Interconnect quality and reliability play a fundamental role in determining overall system quality and reliability. By choosing precision parts, engineers can create an interconnect solution optimized for the unique requirements of each application.
Connectors play a critical role in the electrical systems of just about any product we can imagine, yet the interconnect requirements are frequently considered at the end of the product design phase. The impact of an interconnect is often appreciated only when poorly manufactured or incorrectly specified connectors fail, eroding system performance at a minimum and possibly bringing the system to a halt. For designers, however, advances in connector design, materials, and manufacturing ensure availability of an interconnect solution well matched to each individual application.
The quality and reliability of an interconnect directly influences system performance and reliability as a whole. Indeed, the selection of a suitable connector depends on a design’s performance requirements, configuration limitations, operating conditions, and working environment. For example, the connector requirements for a healthcare application are dramatically different from those for a deep mining application – yet each requires maximum reliability from the connector.
If connector selection is not given proper consideration, the entire application may be subjected to performance and reliability breakdowns. In fact, today’s innovative connectors are high-precision devices, carefully designed and manufactured using a variety of high-conductivity alloys, application-specific platings, and high-temperature, high-strength housing materials.
One of the main components of connectors and discrete interconnect systems is the pin receptacle. Pin receptacles are made by press-fitting stamped and formed “multi- finger” precision contact clips into a machined shell (Figure 1). This style of contact has proven to be an extremely reliable and consistent way to connect critical components.
Manufacturing and Materials
The receptacle itself is a product of precision machining and specialized alloys designed to match specific application requirements. For precision connector lines, high-speed Swiss turning and CNC machines produce parts across a wide range of sizes while holding very tight diameter tolerances of ±0.0005 inches (and even tighter for some applications). Internal stamped finger contacts provide connections for mating leads ranging in diameter from 0.008″ to 0.102″ as well as square and rectangular pins.
Using advanced machining capabilities, interconnect manufacturers such as Mill-Max can offer receptacles with many termination styles, including press-fit, solder-mount, compliant press-fit, and swage mount, and wire termination options including solder cup, crimp, forked, and bifurcated. These same manufacturing capabilities allow creation of specialized receptacles suitable for pressing into plated through-holes in printed circuit boards. Here, polygon press-fit features such as a square, hexagon, pentagon, or octagon are machined on the body or tail of the receptacle – providing stress relief when pressed into the plated through-hole on a PCB. Press-fit features are typically held to a tolerance of ±0.0005 inches to help maintain consistency during the press-fit operation, which is especially important if the application calls for solderless press-fit.
While precision manufacturing allows for a wide range of shapes and sizes, the materials used for interconnect manufacturing endow these parts with specific performance and manufacturability characteristics optimized for different application requirements. A variety of alloys are used in the manufacturing of machined electrical interconnects – mainly copper-based due to their high conductivity – from highly ductile brass to high-strength beryllium alloys.
Brass is most commonly used as it exhibits excellent machinability, is suitable for a wide variety of applications, and is cost-effective. Phosphor-bronze is more ductile, useful when additional strength and bending resilience are required. For higher-current applications, tellurium-copper’s high-conductivity characteristic (93% IACS at 68°F) provides a low-resistance electrical path that produces less temperature rise.
Depending on the desired size and force characteristics, the internal contacts are three-, four-, or six-finger designs stamped from either beryllium-copper alloy C17200 (HT) or beryllium-nickel alloy 360. Beryllium-copper has emerged as the standard for the majority of applications thanks to its excellent strength, spring characteristics, durability, and conductivity. Beryllium-nickel exhibits similar properties and is particularly suitable for use in high-temperature environments above +150°C.
In more advanced interconnect systems, beryllium-nickel contacts fit into the same receptacle shell as their beryllium-copper counterparts and can be specified as a design evolves from the workbench to the field. In fact, this type of configuration flexibility is increasingly important to designers. With more sophisticated interconnect solutions, engineers can test their interconnect designs, modify interconnect strategies, and even switch to different connector materials and sizes without redesigning the overall interconnect design.
For applications that require optimal environmental protection or for PCB press-fit applications, gold-plated shells and contacts are typically the right choice. Because both the outer shell and internal contact are individually plated in interconnect systems, the design engineer has the flexibility to choose tin, tin/ lead, gold, or silver plating based on economic and engineering considerations.
For example, tin- or tin/lead-plated shells with gold-plated internal contacts are a cost-effective option for solder-mount receptacles that accept gold-plated mating leads. Despite the different combinations of metals, the gas-tight press-fit between the contact and shell eliminates the chance of oxidizing interactions. This gas-tight connection ensures that no corrosion arises at the contact-shell junction due to environmental conditions such as high humidity or exposure to gases.
In addition, some interconnect platforms allow designers to change pin sizes due to the wide mating lead acceptance range built into these products. While some interconnect systems have a fairly tight lead acceptance range of 0.004 inches, enhanced interconnect contacts have a much greater range, generally 0.010 inches, with larger contacts exhibiting a range up to 0.020 inches in some cases. The wide acceptance range of receptacles translates into greater tolerance on the mating lead size and position – a useful option when a device, mating board, module, or cable undergoes an unexpected change in pin design or specification. Thus, if a piece of equipment is initially designed to receive a cable of a particular size, and that cable is revised to use larger or smaller pins, the wider acceptance range available in a versatile receptacle design may easily support the change in specifications.
A flexible interconnect platform also allows engineers to choose higher- or lower-force contacts for most mating lead sizes. In one system, for example, 32 of the 39 contacts have at least one alternative force option. Lower forces are desirable for applications such as high-pin-count interconnects; delicate, soft, or flexible leads or wires; socketing leaded glass-sealed (hermetic) devices; and to ease field replacement and repair in tight spaces.
Conversely higher forces are desirable for ruggedized applications facing high shock and vibration, fretting corrosion, high-current connections, and long-term static connections. In addition, higher-force connectors can help overcome oxides caused by environmental conditions, which is especially advantageous in circuits with low currents.
Interconnect quality and reliability play a fundamental role in determining overall system quality and reliability. For designers, highly developed interconnect systems provide a broad array of solutions, precision-machined from alloys designed to meet varying needs for ductility, manufacturability, strength, and temperature resistance. Drawing on these precision parts, engineers can create an interconnect solution optimized for the unique requirements of each application.
To read this white paper in its entirety, including application-specific information on medical, LED lighting, and rugged applications, click here.
This article was provided by Mill-Max.