Introduction to Wire-to-Board Connectors
When an electronic product must interface with external transducers, user interfaces, power storage, or remote sub-assemblies, a wire-to-board (W2B) connector forms the physical junction between discrete wiring and the rigid PCB trace network.
A complete W2B connector system consists of a PCB-mounted header, a female plug housing, and crimp contacts securely attached to individual wire conductors. Engineering a reliable W2B interface requires balancing pin pitch, current density, mechanical latching, and ease of field serviceability.
Anatomical Sub-Components of the W2B System
Designing in a wire-to-board interface requires attention to both sides of the physical boundary.
The PCB Header
The header is the fixed component soldered to the board. Headers come in shrouded or unshrouded configurations. Shrouded headers enclose the male pins in a plastic wall to prevent short circuits and incorrect mating orientation, whereas unshrouded headers save board real estate at the expense of pin protection. Headers are available in top-entry (vertical) or side-entry (right-angle) variants depending on enclosure cable routing requirements.
The Crimp Housing and Terminal
The cable assembly side uses an insulating plastic housing containing individual stamped-and-formed or machined contact terminals. The terminal relies on two distinct crimps: a wire crimp that compresses the metallic core to form a gas-tight electrical bond, and an insulation crimp that clamps the outer wire jacket to provide strain relief against mechanical pulling.
Locking Mechanisms and Mechanical Retention
The choice of locking mechanism directly affects vibration tolerance and field reliability.
Friction Latch
Friction latches rely solely on friction between the housing walls to keep the mated pair together. They offer quick connection and disconnection, making them suitable for low-vibration environments like interior consumer products.
Positive Locking
Positive locking features an integrated plastic latching arm or metal spring clip that snaps into a matching ramp on the header. It requires manual depression of the latch to disconnect. Positive locking is mandatory in high-vibration systems, including automotive modules, aerospace electronics, and motor drives.
Terminal Position Assurance (TPA)
In critical systems, engineers often specify housings with TPA accessories. A TPA clip is inserted after the crimped contacts are pushed into place, physically locking the terminals so they cannot back out under high cable tension.
Electrical and Physical Design Rules
When laying out a W2B interface on your PCB, keep these design considerations in mind:
- Wire Gauge and Pitch Correlation: Compact pitches like 1.00mm to 1.25mm typically accommodate 28 AWG to 32 AWG conductors and carry low currents around 1.0A to 1.5A per contact. Mid-range pitches from 2.00mm to 2.54mm handle 22 AWG to 28 AWG wire with ratings near 2.0A to 3.0A. Power-focused W2B systems with pitches of 3.96mm to 5.08mm handle 16 AWG to 20 AWG wire and can carry 5.0A to 10.0A or more per contact.
- Thermal Derating: Manufacturer current ratings on datasheets are typically calculated with a single contact active in open air at ambient temperature. When multiple adjacent contacts carry maximum current inside an enclosed housing, heat builds up quickly. Always apply a thermal derating curve, often reducing the rated current per pin by 20% to 40% depending on total pin count and operating environment.
