What is the basic appeal of an elastomeric contact ?
- Elastomeric contacts are very short.
- The potential bandwidth is very high.
- The unit cost per contact position is low.
What are the biggest concerns about an elastomeric contact ?
- The compression per contact position is very small.
- The durability of elastomers is limited at high temperatures.
- Elastomer contacts that use a high metal content can take a set.
- Elastomeric interconnects are very different.
What is unique about Paricon’s elastomeric contact ?
- The PariPoser® elastomer is a continuous flat sheet of an anisotropic conductive material.
- Most elastomer products used for contacts are discrete shapes (cylinders, cones, etc.) that have to be positioned at each interconnect location.
- Paricon’s products have a very low metal/elastomer ratio.
What is the basic structure of the PariPoser® elastomer material ?
PariPoser® material is composed of silicone and nickel particles. The nickel particles are aligned into columns by a magnetic field prior to the elastomer being cured.
What is the Paricon product lineup ?
Paricon offers materials, parts, subassemblies, or completely assembled interconnect products using a wide range of technologies.
PariPoser® material sheets
PariPoser® sheets on stretch frames
Hybrid PariProbe® parts and subassemblies
Assembled sockets and connectors.
What is a stretch frame ?
PariPoser® material can be attached to a frame like a tambourine. When this is done, the material is taut and can be handled more easily. It also increases the upper limit of the temperature operating range to 150°C.
What is a PariProbe® ?
A PariProbe® is a metal part or subassembly that is positioned on top of the elastomer. It is used to accommodate unusual shapes of a target (like a solder ball, or a recessed cavity).
What is a Hybrid PariProbe® ?
It is a spring pin assembly that is placed on the PariPoser® elastomer material (the yellow area in the image) to gain additional plunger travel when making contact with a target.
What are the typical lengths of Paricon contacts ?
PariPoser® material is available in the form of thin sheets. The thickness of the sheets range from 0.05mm (0.002”) to 0.38mm (0.016”).
If the PariProbe® options are used, the contact length will increase to about 1-2mm (0.040” – 0.080”). Spring pins are in the range of 3-20mm ( 0.120” – 0.800”) long.
What is the typical bandwidth of an elastomeric interconnect ?
The usual bandwidth rating of an interconnect is the frequency at which a signal has an attenuation of -1 dB as it passes through the interconnect.
PariPoser® material has two characteristics that have a favorable impact on bandwidth results. First, the length of a PariPoser® interconnect is very short. Second, each contact position has multiple conductive nickel particle columns in the elastomer material. The multiple particle columns lower both the contact resistance and the contact self-inductance.
The self-inductance of a contact is a simple indicator of potential bandwidth. The lowest self-inductance measurements (and highest bandwidth) come from a simple PariPoser® sheet. If the additional metal and spring components of a PariProbe® are included in the contact mechanism, the self-inductance value will increase and the potential bandwidth results will decrease.
If a long spring pin or stamped pin contact is used, the self-inductance increases even more.
Here are some reported bandwidth results as a function of self-inductance.
How much do elastomeric contacts cost ?
In large quantities, simple elastomeric material cost pennies per contact. In low quantities, the costs are quite high due to tooling, molds, and application engineering support.
Elastomeric interconnects are most cost effective when the number of contacts per assembly is high or the overall contact surface area is high.
What is pitch ?
Pitch is the distance from the middle of one contact target to the middle of an adjacent target.
Targets can be round, rectangular, or any shape. A target can be a PCB pad or a metal lead on a device. Targets can be recessed or protruding.
PariPoser® sheets are available in pitches from 0.1mm to 1.27mm.
Why are there nine PariPoser thickness options ?
To get the optimal performance from PariPoser® material, the diameter of the nickel columns has to match the pitch. A smaller pitch requires smaller nickel particles. A bigger pitch uses bigger nickel particles.
The PariPoser® material is engineered to have 6-10 nickel columns per target – as shown in the photo below. This is a top-down view of PariPoser® material on an array of circular targets.
What happens when the PariPoser sheet is compressed ?
