Keywords: HDI PCB Manufacturing

The urge to cram more features into smaller containers has increased as the technological landscape has changed. As more components are crammed into a smaller area, PCBs created utilizing high-density interconnect (HDI) techniques often have a reduced overall footprint. An HDI PCB may fit more components into a smaller space by using micro, blind, and buried vias, vias in pads, and extremely thin traces. We'll demonstrate the fundamentals of HDI design so you can build a potent HDI PCB board during HDI PCB Manufacturing.

When researchers began looking for ways to minimize the number of vias in PCBs in 1980, high-density interconnects (HDI) printed circuit design and manufacturing got its beginnings. The first industrial build-ups or sequentially printed boards were released in 1984. Since then, designers and component producers have continuously sought out ways to fit more functions onto a single chip and a single board.

There are certain design and production obstacles to go through when creating an HDI PCB board design.

These are a few challenges you could run into when creating an HDI PCB:

• small boardroom workplace
• tighter spacing and smaller components
• greater number of components stacked up on both sides of the PCB
• increased signal flight durations due to longer trace routes
• For the board to be finished, more trace routes are needed.

You may defy PCB design conventions and produce robust PCBs with extremely high connection densities if you have the correct combination of layout and routing tools built on a rules-driven design engine. When using cutting-edge PCB design software that is specifically designed for HDI PCB board design, working with high-density PCB routing and fine-pitch components is simple. With top-notch design tools, you may construct your own HDI board design and prepare for the HDI production process.

What Makes HDI PCB Board Design and Manufacturing Unique?

There are a few small but significant ways in which the HDI manufacturing process varies from the conventional PCB manufacturing method. It's crucial to note that fabricator constraints will restrict design freedom and place restrictions on the board's routing. Although your design program can still support the usage of thinner traces, smaller vias, more layers, and smaller components, doing so requires taking use of automation. Design for manufacturing (DFM) requirements. The manufacturing procedure and materials utilized to construct the board will determine the precise DFM requirements. When dependability needs are taken into account, DFM requirements also become significant.

These inquiries must be addressed during material selection:

• Will the chemistry of the dielectric employed be compatible with the chemistry of the core substrate material as it is now?
• Will the plated copper adhesion to the dielectric be sufficient?
• Will the dielectric give the metal layers sufficient and dependable dielectric spacing?
• Can it satisfy my thermal needs?
• Will the dielectric offer the desired high Tg for rework and wire bonding?
• Will it withstand thermal shock when covered in several SBU layers?
• Will there be coated, trustworthy microvias?

In HDI substrates, nine distinct types of general dielectric materials are employed. Many of them are covered by IPC slash sheets like IPC-4101B and IPC-4104A, while many are not yet described by IPC standards. The resources are:

• luminous liquid dielectrics
• Dielectrics for photosensitive dry film
• Flexible polyimide film
• Thermally treated dry films
• cured thermally liquid dielectric
• RCC foil that is double-layered, strengthened, and resin-coated
• Standard FR-4 cores and prepregs
• brand-new spread-glass laser-durable prepregs

Thermoplastics

The stackup, via the architecture, components arrangement, BGA fan out, and design restrictions, affects routing efficiency for HDI. Trace width, through size, and placement/escape routing for BGA components are the three most crucial factors to take into account while developing your HDI layout.

Always ask your board house about their fabrication processes for producing HDI PCBs. You must ascertain the limitations of their production techniques because this will affect the size of the features you may include in your plan. The necessary via size is determined by the ball pitch of BGA components, which in turn affects the HDI manufacturing procedure needed to build the board. Micro vias, a key component of your HDI PCB, must be carefully engineered to allow for layer-to-layer routing.

Overview of HDI PCB Board Manufacturing and Design Processes

The conventional PCB manufacturing process involves a lot of phases; however, HDI PCB production requires several special steps that may not be employed in other boards. Like many other procedures, the HDI board design process begins with the following:

• Use the largest BGA component on the board or use the interface + direction count from the largest IC on the board to calculate the number of layers necessary to route all signals.
• To choose materials and acquire dielectric data for your PCB stack up, get in touch with your fabrication company.
• Determine the via style that will be utilized to transport signals via inner layers based on layer count and thickness.
• If necessary, do a reliability evaluation to ensure that the materials won't put too much stress on the interconnects throughout assembly processing and operation.
• To enable reliable manufacture and assembly, establish design guidelines based on fabricator capabilities and reliability needs (need for teardrops, trace widths, clearances, etc.).
• Critical points include stack-up generation and design rule determination since they affect a product's dependability and routing capability. Once these steps are finished, a designer may use their ECAD program to apply the DFM and dependability criteria of their fabricators as design rules.
• Ensuring the design is reliable, routable, and can be manufactured by doing this upfront is crucial.

Create Your Feature Size in a Way That Meets HDI DFM Requirements

Despite the strict DFM requirements for clearances on an HDI PCB, they may be met by making use of the design rules in your PCB design program. Before planning and routing, it's crucial to obtain certain DFM criteria, such as:

• Restrictions for trace width and spacing
• Limitations on the annular ring and aspect ratio, particularly for high-reliability designs
• The board's material system ensures regulated impedance in the necessary stack-up.
• If available, impedance profiles for the chosen stack-up or layer pairs

Your ability to design your HDI circuit board to meet these DFM specifications depends heavily on your design tools. With the appropriate set of design tools, routing impedance-controlled traces on your HDI PCB is relatively simple. Simply set your preferred trace width and an impedance profile while keeping your manufacturer's DFM recommendations in mind. As you design your HDI architecture for HDI PCB Manufacturing, the online DRC engine in your routing software will verify your routing. To make sure you've considered all the pertinent HDI DFM requirements, make sure you obtain a comprehensive set of specifications for your fabricator's process.