“In some applications, connectors are mated during production. In other cases, the connector is an integral part of the device, such as in a docking station or charger. Every application requires a different solution. Properly applied connectors will work better and last longer than those that do not match the application. Gathering and using this knowledge is another connector-related challenge facing designers today.
In some applications, connectors are mated during production. In other cases, the connector is an integral part of the device, such as in a docking station or charger. Every application requires a different solution. Properly applied connectors will work better and last longer than those that do not match the application. Gathering and using this knowledge is another connector-related challenge facing designers today.
There are several ways to create pins used in connectors. The most flexible is precision machining. This not only provides a high level of quality and reliability, but also provides great flexibility in design and materials, allowing designers to specify connectors to meet their exact needs. The resulting high-precision pins have cylindrical geometries, sometimes referred to as turned pins.
Typical swivel foot sizes range from 0.008 inches (0.2032mm) to 0.250 inches (6.35mm). High speed turns consistently produce precision machined pins with tight tolerances of ±0.0005″ (0.0127mm) on all critical features critical to connector pin function. Not only is this process highly accurate, it’s also very repeatable—whether thousands or millions of pins are being made.
The main components in a spring loaded connector (SLC) are spring pins, sometimes called spring contacts, spring probes. They provide highly reliable, precision-manufactured interconnect solutions ideal for a wide variety of demanding applications. Each spring pin is precision machined to ensure a high quality, low resistance and compatible connector, which makes it superior to other technologies.
Spring pins typically consist of three or more machined parts that are assembled with internal springs to provide the desired range of motion. All of these components are plated with nickel-over-gold to ensure excellent electrical conductivity, durability and corrosion resistance over the life of the product. In addition to the basic electrical requirements for spring pin voltage capability, current handling, and contact resistance, there are many options to consider when specifying an SLC.
While vertical mounting is the most common arrangement, some applications require horizontal mating of two or more boards. Right-angle pins and targets are available in 0.1″ (2.54mm) or 0.05″ (1.27mm) pitch through-hole and surface mount configurations, providing a reliable, low-profile solution to this challenge. SLCs often need to carry power and signals within the same component. Standard power pins can handle up to 9A at 10°C (20°C) above ambient. In applications requiring higher current or lower temperature rise, the pins can be doubled, or larger pins can be specified, especially for ground connections.
By specifying spring pins with different lengths and plunger travel in an array, so-called make-before-break connections can be created. These are especially useful in applications where power needs to be applied to the circuit before a signal is connected, thus avoiding undefined states that can lead to erratic circuit behavior. These connections also allow critical signals to be readily patched as required by the application.
Depending on the mechanical configuration of the application, different travel distances and custom spring forces may be required. Most SLCs typically provide 60g of force at stroke, although alternative springs can be used. For complex multi-plate assemblies, double-acting SLCs are available. Once they’re mounted to the stacked mid-board, it’s easy to install boards above and below.
SLC is not limited to PCB applications. This versatile technology can also provide wire termination connections via pins with solder cups or crimp barrels. There are a variety of sizes on the market that can accommodate wire up to 16AWG with 9A current handling capability. SLCs with high temperature nylon 46 insulators compatible with most soldering processes can be used for connections through metal or conductive materials such as conductive housings or enclosures.
When designing in an SLC, it’s usually best to aim to operate around the middle of the travel range. Compression of 25-75% is generally recommended; however, some one-shot compression applications may allow for maximum compression. The best compression range is within 50-85% for ultra-thin spring pins with minimal travel capability.
The spring pins can mate with non-parallel surfaces, but it is important to ensure that the mating force is applied axially to the piston/plunger. Side engagement or side loading of the piston should be avoided as bending or cracking can cause damage to the piston or spring pins.
In applications where mating is less controlled, a good design approach is to incorporate standoff hardware or other features to provide mechanical support to avoid excessive compression of the spring pins.
One of the great benefits of SLC is its versatility and ability to work with a variety of surfaces. A good connection is made as long as the spring pin plunger/piston is in contact with a flat or recessed plated surface. This eliminates one aspect of traditional pin connector systems and reduces component cost, production time and complexity.
