Connectors are sometimes an afterthought in a PCBA. For most simple designs, such as development boards or microcontroller boards, you’ll find a board populated with pin headers, possibly USB, and probably a power connector of some kind. For more complex systems that go beyond prototyping, there can be many unique connectors for power, data, or a combination of these.
This article marks the first in a short series on connector selection, testing, placement, and many other aspects of connectors that are sometimes overlooked. What often seems like a relatively simple choice to make can have major impacts on reliability, signal integrity, and even thermal behavior. In this article, we’ll focus on the main specifications that are important for connector selection, as well as when to consider working with a manufacturer to produce a custom connector.
Which Specifications Drive Connector Selection?
Connectors generally perform a simple task; they provide electrical connections between two devices through a cable. Those connections between two connectors can transfer power, signals, or both. Some connectors are specifically designed for data connections, usually for a specific digital interface (such as Ethernet, USB, etc.). Other connectors are specifically intended to provide high voltage and/or current to a device, possibly alongside data. The range of possibilities is very broad.
Some of the major specifications that determine suitable connector options include:
- High-speed data - Some connectors and their cable assembly/mating connector are specifically designed to allow data transfer up to a specific bandwidth limit, or between two PCBs at high data rates.
- Rugged construction - Rugged connectors will be constructed of harder plastics or stronger metals so that they can withstand harsher environments. Exposure to humidity, noxious substances, saltwater, and crushing forces require more rugged connectors.
- Standard interfaces - Some interfaces like USB, Ethernet, and HDMI will have standardized connectors. However, these standard connectors are not required when working with these interfaces.
- Power ratings - Connectors need to provide some power up to some safe limit, usually specified as a pre-pin limit.
- Form factor - Connectors come in multiple form factors that will drive enclosure design. There is also the mounting option to consider (board-mount or panel-mount).
Connector Form Factor Examples
Most designers are familiar with the standard connectors you’ll find on computers and other consumer products. For some products, where you want the design to be interoperable with a standard cable, you will have to use a standard connector. Some current and older standardized connector plugs are shown in the image below; these are most often used in consumer products, but they can also be found in more technical products that need to interface with a computer or a peripheral device.
Standard connectors for most consumer products.
More specialized options for connectors are used in areas like industrial systems, aerospace, or automotive. In some cases, a standard connector can be built with much more rugged construction, and possibly to a high ingress protection (IP) rating (IP6x or higher) so that the assembly has some resistance to moisture and solid debris ingress.
Circular connectors with a screw retention mechanism.
Data connectors can have a range of form factors as well. These are often surface-mount devices as this will eliminate stubs on these connectors, although they could also have some through-hole mounting pins for added stability. Data connectors can interface with a cable, or they will be used as board-to-board connectors.
Standard or Custom Connectors?
It is possible to contract with a connector manufacturer and have them work with you to build a custom connector assembly. Standardized connectors are important and they are very useful for interoperability, but there are reasons to choose a custom connector for your design. A custom connector could have nearly any of its physical or electrical characteristics customized. The table below compares some connector specifications for standard and custom connectors.
- Custom connectors may have a totally custom housing, pinout, or both
- Depends on conductor sizing, housing construction, and materials used
- Rating may be assigned by signaling standard
- Lower risk as the connector or a comparable part swap will be available from multiple vendors
- Higher risk as the connector could only be available at limited volume from a single manufacturer
- High interoperability as multiple products could interface with the connector
- Limited; requires a custom mating connector
Beyond the points listed above, the mechanical and environmental stability of the connector body will depend largely on the materials used to construct the connector, and how the housing assembly is designed. A mechanical engineer will need to perform some analysis when designing the connector to ensure any specifications on vibration, crushing forces, thermal demands, and retention are met. In addition, environmental exposure will drive material selection; for example, deployment in some industrial settings or in a marine environment will demand different materials than a connector used in a consumer product.
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