Is Contact Wipe Important?
Yes. Contact wipe is a crucial element to examine during the interconnect design and development process. Qualification testing and understanding that sufficient wipe is achieved within a mated connector set provides confidence that interface surfaces will be cleaned of build-up and contamination in end applications. Interconnect companies, like Samtec, consider contact wipe during product development as it’s an inherent part of the connector design itself.
It is equally important to ensure contact wipe specifications meet application requirements during product design-in. Let’s take a moment to walk through exactly what contact wipe is and when considering it seems the most critical.
What is Contact Wipe?
Contact wipe is the mating length of the contacts during a typical mating/unmating cycle with the intent to clean the interface from build-up. Or, an alternative way to define contact wipe is: the insertion depth of the terminal in the socket such that oxidation or other foreign matter is wiped away.
Tin Plating, Removal of Oxide Film
Environmental factors in end applications play a role in contaminant build-up onto contact mating surfaces. Residue such as small particles from surrounding processes, corrosive oxide films (such as when tin plating is exposed to air or humidity), dust and oils can all interfere with electrical contact of the mating interface and cause connection failure. Contaminants being “wiped” away from the “contact” mating area during a connector’s typical mate/ummate process is necessary for maintaining proper signal connection.
Contact wipe is also extremely important in high-reliability applications that need to survive high vibrations and shock. In this scenario, contact point redundancy with proper contact wipe can also be extremely beneficial. Samtec’s Tiger Eye™ products, with multi-finger beryllium copper contacts, are a great example of this.
Stack Height & Contact Wipe
Stack height, or the distance the mated connector set creates between two PCBs, impacts mating length of the contacts. Therefore, distancing PCBs in a way that follows manufacturer’s board stacking guidelines and following minimum and maximum insertion depth allowances helps to confirm sufficient contact wipe is achieved. Tolerance stack-up may also impact contact wipe; therefore, a tolerance stack-up analysis is recommended.
Maximum (fully mated) and minimum wipe example using Samtec’s SEARAY™ .8 mm pitch products.
Low-Profile Connectors & Contact Wipe
Low-profile connectors are widely sought after in embedded or high-density designs. However, when considering contact wipe, the challenge is keeping the connector as small as possible (minimal wipe) but having enough mating length to perform the cleaning action. In addition, strategically placing gold plating at the contact point can minimize corrosion (since gold is resistant to oxidation) and provides a durable and low-contact resistance connection.
A previous Samtec blog (What Plating Option Is Best For My Connector?) does an excellent job breaking down the rationale of when different plating options are used. Spoiler alert! For low-profile fine-pitch connectors, gold is often the only plating option of choice since gold requires a much lower amount of normal force versus other plating options, such as tin. Selective Gold + Tin Plating is Samtec’s most popular plating option since it combines the best of both: reliability of gold + excellent solderability and cost of tin.
Product Impact & Testing
Contact wipe is a very important aspect of the interconnect design process for all board-to-board interconnect solutions due to its impact on signal connection and reliability in end applications. As a result, Samtec qualifies and documents contact wipe, terminal insertion depth and stack height information and makes it readily available to customers. This information may be found on samtec.com using our Series pages. Look under the “Prints” tab, then click on the “Mated Views” document. Using Samtec’s ADM6 Series as an example, here’s what to look for: Mated Views document.
That being said, if you have contact wipe questions on a specific Samtec product, please always feel free to reach out to our Application Support Group at [email protected]. Let’s have a conversation!
