Wire-to-Board Connectors

Wire-to-Board Connectors

Wire-to-board connectors create detachable electrical connections between discrete wires (or cable assemblies) and printed circuit boards (PCBs). They are widely used to deliver power, carry signals, and connect subsystems inside electronic equipment where assembly repeatability and serviceability matter. A typical wire-to-board system includes a PCB-mounted header (through-hole or SMT) and a mating cable-side housing that retains crimped or insulation-displacement contacts. Engineers select these connectors by balancing electrical requirements, mechanical retention, environment, and assembly method.

What is a Wire-to-Board Connector?

A wire-to-board connector provides a removable electrical interface between wires and a PCB. The PCB-side header establishes the board connection, while the cable-side housing manages wire termination and mating retention. Compared to board-in terminations (where wires solder directly to the PCB), wire-to-board connectors support modular design, easier manufacturing, and field serviceability.

Connector Types

Wire-to-board connectors are typically grouped by circuit density, current capacity, and how permanent the connection needs to be. The categories below help narrow the right connector family before evaluating pitch, wire gauge range, locking features, and plating.

Signal Connectors

Signal connectors prioritize density and stable performance for control and data circuits. These families commonly use fine pitch spacing (about 1.0–2.5 mm) and support lower current per contact (often 0.5–3 A). They are available in single- or double-row configurations with vertical or right-angle mounting to suit tight PCB layouts. For noise-sensitive interfaces, some designs support twisted-pair routing or shielding approaches used in applications such as LVDS.

Power Connectors

Power connectors are designed to handle higher current while maintaining safe operating temperatures and appropriate electrical clearance. Larger pitch families (often 3.96–10.16 mm+) accommodate heavier conductors and can support 5–45+ A per contact depending on design and thermal conditions. Polarization and keying features help prevent mis-mating, while positive locks are commonly used to resist vibration-related disconnects in appliances, industrial equipment, and automotive subsystems.

Board-In Connectors

Board-in terminations eliminate the mating header by terminating wires directly into the PCB, reducing component count and saving board space. The result is a permanent, vibration-resistant connection, but it is not detachable—repairs typically require desoldering—so board-in is best suited to fixed connections where service access is limited or disconnects are not expected.

Cable Assemblies

Wire-to-board systems are commonly used with both ribbon cable and discrete wire harnesses. IDC ribbon assemblies support fast mass termination for multi-conductor flat cables, while crimped discrete-wire assemblies provide flexible routing and can mix signal and power conductors within the same housing. The best choice depends on circuit count, harness routing, assembly volume, and service needs.

Key Specifications

Connector suitability depends on electrical limits, thermal performance, and mechanical constraints. In practice, current, ambient temperature, voltage clearance, and retention should be evaluated together—especially when multiple circuits are energized or when vibration and heat are present.

Current Rating

• Signal: 0.5–3 A per contact
• Power: 5–45+ A per contact

Published current ratings are typically based on a defined temperature rise (often ~30°C) under standard test conditions. In multi-position connectors, adjacent energized contacts can increase thermal accumulation and require derating, particularly in compact housings or elevated ambient temperatures. Always verify current capacity using the manufacturer’s temperature-rise or derating data for your configuration.

Voltage Rating

• Logic/signal: <50 V
• Power distribution: 250–600 V AC/DC

Voltage rating influences creepage and clearance requirements, housing geometry, and pitch selection. Higher voltages generally demand increased spacing to reduce flashover and tracking risk, especially in contaminated or humid environments.

Pitch (Centerline Spacing)

• 0.8–1.25 mm: compact electronics
• 2.0–2.54 mm: general-purpose PCB I/O
• 3.96–10.16+ mm: power and higher voltage clearance

Wire Gauge (AWG)

Terminals are designed for specific wire ranges. Staying within the specified AWG range helps ensure correct retention, stable crimp geometry, and predictable electrical performance. Using wire outside the intended range can lead to poor mechanical grip, higher resistance, or inconsistent termination quality.

• Signal: 26–32 AWG
• General: 22–28 AWG
• Power: 8–20 AWG

Operating Temperature

• Consumer: −25°C to +85°C
• Industrial/automotive: −40°C to +105°C or +125°C

Operating temperature affects both contact performance and housing material stability. Higher temperature requirements may drive changes in material selection, plating, and current derating—especially for compact, high-density connectors.

Termination Methods

Termination method affects assembly time, tooling investment, mechanical durability, and serviceability. For most wire-to-board systems, engineers choose between crimp contacts for discrete-wire harnesses and IDC termination for fast, repeatable ribbon cable assembly.

Crimp Contacts

Crimp termination compresses a metal terminal around a stripped conductor to form a gas-tight joint. When formed with the correct tooling, crimps provide strong retention and reliable performance through vibration and thermal cycling. The tradeoff is assembly time and tooling requirements—each terminal family typically needs matched crimp dies and controlled process parameters to maintain consistency.

IDC (Insulation Displacement)

IDC termination uses blades to pierce insulation and contact the conductor without stripping. This supports fast mass termination for ribbon cables and fixed-pitch wire, helping reduce labor cost and improve repeatability in volume production. IDC is generally more limited in wire compatibility and typically less tolerant of sustained vibration than a well-formed crimp, so it is best used where mechanical stress is controlled.

