Elastomeric connectors for PCB connection and test supports - Connecteurs élastomériques pour les connexion entre PCB et les supports de test - compelma

The what, why and how of elastomeric connectors for printed circuit board (PCB) connection and  test supports for electronic cards.

Micro-electronic assembly requires more and more connection density on more and more reduced spaces.
Electronic connections are so done by connector more and more little and dense.
That is for these assemblies that elastomeric connector has been designed. These elastomeric connectors ensure a high density connection (0.05mm pitch between two contact points) and are assembled mechanically (without soldering) by compression.
These elastomeric connectors ensure a connection between sets, even without precise alignment.

Elastomeric Connector - Connecteur Elastomériques - COMPELMA

What is an elastomeric connector?

An elastomeric connector is a connector made with a silicon base, with an alternance of conductor and electric isolating layers. Elastomeric connectors are assembled mechanically without soldering within electric assemblies.

Those elastomeric connectors are also named ZEBRA connectors. This name is a reference to the alternation of black and white strip, reminding the animal.

Elastomeric connector’s not conducting areas are composed of neutral silicone (not charged). The silicon is the basic material because of its excellent properties of aging, its chemical stability, its electric reliability, and its mechanic behavior concerning chocs and vibrations.

Conducting areas are composed of:

Charged silicon : Carbon/Graphite or Silver (a lot more unusual)

Representation of an elastomeric connector carbon charged type (ZEBRA Type)
Side view of an elastomeric connector (silicone) - Vue partielle d'un connecteur élastomérique - Compelma
Standard dimensions of elastomeric connectors (silicone charged Ni/C or Silver)
Specification of elastomeric connector with silicone - Spécification d'un connecteur élastomérique en silicone - Compelma

Gold plated Beryllium Copper wires (the electric conductivity is better whit these elastomeric connectors)

Drawing of an elastomeric connector with gold plated Beryllium Copper wires
Representation of an elastomeric connector - Représentation d'un connecteur élastomérique - Compelma
Standard dimensions of elastomeric connectors (Beryllium Copper)
Dimensions of elastomeric connector - Dimesnions d'un connecteur élastomérique - Compelma
Standard specifications of elastomeric connectors (Beryllium Copper)
Dimensions of elastomeric connector - Dimesnions d'un connecteur élastomérique - Compelma


It also exists a variation with a lateral connection, particularly adapted for connections from LCD screen to PCB or for PCB to PCB with higher currents.

Drawing of an elastomeric connector with gold plated Beryllium Copper wires (lateral contact)
Representation of an elastomeric connector with beryllium copper wires - Représentation d'un connecteur élastomérique avec des fils en cuivre béryllium - Compelma
Dimensions of elastomeric connectors with gold plated Beryllium Copper wires (lateral contact)
Specification of elastomeric connector - Spécification d'un connecteur élastomérique - Compelma
Specifications of elastomeric connectors with gold plated Beryllium Copper wires (lateral contact)
Specification of elastomeric connector - Spécification d'un connecteur élastomérique - Compelma


This alternation of charged silicone and neutral silicone is done on Z axis, in the case of elastomeric connectors in line.
It is possible to add layers of isolating silicon on both sides of the connector to increase its rigidity and/or isolate it from sensitive components and electric tracks nearby. This isolating silicon thickness on the side of the elastomeric connector is from 0.05mm minimum to 1.5mm thickness. The hardness of this silicon can be adjusted according to applications.

For this type of elastomeric connector in Z axis, the ratio between the height and the width must be at least 1.5mm to guarantee the mechanical resistance of the connector.

Insulation of an elastomeric connector - isolation d'un connecteur élastomérique - Compelma


The alternation of conductive and non-conductive strips can also be done on the XY plane, in the case of matrix connectors. It is then equidistant contact points with the same metrics (0.05mm pitch and diameter of 0.03mm minimum) as an elastomeric connector on the Z axis.

Representation of a matrix elastomeric connector - Schéma d'un connecteur élastomérique matriciel - CompelmaElastomeric connector with matrix - Connecteur élastomérique matriciel - Compelma


In these two configurations, materials used still the same (neutral silicon, and charged silicon and/or Beryllium Copper wires).

