PCB manufacturing solder paste s torage and application

Solder paste is the most important process material, and It’s a very important process operation for solder paste’s storage, thawing, stirring and addition .

1 Storage, melting and Stirring

In general, solder paste is quite sensitive to exposure to heat, air or moisture. Heat not only causes a reaction between the flux and the solder powder, but also causes the flux to separate from the solder powder. Exposure to air and moisture can cause drying, oxidation and moisture absorption. It is generally recommended to store the solder paste in the refrigerator and set the storage temperature within the range of 0~10 °C. Before exposing the solder to air, the temperature of the solder paste should be raised to the same temperature as the ambient temperature to avoid condensation. Depending on the size of the container and the storage temperature, the time required for melting is from one hour to several hours.

Some people have done experiments, for ordinary 500g a bottle of solder paste, 1h is enough to make the soldering back to ambient temperature. After melting, if it needs to be added to the stencil, it is necessary to stir the solder paste. On the one hand, the solder paste powder and the flux are evenly mixed, on the other hand, the instant viscosity of the solder paste is lowered, which is good for filling immediately when printing. This is the main purpose. Stirring can be done by hand or by machine agitation. Manual agitation is usually carried out by stirring with a tool for 20 to 30 times, or according to the fluidity of the solder paste--the stirring device is used to pick up, and the solder paste can flow downward is ok. Machine agitation is generally controlled by time, usually 30~60s.

2 Use time and re-use precautions

The solder paste is melted and unsealed and should be used within 48 hours. Melting is not used or opened. It does not need to be refrigerated within 48 hours. If it is not used, it can be refrigerated for future use, but only once. Used solder paste (scrape from the stencil) cannot be collected into unused solder paste and cannot be mixed.