A study of the behavior of flux-stencil interactions.

Understencil wiping has gained increased interest over the past several years. Changes in circuit design due to miniaturized components and highly dense interconnects have increased the importance of stencil cleanliness, both inside the aperture wall and on the seating surface of the stencil. A technology that wets the understencil wipe with a solvent-based cleaning agent is being studied to improve print performance and better understand the behavior of flux-stencil interactions. The cleaning agent dissolves the flux component of the solder paste to improve solder ball release from the stencil’s bottom side and aperture walls.

Kyzen and Indium performed a study to characterize the relationship between wipe processes and bottom-side stencil flux/paste flow. A highly dense circuit board and a stencil with nanocoating was used to study the effects of the understencil wiping process. After each print, the stencil was removed from the stencil printer. The apertures were examined to inspect buildup in both the apertures and bottom side of the stencil. FIGURE 1 shows the flux vehicle and some trace solder balls following the first print.

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