How does elastomeric connectors work?

The density of the alternating contact areas is very high on this type of connector (0.1mm pitch or 0.05mm in standard). This density is much higher than the connection tracks on PCB or on a LCD connection for example. Consequently, each track on the PCB will be in contact with at least one conductive area from the elastomeric connector, and there will be at least one isolating layer between two tracks of the PCB. So, the risk of short circuit is null.

The assembly of an elastomeric connector is done by mechanic compression.

Compression of an elastomeric connector - Compression d'un connecteur élastomérique - Compelma

Metallic particles mixed with the silicon make it conductive and create thousands of passages that conduct electricity. This phenomenon is reinforced by the slight compression of the connector. Non-conductive silicon isolating areas isolate the different contact points to avoid short circuit on the PCB.

How to integrate an elastomeric connector in your electronic assembly?

Without this type of positioning structure, the connector risks not to be in contact with electric tracks because of connector’s buckling or movement on the PCB.
Elastomeric connector must be assembled with a mechanic holster to guarantee the positioning of conductive areas with PCB tracks or captors.

Mechanical holder for elastomeric connector - Structure mécanique pour l'assemblage de connecteurs élastomériques - CompelmaAssembly of an elastomeric connector between 2 PCB - assemblage d'un connecteur élastomérique entre 2 PCB - Compelma

The connector is compressed to ensure the contact. Elastomeric connectors with charged silicon can be compressed more than elastomeric connectors with wires.
The recommended compression is from 5% to 25% maximum. However, elastomeric connectors with wires risk to be deteriorated mechanically if the compression is too high. For these elastomeric connectors, it is better to be close to 10% maximum.

We will see below how to dimension correctly an elastomeric connector.

Why are elastomeric connectors used?

Elastomeric connectors are made from non-abrasive materials (neutral silicon and conductive one). These materials do not damage areas in contact on PCB or on LCD screen for example. Natural silicon resilience ensures a lot of compression cycles(assembly) and decompression (disassembly) without risk to damage the mechanic of the elastomeric connector.

So these elastomeric connectors are widely used for high-density connections between two parallel PCB, or to connect captors or interfaces (microphone, loudspeaker, LCD screen).

Custom integration of an elastomeric connector - intégration d'un connecteur élastomérique - Compelma

One of the advantages of high density of contact points on elastomeric connectors is the possibility to convey mixed signals with a unique elastomeric connector.

Elastomeric connector assembled - mixed signal - connecteur élastomérique - signaux mixtes - Compelma


The reliability and the process of manufacturing of these elastomeric connectors are a reason of the wide range of application. These connectors are widely used for consumer applications (economic and low cost) as well as for on-board flight calculators with high added value.

Some examples of application of elastomeric connectors

Elastomeric connectors in payment terminals:

Our major customers use these elastomeric connectors to ensure electric connections in payment terminals. In these assemblies, elastomeric connectors are integrated in the plastic frame of the equipment. So, they guarantee the electric contact in an environment submitted to shocks and vibrations (example of a payment terminal for bank cards).

Elastomeric conector on a terminal paiement - connecteur élastomérique dans un terminal de paiement - compelma

Elastomeric connectors on test support:

The high density of connection of elastomeric connectors make them a good technical solution choice for test supports of PCB. Especially matrix elastomeric connectors.Pitches of 0.1 or 0.05mm offer large possibilities of contact points accessible simultaneously in permanence without risk of short circuit. Unlike mechanical touch tips, which have to be adjusted,targeted and are much localized (and bigger).

The composition of elastomeric connectors, mostly made from silicon, allow it to withstand several thousand of cycles of compression/decompression without deterioration and without imposing strong mechanical stress on contact points of the PCB.

test connector - elastomeric connector - Connecteur de test - connecteur élastomérique - CompelmaSupport de test électronique (PCB) - Connecteur de test - elastomeric connector for test support - Compelma

Elastomeric connector integrated in a custom and waterproof flexible connector

Elastomeric connectors offer ample possibilities of customization on connectors. They can be integrated into a frame to make a plug with high density of contact points. The silicone base also ensures a high water tightness level IP (to fluids and particles) that we do not find with mechanical connectors. This functionality makes it a strategic choice, especially on connectors for medical application.

