Printed-circuit boards assembly process

It is important that the manufacturing engineer and operator understand the critical steps in the printed circuit board assembly process to ensure the manufacture of a cost-competitive, reliable product. That understanding includes both the general function of the equipment as well as the activity taking place inside the machines. The following sections of this chapter describe in detail the printed circuit board assembly processes. 

Optimization is an activity carried out in almost every aspect of our life, from planning the best route in our way back home from woik to more sophisticated approximations at the stock market, or the parameter optimization for a wave solder process used in a printed circuit board assembly manufacturer optimization theory has gained importance over the last decades. From science to applied engineering (to name a few), there is always something to optimize and of course, more than one way to do it. 

The details of these materials are discussed in other chapters. However, it is important to understand their role in the overall circuit board assembly process. First of all, the functions of these three materials require that they have good adhesion to all surfaces. Therefore, the printed wiring assembly must be cleaned of any flux residues as well as those residues left behind from the cleaning procedure. 

Microelectronic devices are found in appliances of almost every description, and projections unsurprisingly show an industry that is likely to continue to grow in the future [3]. For the purposes of this chapter, the electronics industry will be taken to encompass (1) the manufacture of computer chips and other electronic components, (2) the manufacture of printed circuit boards and (3) the assembly and packaging processes that bring the two together. Clearly, therefore, this arbitrary definition embraces the manufac-... 

The electronics industry has a variety of work processes. Processes in the high end or upstream sectors include semiconductor wafer fabrication, manufacture of printed circuit boards and the assembly of semiconductor devices and printed circuit boards. Relatively few workers work in these operations, which are generally located in the more well-developed countries. 

Surface mount techniques have also been successfully used to assembly hybrid circuits. The metallized ceramic substrate is simply substituted for the conventional printed circuit board and the process of screen printing solder, component placement, and reflow solder is identical. 

Size is often the primary driver for MCM-based systems. The typical multicomponent discrete assembly provides a sihcon-to-board efficiency of <10 f>ercent (actual total die area versus the total printed circuit board area). MCM technology can often increase the sdicon-to-board efficiency to 35 or 40 percent with chip and wire assembly processes, and to 50 percent or higher with some of the higher-density processes. Thus, with reduced size and weight, MCMs offer a practical approach to reducing overall system size while providing enhanced performance due to a reduction in the interconnect distance between chips. Multichip modules typically use three to five times less board area than their equivalent discrete solution. ... 

As the fundamental building block for printed circuits, base materials must meet the needs of the printed circuit board (PCB) manufacturer, the circuit assembler, and the original equipment manufacturer (OEM). A balance of properties must be achieved that satisfies each member of the supply chain. In some cases, the desires of one member of the supply chain conflict with another. For example, the need for improved electrical performance by the OEM, or improved thermal performance by the assembler, may necessitate the use of resin systems that require longer multilayer press cycles or less productive drilling processes, or both. 

PCB performance In addition to the preceding rehability challenges posed by lead-free assembly processes, it also has to be guaranteed that all other performance characteristics of the printed circuit board stay the same. This includes dielectrical properties such as dielectric constant Dc (which influences impedance), dissipation factor Df, and thermomechanical properties such as copper peel strength, glass transition temperature, or coefficient of thermal expansion (CTE). These properties should not be affected by the assembly processes applying higher temperatures. 

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