What Is PCB Solder Mask
Solder mask, commonly referred to as solder resist, is a durable, solid layer that shields copper lines and connections between them that are found on PCBs. The principal function of solder is to resist stopping conductive solder from connecting between electronic components and creating short circuits. There are a variety of PCB solder masks, including Epoxy Liquid, Liquid Photoimageable Dry Film Photoimageable, and Bottom and Top-side Masks.
Bottom and Top Side Solder mask
They are usually employed by engineers to find holes in the solder mask, which is already attached to the PCB. It is a particular type of mask that is applied via film or epoxy. The component pins will be attached to the board using the holes that were registered with the masks.
The lines that run along the top of the boards are referred to as top trace, and the solder mask is known as the top-side mask. Similar to the top-side-mask as well, the bottom one is utilized for the bottom part of the board.
Liquid Epoxy Solder Masks
For solder masks, epoxy would be the most economical choice. It is a type of polymer that is printed on the PCB. Silkscreening is a printing method that utilizes the mesh of a woven weave to support ink-blocking patterns. The mesh permits the unblockable zones to be identified in this process. And the Ink was transferred. The process is followed by curing the thermal.
Liquid Photoimageable (LPI) Solder Masks
It is actually a mixture of two different liquids that makes up LPI solder masks. They are kept separate and then mixed prior to using the mask for a longer shelf-life. LPI is also among the most cost-effective options in comparison to many other kinds.
In addition to curtain coating and screen printing, LPI is also used in spray applications. This mask is made up of different solvents and polymers. A thin layer can be made using this mask and will adhere to the desired surface. When this mask is used, the PCB generally does not need any finish surface finish which is available at the moment.
In contrast to conventional epoxy inks, LPI is tolerant of UV light. The board must be covered by the mask, and then after a brief “tack cure” cycle, the board is then exposed to ultraviolet light with an ultraviolet laser or photolithography.
Before applying the solder mask The PCB boards are cleaned and examined for signs of the oxidation process. This is done with the chemical solution, aluminum oxide solutions, or suspended pumice to clean the boards.
A sought-after method used to expose the surface of the panel to UV radiation is making use of film tools as well as contact printers. Both the top and bottom layers of film are printed with the emulsion process to block off the areas that must be soldered. Film and production panels are then fixed to the substrate using printing tools and exposed to a lighting source that is UV simultaneously.
Direct imaging is a method that utilizes the use of a laser. This method doesn’t require film or tooling since the laser is controlled by Fiducial markers in the templates of the panels made from copper.
LPI solder Masks come in different shades, including black, red, green, white, yellow and blue.
Dry Film Photo-imageable Solder Masks
Dry film photoimageable solder masks are a requirement for vacuum lamination. Dry film is subjected to light exposure and later develops. After development, the openings are identified, forming patterns, and then the components are then soldered to those copper pads. High-density wiring boards get the most benefit from dry-film solder masks since it doesn’t clog the through holes.
Material Used
There are a variety of materials employed based on the budget, the size of the piece, the thickness of copper traces, the size and number of holes, etc. Below are two common materials:
1.Epoxy Liquid
It is one of the most widely used materials to make solder masks because it’s inexpensive and offers the PCB a reliable shield. It’s efficient even when it is surrounded by numerous components and connections.
2.Dry Film Resist
Dry film is applied to ensure that the PCB’s surface is smooth and even.
Resolution Range of Solder Mask
The performance of a solder mask will depend on the following aspects. The range will vary based on the number of components or traces and the thickness, number, and material of the layers:
● Solder Mask Thickness:0.2mil – 1.6mil.
● Solder Dam: 4mil to get a solder mask of green color as well as 5mil for the solder masks in different colors.
● Solder Mask Hole Plug Diameter:10mil – 25mil.
Importance of Solder Mask on Your PCB
● It stops the oxidation of copper traces.
● Special PCB interconnectors can be placed at specific locations within the PCB in order to link one PCB layer to the next. Any other connection type is not recommended. Since the layers are so close to each other that even the tiniest bit of solder can cause unwanted connections between the layers. This is why an additional layer of polymer which is known as the solder mask, assists in ensuring that the solder won’t create unneeded connections.
● It stops unintentional connections between components, even when tolerances are very tight.
● In order to keep electrical connections and substrates clean, solder masks keep dirt and dust at bay.
● It protects the electrical connections from corroding.
Solder masks are utilized for both hands and for automated assembly. It is an essential step in the entire PCB manufacturing process. To ensure that connections are efficient and perform well the solder mask is of vital importance.
What Kind of Solder Masks Can We Find in JarnisTech
As you may have guessed that solder mask is extremely important when making your PCB. Green is the most commonly used color used for solder masks. However, there are numerous colors to choose from. JarnisTech uses the following colors include:
● Green
● Red
● Blue
● Yellow
● White
● Black
● Matte Green
● Matte Black
● Purple
JarnisTech will make every effort to make your PCBs with solder masks that are of the finest standard to satisfy your expectations and we are committed to adhering to the highest standards of PCB manufacturing and assembly.
Please feel free to contact us at [email protected] if you have any questions. We’ll be very glad to assist you.
What’s the most suitable PCB color for your project? Here, we look at 6 of the top commonly used colors that are available currently to find out the advantages and disadvantages of each.
Green
Solder masking with green color is the most popular coloration available today, and it’s for a good reason. It offers some of the most vivid intensity contrasts in any hue between traces, planes and spaces. This makes it a desirable choice to repair and maintain.
