Conductive Silicone Parts for Electronics: Volume Resistivity, Compression and Contact Resistance - Kunshan Fuhongying Electronic Materials Co., Ltd.

Conductive silicone parts combine the flexibility, temperature resistance and sealing capability of silicone rubber with an electrically conductive filler system. They are widely used in electronic keypads, grounding contacts, battery interfaces, EMI shielding gaskets, sensor assemblies and custom electrical connectors.

However, selecting conductive silicone based only on a low volume-resistivity value can produce disappointing results. The finished component’s resistance also depends on its thickness, contact area, compression, electrode surface, contamination and long-term mechanical relaxation.

For reliable electrical performance, engineers must evaluate three connected parameters:

Volume resistivity of the silicone compound
Compression and compression force
Contact resistance of the assembled component

What Is Conductive Silicone Rubber?

Standard silicone rubber is an electrical insulator. Conductive silicone is produced by incorporating conductive particles into the silicone matrix.

Common conductive fillers include:

炭黑
Graphite
Nickel-coated graphite
Silver-coated aluminum
Silver-coated copper
Silver particles
Other metallic or coated particles

Shin-Etsu describes electrically conductive silicone products as silicone rubber compounded with carbon and other conductive materials. Its published product examples also demonstrate that volume resistivity can vary substantially between formulations. Shin-Etsu electrically conductive rubber products

The filler forms conductive paths through the cured silicone. When filler concentration, distribution and particle contact are sufficient, electricity can pass through the elastomer.

Increasing conductive filler loading can improve conductivity, but it may also affect:

硬度
伸長率
抗撕裂強度
壓縮永久變形
Molding flow
表面品質
模具磨損
Material cost

The best material is therefore not automatically the compound with the lowest resistivity. It is the compound that meets both the electrical and mechanical requirements of the assembled product.

Common Applications

Conductive silicone components are used for several different electrical functions.

Electronic Keypad Contacts

A conductive silicone pill or molded contact closes a circuit when a button is pressed against PCB contact pads. The important requirements are usually:

Stable contact resistance
Consistent tactile movement
Low bounce
Long cycle life
Clean release from the PCB
Resistance stability after aging

Grounding Contacts

Conductive silicone pads can connect a PCB, housing or shield to ground while accommodating dimensional variation and vibration.

EMI Shielding Gaskets

Conductive silicone gaskets maintain electrical continuity between enclosure surfaces while also providing an environmental seal.

Parker Chomerics offers conductive silicone and fluorosilicone gaskets with fillers such as nickel-aluminum, nickel-graphite, silver-aluminum and silver-copper. The company notes that conductive elastomer gaskets can provide both EMI shielding and environmental sealing. Parker Chomerics conductive elastomer gaskets

Flexible Electrical Interfaces

Custom conductive silicone components can provide compliant contact where rigid metal springs would be difficult to package or vulnerable to vibration.

Static Dissipation

Some formulations are designed to dissipate static electricity rather than carry operating current. Conductive, static-dissipative and antistatic requirements should not be treated as interchangeable.

Volume Resistivity

Volume resistivity describes how strongly a material resists electrical current flowing through its volume. Lower volume resistivity indicates higher conductivity.

It is normally expressed in:

Ω·cm
Ω·m

The relationship is:

ρ = R × A ÷ L

地點：

ρ is volume resistivity
R is measured resistance
A is the electrode contact area
L is the specimen thickness or current-path length

The approximate resistance through a component can therefore be estimated as:

R = ρ × L ÷ A

This equation demonstrates why two components molded from the same conductive silicone can have different resistance values. A thick, narrow current path usually produces more bulk resistance than a thin component with a large contact area.

