Technical Sheets & Articles

SELF-CLINCHING FASTENERS AND THE ELECTRONICS INDUSTRY

Self-clinching fasteners with their inherent design and performance advantages have proved ideal in the assembly of a wide range of electronic components.

These unique steel, stainless steel, or aluminum fasteners (dozens of types and thousands of variations) provide permanent strong threads in metal sheets too thin to tap or can serve as more reliable alternatives to extruded/tapped or stamped threads. They have enabled the capability to develop many thin-metal designs otherwise impossible.

Self-clinching fasteners are relatively small (even miniature types are available) and require less "real estate" in attachment applications, which satisfies smaller, lighter packaging requirements of today's designs. Once installed, these types of fasteners do not loosen and will not fall out, which ensures that delicate internal circuitry is protected from hardware damage. Self-clinching fasteners further reduce the amount of hardware in an application, which translates to fewer parts to handle during assembly or service.

Every self-clinching fastener is designed with a simple idea in mind: less is better. Why use several pieces of loose hardware when one simple, yet cost-effective permanently installed fastener will do the job?

Some noteworthy examples of electronics-related applications for self-clinching technology:

• One self-clinching fastener replaced four pieces of hardware that had been previously used in a connector housing system for high-speed data exchange equipment.

• An early design for a telecommunications amplifier enclosure had utilized tapped holes in 2.5mm-thick aluminum chassis. However, the tapped holes did not provide adequate torque-out performance, and mating hole alignment problems slowed final assembly of the chassis. Self-clinching nuts and standoffs addressed the torque-out issue, and floating fasteners provided strength and a solution to the alignment problems.

• Low-profile self-clinching panel fasteners were specified to attach an access panel for a card cage assembly in telecom equipment. The panel fastener keeps the cover tight and secure, but allows for easy removal for service and maintenance. The large knurled, slotted head of the fastener makes finger or tool operation possible.

Other real-world electronics applications for self-clinching fasteners include attaching service doors and panels, mounting chassis to frames in desktop computers and workstations, attaching add-on components (such as fan trays, document loaders, and hard drives), and fastening rack-mounted equipment to racks.

Self-clinching fasteners can be installed quickly, easily, and permanently into metal sheets as thin as .020"/0.50mm and can meet requirements for high pushout and torque-out resistances. They can enhance end-product appearance, because their compact design allows them to be installed flush on one side in a panel. In many applications, they can support the switch to a thinner sheet metal or panel material, further reducing installed costs.

Self-clinching fasteners traditionally fall into one of four primary categories: nuts, studs, spacers/standoffs, and threaded access hardware.

Self-clinching nuts are commonly used wherever strong internal threads are needed for component attachment or fabrication assembly. During installation, a clinching ring locks the displaced metal behind the fastener's tapered shank, resulting in high pushout resistance. High torque-out resistance is achieved when the knurled platform is embedded in the sheet metal. Proper installation forces will not distort or damage the threads, because the recommended shank length is always less than the minimum sheet thickness. The clinching action of these nuts takes place on the fastener side of the thin sheet with the reverse side remaining flush and smooth.

Externally threaded self-clinching studs are used where an attachment must be positioned before being fastened. Flush-head studs are usually specified, but variations have been designed for high torque, thin sheet, or electrical applications. Manufactured from a variety of materials, self-clinching studs are offered in a wide range of thread sizes. Studs are also available without threads for use as permanently mounted guide pins or pivots.

Self-clinching spacers and standoffs are designed to allow components to be stacked or spaced away from a panel. Thru-threaded or blind types generally are standard. Their material can be steel, stainless steel, or aluminum. These standoffs are installed with their heads flush with one surface of the thin mounting sheet. When blind-threaded types are used, outer panel surfaces are not only smooth, but closed as well.

Threaded access hardware, or panel fastener assemblies (most spring-loaded), are generally used on enclosures where the screw must remain with the door or panel. These fasteners offer the advantages of ease of assembly and quick panel removal without loose screws. Self-clinching panel fasteners are pre-assembled and manufactured in a range of thread sizes and assorted screw lengths to satisfy the widest range of application demands. Many types can meet UL operator or service access area requirements, can be color-coded, and otherwise offer value-added benefits for specific applications.

Augmenting these primary self-clinching fastener categories, variations of these general types have been developed and enhanced over the years to meet emerging electronics and related-component applications. Each variation offers a particular advantage, whether in terms of meeting a design challenge, performance requirement, or enhancing component appearance. In addition, fastener technology has advanced to enable development of specialized self-clinching fasteners. Examples include types allowing for right-angle attachment of components and others designed exclusively for use in stainless steel.

Regardless of type or variation, all self-clinching fasteners are installed by pressing them into place in a properly sized drilled or punched hole. This pressing or squeezing process causes displaced panel material to cold flow into a specially designed annular recess in the shank or pilot of the fastener, locking the fastener in place. A serrated clinching ring, knurl, ribs, or hex head prevents the fastener from rotating in the metal when tightening torque is applied to the mating screw or nut.

The result is that self-clinching fasteners become a permanent and integral part of the panel, chassis, bracket, or other electronics component in which they are installed.

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