Moving and Stationary Copper Contacts for HVDC Relays: Silver Alloy Brazing & Arc Resistance

Moving and stationary copper contacts in 800V high-voltage DC relays must maintain low electrical resistance while withstanding arc erosion, contact welding, and repeated mechanical impact. A typical contact assembly combines a TU1 oxygen-free copper conductive arm with an AgSnO₂ or AgNi contact tip, joined through a controlled silver-alloy brazing process. Material selection, braze integrity, contact geometry, and opening dynamics must be evaluated together to achieve stable switching performance over the specified electrical and mechanical life.

 

 

 

High-voltage DC relays are used in electric vehicle battery disconnect units (BDUs), power distribution systems, and energy storage circuits. Unlike AC switching, DC has no natural periodic zero-crossing point. Once an arc forms between separating contacts, the relay must extinguish it through its electromagnetic, mechanical, and arc-chamber design.

 

The moving and stationary copper contacts are therefore exposed to combined electrical, thermal and mechanical loading.

Why 800V DC interruption accelerates contact degradation
When the moving contact separates from the stationary contact under load, current may continue flowing through an ionized plasma channel. The arc temperature can locally melt or vaporize contact material, causing material transfer, surface cratering, and erosion.

 

The severity of contact damage depends on several electrical and mechanical conditions:

Circuit voltage: Higher DC voltage increases the challenge of arc extinction and dielectric recovery.
Interruption current: Higher current increases arc energy and thermal loading.
Circuit inductance: Stored magnetic energy can sustain current after contact separation.
Opening velocity: Contact separation speed influences arc duration and contact gap development.
Contact geometry: Contact diameter, thickness, and surface profile affect current density and arc-root movement.
Contact force: Insufficient closed-contact force can increase constriction resistance and local heating.
Arc management: Magnetic blowout, gas pressure, arc runners, and chamber geometry influence arc movement and extinction.

 

This relationship explains why contact material cannot be evaluated independently of the relay's electrical interruption conditions. Two contact materials tested at different current, voltage, or inductance conditions cannot be compared reliably.

Common failure modes in moving and stationary contacts

 

Failure mode	Physical mechanism	Potential consequence	Relevant control
Arc erosion	Local melting and material vaporization	Contact mass loss and surface damage	Contact alloy selection and arc-system design
Material transfer	Directional movement of molten contact material	Uneven contact surfaces	Polarity-specific switching evaluation
Contact welding	Local melting followed by solidification under contact pressure	Failure to open	Anti-welding material and force optimization
Contact resistance increase	Surface oxidation, erosion, or reduced real contact area	Excessive temperature rise	Contact resistance monitoring
Contact bounce	Repeated impact and separation after closure	Electrical arcing and unstable switching	Spring design and moving assembly dynamics
Braze failure	Thermal stress or inadequate joint integrity	Increased resistance or contact separation	Brazing process validation
Copper-arm deformation	Repeated impact or excessive thermal loading	Misalignment and unstable contact pressure	Mechanical design and fatigue validation

 

Moving versus stationary contact design
The two contact positions do not necessarily experience identical operating conditions.

 

Design factor	Moving copper contact	Stationary copper contact
Mechanical loading	Repeated impact and acceleration	Primarily receives impact from moving assembly
Contact bounce	Directly influenced by moving mass and spring dynamics	Influences rebound at the interface
Electrical loading	Carries current through a moving conductive path	Carries current through a fixed conductive path
Assembly requirements	Must maintain alignment throughout travel	Must maintain fixed contact position
Main design concern	Dynamic stability and fatigue	Dimensional stability and joint integrity

 

For both components, the contact tip position, copper-arm stiffness, and braze joint geometry must be controlled relative to the relay's assembly datum.

 

 

Silver-based contact materials are widely used in switching devices because of their electrical conductivity and contact performance.

 

However, the appropriate alloy depends on the switching duty, current level, contact force, arc duration, and required electrical life.

 

AgSnO₂ and AgNi are two material systems that may be considered for relay contacts. Their performance should be evaluated under the intended HVDC switching conditions rather than selected from material composition alone.

 

AgSnO₂ contact material: Oxide dispersion and anti-welding behavior
Silver tin oxide (AgSnO₂) is a silver-based composite contact material containing dispersed tin oxide. The oxide phase influences the contact's resistance to welding and its response to arc heating.

 

Its engineering characteristics include:
Resistance to contact welding under suitable switching conditions.
A dispersed oxide phase that modifies molten-metal behavior.
Good resistance to certain forms of electrical erosion.
Potentially higher contact resistance than high-purity silver, depending on composition and manufacturing route.
Sensitivity to contact manufacturing quality and oxide distribution.

