Solder paste, as the core soldering material in surface mount technology (SMT), directly affects the soldering quality and reliability of electronic products in terms of its performance. The Storage conditions for solder paste are closely related to its composition characteristics. Based on the main components and uses of solder paste, the storage conditions and influencing factors of solder paste are analyzed in detail
Table of Contents
1、 Ingredients and uses of solder paste
1. Alloy welding powder
The main component is lead-free alloy (such as Sn Ag Cu, SAC series), which is responsible for forming solder joints and providing conductivity and mechanical strength. The particle shape, size, and degree of oxidation of alloy powder directly affect the wettability and flowability of welding.
2. Flux substrate
Contains resin (adhesive), activator (removing oxide layer), solvent (adjusting viscosity), and thixotropic agent (preventing collapse during printing). The activity of the flux determines its cleaning ability and oxygen resistance during welding.
Purpose: By using printing, SMT, and reflow soldering processes, electronic components are fixed on PCB pads to form reliable electrical connections.
2、 Storage conditions for solder paste
1. Low temperature refrigeration
-Temperature range: Unopened solder paste should be stored in a dedicated refrigerator at 2-10 ℃ (some standards are 0-10 ℃) to slow down the chemical reaction between the flux and solder powder, avoid oxidation and solvent evaporation.
-Humidity control: It is necessary to maintain a dry environment to prevent moisture from entering and causing solder paste to clump or layer.
2. Heat recovery treatment
-Purpose: The refrigerated solder paste should be left to stand at room temperature (20-30 ℃) for 2-4 hours (at least 3 hours for 500g packaging) to keep the temperature consistent with the environment and avoid condensation water from mixing and causing oxidation or abnormal viscosity.
-Caution: Do not accelerate the temperature return by heating, otherwise it will damage the activity of the flux.
3. Management after opening
Usage time
After opening, it should be used up within 24 hours. The unused part should be sealed and refrigerated, and cannot be returned to the original can to prevent contamination.
-Packaging and storage: It is recommended to package in small batches to reduce exposure to air.
4.Avoid external interference
Keep away from chemicals, avoid squeezing or shaking, and prevent component delamination or leakage.
3、 The impact of improper storage of solder paste
1. Physical performance degradation
-Drying of paste: Prolonged exposure to high temperatures or after opening can cause solvent evaporation, increase viscosity, and easily block the steel mesh during printing, resulting in missed printing or uneven tin plating.
-Layering and clumping: Long term storage or temperature fluctuations may cause “water oil separation” or particle aggregation, reducing fluidity.
2. Decreased chemical activity
-Flux failure: The active agent decomposes or oxidizes, unable to effectively remove the solder pad oxide layer, resulting in virtual soldering, cold soldering, or solder joint voids.
-Alloy oxidation: Thickening of the oxide layer on the surface of the solder powder reduces wettability, and the conductivity and mechanical strength of the solder joint are damaged.
3. Welding defect risk
-Improper storage of solder paste can easily cause bridging, tin explosion (release of residual gas from flux), or decreased reliability of solder joints during reflow soldering. Long term use may lead to failures due to corrosion or fatigue fracture.
4、 Storage suggestions for solder paste in different scenarios
1. High reliability fields (such as medical and automotive electronics)
-After opening for more than 24 hours or slightly expired, it must be scrapped, and the use of expired solder paste is strictly prohibited.
2. Conventional electronic manufacturing
-Tin paste that has slightly expired (1-2 months) and is stored in compliance can be used in limited quantities after assessing risks through viscosity testing and small-scale trial welding.
5、 Key measures to extend lifespan
1. First in, first out management
Use in order of shelf life to avoid backlog and expiration.
2. Regular testing
Evaluate performance through viscometer or wettability testing, and predict scrap requirements in advance.
3. Special equipment
Use industrial grade constant temperature storage cabinets (non civilian refrigerators) to ensure stable insulation and humidity.
Summarize
The Storage conditions for solder paste are directly related to its component stability and welding performance. By strict low-temperature refrigeration, standardized reheating, and opening management, its effective lifespan can be maximized. For key industries, stricter standards need to be followed to avoid batch quality risks caused by storage issues. Enterprises should establish scientific inventory and usage processes, rather than relying on remedial measures after expiration.
