How to select solder paste for processing in PCBA technology?

Solder pasteisSMTThe indispensable solder in the process is widely used in reflow soldering. It has a certain viscosity at room temperature and can initially bond electronic components to the predetermined position. At the welding temperature, as the solvent and some additives evaporate, the welded parts will connect with each other, forming a permanent connection. The following is JJYSolder paste manufacturerLet's explain.PCBAHow to choose solder paste for processing?

At present, solder paste coating is mostly adoptedSMTThe steel mesh printing method has the advantages of simple operation, speed, accuracy and immediate use after production. However, at the same time, there are also disadvantages such as poor reliability of solder joints, easy false soldering, waste of solder paste, and high cost.

1The components of solder paste

Solder paste is mainly composed of alloy soldering powder and flux. Among them, alloy solder powder accounts for the total weight85%～90%Flux accounts for15%～20%.

Alloy welding powder

Alloy soldering powder is the main component of solder paste and alsoPCBAThe most important consideration when choosing solder paste in the process. Common alloy soldering powders include tin/LeadSn pbTin/lead/SilverSu pb Ag"Zinc"/lead/BismuthSu pb BiSuch as, the commonly used alloy components are63% Sn/37% pb and 62% Sn/36% pb/2% Ag. Different alloy ratios have different melting temperatures.

The shape, particle size and surface oxidation degree of alloy solder powder have a significant impact on the performance of solder paste. Alloy solder powder can be classified into amorphous and spherical types according to its shape. Spherical alloy powder has a small surface area and a low degree of oxidation, and the prepared solder paste has good printing performance. The particle size of alloy welding powder is generally200-400Eye. The smaller the particle size, the higher the viscosity. If the particle size is too large, the bonding performance of the solder paste will be poor. If the particle size is too fine, the surface oxygen content will increase due to the increase in surface area, and it is not suitable for use.

Flux

In solder paste, solder paste flux serves as the carrier of alloy powder. Its composition is basically the same as that of common fluxes. In order to improve the printing effect and thixotropy, thixotropic agents and solvents are sometimes needed. Through the action of the active agent in the flux, the oxide film on the surface of the welding material and the alloy powder itself can be removed, allowing the solder to rapidly diffuse and adhere to the surface of the welding metal. The composition of flux has a significant impact on the expansion, wettability, collapse, viscosity change, cleaning performance, weld spatter and storage life of solder paste.

Ii. Classification of Solder Paste

There are many types of solder paste to choose fromPCBASome problems may arise during the process. It can generally be classified according to the following characteristics:

1Classified by the melting point of alloy solder powder

The most commonly usedPCBThe melting point of solder paste is178-183℃. Depending on the type and composition of the metal used, the melting point of the solder paste can be raised to250℃Or higher or lower to150℃ It depends on the temperature required for welding. Choose solder paste with different melting points.

2According to the activity of the flux

According to the general classification principle of the activity of liquid fluxes, they can be divided into non-active ones.RTowel equivalent activityRMAAnd activityRAThree levels. According toPCBThe selection is based on the condition of the components and the requirements of the cleaning process.

3According to the viscosity of the solder paste

The viscosity range is very special, usually being100~60OPa·sThe maximum can be reached1000Pa·s. 

As a solder paste manufacturer with a history of sixteen years, JJY has always been committed to the research and development, production and sales of solder paste. Our products are of stable quality and have the advantages of no solder connection, no false soldering, no monument erection, etc. The solder joints are bright and full, the soldering is firm, and the electrical conductivity is excellent. If you have any related needs, please feel free to contact us. We will serve you wholeheartedly.