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72 SMT007 MAGAZINE I FEBRUARY 2020 ties With Emphasis on New Lead-free Solders— published jointly by the National Institute of Standards and Technology (NIST) and Colo- rado School of Mines in 2003—approximately 50 different lead-free alloys were identified and characterized. Couple that with the myr- iad different fluxes, both clean and no-clean, for reflow and for pastes, and it is evident that narrowing down a single solution has been both a Herculean and a Sisyphean task for pro- cess developers with no perfect solution yet in sight. With that in mind, it is argued in the rest of this brief article that if solder can be bypassed, there are significant prospective benefits to be gained in terms of design sim- plification, cost, performance, and reliability. These areas are each worthy of brief individ- ual discussion. Design Simplification Advanced electronic products are often designed using whatever chips are available to get the job done. Often, those chips have only one function of interest; however, everything must be connected for the chip to function, but all terminals must contact and adhere to It was in this environment that the Occam Process was first conceived and proposed. Put simply, it proposed that it might be the right time to consider ways of making electronic assemblies without the use of solder. The fol- lowing words of William of Occam—a 14 th cen- tury monk, philosopher, and logician—were the inspiration: "It is vain to do with more what can be done with less." Since that time, numerous ways of mak- ing electronic assemblies without solder have been shared, but the basic idea is to assemble a component board with component termina- tions facing up and then build up the circuit layers (Figure 1). No solder is required. The concept was not surprisingly met with ridicule by some (but not all) folks in the solder indus- try, who was clearly not interested in a solu- tion that did not require solder and reducing revenue. A dozen years have since passed the lead- free rollout, and the perfect lead-free solder solution is no closer than it was back then. While there could not be found a current count of the number of different lead-free alloys pro- posed or in use, in Database for Solder Proper- Figure 1: The basic Occam Process steps for a single-sided assembly (double-sided assembly is also possible). Because soldering is not required, the use of aluminum as a substrate is a viable option. The anodizing step for which electrophoretic coating with a polymer could be substituted and is also optional. Both provide very uniform surface coatings. Note: As a metal, aluminum is highly predictable in terms of dimensional stability, a near CTE match to copper, and an excellent thermal conductor.

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