Beam design is a very important part of the job of any connector design engineer. Not being an engineer myself, I will grossly oversimplify, but I hope you will find the conclusions to be helpful and satisfying.
Beams need to perform a couple of functions, including:
- Contact must have lead-in to ensure the parts mate smoothly and completely
- Deflection of the beam when mated creates contact normal force that is sufficient to ensure good electrical contact under all mating conditions.
- This beam deflection also provides added mating tolerance
I told you I would oversimplify. Achieving these functions under all conditions throughout the life of the connector is far from trivial. Design engineers first need to choose an appropriate contact material that has the right spring properties. There are hundreds of copper alloy formulations in the metals catalogs, each having different compromises for machine ability, formability, conductivity, spring characteristics, and corrosion resistance. Connector contacts must not degrade during their life when exposed to heat.
For example, automotive engine compartment connectors need to withstand continuous exposure to temperatures up to 140°C. The designer must also choose contact materials that are safe during manufacturing, normal use, and disposal.
Other characteristics of the strip material also come into play, like purity and surface smoothness. The raw material must be consistent in thickness and how it performs during the stamping operation. One of the reasons that you will find that specifications in catalogs call out “Copper Alloy” rather than a more detailed material specification is to give the connector manufacturer the flexibility to use different alloys from different suppliers that offer comparable performance. This flexibility ensures competitive pricing and continuity of supply.
Connector designers then use a lot of creativity to meet the prime functions while dealing with other constraints, like size, electrical performance, signal integrity, and system reliability. Here are some examples:
Single beam contacts provide the simplest and least expensive contact form. You will find these frequently in edge card connectors and memory card contacts.
Single beams can be improved with shapes like this where the wrap-around contact provides a better lead-in, more gentle mating force, and better long term reliability. Longer springs are a good thing, but they require more room and cost more than simple beams. You will most often find these in the kinds of connectors used in the appliance industry, office equipment, and a multitude of wire-to-wire and wire-to-board connections.
The apex of using long beams with redundant contacts was the Serpent contact used up until the 1990s to connect IBM mainframes together. These connectors could tolerate thousands of mating cycles without degradation. I suspect they are still in computer rooms around the world today.
A typical dual beam contact provides better reliability by having two mating points on opposite sides of the mating pin. Balanced forces from both sides are good and perform very well in high vibration environments.
Bifurcated beams mating on one side of a mating blade allow for higher density while ensuring excellent reliability. These designs are preferred for higher speed electrical performance because the contact geometry causes less of an impedance discontinuity.
Signal integrity considerations are driving modern high speed— greater than 25 Gbps connector beam designs. Traditional contacts where the contact mates to a pin or blade typically have the pin extend 2+ mm beyond the mating point. At speeds greater than 25 Gbps, this creates an electrical stub causing electrical reflections that are quite disruptive to optimized signal integrity. One design uses two hermaphroditic beams that mate with each other in a way that minimizes this stub.
Connector designers continue to use their knowledge of contact physics and material properties to optimize connectors to assure long mating life, optimized signal integrity, and competitive cost.