The WS888 is water soluble lead free solder paste designed to meet the requirements for reliable solder joints in Printed Circuit Board assemblies. WS888 displays previously unseen levels of repeatability and consistency even in a wide range of temperatures (65°-85°F) and relative humidity (25% - 65% RH). Residues can be cleaned using warm water.
- Excellent wetting characteristics on all surface finishes, including osp, Ni/Au, Ni/Pd/Au, Sn/Ag
- Excellent volume transfer efficiency
- High resistance to slump and dry-out, even in extreme humidity conditions 70°-77°F & 45%-65%RH
- High speed stencil printing up to 150mm/sec
- Excellent low-voiding performance that exceeds IPC Class III requirement
- Enhanced tack performance and printer open time
- Very cleanable paste residues with hot DI water (120°- 140°F)
- SN100C - MP = 227°C
- SAC305 – MP = 218°C
- Automatic / Manual Printing
- Automatic / Manual Dispensing
- Type-3 and Type-4 standard
- Type-5 available upon request
- 500gram jars or cartridges standard
- Enclosed print head systems
- Other packaging upon request
- 10CC and 30CC syringes
- Larger package sizes upon request
Stencil aperture design and stencil quality are major factors in achieving excellent print consistency with any lead free solder paste. Laser Cut stencils from Stencils Unlimited are recommended for optimal print performance, and can be custom designed to minimize and improve the yields of any process. Some general stencil aperture design guidelines follow:
- Fine pitch components (<= 0.020”)
A 0.001” reduction (L & W) to minimize bridging and create proper gasketing between the stencil and SMT pad
- Discrete components
A 0.002” reduction (L & W) for water washable and a 0.002” reduction (L & W), with “U-shaped” home-plates, for no clean to minimize mid-chip solder beads.
|Solder Paste Bead Size:
- 2cm (~0.75”) on startup
- Add when bead < 1.4 cm (~0.5”)
- Metal, Slic™ blade preferred
- 60 degrees from horizontal
- 25 to 150 mm/sec. (1 to 6 in/sec)
- Adjust printer for a pull or print demand process
- 0.18-0.27 Kg/cm (squeegee length)
- Slic™ and Ultraslic™ stencils should exceed >10 prints/wipe
|Stencil life / Environment:
- >8 hours
- 70º C – 77º F and 45-60% RH
- 75º F and 45% RH Optimal
Storage and Handling
- Cartridges should be stored tip down.
- Paste can be stored up to two weeks at room temperature.
- To prolong the shelf life of WS888, refrigerate between 5°C~10°C, (41°F~50°F). At this range the shelf life will exceed 6 months.
- WS888 should not be allowed to freeze.
- When refrigerated, lead-free solder paste must be allowed to warm up to room temperature.
- Paste must be >= 22°C, (~66°F) prior to applying to stencil for processing.
- Working range of WS888 is between 22-32°C, (~66°F - 89.5°F).
- First-In-First-Out (FIFO) inventory management practices should be used with all lead free solder pastes.
A linear ramp of 0.7°C to 2.0°C C/second is suggested to gradually remove the solvents and other volatile components in the lead free paste. This also helps in minimizing solder balls, beading and bridging from hot slump.
A linear ramp also helps minimize depletion of flux activity which can occur with excessive temperature, preheat times, and at very high reflow temperatures.
A profile with a soak between 200-210°C for less than 20 seconds can be used to reduce void formation on BGA and CSP devices. (Request FCTA’s profile guide to void reduction).
While a linear profile typically does not produce tombstoning, a short 10-20 second dwell prior to transitioning into the liquidus point of the solder, and minimizing the QR between soak and liquid temperatures will help minimize tombstoning if experienced.
A cooling rate of 2°C-3°C per second is typical for most lead free applications. These parameters should be utilized to insure a fine grain solder structure and minimal IMC layer.
Post reflow residues from WS888 must be removed. It is suggested that the residues are removed as soon after reflow as possible; however, effective cleaning can be accomplished up to 3 days after reflow, allowing time for secondary processing.