Assembly masks

Often, the necessary data for assembly masks is missing from the Gerber files created by the board designer. Especially in cases where assembly is being done by an EMS provider, this missing data can be a problem. It is the EMS provider who knows the processes and needs to specify the masks, but getting this information to the board designer early enough to be included in the design is usually not possible. With the assembly masks feature, the mask areas may be specified by the production engineer while creating the assembly panel.

Masks are specified by drawing rectangles on the panel. The Fill mode determines whether the mask will be applied to the entire rectangle or to all soldermask openings within the rectangle. This is repeated at the same location on all instances of the same board in the panel.

The following assembly masks (top or bottom side) may be defined:

• Peel-off mask (Blue mask): Used to protect a region from the solder process(es). Normally applied to an entire rectangle.

• Paste mask: Defines openings in a solder mask stencil. This data may then be used in the Stencil Module to create a stencil product. Normally applied to pads within the rectangle.

• Glue mask: Defines openings in a glue mask stencil. Normally applied to an entire rectangle drawn between the pads of a component.

• Hard gold: Defines which pads should have a hard (electrolytic) gold (finger contact) finish. Normally applied to pads within the rectangle.

• Carbon print: Defines which pads should have a carbon (finger contact) finish. Normally applied to pads within the rectangle.

• Kapton tape: Used to protect a region from chemical or solder processes. Normally applied to an entire rectangle.

• Legend: The notation layer, sometimes also called silkscreen. Used to create an annotation field.

• Solder: The solder mask layer. Useful for removing solder mask from a region, in order to help prevent cracks in the solder mask when manually cut or otherwise mechanically processed. Note: Care should be taken to avoid inadvertently exposing copper.

A mask is defined by the chosen fill mode when a selection rectangle is drawn. The fill modes are:

• Duplicate pads: The mask duplicates all soldermask openings within the selection rectangle. This mode is normally used for paste mask, hard gold and carbon layers. The mask will normally be somewhat larger than the copper pad it covers, but this should not be a problem. For a paste mask, the actual stencil opening size may be adjusted to a percentage of the copper pad size in the Solder paste stencils module. For hard gold and carbon layers, the mask is simply used to document to the manufacturer which pads should have a hard gold or carbon finish.

• Rectangle: The mask covers the entire area within the selection rectangles. This mode is normally used for peel-off and glue mask layers.

Note: For the Legend layer, you choose a placement method rather than a fill mode. This is the same as for placing an annotation field. You should avoid placing an annotation field over copper traces if the annotation text will be laser engraved (due to the possibility of etching through the solder mask).

Note: Assembly masks are added to the panel, and not to the boards within the panel. For this reason, if a board is moved or rotated, any assembly mask modifications you have created will not follow the board.

To remove all mask objects, click on the Clear all masks button.

To remove individual mask objects, click on the Remove button (so that it is “down”) and then draw a selection rectangle around the mask object(s) to remove.