The race to cram more functions into smaller spaces has been the spark that has driven every electronic component manufacturer to find ways to reduce the size of their products. To a large degree, this evolution has been driven by the dramatic advances in semiconductor technology. Chips, that at one time consisted of a single gate, have evolved into integrated circuits and microprocessors that feature millions of transistors on each die, enabling logarithmic increases in computer power in much smaller spaces.

The quest for greater packaging density continues as the industry develops silicon process technology—evolving from 90 nano meter to 60 nanometer features, with the most advanced devices now utilizing 45 nanometer technology. Bringing computing power into such tiny packages has enabled the advent of multicore processors and multi-gigabit flash memory. Single board computers are now embedded into a wide variety of equipment. The functions of a daughtercard are now available on a single chip, while system-on-a-chip technology has becomes reality. Products that include high-performance laptop computers, personal digital assistants, multifunction cell phones, GPS systems, automated external defibrillators, inventory tracking devices, and games are now portable devices that require small, user-friendly envelopes.

The shrinking of electronic systems has impacted every component in an end-product, including connectors, both internal and I/O. Connector centerlines have gradually migrated from 0.31” X 0.62” posts on 0.156” centers to .025² “ posts on 0.10” centers, to today’s flex circuit connectors that feature contacts on 0.3mm centers. Connectors with reduced centerlines not only enable smaller devices, but also can provide many more circuits per linear millimeter, another demand of advanced equipment.

The current generation of microprocessors feature more than 1,200 contacts, a number that would be impossible to interconnect without high-density zero insertion force land grid array sockets. Active elements on a chip that are physically closer to each other facilitate faster processing speeds and are driving the demand for even denser packaging.









Interfaces of every type have been influenced by the trend of reduced component profile.




Stamped-and-formed crimp contacts continue to shrink to smaller centerlines.

Nano connectors—with up to 266 twist-pin and socket contacts on 0.635mm centerlines and attached to 30 gauge wire—are available from suppliers such as ITT Electronic Components, Glenair, and Omnetics. These separable interfaces are often found in mil/aero, as well as medical equipment applications.

Connector termination methods have also evolved to address greater contact density. Through-hole wave soldered contacts were replaced with compliant pins and pin-in-paste configurations. Surface mount attachment is being considered to avoid large diameter vias that can introduce distortion and make board routing more difficult. Many connectors today are offered in soldered, compliant pin, and surface mount configurations. High-density mezzanine connectors, for instance, are attached to the printed circuit board using ball-grid arrays.

Cinch and others have introduced connectors that utilize compression contacts as an alternative to traditional through-hole soldered or compliant pin attachment.

Backplane connectors that typically feature open pin-field contact grids on 2mm² are giving way to high-speed/density interconnects that often feature integrated ground planes between differential pair contacts on centerlines of 1.5mm and less.

Reduced contact centerline spacing allows designers to address increasing line counts, while reducing the overall size of the product. High-speed electronic systems packaged in smaller envelopes offer shorter circuit path lengths and can result in reduced signal loss and distortion.

On the other hand, moving high-speed contacts closer to each other may result in greater crosstalk unless carefully designed shields or pin assignment is utilized. Very dense low-profile connector housings can assist in managing heat buildup within the system by creating less obstruction to cooling airflow.

The ability to utilize available space between daughtercards makes mezzanine card architecture very attractive. Exceptionally low-profile stacking connectors allow parallel boards to be connected with as little as 1mm stacking heights. Suppliers such as Samtec have specialized in developing extensive offerings of high-density mezzanine interfaces.

The popularity of wireless devices has greatly expanded the market for tiny MMCX coaxial connectors, which are often utilized in PCB to antenna applications.

Portable entertainment, as well as data storage products, must be small and lightweight, which often leaves little surface space available for I/O connectors.

The standard RS-232 connector has been almost entirely replaced by much smaller connectors, such as standard, mini, and micro universal serial bus (USB) interfaces.

Internal disk drive connectors have quickly evolved from the parallel ATA, 40-conductor wide ribbon connector format to the 7-pin Serial ATA assembly, which offers greater bandwidth in a smaller cable, is easier to install, and does not obstruct airflow.

The trend to even greater circuit density will continue to put pressure on interconnect systems. Traditional metallic stamped and formed contacts inserted into molded plastic housings may be reaching their practical limits. Connector manufacturers are exploring new high-density contact designs that withstand mechanical and environmental abuse. Selectively plated plastic technology could eliminate the need to insert contacts in housings and eliminate failures from unseated contacts. The elimination of lead from contact plating, as required by a host of recent environmental mandates, has elevated the problem of short circuits caused by the formation of tin whiskers on small centerline tin-plated contacts. Alternative interconnect technologies, such as conductive polymers, metalized particles, or flex-film-based connector systems, may allow smaller contact centerlines, but each brings it own set of challenges.

New connector structures using materials now emerging from nanotechnology may provide the path to next-generation high-density interconnect systems. Connectors using nanomaterials, such as carbon nanotubes, may offer high conductivity interfaces on micrometer centerlines.

Miniaturization of electronic products has been a characteristic of the industry since its inception, and will continue to stimulate the connector industry to develop smaller, more efficient separable interfaces in the future.

Bishop & Associates Comments

• Market demand for smaller electronic products has driven the connector industry to introduce new connector families with reduced profiles.
• Traditional stamped-and-formed metallic contacts may be reaching the practical limits of manufacturability, requiring new fabrication techniques to be developed.
• Smaller contacts in tiny housings are more susceptible to damage, particularly in consumer applications. Less robust contact designs on smaller centerlines also raises concerns about tighter tolerances required to insure proper mating without damage. Each of these issues will have an impact on the reliability of new interfaces.
• Consumer demand for greater portability of devices, which range from consumer entertainment to medical diagnostic equipment, is adding pressure to develop smaller and lighter devices that may expose I/O connectors to a wide range of potentially damaging environments.