Die-cast metal housing
- Shields and spreads heat without extra steps
- Heavier, and usually needs machining and a finish coat
- Blocks wireless signals, so antennas need a plastic window
Molded part guide: electronic enclosures
Injection Molded Electronic Enclosures
Put a circuit board inside a plastic shell and four new questions appear: how the board is held, how it is shielded, where the heat goes, and what flame rating the resin carries. Each one is easier to answer before the tool is cut.
Holding the board
The board is a datum, so treat its mounts like one
Connectors, buttons, displays, and light pipes all have to line up with openings in the shell. That only works if the board sits in a known place every time.
Most boards sit on molded standoffs and are held by screws, snap tabs, or clips molded into the shell. Pick two locating features that fix the board in position, and let the other supports only carry it. Asking four screws to both locate and support the board usually means one of them is fighting the others after the plastic shrinks.
Leave a keep-out ring on the board around each screw so the screw head does not short a trace, and check that tall components clear the ribs and bosses on the opposite shell once the enclosure is closed. A section view through the closed assembly catches most of these before the quote.
If the product has buttons or light pipes , send the board outline with component heights. The molded features that touch the board are only right if they are designed against the real board.
EMI
Plastic does not shield. Here is how enclosures get shielding anyway
Unfilled plastic is transparent to radio frequency energy in both directions. When the product needs shielding, it comes from one of these routes.
| Route | How it works | What it asks of the molded part |
|---|---|---|
| Shield can on the board | A soldered metal can covers only the noisy or sensitive circuit | Nothing special, beyond clearance above the can |
| Metal liner or foil inside the shell | A stamped sheet metal liner or conductive foil laminate fitted inside the shell during assembly | Molded clips or locating posts to hold it, and contact points that reach the mating seam and board ground |
| Conductive resin compound | Conductive fillers compounded into the resin shield the whole wall | Gating and flow that keep the filler evenly spread, and acceptance that color and cosmetics are limited |
| Conductive gasket at the seam | Bridges the gap between two shielded halves | A seat for the gasket and enough clamp from screws or snaps to keep contact |
Service tiers
Electronic enclosure service tiers and quote path
Housing tier for this family: Board datums, EMI routes, and heat in a plastic box. Upload CAD with seal path, fasteners, and heat sources called out in notes when they are not modeled.
| Tier | Environment | What matters most | Typical molded route | Quote path |
|---|---|---|---|---|
| 1 Board mounts | Standoffs, screws, snaps, or clips | Screws that both locate and support the board | Two locators, and the other supports only carry it | Upload CAD; send the board outline |
| 2 Shield seam | The halves have to touch along the joint | A gap between contact points leaks | Liner to the mating edge, or a conductive gasket | Instant quote; name the shield route |
| 3 Openings | Vents, windows, and connector cutouts | A long slot is an opening in the shield | Keep slots short and spread apart | Upload CAD; note the openings |
| 4 Heat path | Plastic holds heat in the closed box | A board that is cool on the bench can run hot closed up | Intake low, exhaust high, hot parts toward a wall | Instant quote; note the heat path |
| 5 Antenna | Unfilled plastic passes a radio signal | Metal or carbon fill near the antenna | Mark the antenna and keep that area clear | Upload CAD; mark the antenna |
Materials
Resin families: quick reference for quote notes
One primary family per shell line item. Put EMI coatings, inserts, and flame filters in comments.
| Family | Typical use on this part type | Notes for instant quote |
|---|---|---|
| PC/ABS | Housings | Field PC/ABS |
| Unfilled plastic | Shells with an antenna inside | Field the unfilled grade; mark the antenna |
| Carbon-filled | Keep it away from the antenna | Field the grade; mark the keep-out |
Seams
Shielding usually fails at the joint, not in the wall
A shielded shell with an unshielded seam behaves like a box with a slot cut in it.
The two halves of a shielded enclosure have to touch electrically along the whole joint, and the shield has to connect to the board ground. A liner that stops short of the mating edge, or a snap joint that leaves a long gap between contact points, lets energy out no matter how good the shield material is.
Openings count too. Vent slots, display windows, and connector cutouts are all apertures. Keep slots short and spread out rather than long and continuous, and decide early which openings get a conductive gasket or mesh.
