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Why Use Spring Probe Technology

 

Blind Mate Capabilities

One of the key benefits inherent in probe design is the ease of blind mating. Being essentially single-sided in nature, a mating counterpart is no longer required – hitting a target pad or terminal pin eliminates this requirement while allowing a simpler, more rugged interface.

Additionally, interfaces can be non-axial, sliding or rotating in nature – providing a durable, high bandwidth signal path with the ease of a blind mate interconnection.

Applications where Smiths Connectors’ blind mating ability offers added value:
  • Radar Systems
  • Navigation System
  • Medical Equipment
  • Military Electronics

Compliant Connectors

Smiths Connectors’ one-piece compression mount connectors are custom engineered for your specific application. Benefits of compliant or compression mount connectors:
  • Excellent for blind mate applications
  • Virtually transparent signal paths
  • Designed for dual side compression mount, single side surface mount or  single side cabled connection
  • Extremely versatile and flexible in design 
Smiths Connector offers a variety of off-the-shelf spring contact probes and has even more "custom" probes designed specifically for our customers' connector applications.  Design flexibility of IDI spring probe connectors starts with the probe.

Spring contact probes offer design flexibility in all aspects of design:
  • Pitch - Center to center mounting of .010" (0.25mm) and above.
  • Tip Geometry - The contact tip is designed to provide the most reliable connection for the given application.  Tip geometries range from radius tips to more aggressive penetrating spear tips, and many other geometries in between.
  • Spring Force - The spring force can vary from under an ounce to several ounces.
  • Overall Length and Compliance - The overall length of the probe and the compliance or travel are interrelated.  In a longer probe design, more compliance is possible. The overall length of
    the probe can be less than .130" (3.3mm) with .015" (0.38mm) travel or greater than 1.500" (38.1mm) with .400" (10.16mm) travel.
  • Materials and Platings - IDI has a wide variety of materials and platings we utilize for our spring contact probes depending on the application.
Connector designs also offer a variety of design options:
  • Impedance Controlled through coaxial probe design or through field array population pattern.
  • High Bandwidths through short signal paths or impedance controlled designs.
  • Mounting Options:
    • Surface Mount - The probe barrel can be designed to easily accommodated surface mount applications.
    • Thru Hole Mount - A flange can be placed in virtually any location of the probe barrel for thru hole mount or we can design a probe with a tail.
    • Wired or Cabled - The probe barrel can be designed in a number of methods to accommodate wire or cable attachment - either done by IDI or at your facility.

Excellent Electrical Properties

High Frequency
It is vital to appreciate the RF electrical performance of a connector is not a singular, simple value, but a function of the entire RF system. Leveraging our experience in the ATE and Semiconductor markets, our proven spring probe technology enables a new ground breaking approach to high frequency interconnects, which deliver significant benefits to the customer while reducing component count and increasing system life.

Our connectors provide a single sided compliant contact that can directly mount to strip line or PCB tracks while enjoying mating cycle lives of over 100,000 and bandwidths greater than 20GHz. Significant gains in circuit density can also be achieved on centers as tight as .010 (0.25mm). 

Low and Consistent Resistance
Smiths Connectors probes and custom connectors are designed to provide consistent, low resistance, dependably first-cycle, every-cycle. Low resistance is a major benefit of spring probe technology. In the spring probe, the total contact resistance is determined by two primary factors:
  • The bulk resistance of the material
  • The internal contact resistance between the plunger and barrel
These sources of resistance can be engineered in the probe design to keep the total contact resistance low and stable, minimizing fatigue both internally and externally, throughout the life of the contact.

Another method used is to insure that current flow is continuously low is a technique called “biasing”. Biasing is the mechanism that forces the plunger against the internal wall of the barrel.
Four different biasing techniques that can be used in spring probe design:
  • The first method of biasing is the bias spring. The spring is designed to force the plunger to the barrel. This is the least aggressive method of biasing and is a cost effective and sufficient design for many applications.
  • The second method of biasing, a more aggressive approach, is the bias plunger. An angle is cut on the backside of the plunger. The spring bears against this angle, forcing the plunger to the internal wall of the barrel.
  • The third method of biasing is the patented eccentric drill design. This biasing technique involves back-drilling a plunger intentionally off-center creating a lateral force for the spring to press the plunger wall to the wall of the barrel. The eccentric drill design allows for a larger spring cavity, which provides greater compliance or travel in a shorter, more compact probe design.
  • The fourth and most aggressive biasing technique is the bias ball. The bias ball is similar to the bias plunger but with the added value of a ball bearing between the spring and the plunger. The ball bearing aggressively forces the plunger against the barrel wall providing the lowest and most consistent resistance for the most demanding applications. 

High Insertion Life

Almost three decades ago, Smiths Connectors developed spring probe technology to assist the toughest interconnect customer in the electronics industry… the test engineer. Our test customers have relied on our spring probes to perform up to a million cycles, in demanding, no-clean, contaminated environments.  In the semiconductor testing arena, our probes may cycle over 50,000 times within just a couple of days.

In the early 1990’s, Smiths Connectors’s probe technology gained wide acceptance by product designers looking for “first-cycle, every-cycle” reliability over the life span of their products. Our connectors allow for a higher and more consistent spring force that will remain constant — from the first cycle to the millionth cycle. They are extremely rugged and compact, and are able to deal with wiping interconnect motions as well as harsh environments. Mechanical features are designed into the probes to make PCB mounting simple, whether by wave, hand, or reflow soldering processes.
 

Robust Mechanical Properties


Spring contact probes were originally designed for testing printed circuit boards in the late 1970's. By nature of their design, spring contact probes are extremely robust.
 
  • Cycle life in excess of 500,000
  • Contact force remains stable throughout the life of the probe
  • Able to withstand nonparallel compressions - side loading or rotation during compression
  • Tip configuration is easily designed to provide the best mating surface for each application

Resistance to Shock and Vibration

Smiths Connectors’ spring probe connectors provide outstanding resistance to shock and vibration, surpassing the limits of conventional connector technologies. In an effort to provide designers with the documented evidence that probe technology is meeting the challenge under these harsh conditions. IDI Probes that were evaluated by Contech Research, an independent test and research laboratory, under shock and vibration from 3.14G to 9.26G exhibited:
  • No evidence of physical damage.
  • No contact interruption greater than 1.0 microsecond.
  • Resistance remained low with an average change of 4.9 mΩ.
The requirements for the shock test were that there be no evidence of physical damage to the test samples, no interruption greater than 1.0 microsecond and initial and post test change in low level contact resistance shall be measured and recorded. The requirements for the vibration test were that there be no evidence of damage to the test samples, no contact interruption of greater than 1.0 microsecond and the change in low level contact resistance shall be measured and recorded.