Volume Resistivity Is a Material Property—Under Defined Conditions

ASTM D991 covers the determination of volume resistivity for electrically conductive and antistatic rubber products. The method assumes that surface conductivity is negligible compared with conductivity through the specimen. ASTM D991-89(2026)

A published resistivity value should always be reviewed together with:

測試方法
Specimen dimensions
Electrode configuration
Applied voltage or current
Conditioning environment
Cure conditions
Post-cure conditions
溫度
Measurement direction
Applied pressure

A supplier’s datasheet value is useful for material screening, but it does not guarantee the resistance of a finished molded component.

Unit Conversion Must Be Checked

Volume resistivity is commonly reported in both Ω·m and Ω·cm.

1 Ω·m = 100 Ω·cm

Comparing two datasheets without converting the units can result in a 100-times interpretation error.

How Compression Affects Conductivity

Compression changes both the internal conductive network and the interface between the silicone and the mating electrode.

Compression percentage can be calculated as:

Compression (%) = (Original thickness − Compressed thickness) ÷ Original thickness × 100

For example, if a 2.0 mm conductive pad is compressed to 1.6 mm, the nominal compression is 20%.

This number alone is not enough. Engineers must also know the compression force, contact area and tolerance range.

Insufficient Compression

Too little compression may cause:

Incomplete contact with the electrode
High or unstable resistance
Sensitivity to vibration
Intermittent electrical connection
Poor EMI shielding
Leakage at an environmental seal
Greater sensitivity to surface contamination

Controlled Compression

Within a suitable working range, compression generally increases the real contact area and stabilizes the conductive paths between the elastomer and the mating surfaces.

The correct compression range must be established from:

材料硬度
Part profile
壁厚
Contact area
Compression-deflection curve
Required closing force
Enclosure rigidity
長期壓縮永久變形

Excessive Compression

More compression is not always better. Excessive compression may cause:

Excessive assembly force
PCB bending
Housing distortion
Silicone extrusion from the groove
Permanent set
Cracking around thin sections
Accelerated stress relaxation
Damage to nearby components
Difficult disassembly
Reduced service life

Use mechanical compression stops where practical. Stops prevent screws or housing tolerances from overcompressing the conductive silicone.

Compression Force Versus Compression Percentage

Two conductive parts compressed by the same percentage may produce very different forces.

Compression force depends on:

矽膠硬度
Filler type and concentration
Cross-sectional profile
零件厚度
Contact area
Strain rate
溫度
Aging history

A soft, hollow or P-shaped gasket may require much less closure force than a solid rectangular strip. Parker, for example, describes its low-durometer CHO-SEAL 1299 conductive gasket as a lower-compression-force option for EMI shielding applications. Parker Chomerics CHO-SEAL 1299

When the conductive part contacts a PCB or thin plastic housing, calculate the maximum assembly load before finalizing the gasket profile.

What Is Contact Resistance?

Contact resistance is the resistance measured where the conductive silicone meets an electrode, PCB pad, metal housing or other conductive surface.

It is not identical to volume resistivity.

The measured resistance of an assembled conductive silicone contact can include:

Bulk resistance through the silicone
Resistance at the first silicone-to-electrode interface
Resistance at the second interface
Surface-film resistance
Constriction resistance at individual contact points
Fixture and lead resistance
Connection resistance in the measurement system

ASTM B539 explains that contact resistance includes constriction resistance and film resistance. It also notes that real contact surfaces consist of many small contact spots rather than the full apparent surface area. ASTM B539-20(2026)

Although ASTM B539 primarily addresses static electrical connections, this principle is highly relevant when developing a part-level test method for conductive silicone assemblies.

Why Low Volume Resistivity Does Not Guarantee Low Contact Resistance

A compound may have excellent bulk conductivity while the finished assembly still has excessive resistance.