When compressed, the elastomer moves like a balloon filled with water. The nickel particles in the columns bend along with the elastomer, but do not touch the adjacent columns. The uncompressed elastomer fills the interstitial voids between the targets.
How much compression is there in a PariPoser® sheet ?
PariPoser® material compresses by 30%-50% of its thickness.
Since there are nine material sizes, the compression range will be as little as 0.025mm (0.001”) to as much as 0.2mm (0.008”). For a 0.5mm pitch application, the compression is typically 0.05mm (0.002”).
If additional compression is needed, the Double PariPoser® or the Hybrid PariProbe® options can be employed.
How does the PariPoser® material compression convert to a force per target value ?
Each application has its own target geometries and force calculations. Typical Force vs. Compression curves for the Paricon technology options with a 0.5mm pitch are shown here. (The Hybrid PariProbes® will follow the Pogo Pin model, depending on the design of the Hybrid Probe.)
What Contact Resistance (CRES) can I expect ?
The columns of silver-plated nickel particles in the material will conduct current almost immediately at the start of a compression cycle, then stay at the target value for the full compression length.
At a compression of 30%-50%, the CRES is typically 10-30 mΩ.
What is the Current Carrying Capacity (CCC) ?
The typical current carrying capacity per contact location for the 1.0mm pitch PariPoser® material is 10A of continuous current with a temperature rise of 40 °C. This measurement was done in a laboratory environment in open air. The actual CCC for each application will depend on the conditions of the test fixture or connector.
In general, PariPoser® material has good current carrying capacity compared to spring pins and stamped contacts, because the electrical and thermal resistance is very low.
Small Hybrid PariProbes® or spring pins used for device testing have a CCC in the range of 1.5 – 3A. Spring pins designed for battery contacts (or power/ground interconnects) have a CCC of 3-5A.
When PariPoser® material is used as a DC interconnect, the rating for the 1.0mm pitch material is 30 A/mm2.
How does the PariPoser® compression compare to other elastomers ?
All elastomers compress about the same percentage of their length. (30% – 50%)
If an elastomer contact has a high metal content, it might not spring back to the original position (it might take a set). PariPoser® material is about 10% metal content.
How does the PariPoser® compression compare to spring pins ?
Semiconductor spring pins typically compress 0.3mm – 0.5mm. Interface spring pins compress 2mm – 3mm. In both cases, it’s about 10% of their initial length. But, it’s a lot more than an elastomer.
When the Hybrid PariPoser® option is employed, the compression values per contact position are about the same as a spring pin with an equal length.
What is the temperature rating of an elastomer ?
Elastomer material has a much higher Coefficient of Thermal Expansion (CTE) than metal. (About 35X higher) So, when a conductive elastomer gets hot, there might be unpredictable results as the elastomer expands much faster than the metal.
In general, conductive elastomers (including the PariPoser® material) are rated from -50°C to +100 °C. When the PariPoser® material is placed on a stretch frame, the rating goes up to 150 °C.
How durable is an elastomer ?
Pure elastomers are very elastic and will maintain their springiness for millions of cycles. Pure metal, can loose its springiness if pushed beyond the elastic limits – like crumpling a piece of aluminum foil.
Some conductive elastomers are made of 80% – 90% metal and only a small portion of silicone. These elastomers are not very durable, and tend to take a set.
PariPoser® material has about 10% material and 90% elastomer. Testing has shown that mechanical and electrical properties are consistent for millions of test cycles and over 12 years of continuous compression.
How different is an elastomer contact and a spring pin (or stamped pin) ?
When specifying and using an elastomeric contact, be sure to note these issues:
Range of motion per contact location
A good mechanical contact is measured in normal force per contact. (For most spring pins, the force is about 20-40 grams per contact.)
Mechanical contacts usually have a large range of motion that yields an acceptable force per contact location.
Elastomeric contacts have a small range of motion per contact location because the total thickness of an elastomer is very small.
Elastomeric contacts work best when the targets are flat. If the targets have strange shapes, or the devices are not flat, then some kind of a compensating mechanism has to be used with the elastomer.
High metal content elastomers don’t work as well as low metal content elastomers. Be sure to get that specification clarified.
Be cautious when using elastomers at high temperatures.