Rush PCB is now offering a new technology, namely High Density Interface PCBs or HDI PCBs that come with the most advanced capabilities. One of the fastest growing and most-requested PCB technologies in the market, our HDI PCBs offer much higher wiring densities per area compared to that available in standard PCBs. High Density Interconnect PCBs are also called Micro PCBs or Fine Line PCBs, and have finer lines and spaces, smaller vias, and higher density of connection pads.
The portfolio of capabilities from Rush PCB includes Micro PCBs that easily overcome the limitations of standard circuit technologies. Micro PCBs incorporate ultra-thin cores, fine line processing, and alternative via methods that reduce the size and weight of your gadget while enhancing their performance simultaneously.
Advantages of HDI PCB
HDI PCB technology offers several advantages over conventional PCBs:
- Shortens lead times for PCB manufacturing and improves device performance for SIP, MCM, Flip Chip, and BGA technologies typically used in medical devices.
- Allows use of fine line geometries, ultra-thin cores, and alternate via technologies for enhancing thermal transfer in PCBs
- Allows use of 20 µm circuit geometries, 30 µm dielectric layers, 50 µm laser vias, and 125 µm bump pitch processes
- Allows reducing the time to market by combining improved process capabilities with high-speed digital and high frequency RF PCB requirements
- Increases the area available to the PCB designer for placing circuit components as they can be place the components much closer together. This reduces signal losses and results in faster signal transmission.
HDI Technology is Consumer Driven
HDI PCB design technology processes such as via-in-pad offer more copper on fewer layers, contrary to popular belief that bigger is better. Consumers are driving the requirement for smaller devices, and as a result, the size of mobiles, cameras, wearables, and other electronic gadgets is shrinking. While this requires the internal circuits to shrink as well, designers face the increasingly peculiar challenge of offering more features within a reducing space.
Designers are therefore utilising HDI technology to address these transformations, making products with more features that weigh less and are physically smaller. HDI technology uses a thinner material, miniature components, and specialty equipment to shrink the physical size while expanding the quality, speed, and features.
High Density Interconnect PCB Technology follows the changes that consumers demand. Designers can now place more components on both sides of the PCB, thanks to multiple via processes such as via-in-pad and blind via technology. This gives designers more PCB real estate for placing components closer together. With decreasing component sizes and pitches, the design allows faster transmissions of signals and this reduces signal loss and crossing delays significantly.
Vias in HDI Technology
HDI technology makes use of different types of micro-vias for increasing the real estate available to designers for routing traces. This includes through, blind, and buried micro-vias, micro via-in-pad, and landless micro-vias, and HDI technology requires filling all vias.
These are vias spanning the entire thickness of the PCB, starting from one of the outermost layers and reaching the other outermost layer, while connecting the necessary layers in between.
Blind micro-vias start at one of the outermost layers, but end at an intermediate layer, while connecting the necessary layers in between.
Buried micro-vias start at one of the intermediate layers and end at another intermediate layer, connecting the necessary layers in between.
Conventional designs do not allow placing vias within the soldering pad of a component, since the via wicks solder away during reflow, causing dry joints. However, placing vias within a solder pad of a component is no barrier for HDI technology, as epoxy fills all the micro-vias, not allowing solder wicking. This offers a significant increase in channels for routing for fine pitch components such as BGAs.
Vias in conventional designs always have a pad on both sides. HDI technology can use landless micro-vias that do not require pads. In fact, designers can place landless micro-vias directly on the trace, allowing very high density routing. As these vias and micro-vias are laser drilled, their hole diameter can match the width of the thin traces that HDI technology uses.
HDI Technology uses different types of via fill materials such as conductive epoxy, non-conductive epoxy, silver filling, copper filling, and electrochemical plating for filling vias. This is very useful in burying the via within a flat copper pad that solders just as normal pads do. We drill the blind or buried vias and microvias, plate and fill them, and hide them under the SMT pads. This type of via processing requires special equipment and is time-consuming, and we have to execute multiple drill cycles and control the drill depth, which adds to processing time.
Stackups in HDI Technology
Rush PCB offers several types of HDI PCB stackups, most commonly 0-N-0, 1-N-1, and 2-N-2 types.
HDI Type I (0-N-0)
This type of HDI PCB stackup has a laminated core with a single micro-via layer on at least one of its sides along with several through vias, if necessary.
HDI Type II (1-N-1)
This type of HDI PCB stackup has a central laminated core with through vias, a single micro-via layer on at least one side, and buried micro-vias. Designers usually stagger micro-vias and stack them or stagger them in relation to the buried micro-vias.
HDI Type III (2-N-2)
This type of HDI PCB stackup uses a central laminated core, micro-vias, buried micro-vias, blind micro-vias, and may have through vias. At least two layers of micro-vias are present on at least one side. Designers usually stagger micro-vias and stack them or stagger them in relation to the buried micro-vias. HDI Type III stackup is the best configuration for large dense boards that contain multiple high pin-count BGAs.
HDI PCB Design
With proper planning and execution, High Density Interconnect PCB design can be very cost effective as it achieves the same results with a lower number of layers and smaller size as compared to that from a standard PCB.