Heat
Plastic holds heat, so plan where it leaves the box
Most engineering plastics conduct heat poorly. A board that runs cool on the bench can run hot once it is closed up in a molded shell.
- Put intake slots low and exhaust slots high so air moves through by convection
- Move hot components toward a wall, a metal plate, or a heat sink that reaches outside air
- Remember that every vent is also a path for dust, spray, and radio frequency leakage
- Check the resin's continuous use temperature against the hottest spot inside the closed box, not the room
Plastic or metal
Molded plastic versus a die-cast metal housing
Die-cast housings are still chosen for some products. Here is how the two tend to trade off.
Molded plastic housing
- Snaps, bosses, light pipe seats, and texture come out of the tool in one shot
- Lets Bluetooth, Wi-Fi, and cellular antennas sit inside the shell
- Needs a shielding route and a heat path if the electronics call for them
Avoid these
Common design mistakes on electronic enclosures
Two choices that fight the board mounts, or leave a gap in the shield.
Four screws asked to both locate and support the board. After the plastic shrinks, one of them fights the others. Use two locators, and let the other supports only carry the board.
A shield that stops short of the mating edge. The joint then acts like a slot. Carry the liner to the edge, or add a conductive gasket, and connect the shield to board ground.
Before you upload
Details to send with an electronics enclosure
Most of these are decisions the electrical team owns. The mold has to reflect them.
Board outline, mounting holes, and tallest component heights
The flame rating the product needs, and the resin grade that carries it, from the resin supplier listing
Whether the enclosure is shielded, and by which route
Antenna location, so nothing conductive is designed next to it
Connector cutouts and cable exits, with the mating connector or gland
Labels, legends, and certification marks, and how they are applied
Keep reading
Related guides
Sibling housings, resins that show up in electronics, and the features inside the shell.
Enclosures
Splitting, fastening, and sealing any molded shell.
EnclosuresConnector housings
Terminal retention, latches, and polarization.
Connector housingsBattery housings
Cell retention and room for the pack to move.
Battery housingsEMI shielding compounds
Resins that shield without a coating.
EMI shielding compoundsPolycarbonate
Tough and heat resistant, with flame-rated grades.
PolycarbonatePost mold inserts
Post mold inserts for screws that get used more than once.
Post mold insertsTolerance stack up
Getting the board, shell, and openings to line up.
Tolerance stack upSecondary operations
Painting, printing, laser marking, and assembly quoted with the part.
Secondary operationsMolded parts library
Every part-type guide, grouped by family.
Molded parts libraryEMI shielding coating
Shielding options for plastic enclosures.
EMI shielding coatingConsumer electronics
The whole device, not just the case.
Consumer electronicsFAQ
Questions about electronics enclosures
Does NetProto certify the flame rating of my enclosure?
No. A UL 94 flammability rating belongs to the resin grade at a stated thickness and is listed by the resin supplier. We mold the grade you specify. Whether the finished product passes its safety standard is decided by your certification testing.
Will a plastic enclosure hurt my wireless range?
Unfilled plastic passes radio signals well, which is one reason electronics use it. Range suffers when metal liners, metal inserts, or carbon-filled resins sit near the antenna, so mark the antenna area on the drawing and keep it clear.
Can the display window be molded into the enclosure?
Sometimes, with a clear resin for the whole part, but most products use a separate clear lens that is welded, bonded, or overmolded into the opening. That keeps the housing resin free to be tough and opaque.
Is there a minimum order for electronics enclosures?
No. There is no minimum order quantity, and the hardened steel tool stays available for repeat orders as the product ramps.
Why only two locating features on the board?
The board needs a known position. Screws that also try to locate it fight each other after the plastic shrinks. Use two locators, and let the other supports only carry the board.
Why keep vent slots short?
Vent slots, display windows, and connector cutouts are openings in the shield. Keep them short and spread apart, instead of one long continuous slot.
Next step
Send the shell with the board outline
Upload the enclosure CAD and a board outline with component heights. DFM feedback flags standoff, clearance, and cutout problems before tooling is released. NetProto manufacturing is ISO 9001 certified.