Testability and signal integrity in a low cost multichip module

The design process for low-cost multichip modules (MCM's) is presented. Modifications to the design are often made in order to increase testability. Some of these modifications can degrade signal integrity, however. The important aspects to consider in order to make rational design tradeoffs are presented. Test strategies and techniques are discussed. The effects on signal quality of additional test stubs to the internal nets of the MCM are analyzed. It is shown that the addition of unplanned test stubs can degrade the signal pulse quality and any such additions must require further signal integrity analysis.