Possible reasons include:

Insufficient compression
Small effective contact area
Oxide on the metal surface
PCB contamination
Mold-release residue
Silicone oil or processing residue
Dust or fingerprints
Rough or uneven mating surfaces
Incorrect electrode plating
Part warpage
Uneven pressure distribution
Loss of force after aging

For this reason, the product specification should normally contain both:

A material-level volume-resistivity requirement
A component-level contact-resistance requirement under defined assembly conditions

Contact Surface Design

Provide Adequate Contact Area

A larger contact area can reduce current density and improve resistance stability. However, the useful electrical contact area may be much smaller than the visible geometric area if pressure is uneven.

Control Surface Flatness

Warped housings or PCB assemblies can create local gaps. The tolerance stack should include:

Conductive silicone thickness
Groove depth
Housing flatness
PCB flatness
Insert height
Fastener location
Compression-stop height

Review the Electrode Material and Plating

Bare copper, nickel, tin, gold, aluminum and conductive coatings have different oxidation and corrosion behavior.

Gold-plated PCB contacts are often used where stable, low-level switching performance is important, while enclosure grounding applications may use different metal finishes depending on cost and environment.

Material pairs should also be evaluated for galvanic compatibility, especially in humid or salt-containing environments.

Avoid Contaminating the Contact Zone

Mold-release agents, lubricants, adhesives and cleaning chemicals can increase resistance. If these substances are required elsewhere in the assembly, keep them away from the electrical contact area and verify compatibility through testing.

Use Localized Contact Features Carefully

Small domes, ribs or raised pads can concentrate force and help break through light surface films. However, excessive local stress may cause wear, permanent deformation or damage to PCB coatings.

Conductive Filler Selection

Filler system	General characteristics	Typical considerations
Carbon-based	Cost-effective, suitable for switches and static control	Higher resistance than many metal-filled systems
Nickel-graphite	Common for EMI shielding and grounding	Balance of shielding performance and cost
Silver-aluminum	High conductivity with suitability for aluminum enclosures	材料成本上升
Silver-copper	Very high conductivity	Corrosion and galvanic compatibility must be evaluated
Pure silver	Excellent conductivity	Highest cost and not necessary for every application
Conductive-coated particles	Performance can be adjusted through particle core and coating	Supplier-specific conductivity and aging behavior

Filler descriptions are general. Actual performance depends on particle morphology, loading, dispersion, silicone formulation and curing process.

Do not approve a filler system based only on its chemical name. Test the production compound in the actual component geometry.

Material Hardness and Compression Set

Conductive silicone hardness affects both assembly force and contact stability.

Softer Materials

Potential advantages include:

Lower closing force
Better conformity to uneven surfaces
Improved contact at low compression
Reduced stress on PCBs and housings

可能的缺點包括：

Greater extrusion risk
More difficult dimensional control
Increased handling deformation
Potentially lower tear strength

Harder Materials

Potential advantages include:

更好的造型保持力
Higher localized contact pressure
Improved handling
Reduced extrusion in some designs

可能的缺點包括：

Higher assembly force
Greater risk of housing or PCB deformation
Reduced conformity to irregular surfaces

Compression set indicates how much deformation remains after the material has been compressed for a specified time and temperature. Lower compression set is generally desirable for maintaining contact force, but the published test condition must match the application closely enough to be meaningful.

Designing Different Conductive Silicone Components

Conductive Keypad Pills

A conductive pill is normally molded or bonded to the underside of a silicone button.

Important design parameters include:

Pill diameter
Pill thickness
Flatness
Alignment with PCB traces
Button travel
Actuation force
Overtravel
Contact resistance
Release characteristics
Cycle-life requirement

The contact-resistance specification should identify the applied button force or travel position. A resistance limit without an actuation condition is incomplete.

Conductive Silicone Gaskets

For enclosure gaskets, evaluate electrical continuity and environmental sealing simultaneously.

評論：

Gasket profile
溝槽尺寸
Compression range
Closure force
Fastener spacing
Enclosure stiffness
Surface coating
EMI frequency range
Water or dust sealing requirement
Environmental aging

A gasket can maintain a water seal but still lose acceptable electrical continuity, or maintain conductivity while failing the environmental seal. Both functions require separate validation.

