Programming the PLS From Your PC with VFS2 Software
VFS2 can be used with the VF40-series and PLS-series testers.
Running under FreeDOS or under WINDOWS-9X in a DOS window, it remotely programs and controls the tester. You can choose from a selection of plots or choose to collect and log sets of readings. These readings may be saved to disk files and/or displayed on the screen or printer.
All of the programmable characteristics of the tester can be controlled remotely. Communication is via the serial ports of the tester and remote computer (COM1 or COM2). The communication rate historically has 4800 Baud (about 480 characters per second). However some recent testers can communicate at 19,200 Baud. The Baud rate is set automatically by the software for each tester.
The tester does most of the work. It takes forcing conditions, limits, etc., from the host. During a plot these conditions are sent only once. After that, only new values for the independent variable are sent and a 5-digit number is received back. This communication overhead is small, the throughput being determined mainly by the pulse width and cooling time between pulses.
To log a set of readings, the host sends the test conditions to the tester then watches while the tester tests the required number of samples. The only communication per diode is the transmission of the 5 digit reading, plus a “Return” and a “LineFeed”. The readings are stored together with a header and some statistics in a disk file. This data may also be displayed on the screen or printed.
The readings are stored in our proprietary compressed format. The format used is the same as that produced by our MAXX software. As a result, the STATS software used to process MAXX data files will also work with files produced by VFS2.
STATS can process one or two data files to produce statistical reports, with optional histograms and can also produce delta reports for pre and post burn-in files.
STATS can be run directly from the FreeDOS prompt or can be run from within VFS2. Running from VFS2 can be done with a single keystroke <F11> and STATS will open up pointing to the data file just produced by VFS2.
The plots produced by VFS2, such as a “Heating Plot” for example can be viewed on the screen or printed. You will also be asked if you want to save the plot to a file. If you do save the plot it will be in ASCll format which can be viewed, edited, and/or printed using any plain text editor. The “EDIT” program supplied by Microsoft is a suitable editor.
We have provided a single function key to launch EDIT or another editor of your choice.
HARDWARE REQUIREMENTS
DOS or WINDOWS_9x compatible computer running DOS or WINDOWS 9x.
A Serial port is required, either COM1 or COM2. A Printer is required for hardcopy of plots although plots may also be seen on screen.
Any IBM compatible dot matrix printer or LASER or INKJET printer that is compatible with Hewlett Packard PCL may be used.
INSTALLATION
Insert the distribution diskette in drive A: and enter A:SETUP. This will install VFS2 on your hard drive in C:\VFS2. Also a directory *C:\VFS2\FILES will be made for storage of data files. You can change the file locations later if you wish.
SETUP
The program will run as soon as you do the above installation. From the DOS prompt in C:\VFS2 enter VFS2. However, there are many options in the program so you will probably want to set up your preferences.
VFS2 has a file CUSTOM.TXT where you set your preferences. When we send you an update it will not over-write your CUSTOM.TXT file. You will find a new file called CUSTOM.NEW instead. You may want to copy your preferences into CUSTOM.NEW and then rename it CUSTOM.TXT. You can edit this file with a text editor such as “EDIT”. We strongly recommend that you read and possibly edit the file. If you do not have the default “COM2" serial port on your computer, you will need to edit CUSTOM.TXT to change the default to COM1.
Once the program has started, you can program it for any desired test configuration and press <F2> to save the complete setup for later use. You will be asked for a filename for the saved setup. VFS2 will add, or change the extension to .PGM.
The saved setup files will be marked to identify the type of tester being used and VFS2 will not allow you to reload a file that was not made for the current tester model.
You can put the name and path to one of these saved setups in CUSTOM.TXT so that it will be loaded whenever you start VFS2. Of course you can always use <F8> to load a different program at any time.
The name of the program loaded will be displayed and if you have used the menu to change anything other than the headers or output file spec, a message will indicate that the setup may have changed.
TEST DRIVERS
We normally ship the software with the proper driver selected for your tester. If for any reason you should need to change to a different supported tester, you can change drivers by editing *CUSTOM.TXT. You can also change testers with a function key while VFS2 is running
VFS2 MAIN MENU
PLOT
The plot is intended to plot one of the thermal response tests against the heating pulse width. You can set-up all the other characteristics of the test. The software will control pulse width and cooling time. The cooling time is at least 10 times the pulse width.
The values we have chosen for the pulse width are related by a constant multiplier of (1.41 approximately). The lower values are rounded off by the finite resolution of the tester’s timing routines.
The resulting plot will appear to have been plotted on semilog paper.
