PCB accessories are often treated as secondary hardware. In practice, they establish the mechanical and electrical interface between a board, its wiring, and the equipment used to assemble or service it. An eyelet changes the usable hole diameter. A bus strip distributes a common node. A wire-wrap terminal establishes a post for point-to-point wiring. An insertion tool controls how a contact is seated.
Each decision is small. The resulting failure may not be.
For backplane, extender, and prototyping assemblies, accessory selection should be based on the board hole pattern, post geometry, terminal style, connector system, and specified installation method. A contact that appears to fit may still be unsuitable for the intended termination or service operation.
Accessory Categories and Their Intended Roles
Vector’s PCB accessories{:target="_blank"} product line includes handles, eyelets, bus strips, assembly tools, pins, terminals, and slip-on contacts. These categories support different functions and should not be treated as interchangeable.
PCB handles
PCB handles are available in pull-type and ejector-type configurations. They provide a controlled point for inserting, removing, or handling a circuit card. In an extender or test-card assembly, the handle supports repeated handling while reducing the likelihood that force will be applied to components, wiring, or the board surface.
The handle type should correspond to the mechanical requirements of the card and its connector system. A pull handle and an ejector handle do not apply force in the same way. Their role is not simply ergonomic. They influence how the board is moved relative to the mating connector.
Eyelets
Eyelets{:target="_blank"} provide hole-size reduction. The documented reductions include 0.055 inch (1.4 mm) to 0.042 inch (1.067 mm), and 0.062 inch (1.57 mm) to 0.042 inch (1.067 mm).
This makes an eyelet useful where a board pattern must accept a smaller terminal or contact than the original hole would otherwise support. Eyelets can also be used when establishing connections to power and ground planes in compatible prototyping-board constructions.
The eyelet is a mechanical transition, not a universal adapter. The reduced opening, the eyelet geometry, the terminal shank, and the installation tooling must all agree. If the eyelet is installed with the wrong anvil or die, it can deform, split, loosen, or fail to seat correctly. A damaged eyelet may remain visually present while providing an unreliable mechanical or electrical connection.
Bus strips
Bus strips{:target="_blank"} are made from flat cold-drawn copper wire with 0.042 inch (1.067 mm) holes. They provide a way to distribute a common electrical node across a compatible board pattern, particularly where power or ground must be routed across multiple points.
In a prototyping or extender assembly, a bus strip can reduce the amount of individual point-to-point wiring required for a common connection. It is not a replacement for a signal-specific terminal or for a defined backplane connector contact. The board pattern, hole diameter, and intended electrical function remain the controlling factors.
Pins and terminals
Vector’s pins and terminals{:target="_blank"} include wire-wrap terminals, push-in terminals, inboard pins, and socket pins. These options support different board attachment and wiring methods.
Wire-wrap terminals provide square posts for wrapped conductors. Push-in terminals provide a press-fit connection for compatible board holes. Inboard pins are press-fit contacts intended for compatible board patterns. Socket pins combine a board-mounted contact with a socket interface and a wire-wrap tail.
The distinction between these families matters during both design and assembly. A wire-wrap post is not equivalent to a solder-tail termination. A socket pin is not interchangeable with a simple press-in pin. The correct choice depends on whether the assembly requires wire wrapping, soldering, a removable lead, a socketed test point, or a defined connector interface.
Backplane and Extender Assembly Applications
Backplane work often combines fixed connector interfaces with local wiring, jumpers, or test access. An extender board may expose signals that are difficult to reach inside the system, while a prototyping board may provide a flexible area for circuit development or controlled modifications.
A documented use case is VME J1/J2 daisy-chain jumpering by wire-wrap on 0.025 inch square posts, using 0.100 x 0.100 inch push-on jumpers or shunts. In this arrangement, the post geometry and the jumper interface are part of the system definition. The assembly method is not simply “attach a wire.” It requires the correct square post, the appropriate wire-wrap termination, and a jumper or shunt that fits the intended spacing and contact arrangement.
For an extender or prototyping assembly, eyelets may adapt board holes for compatible terminals. Bus strips may distribute power or ground. Wire-wrap terminals may support temporary or reconfigurable point-to-point wiring. Socket pins may support replaceable or accessible contacts where testing and troubleshooting require a removable interface. Slip-on contacts may provide a convenient connection to compatible square posts without changing the board-mounted termination.
These functions support different stages of the hardware lifecycle. A prototyping assembly may prioritize access and reconfiguration. An extender may prioritize test visibility and controlled mating with a backplane. A production backplane may require a specified connector system and a tightly controlled installation process. Accessories should be selected according to that system role rather than based on physical resemblance alone.
