Panelizing Gerber masks for solder paste stencil for tiny PCB’s

Context

You have ordered tiny PCB’s from a fab such as OSHPark. The boards are SMD.  You want to order a solder paste stencil such as from OSHStencils.  You want the stencil to cover many of your PCB’s at once.  This tells how to edit the Gerber paste mask (that you will submit to OSHStencils) to do that.

More background.  For the cheapest service, you order multiples of three from OSHPark.  For very small boards, OSHPark MAY deliver them in panels: multiples still connected together by break-off tabs.   Call that a ‘happenstance panel.’   Then you can paste them many at a time (say three at a time).

You can’t predict what happenstance panels (what size and what orientation) OSHPark will deliver.  You may need to wait till your PCB’s are delivered (to see what panels they are in) before you order your stencil.

Some fabs may break them all apart for you, and these instructions are moot.

Alternative

If you don’t want to rely on the luck of the draw in happenstance panels, you panelize your board before submitting to OSHPark.  This means you design an outer, framing board that contains multiples of your real board.  See Panelizing: OSHPark.  OSHPark delivers the panel without breaking out your contained boards.  You can design a stencil that exactly aligns with the contained boards (since you designed the panel, you know the separation between contained boards.)

One disadvantage is that you pay more, since the panel includes a border of empty board.  The border is a handle for use by the fab, and for your use to hold your boards in alignment for the stencil.  Also, you still must order a multiple of three panels.  E.g. if your panel contains three of your board, you must order three panels, or nine of your boards.

Example

board size: 16mm by 16 mm

OSHPark kerf (width of the saw blade or router that cuts the outline of boards), aka space between boards:  100 mils = 2.54 mm

Repeats of your PCB in a panel: 3

Panel layout orientation: horizontal (side by side.)

How-to

Start GerbV (a GUI app for viewing and editing Gerber files)

Change units to mm (for this example)

  1. Choose View>Units>mm.  Expect the rulers to change, etc.

Open your paste mask Gerber file

  1. Choose File>Open Layers.  Expect a file chooser dialog
  2. Navigate to your Gerber file
  3. Choose OK.  Expect you Gerber file to appear as a new layer

Repeat the above twice more.  That is, open the same Gerber file to create many layers each showing the same paste mask.  Each will be a different color but they overlay each other.

Translate a layer by the width of your board plus the kerf.

  1. Select a layer in the left frame of the GUI. Click on the layer and expect it to highlight in the left frame.
  2. Choose Layer>Modify Orientation.  Expect a dialog
  3. Enter a value in the Translation>X(mm) text box, for example 18.254 (16 for the board plus 2.54 for the kerf)
  4. Choose OK.  Expect the dialog to close.
  5. Zoom out.  Expect to see the translated layer moved to the right

Repeat once more, but offset the layer by a multiple of two ( 2 times 18.54).  Expect to now have three different color layers spread out horizontally.

Merge the layers into one file.

  1. Choose File>Export>RS-274X Merge (Gerber)….  Expect a file chooser to open.
  2. Enter a name and directory for the file, say “MyPasteMaskPanel.gbr” (its traditional to have a .gbr extension, but the file chooser doesn’t add it for you?)
  3. Choose OK.  Expect the file to be created.

Check your work by closing this GerbV project (if you are saving projects), start a new project, and File>Open Layer on the file you just created.  Expect it to show the same graphics, but now in one layer of one color.

That’s it, submit the file to your stencil maker.

Other notes

You don’t need to worry about how the paste mask panel is aligned on a page.  The stencil maker will cut your tiny panel in the center of a page of plastic film.  You will cut it out and mount it in a jig that registers it over a panel of PCB boards.

You probably shouldn’t use a repeat of more than about ten.  Errors may accumulate?  For a repeat of three, you can be sure the center repeat exactly aligns with a board, and the farther you go to the sides, you may see inconsequential errors in alignment?

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