While mating with gold-plated PCB pads is the most common, other mechanical options are available to meet specific application requirements. For through-hole applications, dedicated nail head pins or target pins can be used. In surface mount applications, thin gold-plated target pads are available to provide a highly conductive, wear-resistant extension to the board surface. By combining spring pins with the appropriate target, different mating distances can be achieved to suit almost any application.
Poor connection quality due to poor design or wear has a negative impact on overall system reliability. Therefore, proven and proven reliability is critical when specifying the correct SLC for an application. Since its introduction in 1976, IEC 60512 has been the definitive standard for testing the mechanical, electrical and climatic properties of connectors. The standard specifies a number of tests to evaluate connector quality and reliability, including spring force, contact resistance, random, half-sinus and sinusoidal vibration, rapid temperature changes, dry heat, cyclic heat, cold, and current-carrying capability. These tests are extensive and can be performed on original parts as well as pre-cycled parts to ensure long-term reliability of the connectors in real-world applications. Some manufacturers use IEC 60512 as a benchmark, but add specific additional tests to reflect known applications or to address other potential weaknesses when technology changes.
When specifying an SLC, the designer should examine all available test data. Reputable manufacturers often introduce specific non-standard tests for certain types of connectors, which will provide designers with further assurance that the connector will work reliably in a certain application.
Another valuable criterion for choosing one brand of SLC over another is the availability of design support materials. Most manufacturers will provide a variety of tools, including detailed 3D models (for example, IGES or STEP) for rapid design models and PCB layout recommendations to ensure the correct land pattern is achieved for optimal SLC operation.
Versatile SLC connectors play an important role in supporting future technologies as innovation brings new product categories. One of the most popular SLC applications by far is the board-to-board connection between two or more PCBs. As product sizes shrink, high-end modular design methods are becoming more popular, and manufacturers are increasing the number of PCBs in their products. SLC allows multiple boards to be easily stacked because SLC accommodates tolerance stack-up, including minor misalignments due to non-parallel fixation or PCB warpage. Whether the boards are parallel, vertical or horizontal, the versatility of SLCs makes them a viable solution.
The limited space in today’s designs also means that blind mates are becoming more common. Misalignment of pins to sockets during bonding can result in damaged or bent pins, damaged contacts, and poor or missing connections. SLC is the ideal solution as no insertion is required. Connections are made when the plunger tip touches a conductive surface (usually a pad on a PCB or the surface of a target pin). These mating surfaces are typically larger than spring pin plungers, which further eliminates concerns about alignment and potential damage to components.
As more and more devices become portable, they rely on battery power and require frequent charging (usually in a charging cradle). The SLC is the perfect solution for battery charging in portable instruments and for docking handheld devices for data and power transfer purposes. They can be easily integrated into any system and are available in a variety of heights, travel and spring force options. The contacts employ plunger tips so the spring pins allow for blind mating and some misalignment when placing the battery or device in the holder. This makes it ideal for end-user connected applications.
Navigating all potential speed bumps in the signal path is critical when designing applications that take advantage of high-speed interconnects. The following factors must be understood and mastered: stackup, tolerances, via design, trace width, plating, and copper etch for optimal signal paths. Connectors should be included in any design checklist, and these connectors are often ignored. If not carefully inspected, connectors can seriously affect the signal integrity of the system.
The correct connector should provide several key elements:
Patch Impedance at Target Bandwidth
Insertion loss below target bandwidth
Reliable connection to PCB
Reliable connection to cable systems
To ensure that the connector can provide low loss and mating impedance to the signal, scattering or s-parameters must be looked at. S-parameters characterize a linear grid and determine bandwidth and circuit losses, revealing its performance potential. S-parameter data is provided by manufacturers as a way to characterize their connectors and should be the first criteria to consider when designing high-speed connectors. Designers should also convert and observe s-parameters in the time domain, as well as time domain reflectometry (TDR) plots, and look at the internal impedance curves.
Because connectors come in many varieties (eg, terminal types, internal signal lengths, materials, etc.), designers need to understand how s-parameter files are created. Before blindly putting a touchstone file into a simulation and trusting the results, it is important to ask the vendor several questions, including:
1. Do the pins you want mate with the emulated pins?
2. How are the other pins terminated?
3. What layout was used in the provided data?
4. Is there a stump?
5. What type of terminals are used for characterization? (e.g. plated through hole, surface mount, crimp)
6. How is the fixture embedded or what is included in the measurement?
7. Is this the exact part number I need?
Premium suppliers provide simulation and measurement-related data for each customer’s intended use, providing them with a more accurate assessment of a connector’s impact on the design and enhancing their confidence in the simulation data.
