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22 The PCB Magazine • September 2014 While the use of bare die is possible, the IC components to be used are ideally packaged (CSPs are very well suited) because packaged IC devices are much more easily tested and burned in and because they have standardized lead pat- terns and physical outlines making the design process simpler, especially if a single lead pitch is used for all components (e.g., 0.5 mm). Ad- ditionally, nearly all packaged components use copper as the base metal for interconnections, which is advantageous for more than just that one reason alone, as will be shown. After the components are affixed permanently on one or both sides of the aluminum carrier plate, layers of insula- tion are applied to one or both surfaces of the metal sheet covering the components. At this point, the assembly can be processed as if it were a standard rigid printed circuit with high density build-up layers on one or both sides, us- ing lasers to drill holes down to access component termina- tions and commonly practiced plating and imaging processes to create the circuits. A dif- ference is that a fill step with an insulating material may be required if through-holes have exposed metal. However, if coated with epoxy, this may not be necessary. One caveat for those circuit manufacturers consid- ering exploring processing circuits of this type is that if the aluminum is untreated, the edges need to be sealed to prevent contamination of subsequent processing chemistries that will be used in manufacture. While additional process- ing steps can be performed if desired and or re- quired, this assembly could be in some applica- tions considered complete. The overall number of processing steps is obviously significantly reduced from those required for traditional pro- cessing of printed circuit assemblies. While the foregoing has described a relative- ly simple structure the longer-range potential of these novel aluminum circuit structures is im- pressive and limited more in my imagination than the technology. One such example is il- lustrated in Figure 3. Advantages of Aluminum Circuit Assemblies Beyond the structures just described, there are a striking number of advantages to the de- sign and manufacture of electronic assemblies that do not use solder to make in- terconnections, especially those made with aluminum. How- ever, the advantages of prod- ucts manufactured using SAFE techniques also circumscribe the full range of benefits nor- mally considered desirable for any electrical or electronic product. Following are brief discussions of those benefits: A. Economic Benefits In a highly cost-competi- tive global economy, the cost of manufacturing is always a high order concern. Looking first at material, the reader is asked to note again that the primary material of interest in this discussion has been aluminum. Aluminum is the third most abundant material on our planet (oxygen and sili- con are first and second, respec- tively). As was mentioned earlier, it comprises 8.3% of the earth's crust. Because of its commodity status, aluminum is sold by weight regardless of thickness and it is less expensive per unit volume than com- posite materials. Though aluminum is admit- tedly denser than FR-4 laminate (2.8 g/and in cm 3 aluminum versus 1.8 g/cm 3 for FR-4), the amount of aluminum required can be very cost competitive in the long run. In contrast, the price of polymers varies due to the volatility of the price of oil, so there are advantages to being able to use a material such as aluminum, the price of which is reasonably predictable because of its global abundance. ALuMINuM BASE CIRCuIT TECHNOLOGy continues In a highly cost-competi- tive global economy, the cost of manufacturing is always a high order concern. Looking first at material, the reader is asked to note again that the primary material of interest in this discussion has been aluminum. Aluminum is the third most abundant material on our planet (oxygen and silicon are first and second, respectively). " "