Manufacturing/assembly problems, cause

In many cases, a part or a structure much like the required one has already been designed and tested. This preferred part or structure is typically mature in the sense that variabilities in manufacturing, assembly, and field operation that can cause problems have been identified and corrected. Many design groups maintain a list of preferred parts and structures of proven performance, cost, availability, and reliability. 

Another example might involve a manufacturing assembly line job where an employee is much shorter than other employees. The employee reports persistent shoulder and elbow pain, which the employer observes is caused by reaching higher than the other employees to perform the job tasks. This may also be an appropriate case for you to focus the analysis and control efforts on the employee who reported the problem. 

Dot-matrix printers use a cloth or polyester ribbon soaked in ink and coiled up inside a plastic case. This assembly is called a printer ribbon (or ribbon cartridge). It s very similar to a typewriter ribbon, except that instead of being coiled into the two rolls you d see on a typewriter, the ribbon is continuously coiled inside the plastic case. Once the ribbon has run out of ink, it must be discarded and replaced with a new one. Ribbon cartridges are developed closely with their respective printers. It is for this reason that ribbons should be purchased from the same manufacturer as the printer. The wrong ribbon could jam in the printer as well as cause adverse quality problems. 

It is important to understand that these requirements apply to laminate materials and not the PCBs manufactured from them. Furthermore, the time-to-delamination requirements are for unclad samples. All of the variables outlined in Section 11.2 regarding printed circuit fabrication and assembly must also be considered when specifying a material. It is also critical to understand that no one property will guarantee success in lead-free apphcations. When faced with uncertainty, the natural tendency is to overspecify each property. Not only could this cause the user to pay too much for a material, but overspecifying spedfic properties can also lead to functional problems. These problems can be the result of the interaction between advanced materials and the PCB fabrication processes required to manufacture rehable PCBs. 

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