Multi-Layer Printing Tips

Multi-layer printing as a function for NOVA is currently under development and not fully supported. To be notified when multi-layer launches later this year, please sign up here: https://share.hsforms.com/1q7Z-Skj4SG-8qM1V6cCzrQ34u2a

While we work on Multi-layer printing as a fully supported feature, these are the tips we’ve learned to get the best results currently for Multi-layer printing with NOVA.

File Setup

Printing a Multi-layer design takes a little more planning and time spent on your design than a single layer print. You will need a design file that is specific for each layer and each of those layers has a few requirements.

Base Layer: For your base conductive layer, this is much like printing a single layer file. The main thing to focus on when designing this layer is that there are good references for alignment for the rest of the layers. Specifically leaving ample space for the crossover sections and enough trace space for top conductive layers to reconnect to the base layer. Adding fiducials to each layer for alignment can be very helpful.

Dielectric Layer: Again, the focus here is making sure that this layer is easy to align to the base layer. The other key is to make sure that the dielectric layer has full coverage over the parts of the base layer it needs to isolate.

Top Conductive (Crossover) Layer: The key to this layer is that there is enough overlap between the traces of this layer and the base conductive layer to make a strong connection. This extra overlap should also help with alignment. It’s also worth noting, this layer should just be the crossover portion of your design. This will save time and make it easier to dial in print settings for this portion.

Material Compatibility

It is important to make sure that the materials you plan to print for each layer will be compatible with each other. Not all conductive and dielectric inks are compatible and it is possible to get unwanted reactions between them, like dissolve each other. The material data sheets will be the best tool to double check all of your materials.

The other thing to keep in mind is that you will need to cure between each layer that you print. This will ensure that the layer is ready to be probed and printed on top of. Because of this, you’ll want to ensure that all of your materials and substrate are compatible with the curing requirements of each other. Again, the material data sheets will be the best tool for this.

Probe Pitch

Probing is one of the areas we’re developing further to allow for more consistency when printing Multi-layer. The way we currently generate a heightmap is by probing a subset of points across the design where the distance between points is set by the probe pitch setting on the substrate. The smaller this number, the smaller the distance between probing points and the more accurate the heightmap. With this method we interpolate the data between these points to generate the heightmap.

The problem with this method for Multi-layer is that the changes in height when printing over existing traces can happen drastically and may fall between probing points. The best approach to minimize this is to set the probe pitch setting as low as possible. Currently that is 1mm. This will take more time to probe as there are more probing points. But it will allow for more height map accuracy.

Printing your layers

Starting with your first conductive layer will be much like any single layer print. Follow the prompts in the software to ensure you have good alignment to your substrate. Then in the flow check step you may want to take a couple passes dialing in the pressure to ensure you get a nice, even layer when printing. Then print your layer. Inspect it to make sure it will work for your application and it’s off to curing.

Moving to the second layer is where things start to change. This is where you’ll be adjusting your probe pitch setting down to 1mm. Along with that are a couple other important changes to make, some that may require some experimentation. You’ll want to increase your print height by a decent margin. So if you normally print at 60µm with this material, you may want to increase to 100µm. This is to provide a bit of a buffer to any sudden height changes. Along with the changes to print height, you’ll want to print about 50% slower than you normally would with this material. When printing higher up it can be more difficult for the material to adhere to the substrate, printing at a slower speed will help with that.

The other adjustment that will help the material to adhere at higher height is to increase the dispense pressure you’re printing at. You’ll want to experiment with how much you increase the dispense pressure by watching for even and consistent flow that is adhering to the substrate. Once all those changes are dialed in you’ll be ready to print your second layer over your cured first layer. You may even need to print a second pass 15-20µm higher to get nice, even coverage. After you’re happy with the print you’ll need to cure this layer as well.

Your top conductive layer will require all the same adjustments as the second layer. So it may take some experimenting to dial in these settings for all your layers. But with these tips you should be able to get some Multi-layer prints completed.