal performance and reliability. Packaging techniques, such as chip-on-board (COB) and flip-chip, along with the integration of these technologies directly onto a PCB can be termed ‘substrate like PCB’.

To be defined as an Ultra HDI board, a PCB must have several distinct features. First, it must have a conductor width, isolator distance and dielectric thickness below 50µm. Additionally, the PCB will feature a microvia diameter below 75µm and product characteristics that exceed the existing IPC 2226 level C standard.

At NCAB, a special group in our internal technical council is working to support our factories to build capacity to meet these Ultra HDI requirements. One important method deployed is modified Semi-Additive Processing (mSAP), where copper is built up on a thin initial layer instead of being etched off a thick layer. This process is better for the environment as less copper is used.

The greater level of miniaturisation also requires that the pattern can be transferred to the board with a sufficiently high resolution. As such, the factory needs to have cutting-edge Laser Direct Imaging (LDI) capabilities. Moreover, the surrounding environment has to be extremely clean to avoid contamination and dust which entails considerable investment. Testing processes and automated optical inspection (AOI) equipment also needs to be updated to detect and avoid potential board defects. Likewise, you have to look at the equipment and the chemistry when copper plating. As a result, miniaturisation will generate a need for cleaner and more homogeneous materials.

NCAB's factories are now fully committed to growing their Ultra HDI capabilities, and expect to start delivering Ultra HDI boards in 2023.

To achieve this, NCAB has a new tool to monitor how ready the company is regarding the introduction of a new technology, called the New Technology Readiness Report (NTRR). The report is based on defining what the company will and will not do with transparency towards our customers.

To do this, the first thing we need is internal knowledge regarding our factory management, sourcing, auditing and qualification. We define our capability together with the factory, and based on this we create Design for Manufacture (DfM) and seminars for customers. After a while of lessons learned, we can establish a Failure Mode Effect Analyses (FMEA) which is fed back into our updated DfM and seminars.

During this, we update our readiness in a NTRR that is transparent for customers; during the introduction of a new technology we need to identify security elements at an early stage and update the lessons learned. We can then build an FMEA where we monitor type of failure, add tests and inspection, and then monitor occurrence, detection and severity. The purpose is to increase yield and reach an acceptable level.

Jan Pederson is Director of Technology at NCAB