*You can set the menu item “Stop Plot at” in order to limit the temperature rise in your DUT when a large current is selected. If you do not set a “Stop” point, the plot will contain 20 steps ending at 2 seconds. The maximum of 20 steps is set in CUSTOM.TXT and so you can reduce it globally if you want to.
If you plot THETA (degrees C per watt) some of the lower readings may be shown as “invalid”. We don’t calculate THETA unless the DVF value measured is large enough to yield reasonably accurate results. You can get a pretty good look at these low readings by plotting DVF instead.
The smoothness of the plot at the low DVF end may suffer also from the finite resolution of the ADC in the tester. This can be improved (at the cost of plotting time) by averaging more than 1 reading per point. When setting up the plot you could choose a number greater than the default “1" “READINGS PER POINT”.
TR PLOT
This is a new plot as of this writing and currently available only on VF40CM or PLS1000CM testers. The TR PLOT plots THETA, DVF, or VF vs. time out to a maximum of 1000 Seconds. The plot is roughly semi-logarithmic except that the final point will be exactly on the time that you specify and the other points are pre-programmed. The tester applies heating power nearly continuously but interrupts it briefly every 50mS to take a VF reading and a cumulative DVF reading which are sent to VFS2, which does the calculations and plots. Although all of the readings taken at 50mS intervals are sent to VFS2, they are not all plotted.
When you browse through the available THETA scale choices, you will see that two new choices allow you to choose DVF or VF to be plotted instead of THETA.
COOLING PLOT
The cooling plot plots a thermal response test against the “Delay time”. That is the time from the end of the heating pulse until the “Hot VF” is sampled. The heating pulse width, and other characteristics of the test may be set by the operator.
The cooling times chosen have the same relationship to each other as the heating times in the heating plot. The lowest value may be so low that the readings are invalid. That would happen if either the power supply or the part under test did not completely recover in the time specified.
This is a useful tool for finding the smallest valid delay for a particular part, and test conditions. This plot may also be very useful for analyzing bonding problems that are located thermally close to the junction.
VF vs. IF
This plot is like a digital curve tracer. You can set the first step, the step size and the number of steps and the program plots Forward Voltage vs. Forward Current.
SAVE PLOT
Any of the above plots may be saved to disk as ASCll files. You will be prompted to choose whether to do this. If you save the plot you will be able to edit it using a text editor of your choice. The DOS “EDIT” command is the default. Press <F9> to edit.
LOG READINGS
The program will collect readings up to “Sample size” or until you press <Esc>. You test the parts either manually or with your automatic handler. In any case you or the handler provide the “start test” signal for each part tested.
The serial number and count will be advanced for each part tested if it reads between “Throw out < n” and “Throw out> n”. Readings outside these limits will be discarded, a “beep” will sound, and the serial number and count will NOT be advanced.
You can change the serial number any time you wish by pressing <F6> then entering the new serial number.
Note that it is ok to reuse a serial number already recorded. This will not over-write the old reading. However, if you process the file using STATS, only the most recent part of parts with duplicate serial numbers will be used. This is a useful way to reread parts whose initial readings are incorrect for some reason.
One caution about the above. VFS2 will count all of these duplicate numbers, so the count of readings collected will be high if serial numbers are reused.
Both the current serial number and the count of readings collected will be displayed on the screen as the collection proceeds.
If you have turned “Stop on fail” “ON” the tester will stop collecting and halt the tester when a reading is outside the “Test limits”. A suitable message will appear and you can change the part then retry with <F3> or choose to accept the failed reading with <F9>.
When the sample collection is finished the tester will go back to “Local” control and continue to test if connected to a handler.
It will continue to use the same setup used by “Log Readings”.
When you finish collecting a set, you can run STATS to view the readings and statistics on the screen or printer.
You can collect more readings to the same file or selectively retest parts already tested, by resuming the collection process with <F3>.
RUN STATS
You can run the program STATS from within VFS2 by pressing <F11>.
EXPORTS
Export is similar to LOG but it makes an ASCll file with just the readings in a very terse format containing just serial numbers and readings. The individual data fields are comma delimited in a form suitable for import into a spreadsheet program. You can use <F9> to edit the exported file if you wish to modify the format or add any data.
PROGRAM TESTER
You can use VFS2 to program the tester prior to using the tester for production (or other) testing. Of course you could have done the same using the tester’s control panel but using VFS2 is much easier if the remote computer is already connected.
Please note that programs down-loaded to the tester are not saved in the tester’s non-volatile memory as locally entered