Where in the world do connectors fit?

Whether you design or purchase connectors, understanding connector technology and discussing technology trends requires a basic look at where connectors fit into the world of electrical/electronic applications. This article explains that relationship.

Unlike other components - such as resistors, capacitors, diodes, or even ICs - whose purpose is to change the state of electron flow (eg, resist, store or switch electrical energy), connectors are connecting points with passive metallic conductors or optical fibres.

When plugged together, electrons or light is transmitted. When disconnected, there is an 'open' current between the disconnected contacts. Switches have similar properties except their connection points are inside the switch and have moving parts.

While connectors are designed for repeatable mating cycles, many are plugged in once during equipment assembly and just a few times afterwards. IO connectors need more mating cycles, but are not infinite.

Unlike other components, where the technology thrust is in using electronic materials that change the state of electron flow, connectors are based more on how to make a foolproof, reliable electrical connection - despite being exposed to contaminants, cable tension or vibration - while causing little or no signal distortion between the connected points.

The critical part of connector technology is in how well they hold connections over time.

One could argue that connectors are a simpler challenge than other components. In reality, their design is made non-trivial and also extremely diverse because of the huge variety of connector applications in virtually all equipment.

This almost infinite variety of 'mix-or-match' connector design requirements means that many, many individual connector designs are necessary to match the industry's diverse applications.

Industry standards are necessary because of this fact. In many ways standards are more important with connectors because they must mate with other manufacturers' products in many applications.

Connectors are used in package-to-board, board-to-board, wire-to-board, box-to-box, and wire-to wire applications, all of which influence technology trends in one way or another.

Electronic connector designs are influenced by the ever-increasing sophistication in circuitry (Moore's Law, high speed and bandwidth, and low crosstalk). The days when connectors were primarily a mechanical connection are gone.

Now, high-density contact technology, high-speed signal integrity and other parameters have added new and more challenging dimensions to connector design and its technological evolution.

There are many distinct areas of connector classification which greatly increase the types and varieties of technology required. Some manufacturers offer many of the following types of connectors, though others focus on only one or two specific connector areas. These areas of application can be loosely defined as follows:

• Small signal electronic circuits, eg, less than 1 A and 6 V, ie, digital silicon circuitry. Typically mA and low voltage with medium to high-density contacts;
• Connectors and sockets for production applications and others for test and burn-in - two distinct areas of connector technology. The former requiring low-cost and high-volume, the latter high-cost/high-mating cycles and typically lower volume;
• Higher voltage and high current in electronic circuits, eg, computer servers, telecoms, etc. More robust contact and housing designs, including mixed signal applications but still electronic, with minimal signal distortions;
• High frequency/RF microwave applications requiring coaxial or fibre connections. Typically machined contacts and housings for mobile radio, satellite and CATV applications. In this area there is an increasing number of applications that bridge the gap between metallic connectors and wireless connectivity involving Bluetooth, Wi-Fi or mobile antenna applications;
• Special applications such as medical ultrasound, marine, aerospace and broadcast - most of which fall into the electronics realm but require very specific parameters such as push-and-click stainless steel connectors for diagnostic equipment;
• 12-120 V circuits typical of automotive, appliance, HVAC, POS and other equipment. These are electrical applications involving design challenges similar to electronic connectors but often requiring harsh environmental parameters, many discrete wire connectors and wire terminals;
• AC power 110-240 V, 5-30 A premise wiring, ie, building power distribution. Industrial-grade power and HV circuitry, eg, power distribution, heavy equipment such as electric power generation, industrial process and transport.

This wide variety of applications dictates a broad definition of technology trends, far broader than can be addressed in this space. But, in one way or another, they must include the following core technologies.

Connectors have certain technologies that are at the heart of their design and manufacturing processes. These competencies are well advanced, with many years of experience to draw on. They are both technical and business related and can be generally characterised as follows:

Metals typically used for connector contacts include copper alloys (brass, phosphor-bronze, and beryllium-copper) and other alloy metals suitable for machined or stamped connector contacts and their metallic plating.

