Does solder paste expire?

Solder paste has a shelf life. The shelf life is usually between 6 months and 1 year, although finer ultrafine solder pastes or epoxy pastes have a shorter shelf life and a storage life of 3 to 6 months. The exact shelf life is affected by a variety of factors, such as the manufacturer's identification, storage conditions, and frequency of use. Solderpaste is an important material in electronics manufacturing, especially in the surface mount technology (SMT) of circuit boards. With the continuous development of the electronics industry, the requirements for soldering quality are increasing day by day, and the performance and stability of solder paste have also attracted much attention. One of the key questions is: Does the solder paste expire?

I.. Factors Affecting Shelf Life Composition and Reactivity of Solder Paste Solder paste is mainly composed of solder powder and flux. Solder powder provides the metal joining material required for soldering, and flux contains a variety of components such as activators, solvents, and film formers. Activators in fluxes, such as organic acids, have the function of removing oxides from the surface of circuit boards and component pins. These components are chemically active, and over time, they may react with substances in their surroundings. For example, solvents in fluxes can volatilize, causing changes in the viscosity of solder paste. If the solvent volatilizes too much, the solder paste will dry out, affecting its printability and soldering effect. Production date and manufacturer labeling: The shelf life of solder paste is first determined according to the manufacturer's labeling, and usually the production date and shelf life will be clearly marked on the product packaging. Storage conditions: Storage conditions have a significant impact on the shelf life of solder paste. In general, solder paste should be stored in a freezer with constant temperature and humidity at a temperature of 2°C - 8°C. If the storage temperature is too high, the alloy powder and flux in the solder paste may accelerate the chemical reaction, resulting in degraded performance; If the temperature is too low, some components in the flux may solidify and crystallize and grow, which will also affect the soldering effect. In addition, the solder paste should be protected from moisture and direct sunlight to maintain stable performance.

II. Effect of Metal Oxidation The solder powder in solder paste, especially metal components such as tin, is susceptible to oxidation. During storage, it is difficult to completely avoid oxygen penetration, even when it is sealed. Over time, the oxide layer on the surface of the solder powder may gradually thicken. When the oxidized solder powder is soldered, the wettability of the circuit board and component pins will deteriorate, and the formed solder joints may have quality problems such as virtual soldering and insufficient strength. Frequency of use: The frequency of use of solder paste can also affect its shelf life. Frequent opening and closing of the package can expose the solder paste to moisture and oxygen in the air for long periods of time, which can accelerate its oxidation and performance degradation.

III.. Effect of storage conditions on the shelf life of solder paste Temperature Temperature is one of the important factors affecting the shelf life of solder paste. In general, solder paste is suitable for storage at lower temperatures. If the storage temperature is too high, it will accelerate the volatilization of the solvent in the flux and the decomposition of the activator, and accelerate the oxidation rate of the solder powder. For example, in a high-temperature environment, solder paste may dry up and change color in a short period of time, greatly reducing the shelf life. Humidity Humidity is also not negligible. High humidity environments can cause solder paste to absorb too much moisture. In the case of fluxes, increased moisture may affect their chemical properties, such as reduced activator activity, resulting in ineffective oxide removal during soldering. In addition, excessive moisture can also cause mold and mildew in the solder paste during storage, affecting its quality and performance. Sealing Good airtight storage is an important measure to extend the shelf life of solder paste. If the solder paste package is not well sealed, air, moisture and impurities from the outside world can easily enter. Oxygen in the air accelerates the oxidation of the solder paste, and moisture and impurities can contaminate the paste, degrading its performance before the expected expiration date.

IV.. Consequences of Solder Paste Expiration After solder paste expires, its internal composition may change, such as flux failure, viscosity increase, flow decrease, etc. These changes directly affect the use of solder paste and soldering performance, resulting in a decrease in soldering quality, such as unsmooth tin, blackened solder joints, poor soldering, and bubble production. In addition, expired solder paste can release harmful gases that threaten operator health. Deterioration of soldering quality The most direct consequence of soldering with expired solder paste is a deterioration in soldering quality. Due to changes in the composition of solder paste, such as oxidation of solder powder and loss of flux activity, problems such as insufficient solder joints, virtual soldering, and short circuits may occur during the soldering process. Virtual soldering will make the connection of components on the circuit board unstable, and it is easy to fail in use, which affects the reliability of the entire electronic product. Potential impact on production equipment Expired solder paste can also have a potential impact on production equipment. For example, in the SMT printing process, due to the change in viscosity and rheological properties of expired solder paste, the opening of the printing template may be blocked, affecting the printing accuracy and efficiency. During the reflow process, abnormal solder paste may remain inside the device, requiring more frequent equipment cleaning and increasing equipment maintenance costs.

V.. Storage and use suggestions Storage suggestions: Solder paste should be sealed and stored in a constant temperature and humidity freezer, and the temperature should be set at 2°C - 8°C. Some syringe or epoxy pastes are stored at lower temperatures and need to be kept frozen at -20°C. Unopened solder paste generally has an expiration date ranging from 6 months to 1 year if it meets storage conditions. Solder paste should be used as soon as possible after opening and resealed to reduce contact time with air. Suggested use: When using solder paste, the first-in, first-out principle should be followed, and the solder paste that was opened earlier should be preferred. At the same time, the status of the solder paste should be checked regularly, and if it is found that it is clumping, discoloration and other phenomena, it should be disposed of or discarded in time. Before use, the paste needs to be warmed sufficiently and then stirred to ensure uniformity.

In summary, solder paste expires, and after expiration, it can have a negative impact on solder quality and operator health. Therefore, when using solder paste, the production date and shelf life should be checked, and it should be stored and used in strict accordance with the storage conditions. The shelf life of solder paste is affected by its composition, characteristics and storage conditions. To ensure solder quality and productivity, electronics manufacturers should strictly control the storage conditions of solder paste, including temperature, humidity, and sealing, and follow the expiration date recommendations provided by the solder paste manufacturer to avoid using expired solder paste.