Key Takeaways
- A low magnetic connector assembly is designed to minimize magnetic field interaction by controlling material composition, plating, manufacturing processes, and assembly contamination.
- The primary specification is relative permeability (μr), with demanding applications often requiring values below 1.0005.
- The connector body, contact alloy, plating stack, solder joints, fasteners, and tooling all influence final magnetic performance.
- Beryllium Copper (BeCu), Phosphor Bronze, titanium, and carefully selected non-magnetic stainless materials are commonly used depending on mechanical requirements.
- Nickel underlayers are a frequent source of unexpected magnetic behavior because nickel is ferromagnetic.
- Final qualification should measure the completed assembly, not only the connector component.
What is a low magnetic connector assembly?
A low magnetic connector assembly is an interconnect solution engineered to maintain minimal magnetic susceptibility when placed near sensitive magnetic fields. The goal is not absolute absence of magnetism—no real material achieves that condition—but controlled magnetic behavior suitable for high-performance systems.
The most important specification is relative permeability (μr). A value near 1.0 indicates that a material has little effect on an external magnetic field. Applications such as MRI equipment, quantum computing systems, aerospace navigation sensors, and precision laboratory instruments often require much tighter control than standard electronic assemblies.
Conventional connectors frequently use brass, steel hardware, and nickel barrier plating because those materials provide durability and corrosion resistance. In a low magnetic environment, those same design choices can create problems:
- Magnetic attraction can create mechanical forces in high-field environments.
- Ferromagnetic materials can distort field uniformity.
- Residual magnetism can introduce measurement drift in precision sensors.
- Magnetic contamination introduced during manufacturing can compromise otherwise suitable materials.
A successful low magnetic assembly therefore requires a complete material and process strategy rather than simply selecting a connector labeled “non-magnetic.”
Which specifications define low magnetic connector quality?
Engineers evaluating a connector assembly should define requirements using measurable parameters.
| Metric | Why it matters | Typical target or influence | Verification method |
|---|---|---|---|
| Relative Permeability (μr) | Determines magnetic field interaction | Standard: < 1.01; advanced MRI/quantum applications: < 1.0005 | Low-Mu permeability indicator, Severn Gauge, VSM |
| Magnetic Remanence | Indicates retained magnetization after exposure | Near zero for precision systems | Gaussmeter or fluxgate magnetometer |
| Magnetic Susceptibility (χ) | Measures response to applied magnetic fields | Target approaches zero | SQUID or precision magnetic testing |
| Plating Thickness | Controls corrosion protection and contact reliability | Gold: 0.76µm–1.27µm; Silver: 2.54µm–5.08µm | XRF analysis |
| Conductivity | Affects current handling and RF performance | BeCu: 20–50% IACS; Phos Bronze: approximately 15% IACS | Four-wire resistance measurement |
| Contact Force | Ensures electrical reliability without magnetic materials | Depends on connector geometry | Mechanical force testing |
How do you choose the right low magnetic connector material?
Material selection depends on the application's magnetic limit, mechanical stress, temperature range, and electrical requirements.
| Material option | Magnetic behavior | Strengths | Design considerations |
|---|---|---|---|
| Beryllium Copper (BeCu) | Low magnetic susceptibility | Excellent spring performance and fatigue resistance | Requires careful plating selection |
| Phosphor Bronze | Low magnetic response | Good spring properties and vibration resistance | Lower conductivity than copper |
| Brass | Usually acceptable for moderate requirements | Cost-effective and machinable | Verify plating and impurities |
| Titanium | Very low magnetic response | High strength-to-weight ratio | Higher cost and difficult machining |
| 316L stainless steel | Application dependent | Corrosion resistance | Cold working can increase magnetic response |
What plating options work for low magnetic connectors?
The plating system is often the deciding factor between a successful and failed low magnetic design.
Standard connector plating commonly uses nickel as a diffusion barrier beneath gold. While effective mechanically, nickel is ferromagnetic and may not meet low magnetic requirements.
Common low magnetic plating approaches include:
| Plating approach | Advantages | Engineering considerations |
|---|---|---|
| Direct gold over copper alloy | Excellent corrosion resistance and electrical performance | Requires careful control because there is no nickel barrier |
| White Bronze (copper-tin-zinc alloy) | Non-magnetic diffusion barrier alternative | Requires qualified plating supplier |
| Silver plating | Excellent conductivity for RF applications | Requires tarnish protection |
| High-phosphorus electroless nickel | Can provide improved magnetic performance compared with standard nickel | Must be tightly specified and verified |
A supplier specification should identify the complete plating stack, including prohibited materials. “Gold plated” alone is not sufficient because the underlying barrier layer may determine magnetic behavior.
Which low magnetic connector assembly should you choose by application?
MRI and medical imaging systems
MRI environments typically prioritize field uniformity and safety. Connector assemblies near strong magnetic fields require controlled permeability and verified material purity.
Typical selection:
- BeCu contacts
- Direct gold plating or qualified non-magnetic barrier plating
- Non-ferrous hardware
- Completed assembly permeability testing
MRI systems commonly operate at 1.5T, 3T, or higher field strengths, making small magnetic components significant.
Quantum computing hardware
Quantum systems require extremely low magnetic interference, especially near sensitive cryogenic circuits.
Important considerations:
- Low magnetic contact materials
- Cryogenic compatibility
- Thermal contraction matching
- High-purity solder and assembly processes
Specialized flux free soldering quantum PCB techniques may be required where magnetic contamination or field disturbance could affect operation.
Aerospace navigation and sensing
Navigation sensors and gyroscopes require low residual magnetic fields combined with vibration resistance.
