Aluminum Base Circuit Technology: Structures and Manufacturing Methods


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Abstract

Aluminum is an attractive material for use in the manufacturing of electronic assemblies owing to its low cost, good thermal properties, dimensional stability, environmental friendliness, and ubiquity. Unfortunately, due to its innate thermal spreading ability, it is not easily used when solder is required to make interconnections to components. This article describes ways to manufacture electronic assemblies using aluminum as a base and eschewing the use of solder. 

Introduction

RoHS 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. Since 2006, 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 it not to be the case. The tin-rich alloys, along with the higher temperatures 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 traditional 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.

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Editor's Note: This article originally appeared in the September 2014 issue of The PCB Magazine.

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