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 always needs more connection density on reduced spaces.
Therefore electronic connections are done by smaller and denser connectors. That for those assemblies that elastomeric connectors has been designed. Elastomeric connectors ensure high density connection (0.05 mm pitch between two contact points) and assemble mechanically (without soldering) through compression. 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 silicone base, with an alternance of conductive and electric isolating layers. Elastomeric connectors are assembled mechanically without soldering.

Those elastomeric connectors are also named ZEBRA connectors, because of the alternating black and white strip (remembering the animal).

Elastomeric connector’s none-conductive zone are made of neutral silicone (not charged). Silicone is the base material due to its excellent properties of aging, chemical stability, electric reliability, and mechanic behavior regarding shocks and vibrations.

Conducting areas can be composed of:

Charged silicon : Carbon/Graphite (or Silver, in rare cases)

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

There also exists a variation with a lateral connection, especially adapted for connections of LCD screens to PCB or for PCB to PCB with higher current levels and lower resistivity.

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, for elastomeric connectors in line. It is possible to add isolating silicone layers on both sides of the connector to increase its rigidity and/or isolate it from components and surrounding electric tracks. This isolating silicone thickness on the side of the elastomeric connector is from 0.05 mm minimum to 1.5 mm. The hardness of this silicone can be adjusted as needed.

For this type of elastomeric connector in Z axis, the ratio between the height and the width must be at least 1.5 mm 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. These are equidistant contact points with the same metrics (0.05 mm pitch and diameter of 0.03 mm 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 elevated on this type of connector (0.1 mm pitch or 0.05 mm in standard). This density is much higher than the connection tracks on a PCB or on an LCD connection for example. Therefore, each track on the PCB will be in contact with at least one conductive area of the elastomeric connector, and there will be at least one isolating layer between two tracks of the PCB. Hence, 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?

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

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 must then be compressed to ensure the contact. Elastomeric connectors in charged silicone can be compressed more than wired elastomeric connectors.
The recommended compression is from 5% to 25% maximum.
Warning, wired elastomeric connectors risk to deteriorate mechanically if the compression is too strong. For those elastomeric connectors, it is better to approach 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 clients use these elastomeric connectors to ensure electric connections in payment terminals. In those assemblies elastomeric connectors are integrated in the equipment’s plastic frame. Hence, they guarantee the electric contact in an environment submitted to shocks and vibrations (bank card payment terminal for example).

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 for PCB’s test devices. Notably, matrix elastomeric connectors.Pitches of 0.1 or 0.05 mm on the plane offer plenty of permanently and simultaneously accessible contact points without risk of short circuit. Unlike mechanical touch tips which have to be adjusted,targeted and are very localized.

The composition of elastomeric connectors, mostly made from silicone, allow it to withstand several thousand of cycles of compression and decompression without deteriorating and without imposing strong mechanical stress on PCB’s contact points.

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.Their silicone base also ensures a water tightness level IP (to fluids and particles) that isn’t found with mechanical connectors. This functionality makes it a strategic choice, especially for connectors with 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 increasingly denser electronic assembly, electronic mechanical connectors and other mechanical contact points quickly reach their limits. Given that those mechanical connectors (often pin or tip systems) cannot 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, no tools are necessary to produce elastomeric connectors. As pitch and space requirements, the more elastomeric connectors will be a pertinent technical and economical solution compared 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 application's specified requirements and configuration. This process leaves more wiggle room to integrate those electronic assembly’s components.

However, maximal dimensions are limited. Around 120-150 mm long, 5 mm wide and 10-20 mm high. Those limits are rarely reached 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 furthest one.
We recommend making it go over by 0.5 or even 1 mm 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's 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)

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 electric contact, limit slacks in assemblies and support vibrations.
For elastomeric connectors composed exclusively of silicone, the recommended compression goes from 5% to 25% (the global connectors height also affects on compression rate). So, the height indirectly depends on compression strength needed to compress the elastomeric connector.
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 silicone, you can use this formula:

F = 9 x D x W x L x 9.8×10-3

F = Strength (N)
D = H – H1

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!

If you have any question, samples need or any technical point you want to talk about:
Contact us using the contact form below, or the chat on the below right corner

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