• Alloy: SAC305 (99.5Sn/3.0Ag/0.5Cu)
• Type 4 (88.25 percent metal load)
• Quantity: 600g cartridge
• Air or nitrogen reflow, water-soluble solder paste specifically formulated to accommodate the higher processing temperatures required by the SnAgCu, SnAg, SnSb, and other Pb-free alloy systems
• Consistent fine-pitch printing performance with high transfer efficiency from stencil apertures

Pb-Free Water-Soluble Solder Pastes

Over the last decade, the electronics industry has shifted to no-clean fluxes for surface mount assembly. Despite this industry trend, Indium Corporation has not only maintained a variety of water-soluble solder pastes and fluxes but has revolutionized the category with the release of several new and versatile solder pastes. These solder pastes allow current water-wash manufacturing processes to not only survive, but to thrive.

Indium3.2 is an air or nitrogen reflow, water-soluble solder paste specifically formulated to accommodate the higher processing temperatures required by the SnAgCu, SnAg, SnSb, and other Pb-free alloy systems. This product formulation offers consistent, Standard Product Specifications Alloy 96.5Sn/3.0Ag/0.5Cu (SAC305) Metal Load 88.5% Printing 95.5Sn/3.8Ag/0.7Cu (SAC387) repeatable printing performance combined with a long stencil life and sufficient tack strength to handle the challenges of today’s high-speed as well as high-mix surface mount lines. In addition to consistent printing and reflow requirements, this solder paste offers superb wetting to the various Pb-free metallizations and has exceptional low-voiding performance on fine-pitch components, including BGAs and CSPs.

• Rework Flux: TACFlux 025-NP
• Flux Pen: FP-1095-NF
• Cored Wire: CW-301
• Wave Flux: 1095-NF

Stencil Design:

Electroformed and laser cut/electropolished stencils produce the best printing characteristics among stencil types. Stencil aperture design is a crucial step in optimizing the print process. The following are a few general recommendations:

• Discrete components-A 10–20% reduction of stencil aperture has significantly reduced or eliminated the occurrence of mid-chip solder beads. The “home plate” design is a common method for achieving this reduction.
• Fine-pitch components-A surface area reduction is recommended for apertures of 20mil pitch and finer. This reduction will help minimize solder balling and bridging that can lead to electrical shorts. The amount of reduction necessary is process-dependent (5-15% is common).
• For optimum transfer efficiency and release of the solder paste from the stencil apertures, industry standard aperture and aspect ratios should be adhered to.

Indium3.2 flux residues are water-soluble and best removed by an inline or batch type cleaning process using spray pressure and heated DI water. A spray pressure of 60psi and a DI water temperature of 55°C can be used as a starting point. The optimal spray pressure and temperature are a function of board size, complexity, and the efficiency of the cleaning equipment and should be optimized accordingly. We recommend cleaning the flux residue 12 hours (or sooner) after reflow for optimal test performance. Electrical testing should be completed after the flux residue is removed.

This is best performed using an automated stencil cleaning system for both stencil and misprint cleaning to remove extraneous solder particles. Most commercially available stencil cleaners and isopropyl alcohol are acceptable.