Software Package RCutSim for Laser Trim Simulations of Film Resistors

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Important note: The following version is obsolete, but currently a simplified free demo-version of RCutSim simulator is available for MS-XP. After download please unzip the archive in a separate directory and start the executable. However, a whole new and highly improved numerical algorithm was developed and tested in a special environment. Thus, any work on version v2.x has been stopped. Unfortunate, coding the new numerical kernel will also cause a complete re-design of all package components. Because of the constant low public interest in this package no real work has been done for a new version v3.x since a long time. On the other hand, v2.x will be stay in unfinished 'as is'-state and it remains as a *NON* public version.
The support for those licensed users of RCutSim v2.x still continues until cancelled (i.e. license expirations). But no bug-fixes or updates are currently possible.


The Version v2.7 for Win-NT, Win-XP, eCS and OS/2:

The package consists of five components:

  1. ShapeInp a program for a quick creation and calculation of film resistors and cut path ways
  2. RCutSim the simulator itself to compute the trim characteristic, trim sensitivity and maximum post-trim drift behavior
  3. PcxFGen a tool to generate the isoline, current density and power density maps and to determine local voltages and current (or power) densities
  4. PTDrift an experimental tool for dynamic post-trim drift estimations
  5. ShowDia a little tool to plot and compare of simulator output curves
The following figure shows a screen shot of the ShapeInp tool version 2.7:
shape generator
This image shows a top-hat resistor with its edge lengths (blue and red are the terminals). The resistor has three cut paths, one side cut and two inner cuts. The resistance approximation of this untrimmed resistor pattern is shown at top right position of the screen. The final resistance of each cut can be seen in a dialog box (not shown here).

The simulator RCutSim v2.7:

trim simulation
The simulator works in the same manner as real laser trim equipments - bite by bite according to the cut path descriptions - and computes the resistance changes step by step. This creates the so called trim characteristic that is shown in the upper left plot. The vertical bars at the graphs show the expected maximum post-trim drift ranges (positive and negative). In the upper right plot you can see the trim sensitivity at each bite. This is the first derivative of the trim characteristic which is very imortant for calculations resistor layout dimensions and can be used to control the trim equipment itself, as well. The lower left quarter shows the current resistor geometry and can also be used to create or manipulate cut path ways via mouse. The lower right quarter shows status information, like the current nominal resistance and the laser position. This section is also used to control all simulator actions. The time consumption for an entire trim characteristic depends on the trim way length, laser parameters, desired precision, and the computer speed. It usual takes a couple of minutes. The computation of the post-trim drift can be suppressed, because it doubles the necessary calculation time.

The next figure shows an additional PTDrift-simulation of resistance drift by aging due to changes in the Heat Affected Zone (HAZ) along trim path ways. (The cut surrounding red dots mark the assumption of HAZ border.) You can watch the equivalent trim path geometry degenerations are happening within 20 time steps of resistor use. But notice: these geometrical changes cannot be seen in reality! This tool finally creates a view graph of the estimated post-trim drift by time. (not shown here)

trim paths drift in time behavior
(That's of course another resistor as above with a more interesting trim cut behavior and an extreme wide heat affected zone assumption.)

Finally, here are the dedicated isoline and power density maps created with PcxFGen:

Isoline and power density map
The main application of this tool is to investigate the current or power density stress of the resistor film material. This is one important parameter in search for the right minimum dimension of a film resistor shape. It is not necessary to compute an entire map for that issue (it takes a long time). With some experiences these values can be taken just by a mouse click at the right position within the resistor domain. This tool will show those values in its main window (not shown here). The maps, however, are useful to gain the necessary experiences for locating the right position for picking up the maximum average current density.

The ShowDia tool make it possible to get an offline view of simulation diagrams by using of the simulator output files (they are all in ASCII format, thus they are also usable for a lot of other softwares like MS-Excel). ShowDia is able to show more than one at once, so that you can see entire characteristic graph sets, if you want to. It is also possible to stretch, shrink or move a group of graphs or a single one for the purpose of quality and quantity comparison.

The ShowDia tool

The next figure shows a real data comparison of three measured trim characteristics with a simulated one of the resistor shown left hand side. In fact, there wasn't no single example found where it was impossible to bring the interesting part of a trim characteristic underneath any practical measure resolution. The one and only observed difference occurs by the last bites before through cut of trim path ways who end up with an infinite resistance. But this isn't happen by a side-cut as here.


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