Manufacturability of HDI PCB: PCB materials and specifications

Without modern PCB design, high density interconnect (HDI) technology, and of course high-speed components, none of these would be usable. HDI technology allows designers to place small components close to each other. Higher package density, smaller board size and fewer layers bring a cascading effect to PCB design.


The advantage of HDI

Let’s take a closer look at the impact. Increasing package density allows us to shorten electrical paths between components. With HDI, we increased the number of wiring channels on the inner layers of the PCB, thus reducing the total number of layers required for the design. Reducing the number of layers can place more connections on the same board and improve component placement, wiring and connections. From there, we can focus on a technique called interconnect per Layer (ELIC), which helps design teams move from thicker boards to thinner flexible ones to maintain strength while allowing THE HDI to see functional density.

HDI PCBS rely on lasers rather than mechanical drilling. In turn, THE HDI PCB design results in a smaller aperture and smaller pad size. Reducing the aperture allowed the design team to increase the layout of the board area. Shortening electrical paths and enabling more intensive wiring improves signal integrity of the design and speeds up signal processing. We get an added benefit in density because we reduce the chance of inductance and capacitance problems.

HDI PCB designs do not use through holes, but blind and buried holes. Staggered and accurate placement of burial and blind holes reduces mechanical pressure on the plate and prevents any chance of warping. In addition, you can use stacked through-holes to enhance interconnect points and improve reliability. Your use on pads can also reduce signal loss by reducing cross delay and reducing parasitic effects.

HDI manufacturability requires teamwork

Manufacturability design (DFM) requires a thoughtful, precise PCB design approach and consistent communication with manufacturers and manufacturers. As we added HDI to the DFM portfolio, attention to detail at the design, manufacturing, and manufacturing levels became even more important and assembly and testing issues had to be addressed. In short, the design, prototyping and manufacturing process of HDI PCBS requires close teamwork and attention to the specific DFM rules applicable to the project.

One of the fundamental aspects of HDI design (using laser drilling) may be beyond the capability of the manufacturer, assembler, or manufacturer, and requires directional communication regarding the accuracy and type of drilling system required. Because of the lower opening rate and higher layout density of HDI PCBS, the design team had to ensure that manufacturers and manufacturers could meet the assembly, rework and welding requirements of HDI designs. Therefore, design teams working on HDI PCB designs must be proficient in the complex techniques used to produce boards.

Know your circuit board materials and specifications

Because HDI production uses different types of laser drilling processes, the dialogue between the design team, manufacturer and manufacturer must focus on the material type of the boards when discussing the drilling process. The product application that prompts the design process may have size and weight requirements that move the conversation in one direction or another. High frequency applications may require materials other than standard FR4. In addition, decisions about the type of FR4 material affect decisions about the selection of drilling systems or other manufacturing resources. While some systems drill through copper easily, others do not consistently penetrate glass fibers.

In addition to choosing the right material type, the design team must also ensure that the manufacturer and manufacturer can use the correct plate thickness and plating techniques. With the use of laser drilling, the aperture ratio decreases and the depth ratio of the holes used for plating fillings decreases. Although thicker plates allow for smaller apertures, the mechanical requirements of the project may specify thinner plates that are prone to failure under certain environmental conditions. The design team had to check that the manufacturer had the ability to use the “interconnect layer” technique and drill holes at the correct depth, and ensure that the chemical solution used for electroplating would fill the holes.

Using ELIC technology

The DESIGN of HDI PCBS around ELIC technology enabled the design team to develop more advanced PCBS, which include multiple layers of stacked copper filled microholes in the pad. As a result of ELIC, PCB designs can take advantage of the dense, complex interconnections required for high-speed circuits. Because ELIC uses stacked copper-filled microholes for interconnection, it can be connected between any two layers without weakening the circuit board.

Component selection affects layout

Any discussions with manufacturers and manufacturers regarding HDI design should also focus on the precise layout of high-density components. The selection of components affects wiring width, position, stack and hole size. For example, HDI PCB designs typically include a dense ball grid array (BGA) and a finely spaced BGA that requires pin escape. Factors that impair the power supply and signal integrity as well as the physical integrity of the board must be recognized when using these devices. These factors include achieving appropriate isolation between the top and bottom layers to reduce mutual crosstalk and to control EMI between the internal signal layers.Symmetrically spaced components will help prevent uneven stress on the PCB.

Pay attention to signal, power and physical integrity

In addition to improving signal integrity, you can also enhance power integrity. Because the HDI PCB moves the grounding layer closer to the surface, power integrity is improved. The top layer of the board has a grounding layer and a power supply layer, which can be connected to the grounding layer through blind holes or microholes, and reduces the number of plane holes.

HDI PCB reduces the number of through-holes through the inner layer of the board. In turn, reducing the number of perforations in the power plane provides three major advantages:

The larger copper area feeds AC and DC current into the chip power pin

L resistance decreases in the current path

L Due to low inductance, the correct switching current can read the power pin.

Another key point of discussion is to maintain minimum line width, safe spacing and track uniformity. On the latter issue, begin to achieve uniform copper thickness and wiring uniformity during the design process and proceed with the manufacturing and manufacturing process.

Lack of safe spacing can lead to excessive film residues during the internal dry film process, which can lead to short circuits. Below the minimum line width can also cause problems during the coating process because of weak absorption and open circuit. Design teams and manufacturers must also consider maintaining track uniformity as a means of controlling signal line impedance.

Establish and apply specific design rules

High-density layouts require smaller external dimensions, finer wiring and tighter component spacing, and therefore require a different design process. The HDI PCB manufacturing process relies on laser drilling, CAD and CAM software, laser direct imaging processes, specialized manufacturing equipment, and operator expertise. The success of the entire process depends in part on design rules that identify impedance requirements, conductor width, hole size, and other factors that affect the layout. Developing detailed design rules helps select the right manufacturer or manufacturer for your board and lays the foundation for communication between teams.