PACKAGING AND MANUFACTURING 91

Corp. (GR) tester of the type first used (Figure 25) to detect this type of fault. A module-specific program in the tester guides the operator through a fault-finding procedure. Approximately 95 percent of all Type 1 failures are diagnosed and repaired at this step.

Type 2 is dynamic. It seeks to detect faults which are caused by timing parameters being out of specification range, by logic incompatibilities, and by other functional problems. Figure 27 shows a tester (Figure 25) performing this type of test.

Type 3 is the reliability or burn-in test. The manufacturing process includes extensive thermal cycling to ensure that component "infant mortality" cases are discovered early during manufacturing because it is more expensive to find defective components at the later, more integrated systems level. For some components,

notably integrated circuits, thermal cycling is done when the components are received from the vendor. In addition, thermal cycling and burn-in are done near the end of the production process for entire processors and options. The temperature/humidity environmental chambers used, which house twelve or sixteen processors each, are shown in Figure 28. Test chambers to heat entire computer systems are also used.

We gratefully acknowledge the following colleagues who provided data for this chapter and valuable critiques of earlier drafts: Jim Cud more, Russ Doane, Sam Fuller, Lorrin Gale, Dick Gonzales, Jim Scanlan, Henk Schalke, Joe Smith, Steve Teicher, and Dave Widder.