Board-to-Board Connectors

What Is a Board-to-Board Connector?

A board-to-board connector is a mated PCB-mounted interconnect that creates a direct electrical path between two PCBs. Unlike wire-to-board connectors (which bridge components with a cable), BTB connectors are designed as part of the PCB and enclosure architecture, so mechanical alignment, spacing, and electrical performance must be considered together.

BTB connectors are commonly used to modularize electronic systems, enabling boards to be designed, manufactured, and tested independently before final assembly. This supports design flexibility and serviceability across many industries and product form factors.

How Board-to-Board Connectors Work

A typical BTB system consists of a plug/header and a receptacle/socket that mate to form a connection. These components are attached to the PCB using surface-mount (SMT) or through-hole (THT) termination.

When mated, contacts engage with a defined amount of wipe (axial overlap) that helps disrupt surface films and supports a stable electrical interface. Connection integrity is maintained through contact normal force and, in some designs, additional retention features (e.g., latches or locking mechanisms). Because PCBs are rigid, the connector system must tolerate alignment variation without placing excessive stress on solder joints, contacts, or board structures.

Key Specs at a Glance

• Board orientation: stacking (parallel), coplanar (edge-to-edge), orthogonal (90°)
• Pitch: primary driver of density, routing difficulty, and tolerance margin
• Stack height: driven by enclosure spacing and component clearance
• Termination: SMT or through-hole
• Power vs signal: current/thermal constraints influence contact selection
• Reliability: vibration exposure, fretting risk, and mating cycles vary by design

Types of Board-to-Board Connectors

BTB connectors are most commonly classified by the orientation of the boards they connect.

Stacking (Parallel Boards)

Two PCBs are stacked parallel using vertical plug-and-receptacle connectors. Stack height—the distance between board surfaces—is controlled by selecting connector height combinations within a family. This orientation reduces footprint by building upward rather than outward, making it common in compact and high-density electronic designs.

Mezzanine (Compact Parallel Interconnect)

Mezzanine connectors are a specialized form of parallel board stacking designed for shorter stack heights, finer pitch, and higher contact density. They are frequently used in space-constrained applications such as embedded systems, computing modules, and communications hardware where signal density and controlled impedance are critical.

Coplanar / Edge-to-Edge

Two PCBs connect in the same plane using right-angle connectors or edge-to-edge arrays. Coplanar configurations are used when a long, slim form factor is needed or enclosure geometry favors an extended PCB layout.

Orthogonal / Motherboard–Daughterboard (90°)

Boards connect at a 90-degree angle, typically joining a daughterboard to a motherboard or backplane. This architecture supports modular expansion and high connector density, common in computing, networking, and storage systems.

Common Connector Styles and Contact Designs

Pin Headers and Sockets

A widely used, cost-effective style consisting of mating pins and sockets. Shrouded variants can improve alignment and protect contacts, while unshrouded variants can reduce size.

Micro-Pitch Stacked Arrays

Micro-pitch connectors (commonly in the 0.4 mm to 0.8 mm range) provide high contact density for compact designs. They are typically SMT and may require tighter process control and layout precision.

High-Speed Differential Arrays

High-speed BTB connectors use controlled geometry and grounding strategies to manage impedance continuity and reduce crosstalk. These are selected when signal integrity margins and channel budgets are tight.

Card-Edge and Hermaphroditic Systems

Card-edge designs allow a PCB edge with plated contacts to mate into a receptacle, reducing the need for a separate mating half on the module. Hermaphroditic designs use identical mating faces and can support rugged, long-wipe engagement in modular systems.

Mechanical Design Considerations

Alignment and Tolerance Stack-Up

Small misalignments can reduce contact engagement or introduce mechanical stress. Some designs incorporate floating or compliant features that allow limited movement to absorb assembly tolerances and support blind mating.

Mating Force and Retention

Total mating force is the cumulative force of all contacts, so high-pin-count connectors can require significant insertion force. Retention features (mounting posts, latches, friction locks) help maintain connection stability under shock and vibration.

Stack Height and Profile

Connector families are offered in height increments to meet mechanical envelope needs. Stack height must be chosen to satisfy enclosure spacing, component clearance, and mechanical robustness requirements.

