SOLDER MASKS

During PCB fabrication, you need to choose the recommended solder mask colors.

This guide will take you through all the fundamental aspects of solder mask colors – keep reading to learn more.

What is a Solder Mask?

A solder mask is a protective layer that is applied over the conductive copper track on a PCB.

The mask shields the trace from oxide formation and solder encroachment through bridge formation observed with close-packed pads.

Solder mask finds prevalent use in large scale board productions with automated soldering process.

Green solder mask

You find when a solder mask is laid, the component landings are left uncovered by employing a photolithographic procedure.

Solder mask can be silkscreened, sprayed or vacuum laminated followed by a curing process.

Materials used in solder masks include epoxy and dry film and liquid photo imageable ink.

Why are different Colors used for the PCB Solder Mask?

The choice of solder mask color is usually one of personal inclination.

Solder masks can essentially be furnished in one color as green has been until recent times.

Otherwise, here are some of the reasons attributing to the use of different solder mask colors.

• Solder masks are furnished in different colors as a brand identity for manufacturers.

You find some manufacturers provide printed circuit boards with a particular solder mask color to distinguish its product from others.

• Different colors for solder masks are purely provided for aesthetic purposes. You find colors used to impress the users by their impressive hues.
• Some solder mask colors are employed to offer better contrast with the board features such as the copper traces.

You find the surface finishes for the conductive trace to offer better contrast with different solder mask colors.

• Additionally, you can achieve a better board surface appearance by combining different colors for the solder mask and silkscreen.

For instance, using a white solder mask and a silkscreen with black markings has a high resolution.

• Some applications, for effective performance, will work better with a solder mask of a particular color.

You find LCD applications are better placed with a blue solder mask color for its PCBs.

Sharp contrasts and brightness that can affect the quality of images are avoided in this case.

What are some of the Solder Mask Colors used in PCBs?

You will find a variety of color options for your PCB solder mask.

Some of the common solder mask colors used in PCBs are:

Different colors for PCB solder mask

· Green

The green solder mask is one of the most common in the PCB industry.

Many PCB manufacturers use green as the default solder mask color.

You find this is typically when the customer has made no color preference.

· White

Printed circuit boards can be furnished in white color which is favored for the clean appearance they lend PCBs.

Additionally, you find a white solder mask appealing when used with a silkscreen with black markings.

· Yellow

While yellow is a relatively new solder mask color used in PCBs, it has gained quite some prominence.

A yellow solder mask color is preferred for its visual aspects such as brightness and form.

· Blue

Blue solder masks have found massive employment in PCB construction.

You find the contrast ability of a blue solder mask when used with silkscreen to be remarkably significant.

Furthermore, the visual aspect of a blue solder mask is beguiling.

· Red

You find the adoption of the red solder mask to be on the rise in the PCB making industry.

The red solder mask is bright enough to be deciphered.

Additionally, you find this solder mask color to contrast well with conductive copper path and board populates.

· Black

Black as a primary color offers a simple and visually compelling choice for a PCB solder mask.

Also, using a black solder mask allows large board populates to be highlighted due to its low contrast.

What Guides the Selection of Solder Mask Color in PCBs?

There is a rich color pool to make your choice of solder mask color.

You can test a color choice through sampling before making a final decision.

Your PCB manufacturer can also guide you in an appropriate color choice for your needs.

Some of the aspects influencing solder mask color choice are:

• The nature of the application of the printed circuit board.

For instance, black solder mask color is unfavorable for high-temperature applications.

• The amount of information to be provided by the silkscreen.

Boards with heavy silkscreen markings will require a solder mask color with the best contrast.

• The coating applied over the conductive traces will need to contrast remarkably with the solder mask color.

You can identify the path easily this way.

• Some PCB manufacturers only furnish boards in a single solder mask color. Therefore, requesting a different will be considered a custom quote increasing the board cost.

What are some of the Drawbacks of using Black Solder Mask Color in PCBs?

A black solder mask is limited in the following ways when used on a printed circuit board.

• Black solder mask encompasses carbon derived pigments and cobalt both of which are electrical conductors.

Thus, you find a limited electrical presence when using a black solder mask.

• You also the black solder mask incompatible for use in applications with large thermal dissipations.

As a good absorber of heat, the black solder mask can hamper the clarity of the silkscreen as a result.

• Formation of shadows, especially by large components, causes traces to be blacked out making them indistinguishable.

What Solder Mask Color is Preferred for PCBs with Heavy Labels?

Printed circuit boards with heavy labeling need a solder mask color with a high contrast level.

The contrasting element is useful in helping you to identify the information used on the silkscreen without difficulty.

For modern PCBs, blue solder mask color is deemed to be exemplary for such usage.

Why is Green Commonly used as the Standard Solder Mask Color in PCBs?

The use of a green solder mask has been entrenched in the industry as an unwritten standard.

However, using green as a solder mask color is fueled by the following qualities.

 Green solder mask

• A green-colored solder mask contrasts remarkably well with a silkscreen employing white markings.

You find such a combination provides clear motifs that make the board details quick to the eye.