Conductive Contact Pads

A conductive pad placed between a PCB and housing should be thick enough to accommodate tolerances without generating excessive force.

Large unsupported pads may buckle, slide or compress unevenly. Alignment ribs, pockets or adhesive-backed carriers can improve assembly repeatability, provided the adhesive does not enter the conductive path.

Multi-Material Silicone Parts

Conductive and nonconductive silicone can be combined within one component to create isolated conductive zones.

Critical issues include:

Material bonding
Positional accuracy
Conductive-path separation
Flash between zones
Cure compatibility
Shrinkage difference
Tooling complexity
Electrical leakage between adjacent contacts

Each conductive zone should be tested independently.

Measuring Contact Resistance

A four-wire Kelvin method is normally preferred for low-resistance measurements because it reduces the influence of test-lead resistance.

The test fixture should define:

Electrode material
Electrode plating
Electrode dimensions
表面處理
清潔方法
Compression percentage
Applied force
Compression speed
Dwell time before measurement
Test current
Open-circuit voltage
Temperature and humidity
Number and location of measurements

IEC 60512-2-1 defines a millivolt-level method for measuring contact resistance across mated contacts or a contact with a measuring gauge. IEC 60512-2-1:2002

IEC 60512-2-2 provides a specified-test-current method. IEC 60512-2-2:2003

The most appropriate method depends on whether the conductive silicone is used for low-level signals, switching, grounding, EMI control or current transmission.

Test Resistance Across the Compression Range

Do not test only at nominal compression. Measure at:

Minimum compression
Nominal compression
Maximum compression

This reveals whether tolerance variation can produce an open circuit, excessive resistance or damaging assembly force.

A useful validation graph plots:

Contact resistance versus compression
Compression force versus compression

The acceptable production window is the region where both electrical resistance and mechanical force meet the design requirements.

Environmental and Life Testing

Conductive silicone performance should be checked before and after relevant environmental exposure.

Possible tests include:

High-temperature aging
Low-temperature exposure
溫度循環
Damp heat or humidity
Salt mist for exposed metal interfaces
Chemical exposure
UV and weathering
振動
Mechanical shock
Repeated compression
Keypad actuation cycling
Long-term static compression
Storage aging

Record both the initial resistance and the change after exposure. A component that initially passes but shows unstable resistance after aging may not be suitable for production.

Current-Carrying Limitations

Conductive silicone should not automatically be treated as a replacement for a copper conductor.

The acceptable current depends on:

Volume resistivity
Current-path length
Contact area
Contact resistance
Duty cycle
Heat dissipation
Ambient temperature
Allowable temperature rise
材料老化
Failure consequences

High resistance can generate localized heat according to:

Power = Current² × Resistance

Applications involving meaningful current should include temperature-rise testing under worst-case compression, voltage, current and ambient-temperature conditions.

Manufacturing Considerations

Conductive silicone parts may be manufactured by:

壓縮成型
轉注成型
射出成型
Liquid silicone rubber molding
Extrusion and cutting
Die cutting from conductive silicone sheet
Co-molding with nonconductive silicone
Overmolding onto metal or plastic inserts

High filler loading can affect flow and mold filling. Thin ribs, narrow channels and small conductive zones may require different tooling and process conditions from conventional silicone parts.

