The Challenges of Testing Low Voltage Technologies at In-Circuit Test

This paper discusses the challenges of performing powered-up vector testing of low voltage technologies on In-Circuit testers and the safeguards that are necessary to ensure that test vectors do not violate the increasingly tight specifications of low voltage parts. Topics include why manufacturers are adopting low voltage technologies, what happens when low voltage components are exposed to stressful conditions, design for test considerations, accuracy of different ICT pin designs, and the importance of features that report and control harmful test events that can unduly stress components. Benefits of Low Voltage Technologies The popularity of low voltage technologies has grown significantly over the last decade as semiconductor device manufacturers have moved to satisfy market demands for more powerful products, smaller packaging, and longer battery life. By operating semiconductor devices at lower voltages, product designers benefit from lower power consumption requirements, reduced cooling requirements, and faster processing speeds. These benefits have made it possible for the performance of the PC to increase over 400-fold in the past 18 years, even though the energy consumed by the PC has remained largely unchanged. [1] The use of 5V VCC had long been the standard for both core and memory logic. However, the increasing complexity and functionality of application-specific integrated circuits (ASICs), microprocessors, and digital signal processors (DSPs), have resulted in modern CMOS manufacturing processes that produce smaller structures where the thickness of the gate oxide of each single transistor is sensitive to electrostatic field strength. Because the field strength is proportional to the supply voltage, the supply voltage must be reduced for reliable operation of the smaller structures. Put another way, making electronic devices more complex, without enlarging the overall size of the chip area, requires reducing the structure size, which also requires reducing the VCC power supply voltage. The limit for reliable operation at less than 5V is reached at a structure size of 0.6 micron, and the use of a 0.35-micron manufacturing process requires 2.5V VCC for proper operation. Reducing the power supply voltage also produces an exponential decrease in power consumption; therefore, the trend is to reduce power-supply voltages. [2] The technology roadmaps of the major semiconductor manufacturers show that logic voltage thresholds have been steadily declining over the past decade. Figure 1 shows the progression of low voltage components introduced by Texas Instruments over the last decade from 5V to 3.3V to 2.5V to 1.8V to 0.8V. Table 1 shows the variety of low voltage logic levels that are being used by Intel’s Pentium chipset on PC motherboards today.