Manual switch curve trace techniques are still popular for various reasons. Low cost, lightweight portability, easy to configure, and straightforward to replicate in other labs are popular reasons. However, compared to automated curve tracing, the tradeoff is labor. It takes more time to configure and collect data with the manual setup, but it is possible to configure most measurements using switch boxes, a curve tracer, and, occasionally, some power supplies.
Cable & Connectivity Options
Switch boxes can be used alone or in gangs to increase the range of devices and applications they can support. When connected to external instrumentation and DUT board, a complete setup is configured.
RTI switch boxes offer a choice between a 100-pin connector with 96 pins connected and 4 pins grounded, or three 32-pin ribbon cable headers. DUT boards are usually designed with the same connector interface and a jumper cable is used to connect between the two.
We can configure multiple switch boxes side-by-side to increase pin count. RTI can also provide overlay panels with preprinted pin names or numbers which are useful when testing BGA and LGA devices where the switch number may not correlate to the pin on the device.
We can also configure multiple switch boxes in parallel to increase switchable nodes (like busses on the MultiTrace). It’s also not unusual to combine manual switch boxes with MultiTrace to expand switching capacity.
Basic Operation of the Manual Switch Box
Basic Schematic of Manual Switch
RTI’s manual switch box has 3 position toggle switches for each pin and several banana jacks relevant to each switch. The V+ and V- banana jacks lead to a common node that leads to all pins. Normally, the operator connects the V- to ground of a curve tracer or the Emitter (E) input. For example, if you are using one of the Classic Tektronics analog curve tracers, the V+ jack is connected to the curve tracer output or the Collector (C) input of the Tektronics and the V- jack is connected the (E) Emitter terminal which is configured as ground. When the switch is toggled to the left, the pin is grounded. When the switch is toggled to the right, the pin is connected to the curve tracer. When the toggle switch is centered, the pin is floating. By selectively positioning the switches, the operator can emulate the all pins grounded, the pin-to-pin, and the group-of-pins to group-of-pins test conditions.
Every pin also has a banana jack of its own permanently connected to the pin [on the cable] and the common switch node. You can plug measurement instruments or bias supplies into these banana jacks to access the pin without flipping the switch. While most operators will toggle switches to move among pins to test, they can configure it to move the banana jack from hole to hole.
The vast majority of the tests that are done using manually switched hardware are analogous to the unpowered curve trace methods. All pins grounded are configured by pushing all switches to the left, then one by one flipping switches to the far right position, then moving back to the left. Selectively grounding pins works similarly, but more care is taken to choose the right pin numbers to ground. Pin-to-pin testing is emulated by toggling only one switch at a time to ground and only one switch at a time to curve trace.
Powered Curve Tracing with Manual Switch Box
Powered curve tracing can be accomplished using a single switch box, even with multiple VDD domains and different voltages. For this configuration, extensive use of the banana jack array is used, and external supplies are configured to voltage and compliance limits and plugged directly into one or more banana jacks. Ground pins are configured by pushing the switch to the left and using the V- node or by using banana cables to connect pins directly to the ground return of the external supply. Finally, the curve tracer is switched into the pins under test by toggling the corresponding switches to the right. It is important to center the toggle switch for any pin connected to a source by the banana jack, so it does not get shorted to the V+ or V- node.
Supply Current Measurements with Manual Switch Box
Supply current measurements are made similarly to powered curve trace setup, except the curve tracer is not used. Only power supplies are needed, but the curve tracer can be used as a power supply most times. The V+ and V- nodes can be used instead for input logic levels high and low. The operator can then easily toggle the switches to bias the logic inputs and obtain supply currents from the measurement instruments.
Curve Tracers & What to Look for
Most often, the manual switch boxes are used with a manual curve tracer but can be used with other hardware like power supplies. Most common one is the Tektronics Analog curve tracer models. Unfortunately, those models are essentially obsolete despite their popularity. Some people use the manual switch boxes with parametric analyzer (Agilent, Keysight, etc.) hardware and there are digital USB interfaced instruments available in the marketplace from Fluke and Keithley.
When using external supplies, it is important that they can be configured reliably. Knob adjustments are very hard to get exact values. A digitally controlled power supply with integral current measurement is recommended and a 4 quadrant SMU is one of the best options. Whatever the configuration, pay close attention to common grounding for all supplies, logic levels, and curve tracer reference.
RTI supports failure analysis and curve tracing with sockets, fixtures, and systems. Many DUT boards compatible with the manual switch box are also compatible with the automated MultiTrace curve tracer. Contact us if you have questions about our manual or automated curve trace systems.