TABLE OF CONTENTS Manufacturing processes must be stable, repeatable, and of high quality to produce products with acceptable performance. This implies that all individuals involved in manufacturing a product (including operators, engineers, and management) must continuously seek to improve manufacturing process output and reduce variability. Variability reduction is accomplished in large part by strict process control. The application of process control in manufacturing continues to expand in the electronics packaging industry. The focus here is on statistical process control techniques as a means to achieve high-quality products.
Statistical process control (SPC) refers to a powerful collection of problem solving tools used to achieve process stability and reduce variability. Perhaps the primary, and most technically sophisticated, of these tools is the control chart. The control chart was developed by Dr. Walter Shewhart of Bell Telephone Laboratories in the 1920s. For this reason, control charts are also often referred to as Shewhart control charts.
A control chart is an on-line SPC technique which is used to detect the occurrence of shifts in process performance so that investigation and corrective action may be undertaken to bring an incorrectly behaving manufacturing process back under control. A typical control chart is shown in Figure 20.12. This chart is a graphical display of a quality characteristic that has been measured from a sample versus the sample number or time. The chart consists of: (1) a center line, which represents the average value of the characteristic corresponding to an in-control state; (2) an upper...
