Connector miniaturisation
Connectors continue to shrink in size but how much smaller can they really get?
The connectors in our phones, laptops and TVs all seem to be getting smaller and denser. Even the military is demanding smaller and lighter connectors for their portable electronics. Bob Stanton* from Omnetics discusses the factors that will enable further connector miniaturisation, as well as what limitations there might be.
It’s important to remember that different applications have different performance and reliability requirements. The low-cost products designed for home use are dramatically different from those designed for aircraft and deep space applications.
Technological advances have led to rapid development of application-specific connectors and size reduction. As circuit chip technology evolves, the chip performance and capability is improving. The evolving circuit chips demand much lower voltages and current flow but also run significantly faster, store and process substantially more data, and provide long battery life.
New software solutions facilitate easy modelling of smaller connectors, and CNC machines offer the ability to manufacture or cut out new shell sizes and shapes within minutes. These developments allow designers, who are bent on using every last millimetre of space on their interconnection systems, to create prototypes faster at a reasonable cost. Often, designers pick a standard connector off the web to begin their circuit testing but eventually require 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 a 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
Even 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 oftentimes protect from electromagnetic emissions and/or reception of other signal noise in and about the system. Some modern shielding tricks and/or filtering often allow for additional size reduction.
Environmental conditions
Ruggedised connector designs are often controlled by specifications that ensure continuous signal flow during high shock and vibration and/or performance during extreme heat and cold cycles. In some portable applications, connectors are subject to immersion, water spray and, in extreme cases, salt spray. Ingress protection ratings (IP standards) are 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 seals will be needed as the connectors continue to miniaturise.
Circuit mobility
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.
Standard designs are reviewed for potential fit and function, then tailored using solid model designs to meet both size and reliability requirements. 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. The trend of combining two or three connectors into one has now taken centre stage. Power, RF and digital signals are all run through one connector with isolation techniques to avoid crosstalk and EMI concerns.
The market
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 offers 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.
Larger connectors like the circular 38999 are now being replaced by smaller and lighter micro-circular connectors that use 0.050″ pitch. We are now seeing nano-circular connectors at 0.025″ pitch handling multiple high-speed signals well.
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.
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