• While green is visible, it is not extravagantly bright.

Consequently, you find limited reflection when employing a green solder mask.

Thus, viewing such a board is not optically discomforting more so when carrying out a manual assessment.

Why are Blue Solder Masks used for LCD Applications?

LCD is short for liquid crystal display. LCD is a common feature of visual electrical devices such as televisions, smartphones, and cameras.

Solder masks of blue hue are employed in LCDs since they form dull edges without the sharpness of contrast.

Furthermore, a blue color provides a background devoid of brightness that would hamper the image quality.

What are some of the Disadvantages of using a White Solder Mask Color in PCBs?

While white is a primary color that offers impeccable use in many applications, its use on PCBs is still limited.

Some of the reasons contributing to its disfavor are highlighted.

• White color reflects light, and when used for the solder mask, it causes reflection that obscures the conductive path.
• You also find carrying out a manual inspection of a PCB with a white solder mask to be a strenuous exercise.

Why is Yellow not a Common Solder Mask Color in PCBs?

Yellow is a striking color that catches the eye.

However, its use on PCBs as a color option for solder masks is limited by its shortcomings in the contrast department.

Picking out the conductive tracks on the PCB surface from the yellow color is a strenuous exercise.

Additionally, yellow is lowly compatible with many silkscreen marking colors making it unfavorable.

You find deciphering silkscreen information on a yellow solder mask background is an arduous process.

What Causes the differences in Solder Mask Colors in PCBs?

You can find solder masks in many different colors as highlighted.

However, the colors may appear in different shades of a similar color background.

Additionally, the green provided by two different manufactures may not be similar.

The differences in color can be attributed to the following:

• Solder masks are derived from chemical mixtures of polymers and dye.

Consequently, the composition ratio of the dye and polymer will affect the overall color.

You find when the ratio of either element is increased or reduced, the shade of the resultant color is affected.

• You find the method of surface finish application to affect the solder mask color.

For instance, the hot air level used in the coating process of conductive traces affects the final solder mask color outcome.

You find the stress effect of this application process to be the cause of the color difference.

• Colors are typically identified traditionally such as black, white, green red, or blue. However, variants of these colors depending on the intensity such as dark green or light blue can be achieved.

Failure to mention the exact color can lead to a different color variant than desired.

• The difference in color can be attributed to the different processes used by manufacturers.

While the raw elements can be similar, the manufacturing approaches of the solder mask can differ.

Subsequently, you find different color results.

• The color differences can also be attributed to the external copper features.

An excess of copper will result in a different solder mask color shade compared to one with less copper showing.

Can a Solder Mask Color be Produced in Different Variants?

Yes, it can.

Solder masks colors are derived from dyes used with resin-based polymers.

You can thus achieve different shades of a single color by altering the dye and resin ratio.

To achieve a more pronounced color, you can increase the dye amount or reduce the resin amount.

Conversely, a lighter shade can be achieved by decreasing the dye amount or increasing the resin amount.

While green is a common PCB solder mask color, there are many variants of green available.

You will find dark and light green color options, matte green, and even sun green to mention a few.

The color intensity affects the contrasting ability of the solder mask with other board features such as the conductive path.

Does the Type of Solder Mask Color affect the Performance of the PCB?

The performance of the Printed circuit board is not significantly affected by the choice of solder mask color.

You find the solder mask color can affect only non-performance related aspects such as the inspection process.

For instance, carrying out a manual optical inspection on a board with little contrast can be a strenuous activity.

In such cases, you find that identifying the conductive traces is difficult.

However, some solder mask colors such as black and blue employ the use of carbon and cobalt elements in their makeup.

You find these elements are responsible for some electrical charge movement within the solder mask layer.

Electrical flow in the conductive traces can be affected by this movement that could result in shorted circuit paths.

How Important is the Viscosity of the different Solder Mask Colors?

Viscosity is a fluid property that demonstrates the tendency of a fluid to resist movement.

You find the inks used for the different solder mask colors have different viscosities.

The green color pigment has the least viscosity while black exhibits the greatest resistance to flow.

The other color options have viscosities ranging in between.

Viscosity is useful especially in PCBs with a large component density.

Here, you find reduced space between component landing pads.

The difficulty in applying a solder mask on such board increases with increasing viscosity.

Consequently, you will find the application of a green solder mask to be easier in such a case.

Can Solder Masks Colors be Hazardous?

You can find solder mask colors to be toxic particularly when they are subjected to high heat or burning.

The toxicity of the solder mask color can be attributed to the pigments used in the solder mask preparation.

Some solder mask inks contain elements that emit poisonous gases when they burn or decompose.

You find black and blue solder masks contain elements that can release poisonous gases on heat-induced decomposition.

As a result, they are unsuitable for thermal intensive applications.

Solder masks that are green in color employ no harmful substances in their makeup.

Subsequently, they pose no threat to the environment through harmful emissions.

At Venture Electronics, we offer a range of PCB design and layout, PCB assembly, PCB prototyping and PCB fabrication capabilities.

Contact us today for all your PCB solder mask technologies.