Entrepreneurs, hackers, and enthusiasts are developing original electronic products mounted on PCBs faster than ever…only to find out that there was one thing left behind — the enclosure.
What comes first — enclosure design or PCB design? It is a little bit of a chicken-and-egg dilemma. Electronics engineers have their own specs and components-related restrictions, while designers and manufacturers have user experience, ergonomics, visual identity, and manufacturability in mind. Ideally (and in a world where chaos is fostered), PCBs and enclosures are worked concurrently. Sometimes, manufacturing limitations determine shapes in the PCB, and sometimes specific PCB properties define aspects of the product design. The keyword here is communication.
I would recommend being as liberal as your budget permits when printing 3D samples and making and custom PCBs. Granted, you will end up with some useless prototypes, but it is much less waste than having a final product with a long list of “oh, I wish I had done this differently,” or worse, having to recall a batch. There are excellent tools to get you going in the prototyping phase of your project.
It is difficult to beat the cost of a Monoprice 3D printer, but if you do not have or do not want a 3D printer around, there are 3D printing bureaus everywhere, domestically and overseas that happily print models for you with great detail. PCBs can be made in the US as well, with services such as OSHPark.
Sourcing multiple electronic components at once can be done with Supplyframe’s Findchips, or through some resellers. Many components can be bought in small quantities as vendors recognize the need for testing. McMaster-Carr is an excellent resource with reliable specs and fast delivery.
Adding some aspects in advance to your enclosure design, and planning your PCBs for such elements — even if they are not made to the exact specification yet — make the transition to production much more manageable.
Let’s review some of the most common things you find in plastic injection casings:
- Bosses and assembly pins: This is where a screw or plastic pin goes through and assembles to the other side; this is how most enclosures are assembled.
- PCB assembly pins or bosses: Just like the previous ones, but their function is to fix the PCB to one of the enclosure’s walls.
- Snap fits are cantilever shaped beams that “hook” to a section of the opposite component. For mass production, these fits are relatively cheaper than using screws but are not a free pass by any means. They have to be precisely calculated, from entry and exit angle to deflection, torsion, shrinkage, and material mechanical properties. Indeed not a free pass.
- Assembly recess: This is often overlooked, and it is quite important from a visual standpoint. You want a shadow effect that prevents the inside from being seen.
- Window: If the PCB has a display, it is imperative to know its orientation concerning the main PCB from the very beginning. Mold making is more straightforward if the screen is aligned perpendicular to the assembly pins (this is the case most of the time).
- Sprue gate: This is where molten plastic enters the mold and starts shaping the product. It is unlikely that you will define its final design and location, but it is a good idea always to keep it in mind.
- Structural ribs: Ribs are not always necessary, but they can add rigidity and prevent warping. The larger a part, the more likely they are necessary. Structural ribs are very useful when a product involves mechanical work. They are usually next to the walls or attached to long bosses.
- Wall thickness: Plastic walls on average range from 0.05" to 0.13,” depending on the material, and function. Tip: grab a product with a similar function and measure the walls’ thickness to get an idea.
- Parting lines: This is where different walls or sections of a product meet. The flatter parting lines are, and the more ejectable the part as a whole is, the cheaper a product will end up. Do not reject ideas just because they do not feature perfect parting lines, though it is always good to consider how the part will eject from the mold.
When prototyping enclosures, planning them with these features will make the transition to production much smoother and less expensive. When ready, it is still a good idea to consult with plastics professionals. Dealing with material mechanical properties, understanding mold manufacturing, and production requires a vast wealth of knowledge that ultimately leads to greater efficiency and cost optimization.