A PariPoser® Primer

PariPoser® material on a blue background

Introduction

This document is a collation of internal test data and independent reports. The actual reports and data are available to those who wish to examine them in greater detail.

 

Origin of PariPoser® Technology

The PariPoser® technology was developed at Bell Labs in the 1980s. Bell Labs anticipated the future needs of the electronic industry for higher speeds and increased densities, and knew that interconnects would play a big part in meeting those goals. When the lab was broken up in the 1990s, Paricon acquired the technology, the equipment, and the patents with the goal of commercializing the technology.

 

What it is ?

PariPoser® material is an anisotropic conductive elastomer. (It conducts an electric current vertically through the elastomer, but not horizontally.)

 

How is it made ?

Nickel particles (silver or gold plated) and silicone are mixed together, then placed in a magnetic field. The magnetic field causes the particles to line up with the magnetic flux lines. When the material is cured, the particles stay lined up and conduct current along the columns. The silicone between the columns acts as an insulator. The particle columns are formed uniformly over large sheets of the material, then the sheets are cut to the desired size.

A cross section of PariPoser® material

 A cross section of a particle

 

What good is it ?

PariPoser® material is good for high-speed interconnects, because it is so thin. It’s good for power interconnects because it has a high Current Carrying Capacity (CCC). It’s good for high-durability applications because the material does not take a set. And, it’s good in wet environments because it is impervious to liquids.

 

How does it work ?

When the material is relaxed, the nickel particles at the end of the columns stick out a bit from the silicone. So, as soon as contact is made, the columns of nickel particles immediately conduct current. As the material is compressed (typically <30% of the thickness), the nickel particles push against each other and the CRES drops down to about 10-20 mΩ.

 
Relaxed Compressed

 

Silicone has a unique way of compressing. It actually changes shape – like a water balloon being squeezed in your hands. To facilitate compression at the pad locations, there needs to be some adjacent area into which the silicone can squeeze. Typically, that area is the space between the PCB or DUT pads – as shown in the illustration below. The expansion areas need to be uncluttered (no solder mask, no traces, and no components).

To allow enough space, the combined height of the two PCB/DUT pads (or interstitial spaces) should follow these guidelines.

PariPoser® material does not compress much. But it doesn’t have to compress like a spring pin because the target CRES is reached after only 0.02mm (0.0008”) of compression. Spring pins require 10X to 20X more compression to reach their target CRES.

 

 

9 PariPoser® material versions: what and why ?

There are 9 versions of PariPoser® material. Each one is designed for a specific pitch.

 

The illustration below is looking down through a semitransparent sheet of PariPoser® material onto an array of circular PCB pads. There are 6-10 columns for each pad. (There are also many unused columns in the locations between the pads.)

 

If the pitch of the contacts (and the size of the pads) gets bigger or smaller, there should still be 6-10 columns of nickel particles for each pad, so the spacing of the nickel columns and the size of the nickel particles has to be adjusted for each pitch. (Small PCB pads need small nickel particles whose columns are more closely spaced.) Each column of nickel particles has 4-5 particles, so when the diameters of the particles change, the overall thickness of the elastomer sheet will also change.

 

Stretch frames

PariPoser® material can be attached to a metal or plastic frame like a tambourine. When this is done, the material is taut and easier to handle. It also has a higher temperature rating (up to 150°C). When not mounted on a stretch frame, the material’s temperature rating is 100°C.

 

 

Silicone has a CTE (Coefficient of Thermal Expansion) that is much greater than nickel.

When exposed to high temperatures, the silicone expands so much that it could push the PCB contacts away from the nickel balls. When exposed to low temperatures, the silicone contracts, but leaves the nickel particles in normal contact with the PCB pad.

Room temperature Hot temperature Cold temperature

 

When mounted taut on a stretch frame, the silicone is already a bit thinner than normal due to the stretch, and it takes more thermal expansion to create a problem.

Thermal cycling within the specified limits of -50°C to +150°C will result in very little variation in CRES. Actual thermal cycle results for 1.0mm pitch material are shown below.  The cycles were repeated many times with consistent results.In addition to the vertical CTE effect, there might also be horizontal expansion and contraction. The CTE differences among the interconnection materials (PariPoser® material, the PCB, and the DUT) might result in horizontal misalignments.

