LGA and Solderballs

J Rose at EMPF says: The introduction of no-clean solder fluxes in electronics manufacturing has given rise to greater levels of solder balling simply because the opportunity to remove them in the wash process does not exist. They are typically caused by any one, or a combination of, the following: * Solder Beading. The result of solder paste squeezing out from under the component body during part placement. The solder trapped under the component body cannot wet to either the lead of the device or the PCB material. This condition can be minimized by changing stencil aperture design to limit paste deposition size to match the component terminations rather than the PCB pad size. * Solder Paste Segregation. Results from a blob of solder paste becoming separated from the main deposit. Gravity forces the solder out onto the surface of non- solderable areas and solder balls form that are larger than the individual solder particles initially present in the paste. This condition is usually caused by cold or hot slump, paste deposit thickness and stencil cleanliness. * Solder Splatter. Occurs during reflow and is characterized by finding the solder balls far away from the pads where the paste was deposited. It may also turn up on gold/nickel surfaces where it is usually called "solder splash". Solder splatter can be caused by rapid heating of the solder paste which causes the evaporation of solvent present in the solder paste flux during reflow. The expanding pressure separates some of the paste and prevents complete coalescence. Improper board storage can also be a contributing factor. * Lack of Coalescence. Usually seen as one or more balls of solder powder failing to coalesce with a re-flowed area of solder paste.

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