Slip-On Contacts and Wire-Wrap Compatibility
Slip-on contacts{:target="_blank"} include contacts with 28 AWG wire that slip onto 0.025 inch (0.635 mm) square posts. Vector also identifies Tefzel insulated silver plated wire as available for this accessory category through its slip-on contact and wire accessory information{:target="_blank"}.
The defining compatibility condition is the square post. A slip-on contact intended for a 0.025 inch square post should not be assumed to fit a round pin, a different post size, or a terminal with a different surface geometry. The wire gauge and insulation construction also affect how the contact routes and how much space is required around adjacent points.
Wire-wrap terminals require the same discipline. A poor wrap can result from using the wrong wire gauge, an unsuitable wrapping method, or a mismatch between the wire-wrap terminal and the square post. A connection can appear complete while failing to provide the intended contact pressure or mechanical stability.
The termination method should be identified before selecting the contact. Wire-wrap, solder-tail, push-in, and slip-on interfaces impose different mechanical requirements. Substituting one for another without reviewing the board pattern and connection method creates avoidable rework.
Tool Selection Is Part of the Contact System
The tools category{:target="_blank"} includes pad cutters, hand insertion tools, anvils, and dies. These tools are not generic accessories. They control how a terminal, eyelet, or related contact is installed into the board.
A hand insertion tool must support the contact being installed. An anvil and die must match the eyelet or terminal geometry. If the tool is too large, too small, or shaped for a different contact, the force may be transferred into the wrong area. The result can be a deformed eyelet, damaged plating, an enlarged hole, a loose terminal, or a board that no longer meets the intended assembly condition.
The same principle applies to connector maintenance. Insertion and extraction tools should be matched to the connector system. Using an improvised tool can damage the contact, housing, card edge, or adjacent positions. It can also make subsequent failures harder to isolate because the original damage may not be obvious during visual inspection.
The Cost of Using the Wrong Contact
The cost of an incorrect accessory is usually not limited to the accessory itself. It appears as rework, inspection time, damaged boards, intermittent connections, troubleshooting effort, and lost confidence in the assembly.
Several failure modes are predictable:
- An eyelet installed with the wrong anvil or die may be damaged before the board enters system test.
- A terminal selected for the wrong hole size may not retain correctly or may require excessive insertion force.
- A wire-wrap connection may be mechanically weak when the wire gauge and square-post geometry do not match.
- A slip-on contact may fail to seat on a post with incompatible dimensions.
- A solder-tail contact may be selected where a wire-wrap interface is required, creating a termination problem rather than solving one.
- An extraction tool that does not match the connector system may damage the contact or housing during service.
- A bus strip may be used where an isolated signal connection is required, creating an incorrect electrical path.
These failures are particularly disruptive in extender and backplane work because access is often the reason the assembly exists. If the accessory introduces an intermittent connection, the extender can make troubleshooting more difficult instead of making the circuit easier to observe.
The disciplined approach is to define the interface before assembly: board hole diameter, post size, contact style, termination method, wire gauge, connector system, and applicable insertion or extraction tool. Those characteristics should be recorded in the build documentation and checked against the selected accessory.
What Engineers and Program Teams Should Consider
Before releasing a backplane, extender, or prototyping assembly to production, review the following points:
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What is the board hole diameter?
Confirm whether the design requires a direct-fit terminal or an eyelet to reduce the hole size. -
What is the intended termination method?
Separate wire-wrap, solder-tail, push-in, socket, and slip-on requirements. They are not interchangeable categories. -
What post geometry is required?
A 0.025 inch square post is a specific interface. Wire, jumper, shunt, or slip-on contact selection should match it. -
Is the connection common or isolated?
Bus strips can support common power or ground distribution in compatible patterns, but they should not be used where individual signal isolation is required. -
Which tool installs the contact?
Select the hand insertion tool, anvil, die, pad cutter, or extraction tool for the actual contact and connector system. -
How will the assembly be inspected?
Define checks for seating, damage, retention, wire-wrap quality, contact alignment, and unintended electrical continuity. -
Will the assembly be serviced or reconfigured?
Extenders and prototypes may require socket pins, slip-on contacts, handles, or other features that support repeated access without damaging the board or connector.
PCB accessories are small components with system-level consequences. Eyelets, bus strips, terminals, contacts, and tools should be selected as one coordinated interface. When the hole pattern, contact geometry, termination method, and installation tooling agree, the accessory performs its intended function. When they do not, the resulting rework can exceed the apparent simplicity of the original choice.