BeCu will be reduced due to toxicity, while CuNiSi and designer alloys will increase as a substitute. Eventually, the size limits of conventional stamped contacts will be breached in some high-density applications requiring chemical milling processes.

This will happen because conventional stamping reaches a barrier in the 5-10 mil range. Fine blanking and micro-mechanical fabrication will be more widely used.

In some cases, the contact edge will become the active contact surface due to high-density requirements. Long term, there will be semiconductor-like processes involving silicon bench/photolithographic tools.

Gold plating is preferred in connector construction, but is expensive, as is palladium. Both are heavily dependent on selective plating processes and the fluctuating cost of these metals. Many applications use a flash coating rather than micro-mm of gold.

Fine geometric control of selective plating is outpacing mechanical contact fabrication. Tin plating is widely used in low cost applications. Pb-free solder plating of connector solder tails and through-hole mountings will increase. Associated tin whisker issues are being addressed.

Critical issues involving fretting corrosion are well understood in the industry but there are limits to reliable contact design. Contact physics is the technology that binds and limits most applications.

One critical issue is between the wiping or scrubbing action with most linear or conventional pin/beam contacts and the area array z-axis compression contact physics applied to some LGA and contact-to-pad applications that require high-mating forces.

Thermal and micro-miniature packaging issues will emerge in connector manufacturing. Materials technology is typically a third-party development via Dow, DuPont, Hitachi, Honeywell or Shipley.

However, injection moulding of small, thin-walled precision parts is a sweet-spot requisite in the connector industry. A major factor in connector evolution will be fine geometric moulding and the use of inert moulding.

A key point here is the large variety of LCPs and other primary plastic materials and the constant possibilities for new developments that can be adapted to the connector industry.

Offshore assembly is influencing the degree and type of connector assembly and automation. A preferred methodology is flexible bench assembly, using low-cost labour to use semi-automatic equipment.

This avoids high capital investments for what are increasingly short product life cycles. Advanced in odd-shaped component placement will alleviate issues with applying connectors via SMT, although tape and tray packaging for automation will become increasingly important.

Higher melt temperatures will have an impact on connectors and other components, requiring some changes in encapsulating materials. This issue will go through a transition with the full force of electronics assembly behind it as lead-free becomes mandatory.

Design tools are adequate, but there will be increasing dependence on modelling and simulation tools in designing electronic connectors. This type of connector design will, in some cases, become primary rather than secondary to mechanical design.

In designing for manufacturability and assembly, the issue here is to design for the most cost-effective global manufacturing assembly possible. The discipline required to do this will elevate this requirement to one of major importance.

Global supply chain management is a business technology every bit as important as design, materials and process.

Outsourcing has become commonplace among OEMs. It will also be important to connector suppliers who must satisfy global OEM and CM needs.

The Restriction of Hazardous Substances Directive (RoHS) will have a noticeable effect on the electronics industry as we approach 2006. This will include:

• Lead-free soldering and solder coatings;
• Other lead-containing materials in PVCs, plastic colorants, etc;
• X-chrome, Cd, flame-retardants, Hg and other hazardous materials;
• Tin whisker mitigation for Pb-free coatings;
• Substitutions exist for other banned materials, including Deca BDE exemption;
• Labelling, date codes, part numbering systems and other logistics are being addressed. There is not an industry-wide consensus on part numbering issues;
• Increased costs associated with new logistics, materials and processes;
• All these issues are being worked in committee meetings.

Connector design and manufacturing is imbued with these core capabilities. Rarely do key industry design initiatives, usually backed by major OEMs or consortia, stray from this comfort zone. Connector design is broad and deep - there is no shortage of ingenuity in this industry.

By their very nature, electronic connectors are extremely adaptable to new application requirements. They display a constant array of improvements in both electrical and mechanical design made possible by their multi-component electromechanical assembly.

