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26 The PCB Magazine • September 2014 B. Electrical/Electronic Benefits Such constructions as have been described offer several electrical/electronic benefits. For example, where connections are made to ter- minations on component lands, the point of interconnection can be made without benefit of a large pad, which can reduce parasitic capacitance. This also frees routing space, allowing for a potential reduc- tion in total layer count, and further reduces cost (Figure 4). If proper planning is used in choosing components of a common grid pitch (e.g., 0.5 mm) the integrated power mesh system (IMPS) design layout approach may be em - ployed, thus reducing layer counts while improving sig- nal integrity. With proper preparation, the aluminum core can serve as power or ground as mentioned ear- lier. This makes it possible to provide both power and/or ground immediately adjacent to every component. Finally, the completed assembly can also be relatively easily pro- vided with metal plating after the assembly is complete mak- ing the entire assembly metal jacketed and thus EMI- and ESD-immune, as well as nearly hermetic, exclusive of those areas left open for external I/O connections. C. Thermal Benefits of Aluminum Substrates When aluminum is used as carrier, it be- comes by default a heat spreader which is an integral part of the assembly. This allows the de- signer to address thermal concerns early. Given the inverse relationship between long-term reli- ability and the number, temperature extremes and durations of the thermal exposures a com- ponent experiences, having a built-in thermal management solution is an intrinsic value-add- ed feature. D. Mechanical Performance Improvements Since the components are encapsulated in the aluminum assembly and thus part of an integrated whole, they are fundamentally im- mune to the effects of shock and vi- bration. The CTE (coefficient of thermal expansion) of alumi- num and copper are relatively close (22ppm/C vs. 18ppm/C), which reduces the potential stress on interconnections; moreover, the materials ex- pand predictably in all di- rections, whereas reinforced laminates have CTEs that may vary in X, Y and Z dimen- sions, sometimes quite appre- ciably (e.g., X ~20ppm/C, Y ~23ppm/C and Z ~80ppm/C). The microvias which are used to make connections to components and to any ad- ditional build-up layers have been proven superior to sol- der joints, and (though there was recent report of microvias also being damaged by the lead free soldering process). Moreover, there is possibility in some cases to use relatively thin aluminum base material, which could allow the devel- oper to bypass the final etching process and permanently form the final assembly into the desired shape, opening up new possibilities to the clev- er product designer. E. Design Security The methods suggested offer a design secu- rity benefit that may not be immediately obvi- ous to many product developers. The methods employed obscure the components used in fab- rication, making tear-down and reverse engi- neering of a product much more daunting and difficult for those wishing to understand what might differentiate the product in hand with previous competitive products. This benefit ex- tends to all kinds of products, from consumer ALuMINuM BASE CIRCuIT TECHNOLOGy continues When aluminum is used as carrier, it becomes by default a heat spreader which is an integral part of the assembly. This allows the designer to address thermal concerns early. Given the inverse relationship between long-term reliability and the number, temperature extremes and durations of the thermal exposures a component experiences, having a built-in thermal management solution is an intrinsic value-added feature. " "