Posted on July 08, 2019
Connectivity is the lifeblood of today’s technology-driven world. The term has taken on many dimensions, from reference to the internet and data networks, to home appliances and devices of all sizes.
With continuing advances in technology, the connection between parts of any design is becoming increasingly important. Whereas design engineers could have previously relied on their “fall back” or favourite connector for all projects, demands for increased bandwidth and the need to eliminate crosstalk or environmental impact creates impetus for engineers to find new, more capable connectors to optimize their design and ensure the best results. Connectors have never had such an important role to play in the success of an embedded-system design.
Increasing Demands on Connector Integrity and Performance
Prior to today’s high-speed design requirements, the main potential obstacle for connectors was the physical aspects of their designs, such as stack height, distance between boards, current requirements, or processing and operating temperature.
As system speeds have increased, interconnected designs are no longer based solely on mechanical requirements. Now, a number of additional electrical performance issues should now also be considered. Today’s designers have to take into account issues such as crosstalk, skew, and propagation delay, just to name a few. The successful design of any connector involves achieving the right balance between maximising its physical and mechanical strength while optimising signal integrity. Connectors form an important link in a signal’s transmission chain and should not be overlooked when designing high-speed systems. In fact, connector design and manufacture should be approached as part of the overall system-level design process.
Increasing Bandwidth Demands
The constant demand for increased bandwidth requirements necessitates connectors capable of handling ever-higher data rates for all types of applications. Cutting-edge technology is now sought after for more than just mission-critical military and aviation designs. It can now be found in everything from automotive to consumer IoT devices. Today’s rapidly increasing bandwidth needs challenge the capability of traditional design approaches that utilise existing technology components. While connectors are often considered to be the “back end” of many product implementations, they need to be held to the same design criteria as all other elements within any high-speed/high-bandwidth product.
Electrical Performance Issues to Consider
Crosstalk is an undesirable transmission of electrical signals between two or more transmission media due to inductive or capacitive coupling. Crosstalk can also be created by inhomogeneities of the transmission media and skew effects in the signal transmission pair. With high speeds, circuits can cause electrical noise that affects crosstalk between signals and can possibly generate electromagnetic interference noises that disrupt other circuits. These realities mean that signal integrity and reliability become huge factors.
Historically, crosstalk was attributed to cables, but as LAN speeds increased and cable quality improved, other channel components started to contribute to crosstalk performance. Connector crosstalk can be quite a problem, unless allowed for in the design of the connector.
Skew or Propagation Delay — Intra-pair and inter-pair skew describes the difference of the propagation delay between electrical signals within a signal wire pair, and between two or more signal wire pairs in one cable, respectively. Both impact available bandwidth. Intra-pair skew causes signal distortions, and a decrease of the transmission bandwidth creates higher electromagnetic emissions and lower noise immunity. Inter-pair skew leads to a reduction of bandwidth due to the fact that, as with most of the multi-channel data bus systems, all data must be valid simultaneously. Both issues can be influenced by the mechanical length differences of conductors within a signal pair or by different dielectric constants and mainly appear in 90° variants of connectors. HSD 90° headers have a basic grid of 2mm, which results in a length difference of 4mm between conductors of a pair and implicates approximately 20 ps difference in time delay.
Environmental Impacts — Many of us work indoors in moderate and controlled conditions, so the devices and appliances around us lead comfortable to only moderately stressful lives. However, most of the electrical and electronic systems and machinery that make our lives run smoothly must operate in harsh conditions, exposed to the elements of nature.
If the connectors need to be used in harsh operating environments, the design engineers should give care to the choice of connector and check the manufacturer’s IP (ingress protection) rating for sealing to solid objects and water at various angles, depths and operating time frames. They should also consider the end-use environment for the connectors and compare that scenario with the details behind the connector’s IP rating. Most of the IP designations have specific conditions, but the IP68 rating may be defined differently by each manufacturer, so when looking for a connector with an IP68 sealing rating, design engineers should be sure to inquire exactly how the manufacturer’s IP68 rating is measured. For example, a system submerged at two meters for 24 hours has a different impact on the connector than at 120 meters for 24 hours, but both situations can be defined as an IP68 rating.
Choosing the Right Connector
In terms of the connectors chosen for high-speed performance printed circuit boards (PCBs), connectors must be evaluated in the context of their use in a real-world environment. Connector-only data can be useful for comparing the relative performance between two similar connectors, but it may be far removed from the performance obtained in an actual application.
Laminate choice is another increasingly important factor in cable and connector design. While FR-4 isn’t the best laminate choice for high-speed/high-bandwidth designs, it’s still the preference of many product developers, due to its low cost and broad availability.
All connectors need to be both routable and palatable. For example, if 16 layers are required for the routing of a connector, the design engineer has to ensure that the connector used will design itself out of a lot of systems. This is why it’s important to have a thorough understanding of the PCB to which the connector is linked while also taking into account factors such as design optimisation, manufacturability, and final product implementation.
Conclusion
Connectors should be a central focus and interest for engineers in today’s network-centric and data-intensive market. Without proper connectivity, our interconnected world would quickly come to a halt. Connectors, the building blocks of connected devices, play a critical role in providing safe and reliable electronics designs for all aspects of our lives.
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