A Complete Guide on the Difference Between Solder Mask and Solder Paste

Printed circuit boards, abbreviated as PCBs, have become an important part of electronics, and we need to explore important things about their designs. If we look deeply into the design of PCBs, we observe two types of layers called the outer upper layer and lower layer of the circuit, usually termed as solder mask and solder paste layer. PCBs are green printed circuit boards usually serving in making assemblies for electronic devices.

They need a protective covering and a covering connecting the assemblies of the circuits. To understand the proper working and ensure the conductivity of PCBs, we need to know a complete guide on the difference between solder masks and solder paste. It will tell us how important solder masks are and solder paste.

What is a solder mask?

While covering the topic and developing the concept of PCBs, you need to know the complete guide on the difference between solder masks and solder paste. While handling the difference between solder mask and solder paste, here we will explain the solder mask properly. The solder mask is a layer of green colored part on the printed circuit board that covers it from both sides.

• Usually, the color used for the solder mask is green, but it can be another color like red, blue, or yellow.
• The basic reason for using this solder mask for the circuit board is to prevent the surface of the metal from oxidation.
• The solder mask is basically the layering of liquid-type polymer mixtures on the surface of the printed circuit board.
• It helps to prevent the oxidation of metal used in the circuit building and board base.
• A solder mask is also important in the sense of keeping the components of the circuit in their right places and helping to avoid short circuits.

The solder mask is necessary sometimes, but sometimes, you can quit it while building a self-made printed circuit board. Solder masks can be many easily removable types, so using such a solder mask is a plus point as you can change or remove it when needed.

Solder mask making and types

Soldering masks come with great importance in the field of PCB manufacturing, and the green color of the soldering masks is trending all over the world. Commonly we prefer to use epoxy as the material for making solder masks to cover up the exposed metal of the PCB.

 We can make solder masks in different ways by using different of the same material but different techniques. So, some of the basic and most important types of solder mask are as follow.

• Epoxy Solder masks

Epoxy liquid mask is the most common type of epoxy solder mask, and the cost of this mask is much cheap. That's why it is trending most than the other masks.

For preparing the epoxy mask, the manufacturer mixes the solder dyes in epoxy liquid. Then they spread a layer of this epoxy dye-containing solution on the PCB surface through a brush.

It seems like silkscreen spreading over the metal to print the circuit board. It is a removable material, so if someone wants it to remove, they can, but after doing that, the chances of short-circuiting enhance, and the metal is also exposed to air for oxidation.

During this process, you need to use some amount of heat to fix the epoxy liquid in the form of a layer, as the epoxy liquid is a thermostat polymer.

• Photo imageable solder mask

Liquid photography solder masking is somehow different from the dry film and epoxy solder mask, but in this case, a film or photograph is prepared as per the requirement of the printed circuit board. In a photo-imageable solder mask, you can use the same method of spreading the layer over the circuit board, just like in the epoxy liquid or using the lithography process. The manufacturer adds pads by forming holes and mounting holes.

In this method, a few parts of the board metal are kept exposed in the form of black, and the other is covered with a solder mask from both sides of the circuit. Photo imageable solder mask is a unique technique in which the manufacturer dries up the solder by using heat from an oven or UV rays. Then dip it in a solvent to solidify the layer of the epoxy material.

• Dry film solder mask

This type of solder mask also seems like a Photo imageable solder mask in the sense of applying the prepared sheet instead of applying the liquid like in the epoxy liquid technique. In this method, the manufacturer covers the areas of PCB except for a few.

Dry film is applied to the circuit board, during which the air is removed through the vacuum to remove the air bubbles present between the PCB sheet and dry film. Then a solvent is poured over unexposed areas and let dry.

An insight into What is solder paste?

Solder paste sounds like the solder masks, but it is not because of its main purpose of using it in PCB. When we develop a PCB or a PCBA, we assemble different electronic parts to create a circuit or a proper assembly for the electronic devices. So, for soldering the electronic component, we are using the solder paste, which can be made of different materials depending upon the nature of fixing or assembling the PCB.

• The engineers prepare a sketch map so that they can check where the solder pastes should be applied to fix the electronic circuit.
• The solder paste comes in different sizes and materials but usually in the shape of a little sphere.
• The engineers apply of fix these little spheres on the circuit to develop a connection between different parts.
• Mainly, solder paste is used for connecting different electronic parts with PCBs and forming the PCB assembly.

The solder paste is not a liquid but made of some material that is present in solid form. The engineers put the solder paste on PCB and allowed it to be heated in either oven or under UV light.

Solder paste manufacturing

It is necessary to discuss the manufacturing so that you can get a complete guide on the difference between solder masks and solder paste. Solder paste is mainly made up of two parts which a solder paste may include are

Flux

The flux of solder paste is the component that contains further more components like activation, solvent, resins, and thixotropic. These components are responsible for keeping the PCBs and PCBAs long-lasting by protecting them from corrosion of copper metal, keeping the parts organized by developing uniformity, and adjusting the viscosity.

These ingredients of the flux tell us how solder paste is important for PCBs. Sometimes it seems impossible to develop the PCBs and PCBAs without solder paste, and it is true enough.

Solder powder

The other part of the solder paste is solder powder which is usually made up of a mixture of tin and some other metal like lead, copper, or bismuth. The tin powder is directly involved in bringing uniformity to the PCB. The size of solder powder may vary, but it keeps its function on while adding different ratios.

The solder paste is not heat resistant like the solder masks, so the experts recommend keeping the solder paste at a low temperature, i.e., 1 to 10 degrees Celsius, and avoiding getting exposure to sunlight directly on the PCB; otherwise, it will be expired after melting.

Based on the nature of the material, temperature, and environmental effects, you can find different types of solder paste.

• Leaded solder paste
• Lead-free solder paste
• High-temperature solders paste
• Medium temperatures solder paste
• Low-temperature solders past
• Disposable solder paste
• Non-disposable solder paste

Major differences between solder mask and solder paste

While going through the detailed study to get a complete guide on the difference between solder masks and solder paste, we find the following main differences.

The solder mask is the just like the coating or a layer formation on the circuit board, while solder paste is basically used for assembling or organizing the different components of PCB and other electron components to prepare PCB assembly.

• A solder mask is just a layering of the printed circuit board to avoid the exposure of circuit board metal to the air, while solder paste is a connection-creating material.
• Solder mask is available in both liquid and dry form, while solder paste is prepared by adding two major components, flux, and powder, which is usually an alloy of tin and some other metals.
• The solder mask needs to be dry after spreading on the surface circuit board, while the solder paste needs some heat to melt the balls and adjust the circuit components.
• Solder masks are heat resistant and can bear high temperatures, while solder paste has such ingredients that cannot bear high temperatures but need to be kept on temperature from 1 to 10 degrees Celsius.
• Solder masks usually use epoxy liquid, while the solder paste contains some metal, viscosity-maintaining chemicals, and resins.
• Solder masks do not need much cleaning and proficiency, while solder paste needs.

Conclusion

When going through a complete guide on the difference between solder mask and solder paste, we come to know that solder mask and solder paste are two very different things that are confused by some early birds.