Design Considerations for HDI PCBs

Designing HDI PCBs requires careful consideration of several key factors, including manufacturing processes like sequential lamination, via-in-pad, and laser drilling. These factors play a crucial role in ensuring high performance, reliability, and space efficiency in complex electronic designs. In this article, we’ll outline the most important considerations for HDI PCB design and how they impact the final product.

● Sequential Lamination: During lamination, PCB core or cores are fused with copper and, in the case of multi-layer PCBs, with pre-preg layers, utilizing heat and pressure. The requisite heat and pressure fluctuate across different boards. Post-lamination, the manufacturer drills vias into the PCB. Unique to HDI boards is the repetition of this process, which aids in averting misalignments and fractures during drilling.

● Via-in-Pad Process: This procedure enables the placement of vias on the PCB’s flat lands by plating the via, filling it with a selected material, capping, and then plating over it. Typically comprising 10 to 12 steps, this process mandates specialized equipment and adept technicians. It’s a prudent choice for HDI PCBs, facilitating improved thermal management, space conservation, and offering an efficient route to bypass capacitors in high-frequency designs.

● Via Fill Types: The selection of via fill should align with your application and PCB specifications. Commonly used fill materials include electrochemical plating, silver-filled, copper-filled, conductive epoxy, and non-conductive epoxy, with the latter being prevalent. Ideal fills meld seamlessly with the flat land, akin to traditional lands, and accommodate both microvias and standard vias to be blind, buried, or drilled, then plated to obscure them beneath SMT lands. Precise control over drill cycles at defined depths is essential, requiring specialized equipment and an extended development timeframe.

● HDI Structures: HDI PCBs offer a variety of layout choices like 1-n-1 PCB and 2-n-2 PCB. The 1-n-1 PCB embodies a singular high-density interconnect layer build-up, mandating one sequential lamination on each core side. Conversely, the 2-n-2 PCB hosts two HDI layers, allowing for staggered or stacked microvias across layers. Complex designs may feature copper-filled stacked microvia structures, although the ascent to higher X-n-X levels is often curtailed by cost and complexity. The any-layer HDI, a denser layout enabling free interconnection among conductors on any layer with laser microvia structures, is notable, especially in smartphone GPU and CPU chips.

● Laser Drill Technology: Any-layer HDI designs frequently necessitate laser microvias, created using laser drills capable of generating up to 20-micron diameter lasers to precision-cut both metal and glass, yielding minuscule yet pristine holes. Utilizing materials like uniform glass with a low dielectric constant can further shrink hole dimensions.

● LDI and Contact Imagery: As a leading HDI PCB supplier, Hitech Circuits pushes the envelope with cutting-edge technology and clean rooms to deliver finer lines with safe and secure processing. For these delicate details, repairs are impossible, so it is essential to do it right with extreme precision the first time. We alternate between contact imaging and LDI imaging based on your equipment verification needs. LDI is the go-to for fine lines and minute spacing, as it can verify even the most demanding processes. This continually expands our capabilities and allows for smaller form factors.

If you have the HDI PCB design, you can send the Gerber files to us for a quick quote. Just emai:sales3@hitechpcb.com For more information, you can visit https://hitechcircuits.com/pcb-products/high-density-interconnect-pcb/