Working with Rivets

What is a rivet?

When creating double sided boards with the Voltera V-One, there are 3 options for connecting the top and bottom layer after holes have been drilled.

• Threading a wire and soldering on both sides of the holes

• Plugging the drilled holes with conductive ink and bake

• Using rivets and a rivet tool

Threading a wire is the familiar approach, but it can be tedious to do. Plugging holes with ink provides a nicer experience but requires an extra baking step. In both methods, the holes made are filled in.

At Voltera - we recommend using rivets. A rivet (or eyelet) is a small hollow copper tube that can be inserted on one side of the board, then - using a specialized rivet tool - the rivets are pressed and deformed to connect both sides.

A mechanical connection is made between the ink and copper and can be later touched up with solder to form a stronger chemical bond.

Since rivets are hollow, they can also be used as plated through holes and will help secure your 0.1" headers or similar parts.

Designing with rivets

We offer 2 rivet sizes on our store. Dimensions below:

Size	Inner Diameter	Outer Diameter	Length	Head Diameter
Small	0.4 mm	0.6 mm	2.2 mm	0.9 mm
Large	1.0 mm	1.4 mm	2.5 mm	2.2 mm

There are 2 things to keep in mind when designing with rivets - the drill hole and the head diameter.

1. The Drill Hole

To ensure the rivets fits in the hole nicely, the hole diameter needs to be 0.1 mm larger than the rivet outer diameter.

Use a drill size of 0.7mm for the small rivet and 1.5mm (or 1.6mm) for the large rivet.

When placing vias and component footprints that use through holes in your design program, ensure the right hole size is used so the V-One accurately probes the substrate and leaves enough space when printing the ink. The hole size should be equal to the size of the drill bit being used.

2. The Head Diameter

The head diameter is the widest part of the rivet, this is the flange that will be in contact with your trace. This parameter determines how close the rivet can be to other parts or rivets in your design and how large the ink pad will print around the hole.

In your design program, your via outer diameter should be equal or greater than the rivet head diameter. For the rivets supplied with the V-One the smallest parameter used should be 0.9 mm for the small rivet and 2.2 mm for the large rivet. We recommend increasing this size to ensure that the rivets have a good connection to the cured ink and a lower likelihood of ink delamination from riveting.

The large rivet has an inner diameter of 1.0 mm and is suited for standard 0.1" headers. However - the head diameter is quite large and traces cannot be routed in between the pins. Please adjust your layout accordingly - otherwise the rivet may end up shorting two traces!

Ensure that all through-hole components and vias have been adjusted accordingly to the drill bits and rivet sizes being used. This may require custom editing of component footprints.

Pressing Rivets

After drilling, rivets need to be inserted and pressed. Once you are familiar with the process it is straightforward, but for beginners we recommend practicing on a sample board first.

When working with multiple sizes of rivets, start with the smallest size first and work your way up to the larger rivets. This method limits the amount of flexing the board will do during striking and reduce the risk of ink delamination.

1. Insert the rivet

Using fine tweezers, carefully pinch the rivet and place it in the hole. Repeat this process for all the rivets.

The small (0.4 mm) rivets can be tricky to handle; we recommend placing the substrate flat on a table then pinching the rivets from their side. Pinching them from the head can send them shooting across the room.

2. Flip the board.

Place a flat plate on top of your PCB and flip the board upside down so that all the rivets are facing up. Ensure you are working on a hard surface/table that will not deflect.

Be careful: all your rivets may fall out if the boards are not pressed together!

3. Position the rivet tool

The V-One Drill ships with two rivet tools, one for each size. Position the rivet tool on top and ensure the tip of the tool is centered on the rivet. Ensure the tool is centered before pressing down. Otherwise the rivet may buckle inwards.

4. Strike down.

Use a small mallet or similar tool to apply a download force on the rivet tool. You do not need to apply large amounts of force, just enough to deform the copper. The rivet should not be 'loose' after striking, if the rivet is loose try striking it again a bit harder.

Important: Applying too much force can damage the printed traces and the FR1 underneath.

Repeat these steps for all rivets.

Touch Up

After the rivets are pressed, we recommend taking a few minutes with the multimeter and ensuring all electrical connections between the top and bottom layer are conductive.

Tip: 2 or 3 minutes with the multimeter, can save 20-30 minutes of debugging.

If you find a rivet has not made a secure electrical connection, then you can touch up the connection by adding a little bit of flux and solder wire.