This research focused on the deposition of adhesive on to printed circuit boards using a plastic stencil. The passive surface mount components considered ranged from 1210s to 0402s. Three different adhesive types were used. Experimentation indicated that their viscosities could be classified as high, medium and low. The plastic stencil used in this research had a thickness of 1 mm (40 mils) with circular apertures. 'Optimal' settings were obtained for each adhesive type. A systematic experimental approach that used "Taguchi" methodology was adopted.
It was seen that a low viscosity adhesive is ideal for stencil printing when a board has a large range of components on it. A high viscosity adhesive is suitable for larger components (such as 1210s) since the green strength of these adhesives is higher and larger components require higher green strength values. The deposits obtained for these larger components had tails. The medium viscosity adhesive and the low viscosity adhesive considered had deposits which were hemispherical in shape. These two adhesives worked better with smaller components (such as 0603s and 0402s).
The deposit heights for the smaller apertures were observed to be higher for the medium and low viscosity adhesives. This was not the case for the large apertures (1210s) where the heights obtained were comparable to the 1206s. This was due to the slumping characteristics of the lower viscosity adhesives. 'Optimal' settings were recommended for each component type. In general, when there are different component types on a board, the recommendations for the smallest component type should be used.