Authored By:
Joseph Fjelstad
Verdant Electronics
Summary
RoHS legislated restrictions on the materials used in electronics manufacture have imparted significant challenges on the electronics industry since their introduction in 2006. The greatest impacts have been felt by the mandated elimination of lead from electronic solder followed by the demand for the elimination of haloids from flame retardants used in traditional PCB laminates.
In the years which have followed the electronics industry has been beset with a host of new challenges in its effort to comply. Failure mechanisms, both new and old, have surfaced which demand solution and the industry suppliers and manufacturing technologists have worked diligently to remedy those vexing faults through the development of a wide range of new materials and equipment for both board manufacture and assembly, along with modifications to the processes used in the manufacture and assembly of printed circuit boards.
Most of the problems which have confronted the electronics manufacturing industry have related to the solder assembly process. Lead-free solders were advertised early on as a drop-in replacement for traditional tin lead solders however field experience proved is not to be the case. The tin rich alloys along with the higher temperatures which were required for assembly cause the industry to scramble for solutions to such problems as champagne voids, poorer wetting, brittle solder joints, copper dissolution, tin whiskers, head in pillow, greater vulnerability to damage caused by explosive outgassing of absorb moisture in packages among others including cleaning of baked on fluxes following the high temperature assembly process. Lead-free solder also had spillover effects on the PCB laminate material itself as manufacturers experienced delamination and degradation of the resins used in circuit construction.
One more recently encountered problem is a phenomenon referred to as pad cratering wherein resin beneath the copper land to which a component is attached is actually torn loose from the surrounding resin breaking through the copper and causing an open.
In this environment, an alternative approach to manufacturing electronic assemblies has been conceived and is presently being developed. The new method in simplest form is one which eschews the use of solder and is predicated on the use of aluminum substrates which house fully tested and burned in components to create what can be best described as a component board wherein the terminations of the components are proximately planar with the surface of the aluminum. In subsequent processing the aluminum component board is first coated with an insulating material and then circuits which interconnect the components are applied using buildup technologies.
Conclusions
Such aluminum circuit structures as have been described in this paper are simple to design and eminently possible to manufacture. They can be easily produced using well-established manufacturing infrastructure tools, equipment and processing techniques which are simply reordered to make highly useful electronic products suitable for use in everything from consumer to high-reliability automotive, military and aerospace products. The limits are likely to be defined more by the imagination of the designer than the limits of the fundamental technology which has been described.
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