Just as there are a number of causes of solder balling there are also several factors which can lead to or encourage the formation of solder beads.
- During the placement of the component solder paste may be squeezed out from underneath the component and coalesce on the free surface of the substrate pad with the rest of the paste forming the solder joint. During reflow this squeezed out solder will take the form of a solder sphere in an attempt to reduce its surface tension. This is why the solder bead forms near the component. The volume of the solder printed and the extent to which it becomes squeezed out by the component will determine its size. Too much pressure or too much paste can also cause squeeze out.
- Misregistration between the stencil aperture and the pad can lead to solder paste printing onto the board mask resulting in beading.
- Operators can inadvertently transfer solder paste to the mask in an attempt to straighten out a misplaced component. Usually it is advisable NOT to attempt to straighten a component prior to reflow. Tweaking the placement, usually done with tweezers, can also lead to insufficient, shorts, and voiding. Allow the paste and the reflow oven to float the component to the lands and straighten the component. - Worn equipment, stencils, and squeegees as well as warped boards or insufficient stencil wiping can also contribute to beading and micro balls as well.
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