Malander Engineering LLC

The Situation

A company that designed Micro-Electro-Mechanical Systems (MEMS) needed to characterize their devices. The devices were electrically actuated micro mechanical switches, which are similar to a relay. They needed to have these switches tested by:

Using a manually controlled variable power supply connected to the control pads of a switch (via micro probes) to control and test the opening and closing of the switch.
Connecting an ohm-meter across the signal pads to measure resistance before, during, and after actuation of the switch.
While the switch was closed, use a current source to test if the current capacity of the signal path met, or exceeded, the design specification.
Record all of the voltages applied, as well as the resistances and current capacities.

The Initial Process

Initially, the process of testing a MEMS device to failure at that company was done by hand, with each iteration consisting of the following steps:

Record the initial conditions, then turn up the power supply slowly until the resistance seen on the ohm-meter drops dramatically, and record the result.
Pass the design specfied current through the signal pads to see if the path between them could handle that level of current, and measure the result.
Lower the voltage of the power supply slowly until the resistance jumps up, ideally back to its initial value, and record the resulting voltage and resistance as in the previous steps.
Repeat the process until the device fails, then compile the results.

Though this process typically would take only a few minutes by hand, since the desired lifetime of each device was in the tens of millions in terms of open and close cycles, testing even one such device to failure in this manner would take a number of years.

The Observation

After performing the above process for a couple of days, and successfully collecting relatively few data points, it seemed clear that unless an automated approach was taken, we would probably never reach the desired cycles to failure of approximately 90 million.

On top of that the prescribed process introduced a lot of variables, such as:

the lack of uniformity in voltage ramp rates
sensitivity to closing (switch actuation) voltages
etc.

These complicated the process of engineering a better device based on the data collected. The more consistency one attempted in these areas, the longer the process would take. An automated solution could at once eliminate most, if not all, of this variability.

The Approach Taken

As a result, a proposal was created and presented that they allow us to create an automated test system. The opportunity was granted, with much enthusiasm from the engineers waiting for the data. The steps then taken were:

connect all of the electronic test equipment to a PC, using a GPIB card and cabling.
Use HP VEE to programmatically implement the test procedures.
A circuit board was created to extend their capabilities, as the electronic test equipment available to test the switches was not quite capable of doing all the needed measurements without human intervention.
Since the end result of the testing was to be an Excel spreadsheet, Microsoft Visual Basic (VB) was used to create components that could write to a spreadsheet. These components were integrated into the HP VEE system, so the measurements could be written directly into the spreadsheet.
In addition, VB was used to perform the statistical analysis and generate the charts used by management and the engineers to determine how best to improve the design in subsequent iterations.

The Result

The result was that measurements could be taken much more quickly and in a consistent manner. In fact, the results came in so quickly that we were actually able to test devices to failure, which generally occurred in the 1.6-2.6 billion cycle range.

In a real sense the test system created could achieve the original service that was requested and varify that a given device did indeed have a lifespan of greater than 90 million switching cycles, even while carrying the desired current. While at the same time collecting and preprocessing all data requested by the engineers.

This success gave rise to new opportunities that were beyond the scope of the company's initial request. The main one being that there was now a need for failure analysis to be performed on the switches after they failed.

The company again looked to us for help, and we were able to use various resources in the lab to successfully complete failure analysis.

Micro-Electro-Mechanical
System Characterization

The Situation

The Initial Process

The Observation

The Approach Taken

The Result

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