User's guide to enclosures

Your latest industrial electronic product has been designed. The board components have been debugged, tested, tweaked, tested again and finally signed off for production. Now all you need is an enclosure.

This guide explores the key things to consider:

1. Size

The first question is usually “what size enclosure do I need?”

How big is the PCB? Is it to be mounted horizontally or vertically? Many plastic enclosures have built-in slots along the sides of the enclosure for direct vertical mounting, as well as PCB mounting bosses in the top and base for horizontal mounting. Extruded aluminium enclosures will typically have full length slots in the sides for horizontal PCB mounting.

How much space is needed on the external surfaces for indicators, switches, connectors, cable entries, or other components? What height is required for board-mounted components or multiple horizontal boards?

2. Installed environment

Where will the product be used?

For outside installations, UV resistance is a key consideration for plastic enclosures. For mobile applications such as road and rail, could shock and vibration be an issue? What about the ingress of dust and water or the presence of oils and chemicals? Is impact resistance a potential concern? If so, metal enclosures generally provide better protection than plastic ones. Are extreme high or low temperatures expected?

3. Material

For small enclosures, the most common choices are plastic, aluminium and GRP. The most widely used plastic materials are ABS and polycarbonate. The UL94 fire resistance tests classify material as V0, V1 or V2, with V0 being the highest performance. For outdoor use, polycarbonate or GRP is typically preferred due to its better resistance to UV embrittlement and colour fading.

Aluminium enclosures are available in either die-cast or extruded designs. Both are robust, impact-resistant, and are intrinsically electrically conductive. However, painted or anodised finishes must not cover mating areas to maintain electrical continuity throughout the enclosure. Some extruded enclosures feature multiple fins to significantly increase the surface area to improve heat dissipation.

For applications where protection against shock damage is important, where EMC is likely to be an issue or where high temperatures, dust or water are expected to be present, a die-cast enclosure is often the most cost-effective solution.

4. Environmental sealing

Sealing typically relies on an interlocking tongue and groove construction between the mating halves. For higher levels of protection, a compressible gasket will also be used at the interface.

The relevant international standard is IEC 60529. Enclosures rated at IP54 are suitable for general purpose use. For environments where dust and water are likely to be present, IP66, 67 or 68 are recommended. The highest rating is IP69K, which protects against steam cleaning at high pressure.

5. Appearance/styling

This is often the most subjective factor. Plastic enclosures are available in opaque and translucent, and transparent materials in a variety of colours. Styled lids with recesses for membrane keypads and displays are available.

Die-cast aluminium enclosures can be painted in different finishes and colours, while extruded enclosures can have a natural, clear or coloured anodised finish.

6. EMC

In many applications EMC capability is of no interest, but in others it can be a design concern.

Plastic enclosures offer no intrinsic attenuation. However, internal coatings in a variety of materials can be applied to the inner surfaces of a plastic enclosure to give degrees of attenuation. By selecting different materials in a range of thicknesses, the most cost-effective and technically sound solution can be provided. Metal enclosures will naturally provide a sufficient level of EMC. A conductive gasket is typically used to electrically bond the enclosure’s two halves.

7. Fixings

There are two main fixing methods for plastic and die-cast enclosures: self-tapping or machine screws.

Self-tapping screws fasten directly into the material of the base;, making them suitable for one-time assembly applications. Machine screws, on the other hand, mate with a threaded bush moulded into the base, making them preferable for enclosures that require frequent access.

A further refinement is the use of captive screws, which prevent the possibility of screws being lost when the enclosure is opened.

8. Downloadable drawings and technical support

A reputable enclosure manufacturer should provide a detailed library of technical information and resources on its website. Downloadable content should include dimensioned drawings, technical specifications, and product attributes to assist with the design and modification requirements.

Distributors are increasingly offering manufacturers technical support, working with customers at the design stage to help choose the most appropriate enclosure for their application.

9. Manufacturer modification capability

In order to make a standard enclosure suitable for a specific application, modifications are often necessary.

Enclosure manufacturers will typically be able to provide milling, drilling, punching, engraving, printing, painting and EMC coatings. Additionally, enclosures can be moulded in custom colours to meet branding requirements or identification needs.

The modification service that Rapid offers in partnership with Hammond Manufacturing and CamdenBoss provides customers with all these options.

10. Work with the manufacturer

The electronics and electrical industries rely on a vast selection of enclosure designs, produced in a wide range of sizes, materials, and configurations by specialist manufacturers.

Although an moulded, extruded or die-cast enclosure may appear to be just a simple box, it’s actually the result of careful engineering and extensive design expertise that has resulted in a feature-rich housing.

Manufacturers are now able to provide significant support, from technical assistance to custom design modifications. The best approach is to work as closely as possible with the enclosure manufacturer from an early stage to tap into their wealth of experience.

Explore our enclosure modification service available at Rapid, to find out more.