Choosing Connectors for Test Fixturing (Test Adapters)

 

If Your Device Under Test Has

Your Fixturing Should Have

Discussion

Contacts that oxidize (such as silver, tin, or nickle) Pins that can scrape or poke through the oxide on the contacts. You'll find test block pins may need to use spring-loaded contacts.

When you use contacts that can oxidize, you'll find the fixturing connector must work harder to scrape or poke through the (usually non-conductive) oxide. Your fixturing pins need a higher contact pressure or a longer wiping distance. This increased pressure or wiping distance causes your fixturing connector to wear out sooner. You'll find the connector on your device under test also wears out quicker.

Spring loaded pins can focus the contact force on a tiny spot and break through the oxide without damaging the contact. These pins tend to last longer than standard contacts and the spring-loaded pins are usually replacable.

Contacts with "gold flash" Connectors with gold plated contacts. 15 to 30 micro-inches of gold plating works well. Gold flash is extremely thin. If the gold flash on a contact wears away the contact's base metal will be exposed. Usually this base metal will oxidize and create a poor contact. If your fixturing contacts have a thick layer of gold plating, you'll reduce the wear on the gold flash contacts. Oftentimes a connector manufacturer will offer a few contact plating options for a connector. Select the option with 15-30 micro-inches of gold plating.
Contacts with gold plating Connectors with gold plated contacts. 15 to 30 micro inches of gold plating works well. Gold plating on both connectors generally gives the best results. If the connector on your device under test and the connector on your fixture both have 15-30 micro inches of gold plating, you'll find your fixturing lasts thousands of cycles.
Pins Select sockets made with gold plating over beryllium copper. Sockets wear out fast. They tend to lose their elasticity and tension. Once the tension starts dropping,  you'll begin having intermittant or high resistance connections. Beryllium copper holds up well. It maintains its tension and elasticity for more cycles than other metals.
Sockets Avoid stamped pins that have sharp edges. Use beryllium copper pins  when the pin diameter gets near 0.025".

You want to use pins that have properly formed corners. Some stamped pins have a sharp metal flash on the edge of the pin. This flash can cut or wear the socket. Poor quality pins often damage the sockets.

As the pin diameter gets thinner you'll want to select a stonger pin. Beryllium copper pins work well when the pin diameter gets near 0.025".

Replace Your Adapters Before the Wear is Severe.

Even when you follow the above guidelines adapters will wear out. If adapters wear out fast, consider using our Replaceable Connector Adapters.

Your regular maintenance schedule should verify your adapters are not worn out. Also, if you notice an increase in intermittent or high resistance connections you'll want to check your adapter. See our Adapter Testing page.

Inspect adapters regularly for damaged contacts. A damaged pin in an adapter can cause damage in the assemblies you are testing.

These rules are generalizations based on the problems of contact wiping action, micro-fretting in tin based contacts, and fatigue in spring forces in female contacts. There are exceptions where you may get thousands of mating cycles on an adapter that violates these rules. This can be learned with experience but usually does not justify the time and attention needed