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Assembly and the Quest for Solder Alloy-Free Electronics (SAFE)

 

As first brush, the title’s suggestion that solder can be eliminated from the electronics assembly process may appear absurd. Everyone related in any way to electronics manufacturing industry knows that solder is the universally accepted way of connecting components to printed circuits in electronic assemblies. Thus, the fact that many seasoned and knowledgeable people in the electronics industry might scoff at the notion that solder can be eliminated comes both without surprise and a certain amount of resignation.

However, in reality, solderless interconnections are all around us. Many interconnections in electronic products, both permanent an intermittent, are made without the use of solder. Some noteworthy examples include press-fit interconnection of backplane connectors, separable interference interconnection between daughter cards and mother boards, wire wrap techniques to connect between component or connector pins, wire bonding used to interconnect chips to packages, resistance welding, and conductive adhesives. However, perhaps the most ubiquitous and yet least acknowledged form of solderless interconnections, are the trillions of electrolessly and electrolytically copper plated electrical and electronics interconnections made every year in printed circuits to make interconnections on multilayer circuits and more recently, for the circuits and interconnection of semiconductor chips.

The fundamental idea behind solderless assembly based on plating is simple enough. It is perhaps best illustrated by contrasting it with the traditional approach to electronics assembly. In everyday assembly, electronic components are placed on and interconnected to circuit boards using a soldering process such as wave solder for most through-hole components or a reflow oven to melt solder paste, which affixes surface mount components. However, when solder is eliminated and copper is substituted, electronic assemblies are created by building up circuits on what can be best described as a component board. It eliminates a great number of steps from manufacturing, each step offering its own potential to yield a defect. The simple graphic that compares processing steps between the two approaches, which accompanies this article, bears quiet witness to the potential.

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Editor's Note: This article originally appeared in the October 2014 issue of SMT Magazine.