No clean material for advance packaging assembly

Abstract

Assembly process for most packages involves using some form of soldering material, either fluxes or solder pastes, to create a reliable solder joints. Flux, which is also part of the constituent of solder paste, is needed to remove the oxides from the interconnect surfaces, so that a reliable solder joint can be formed between the two metallic surfaces. Unfortunately, most of the fluxes leave certain amount of residue behind after the soldering process. This flux residue, if it's not cleaned properly, may interfere with the subsequent processes, e.g. the underfill or molding process. If the flux residue is not compatible with the underfill or molding material used, it may eventually cause delamination issue. On the other hand, as technology drives toward finer pitch components, combined with reduced bond line thickness or standoff of the IC packages, makes cleaning of flux residues more challenging. The shift towards using semiconductor-grade ultra-low residue no-clean fluxes or solder pastes, which eliminates the cleaning process, is therefore the solutions for overcoming these challenges. The flux residue left behind after soldering process is minimal, and compatible with the underfill or molding material used in the subsequent process. Besides, eliminating the cleaning process, will also help to reduce the total process time, cost and resources for the packaging assembly process. These are crucial factors for the IC packaging industry. This paper discusses the use of such ultra-low residue no-clean fluxes or solder pastes for various applications in the packaging industry.