PRIORITY CLAIM

Not Applicable

CROSS-REFERENCE TO RELATED ARTICLES

1. TSIRONIS, C. U.S. Pat. No. 7,102,457, “Mechanically balanced microwave load pull tuner”.2. “Computer Controlled Microwave Tuner—CCMT”, Product Note 41, Focus Microwaves Inc., January 1998.3. TSIRONIS, C. U.S. Pat. No. 9,431,999, “Intelligent mechanical balancing apparatus for slide screw tuners”.4. BlueDial Bluetooth Dial Indicator, Mitutoyo indicator, model BD10-793 Datasheet [online], Motionics LLC [retrieved on Nov. 9, 2020]. Retrieved from Internet <URL: https://www.motionics.com/downloads/BlueDial.pdf>.5. TSIRONIS, C. U.S. Pat. No. 7,135,941, “Triple probe slide screw tuner and method”.6. High Performance Probe Stations [online], Cascade Microtech [retrieved on Nov. 9, 2020]. Retrieved from Internet <URL:https://www.cascademicrotech.com/products/probe-systems/dedicatedsystems/vacuum-probe-systems>7. What is a Vector Network Analyzer and how does it work?” [online], Tektronix [retrieved on Jun. 10, 2020] Retrieved from Internet <URL: https://www.tek.com/document/primer/what-vector-network-analyzer-and-how-does-it-work>.

BACKGROUND OF THE INVENTION

This invention relates to on-wafer load pull or source pull measurement setups, allowing controlling and eliminating the mechanical tilting caused by the electro-mechanical microwave tuners used in these setups, by adding a remotely controlled balancing counter-weight on the mechanism supporting and positioning the tuner (FIG. 1).

“Source pull” and “load pull” are test methods used in generating data used in designing high-power and low noise microwave amplifiers for various telecommunication systems. These measurement techniques employ microwave tuners and other microwave test equipment. The microwave tuners are used in order to manipulate the microwave impedance conditions under which the Device Under Test (DUT, or transistor) is tested (FIG. 2).

A basic load pull measurement system (FIG. 1) includes a signal source, a source tuner, a test fixture housing the DUT, a load tuner and an output power meter. The tuners and the overall test system are controlled by a control computer. Through digital commands from the computer the tuner's motors position the tuner's metallic tuning probes appropriately and create impedances, which allow characterizing the DUT (see ref.1).

Electro-mechanical slide screw tuners include a solid housing (box)27,FIG. 2, a low loss transmission media23for microwave energy (slotted transmission airline or slabline) with a test port attached to a rigid extremely low loss bent airline25, a moving carriage20holding the microwave tuning probe and electrical stepper motors ensuring the horizontal and vertical movement of the carriage and the insertion of the tuning probe into the slabline slot. The tuner is placed on a tuner positioner26, which has bearings or gliders allowing a 3-axis geometrical movement (X-Y-Z). The carriage20holding the probe comprises a housing, a precision vertical axis and gear and a vertical stepper motor; this makes such carriages20massive items with a typical mass of around 1 kg.

The low loss bent airline25forms an extension to the tuner slabline and is used to maximize the tuning range of the tuners; the bent airlines are either externally attached airlines or simply the seamless continuation of the slabline beyond the tuner housing and are connected directly to the wafer probes; they create a rigid mechanical link between the tuners and the wafer micro-probes21(FIG. 2). Any mechanical movement inside the tuners, especially tilting24, caused by the horizontal movement of the tuner carriage(s), is translated on to the wafer probes21and creates a vertical wafer probe movement of, typically, several dozens of micrometers. Microchip contact pads on a wafer22being 100 μm to 200 μm square, even a small mechanical movement of the wafer probes may create loss of contact and/or damage.

The tilting problem and vertical movement of the wafer probes31has been addressed before using a mechanically coupled counter weight30(FIG. 3), which moves synchronous and opposite to the carriage32(see ref.1). The problem with this, mechanically simple, solution is that the counter-weight30must have the exact same mass as the carriage32within a fraction of one gram and that the belt33linking both moving masses tends to be unreliable and unprecise over longer distances.

The contacting of the wafer probes with the DUT pads is done either using sophisticated automatic wafer probe stations (see ref.6) or by adjusting each time manually the Z axis of the 3-axis positioner under careful observation under the microscope, a not securely reproducible operation in itself.

It is the purpose of this invention to solve both the tilting-balancing problem and automate the contacting process of the wafer probes with the DUT pads, using an intelligent automated mechanism.

BRIEF SUMMARY OF THE INVENTION

The problem referred to in ‘BACKGROUND OF THE INVENTION’, is solved by introducing, outside of the tuner housing (box)27, an independently controllable mobile compact and mechanically simple counter-weight mechanism, moving synchronous and opposite to the movements of the carriages inside the tuner, in order a) to maintain the balance of the system by keeping the center of gravity of the assembly “tuner positioner & tuner & tuning probes” constant and b) to control the elevation of the wafer probes themselves to create an automated, repeatable electrical contacting of the wafer probe(s) with the DUT pads. The built-in capacity of independent control and movement of the counter-weight offers the major advantage that the counter-weight mass and the mobile carriage mass should be similar but not identical, as in other purely mechanical solutions, because independent remote control allows changing the momentum M=L*W (length times weight) by adjusting L at will.

To build this assembly, a thin large disc, with belt teeth cut on its on its periphery, forming a timing belt pulley of large diameter, carries a properly dimensioned counter-weight on its edge, is attached to the tuner positioner and is independently rotated by a remotely controlled stepper motor, which is mounted, preferably, on the tuner housing, for reasons of economy of space, or on the tuner support block. An overall balancing control procedure determines the rotation angles (corresponding to the controlling motor steps) of the disc relative to the tuner carriage movement for balancing the system and any desired elevation of the wafer probe by controlled unbalancing the system, and determines the rotation angle of the disc in two steps: a) balancing the carriage movement and b) making or breaking contact of the wafer probe with the microchip DUT pads on wafer.

