Shrinking Connectors Create Challenges and Opportunities
By Bob Hult, Bishop & Associates Inc.

We may be living in the age of big homes, big cars, and huge federal deficits, but “small” has been a key objective in the electronics industry for many years. Computing power that once required room-sized equipment now fits comfortably in the palm of your hand. The promise of Moore’s law has given us multicore processors that provide functionality and speed only dreamed of a few years ago. The ability to reduce feature dimension on a chip—from 90 nanometers to 65nm, 45nm, 32nm, and eventually 20nm—continues to provide the roadmap to cramming more transistors into smaller spaces.

While chip dimensions are shrinking, wafers are becoming larger, which results in more die per wafer and lowers the cost per chip. Intel recently showed a 300mm diameter wafer using a 32nm process that will allow each chip to contain 1.9 billion transistors.

Chip scale packaging, including system on package (SOP), has reduced the physical size of electronic devices as well as the number of interconnects required. In many cases, a single ball grid attached (BGA) device has replaced a pluggable printed circuit board module. Those interconnects that remain must often be small enough to fit in a tiny amount of space.

The continuing process of increased computing power in smaller devices has influenced all product categories, from advanced avionics to a host of consumer products. Mobile devices, focused on the consumer segment, demand interconnects that offer extreme circuit density, low profile, durability, and rock-bottom prices. In some applications, traditional I/O connectors have become one of the largest components in the box.

Two equally important factors challenge the high-density connector developer: The connector must be designed for mechanical durability and  have the ability to maintain stable contact resistance in harsh environments. As contacts become smaller, tiny contacts fabricated from thin materials are typically more fragile. The ability to design a contact structure that ensures adequate normal forces and wipe at the separable interface becomes critical. Smaller conductor cross-sections result in correspondingly higher bulk resistance. Low signal levels demand minimal loss from resistance. System designers are also looking for ways to distribute increased power in smaller contacts. Connector manufacturers have introduced new copper alloys that feature greater conductivity, while maintaining adequate spring characteristics. Tiny contacts fabricated from thin materials can also pose serious challenges to designers of fully automated connector assembly machines, which are necessary to achieve high production rates at a lower cost.

Digital clock rates continue to increase into the gigabit/second range. Contacts placed in closer proximity are more susceptible to crosstalk, which can distort low-voltage differential signals. High-speed connectors may require the addition of integrated ground planes to electrically isolate differential pairs, but they reduce the effective signal density. Connector designers must take each of these factors into consideration when developing new high-density interfaces.

In the past, pin grid array connectors with contacts on 1.0mm pitch were considered high density. Today, flat flex connectors offer some of the highest density separable interconnects, with centerlines down to 0.2mm circuit pitch and a connector height of only 0.7mm.

High-density, low-profile FFC connectors have become the primary interconnects in many consumer products, including cell phones, tablet PCs, game controllers, and portable audio devices.


Traditional stamped-and-formed two-piece contacts have served the industry well for many years, but the demand for tighter packaging density may require a fresh look at alternatives.

Several unique spring contact configurations have been developed over the years to address the issue of density. Looking at the IC production and test socket markets for the future is a logical choice, as this industry has faced the challenge of high pin count and signal density for many years. Precision-stamped contacts have been utilized in a variety of land grid array sockets where high pin count and density are critical. 






The Cinch iQ™ contact offers low compression forces with centerlines down to 1mm pitch.








The cLGA LGS socket from InterCon Systems uses a simple C-shaped contact that provides compressive connection between pads on a device and the PCB.

Rather than formed contacts, some connectors now use flat stock using fine blanking technology that results in smooth edges, and allows the use of the edge as the mating surface. These contacts can provide very narrow, high normal-force contact points on reduced centerlines. Even smaller contacts can be formed from very thin stock using chemical etching techniques.







Mezzanine architecture, where printed circuit boards are stacked over each other, has become very popular. A host of new stacking connectors have entered the market, including those that use traditional stamped-and-formed contacts.

In order to further reduce contact centerlines, suppliers have developed assemblies that consist of a matrix of compressive contacts in a PCB interposer.








Neoconix offers a unique PCBEAM interconnect that can be used in board-to-board, board-to-flex, and board-to-device applications. A contact density to 0.8mm, with a compressed height of 0.25mm, is possible.





Stacking heights as low as 0.014-inches can be achieved using Fuzz Button®-type contacts. Connector assemblies are available from Custom Interconnects and Cinch Electronics.