Custom sensor with elastomeric connector - capteur custom avec un connecteur élastomérique - compelma

Why use an elastomeric connector rather than a mechanical connector?

In more and more dense electronic assemblies, electronic mechanical connectors and other contact points are quickly limited. Moreover these mechanical connectors (often pin or tip systems) do not allow to reach densities and a precision of connection as high as elastomeric connectors.

Elastomeric connectors also simplify electronic assemblies (with lower tolerance limits),while reducing costs (no tooling cost) and lead time (not tips conception or custom pins).

Elastomeric connectors, made from silicone, also have much higher mechanical resistance to vibrations and shocks compared to pure metal connectors.

In terms of cost, unlike mechanical connectors, there is no tooling cost required to produce elastomeric connectors. So, the more the pitch and space requirement are tight, the more the elastomeric connectors are a pertinent solution. Technically and economicallys, compares to mechanical connectors.

elastomeric connector - connecteur élastomérique - Compelma - Holder mécanique

How to dimension and choose the right elastomeric connectors?

Elastomeric connectors are made on request according to the specification of each application and configuration. This manufacturing process give more possibility of integration of these components into the electronic assembly.

Maximal dimensions are limited. Around 120-150mm length, 5mm wide and 10-20mm high. These limits are however rarely meet on electronic assembly.

Length of the elastomeric connector

The elastomeric connector must be sightly larger than the space between the first contact track and the most distant one.
We recommend to make it overpass by 0.5 or even 1mm more on each side to ensure the electric contact.

Width of the elastomeric connector

The elastomeric connector width must be determined by 3 parameters:

- Reliability: The contact pad must be sufficient

- Strength: The larger the elastomeric connector is, the more significant the compression strength will have to be. So be careful not to over-dimension the connector.

- Stability: you will have to find the compromise to avoid that the connector buckles (bend) when assembled in compression and to avoid a significant compression strength and bulk risks.

Effort de flambement - elastomeric connector - connecteur élastomérique - compelma

The formula for the calculation of the recommended width is:

Width = Height / 2.5 (recommended between 1 and 5mm).

Calculation of the electric resistance of an elastomeric connector

The track width and so the global length of the elastomeric connector can also be determined by the required electrical resistance of the connector (depends on the contact area size).

For an elastomeric connector with carbon loaded silicon, the calculation of the resistance will be as follow:

R = ( 60 x H ) x (Ew x W)

With:
W = Width of the elastomeric connector
Ew = Width of the conductive area of the conductor (conductive silicon only)
H = Height of the elastomeric connector

Height of the elastomeric connector:

Elastomeric connectors must be sightly compressed to ensure the electric contact, limit gaps in assemblies and to support vibrations. For elastomeric connectors composed exclusively of silicon, the recommended compression goes from 5% to 25% (the global height of the connector also affects the compression rate).
So, the height indirectly depends on the necessary compression strength to compress the elastomeric connector.
To calculate the necessary compression strength for elastomeric connectors in charged silicon, you can use this formula:

F = 9 x D x W x L x 9.8×10-3

With
F = Strength (N)
D = H – H1

Where
H1 = Height of the elastomeric connector compressed (mm)
H = Height of the elastomeric connector not compressed (mm)

W = Width of the elastomeric connector (mm)
L = Length of the elastomeric conductor (mm)

A question about the use of elastomeric connectors for your application?


Thanks for reading this article until the end!

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Elastomeric connector with Beryllium Copper Wires - connecteur élastomérique avec fils en cuivre béryllium - compelmaMatrix elastomeric connector - connecteur élastomérique matriciel - CompelmaElastomeric connectors with silicone loaded (Ni/C) - Connecteurs élastomériques avec silicone chargé - Compelma

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Bureau d'étude CEM et thermique Compelma - EMI and thermal management