SMD Pastes

Solder paste for SMT technology is a homogeneous suspension of metallic particles (alloy powder) in an organic vehicle containing flux and rheological additives. Its function is twofold: to allow precise deposition through stencil and to guarantee, in reflow, the formation of wetted and uniform joints. For this reason, the formulation must balance viscosity, thixotropy, stencil life and flux activity. The most common alloys are SAC (particularly SAC305), with lower silver variants (SAC0307) to reduce costs or limit pad erosion. For low temperature applications, bismuth-based alloys (e.g. 42Sn57Bi1Ag) are used, useful for heat-sensitive substrates or to reduce thermal stress. Powders are classified by particle size (Type 3: 20–45 µm; Type 4: up to ~20 µm) and selected based on component pitch (fine-pitch, µBGA, CSP). During stencil printing, the paste must maintain stability (no slump), good release from the frame and sharp deposit profiles. In reflow, the flux must activate without leaving problematic residues, guaranteeing wettability on ENIG, OSP or HASL pads and minimizing voiding phenomena, particularly under BGA and LEDs. Our no-clean formulations reduce the need for washing; water-washable versions are available for those who plan a cleaning process. Operational best practices include refrigerated storage, acclimatization to room temperature before use, control of metallic content and maintaining adequate line humidity. We provide support for defining thermal profiles (soak, peak, ramp-down) according to alloy and PCB thermal mass, as well as recommendations on stencil thickness and aperture geometry. Compliance and quality: pastes are classified J-STD-004 (flux type) and J-STD-005 (paste requirements), with batch traceability and analysis certificates on request