What are the main components of solder paste for smt in circuit boards?

When we finish the PCB production, it is time to enter the SMT placement link, when SMT mounting, we will use solder paste, the types of solder paste are also different, often contact with three kinds of paste, namely solder paste, solder paste and flux paste. The three creams sound similar in name, but from a professional point of view, they will be very different, so let's take a closer look at them today.

First of all, we need to understand what is the main component of SMT's solder paste. Solder paste is a new type of soldering material that comes into being with SMT, which is a paste-like mixture formed by mixing solder powder, flux and other surfactants and thixotropic agents. It is mainly used for the soldering of electronic components such as PCB surface resistance, capacitors, and ICs in the SMT industry.

In fact, in a way, solder paste, solder paste and solder paste are the same thing, that is, solder paste, but the name is different, and the English is solder paste. However, there are many people who think of solder paste and flux paste as a product, but they are not.

It can be seen from the appearance alone that there is a difference, flux can be divided into solid, liquid and gas, the common flux in the solder industry, people often mention that the flux is liquid, and the flux paste and solder paste are paste, the color of the flux paste is transparent and yellowish, and the solder paste is gray or black.

Solder paste is solder paste. Its main component is a paste-like object composed of metal alloy powder. Flux paste is different, mainly playing the role of a flux, its main components are rosin, active agents and solvents. A certain percentage of flux paste is added to the solder paste during the production process.

The role of solder paste: alloy powder; Complete the mechanical and electrical connection between the electronic components and the circuit board. Solder powder

Solder powder is the core ingredient of solder paste, which mainly provides the metal connections required for soldering. Usually, the main component of solder powder is tin (Sn) because of its good soldering properties, it is able to form a strong intermetallic compound with the metal pins and pads on the circuit board at the right temperature. For example, in the common tin-lead (Sn-Pb) alloy solder powders, the tin content is higher, and the lead plays a role in regulating the melting point and improving the soldering properties. However, due to the harm of lead to the environment and human health, lead-free solder powder is becoming more and more important. Common alloy components of lead-free solder powders include tin-silver-copper (Sn-Ag-Cu), where silver (Ag) can improve the strength and fatigue resistance of solder joints, and copper (Cu) helps lower melting points and improve wettability.

The particle size and shape of the solder powder also have a significant impact on the performance of the solder paste. Generally speaking, the smaller the particles, the higher the printing resolution of the solder paste, which can meet the needs of finer circuit board soldering. However, particles that are too small may also cause the solder paste to oxidize faster, affecting the quality of the solder. The shape of the solder powder is usually spherical, and the spherical particles have better flowability, which makes it easy to evenly fill the opening of the stencil during the printing process, thus ensuring that each solder joint gets the right amount of solder paste.

The key point is that the main components and functions of SMT's solder paste have been sorted out for you

The main components of flux and their functions:

The role of flux in solder paste cannot be ignored. It is mainly composed of activators, solvents, film-forming agents, rheology regulators and other components. Activators are a critical part of fluxes that remove oxides and contaminants from the surface of circuit boards and component pins, creating a good metal surface for soldering. Common activators include organic acids, such as rosin acid. During the soldering process, the activator chemically reacts with the oxide at high temperatures, converting the oxide into a solvent-soluble compound, allowing the tin to come into contact with the pure metal surface and form a solder joint.

Solvents dissolve components such as activators and film formers in fluxes, and also regulate the viscosity of solder paste. Commonly used solvents are alcohols, such as ethanol, isopropanol, etc. The film-forming agent forms a protective film around the solder joint after the welding is completed to prevent the solder joint from oxidizing again. Rheology modifiers are used to adjust the rheological properties of solder paste, so that it has the right fluidity during the printing process, and can maintain a certain shape when it is stationary, without collapsing

• A. ACTIVATION: THIS INGREDIENT MAINLY PLAYS THE ROLE OF REMOVING OXIDIZING SUBSTANCES ON THE SURFACE OF THE PCB COPPER FILM PAD AND THE WELDING PARTS OF THE PARTS, AND HAS THE EFFECT OF REDUCING THE SURFACE TENSION OF TIN AND LEAD;
• B. THIXOTROPIC: This ingredient is mainly used to adjust the viscosity and printing performance of the solder paste, and play a role in preventing tailing and adhesion in printing;
• C. Resin (RESINS): This ingredient mainly plays a role in increasing the adhesion of solder paste, and has the effect of protecting and preventing PCB re-oxidation after soldering; This component plays a very important role in the fixation of parts;
• D. SOLVENT: This ingredient is the solvent of the flux component, which plays a uniform role in the stirring process of the solder paste, and has a certain impact on the life of the solder paste;

