Undoubtedly, one of the greatest inventions of the twentieth century was the transistor by Drs. William Shockley, John Bardeen and Walter Brattain of Bell Labs in 1947. Although not an end-user product, transistor-based technology is the reason behind the explosion in electronic technology that we have enjoyed over the last several decades. Transistors allowed us to replace the large, heavy and sometimes dangerous vacuum tubes with much smaller, lighter, safer, and eventually more capable devices. The subsequent and ongoing technological revolution has led to innovative design and manufacturing methods that are producing ever smaller and more powerful PCB electronics products.
One of the most significant innovative advances in PCB electronics manufacturing that has led to smaller and smaller electronics products is high density interconnect (HDI) technology. HDI may be described as electronic development that leverages advanced circuit board manufacturing equipment and processes to optimize SMD trace routing and meet the higher component density and smaller packaging demands of the competitive electronics product industry. HDI PCB electronics development requires coordination between board design and manufacturing, which can only be achieved with an understanding of board fabrication and PCB assembly. Before laying out the design and manufacturing considerations that should guide your development process, it may be helpful to better define HDI PCB electronics.
HDI PCB Electronics
HDI PCB electronics are devices and systems comprised of components where input and/or output (I/O) connections (pads or pins) are closely spaced. These tight or dense interconnections allow for the use of smaller components that can be mounted into smaller spaces on smaller boards. The compactness of these devices and systems enable the creation of smaller product packages with greater functionality and capabilities and consequently increased deployment and application opportunities like the ability to transmit and receive signals faster. However, before deciding to take advantage of HDI PCB electronics technology, you should consider the manufacturing costs.
HDI PCB Electronics Manufacturing
After a humble beginning and with a few significant milestones, PCB electronics manufacturing has evolved into a well-defined, precise series of steps requiring specialized processes and equipment. The efficiency of the manufacturing stage, however, is highly dependent on how well your design decisions are tailored to your contract manufacturer’s (CM’s) specifications. This is especially true for HDI PCB electronics manufacturing where PCB design considerations define the HDI PCB manufacturing process and influence whether and how much additional time and cost is required to make your boards.
PCB Design Considerations
Typically, HDI boards contain ICs or surface mount devices (SMDs) with high numbers of pins or pads, such as ball grid arrays (BGAs). The spacing or pitch between these interconnection points helps define trace widths, via types and PCB stackup.
- Trace Widths
For HDI, trace widths are smaller, which allows for an increase in routing channels. This reduced spacing can affect signal propagation and necessitates that special attention is paid to avoid any negative impact on signal integrity.
- Via Selection(s)
Your choice of via(s) and the corresponding number of layers are the most significant determinants of the HDI PCB electronics manufacturing process. For most boards, drill hole aspect ratios allow for mechanical drilling, while HDI boards most often require laser drilling and sequential construction.
- PCB Stackup
Using HDI technology leads to a reduced number of layers than your standard PCB stackup would require. This construction improvement for tightly-spaced, high-speed signal transmission depends on your material selection.
HDI PCB Manufacturing Process
The overall process for building HDI boards is essentially the same as for building other PCBs, with notable differences for PCB stackup and hole drilling. Since HDI boards generally require smaller drill holes for vias, laser drilling is usually required. Although laser drills can produce smaller and more precise holes, they are limited by depth. Therefore, a limited number of layers can be drilled through at a time. For HDI boards, which are invariably multilayer and may contain buried and blind vias, multiple drilling processes may be required. This necessitates successive layer bonding to achieve the desired stackup or sequential lamination cycles. Not surprisingly, this can significantly increase manufacturing time and cost.
HDI PCB electronics manufacturing is an advanced technology and therefore requires expertise along with specialized equipment like laser drills, laser direct imaging (LDI) capability, and special clean room environments. In order to efficiently manufacture high-quality and reliable products, you must understand the HDI manufacturing process and coordinate with your CM to implement good DFM for HDI.
The electronics industry is largely consumer-driven and the directive for smaller, more capable products with increased functionality will only intensify in the years to come. At Tempo Automation, we are well-positioned to assist you in meeting this demand with advanced equipment, processes and expertise to build your HDI boards quickly and precisely. To learn more about how we partner with you to meet HDI challenges, download this e-book on DFM for HDI.
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And to help you get started on the best path, we furnish information for your DFM and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on HDI PCB manufacturing or are interested in helpful tips to incorporate into your design, contact us.