Contact Materials & Plating

Plating impacts contact resistance stability, mating durability, and cost. Selection should reflect circuit type (power vs. low-level signal), expected mating cycles, and vibration exposure.

Gold (Au)

Gold plating is commonly specified for low-level signals and dry-circuit conditions where oxide formation can affect contact stability. It also supports higher mating cycles and improved corrosion resistance, though cost often limits gold to selective contact areas.

Tin (Sn)

Tin plating is economical and widely used for general-purpose interfaces, especially where sufficient normal force and wiping action manage oxides. In vibration-prone designs, tin can be more susceptible to fretting unless the connector system maintains contact stability.

Silver (Ag)

Silver offers high conductivity and is sometimes used where minimizing voltage drop and heat rise is critical. Depending on environment and bias conditions, silver can tarnish and may require additional consideration for long-term stability.

Locking & Retention Features

Retention features reduce the risk of partial mating, terminal back-out, and vibration-related disconnects. For higher-vibration environments or critical circuits, prioritize positive locking and secondary retention that confirms full seating.

• Friction lock: relies on fit/interference; common in low-vibration internal assemblies
• Positive lock: latch mechanism (often audible/tactile) for higher vibration or critical power
• TPA/retainers: secondary retention to prevent terminal back-out and confirm seating
• Solder tabs/fitting nails: mechanical anchoring to reduce stress on solder joints (especially SMT)

Environmental Protection & IP Ratings

Environmental requirements determine whether sealing, potting, and material ratings are needed. Many wire-to-board connections rely on enclosure-level protection, but sealed interfaces and compatible housings may be required where moisture, dust, or washdown exposure is expected.

Ingress Protection (IP Code)

• Solids: IP2X (finger safe), IP5X (dust protected), IP6X (dust tight)
• Liquids: IPX4 (splash), IPX7 (immersion), IPX9K (high-pressure washdown)

Potting (Resin Sealing)

Some connector interfaces support potting to help block moisture and reduce stress concentration at the PCB interface. Potting can improve robustness in challenging environments, but it should be evaluated for serviceability and manufacturing process compatibility.

Flammability & Safety

• UL 94 V-0: self-extinguishing plastics with no flaming drips under specified conditions
• Glow Wire Test (GWT): used for unattended appliance safety requirements

Reliability & Testing Standards

Reliability depends on both connector design and exposure conditions. Common issues include vibration-induced micro-motion, termination defects, and contamination that increases contact resistance over time.

Common Failure Mechanisms

• Fretting corrosion: micro-motion can increase resistance in oxide-forming plating systems
• Galvanic corrosion: dissimilar plating pairs can accelerate degradation
• Electromigration: dendritic growth risk under DC bias and humidity for certain materials

Testing Protocols (Examples)

• EIA-364 environmental methods: temperature, humidity, and related conditioning
• MFG (Mixed Flowing Gas): accelerated corrosion exposure
• LLCR (Low Level Contact Resistance): low-current resistance stability evaluation

Application Guidance

Selection should reflect vibration exposure, service expectations, and environment. As a practical starting point, choose the termination method and retention features based on mechanical stress, then refine pitch and plating to meet electrical and reliability requirements.

High Vibration (Automotive / Industrial)

Use crimp termination with positive locks and TPA/retainers. For power circuits, tin is common when contact stability is maintained; for low-level sensors and data circuits, gold is often preferred where resistance stability is critical.

Consumer Electronics (Static, Internal)

Fine pitch and friction locks are common for internal assemblies with minimal vibration. IDC can be appropriate for ribbon cable harnesses where fast, repeatable termination is valuable and mechanical stress is controlled.

High Power (Appliances, HVAC)

Larger pitch families support higher current and clearance requirements, with robust retention features preferred for serviceable assemblies. Depending on end-product requirements, material ratings such as glow wire may be required.

Selection Guide & Decision Matrix

Use termination method and plating selection to match environment and service needs.

Quick Selection Checklist

• Required current per contact
• Available PCB space and pitch
• Wire gauge range
• Vibration level
• Required IP rating
• Expected mating cycles
• Termination method (crimp or IDC)

Common Design Mistakes

These issues frequently cause field failures or intermittent performance.

• Mixing gold and tin platings: dissimilar plating can accelerate galvanic corrosion and increase resistance.
• Using tin in high vibration without adequate normal force: increases fretting corrosion risk.
• Undersized creepage/clearance: pitch too small for voltage can increase flashover risk.
• Insufficient strain relief: harness loads transfer to terminals and degrade the interface.
• Incorrect IP rating: moisture or contamination intrusion can increase resistance or cause shorts.

Product Finder

Use these buckets to narrow selection before choosing a specific family.

EDAC Wire-to-Board Solutions

EDAC provides wire-to-board connectors in standard and semi-custom configurations covering fine-pitch signal through high-current power applications. Many designs can be adapted with alternate pin counts, keying options, plating changes, or housing modifications with minimal tooling or NRE. Engineering support is available to help match electrical, mechanical, and environmental requirements across prototype and volume production.