Production controls may include:

物料批次可追溯性
Controlled mixing
Cure-temperature monitoring
Cure-time verification
Post-cure control
Part-weight monitoring
尺寸檢測
Resistance testing
Visual inspection for contamination and flash

Common Problems and Corrective Directions

Problem	Possible causes	Corrective direction
Resistance too high	Incorrect material, long current path, small area	Review resistivity, thickness and contact area
Resistance changes with movement	Insufficient compression or uneven pressure	Improve support and compression control
High initial resistance	Surface contamination or oxide	Review cleaning and electrode finish
Resistance increases after aging	Compression set, corrosion or material degradation	Test alternative material and interface finishes
PCB bends during assembly	Excessive compression force	Use softer material, revised profile or compression stops
Conductive part extrudes from groove	Excessive compression or poor retention	Adjust groove, tolerance and material hardness
Inconsistent keypad response	Pill misalignment or variable button travel	Improve tooling, assembly location and travel control
Gasket passes sealing but fails grounding	Environmental seal and electrical path are not equivalent	Validate both functions independently
Adjacent contacts short circuit	Conductive flash or inadequate spacing	Improve shut-offs, inspection and contact separation

Prototype and Validation Plan

A practical development sequence includes:

Select candidate compounds based on resistivity, hardness and environmental requirements.
Mold simple material specimens and production-representative parts.
Measure volume resistivity using a defined method.
Generate compression-force curves.
Measure contact resistance at minimum, nominal and maximum compression.
Test the intended electrode material and plating.
Complete temperature, humidity and cycling tests.
Evaluate dimensional and electrical variation by cavity.
Run pilot production using the intended manufacturing process.
Establish production inspection limits and sampling frequency.

Do not finalize the production specification using only prototype parts manually selected for good performance.

詢價單核對清單

Provide the following information when requesting a quotation:

2D drawing and 3D model
Part application
Required electrical function
Target volume resistivity
Maximum assembled contact resistance
Test current and voltage
Required current-carrying capacity
Nominal, minimum and maximum compression
Maximum allowable compression force
Electrode material and plating
工作溫度
Humidity and chemical exposure
EMI shielding requirement
Environmental sealing requirement
Hardness range
Color limitations
Flame-retardant requirements
年產量
Required cycle life
監管要求
Inspection and traceability requirements

If the electrical specification is not yet established, provide the complete assembly geometry and functional requirement. The molding supplier can then help develop suitable test conditions and material options.

常見問題

What volume resistivity should conductive silicone have?

There is no universal target. Static-dissipative parts, keypad contacts, EMI gaskets and current-carrying contacts require different conductivity levels. Define the maximum finished-part resistance and operating conditions before selecting the material.

Does compressing conductive silicone reduce resistance?

Controlled compression usually improves contact stability and can lower the measured assembly resistance. However, excessive compression can damage the part, overload the housing and reduce long-term reliability.

Is volume resistivity the same as contact resistance?

No. Volume resistivity describes the bulk material, while contact resistance includes the interfaces between the silicone and mating electrodes.

Why does a sample pass but the assembled product fail?

The assembly may have insufficient compression, surface contamination, uneven loading, electrode oxidation or an unfavorable geometry even when the material itself meets its resistivity specification.

Can conductive silicone carry electrical current?

It can carry current within application-specific limits, but it generally has much higher resistance than metal conductors. Temperature-rise and aging tests are required for current-carrying applications.

Can conductive and insulating silicone be molded together?

Yes. Multi-material molding can create isolated conductive contacts within an insulating silicone body. Bonding, positional tolerance, material compatibility and conductive flash must be carefully controlled.

How should conductive silicone contact resistance be measured?

Use a defined fixture—preferably with a four-wire measurement arrangement—and specify electrode material, surface finish, compression, force, dwell time, voltage, current and environmental conditions.

Can conductive silicone provide both EMI shielding and waterproof sealing?

Yes, some conductive elastomer gaskets are designed for both functions. Electrical continuity and environmental sealing must still be validated separately.

結論

A reliable conductive silicone component cannot be specified with one resistivity number alone. Volume resistivity determines the material’s bulk conductivity, while component geometry, compression and electrode conditions determine the actual assembled contact resistance.

The best development process combines material testing, compression-force analysis, part-level resistance measurement and environmental validation. Send your drawing, assembly structure, electrical requirements, compression range and operating environment for a conductive silicone DFM and material-selection review.