Weatherproof Container:
  1. Plastic Cases
  2. Sealing Wires
  3. Punching Holes

Securing a Circuit Board to a Liner with Punched Holes

We’re weatherproofing an electronic project using a Pelican 1050 Clear Plastic Case. Previously, we provided tightly sealed wire path using either poster tack (gasp) or PVC pipe. Now we’re going to attach the circuit board to the project case so that the components won’t be damaged if the case is dropped.

The Pelican cases have a nice rubber liner that acts as an O-ring to seal the box when closed. The liner also reduces physical damage to anything bouncing around inside, or more likely, prevents loose contents from shifting and sliding.

Rather than drill holes in the plastic case, we’re going to punch holes in the rubber liner and attach the circuitry to the liner.

I prefer #4-40 screws, because they are relatively small and readily available. The proper clearance drill size for these screws is 1/8″. But, drilling through rubber is awkward. So, we'll use a punch.

Hole punch one eighth inch

Hole punch, one-eighth inch diameter.

The plastic/rubber/leather punch is available from McMaster-Carr for $6.42, part #3424A12.

To keep the punch sharp and to get a clean hole, you'll want to punch through the material with a firm (but not hard) surface underneath. I recommend polyethylene, such as a kitchen cutting board.

Rubber mallet and polyethylene cutting board

Rubber mallet and polyethylene cutting board.

Don’t use literally the same cutting board as you use in the kitchen, because you'll end up with notches where bacteria can accumulate. Instead, swap your old plastic cutting board to your shop (after cleaning it in the dishwasher) and buy yourself a nice new cutting board for the kitchen.

You'll also need a rubber mallet or plastic hammer. Never strike a stamp or punch with a metal hammer. A rubber mallet comes in handy for other jobs in the shop, such as loosening a chuck or any part where you don’t want to damage the surface.

I placed the circuit board onto the rubber liner and marked the holes with a fine-tip black marker. I removed the circuit board, placed the rubber liner on the polyethylene board, and struck each of the marks with the punch using a moderate blow.

Residual hole material from punching hole

Residual hole material from punching hole.

An interesting scrap material is created by the punch. Inside the waste slot of the punch you'll find little rubber discs. If you want to make custom rubber washers or pads, you could use one or more punches of various sizes.

Attaching the Circuit Board to the Liner

A concern with screwing the circuit board directly to a rubber liner is the potential to trap or accumulate a liquid. To address this, I added nylon standoffs between the board and the liner. This provides a generous air gap such that liquid on the liner won’t make contact with the circuit board.

The screw head goes underneath, and the screw goes through the liner, through the standoff, and is either screwed into threads in the circuit board or attached with nuts on top. Alternatively, if the standoff is threaded, then screws can be inserted on the top and bottom, which is more serviceable.

Nylon standoff raises circuit board above inner liner

Nylon standoff raises circuit board above inner liner. Nylon screws on both the top (left photo) and bottom (right bottom).

To avoid scratching the plastic case, use nylon screws instead of metal. If you insist on using metal, opt for brass or stainless steel to avoid corrosion in any project exposed to wet conditions.

Even if you think your project won’t be exposed to liquid, think again.

Condensed moisture in sealed clear case

Condensed moisture in sealed clear case.

A sealed case traps air, which leads to condensation. I tried wiping it dry several times, but ultimately I was just cycling in new moisture each time I opened the case. Perhaps throwing in some silica gel packets would keep the circuits dry.

Weatherproof Project?

The modified Pelican cases work wonderfully!

Weather station buried in snow

Frozen weather station safe and snug in a Pelican 1050 case

Frozen weather station buried in snow,
but safe and snug in a Pelican 1050 case.

The weather stations are surviving the Chicago winter without damage. There is an additional benefit: Because the boxes are relatively sealed and the plastic is reasonably thick, the electronics appear to be kept a little warmer.