Optimizing Type 7 Solder Paster Formulation and Compatibility with Assembly Technology for Sub-75um System-in-Package Applications

Abstract

For System-in-Package (SiP) assembly, solder paste printing remains the preferred solder application method of choice. However, as passive components (008004) and next-generation flip-chip components continue to shrink, smaller stencil openings are needed and these small stencil apertures still need to achieve consistent printing. In addition, as component standoff height continues to decrease for fine-pitch applications, the cleanability of the final SiP build becomes a concern; for many applications which require water-soluble pastes, pure DI water becomes difficult to use when the standoff height lessens. This paper will investigate important parameters from a materials supplier’s perspective for meeting the challenges of fine-feature solder paste printing and package assembly. First, innovations in solder powder technology will be discussed which allow for consistent solder paste (Type 7) printing at 60um apertures. Next, the effect of stencil technology will be discussed. Many stencil manufacturers are approaching a manufacturing limit both with respect to stencil thinness and aperture size. This paper will discuss two common stencil manufacturing designs, laser-cut and electroform, and present findings on the effect these designs have on solder paste print consistency. Lastly, solder paste cleanability will be discussed; the results of a study investigating novel Type-7 solder pastes for use with semi-aqueous cleaning technology will be presented. Important process considerations with respect to stencil and package cleaning will also be discussed.