Typical choices:
- Phosphor Bronze contacts
- Carefully controlled gold finishes
- Titanium or brass hardware
- Low magnetic fasteners
RF and microwave systems
RF systems balance magnetic performance with electrical loss.
Selection priorities:
- Low PIM performance
- Controlled impedance
- Low-loss plating
- Mechanical repeatability
Silver plating may provide conductivity advantages, but environmental protection must be considered.
Laboratory instrumentation
Laboratory equipment often requires a balance between performance and cost.
A moderate permeability target such as below 1.01 may be acceptable for many instruments, while primary measurement systems require tighter specifications.
What manufacturing controls are required?
A low magnetic connector assembly can fail after component selection if manufacturing introduces magnetic contamination.
| Manufacturing checkpoint | Engineering requirement | Verification |
|---|---|---|
| BOM review | Specify exact connector part number and magnetic requirements | Supplier documentation and sample testing |
| Material selection | Confirm alloy grade and plating stack | Material certificates |
| PCB selection | Verify substrate compatibility | Datasheet review |
| Assembly tooling | Use non-magnetic tooling where required | Tool inspection |
| Solder process | Control alloy purity and contamination sources | Paste documentation and testing |
| Mechanical hardware | Specify titanium, brass, or approved alternatives | Incoming inspection |
| Final assembly | Measure complete assembly magnetic performance | Permeability testing |
What are the most common low magnetic connector failures?
Hidden nickel underplating
A connector may appear gold plated while containing a nickel barrier underneath. This can increase magnetic response beyond the design limit.
The solution is a complete plating specification that identifies each layer.
Magnetic contamination during assembly
Steel tweezers, screws, fixtures, and machining debris can introduce localized magnetic regions.
Assembly controls should include:
- Non-magnetic tooling
- Controlled work areas
- Material traceability
- Final magnetic inspection
Stress-induced magnetism
Cold working, bending, machining, and forming processes can change magnetic properties in some alloys.
Material processing history should be considered during supplier qualification.
Testing only the connector component
The final PCB assembly can contain additional magnetic sources:
- Solder joints
- Screws
- Shields
- Mechanical brackets
- Contaminants
Qualification should measure the assembled product.
Supplier checklist for low magnetic connector assembly
Use this checklist during RFQ and supplier review:
| Requirement | Supplier response |
|---|---|
| Target permeability (μr) defined | Confirm value and test method |
| Connector alloy identified | Confirm material grade |
| Plating layers documented | Confirm every layer |
| Nickel restriction stated | Confirm no prohibited barrier layers |
| Magnetic testing available | Confirm sampling or 100% inspection |
| Assembly tooling controlled | Confirm manufacturing process |
| Hardware materials specified | Confirm screws and brackets |
| Application environment provided | MRI, cryogenic, aerospace, RF, or laboratory |
FAQ
What is the difference between non-magnetic and low magnetic?
Non-magnetic describes a material category, while low magnetic describes an engineering requirement with measurable limits such as permeability and residual magnetism.
Why is BeCu commonly used in low magnetic connectors?
BeCu provides strong mechanical spring performance while maintaining low magnetic behavior, making it useful for repeated mating cycles.
Can standard SAC305 solder be used?
For many applications, standard solder may be acceptable. However, highly sensitive environments may require specialized alloys, contamination controls, and qualification testing.
How is a low magnetic connector tested?
Component and assembly testing may use permeability indicators such as a Severn Gauge, vibrating sample magnetometer, or other calibrated magnetic measurement equipment.
Does low magnetic assembly increase cost?
Yes. Costs increase due to specialized materials, plating controls, supplier qualification, and additional inspection requirements.
Can APTPCB support low magnetic PCB assembly?
Yes. APTPCB supports advanced PCB manufacturing requirements. Designs can be submitted through the Quote page with magnetic specifications included.
Does PCB material affect magnetic performance?
Most FR4 materials are suitable, but specific pigments, fillers, hardware, and assembly materials should be reviewed for sensitive applications.
What is White Bronze plating?
White Bronze is a copper-tin-zinc alloy plating system used as a non-magnetic alternative diffusion barrier in some connector applications.
Related pages & tools
- PCB Materials: Explore substrates suitable for high-frequency and low-loss applications.
- PCB Manufacturing: Learn about assembly capabilities and quality control standards.
Glossary
| Term | Definition |
|---|---|
| Permeability (μ) | Ability of a material to support magnetic field formation. |
| Relative Permeability (μr) | Ratio between material permeability and free space permeability. |
| Diamagnetic | Materials with slightly negative magnetic response. |
| Paramagnetic | Materials with weak positive magnetic response. |
| Ferromagnetic | Materials strongly attracted to magnetic fields. |
| Retentivity | Ability to retain magnetization after field exposure. |
| BeCu | Beryllium Copper alloy used for high-strength contacts. |
| Passivation | Chemical treatment used to improve stainless steel surface properties. |
| Severn Gauge | Instrument used for magnetic permeability comparison testing. |
| Diffusion Barrier | Plating layer preventing base material migration. |
| Tesla (T) | SI measurement unit of magnetic flux density. |
| Cold Working | Mechanical deformation that can alter metal properties. |
Conclusion: How to specify a low magnetic connector assembly
A reliable low magnetic connector assembly requires coordinated decisions across materials, plating, PCB design, manufacturing, and validation.
When requesting a DFM review or quotation from APTPCB, provide:
- Target permeability requirement (for example, μr < 1.0005).
- Required plating construction and nickel restrictions.
- Magnetic testing requirements.
- Application environment, including cryogenic, RF, MRI, or vibration conditions.
For MRI, aerospace, quantum, and precision instrumentation projects, magnetic performance should be treated as a system-level design requirement rather than a connector-only specification.
Visit the Contact page to discuss low magnetic assembly requirements with the engineering team.