• Alloy: Sn63/Pb37
• Type 3 powder (90.5 percent metal load)
• Quantity: 600g jar
• Wide reflow process window
• Consistent fine-pitch print deposition

RMA-SMQ 51AC is an air reflow, RMA solder paste designed for use in a wide range of environmental conditions. It has exceptional stencil life and tack strength, and offers consistent print definition even in ultrafine-pitch applications. RMA-SMQ®51AC’s wide processing window allows it to be used with standard eutectic SnPb, SnPbAg, and high-temperature alloys, including AuSn, SnSb, and SnAg.

Alloys

Indium Corporation manufactures low-oxide spherical solder powder composed of SnPb and SnPbAg in standard Type 3 and 4 mesh sizes (J-STD-006). Other non-standard mesh sizes are available upon request. The weight ratio of the solder powder to solder paste is referred to as the metal load and is typically in the range of 82–91% for standard alloy compositions.

Storage and Handling Procedures

Refrigerated storage will prolong the shelf life of solder paste. Solder paste packaged in cartridges should be stored tip down.

Solder paste should be allowed to reach ambient working temperature prior to use. Generally, paste should be removed from refrigeration at least 2 hours before use. Actual time to reach thermal equilibrium will vary with container size. Paste temperature should be verified before use. Jars and cartridges should be labeled with date and time of opening.

Cleaning

RMA-SMQ®51AC is designed for no-clean applications. However, the flux can be removed, if necessary, by using a commercially available flux residue remover.

Stencil cleaning is best performed using isopropyl alcohol (IPA) as a solvent. Most commercially available non-water-based stencil cleaners work well.

Printing

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.