 

 

CCC (Current Carrying Capacity)

PariPoser® material has multiple short columns of nickel particles per contact position. This results in a low resistance and low inductance path for the current compared to most connector geometries.

 

CRES (Contact Resistance): Durability over 500K cycles and over Time

A common test of spring durability is to quickly cycle the contact for up to 500K cycles while measuring the CRES. For a test of 1.0mm pitch material, the average CRES remained at 5-10 mΩ for the full range of 500K cycles.

 

 

A lot of 1.0mm pitch PariPoser (used in a connector) was measured for CRES every year for 12 years without taking a set and with minimal changes to its CRES. The test was designed to detect a “set” of the material that could be measured in a change of CRES.

Alignment

The contact pads on either side of the PariPoser® material need to be precisely aligned. If they are not aligned, they might make a connection to the wrong pad – as shown below:

 

 

Stickiness

Silicone is slightly sticky. It feels like a yellow “post-it” note. This characteristic can be helpful during the handling of PariPoser® material – since it will tend to stay in the place where it is positioned. It can be a nuisance though, because small particles of dust are not easily blow away.

 

Handling & Cleanliness

All interconnects need to be clean – and PariPoser® material is no exception. Since the material is so thin and stretchy, cleaning contamination off the material has to be done delicately.

When handling the material, special care need to be taken to avoid contamination from Sulphur.

Sulphur reacts with the Silver plating on the particles to form Silver Sulfide – the same thing that is called “tarnish” on silverware.  Silver Sulfide has a high resistivity.  Sulphur compounds are sometimes found on clean room gloves and in hand lotions.

Since each application is unique, please contact the Paricon sales engineers for advice on handling and cleaning procedures for your project.

 

Normal Force

The integrity of a contact is often determined by the force exerted on a target by the contact. Spring pins typically have a normal force rating from 15 – 100 grams. Some high-power spring pins have a normal force of up to 200 grams. Cantilever beam contacts used in connectors typically have a normal force of 30 – 100 grams depending on the plating material and the degree of shock and vibration that will be experienced. In most cases, the contact geometry has a reduced-sized touch point that concentrates the force.

 

The integrity of a PariPoser® contact is determined by the pressure exerted on the target. The required pressure per contact target is 240 psi (171 grams per mm2). Since the size of the pads gets smaller or larger when the pitch changes, the amount of force per contact also needs to change to maintain the proper pressure.

 

This table will give you an idea of how to determine the force per PCB contact.

 

Low force might result in higher CRES, and high force might result in crushing the nickel particles.

 

The Force vs. Compression curve of an elastomer is very different from a traditional spring pin. To get the right force using an elastomer, the compression needs to be carefully calculated and controlled.

 

RF characteristics and simulations

 

Because of the potential benefits PariPoser material offers for high-speed interconnects, there have been many test reports done under many circumstances. Many of the test results were favorable at bandwidths of 40Gz – 60Gz. One experiment conducted at the University of Erlangen in Germany, reported favorable attenuation results ( < -1 dB) up to 110 GHz.

 

There have also been many simulations conducted under many different circumstances.  The simulation of only the PariPoser material and the PCB pads starts with this kind of a geometry. The green columns are the nickel particles and the red circles are the PCB/DUT  pads. Some of the pads are assigned to be Ground, and some are assigned to be Signal.

 

Variables that impact the simulated RF results are pitch, material thickness, size of the particles, pad shape/size, the ground/signal patterns, and the traces used to approach the pads. Some typical ANSYS HFSS simulation results done with standard Paricon design standards and a pattern of one signal surrounded by eight grounds are summarized below:

 

 

The simulated curves for the 0.4mm pitch material:

 

 

 

Further simulations with different patterns of PariPoser® configurations can be done at specialized signal integrity consulting firms. For a complete simulation study, all the trace geometries to/from the PariPoser® material have to be included.

 

Comparison of PariPoser® material to other conductive elastomers

 

Some conductive elastomers use small diameter, insulated, cut wires.

 

Some conductive elastomers are made with conductive plugs that are inserted into a non-conducting carrier. The carrier might be a polyimide sheet or a layer of non-metallic elastomer.

 

Comparison of PariPoser® material to Spring Pins

 

PariPoser® contacts are much shorter than spring pins, and have the potential for very high bandwidths.

PariPoser® contacts have a low CRES and limited compression per contact location.