AgSnO₂ is commonly considered where anti-welding performance is an important selection criterion. Its suitability for HVDC relays still requires testing at the specified DC voltage, interruption current, and circuit inductance.

AgNi contact material: Conductive performance and switching behavior
Silver nickel (AgNi) contains nickel distributed within a silver matrix. The nickel phase contributes to the mechanical and electrical behavior of the contact material.

 

Its characteristics include:
Good electrical conductivity relative to many oxide-dispersion contact materials.
Resistance to contact material deformation under suitable loading.
Established use in selected relay and switching applications.
Switching performance depends on nickel content, microstructure, and operating conditions.
Potential for contact welding under severe electrical loads if the material and relay design are not correctly matched.

AgNi should not be assumed to outperform AgSnO₂ in high-current DC interruption. The actual ranking depends on contact geometry, electrical duty, and arc-control architecture.

AgSnO₂ versus AgNi: Engineering selection matrix

 

Evaluation factor	AgSnO₂	AgNi
Material structure	Silver matrix with dispersed tin oxide	Silver matrix with dispersed nickel
Main material contribution	Anti-welding and arc erosion resistance	Conductivity and mechanical contact performance
Electrical conductivity	Depends on oxide content and material grade	Depends on nickel content and material grade
Welding resistance	Often selected for demanding anti-welding requirements	Depends on grade and switching duty
Arc erosion behavior	Requires validation under actual DC interruption conditions	Requires validation under actual DC interruption conditions
Contact resistance	Influenced by oxide distribution and surface condition	Influenced by nickel content and surface condition
Typical design consideration	High-current switching and welding resistance	Relay switching and conductive contact applications
Final selection basis	Electrical life, welding and erosion tests	Electrical life, welding and erosion tests

 

The material specification should define the exact alloy grade and applicable supplier standard. The designation AgSnO₂ alone does not establish oxide content, microstructure, density, or switching performance.

Contact material qualification under HVDC conditions
Material qualification should use representative contact assemblies rather than relying exclusively on material certificates.

 

Recommended test parameters include:

 

Test parameter	Required definition
Rated operating voltage	System-specific DC voltage
Make current	Current during contact closure
Break current	Current interrupted during opening
Circuit inductance	Test circuit inductance
Contact force	Initial and operating contact force
Contact gap	Specified open-contact distance
Switching frequency	Defined operating cycle rate
Ambient temperature	Application-specific temperature range
Electrical endurance	Defined number of switching cycles
Contact resistance	Initial and post-endurance measurements
Welding assessment	Separation force and failure inspection

 

A relay intended for an 800V DC system must be tested against its actual switching envelope. Material-level results cannot replace complete relay qualification.

 

Request Contact Material and DFM Evaluation

 

 

The connection between a silver-alloy contact tip and a copper conductive arm is a major electrical and mechanical interface. A poorly controlled braze joint can introduce localized resistance, thermal concentration, and mechanical separation during repeated switching.

 

TU1 oxygen-free copper is suitable for conductive arms where high electrical conductivity and controlled forming behavior are required.

 

The contact tip and copper arm must be joined through a process that provides adequate wetting, joint continuity, and mechanical strength without damaging the contact material.

Why TU1 oxygen-free copper is used for relay conductive arms
TU1 copper is a low-oxygen copper grade with high electrical conductivity. Its material characteristics support current-carrying conductive arms and precision-formed relay components.

 

The selection should consider:
Electrical conductivity and resistivity.
Material thickness and current-carrying cross-section.
Forming and bending requirements.
Thermal conductivity.
Surface condition before brazing.
Dimensional stability after thermal processing.

The actual conductivity value depends on the material specification, temper, and test condition. Procurement documents should identify the applicable copper grade and conductivity requirement rather than assuming that all copper arms meet the same IACS percentage.

Silver-alloy brazing versus other copper-to-contact joining methods

Silver-alloy brazing is one potential joining route for attaching silver-based contact tips to copper arms. The process uses a filler alloy with a liquidus temperature below the melting point of the base materials.

