Charles Murray

September 15, 2015

5 Min Read
7 Essentials for Designing with Micro-Miniature Connectors

As connectors get smaller, their importance is getting bigger.

The reason for that is simple: products are shrinking. The electronics in cell phones, tablet computers, blood glucose monitors, and myriad handhelds are getting packed tighter, leaving little room for connectors. The same holds true in defense and aerospace, where satellites, guided munitions and avionics systems, among others, need the compactness that so-called "micro-miniature" connectors can deliver.

As demand for smaller connectors grows, however, design engineers face a new set of challenges. They can no longer defer their connection designs to the waning days of the project. Micro-miniature connectors require forethought. They require that designers consider packaging, durability, current-carrying ability, ease of replacement, and other factors early in their designs.

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Following are a few design recommendations from suppliers of micro-miniature connectors. They're based, not only on the expertise of connector designers, but on the painful stories of engineers who failed to think ahead, and ended with unexpected last-minute challenges.

1.Consider your connectors early in the design. "Engineers tend to be so focused on designing the overall system that they consider the connectors to be an afterthought," Mitch Storry, manager of product development engineering for TE Connectivity told Design News. "They feel connectors are simple, so they can be deferred to the end of the design process. And then they design themselves into a corner."

Storry sees the frenzied outcomes of 11th-hour connector design all too often. In many cases, he told us, design engineers have to opt for non-standard connectors as a last-minute fix, leading to higher costs and longer lead times.

To avoid those problems, experts who spoke to Design News recommended these steps: Early in the process, decide where your connectors will go. Then make sufficient room for them and design everything around them.

"No one likes to hear, 'First, decide where your connectors will go,'" notes Stephen T. Morley, product development engineer for TE Connectivity. "But if they do it, they can save themselves a lot of time and trouble."

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2.Be aware of space limitations. Although micro-miniature board-to-board connectors often have a pitch of less than 1 mm, they are typically being placed into tightly packed applications. To deal with potential packaging problems, designers need to consider the traces on the printed circuit (PC) boards, as well the cables that attach to the connectors. "As the pitch gets smaller, you have to make the traces and the cables narrower," said Mike Higashikawa, regional product manager for Molex Inc.

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Also, remember that some connectors (flex cable connectors, for example) offer an option for front-flip or back-flip actuation. When designing the system, you'll need to account for those actuation methods. A back-flip connector, for example, can't be easily accessed if there's another component directly behind it.

Finally, designers need to be aware that surface mount machines occasionally can't handle the smaller parts. In some cases, they may need new vacuum nozzles to deal with handling issues.

3.Be aware of current-carrying capabilities. As connector sizes decrease, current-carrying capability drops, too. Typically, a micro-miniature connector can handle between 200 mA to 500 mA -- about half the current of a larger, board-to-board connector. To compensate for that lower current-carrying capability, designers may need to increase the number of terminals.

4.Consider the robustness of small connectors. "When you put things one-tenth of an inch apart, you run out of places to put material for your (connector) walls," notes Morley of TE Connectivity. "Accommodations need to be made, not only in the design, but in the assembly process, to make sure they don't get damaged."

Morley, an expert on micro-miniature connectors for RF applications, recalls military-aerospace applications where half of the connectors were damaged during testing.

Failing to understand these potential issues up front can be costly, he said. Damaged connectors may need to be repainted, refinished, and/or remarked. Or they might need to be replaced by expensive, field-replaceable connectors. Making such changes could set the design back by as much as four or five weeks.

The good news is that a pound of prevention can eliminate such 11th-hour cures, Morley said. "The lesson is that you should always use connector savers if they are available," he told us. "If they're not available, design one. It will save you from having to do a lot of repairs before you ship the products."

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5.Consider ease of replacement. If a product enclosure is hermetically sealed, then you need a connector that is replaceable from the outside. Otherwise, Morley said, you may end up doing some unsoldering and resoldering.

"The more you handle it, solder it, and go at it with tools, the more you will run a higher risk of damaging the entire assembly," he said.

6.Understand the functional requirements of your connector. Suppliers need customers to thoroughly express their needs, otherwise misunderstandings can follow. That's especially important in applications that call for custom-designed connectors.

"Properly articulating the functional requirements of the connector is critical," notes Storry of TE Connectivity. "Without it, we can miss some key requirements."

The requirements include durability, temperature, shock and vibration, among others. Applications that call for connectors to be mated 500 times are altogether different than those that may be mated five times, Storry said. Similarly, temperatures in downhole applications are far different than those in handheld devices.

"We don't want to go down on a path and design a custom connector that is inherently incapable of meeting the requirements of the application," Storry added. "If you go too far into the design cycle and find there's a new requirement, it can turn the whole design on end."

7.Consider mechanical stresses. Temperature, shock, and vibration can cause mechanical stresses between the package and circuitry. Experts recommend that you choose connectors that isolate those stresses.

"I see an awful lot of fractured solder joints on PC boards," said Morley. "When a connector mounts rigidly to a board and to the wall of an enclosure, and it has to withstand a lot of shock and vibration, you're going to induce cracks before long."

Morley recommends engineers use interconnect systems that minimize the build-up of stresses between the mounting structure and the connection point. "A number of suppliers offer them," he told us. "It's a feature that the designer should always ask about."

Senior technical editor Chuck Murray has been writing about technology for 31 years. He joined Design News in 1987, and has covered electronics, automation, fluid power, and autos.

About the Author(s)

Charles Murray

Charles Murray is a former Design News editor and author of the book, Long Hard Road: The Lithium-Ion Battery and the Electric Car, published by Purdue University Press. He previously served as a DN editor from 1987 to 2000, then returned to the magazine as a senior editor in 2005. A former editor with Semiconductor International and later with EE Times, he has followed the auto industry’s adoption of electric vehicle technology since 1988 and has written extensively about embedded processing and medical electronics. He was a winner of the Jesse H. Neal Award for his story, “The Making of a Medical Miracle,” about implantable defibrillators. He is also the author of the book, The Supermen: The Story of Seymour Cray and the Technical Wizards Behind the Supercomputer, published by John Wiley & Sons in 1997. Murray’s electronics coverage has frequently appeared in the Chicago Tribune and in Popular Science. He holds a BS in engineering from the University of Illinois at Chicago.

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