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Miniature, Microminiature, and Ultraminiature: How Small Can Connectors Go?

As connectors continue to shrink in size, we wonder how much smaller they can go. Bob Stanton of Omnetics discusses the factors that will enable further miniaturization, as well as what limitations there might be.

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24-pin double stack on .025" center connectors

24-pin double stack on .025” centers

What’s happening with connector sizes these days? The evolution of connectors in our phones and laptops, the change in TV connectors – all seem to be getting smaller and denser. Even the military is demanding smaller and lighter connectors for their portable electronics. The question is, how small can connectors go – miniature, microminiature, and ultraminiature.

We must remember this is a very broad industry and the applications that use connectors demand a number of performance and reliability requirements. Those products aimed at lower costs and home use are dramatically different from those needed for aircraft and deep space applications.

Application-specific connectors and size reduction have come on rapidly. Fueling the rapid change is a combination of technology advances. Circuit chip technology has driven us all to new heights in performance, capability, and demand. The evolving circuit chips demand much lower voltages and current flow but also run wildly faster, store and process significantly more data, and protect long battery life. Reduced connector sizes are easily modeled with the new software available and the ability to directly manufacture or cut out new shell sizes and shapes with CNC machines within minutes. These changes provide a faster prototype cycle at a reasonable price to designers that are bent on squeezing every last millimeter of space out of their interconnection systems. Often, designers pick a standard connector off the web to begin their circuit testing but eventually need a quick-design variation of that standard. Now many connector manufacturers offer online design consultation and/or two-day turnaround on new connector formats.

Connector size requirements, however, are often based on a few key application factors and performance constraints.

Electrical Current Load

Each connector contact must offer low resistance interface with its mate and carry enough electrical current to satisfy the circuit it is serving. Fortunately, current flow rate is reducing, which allows interconnecting elements to get smaller as long as they stay within a safe range for good performance, with some variations for power and signal surges. Often, the current limits are going to be set by the diameter of the wire in the cable because wire length times resistance will set the performance and thermal capabilities of the interconnection system.

Signal Integrity

As connectors and circuit modules squeeze into tighter spaces, circuits must still function independent of adjacent circuits. Designs must include protection against signal cross-talk and often times protect from electro-magnetic emissions and/or reception of other signal noise in and about the system. Some modern shielding tricks and/or filtering often provide additional size reduction.

Environmental Conditions  

nano circular breakaway connectors

Breakaway ruggedized waterproof nano-circular connector

Ruggedized connector designs for performance in extreme environments are often controlled by specifications that ensure continuous signal flow during high shock and vibration and/or performance during extreme heat and cold cycles, such as basic survival during significant thermal expansion or contraction in deep space.

In some portable applications, connectors face immersion and/or water spray and, in extreme cases, salt spray. Ingress protection ratings (IP standards) are often specified to meet international standards in moisture conditions. Elastomeric seal rings are often built into the connectors to ensure moisture does not penetrate the connector and enter into the circuitry. Smaller and smaller seals will be needed as this industry continues to miniaturize.

Circuit Mobility

Nano-circular with 46 pins and .025" centers

Nano-circular with 46 pins and .025” centers

Connecting an active chip technology placed in minute sections of portable equipment is an example of the demands on today’s miniaturization movement. Fitting interconnects into robotic hands, squeezing them into probe tips, adding cable to small weather satellites, and mounting cameras on soldier helmets are examples of the drive to squeeze more and more into portable electronics.

This is where size reduction begins. Standard designs are reviewed for potential fit and function, then tailored using solid model designs to meet both the size and the reliability functions. Pin-and-socket sizes are reduced to minimum sizes that meet the above criteria and still squeeze into the space allowed. Flat leads are used and can be reduced even further when some of the performance and rugged reliability requirements are reduced. Circuit design can also help by combining signal systems for fewer lead counts. Connectors being used as an assembly technique can be changed as the number of mating cycles is not a critical element. Recently, the evolution of combining two or three connectors into one has taken center stage. Power, RF, and digital signals are all run through one connector with isolation techniques to avoid crosstalk and EMI concerns.

The Challenge and the Market

As we see in our personal cellular phones, miniature connectors provide great performance, carrying charging power and signal routing in one element. This method of using a single flat-strip or lead-frame interconnection has led the way for higher-speed digital signal processing. Careful use of shape and spacing has allowed another level of high-density interconnection. Use of unique low-dielectric-strength insulator materials also allows size reduction as circuit speed increases and size decreases. Price and ruggedness continue to play key roles in how small we can design our connectors. Board-to-board connectors that use pins or press connections consume very little space and cause only minute aberrations in signal transfer.

The future of more ruggedized technology is advancing and we have yet to see how small we will go. We are currently seeing larger connectors like the circular 38999 being replaced by smaller and lighter micro-circular connectors that use .050″ pitch. More and more, we see nano-circular connectors at .025″ pitch handling multiple high-speed signals well.

Nano PZN connectors

Nano PZN connectors

There is also the latest trend, which employs flat array grid or interposer connectors. Companies like Neoconix are finding new ways to reduce connector profile height, size, and weight for highly mobile instruments. As routing limitations on the printed circuit boards are overcome, these high-density arrays will route flat flex-like cable into and out of highly stacked sets of boards to further reduce electronics’ size and weight. The key for us all is to know our application needs and the limits of how tiny we can go to still ensure signal integrity in our electronics.

Author Bob Stanton is director of technology for Omnetics Connector Corporation.

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