 

Joining method	Joining mechanism	Potential advantages	Main process risks
Silver-alloy brazing	Molten filler wets and joins the contact and copper surfaces	Suitable for conductive dissimilar-material joints	Incomplete wetting, voids, excessive filler
Resistance brazing	Localized electrical heating melts the filler	Localized heat input and cycle control	Electrode wear, uneven heating, inconsistent pressure
Laser welding	Focused laser energy melts base materials	Precise localized joining	Cracking, porosity, alloy dilution, and reflectivity effects
Resistance welding	Electrical resistance generates heat at the interface	Short cycle time for suitable geometries	Expulsion, electrode marks, and variable joint formation
Molecular diffusion welding	Pressure and temperature promote solid-state atomic bonding	Avoids bulk melting of the base materials	Surface preparation, pressure, and temperature sensitivity

 

For AgSnO₂ contact tips, the joining process must account for the thermal sensitivity of the oxide-dispersion microstructure. Excessive local heating may alter the contact material or produce an inconsistent interface.

 

The selected process must therefore be validated against contact material composition, filler alloy, joint dimensions, and required electrical performance.

Braze joint design: Wetting, clearance and filler distribution

A stable braze joint requires controlled surface preparation and joint geometry.

Key design variables include:
1. Contact-tip seating: The copper arm must support the contact tip without rocking or uneven gaps.
2. Surface cleanliness: Oil, oxide, stamping residue, and contamination can interfere with filler wetting.
3. Joint clearance: Excessive or insufficient clearance can affect capillary flow and joint continuity.
4. Filler quantity: Too little filler can produce incomplete bonding; excessive filler can create unwanted fillets or contaminate functional contact surfaces.
5. Heating profile: The assembly must reach the required brazing temperature without unnecessary thermal exposure.
6. Cooling conditions: Controlled cooling reduces the risk of distortion and residual stress.

The appropriate joint clearance and brazing temperature depend on the selected filler alloy and component geometry. They should be established through process trials and documented in the approved manufacturing specification.

Braze defects and their effect on relay performance

 

Defect	Possible cause	Electrical or mechanical consequence	Inspection approach
Incomplete wetting	Surface contamination or inadequate heating	Reduced bonded area	Visual inspection and section analysis
Internal voids	Trapped gas, poor filler flow, or unsuitable clearance	Increased local resistance	Metallographic section or suitable NDT
Excessive filler	Incorrect filler quantity or joint gap	Interference with assembly or contact geometry	Visual and dimensional inspection
Contact-tip displacement	Fixture instability or thermal movement	Misalignment of contact surfaces	Optical measurement or CMM
Thermal damage	Excessive heating or long dwell time	Contact material microstructure changes	Metallographic and material evaluation
Copper-arm distortion	Uneven heating or residual stress	Incorrect contact position	Dimensional inspection

 

 

 

Contact material and brazing quality determine only part of the relay's service performance. Moving and stationary contact assemblies must also withstand repeated mechanical impact, contact bounce, short-circuit closing forces, and thermal cycling.

 

The mechanical design must maintain sufficient contact pressure while preventing excessive impact energy and unstable rebound.

Contact bounce and rebound time
Contact bounce occurs when the moving contact strikes the stationary contact but separates again briefly before reaching a stable closed state.

 

This can result from:
Excessive moving contact mass.
Insufficient damping.
Incorrect spring stiffness or preload.
Misaligned contact surfaces.
Excessive operating velocity.
Structural resonance in the moving assembly.

During bounce, the electrical interface may repeatedly open and close. Under load, these repeated interruptions can generate additional arcs and accelerate contact surface degradation.

 

The following parameters should be evaluated together:

 

Parameter	Engineering significance	Validation method
Moving mass	Influences impact energy	Mass measurement
Closing velocity	Determines impact conditions	High-speed displacement measurement
Contact force	Affects interface stability and resistance	Force-displacement testing
Spring stiffness	Controls contact pressure and rebound behavior	Spring load testing
Bounce duration	Measures time until stable closure	High-speed voltage/current recording
Contact resistance	Indicates electrical interface condition	Four-wire resistance measurement

 

A universal bounce-time limit should not be applied to all HVDC relays. The acceptance threshold must be defined by the relay design and customer specification.

Short-circuit closing impact and contact welding
When a relay closes onto a short-circuit condition, the current can rise rapidly according to the circuit impedance and inductance. The resulting electromagnetic forces may act on the moving and stationary contact structures.

 

Potential consequences include:
Contact repulsion.
Mechanical displacement.
Contact welding.
Localized thermal damage.
Deformation of conductive arms or support structures.

The design must consider the prospective short-circuit current, peak current, current rise rate, and relay closing dynamics.

 

The contact assembly should not be evaluated only by its static contact force. Dynamic force conditions during short-circuit making can differ significantly from normal closed-state operation.

