Navy Electricity and Electronics Training Series - Historic Naval ...

LEVEL III.—Drawers or pull-out chassis are level III units, as shown in figure 1-36. These aredesigned for accessibility and ease of maintenance. Normally, circuit cards associated with a particularsubsystem will be grouped together in a drawer. This not only makes for an orderly arrangement ofsubsystems but also eliminates many long wiring harnesses. Defective cards are removed from suchdrawers and defective components are repaired as described in level II.LEVEL IV.—Level IV is the highest level of packaging. It includes the cabinets, racks, and wiringharnesses necessary to interconnect all of the other levels. Other pieces of equipment of the same systemclassified as level IV, such as radar antennas, are broken down into levels 0 to III in the same manner.During component troubleshooting procedures, you progress from level IV to III to II and on to level0 where you identify the faulty component. As you become more familiar with a system, you should beable to go right to the drawer or module causing the problem.Q40. Resistors, capacitors, transistors, and the like, are what level of packaging?Q41. Modules or submodules attached to a mother board are what packaging level?Q42. What is the packaging level of a pcb?INTERCONNECTIONS IN PRINTED CIRCUIT BOARDSAs electronic systems become more complex, interconnections between components also becomesmore complex. As more components are added to a given space, the requirements for interconnectionsbecome extremely complicated. The selection of conductor materials, insulator materials, and componentphysical size can greatly affect the performance of the circuit. Poor choices of these materials cancontribute to poor signals, circuit noise, and unwanted electrical interaction between components. Thethree most common methods of interconnection are the conventional pcb, the multilayer pcb, and themodular assembly. Each of these will be discussed in the following sections.Conventional Printed Circuit BoardPrinted circuit boards were discussed earlier in topic 1. You should recall that a conventional pcbconsists of glass-epoxy insulating base on which the interconnecting pattern has been etched. The boardmay be single- or double-sided, depending on the number of components mounted on it. Figures 1-37 and1-38 are examples of conventional printed circuit boards.Multilayer Printed Circuit Board.The multilayer printed circuit board is emerging as the solution is interconnection problemsassociated with high-density packaging. Multilayer boards are used to:• reduce weight• conserve space in interconnecting circuit modules• eliminate costly and complicated wiring harnesses• provide shielding for a large number of conductors• provide uniformity in conductor impedance for high-speed switching systems1-36