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November 30, 2017

What is the Shelf Life for a Syringe of Solder Paste

At room temperature storage, what is the practical shelf life for a syringe of solder paste?

What symptoms would one see when the syringe is getting too old?



D. P.

Experts Comments

The shelf life of our solder pastes is product specific. Most of our pastes have a shelf life of 4 - 9 months, if stored between 5C and 10C (41F - 50F).

When the paste is stored at room temperature and <55% relative humidity, it will have a shelf life of approximately one week. Never open a cold syringe of solder paste as this can introduce moisture into the paste which will have adverse effects on the material.

The syringe should remain sealed until it has had a proper amount of time to thaw (a minimum of 4 hours is highly recommended). You should also make sure the syringe is being stored vertically, tip side down. This will help prevent paste separation.

As a general rule, paste that has been in use for more than 8 hours should be disposed of. Paste which has been on the printer for up to 4 hours can be stored at room temperature for up to 24 hours before being re-used.

Always store used paste in a separate container to prevent contamination of the unused paste. Do not mix fresh paste with used paste unless adding more to the printer itself. 1

The first identifiable defect you will see is more solder balls after reflow, followed by deterioration in dispense quality. After that, there may be possible separation of the flux in the syringe and finally, blocking of the dispense equipment.

A simple solder balling test can quickly determine the condition of solder paste after prolonged use. Simply print a small disk of paste (around 4-5mm dia) onto a non-wettable substrate and re-flow as normal. A single solder ball in a clear pool of residue indicates good coalescing ability. A large number of solder balls remaining in the flux residue pool could be an indication of poor coalescing ability and the paste may be unfit for use. 1

1. Taken from the Henkel Solder Paste Handling Guidelines technical bulletin

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Doug Dixon
Global Marketing Director
Henkel Electronics
Mr. Dixon has been in the electronics field for over twenty years and is the Global Marketing Director with the electronics group of Henkel. Prior to joining Henkel, he worked for Raytheon, Camalot Systems, and Universal Instruments.

Most of the latest syringe samples that I have encountered have an expiration date stamped next to the manufacturing date. But I don't if that refers to chilled or room temperature.

Typically when the syringe goes bad, you can see a change in the color uniformity of the solder paste, you might see some discoloration near the open end. If you fail to cap the syringe, the solder paste will start to dry out as the solvents are wicked out thru the needle.

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Edward Zamborsky
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

The shelf life of the solder paste is established by the Manufacturer based on their internal studies. The expiration date should be either on the label or the paperwork that came with the shipment.

Depending on vendor, the most likely shelf life will be 3 or 6 months at room temperature. However, many vendors will request the syringed solder paste be refrigerated to extend the shelf life.

Classic symptoms of expired paste or paste that has changed significantly from its original properties include: Significant Separation of flux and powder, Increased viscosity (leads to difficult dispensing), and in some cases large air bubble formation in the syringe.

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Brian Bauer
Business Manager
Heraeus Incorporated
Mr. Bauer has been in the SMT industry since 1982. He has been involved with the development, manufacture and technical support for the full range of Heraeus SMT products, including adhesives, conductive adhesives, fluxes and solder paste.

This depends on the type of solder paste as well as the manufacturer. For our No Clean pastes we typically get around 4-6 month shelf life at room temperature. On Water Soluble pastes we get a little less shelf life.

What you probably will run into is that paste thickening up over time which is attributed to the flux medium reacting with the solder powder. You might also see some separation of the flux.

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Mike Scimeca
President
FCT Assembly
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.
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