The right way to select the color for your PCB . Tips& Trick

1. PCB: HOW TO CHOOSE SOLDER MASK COLOUR
PCB: HOW TO CHOOSE SOLDERMASKCOLOUR
Figura 1 Work of theartist Michele Penna,made with PCBs ofmultiple colors
Written by Guglielmo Martinelli , Chief Commercial Officer, Tecnometal srl , April 2021
Soldermask is a protective coat placed on the top and bottom of PCBs.
In most cases the color of the soldermask does not have an appreciable impact on the performance
of the PCB in terms of functionality or technological limitations, except for a few
cases described below .
Some colors can make reading the silkscreen more difficult, for example, the black screen
printing on a white solder mask.
The color of the solder mask affects the ease of ispection and visual PCBs.
The soldermask is a compound of insulating resins permanent protective, that is plated on the areas
that should not be soldered in order to protect the PCB from the processes of the welding,
high temperatures ,contaminants and downgrade during the life of the electronic board .
It is also an insulator between components and tracks.
However the characteristics of the soldermask are many, the IPC -SM-840 D standards clearly
qualify the performance required of a solder mask.

2. PCB: HOW TO CHOOSE SOLDER MASK COLOUR
In this article however, we will treat only those concerning the choice of the color .
The colors of the soldermask usually doesn’t produce any impact or effect on the performance of
the PCB , however, for the use of different colors of the PCB the resolution will be different, to be
noted that the soldermask with a light tone have a high resolution
.
GREEN
More than 95% of printed circuit boards use green soldermask, so PCB manufacturers' processes
typically refer to green as the “standard” color.
Other colors are also available such as red, black, blue, white, etc., which are required and used in
different applications.
For example, in the prototyping phase, some users prefer the red color to distinguish the boards
from subsequent series production, some "visible" PCBs are often requested with black because it is
very elegant and to better match the color to the devices in which the board will be exposed. LED
light panels often use the white color to have a better optical refraction or even the black color if
optical absorption is required.
Despite the chromatic monotony, however, the use of green as a standard has now been a
consolidated condition for decades and it is undeniable that green is the best of the colors available,
even today.
WHY PREFER GREEN
The green soldermask is highly recognizable, which allows for easy visual inspection to check for
manufacturing defects. Combined with white screen printing, it guarantees clearly identifiable high
contrasts, the flux residues can be clearly noticed visually, in addition the AOI machines, displays,
sensors and cameras have standardized the wavelength to green.
Finally there is an important technical aspect that allows today to green to be the only color capable
of being deposited on PCB for insulations lower than the other colors i.e. with Solder Dam for
minimum admissible values around 0.100 mm (variable data in depending on the thickness of the
copper)
In summary, green is the most recommended color

3. PCB: HOW TO CHOOSE SOLDER MASK COLOUR
RED
The red solder mask has a strong impact and a "professional look".
It highlights a good contrast between copper-free slopes, floors and areas, but is still inferior to that
of green.
An enlarger may be required for visual inspections, particularly in the presence of fine lines.
The screen printing has a good contrast as well as flux residues can be removed well, like on green
Red is very nice if the PCB is visible from the outside or is a front panel.
It is not usually used for LED applications
BLUE
Blue color usually comes in a dark pigmentation.
The contrast between tracks and copper-free areas is very low, so an enlarger is always required for
visual inspection or to check for manufacturing defects.
The contrast between screen printing and blue soldermask is high with a consequent greater
difficulty in visual inspections.
Blue has a dark and unclear shade like green or red, so dirt is easily visible as well as flux residues
are difficult to remove.
However it has a pleasant appearance in particular with silver and gold finishes, which is why it is
sometimes used in applications for the audio sector, broadcast and generally on sight.

4. PCB: HOW TO CHOOSE SOLDER MASK COLOUR
BLACK
The contrast between tracks and areas without copper is quite low, so PCB inspection does not only
require high enlargement but you also have to tilt the light on PCB so that show a shadow and
makes the track more clear
On the other hand silkscreen has a good visual contrast.
In general when using a black color it is necessary to consider the thermal characteristic of this
color, by the way it absorbs heat, in particular this can be a problem during reflow.
A black soldermask absorbs heat increasing the risk of overheating sensitive components.
In these cases it is necessary to make sure that the temperature sensor is well positioned on the
board to eventually redefine the welding profiles.
Screen printing may tend to darken during the reflow process if the underlying PCB absorbs a lot of
heat.
Dirt then on a black surface is easily visible and difficult to remove well.
Chromatically, however, black is a truly elegant and beautiful color, with gold and silver finishes it
is often used in LCD panels.
A black background color covers the distracting details on the screen.
The black then absorbs a lot of light, so it is particularly suitable for applications with this type of
need (e.g. night viewers)
Finally, black is also commercially available in glossy and matt shades.
Matt black has a slightly better contrast than glossy black, but gets dirty more easily, and with this
color, repairs are more difficult

5. PCB: HOW TO CHOOSE SOLDER MASK COLOUR
WHITE
White has a more difficult production cyle among colored solder masks, so the costs for PCB
manufacturers are higher.
Contrast is the lowest of all colors and tracks cannot be displayed correctly, even under lighting and
enlargement ispection.
Cleaning is difficult and very challenging to remove flux stains, the contrast of the black silkscreen
on the white soldermask is pretty good, so the silkscreen will stand out well.
Thanks to its excellent reflectivity properties, the white soldermask is used in many LED
applications and even where exposed PCB is required it gives it a pleasant appearance.
It significantly improves brightness, reflects light and that is why it is in great demand for LED
applications and in lighting engineering in general.
YELLOW
It has a good contrast between layers, tracks and copper-free areas, comparable to that of the green
color.
The yellow solder mask is normally presented with dark tone.
White screen printing does not have a high contrast therefore often, black screen printing is
necessary even if sometimes it does not arrive at satisfactory visual effects.
Yellow is fairly easy to clean.
Although used very little, yellow could be a suitable choice for exposed PCB applications, as long
as this vibrant color is appreciated.

6. PCB: HOW TO CHOOSE SOLDER MASK COLOUR
PURPLE
You will rarely see purple PCBs, it is a risk choice, it has relatively good contrast but not enough to
match green.
It is a beautiful color to combine with an Enig finish and in this case it is purely an aesthetic choice
with a strong visual impact for exposed PCBs.
With the exception of the latter color, Tecnometal srl can develop all the solder mask colors
described in this article