Solder Paste Handling and Storage

 A highly overlooked aspect of stencil printing and a major cause of solder printing defects is the improper handling and storage of solder paste. It is commonly accepted that 60% to 70% of solder defects occur during the stencil printing stage. Improving storage and handling practices are one of the simplest and most cost efficient improvements that you can make during your print process. Here are some tips to remember to help you get the best print every time.

Solder Paste Handling Tips:

Solder paste is a perishable item and should be stored accordingly. Refrigerated storage prolongs the shelf life of solder paste; -20 to 10°C is common, although some solder pastes should not be frozen. Consult the product data sheet for specific information.

Solder paste packaged in syringes and cartridges must be stored with the tip pointed down for best dispensing performance.

Always check the date on your solder paste. Indium Solder Paste has a refrigerated shelf life of 1 year. When stored properly in refrigeration, solder pastes are often viable after the “use by” date. It is up to the user to validate use of paste after this recommendation.

Solder paste is a shelf-life dependent item and should be stored as such (in a First In-First Out manner).

Upon delivery, solder paste packages should be directly put into a storage refrigerator (<10°C).

Solder paste should be stored by lot, ensuring use of the older lots first for optimal material management.

Paste Handling During Stencil Printing:

Let your solder paste acclimatize to room temperature before use.

It is important to remove sealed containers from refrigeration and equilibrate to room temperature before opening (typically at least two hours, up to four for large or frozen containers). 

Note: Opening cold solder paste in a warmer environment can result in condensation and potential performance impact.

Recommendation: Remove a jar or cartridge of solder paste from refrigeration one day before use to allow plenty of time for equilibration in the environment (not recommended for syringes).

Do not expose solder paste to heat (>25°C) to bring it up to temperature. For quickest equilibration, a temperature-controlled water bath ≤25°C is recommended.

It is not typically necessary to re-homogenize paste prior to use. However, if needed, hand stirring with a plastic spatula is the best method for solder paste in jars.

When solder paste is removed from the stencil, always store in a separate jar; DO NOT CONTAMINATE THE FRESH PASTE.
Re-introduction into fresh paste can result in process inconsistency.

It is not necessary to return solder paste to the refrigerator after opening. It is possible that refrigeration can cause condensation and compromise performance (unless use environment is uncontrolled or >30°C).

Label containers with date of removal from refrigeration to monitor exposure.

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