Another important criterion when choosing a connector is the PCB termination option. Connectors typically come in a variety of termination styles, including (but not limited to) surface mount, press-fit, and through-hole solder (PIH), each with their own unique advantages and disadvantages. Crimp terminals are very robust in construction and provide maximum retention and connectivity to the PCB, but also present serious challenges for high-speed applications. Sending signals from a high-density press-fit connector may require a high-level PCB that extends up through plated holes for the longest path to reach the connector. The elongated path and fixed diameter of the borehole can create significant discontinuities for higher frequency signals and can hinder high data rates.
Surface mount termination is more suitable for high-speed designs, and the mating impedance of the connector launch point allows for maximum flexibility. Designers can access the connector’s pads directly or use selected drill holes to provide a path through the PCB. Additionally, vias can be buried into the PCB or back drilled to reduce unused via stubs and improve the frequency response of crimp terminations. This termination method offers the greatest benefit for high-frequency designs, but is not necessarily robust. Surface mount connectors usually require some additional reinforcement, such as mounting hardware, to ensure a solid connection to the PCB.
PIH termination is a mix between the first two styles. Similar to crimping, PIH contacts have short, non-crimping pins that are inserted into the plated-through-hole footprint and soldered into place. The main difference is that it has a much shorter pin, and the drilled hole can be back-drilled to remove the excess stump on the signal. There are still challenges in making such high-density connectors into PCBs. Select suppliers offer these pins as short as 10mm, which can provide improved high frequency response and a robust connection to the PCB. Each termination type has some signal impedance discontinuities when transitioning from a PCB to a connector, and each gives the designer the freedom to change the degrees of freedom to minimize the impact of the discontinuity on signal integrity.
When choosing a connector for a high-speed design, it is also important to consider how the mating connector will be contacted. There are several methods of mating contacts, each with a unique set of advantages and limitations that affect the signal integrity of the overall design. Edge mount connectors are a popular method of mating contact. These connectors feature spring fingers that slide along the PCB pads for electrical contact at a single point, minimizing signal discontinuities, but can be detrimental (or require additional retention methods) in high shock and vibration applications. Many MSA standard designs such as SFP, SFP+, and QSFP use this type of electrical interface.
Crimp connections are more widely used in rugged applications. This fairly basic system consists of a female header with a socket and a male header with pogo pins. This mating category has two or more points of contact and can offer several advantages over the single point of contact provided by edge mount mating systems. Specifically designed for high-reliability, high-speed products, the multiple contact points shown in Figure 1 enable low contact resistance and signal inductance, as well as a reliable and durable connection that can withstand extreme vibration. However, pin and socket contacts can be longer than edge contacts, and if not designed properly, large discontinuities can occur. Therefore, it is critical to study the s-parameters and impedance maps provided by the manufacturer.
Figure 1: Airborn’s verSI® crimp pin and socket connectors provide robust, reliable, low-inductance connections in high-speed applications with extreme vibration.
Also, when designing for speed, it is important to consider throughput relative to footprint. Figure 2 compares two basic systems: one with 25G/lane QSFP connectors and the other with 10G/lane HD4 connectors. The resulting outputs (4320Gbps vs. 3600Gbps) demonstrate the superior density achieved through the connector design, with 10G HD4 connectors producing higher data rates than higher speed 25G QSFP connectors in the same bay system throughput, thereby saving on component and energy costs, and even data center square footage has more potential.
Figure 2: Designed for high density, AirBorn 10GHD4® connectors provide higher throughput than 25G QSFP connectors within the same bay system, resulting in component and energy cost savings.
Ultimately, designers need a strong, undisturbed signal from point A to point B, and the right connectors are a key element of this journey. After all, even the highest speed connectors are disadvantageous if they experience intermittent openings. Top quality suppliers offer a wide range of connectors to provide high speed and high reliability solutions, end-to-end channel solutions, work closely with customers to assess their individual needs and develop optimal interconnects with minimal signal attenuation solution. Designers have a variety of connectors to choose from, so pay close attention to linked data and choose wisely.