PCB Solder Mask, Mask Options, Colours & Impact of Mask Colour

Bittele electronics offers a variety of different solder mask options, including custom colours, LPI, and DFSM masks.

What is a solder mask?

A solder mask is also known as a solder stop mask or solder resist. It is a thin polymer layer that is applied to a bare printed circuit board (PCB). The objective of the solder mask is to protect the surface of the PCB, and help prevent solder bridges. Solder bridges are an unintentional connection between two conductors, usually due to the presence of a small blob of solder. It is important to note that the solder mask is treated as its own separate layer the same way each copper layer and silkscreen layer is, as defined in the Gerber files.

Solder Mask Options

Solder masks can come in a variety of forms. In terms of cost, the lowest cost solder mask would be epoxy liquid where the pattern is silkscreened onto the PCB. Liquid Photo-Imageable solder mask (LPI) and Dry-film Photoimageable (DFSM) are two other types of solder mask option available. All three processes must go through some type of thermal cure, but only LPI solder masks are available in an ultraviolet cure. More information regarding this can be found in our Design for Manufacturability Guide.

Standard Colors

While the actual colour of the solder mask has little impact on the electrical performance of a board, it is important to note the aspect of contrast between traces, planes and empty spaces to consider. The colour can also play a large part in future troubleshooting with the board, as it can impact the difficulty. Bittele offers a number of standard colours such as:

Green
Matte Green
Red
Blue
Matte Blue
Yellow
Black
Matte Black
White

Custom Colours

Bittele electronics offers a variety of different custom solder mask colour options. These include colours such as purple and orange, however, we do not keep stock of these colours. These colours must be ordered in advanced and also come with a minimum order quantity. There may be an increase in price and turn time depending on the custom colour ordered. Once you have placed your RFQ, you may contact your account manager to request more detailed information regarding the custom colour that you would like to order.

Impact of Solder Mask Colour

For the most part, the colour of the solder mask does not have any effect on a given printed circuit board in terms of its functionality. Depending on the colour of the silkscreen, certain colours may make reading the silk screen more difficult to read (for example, a black silkscreen on a light black solder mask). The solder mask will also affect your ability to visually inspect the PCBs. Below you will find a solder mask comparison from the highest contrast to the lowest.

Green

An overwhelmingly large proportion of PCBs utilize a Green solder mask. Since Green is easy on the eyes and allows for high contrast between traces, planes, and empty space on the PCB Green solder mask has become an industry standard. High contrast allows technicians to most easily review for manufacturing defects. Due to its popularity, Green solder mask has expectedly undergone the most research and development of all the solder masks and therefore is the only solder mask colour capable of 8 mil solder mask dams.

Yellow

A Yellow solder mask also offers excellent contrast between planes, traces, and empty spaces, however, the colour is unpopular.

Red

A Red solder mask will provide a bold and clean looking PCB, however the contrast between traces, planes, and empty space significantly lower than it is with a green solder mask. Magnification may be needed when inspecting fine traces on the board for defects with a Red mask.

Blue

Blue solder masks have even lower contrast, and magnification becomes required when inspecting for manufacturing defects. These PCBs look visually pleasing and professional and are a good choice for fully-developed products that will not require trace visibility.

Black

Black masks have almost no contrast between traces, planes and empty space. A Black mask will absorb heat, increasing the danger of overheating for sensitive components. Also, black solder masks require an extra day added to the turn time for PCB fabrication orders. This is due to the large increase in heat that is required during production when compared to the other colours.

White

A white mask will be the hardest to clean, and also has the lowest contrast. If possible, we suggest that you avoid choosing white, especially in the prototyping stage.