Solder paste usage continues to grow in Printed Circuit Board (PCB) assemblies as SMT components have become more commonly used.
Solder paste viscosity is precisely engineered to give you the printing performance that yields low-defect reflow results. The shelf-life and storage of the solder paste can have an impact on the viscosity.
What Is The Shelf Life for Solder Paste?
To meet the ISO requirements, solder paste manufacturers are regulated to apply production expiration dates that occur well before the material could possibly produce a defect.
For example, most Alpha solder pastes have a 25.5 week (5.8 month) shelf-life from the date of manufacturing. However, like most solder pastes, if the solder is stored under refrigeration in the original sealed package, the paste could be fully functional for a year or even longer.
How do you know that the Solder paste is fully functional after the expiration date?
The best ways to determine if the solder paste is fully functional after the expiration date are the following:
1) If the viscosity has remained stable, the paste will print normally.
2) If there has been no flux evaporation and the paste prints normally, it should therefore reflow correctly to the edge of the pads.
A good way to check this is to test a few assemblies for printing and reflow characteristics: If it prints well and solders normally, then it is fully functional and has formed reliable solder joints.
In fact, some PCB assemblers have used solder pastes that are two to three years old and have not had an issue. However, this is not our recommendation. Three to four months past the expiration date should not be an issue in most cases.
What is the best way to store solder paste?
To ensure that the solder paste continues to perform optimally, it is necessary to store the solder paste correctly. Solder paste should always be stored in an airtight container so that is doesn’t oxidize, but once the factory seal has been broken, the paste will only have a short life remaining.
It is best to store opened jars of solder paste at room temperature, as temperature cycling could cause moisture from condensation.
Sealed, unopened jars of solder paste should be refrigerated at the temperature shown on the technical bulletin to achieve the longest possible shelf-life.
It is, of course, the best practice to use the solder paste prior to the expiration date if possible. When you receive a new order of solder paste, make sure that you or your staff rotates the stock of solder paste to use the oldest lot first.