Electrical Design Considerations

Current Ratings and Derating

Current capability varies with contact size, pitch, material selection, and thermal conditions. Micro-pitch signal contacts generally support lower current than larger power contacts. In practice, current ratings should be evaluated with derating based on ambient temperature, airflow, and the number of simultaneously energized positions to control temperature rise.

Voltage, Creepage, and Clearance

Voltage ratings depend on insulation systems and spacing between contacts (creepage and clearance). General-purpose board interconnects are often specified for working voltages in the low hundreds of volts, while fine-pitch designs may have stricter limits due to reduced spacing.

Contact Materials and Plating (Reliability Implications)

Contact alloys such as brass, phosphor bronze, and beryllium copper are commonly used depending on performance and cost targets. Plating choices (e.g., gold vs tin) affect corrosion resistance, stability of contact resistance, and suitability for vibration exposure.

Signal Integrity and High-Speed Performance

At higher data rates, the connector becomes part of the transmission channel. Key considerations include:

• Impedance continuity through the connector interface
• Crosstalk control (NEXT/FEXT), affected by pin mapping and ground structure
• Insertion/return loss behavior as part of the overall channel budget
• PCB breakout and reference planes, which can dominate performance if not controlled

High-speed performance should be assessed as a system (connector + PCB stack-up + routing + vias), since published connector capability depends on implementation details.

Pitch and Stack Height Selection

Pitch is the primary driver of density and often influences routing difficulty and mechanical tolerance margins.

• Micro pitch (0.4–0.8 mm): maximizes density; often requires tighter layout/assembly control
• Standard pitch (1.0–2.54 mm): balances density, robustness, and ease of routing
• Coarser pitches (≈3.96 mm and above): often selected where higher current capacity or mechanical robustness is prioritized

Reducing pitch can increase density but may reduce per-contact current capacity and tolerance margin, requiring careful PCB layout and manufacturing controls.

Environmental and Reliability Considerations

Operating Temperature and Materials

BTB connectors are commonly specified for defined operating temperature ranges. Housing materials and contact systems should be selected to maintain mechanical stability and electrical performance at temperature.

Vibration, Fretting, and Contact Stability

In vibration environments, micro-motion at the contact interface can contribute to fretting wear and intermittency over time. Design choices such as contact normal force, retention features, and plating selection influence robustness.

Durability (Mating Cycles)

Durability is typically specified in mating cycles and varies widely by connector class and intended use (internal module connections vs service-accessible interfaces). Cycle expectations should be matched to the application’s lifecycle.

Standards, Testing, and Qualification Context

There is no single BTB-only universal standard. Manufacturers commonly qualify connector performance using recognized test methods and sequences, such as:

• EIA-364 series for electrical, mechanical, and environmental tests (e.g., durability, vibration, thermal shock)
• EIA-364-1000 for grouped environmental test sequences intended to simulate life conditions
• IEC 60529 for IP code definitions where sealing claims apply
• Common material and safety classifications may also be referenced depending on the application and market expectations

Common Applications and Design Priorities

• Industrial automation: vibration exposure, secure retention, and environmental robustness
• Automotive/transportation: thermal cycling, vibration endurance, and power delivery needs
• Medical equipment: reliability, consistent performance, and long lifecycle expectations
• Computing/data centers: signal integrity, density, and thermal constraints
• Consumer electronics: miniaturization, low profile, and high interconnect density

How to Choose the Right Board-to-Board Connector

• Define board orientation: stacking, coplanar, or orthogonal
• Set required stack height: confirm connector height options support the envelope and tolerance
• Clarify electrical needs: current per contact, voltage environment, and signal speed requirements
• Assess mechanical constraints: PCB real estate, insertion force limits, and retention needs
• Match the environmental profile: temperature, vibration exposure, durability expectations, and contamination risk

Board-to-Board Connector Solutions from EDAC

EDAC supports board-to-board connector requirements across a range of pitches, stack heights, and mechanical configurations, including applications that prioritize signal integrity, power delivery, and mechanical robustness.

In addition to standard offerings, EDAC provides semi-custom and full custom solutions to meet application-specific constraints. For many programs, EDAC can support low to high production volumes and, where the design change is a slight modification to existing tooling, it may be possible to do so with little to no non-recurring engineering (NRE) or new tooling—depending on the scope of change and end-application requirements.