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April 2016 • SMT Magazine 21 Another example would be the economics of producing a smart hand held device. If even as much as 0.5g of solder paste is used per as- sembly, at $100/kg, $0.05 worth of paste is con- sumed per assembly. If the price is decreased by 25%, the savings potential would be $0.0125/ assembly. Let's look at the cost of one defective as- sembly per day. One scrapped assembly per day, even with a $50 bill of materials, outweighs the cost savings on lower priced solder paste by a factor of 4,000:1. ($50/$.0125). How many times do you think opting for a risk to reward ratio of 4:000:1 helps the long term profitability of your manufacturing business? In conclusion, solder paste first pass yield is a tremendous driver for maximizing the profit- ability of an EMS provider. The price of solder paste multiplied by the volume used per assem- bly usually proves to be the lowest cost mate- rial on a bill of materials. Therefore, using lower priced solder paste while reducing first past yield may be the costliest mistake that can be made. Consider paying a fraction of a cent more per assembly while getting higher yields, it might be the best fiscal decision you make. SMT Mitch Holtzer is global director of customer technical service (CTS) for Alpha Assembly Solutions. To reach Holtzer, click here. meter 2 . At $0.10/gram, the cost of solder paste used converts to $0.059/meter 2 . This converts to 1/1000 of a typical substrate cost. Components represent an even larger pro- portion of the bill of materials cost. Even the least expensive passive components may cost $0.01 each. Sophisticated processors used in smart phones, tablets, PCs and other common devices can easily cost tens of dollars each. It is therefore easy to show that even high silver al- loy solder paste is the least expensive material placed on a circuit board. Eliminating rework, contributing to low cycle times, high in-circuit pin test yield, PPM levels of print volume transfer issues are all key success factors in a solder paste. Any shortfall in performance in any of these areas translates to a cost many times the cost of a solder paste. One real world example occurred as a large consumer of solder paste converted from tin- lead to a lead-free alloy. As this happened, the price of both tin and lead escalated, essentially doubling the unit price of the solder paste. The paste consumer performed in-circuit pin test- ing to assure that shipped assemblies were in working order. Because the new lead-free solder paste reduced the number of false negative re- sults in the testing procedure, a value in use cal- culation showed that the tin-lead solder paste manufacturer should have been paying the cus- tomer to use their paste. This was an extreme example of the value that high yielding solder paste can offer, but if any of the key success fac- tors is lacking, the price of the solder paste does not matter. cosT vs. causE: WhaT is morE criTical To Ems ProfiTabiliTY? A new study by an international team of research- ers affiliated with UNIST has found a new way to produce electronic devices, such as diodes and logic gates without the need for semiconductors. In their study, published in nano Technology, the team used metal nanoparticles coated with charged organic ligands to create versatile electronic circuits, which they have named "chemoelectronic" circuits. each ligand produces a different, charge-related ef - fect when put in water or a humid environment. This newly developed nanoparticle diodes and de- vices are durable enough to withstand salty, aque- ous environments, and flexible enough to be oper- ated even under significant bending, thereby over- coming the limitations of the present semiconductor technology. This study was jointly conducted by Prof. Bartosz Grzybowski (School of Natural Science) of UNIST, Prof. Yong Yan of the national Center for nanosci - ence and Technology in Beijing, Prof. Scott C. War- ren of the University of north Carolina at Chapel Hill, and Patrick Fuller from nuMat Technologies. Producing Electronics without Semiconductors is Now a Reality