Page 43 - 2021 High-Reliability, Harsh Environment Connectivity eBook

Fine-Wire-Spring Contacts: One of the earliest solderless interposer designs made use of fine-wire-spring contacts. Often referred to as Fuzz Buttons, a registered trademark of Custom Interconnects, fine-wire-spring contacts are constructed of gold-plated molybdenum or beryllium copper wire wound and compressed into a dense, sponge- like cylindrical shape with diameters ranging from a few tenths of a millimeter to a millimeter. These contacts have simple, single-piece designs that help lower costs and increase reliability, and they also offer the tightest pitch of the different interposer contact types. However, they don’t offer wiping action during engagement, which is critical for removing foreign object debris (FOD) or oxidization from mating pads, and they require careful handling since there is no retention mechanism to hold the contacts in place.
Spring-Loaded Contacts: Also known as spring-loaded pins, spring probes, or Pogo Pins, a registered trademark of Everett Charles Technologies (ECT), these solderless compression contacts are typically made up of several machined components, including internal helical springs that apply constant normal force against the back of the mating receptacle or contact plate. These springs are what gives spring-loaded compression contacts the unique ability to engage with any flat or concave metal surface, whether it’s incorporated within a mating interface or just a plated area of a PCB.
A typical spring-loaded pin consists of three main parts: a plunger or piston, a barrel, and a spring. When force is applied to these pins, the plunger compresses the spring within the barrel. These types of pins enable certain interposer designs that are not achievable using other connector solutions, are available for cable terminations, and are ideal for applications where the contacts will be exposed to the outside environment. However, each of the pieces that comprise these contacts adds another potential point of failure, with the most common failure mode being seized springs that prevent contact. In addition, these are often the most expensive option and, like fine-wire- spring contacts, also don’t wipe across the mating face during engagement to remove potential FOD or oxidization.
Ball-Spring-Loaded Contacts: A specific version of spring-loaded contacts, ball-spring-loaded contacts replace the traditional plunger with a ball that supports omnidirectional mating and are ideal for connections with a rotational feature, like twist-and-lock connectors. Due to their omnidirectional mating design, these contacts do perform wiping action on mating surfaces, just not as strongly or effectively as some other interposer types.
Spring Contacts: Spring contacts were some of the earliest compression contacts. These single-piece contacts have a literal spring form factor but generally incorporate either a braided spring or an elastic coil with the contact design. Spring contacts also tend not to deliver any lateral wiping movement across mating faces, and their geometry can be detrimental to signal integrity performance in high-speed and high-frequency applications.
Compression Contacts: More modern interposer designs have incorporated simple, single-piece compression contacts, which are designed to both leverage the most beneficial qualities and overcome the limitations of previous designs. Single-piece compression contacts simplify the design of spring-loaded contacts by incorporating integral spring members, which eliminates the multiple potential points of failure inherent to spring-loaded contacts and enables both very high contact densities and lower costs.
One of the most unique features of these contacts is their ability to be ganged up within the same slot in an interposer body. This can be done to create multiple points of contact for added redundancy in especially high-reliability, harsh- environment applications, or to increase the rated amperage of some contacts within the interposer.
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