What is solder mask for PCB design

A solder mask is a thin polymer coating on your board which surrounds your pads to help prevent solder from bridging between pins. 

This is essential for surface mount and fine pitch devices. The solder mask typically covers everything except pads and vias. 

Your PCB program will automatically remove solder mask from pads and vias. The gap it leaves between the pad and the solder mask is known as the “mask expansion”. 

The mask expansion should usually be set to at least a few thou. Be careful not to make it too big, or there might be no solder mask between very fine pitch devices.

Your solder mask is displayed in your PCB package as a negative image, just like your power plane. 

Under normal circumstances you don’t need to put anything on your solder mask layer.

 But if you want to leave the solder mask off a certain part of your board, you can place tracks and fills on your solder mask layer. 

It is often handy to remove a small square of solder mask from the top of your board, where there are no tracks underneath. 

This leaves a nice bare and visible part of your board to write something with a pen.

Solder masks come in two types, silkscreen, or “photo imageable”. 

solder masks for different layers of pcb

Solder masks are applied to the surface of a printed circuit board (PCB) to protect the copper traces and to insulate the components. 

Different layers of a PCB can have different solder masks, and the choice of color and material depends on the specific requirements of the design. 

Some common colors for solder masks are green, blue, red, and black. The material used for the solder mask is usually a photo-imageable polyimide or an epoxy-based liquid coating. 

The purpose of the solder mask is to ensure that there is no unintended soldering between the different layers and to protect the PCB from damage during assembly and use.

How to make solder mask in pcb designing in ORCAD  layout

To make a solder mask for a PCB layout in Orcad, you can follow the following steps:

1.Open Orcad and create a new project.

2.Load the schematic and then run the "Layout" tool.

3.In the Layout window, go to the "Layer Stack Manager" and select the "Solder Mask" layer.

4.In the "Solder Mask" layer, draw polyggon shapes around the copper traces and components to define the areas that should be covered by the solder mask.

5.Set the properties for the solder mask layer, including the color, line width, and fill type.

6.Save the design and then run the "CAM" (Computer Aided Manufacturing) tool to generate the Gerber files needed for PCB fabrication.

7.The Gerber files can then be sent to a PCB manufacturer for fabrication, which will include the application of the solder mask.

Note: The exact steps may vary slightly depending on the version of Orcad you are using, but the overall process should be similar.

Photo imageable masks provide better resolution and alignment, and are preferred over silkscreened. You can get different colour solder masks, but the standard colour is green.

On most standard quality boards, the solder mask is laid directly over the bare copper tracks. 

This is known as Solder Mask Over Bare Copper, or SMOBC. You can get other coatings over your tracks in addition to the solder mask, but these are usually for fairly exotic applications.

You can have vias covered with solder mask if you wish, this is known a tenting. This is useful for close tolerance designs, to prevent solder from flowing into vias.

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