Mechanical endurance testing to 100,000 cycles
A mechanical endurance target of 100,000 cycles can be used as a design or qualification requirement when specified by the customer.

 

Mechanical endurance testing should be distinguished from electrical endurance testing.

 

Test category	Operating condition	Main evaluation
Mechanical endurance	Repeated opening and closing without switching load, where specified	Wear, alignment, spring stability, and mechanical failure
Electrical endurance	Switching under specified voltage and current	Arc erosion, contact resistance, and welding
Temperature cycling	Repeated exposure to defined temperature limits	Joint integrity and dimensional stability
Contact resistance monitoring	Before, during, and after endurance	Resistance drift
Short-circuit making test	Defined prospective fault current	Contact repulsion, welding and structural deformation
Dielectric withstand test	Specified insulation voltage and duration	Insulation integrity

 

A 100,000-cycle mechanical test does not establish 100,000-cycle electrical switching life. Electrical endurance must be tested under the rated switching conditions and relevant test sequence.

Recommended endurance and inspection sequence
A practical qualification sequence can include:

1. Record initial contact resistance using a four-wire measurement method.
2. Measure moving contact travel, contact force, and initial bounce behavior.
3. Conduct the specified mechanical endurance cycles.
4. Repeat dimensional and contact resistance measurements.
5. Perform electrical switching endurance under the approved load profile.
6. Inspect contact erosion, material transfer, and welding.
7. Section selected brazed joints to assess interface integrity.
8. Record the failure mode and compare results against customer acceptance criteria.

The test report should include the test circuit, voltage, current, inductance, ambient conditions, switching frequency, and measurement method. Without these details, endurance results are difficult to compare or reproduce.

 

Request Copper Contact Assembly Review

 

 

Moving and stationary contacts require coordinated control of copper-arm geometry, contact-tip position, braze quality, and assembly interfaces. Manufacturing should begin with the approved drawing and material specifications, followed by process planning for stamping, forming, brazing and inspection.

Copper-arm stamping and forming controls
Precision stamping is used to produce the conductive arm profile, mounting features, and locating geometry.

 

Important characteristics include:
Strip or sheet material thickness.
Hole position and diameter.
Bend angle and radius.
Contact-tip seating surface.
Flatness and profile tolerance.
Burr direction and height.
Position relative to the relay assembly datum.

The forming sequence must minimize distortion around the contact-tip mounting area. Excessive deformation near the braze interface may affect seating geometry and increase the risk of joint misalignment.

Contact-tip brazing and assembly sequence
A representative manufacturing route may include:

 

Process stage	Operation	Key quality control
1	TU1 copper material inspection	Grade, thickness, and conductivity documentation
2	Precision stamping	Profile, holes, and burr condition
3	Copper-arm forming	Bend geometry and flatness
4	Contact-tip preparation	Alloy identification and seating dimensions
5	Surface cleaning	Removal of oil and surface contamination
6	Silver-alloy brazing	Heating profile, filler quantity, and joint continuity
7	Post-braze cleaning	Residue and surface condition
8	Dimensional inspection	Contact position and assembly geometry
9	Electrical and mechanical validation	Resistance and joint strength
10	Final identification and packaging	Part number and batch traceability

 

The process route may vary according to contact geometry, material combination, and production volume. Brazing fixtures should control the relative position of the contact tip and copper arm throughout heating and cooling.

CMM inspection and contact-position control
For HVDC relay assemblies, contact alignment influences the real contact area, contact pressure distribution, and opening gap.

 

CMM inspection can be used to evaluate:
Contact-tip center position.
Contact surface height.
Copper-arm flatness.
Mounting-hole position.
Formed arm profile.
Datum-to-contact positional relationships.

Optical measurement may be more suitable for selected contact-surface features or small geometric details. The inspection method should be selected according to the drawing tolerance and feature accessibility.

 

A tolerance such as ±0.01 mm should only be specified where the component design, tooling capability, and measurement system support it. It should not be treated as a universal tolerance for all relay contact dimensions.

 

 

A contact assembly should be controlled as a functional electrical and mechanical component rather than as a copper stamping with an attached silver tip.

 

The quality system should connect material certification, stamping parameters, brazing records, dimensional inspection, and final validation.

