Solder Connection

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WS-709 Water Soluble Solder Paste

ALPHA® WS-709 is a completely water-soluble, halide free solder paste which is designed for stencil application in surface mounting processes where aqueous post reflow cleaning is required. 

WS-709 is especially suitable for ultra fine pitch applications when used in conjunction with ALPHA CUT stencil apertures as small as 8 mil (0.2 mm) generating well defined print definitions on 16 mil (0.4mm) pitch pads.

Key Products Features & Benefits: 

  • Long Stencil Life: Exhibits resistance to slumping and drying at temperature up to 21- 26°C (70 – 78°F), and relative humidity extremes. (25%-75% RH) (>36 hr stencil life exhibited at ambient conditions).
  • Excellent Water-Soluble Printing Process Window; very good prints/wipe performance even after 3 hrs exposure at 75% RH.
  • High Throughput and Yield; consistent print volumes at print speeds ranging from 1–6 inches/second. 
  • Water Cleanable after double reflow and hot water cleaning.
  • Fine-pitch printing; consistent shape and volume (e.g.16 mil).
  • Low BGA voiding; exceeds IPC Class III requirement.
  • Low foam generated from cleaned flux residues in recirculating post-clean equipment
  • J-STD Classification: 0RH0


Product Number : WS709

Prod. No. 142861
Alpha WS-709 63/37 700g

Data Sheets and Info

Health & Safety

Technical Bulletin

ROHS Certificate


Q - Do I need to change my printing process when I go to finer printing from size 3 to size 4 paste?
A - Generally when changing from T3 to T4 there is not much difference in printing setup. Depending upon the paste used you may have to make slight adjustments to print parameters such as release speed as aperture fill is greater with finer powders on small apertures but this is just to optimise the print as you would do when changing any paste. It’s by no means certain you will need to do this but it may give you further benefits.

Q - Do we need to return to fridge after use?
A - If you are going to continue the next day, then no you should not return the paste to the fridge.

Q - How long do l have to leave the paste before l can use it once taken from the fridge?
A - Always allow the paste to come up to ambient temperature, take it out of the fridge the night before seems to work well.

Q - I need to achieve better print definition, should l look at a finer solder particle size?
A - Your first call should be to your stencil manufacturer, and see if the aperture design is correctly optimised for you design and process capabilities?

Q - Is a framed stencil a more stable print platform than a stretched foil ?
A - Not today, most foil tensioning systems will give similar print stability as would framed stencils. Much is down to cost or personnel choice.

Q - Once printed how soon before l need to place my components?
A - Always place components before the end of your shift, this has to be good practice.

Q - What kind of print speeds can l use.
A - Always refer to the Technical Data sheet for the specific product, but, to initiate and create excellent shear thinning of the solder paste and promote paste roll a suggestion would be to start at 40mm/s and adjust according to process requirements, changes to pressure / release speed / release height could also be considered to achieve maximum performance.

Q - How long can l leave the paste container out at room temperature?
A - You can safely leave the paste out on the bench for the duration of your shift.

Q - What is colophony and can it cause any health issues?
A - Colophony is a generic term for rosin, this is the sap or sticky substance that derives from pine and spruce trees. Its "stickiness" lends itself to being used in a wide range of products. We have traditionally used this product in fluxes due to these specific properties it can however lead to breathing difficulties and skin sensitivity. Always use fume filtration when soldering and change filters regularly.

Q - What is the difference between rosins and resins?
A - The terms are often used interchangeably, but rosin is a naturally occurring substance, and resin is either a modified rosin or completely synthetic material. Rosins are plant based products and are subject to more natural variation than resins, however resins are commonly used in newer flux formulations due to their more consistent performance.

Q - Do I need to change my printing process when I go to Ultra Fine printing from size 4 to size 5 paste?
A - The biggest change will be going to PS5 and its not so much the printing parameters changing but the stencils are invariably a lot thinner and so you need good support and setup such as making sure you have a release distance of 3 mm set (the distance over which release speed is controlled as the stencil acts more like a drum skin) I would also run with the minimum pressure to avoid stencil damage (coining) this is as most PS stencils are <100µm typically 75µm in thickness. It’s not as bad with PS4 as most stencils are in the 100µm or slightly above range and are more robust.

In all cases (can’t really think of an exception) smaller powder sizes go hand in hand with printing smaller features. Smaller features as we approach Area Ratio 0.66 and in some cases people try to/do operate in the region of AR 0.6-0.66 mean that the printing process has to be good, you have to “respect the fundamentals” i.e. board support, calibration of such things as print height, squeegee condition, decent PCB quality, registration etc.

Again more a feature of small apertures rather than the powder size of paste itself you may need to look at what is your maximum ‘abandon’ time with any paste if you run a start stop process and work to it i.e. don’t exceed and use automatic under screen cleaning where needed. Smaller apertures tend to ‘clog’ more readily and so may need a more frequent aperture clean regime.

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