To which enclosure will you confide your project?
As we all know, it´s more than advisable to think of an enclosure already at the very beginning of the device design and to partially adjust a PCB design to a given enclosure.
Otherwise, it can easily happen that despite a huge offer of enclosures on the market, we cannot find a suitable size for a given PCB, mainly with respect to the position of connectors and mounting openings.
Material choice alias Plastic or Metal?
The most widely used plastics for the production of small electronic enclosures are ABS, PC (polycarbonate), and polyester (glass reinforced).
Advantages of plastic enclosures are mainly insulating features, considerable shock resistance (however, from a certain level of deformation, cracking may occur), easy machining (milling, drilling, …), resistance to many aggressive agents, mainly acids and alkali.
As for drawbacks, plastic enclosures are usually fragile at very low temperatures, they have weak heat conductivity resulting in a lower cooling of components (unless the enclosure has ventilation openings).
Resistance to organic solvents and UV radiation is usually relatively lower, even though it depends on a given material.
If you go for plastic ones, then in the wide portfolio of Hammond brand you´ll probably find the right solution for you. Hammond enclosures are very precisely moulded, without faults, sharp edges etc.
Colour shade is the same from batch to batch and a wide range of sizes and accessories further simplifies the choice of the right type for your PCB.
Small metal enclosures are in majority of cases made of Electronic Project Box Aluminum or aluminum alloy (AlMgSi).
Some of the advantages of aluminum are rigidity, shock resistance (from a certain level of shock, permanent deformation occurs, however, it cracks only rarely), resistance to a wide temperature range, good thermal conductivity, resistance to organic solvents, and UV radiation.
Electric conductivity is a base of great shielding properties (EMC), even though for a really good shielding, it´s necessary to use a conductive sealing or a design of an enclosure that ensures a continuous conductive joint of enclosure parts.
There are only a few disadvantages of aluminum enclosures, probably the only main one is a weak resistance to acids and strong alkali.
For a harsh environment, a stainless steel (inox) enclosure is usually an ideal choice. Inox can be labeled as an almost ideal material in terms of resistance to all adverse effects.
However, as for production and consequent machining (drilling, milling), the inox is a very demanding material, and moreover relatively quite expensive.
If you decide on aluminum, then you´re at the right address. Hammond has a wide range of types in a huge amount of sizes, with a rich offer of accessories, moreover with various surfaces and in various colors of bezels.
This is really individual and mainly given by aesthetic feeling of a designer, as well as by requirements of a PCB design.
For example, an elongated shape of a PCB (and an enclosure) makes it easier to separate the power (noisy) part from the sensitive low noise part.
On the other hand, a squared shape usually enables an easier PCB design and shorter tracks.
With or without a flange?
Almost every enclosure can be mounted to a panel or a wall even if it doesn´t have a flange. A similar service is provided by additional mounting holders that are available to many enclosure types.
Several industrial enclosures, like for example Hammond 1457, have inner mounting openings outside the sealing, thus they are enabling to fix the enclosure without decreasing the IP rating and also to hide mounting screws below the top cover.
The flange has a big advantage in a totally trouble-free mounting of enclosure. There´s no need to pen the lid or even to mount screws near sensitive electronics.