Recommended CTQ inspection plan

 

Critical-to-quality item	Inspection method	Quality objective
Copper grade	Material certificate and verification	Confirm specified copper material
Copper thickness	Micrometer or dimensional measurement	Control conductive cross-section
Contact alloy	Supplier certificate and material verification	Confirm AgSnO₂ or AgNi specification
Contact-tip dimensions	Optical measurement	Maintain contact geometry
Braze joint integrity	Visual inspection and metallographic validation	Verify bonding continuity
Braze void assessment	Section analysis or suitable NDT	Evaluate internal joint quality
Contact-tip position	CMM or optical measurement	Maintain assembly alignment
Contact resistance	Four-wire measurement	Monitor electrical interface
Pull or shear strength	Mechanical test	Verify joint retention
Contact bounce	High-speed electrical measurement	Assess dynamic closure
Endurance	Mechanical and electrical cycling	Verify specified operating life

 

Process documentation and PPAP Level 3
For automotive supply programs, customers may require a documented approval package under PPAP Level 3 or their own supplier quality requirements.

 

The submission scope may include:
Process flow diagram.
Process Failure Mode and Effects Analysis (PFMEA).
Control Plan.
Material and component certificates.
Dimensional inspection results.
Measurement System Analysis (MSA).
Statistical Process Control (SPC), where applicable.
Brazing process validation.
Contact resistance and mechanical test results.
Endurance test reports.
Approved sample records.

The applicable requirements should be agreed during the project launch. IATF 16949 certification status must be confirmed for the specific manufacturing entity and production site before it is stated in supplier documentation.

Batch traceability for silver contact and copper components
Traceability should connect each finished contact assembly to its key material and process records.

 

A suitable traceability structure includes:

 

Traceability field	Record
Finished part number	Moving or stationary contact assembly code
Drawing revision	Approved engineering revision
Copper material batch	TU1 material lot
Contact material batch	AgSnO₂ or AgNi supplier lot
Brazing filler batch	Silver-alloy filler identification
Production date	Manufacturing date and shift
Tooling identification	Stamping die and fixture reference
Brazing process record	Approved process parameters and batch
Inspection record	Dimensional and electrical results
Test record	Mechanical and endurance validation

 

This information supports defect containment, engineering change control, and customer complaint investigation.

 

 

Procurement evaluation should cover material control, joining capability, dimensional inspection, and component-level validation. A low unit price does not establish the ability to maintain contact resistance, joint integrity, or switching endurance across production batches.

Supplier evaluation matrix

 

Evaluation area	Questions for the supplier	Evidence to request
Contact materials	Can the supplier process the specified AgSnO₂ or AgNi grade?	Material certificates and batch identification
Copper conductive arms	Can TU1 copper be stamped and formed to the drawing?	Material records and dimensional reports
Brazing process	How are filler flow and joint consistency controlled?	Process specification and joint validation
Stamping capability	How are contact position and arm geometry maintained?	Tooling plan and inspection data
Electrical testing	Can contact resistance be measured consistently?	Four-wire measurement records
Mechanical testing	Can pull, shear, and endurance tests be performed?	Mechanical validation reports
Quality management	Can the supplier meet customer-specific APQP and PPAP requirements?	Quality documentation and approval records
Traceability	Can finished parts be traced to material and process batches?	Traceability sample records

 

Complete contact assembly sourcing
For some HVDC relay designs, procurement of the copper contact arms alone is insufficient. The component architecture may also include moving and stationary contact assemblies, ceramic sealing structures, and other mechanical or electrical interfaces.

 

A coordinated sourcing scope may include:
Moving copper contact arms.
Stationary copper contact arms.
AgSnO₂ or AgNi contact tips.
Silver-alloy brazed contact assemblies.
Precision-stamped relay components.
Ceramic sealing body or ceramic enclosure components.

The final supply scope should follow the approved relay architecture and drawing package. Ceramic sealing components require separate dimensional, insulation, and sealing validation; contact-arm qualification alone does not establish complete relay performance.

 

 

1. Should AgSnO₂ or AgNi be selected for an 800V HVDC relay?
Selection depends on interruption current, circuit inductance, contact force, arc-control design, and required electrical life. AgSnO₂ is often considered for anti-welding requirements, while AgNi is used in selected relay applications. Both require application-specific switching tests.

 

2. How is the brazed joint between a TU1 copper arm and an AgSnO₂ contact tip inspected?
Inspection can combine visual examination, dimensional measurement, metallographic cross-section analysis, and mechanical strength testing. Electrical resistance measurement should also be included to evaluate the assembled current path.

 

3. Does a 100,000-cycle mechanical endurance test prove the electrical life of an HVDC contact assembly?
No. Mechanical endurance evaluates repeated operation without necessarily switching electrical load. Electrical endurance requires testing at specified DC voltage, current, circuit inductance, and switching conditions.