Specifying small metal and plastic enclosures correctly

When an industrial electronic product is developed, specifications for the PCB components, prototype development, debugging, testing, optimisation, and production approval are usually established prior to choosing the enclosure. Ideally, however, the choice of enclosure would take place much earlier, so that the size specifications of the enclosure, for example, based on the PCB, are already known – in reality, however, this is usually not the case. Instead, the question ''What size enclosure do I need?'' only arises later.

1. Size: This includes questions about the size of the PCB and its horizontal or vertical installation, the space needed on the outside for displays, switches, connectors, cable ducts and similar components, and the height.

2. Installation environment: Is the application to be used inside or outside? If used outside, UV stability presents a potential problem for plastic enclosures. Shock and vibration for mobile applications, dust, water and other forms of contamination, and also temperatures need to be considered. As a rule, metal enclosures offer better durability than plastic ones.

 
3. Material: For small enclosures, plastic (ABS, polycarbonate, etc.), aluminium and glass-reinforced plastic (GRP) are usually available. The flame retardant characteristics with the relevant UL94 standard need to be taken into consideration here – the more stringent test is the vertical burn test (V0, V1 or V2 flammability rating). Polycarbonate or GRP are usually preferred for exterior applications, because they demonstrate better UV stability and colour fastness than ABS.

4. Environmental influences: The relevant international standard is IEC 60529. Enclosures with IP54 protection class are suitable for universal use. For dusty or wet environments, IP66, 67 or 68 is normally specified. The highest protection class IP69K offers protection against the ingress of water under high pressure.

5. Design: Plastic enclosures offer a selection of opaque and translucent materials in various colours, as well as transparent material. Die-cast aluminium enclosures allow a wide range of surfaces and colour options, while extruded enclosures are available with clear or coloured anodising.

6. EMC: Unlike metal enclosures, plastic enclosures do not provide any intrinsic attenuation – a problem with electromagnetic radiation caused by the electronics itself, or if the equipment is susceptible to external fields. The solution: interior coatings of different materials. Metal enclosures, on the other hand, offer an EMC level sufficient for most application.

7. Sealing: There are two main approaches to sealing plastic and die-cast enclosures: connecting the parts of the enclosure using a self-tapping screw, or using a bolt that screws into a threaded sleeve moulded into the base. The latter is a good choice when repeated opening and closing is likely, while a self-tapping screw is sufficient for one-off sealing.

8. Downloadable drawings and other useful material: Every reputable enclosure manufacturer makes a comprehensive library of technical information available on its website.

9. Modification options: Enclosure manufacturers generally offer milling, drilling, punching, engraving, silk-screen printing, painting and EMC-shielding for their standard products. Producers of moulded enclosures also deliver enclosures in customer-specific colours.

10. Technical support: For the manufacture and modification of appropriate standard enclosures for the electronics industry, extensive design expertise is usually a must.

At Schukat, we maintain in-stock inventory of standard enclosures and offer our customers technical support alongside enclosure producer Hammond. We work closely with our customers even in the planning stage, offering assistance with the choice and specifications of the most suitable enclosure for their specific application. Ask us