Assembly process Accuracy

DCA refers to the assembly of an unpackaged active semiconductor device directly onto the circuit board. The interconnections are made either by wirebonding or by solder bumps on the front side of the die. The latter application is referred to as FC attachment and can be implemented into a surface-mount assembly process as long as existing equipment can accommodate the placement accuracy required for the very small solder bumps and pads. Otherwise, a dedicated cell may be required. 

Correct equipment setup is very important to ensure high throughput and yield because it impacts the consistency and accuracy of the results. The setup used at every stage of a PCB assembly process must be performed by certified personnel and validated to be in accordance with the... 

Specialized equipment for industrial measurements and automatic control have been developed (18) (see Process control). In general, the pH of an industrial process need not be controlled with great accuracy. Consequendy, frequent standardization of the cell assembly may be uimecessary. On the other hand, the ambient conditions, eg, temperature and humidity, under which the industrial control measurements are made, may be such that the pH meter must be much more robust than those intended for laboratory use. To avoid costiy downtime for repairs, pH instmments may be constmcted of modular units, permitting rapid removal and replacement of a defective subssembly. 

A hot alignment check is performed exactly like an ambient alignment check with the added safety precautions required for hot machinery. The accuracy of a hot alignment check depends on how soon after shutdown dial indicator readings can be taken. Readings may be taken within a few minutes with the use of shaft-mounted brackets that span a flexible coupling. To speed up the process, assemble the brackets to the fullest extent possible prior to shutdown so that they need only be bolted to the shafts once the machine stops rotating. 

In addition to material variables, as reviewed in Chapter 6, there are a number of factors in equipment hardware and controls that cause processing variabilities. They include factors such as accuracy of machining component products, method and degree of accuracy during the assembly of component products, temperature and pressure control capability particularly when interrelated with time and heat transfer uniformity in metal components such as those used in molds and dies. 

This process is used to produce intricate, thin-section parts with great dimensional accuracy, fine detail, and very smooth surfaces. All ferrous and nonferrous alloys can be cast in investment molds. Investment casting begins with expendable wax patterns that are assembled into clusters, then coated with a series of successively coarser ceramic slurries. The assembly is then fired in a furnace to dry and harden the ceramic shell and to melt out the wax, leaving a cavity into which molten metal is poured to form the casting. 

As you assemble this information, focus on providing as much specific information as possible. If you re writing about your skills as an administrative assistant, for example, in addition to listing your typing speed and accuracy, list specific word processing programs you re proficient in using, such as Microsoft Word, WordPerfect, and so forth. 

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