Insulation displacement contact (IDC) and press-fit or compliant pin technology have proven to be two of the most reliable contact systems in critical automotive applications for well over a decade. Utilized in systems including airbag, engine, and transmission control units (i.e., vehicular computers), these high-reliability contacts provide continuous gas-tight or cold-welded terminations throughout the life of the vehicle.
To achieve these ultra-reliable connections, each contact goes through different levels of both elastic and plastic deformations during the wire or PCB insertion process. Once in the final seated position, both IDC and press-fit contacts apply continuous force to achieve high-contact integrity especially designed to withstand extreme temperatures, shock, vibration, and thermal expansion.
IDC connections are made by inserting a solid or stranded wire in a specific diameter between opposing contact tines that are dimensionally matched to the wire gauge. When intended for use in demanding environments like automotive applications, these tines are typically made of phosphor bronze, as this material exhibits superior fatigue resistance over extreme temperature and deflection ranges. During the insertion process, the individual wire strands are physically altered as they are compressed into the corresponding “U” slot of the contact. The material thickness and contact geometry of the IDC tines provide enough elasticity to smooth out the forces generated during the wire insertion process. This prevents the tines from cutting into individual conductors and weakening the connection. The opposing tines then maintain a high level of wire compression force to provide a continuous gas-tight connection capable of surviving extreme environmental conditions.
Electronic modules and wire terminations in automotive applications are often encapsulated with potting compounds to weatherproof and protect them from moisture, dust, dirt, and chemical ingress. Traditional elastic-only contact systems, which only utilize a compression spring, cannot guarantee that potting material won’t migrate into the contact joint during the potting process, or later as a result of thermal expansion. Failures in spring-force-only connections frequently occur after longer-term use and not visible during the assembly process. In contrast, properly designed IDC terminations eliminate the possibility of potting material leeching between the contact and the conductor under any circumstance.
Press-fit pins are inserted into plated-through-holes (PTHs) on PCBs (Figure 2) and, during this process, experience the very same elastic and plastic deformation as wires in IDCs. The unique eye-of-the-needle geometry of press-fit pins and the inherent properties of the phosphor bronze material they’re generally made of provide sufficient flexibility to deform and compress during the insertion process. This flexibility sufficiently prevents any damage or scarring of the PTH, which can jeopardize the long-term reliability of the connection. Once mated, these active, high-opposing-force contact systems adjust as needed to maintain high-integrity connections in even the harshest conditions.
Over the past few decades, vehicle lifetimes were extended by several years. At the same time, vehicle electronic systems have continually become more sophisticated. As a result, the hand-soldered connector systems that were long standard in the automotive industry—even in critical systems including master/slave cylinders, clutch servos, linear and rotary actuators, gear shift and throttle systems, and gear control units—began to fail due to age or solder embrittlement. In response, the automotive market has switched many connections over to press-fit technology.
The design, development, and integration of IDC and press-fit contact technologies into connection systems are backed by many years of experience. IDCs were developed in the early 1960s, and compliant pin technology emerged in the late 1970s. Both were introduced to market as computer-level connection systems and then went through several different iterations of geometry and material selections as they morphed into the high-reliability, industry-proven automotive wire and PCB-level connection solutions they are widely recognized as today. Both IDC and press-fit contact systems are also almost always made of phosphor bronze materials, which exhibit superior high-reliability performance characteristics and are available in various grades or compositions (e.g., CuSN6, CuNiSi, and STOL78) that can be adjusted to suit individual end-customer application requirements, including temperature extremes, enhanced conductivity, and challenging tensile or yield strength requirements.
A new generation of connectors that combine these two high-reliability contact technologies was recently released to market. Featuring the perfect marriage of materials and contact geometries, these new combined IDC/press-fit connectors deliver double-ended, gas-tight, wire-to-board (WTB) connections especially designed to satisfy the demands of both current and future harsh-environment automotive applications. This evolution from individual solutions to a combined connector system (Figure 3) provides automotive design engineers with rugged, high-reliability solutions for discrete WTB connections that are based on decades of proven performance in automotive applications and deliver the robust mechanical reliability, process repeatability, and cost savings that this market demands.
One of the most significant advantages of this innovative new contact system is it eliminates the need for costly two-piece connector systems in demanding, harsh-environment applications that currently rely on elastic-only, spring-force contact systems. These new IDC/press-fit combination connectors were also especially designed with dual-assembly methodologies in mind. They can be pre-installed on PCBs during the board build process, allowing wires to be inserted and pressed into place with any standard flat-rock seating tool upon final assembly, or pre-installed on wire harnesses, allowing them to be pressed into PCBs upon final assembly. This second process is especially suited for use in applications subjected to conformal coating processes, as the PTH pattern can easily be covered with Kapton® or another tape with similar removal properties during the coating process and, post removal, allow the connector harness to simply be pressed into place.
Combination IDC/press-fit contact technology is available in standard WTB configurations and new packaging options designed for connecting two PCBs in close proximity, but not in the same orientation or alignment location as required by traditional board-to-board connectors. These types of connections are often made with an FFC/FPC cable, which jumps between two zero-insertion-force (ZIF) connectors. However, while functional, ensuring the proper manual insertion of the full depth of cable into these types of connectors requires special care and inspection, especially in high-vibration applications in which the actuator could potentially open up. In these instances, the IDC/press-fit combination connectors can establish reliable connections with easy-install jumper assemblies, allowing automotive engineers to eliminate even more expensive, two-piece connectors from their systems. Another advantage that the new combined connectors provide over FFC/FPC connectors is the ability to use multiple color-coded discrete wire gauges (18–24AWG) to address higher current-carrying capabilities up to 10A, which is critical for electromechanical devices and systems that turn electrical power into motion and can facilitate easier and more traditional wire dressing and routing throughout a vehicle.
The evolution of individual IDC and press-fit connector technologies into a combined solution that capitalizes on the high-performance phosphor bronze materials and proven contact geometries of these proven technologies provides automotive engineers with a new generation of interconnects especially designed to deliver the robust mechanical reliability, rugged performance, and cost savings that automotive electronics applications demand.