Developer's Kit
MULTI-MATERIAL 3D PRINTER
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Design Guidelines

Contents


Overview

When designing printed projects for the Voxel8 printer, you should keep in mind that you are working with more than one material (i.e. "multi-materials"). With the first generation Developer's Kit this means printing thermoplastic (i.e. PLA) and the Voxel8 conductive silver ink.

There are considerations to make that appear outside of the common constraints found FDM/FFF thermoplastic extrusion printing. There are also certain inherent restrictions and constraints on what you are able to print effectively on the Developer's Kit given software, hardware, and material properties and interactions.

Having a good understanding of the material capabilities and printer limitations will allow you to properly design your parts.

Below are some guidelines and things to be aware of when printing multi-materials for the Voxel8 Developer's Kit Printer.


Basic Design Guidelines

Below are the basic guidelines to bear in mind when printing Voxel8 Conductive Silver ink.

  1. Trace Width: Traces should be 500 microns wide where possible (Figure 1A). Minimum trace width should be no less than 250 microns (Figure 1B). Anything less than 250 microns is likely to be an unreliable trace depending on your particular design (Figure 1C).



    Figure 001A-C: Trace widths.

  2. Trace Path: Silver traces should be constrained to travel in either X (see Figure 002A), Y (see Figure 002B) only or Z (see Figure 002C) only. If sloped vertical trace is necessary (see Figure 002D), try to stay less than 30 degrees from vertical (see Figure 002E).



    Figure 002A: Trace paths (X Axis).



    Figure 002B: Trace paths (Y Axis).



    Figure 002C: Trace paths (Z Axis).



    Figure 002D: Trace paths (Vertical trace - Correct).




    Figure 002E: Trace paths  (Z Axis angle - Correct).




    Figure 002F: Trace paths (Z Axis angle - Incorrect).
  1. Horizontal Trace Spacing: Where possible traces should be spaced far apart. To guarantee a plastic separator is printed between traces the minimum edge to edge distance should be 1.31mm.

    A.) Center of trace to edge of part:

      Minimum: 0.96mm (Assuming .250 trace)
      Ideal distance: 1.31mm

    B.) Pitch distance between center of traces:

      Minimum: 1.56mm
      Ideal: 1.92mm

    C.) PLA between traces:

      Minimum: 0.36mm
      Ideal: 0.72mm

    D.) Trace width: 0.25mm

    E.) Horizontal Air Gap: 0.475mm

    F.) Vertical Air Gap: 0.19mm (one layer)





    Figure 003A: Horizontal Trace Spacing (Side profile view).




    Figure 003B: Horizontal Trace Spacing (Isometric view)
  1. Vertical Trace Spacing: Where possible separate vertical traces by more than 2mm. Minimum vertical separation is 1.31mm (see Figure 004A).



    Figure 004A: Vertical Trace Spacing.

  1. Inter-layer Trace Spacing: There should be at least 2 layers of plastic between traces in different planes (see Figure 005A). If trace headroom is used there should be three layer separation.




    Figure 005A: Correct Inter-layer Trace Spacing.




    Figure 005B: Incorrect Inter-layer Trace Spacing.
  1. Volume Geometry: All silver features should be ideally less than 500 microns thin where possible (see Figure 006A). Where possible silver features should be planar. Should be <= 500 microns in at least one dimension where possible.  



    Figure 006A: Volume Geometry (Correct).



    Figure 006B: Volume Geometry (Incorrect).
  1. Trace Support: Traces should have plastic or silver supporting them (see Figures 007A-B), otherwise your print with have errors (see Figures 007C & 007D)



    Figure 007A: Trace Support (Correct).



    Figure 007B: Trace Support (Correct).



    Figure 007C: Trace Support (Incorrect).




    Figure 007D: Trace Support (Incorrect).

  1. External Silver Features: External silver features should be planar (not traces) and should supported by plastic at a slight incline (see Figures 008A and 008B). otherwise errors can occur (see Figure 008C).



    Figure 008A: External Silver Features (Correct).



    Figure 008B: External Silver Features (Correct).



    Figure 008C: External Silver Features (Incorrect).

    For best results complex external features should be on the top.

    NOTE: Avoid printing silver directly on the build plate as it adheres strongly to it. You may also have difficulty removing the build tape from the plate in doing so.
  1. Plastic can't be adhered directly to silver: The plastic does not reliably adhere to planes of silver ink. When printing silver on top of plastic, you can think of the silver as air. So plastic must bridge over planes of silver. This also means that you can't have plastic holes directly on top of silver planes, because this would lead to the creation of unsupported plastic perimeter.
  1. Layer Height: Vertical trace spacing should be multiples of the layer height where possible (defaults to 0.19mm). While the slicer will modify the layer height to hit the geometry specified, hitting the default layer height will result in the best quality silver traces.
  1. Place components in the same layer whenever possible: This will require both you and the print job to be disturbed less during print jobs when the printer pauses for component insertions.

Advanced Design Guidelines

Below are some more advanced guidelines for printing Voxel8 conductive silver ink.
  1. Component Connections: When designing, in general, you should print traces on top of your components (see Figure 010A). This means you will place a component and then the Printer will deposit your trace onto the component after, making a more reliable connection. Overlap of 2mm onto the component is ideal to meet it's connection points/pads.



    Figure 010A: Component Connections (traces on top) - Top down view.



    Figure 010B: Component Connections (traces on top) - Side profile view.

  1. Component Pads: If traces traces make connection with the bottom of a component they should reach at least 2mm in to provide a reliable connection (see Figure 011A & 011B).



    Figure 011A: Component Connections (traces on bottom) - top down view.



    Figure 011B: Component Connections (traces on bottom) - side profile view.
  1. Silver Shrinkage: If final silver geometry is very important to your application you should account for 40% shrinkage of any silver surface that is not in contact with plastic.

  2. Achieving a finer pitch size: It is not necessary that that silver always have plastic in between. 

  3. Try to contain complex geometries to XY planes: Silver printing is more robust when printed in XY, so if you have things you want closely spaced, you can print them in an xy plane, then only bring a few wires with you to the next plane.

  4. Place complex silver geometries closer to the bed: For untested silver print geometries, the closer they are to the bottom, the faster you will find out if they work.

  5. Components that are too thick must be placed upside down. If they are thicker than the nozzle offset between silver and plastic.



Plastic Design Guidelines
  1. Try to avoid parts that need long bridging or support, as these processes affect surface quality.

  2. Some external 3-D Printing guidelines: http://makezine.com/2013/12/11/top-ten-tips-designing-models-for-3d-printing/

  3. Minimum feature thickness is 0.35mm. For stronger plastic walls, design parts to be at least 1mm thick.

  4. Avoid large flat parts as they tend to peel up from the build plate as the plastic cools. If such a feature is required, using rounded corners or enabling the brim setting within Dashboard should help with adhesion to the build plate.

  5. Avoid printing horizontal circular holes. Square or triangle cuts are more desirable. If a circle hole is required, the top of the hole may droop due to the large overhang angle.
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