Introduction to White PCBs

A white printed circuit board (PCB) refers to a PCB that has a white solder mask color instead of the more common green solder mask. White PCBs provide an attractive aesthetic option and offer some potential benefits compared to green PCBs in certain applications.

This article will provide an overview of white PCBs covering:

• Differences from standard green PCBs
• Materials and manufacturing process
• Applications and advantages of white PCBs
• Challenges and limitations to consider
• PCB surface finish options
• Design considerations
• Cost comparisons to green PCBs

Green vs White PCBs

Most PCBs use a green solder mask color by default. This masks the bare copper traces to prevent short circuits.

White PCBs substitute a white solder mask material instead of the standard green. This gives the PCB a bright white appearance instead of the typical green hue.

Aside from the different color, white PCBs share the same fabrication process and materials as regular PCBs. The differences are purely cosmetic.

However, the white color can provide some advantages in certain applications as discussed later.

White PCB Materials and Manufacturing

White PCBs use the same FR-4 substrate material and base copper layers as standard PCBs. The same lamination, drilling, plating, and etching processes are employed.

The key difference lies in application of the solder mask. For white PCBs, manufacturers substitute white solder mask material in place of the typical green.

Multiple options for white solder mask material exist:

• White epoxy ink – most common and cost effective
• White LPI (liquid photoimageable) – provides higher accuracy and resolution
• White IG (inkjet) solder masks – digital process allows custom masking

The white solder mask is applied over the entire PCB surface using screen printing, inkjet printing, or photolithography techniques. It coats the bare copper while leaving bonding pads exposed.

The rest of the PCB fabrication process remains the same. Components are assembled and soldered onto the finished white PCB.

Applications and Advantages of White PCBs

Here are some of the benefits driving adoption of white PCBs in certain applications:

Aesthetic Appeal

White PCBs provide a clean, professional look for consumer products where the PCB is visible. The bright white colorway fits with light-colored product enclosures.

LED Applications

The white soldermask reflects light better. This improves luminance and efficiency in LED circuits and lighting products.

Medical and Scientific Devices

White PCBs paired with white enclosures give medical devices a clean clinical look and feel.

RF/Wireless Circuits

Some tests suggest the white mask may improve performance of certain RF and high-frequency circuits compared to green.

High Voltage PCBs

White masks theoretically provide slightly better insulation resistance for high voltage boards.

Debugging and Testing

Component markings and PCB layers can be more easily discerned against the white background to assist debugging and testing.

For these reasons, white PCBs are becoming popular for consumer electronics, LED lighting, medical products, communications devices, and other applications where aesthetics and technical factors motivate adoption.

Challenges and Limitations

However, white PCBs also introduce some potential downsides to consider:

• More expensive than standard green PCBs
• Can show scratches, dust, and fingerprints more easily
• Not as readily available from all manufacturers
• Some fabrics such as inkjet masks require extra process validation
• Reflectivity may impede optical inspection
• Debated RF performance improvement vs green
• Potential for higher lead times initially

While the downsides are generally manageable, they should be evaluated when deciding between white and green PCBs.

PCB Surface Finishes

Various surface finishes can be used on white PCBs just as with standard green PCBs:

HASL (Hot Air Solder Leveling)

The default and most cost-effective finish. Provides good solderability.

Immersion Tin Plating

Suitable for fine pitch components. Offers excellent solderability but higher cost.

Immersion Silver Plating

Higher cost finish with excellent shelf life and solderability.

ENIG (Electroless Nickel Immersion Gold)

Premium finish for reliability. Combines nickel corrosion protection with gold solderability.

The choice depends on budget, soldering process, and longevity requirements. Any finish can be applied to white or green PCBs alike.

White PCB Design Considerations

From a design perspective, white PCBs introduce a few considerations:

• Avoid using white silkscreen text or outlines over white masks if possible. Use black outlines and text instead.
• Increase silkscreen text sizes slightly or use thicker fonts since text won’t contrast as sharply against the white background.
• Take the white background into account if using copper polygons for RF ground planes or heat sinks. The thermal characteristics will differ slightly from green.
• Account for the higher visible scratches and dust when defining fabrication and handling specifications.

Overall, only minor design tweaks may be needed when switching to white PCBs.

Cost Comparison vs Green PCBs

Let’s compare rough cost estimates:

PCB Type	Cost Per Unit
Green solder mask	$5
White epoxy ink mask	$7
White LPI solder mask	$10
White IG inkjet mask	$15

White PCBs cost anywhere from 1.5 to 3 times more than standard green PCBs depending on the solder mask fabrication method.

More complex PCBs also tend to increase the relative expense delta since matching white mask alignment tolerances usually requires more process tuning.

However, for many applications the aesthetic and technical benefits outweigh the moderate cost premium of selecting white over green PCBs.

Conclusion

• White PCBs substitute white solder mask for the traditional green to provide an attractive high-visibility appearance.
• The base materials and fabrication process are otherwise identical to standard PCBs.
• Applications range from LED lighting to consumer electronics where aesthetics matter. Technical benefits are also possible.
• Design considerations are minor and mostly center around contrast against the white background.
• White PCBs cost approximately 1.5 to 3 times more than green equivalents, but provide advantages that often justify the premium.

For products where the PCB is visible, white PCBs present an excellent high-visibility aesthetic choice. With some smart design adaptations, their benefits can outweigh their limited downsides in many applications.

Frequently Asked Questions

How are white PCBs different from regular PCBs?

The only difference is the white solder mask color instead of the typical green mask. The board materials, layer stackup, and fabrication process are the same.

Why use white PCBs instead of green?

White PCBs provide an attractive high-visibility appearance for consumer products. They also offer potential technical benefits for LED, RF, and high voltage applications.

Are white PCBs more expensive than green?

Yes, white PCBs cost approximately 1.5 to 3 times more than equivalently specced green PCBs. But the benefits often justify the cost premium.

What are some challenges with white PCBs?

They show scratches and fingerprints more easily. Reflectivity can impede inspection. Fabrication requires close process control to match green PCB tolerances and avoid delays.

Do I need to design white PCBs differently?

Minor adjustments like increased silkscreen text size and avoiding white overlays on the mask may be advisable. Thermal characteristics also differ slightly.