The HDI PCB manufacturing process differs from the traditional one in a few ways. Thinner traces, smaller vias and more layers make these boards more complicated to fabricate.
Fabricator limitations can limit design freedom and impact routing capability. To avoid these issues, it’s important to consult with your fabricator and understand their capabilities.
Layout Design
HDI PCBs feature more interconnections in smaller areas. These compact boards offer greater functionality and are ideal for advanced technology systems, such as smartphones, video games consoles, and medical equipment like miniature-sized cameras that assist doctors in patient diagnosis.
The HDI technology eliminates via stubs, which reduces signal reflection and improves signal quality. Moreover, it offers faster transmission capability and is resistant to extreme environmental conditions. The fewer layers also lower the manufacturing costs and allow for more functions per board.
While designing an hdi circuit board, it’s important to consider the impedance requirements. It’s also necessary to ensure that all components are positioned appropriately in order to meet normal soldering demands. In addition, spacing between signals should be enlarged no matter whether they are on the same side or different sides of the board.
Using the right design tools can make this process easier. These tools can help you route impedance-controlled traces while keeping the fabricator’s DFM guidelines in mind. They can also reduce noise and improve signal timing, even for the most complex layouts.
Laser Drilling
Laser drilling offers high accuracies and a wide range of hole sizes. It can even drill alloys and composites that are challenging to drill mechanically. The peak energy from the laser causes the material to vaporize, creating small-diameter holes in a variety of geometries.
Fabricators use laser drilling to create hdi pcb manufacturing process the microvias that are a central feature of an HDI PCB. This process allows for thinner traces and lower component footprints. It also reduces crossing delays and transmission time between the components, boosting signal strength. It also helps eliminate the need for external components and improves power distribution.
Depending on the layer count of your HDI circuit board, you may need to design for laser drilling. The number of layers, vias, and other manufacturing processes will affect your route density. The higher the layers, the more difficult it will be to achieve your design goals. You can minimize the difficulty by incorporating features like blind and buried vias in your layout.
Electroless Copper Plating
The metallization of microvias, blind vias and buried vias is one of the most critical processes in PCB manufacturing. This is because these conductive layers establish reliable electrical connections between the different layers of the board.
To do this, PCB fabrication companies use a combination of electroplating and electroless copper plating. During the electroplating process, electricity is used to deposit copper on the surface of the PCB and into the holes. This creates a copper layer that provides initial conductivity for the next steps of the metallization process.
Before the electroless copper plating process, the circuit board must be cleaned. This is done through a series of processes, including deburring, alkaline degreasing and desmear. These processes remove impurities on the hole walls and make them more absorptive for the plating solution.
After the barrier layer and conductive layer have been applied, the object which is provided with this copper layer may be galvanic-ally treated, painted or coated (for example, with powder lacquer or cathodic dip paint). The coating can also be joined to another object by gluing or clinching.
Electrolytic Copper Plating
Copper plating adds conductive traces to the PCB’s surface and microvias, connecting each layer. The process involves cleaning the material to prevent imperfections, then directing an electric current through a solution of copper salts and electrolytes. This creates a thin copper deposit. The process is repeated to increase the thickness of the copper.
The choice of plating technique affects the achievable hdi pcb manufacturing trace widths and spacing, influencing the design layout and electrical performance of the PCB. Plating techniques also influence the manufacturability of via-in-pad designs, which improve component density and reduce signal path lengths.
During the plating process, technicians must ensure that global current density is within limits to avoid plating burn and maximize plating rate. They must also monitor the copper surface for small pits, growths and ridges. These are caused by impurities or additive depletion in the copper plating solution and can result in uneven plating.
The copper surface is then plated with a solder mask, which covers and insulates the traces except where they connect to component pads. A surface finish is then applied to enhance solderability and protect the copper from oxidation. The most common finishes are Hot Air Solder Leveling (HASL) and Organic Solderability Preservatives (OSP).
Assembly
A key difference between HDI PCBs and conventional PCBs is that the former uses buried and blind vias instead of through holes. This allows for smaller traces and more layers to be used in the board. This increased density also leads to better electrical performance, which is why these circuit boards are widely used in military communications devices and other strategic equipment.
Using shorter trace widths helps achieve better signal integrity. This is especially important for high-speed signals. However, it is also essential to ensure that the signal traces are spaced apart enough to meet ordinary soldering requirements. This is because close spacing can increase electromagnetic interference in the traces, and it also reduces their lifespan.
Another important consideration is the fabrication procedure. The precise design rules that fabricators use will affect a board’s dependability and routing capability. A good designer will always ask the board house about these constraints and make sure to incorporate them in their design plan. This will prevent them from having to go back and rework the design later on.