Cost technology is where the 'rubber meets the road'. Cost reductions of 2-5% per year are not uncommon. Cost reductions require design changes, new materials and processes that draw on all the technology resources that a manufacturer can muster.

In order of importance, here are some of the key factors affecting cost reduction:

• Low cost manufacturing regions, using direct labour, materials and benefits, engineering, management overhead, equipment, supplies, land taxes, shipping and other costs;
• 'Lights out' automation which may be applicable to long running, very high-volume designs such as RJ45, USB, etc;
• Global supply chain management, including the outsourcing of non-critical components and assembly operations;
• Business practices that maximise cost reductions, such as lean reorganisations, e-commerce, global design teams, and user co-located manufacturing plants.

A common denominator in manufacturing trends is simply determined by where the products are going to be used.

As OEM and CM manufacturing have migrated to China, for example, it is not only the lower labour costs in that region, but the fact that this is where customers are using the product. This produces the lowest possible cost where direct labour alone is but a fraction of the total cost.

There has been a tradition in the connector industry to do this. During the past few years this trend has accelerated dramatically and is expected to continue.

Specific areas of connector manufacturing trends include:

• Modular assembly - automatic in-process material handling in developed countries, and standalone operator-assisted bench stations in developing world countries (primarily China). These are/will use re-toolable process stations;
• State-of-the-art metal forming - both tool materials and design, implemented with inline assembly.
• Tight tolerance stack-ups - traditional assembly methods will become obsolete. The solution may be critical contact forming and insertion, controlled by adaptive servo controls. Measurements taken on the fly will automatically alter set-ups. Measurements will be direct, sensing critical component features/dimensions, or indirect, monitoring equipment/tool characteristics;
• Marking and packaging - integrating the connector component flow seamlessly into OEM/CM production control systems. Web-based access to networked machines, employing remote diagnostics with automated preventive maintenance. Solving RoHS and other traceability issues via date codes or other methods.

The 2004 iNEMI roadmap includes a chapter on connectors. One of the disciplines in roadmapping is the identification of barriers or roadblocks to the technological evolution required by other forces - such as size reductions, higher density, or higher performance. No significant barriers were identified for connectors. However, the view of some OEMs is somewhat more sceptical.

The chart summarises key types, applications and requirements. Most barriers will be overcome by continued evolutionary design and engineering advances, including cross-linkages to other technologies such as printed circuits, flexible etched circuitry and fibre optics:

Connector developments will follow OEM requirements. Key areas of development will include materials and process technologies, high-speed electrical performance and miniaturisation. Mobile/system-in-package interconnect requirements may drive future micro-scale robotic connector design, plus other dimensional requirements which are beyond the realm of conventional stamp and form/mould connector processes:

• BGA attachment for advanced area array SMT applications;
• 10-40 GHz and high-density connectors >100 signal contact per inch, both differential and single-ended signal applications or low pin count serialised interfaces such as USB 2.0 or PCI Express;
• High-speed copper cables (infiniband, fibre channel, 10 gigabit ethernet, etc);
• IC sockets (high I/O >1000 contacts on less than 1.27 mm pitch) such as the socket-T, LGA 775 at Intel. Sockets for IC test as the industry moves toward waferscale;
• High performance memory sockets, DIMM sockets may be inadequate for the next-generation memory bus signals. This will be dependent on PCB layout. DIMMs may have to go to a two-piece design for future advanced memory applications;
• Optical interconnects, though hobbled by the 2000-2004 telecom downturn, with board level lightwave packaging will become more important in future equipment designs. Recent developments in on-chip optical interconnect may be a sign for the future;
• Value-added connector assemblies will be of higher interest to reduce system cost and complexity and aid in outsourcing subsystems;
• Low cost wire-to-board connectors and small form factor designs will increase as consumer electronics merges with computer and telecom applications, (digital cameras, HDTV, DVR, flat panel displays, navigation systems, satellite radio and smart phones);
• New IC developments such as system-on-chip wireless connections will determine how the connector industry deals with these paradigm shifts.