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ECWC 2014: The Metal-base PCB Technology Session

The presentation that attracted most interest and provoked plenty of interactive discussion came from Joe Fjelstad of Verdant Electronics who described an alternative approach to the manufacture of electronic assemblies, which used aluminium as a substrate and eliminated the soldering process. Aluminium had many attributes which made it attractive as an alternative circuit substrate: Abundance, low cost, thermal conductivity, light weight, dimensional stability, thermal expansion comparable with copper, ease of processing, and capable of being anodised or electrophoretically coated.

Ironically, the main reason aluminium had not been considered for traditional PCB applications was its high thermal conductivity and heat-sinking ability, which limited the practicability of the soldering process. Except in applications such as LED substrates, designers had preferred to specify resin-based laminates and then deal with thermal management issues after completion of assembly. And even in the knowledge of the thermal issues and intrinsic reliability problems associated with the introduction of lead-free soldering, human inertia--“better the devil you know” attitudes--had tended to preclude the consideration of radical alternative concepts.

Fjelstad advocated reversing the assembly process to eliminate the solder issue, by positioning and bonded all the components on an aluminium carrier with leads facing up, encapsulating the components in place, exposing the terminations, and interconnecting them by additive or semi-additive PCB fabrication techniques or alternative direct interconnection methods. Because solder lands were not required, conductor routing density could be higher so that fewer layers would be required. The basic manufacturing infrastructure was already in place, semi-additive fabrication processes were well-established, and the concept was appropriate for all classes of products including flex.

The benefits of solderless assembly were many: No PCB was required, no soldering was required, component concerns were reduced, circuit design layout was easier, design security was increased, thermal management was integral, reliability was enhanced, and multiple novel structure options were possible--modular array assemblies, aluminium-core rigid-flex, direct-write prototyping. The limits were more likely to be defined by the imagination of the designer than by the fundamental limitations of the technologies that Fjelstad had described. “Change may happen slowly, but change always comes…”

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