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AUGUST 2019 I SMT007 MAGAZINE 91 parable or higher UPH for the same 25 mm x 25 mm package. With the low cost of the spray coater itself and the ability of the oven to serve multiple coaters, the equipment cost for start- ing a small coating production and increas- ing production capacity as loading increases is much more practical. While the overall cost of ownership is lower for spray, consumable material costs for spray coating will naturally show a higher cost per unit. Sputtering for EMI shielding generally uses pure copper as the core shielding layer; therefore, the consumable cost is relatively low. Spray materials for EMI shielding can include different metals, including silver as well as other value-add technologies; this results in a relatively higher cost compared to sputtering pure copper. However, in large volume man- ufacturing conditions and with an optimized spray process, the overall cost per unit of spray coating is lower than sputter. Thus, opti- mized spray material consumption can further improve the cost advantage of spray. Resulting from this study on reducing fluid consumption, there has been a further evolu- tion of the spraying and dispense technology for applying the EMI shielding fluid to differ- ent substrates. Recently, modifications to the spray coating equipment have resulted in a marked improvement in the overspray condi- tions and width of the overall spray pattern. Current default spray patterns result in roughly an 8-mm wide spray area. The most recent design changes to the spray head have allowed the ability to adjust and control the width of the spray pattern (overspray condition) from the 8-mm width down into the 2-mm width range while maintaining target coating thick- ness and uniformity (Figure 7). Reducing the spray width has been a significant improve- ment in the process capability as it opens the door for more selective coating to only tar- get areas, significantly reducing material con- sumption. In at least one case example, this ability to selectively spray-coat target areas of a substrate allowed for reducing the cost of the spray coating process by more than 50% of the cost of the end customer sputter process. Jet Dispensing for Greater Selectivity With the desire to further improve on selec- tively coating or compartment shielding struc- tures, jet dispensing offers an attractive poten- tial solution. Figure 8 shows an example process found in a growing number of SiP devices where an integrated EMI shielding structure creates partitioning within a single package. To fill such a trench, a highly con- Figure 7: An 8-mm spray pattern (L) versus 2-mm spray pattern (R). Figure 8: Cross-section example of a filled trench with Paste C.