The role of flux paste:

• 1. The carrier of tin powder particles provides suitable rheology and wet strength, which is conducive to heat transfer to the soldering area, reduces the surface tension of the solder, and prevents the re-oxidation of the solder and the soldering surface during soldering.
• 2. Remove the oxide layer of the soldering surface and tin powder particles, and form a protective layer and a safe residue layer on the surface of the soldering joint.
• 3. The ratio of flux paste can be arbitrarily proportioned with all kinds of solder powder (tin, silver, copper, bismuth, lead), and can also be proportioned with high, medium and low temperature solder powder (100-260) °C. After being mixed into solder paste, it has the advantages of good solderability, continuous printability, and less residue.

<!--[if !supportLists]-->·         <!--[endif]-->Solder paste may also contain some additives, such as tackifiers. The main function of tackifiers is to improve the viscosity of solder paste, so that it can better adhere to stencils and components. During the SMT printing process, the solder paste needs to maintain a certain shape on the stencil and be able to hold the components firmly after placement until they enter the reflow oven. The tackifier can be adjusted according to different process requirements to meet the adhesion needs of different circuit boards and components. In addition, there are additives that may be used to improve the collapse resistance, moisture resistance, etc. of solder paste.

To sum up, solder paste, solder paste, and flux paste are actually two kinds of products - solder paste and flux paste. It is also very simple to distinguish the three, you can distinguish the flux paste from the solder paste from the appearance color, the flux paste is yellowish, and the solder paste will be gray or black. This is because the solder paste is added with the ingredient of tin powder, and the flux paste is just a simple paste that plays a certain role in flux.

Flux and flux paste play a role in assisting soldering, in addition to removing surface oxides and preventing oxidation during soldering operations; Reduce the surface tension of the material, thereby improving the welding quality and significantly improving the wetting performance. Solder paste is like a medium between soldering, its main role is to weld electronic components, it can directly solder different components together, just like building a bridge. The main components of SMT solder paste in PCBs include solder powder, flux and additives. Together, these components enable the solder paste to perform a variety of functions in the SMT process, such as providing metal bonding, removing oxides, adjusting viscosity, and improving solder joint quality. With the continuous development of electronic manufacturing technology, the research and optimization of solder paste composition is also ongoing to meet higher soldering quality requirements, environmental standards, and the needs of different application scenarios.

Citing the article, it can be seen that the article elaborates on the difference between solder paste and flux paste, including appearance color, composition and function. In today's fast-growing field of electronics manufacturing, the development trends of these products are worth exploring in depth.

With the increasing awareness of environmental protection, the research and development of solder paste and flux paste is also paying more and more attention to environmental protection. For example, in the composition of solder paste, researchers are looking for more environmentally friendly additives to reduce the impact on the environment. From the perspective of flux paste, how to reduce the emission of harmful substances while ensuring the effect of flux paste is also an important research direction.

The performance requirements of solder paste and flux paste vary in different application scenarios. For some high-precision electronic component soldering, the viscosity of the solder paste and the stability of the metal connection are extremely high. In some mass-produced electronic device assemblies, the cost-effectiveness and ease of use of flux paste is a key factor. For example, in the mobile phone manufacturing industry, the tiny particles and precise ratio of solder paste can ensure the precise soldering of small electronic components, while flux paste can increase soldering speed and reduce costs in some simple wiring connections.

In addition, as electronic devices become smaller and more performant, the performance of solder paste and flux paste needs to be continuously improved. Not only do they have to meet basic welding needs, but they also have to adapt to new welding technologies such as laser welding. The development of solder paste and flux paste will continue to be closely linked to the development of electronic manufacturing technology, which is constantly optimized to meet new needs.

The above is the relevant content of the main components of SMT solder paste, and at the same time, I also told you the difference and connection between different solder pastes, Suzhou Norfil hopes that this article can provide you with some reference in the process of understanding the SMT placement process.