The SN97C WS157 is not longer available. It has been replaced by the WS888

Product Description
The SN97C (Sn/3.0Ag/0.5Cu) WS157 water soluble solder paste is specifically designed for lead free solder processes. It displays previously unseen level of repeatability and consistency. This paste offers an excellent open time, extended abandon time and good soldering activity at the elevated processing temperatures required for lead free alloys.

Attributes

Stable at Lead Free process temperatures

Enhanced activity for tough to solder boards and components

High speed stencil printing up to 150mm/sec

Excellent tack performance and printer open time

Extended “between-print” abandon time

Very cleanable post solder residues

Performance
The performance of solder paste depends in part on the metal content, solder alloy and the solder particle size range. Increasing metal content reduces the tendency to slump and reduces the tack life of the paste, while the solder balling performance improves.

Refrigeration and storage
It is recommended to store the WS157 water washable solder paste at 5-10°C. The paste should be removed from cold storage a minimum of 8 hours in the unopened container prior to use. If the paste does not reach room temperature, it may stick to the stencil, not deposit onto the SMT pads, de-wet pads during reflow, outgas during reflow, or produce solder balls. Avoid direct sunlight.

Handling and shelf life
The optimum temperature and humidity are 75°F and 60% or below respectively. Provided WS157 water soluble solder paste is stored tightly sealed in the original container at 5-10°C, a minimum shelf life of 6 months can be expected. Air shipment is recommended to minimize the time that containers are exposed to higher temperatures.

Printing
The WS157 lead-free water soluble solder paste is currently available for stencil printing down to 16 mil (0.4mm) pitch devices with type 3 powder (-325+500 mesh). Printing at up to 100 mm/sec. can be reliably achieved in production using a metal squeegee blade. This is due to a unique rheology, which ensures that the higher shear rate viscosity is relatively low and the thixotropic index is high enough to ensure excellent definition and slump resistance, while maintaining good roll and drop off behavior. High squeegee pressures are not required, making WS157 particularly useful for second side printing processes.

Reflow
SN97C alloy melts at 217-221°C. Reflow should be performed with a peak of 15-35°C above the liquid temperature of the alloy (depending on the type of board). This temperature should be maintained for 30-60 seconds. Profiles should have less than a 3-minute preheat time above 260°F(130°C) to insure proper wetting of fine pitch leads.

Cleaning
The post reflow residue of WS157 water soluble solder pastes must be removed. It is suggested that the residues are removed as soon after reflow as possible, although effective cleaning can be effected up to 3 days after reflow allowing time for secondary processing. Cleaning can be achieved using moderate temperatures 25-70°C in most conventional aqueous cleaners. Cleaning takes typically 2-5 minutes.
The best cleaning results are obtained when the peak reflow temperature is maintained between 235°C and 250°C. If the peak reflow temperatures for the solder creams are substantially exceeded, some residues may persist and it will be necessary to use a saponifier such as RA2000 at 6% to remove the residue remaining.

Health & Safety
This product, during handling or use, may be hazardous to health or the environment. Read the Material Safety Data Sheet and warning label before using this product.

Packaging
The WS157 lead-free water soluble solder paste is also available in: 500gram or 250 gram plastic jar. 1 Kilogram, 500 gram or 250 gram cartridge for direct application. DEK ProFlow cassettes available upon request.