Surface-mount PCB fasteners for automated pick-and-place assembly

Paul Boughton

The integration of PEM PCB fasteners into the normal pick-and-place assembly process offers OEMs and contract manufacturers significant benefits over through-hole or broached fixings. These benefits include:

* Faster parts handling and assembly;

* Enhanced manufacturing quality and yield;

* No risk of loose components being lost or mixed;

* No need for slow, manual placement of components.

The challenge of conventional fasteners

Conventional through-hole or broached fasteners present designers and contract manufacturers with a number of challenges and restrictions. The designer must ensure that the fastener’s location on the board is easily accessible to allow for manual placement during assembly.

The through-hole fasteners are also typically supplied as loose components which increases the complexity of parts handling prior to, and during, the manufacturing process. Placing loose components into bowls next to the production line frequently leads to some devices being lost, or mixed with other loose components.

Quality can also be compromised as the boards can be susceptible to cracking and misalignment which reduce the overall manufacturing yields and increase field failures.

Surface-mount solutions

The use of surface-mount fasteners, supplied on a tape-and-reel, eliminates the need for fasteners to be placed manually onto the PCB. Instead, the fasteners simply become another component which can be included in the automated pick-and-place assembly and reflow soldering process.

For the design engineer this means more flexibility in placing the fasteners and the assurance that they will be positioned and soldered to the same high quality as other surface-mount components. As the fastener is attached to the board using a non-intrusive process, unlike through-hole or broached attachment, the board is not exposed to the risk of cracking, and the fasteners can be placed closer to the edge of the board.

Surface-mount fasteners are available in a range of configurations which allow them to replace many types of conventional PCB hardware.

Spacers and nuts can be used to stack, space and attach PCBs. Available with or without threads, surface-mount spacers can typically be used with boards with a thickness of just .060”/1.53mm.  Standard steel fasteners are plated with tin to aid in the soldering process.

Panel fasteners in different variations use a threaded screw or pin that retracts and advances to engage a nut or internally threaded fixing.  The retainer is placed on the board prior to going through the reflow oven. An ABS plastic cap and threads are then snapped onto the retainer to complete the assembly.

Right-angle fasteners provide reusable threads, parallel to the board, to create permanent right-angle attachment points on PCB. As viable alternatives to conventional angle brackets or threaded right-angle blocks, they can be used for board-to-chassis, chassis-to-board, or component-to-board attachments on boards down to a thickness of .040”/1mm. Two pins at the bottom of the fastener act as pilots, ensuring stability and accuracy during placement.