The PCB Design Process

The tools used in the PCB design process must be supplied a variety of information about each part in order to complete each step. This information is entered into a library or set of libraries, one entry per component. Among the pieces of data needed are ... 

From the definition of the objective of the PCB design process it can be seen that the process extends from concept all the way through fabrication to assembly and test. Computer-based tools have evolved to automate or improve the speed and accuracy of every step in the process. These tools can be divided into three major groupings based on where they are used ... 

CAM tools are CAD systems tailored to the needs of the fabrication process.The output of the PCB design process is a set of CAD files that describes each artwork layer of a PCB, the sUk screen requirements, drilling requirements, and netlist information. This information must be modified before it can be used to build a PCB. For example, if a fabricator needs to build several copies of a PCB on a single panel, the fabricator will need to add specialized tooling patterns to the artwork and alter trace widths in order to compensate for etching. Initially, these operations were done manually with a high potential for error and significant labor costs. CAM stations or tools allow the fabricator to do all of these operations automatically and rapidly. 

This chapter describes the PCB tooling process, as defined in Fig. 20.1, including the transfer of information, design reviews, optimization of materials, definition of BOM and routings, tool creation, and additional processes that are required. 

Consistency in the plating process versns selected drilling hole size and plating densities has significant impact on the capability to control hole tolerances. Adjustments to the PCB design, drill hole size selection, or process parameters may be required to produce an acceptable prodnct with tighter tolerances. 

All inducers do not fall readily into one or the other of these classes. Some oxidative processes can be induced by either type of inducer, such as the hydroxylation of aniline and the A -demelhylalion of chlorcyclizine. Some inducers, such as the mixture of PCBs designated Arochlor 1254, can induce a broad spectrum of CYP isoforms. Many variations also exist in the relative stimulation of different oxidative activities within the same class of inducer, particularly of the phenobarbital type. 

A New Bedford Harbor Sawyer Street site in Massachusetts has been designated as a superfund site due to PCB contamination of river sediments. Commodore was one of three companies chosen to conduct demonstration studies on-site under contract to Foster Wheeler Environmental Company. The river sediment was first washed with diisopropylamine by the Ionics RCC B.E.S.T process [35], producing an oil concentrate. The PCB level in the B.E.S.T concentrate was approximately 32,800 ppm. Dioxins/furans (TEFs) were also present at 47 ppm. This concentrate was reacted with SET in the SoLV process to destroy the PCBs and dioxins (Table 4). After treatment, the PCB level was 1.3 ppm, well below regulatory requirements for disposal in nonhazardous waste landfills. Dioxins were also readily remediated. This study also illustrates that the SoLV process can remove metals from substrates. The concentrate received was found to have lead, arsenic, and selenium in high parts-per-billion levels. After treatment with the SoLV process, the levels were below detection limits. The metals were... 

Quite obviously, the PCB content in the sludge before solvent extraction (henceforth pre-processed sludge) and that in the sludge after solvent extraction (henceforth post-processed sludge) are essential information for the design and evaluation of the performance of the extraction process. In our study, the PCB contents in the sludge samples were measured by the EPA recommended Soxhlet procedure [2 ]. 

The first requirement for the designer is to understand the flow of power-related currents in the converter. This leads to an identification of the troublesome or critical traces of the PCB we must pay the closest attention to these traces. We will also see that this identification process is very topology-dependent. So we can t, for example, design the PCB for a buck-boost, the same way we would do it for a buck. The rules change significantly We may thus also realize that very few PCB layout persons out there would understand this too well Therefore it really is a good idea for the power supply designer to do the layout personally, or at the very least, closely supervise the PCB person in the act. 

As noted previously, substrate (typically PCB) design has an effect not only on board/component layout, but also on the actual manufacturing process. Incorrect land design or layout can negatively affect the placement process, the solder process, the test process, or any combination of the three. Substrate design must take into account the mix of surface mount devices that are available for use in manufacturing. 

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