Due to its popularity, it is available to nearly every PCB manufacturing facility in large quantities. It is considered to be the universal color for circuit boards across the globe. It is also the most affordable circuit board color available. It is one of the tiniest coats, and due to intensive research and development can contain the tiny solder mask dams in order to keep solder from breaking.
Red
Solder masking in red is an attractive option that is typically used for designs that show internal hardware. While it is among the top sought-after alternative colors for PCBs however, there is an issue that the contrast and visibility are less than those of a normal green PCB.
Technicians working on maintenance tasks on a PCB with a red color may require more magnification to solve problems on the board.
The color red is often chosen because of its aesthetic appeal more than its practicality.
Blue
The second-most popular color is employed in PCB production. However, it has less contrast than yellow, green, and red circuit boards.
Since silkscreens display exceptionally well on these screens, they have been the primary color for Arduino boards. They are usually used in electronic prototyping that is open source. Furthermore, the blue solder masking’s hue makes it ideal to be installed on LCDs.
Black
Masking with black solder is among the most costly color options available and often takes longer to make when compared in comparison to the other color options. As a result, it is not recommended for high-temperature applications due to its prone to absorb heat. Furthermore, it has minimal contrast, which makes the repair difficult and maintain. Additionally, it has the highest rate of failure in the manufacturing process.
With so many caveats, companies such as Apple choose black PCBs as their most popular color, why?
The contrast of trace isn’t great on black PCBs. Silkscreen performs exceptionally well in this particular coloration. Furthermore, It also has the lowest light reflection, making it ideal for circuits where light is undesirable.
The aesthetic appeal of black soldering could be important to companies such as Apple, which value beautiful design. Despite this, it is regarded as a challenging color from a practical perspective. It is important to think carefully before choosing the black printed circuit board.
White
A white PCB is even lower contrast when compared to a black PCB which makes it the most difficult color to inspect visually. Additionally, they accumulate dirt with time. What potential uses could this color be used for?
LED lights usually utilize white solder masking, particularly when placed on lighter-colored surfaces. White is the least disruptive shade in the event that lights are switched on, and they blend well when they are turned off. Since white is among the colors that reflect light it also emits a clear white glow when it is illuminated.
The solder colors of the solders are not the same. When white PCBs are used for LED-based applications, be sure that the manufacturer you choose uses solder that has a high reflectance.
Yellow
A variety of new colors are being developed. However, they are difficult to control. Yellow is a beautiful color. However, it does not contrast well with silkscreens as well as traces, making it hard to work with in any real-world setting. Different colors can meet various requirements, including clarity, cleanliness and style. Always test a color before you make a final decision on your color preference.
The Process of Using Solder Mask on PCB
Below is the procedure to apply the solder mask layer on the PCB:
Cleaning The Board
Cleaning the board to eliminate the dirt and other contaminants and the surfaces are dried.
Solder Mask Ink Coating
The board is then put into a vertical coating machine to solder ink masks. The thickness of the coating is determined by factors like the level of reliability required by the PCB as well as the specific domain that it is employed. The thickness of the solder mask will differ when being applied to various parts on the board like the traces, the copper foil and the substrate. The thickness of the mask layer will depend on the machine’s capabilities and PCB’s capabilities for manufacturing.
Pre-hardening
The process differs from complete hardening since pre-hardening focuses on making the coating fairly solid within the PCB. This allows for the removal of unneeded coating that can be removed easily from the PCB at the development stage.
Image and Hardening
Imaging is accomplished by using a film that is laser plotted to determine the solder mask’s surface. The film is then aligned with the panel, which is coated with solder and then dried with tack. In this process of imaging, the film that is aligned to the panel is exposed to UV light. After receiving the UV light, the opaque surface allows to allow the UV light to penetrate the film and the ink that is below the opaque becomes the polymerization (hardened).
In the scenario of LDI imaging, the photo film is not necessary since the UV laser is able to directly melt the areas on the board that need to hold an ink mask for soldering.
Developing
The circuit board is then submerged in the developer to wash away any solder masks that are not required to ensure that the copper foil is exposed correctly.
Final Cleaning and Hardening
Final hardening is essential to ensure that the solder mask ink is accessible for mounting on the PCB’s surface. After that, the boards that are covered with solder masks must be cleaned prior to further processes like applying the finish on the surface.
Surface Finish
No matter what PCB solder masks are used, the mask leaves behind open areas on the board. The exposed areas must be coated with an appropriate top-quality surface to stop oxidation. A very sought-after surface finish is hot air solder leveling (HASL). In accordance with the need, other finishes can be used, for instance, electroless nickel electroless palladium gold (ENEPIG) and electroless nickel immersion gold (ENIG). If needed, there are holes added to the surface layer remain to create an additional mask. The paste mask is used to secure parts or pads to the boards according to the manufacturing process employed.
Summary
Why Choose JarnisTech
Solder masks for printed circuit board alternatives provided by JarnisTech Limited are specifically designed to meet your business requirements. We concentrate on the technical aspect of the PCB, for example, elements such as controlled impedance. We also let your team select the best PCB mask depending on what is best suited to your needs and the desired design.
Production engineers from our team have dealt with virtually every color and finish that is available and will ensure that the PCB you order is printed how you want it. Talk to a representative today to find out more about the possibility of using liquid photos to create solder mask colors that could be popular in your field or could help you stand out in your next presentation. Contact Us Today!
