Factors Impacting Solder Extrusion In Reworkable UnderfillsAuthors: Neil Poole, Ph.D.
Company: Henkel Electronic Materials LLC
Date Published: 10/13/2013 Conference: SMTA International
Anecdotal evidence suggests that if the underfill breaks cleanly from the PCB (i.e. an adhesive failure) during component removal, it is more prone to solder extrusion then those that leave a significant film of underfill (i.e. a cohesive failure). It has also been suggested that environmental conditions can impact the tendency for solder extrusion. This paper investigates the causes of this phenomenon by analysing the relationship between a range of physical properties of the underfill (CTE, Tg, flex modulus, elongation to break and die shear) and their impact on the tendency for solder extrusion during rework. The impact of the presence of solder flux residues and environmental exposure are also studied to give a broad view of the factors impacting solder extrusion.
Different underfills were observed to have varying responses to environmental conditions. The presence of flux (a potentially a weak boundary layer) was not observed to be of significance with the underfills evaluated in this study. Both Tg and die shear are determined to have a significant relationship with the tendency for solder balling. Hot adhesion was also determined to be a key parameter.
Underfill Rework, Extrusion
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