Understanding Micro Fastener Technology In Subcompact Electronic Assemblies

May 17, 2012
Micro fasteners enable lower part counts and assembly time resulting in smaller, lighter, thinner, and cheaper consumer electronics.

Extremely small micro fasteners have made significant inroads in the global marketplace, especially with the ongoing evolution of smaller, lighter, and thinner subcompact consumer electronic devices ranging from cell phones to tablet computers and everything in between. Looking back, threaded micro screws were among the first types of hardware that fit well in applications characterized by restrictive design envelopes and limited footprints for fastener placement and installation.

Table Of Contents

  1. Screws Or Fasteners
  2. Fasteners Are Forever
  3. One Type Of Fastener
  4. Other Types Of Fasteners
  5. Onward & Upward

Screws Or Fasteners

Micro screws in a variety of materials, head styles, and driver types may remain viable options in many applications. Yet their specification typically will require the use of additional hardware and locking patches, which are usually applied over screw threads to provide a tight interference fit. This inherently runs counter to the ultimate goal of minimizing the hardware and end-product weight.

Threaded micro screws marked only the beginning of a new dawn in micro fastener technology, though. Most notably, self-clinching micro fasteners, some threaded and some not, have been introduced offering even more choices and accompanying benefits.

Especially in contrast with micro screws, clinch fasteners can dramatically reduce the amount of necessary hardware in an assembly, particularly in applications where disassembly will not be a factor during the lifetime of the product. Also, they usually require at most only a single mating piece to complete final component attachment.

Other advantages flow downstream, including savings in production time and money accrued from reduced assembly steps. The benefits of self-clinching fasteners arise from their design, which features a unique annular recess for locking the fastener in place and an element to prevent fastener rotation in service.

Fasteners Are Forever

Regardless of type, self-clinching fasteners install permanently in thin ductile metal sheets by pressing them into place in a properly sized hole and applying sufficient squeezing force. This forces a clinching ring, knurl, ribs, or hex head into the panel surface, displacing sheet material into a specially designed annular recess in the shank or pilot of the fastener, known as an undercut.

The metal forced into the undercut secures the fastener against axial movement, while a non-round displacer secures the fastener against rotation. No secondary operations are necessary. All self-clinching fasteners become integral parts of an assembly by clinching permanently in place. They won’t loosen or fall out, and they never have to be handled again.

The specialty design and engineering behind micro fasteners underscores how they are not simply scaled-down versions of their larger self-clinching counterparts. As fastener types are downsized to lengths as short as 2 mm, thread sizes as small as M1.0, and diameters of 1 mm, issues relating to tight tolerances and performance values, among others, become magnified. Unique features engineered into the fastener often become both critical and essential.

One Type Of Fastener

The self-clinching microPEM TackPin (Type T) permanently and reliably attaches super-thin membranes to very thin cosmetic substrates such as keyboards (Fig. 1). In addition to the displacer and undercut, it incorporates a tapered tip and tangential interference band.

1. The microPEM TackPin (Type T) fasteners include a displacer and undercut and employ a tapered tip and tangential interference band.

The tip and band work together both to guide the fastener into the small-diameter and shallow hole in the panel and to create a slight interference fit between the hole and the fastener at the interference band. This creates minimal stresses in an aluminum host sheet, which can be as thin as 0.5 mm for through holes or 0.89 mm for blind holes and absorbs any tolerance between the diameter of the hole and the diameter of the clinching pin.

Among other key criteria for this TackPin design, engineers use proportions and ratios to determine the proper clinch profiles and apply state-of-the-art software modeling and custom programs to achieve maximum pullout performance.

The fasteners install into properly sized mounting holes in the sheet to be attached and the base panel. After insertion into these holes, the fastener is pressed into place. The fastener clinches into the base panel. The fastener’s head subsequently holds the top sheet, which is as thin as 0.2 mm, firmly and permanently in place. The self-clinching action results in full 360° metal contact and, upon installation, the fastener’s potential for loosening due to vibration or other factors becomes moot.

While the TackPin fastener shares the fundamental self-clinching hardware advantage of minimizing parts count, it additionally tackles historically vexing screw-related issues. For example, one particular keyboard historically required more than 80 M1.2 screws and more than 80 tapped holes in each assembly.

Handling dozens of tiny screws for each unit without the benefit of automation proved time-consuming, tedious, and costly. Threads or drives would strip when the screws were not properly driven, and locking patches contributed more cost. A switch to TackPin fasteners eliminated all tapping operations, the potential for stripped hardware, any need for patches, and all other screw-related concerns.

Other Types Of Fasteners

Among other micro self-clinching fasteners in the marketplace allowing designers to reduce the amount of hardware in subcompact electronic assemblies and gain all the associated benefits are threaded self-clinching micro standoffs for spacing or stacking internal components (Fig. 2). Standard types are available with threads as small as M1.0/#0-80 and in lengths as short as 2 mm/0.080 in.

2. Threaded self-clinching micro standoffs provide reliable spacing between components and enable safe, space-saving component stacking.

Products made from 400 Series stainless steel can be installed into sheet metal, including 300 Series stainless steel, as thin as 0.3 mm/0.012 in. with maximum hardness up to HRB 88 on the Rockwell “B” scale. Applications requiring installation in sheets as thin as 0.2 mm can be accommodated with specially engineered standoff designs.

Unthreaded self-clinching micro locating pins for locating, positioning, and/or alignment applications also are options (Fig. 3). Standard types are manufactured from age-hardened A286 stainless steel and designed with diameters as small as 1 mm/0.040 in. and in lengths as short as 2 mm/0.080 in. They can install permanently into stainless steel or other sheet materials as thin as 0.5 mm/0.020 in. with hardness up to HRB 92 on the Rockwell “B” scale.

3. Made from age-hardened A286 stainless steel, the unthreaded self-clinching micro locating pins are used for locating, positioning, and/or alignment applications.

Onward & Upward

Moving forward, innovations in micro fastening technology for subcompact electronic assemblies will advance, in part as a response to particular designer and customer challenges and needs. A promising trend has been a steadily growing partnership between OEM designers and fastener manufacturers to develop the most practical solution for applications. Knowledge that a hardware design team is equipped to deliver, based on experience, ultimately can make all the difference as consumer electronics and similar products turn even smaller, thinner, and lighter.

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