Several unique metallic contact systems have been developed to address high-density applications. Manufacturers have introduced a variety of spring structures in multiple shapes that offer low profile, high normal force, redundant points of contact.

The search for extreme density is driving consideration of even more exotic interfaces. Years ago, IBM investigated connectors that utilized contact pads consisting of hard dendritic spikes of palladium. This interface proved to have a very limited mating cycle life and created some serious planarity problems.

Another approach replaces individual metallic contacts with metalized particles in a non-conductive matrix. The Paricon Pariposer® consists of columns of conductive particles in a dielectric polymer material.

Contact pads, on as small as 0.1mm centerlines, can be connected using this concept. The need to provide tight registration is also minimized, with two or more columns providing redundant contact per pad.

Tyco Electronics offers their MPI system, which consists of metal particles embedded in elastomeric material. 

Truncated columns of this material are molded onto both sides of a thin alignment board, creating a low-profile elastomer interposer.





Another unique interconnect from PITek is based on the use of very sharp metalized particles that are electro-deposited as bumps on conductive pads. When pressed between mating surfaces, these particles deform and penetrate oxide surface films to establish gastight electrical connections.






Research continues as demand for high pin count, high-density connectors continue to grow.

Molex currently offers their Plateau HS Mezz™ Connector System using a plated plastic housing. Gold-plated precision molded contact fingers could offer some unique advantages over stamped and formed metallic contacts.

Researchers at Interuniversity Microelectronics Centre in Belgium recently fabricated elastic interconnections by embedding horseshoe-shaped metal wires in an elastic base material

Additional low-force contact designs currently being used in the semiconductor wafer probe industry may provide some clues on how connector contact density can be increased. The MicroSpring contact from Form Factor is an example of this technology. Its contacts offer low force, low profile, low resistance, and fine pitch. Contacts are fabricated using micro-machining technology

New products based on microelectromechanical systems (MEMS) assembly technology have entered the market in medical, automotive, and consumer applications. As an example, 3M recently released details of a micro projector designed to fit inside a mobile phone or gaming device. It is only 0.5-inch thick, but is capable of projecting a 40- inch VGA image. Internal and I/O interconnects must offer comparable density.

Developing separable interconnects at comparable scales will be a major challenge to the connector industry. Rather than measured in millimeters, it is entirely possible that future interconnects may be measured in µm. A strand of human hair is about 100 μm wide.



Research into MEMS electrical contacts is being done at a variety of companies and Institutions. The Imperial College in London has developed a MEMS separable connector using electro-deposited photo resist on a silicon substrate. Ten-position connectors on 250µ centerlines have been demonstrated with contact only 200µ wide. Initial measurements indicated contact resistance of only 30 milliohms.




The ability to fabricate prototype subminiature connectors via fine-line high-resolution stereo lithography assembly (SLA) equipment is becoming available. Connectors with features as small as100µm have been produced. Advanced laser control and organic polymers are enabling the ability to fabricate complex 3-D structures with resolution of 100nm or better.



Bishop & Associates Comments

1. New products in nearly all market segments are demanding higher pin count connectors on smaller centerlines.

2. Semiconductor fabrication and packaging technology has eliminated the need for many board-to-board internal interconnects, and allowed the shrinking of the box, reducing the space available for traditional connectors.

3. Flat-flex connectors offer some of the greatest contact density today, and are commonly found in personal communication and entertainment devices.

4. The connector industry may be nearing the practical limits of traditional stamped and formed metallic contacts, and has begun exploring alternatives.

5. Faster clock rates can create signal distortion challenges with small centerline connectors.

6. Small profile connectors minimize cooling airflow obstruction, but often carry reduced current ratings.

7. We are in the very early research phase of exploring entirely new interconnect schemes that can support MEMS scale devices.  

Robert Hult
Director of Product Technology, Bishop & Associates Inc.
Robert Hult has been in the connector industry for more than 36 years. Hult began his career as a sales engineer for Amphenol. He joined AMP in 1972 and served in several management positions through 1996. In 1997, Hult joined Foxconn as group marketing manager for Intel in Chandler, Arizona, U.S. Prior to joining Bishop & Associates, Hult was the regional application engineering manager for Tyco Electronics.

Hult graduated in 1968 from Bradley University with a bachelor of science degree in electronics technology and a minor in business.