DE2120896B2 - Trimming process for flat electrical resistor - cuts non conducting separating slots transverse to current flow - Google Patents

Abstract

A flat electrical resistor is trimmed to achieve a nominal value, by cuting at least non-conducting separating slots transverse to the direction of current flow. The slots will not all have the same length, and the first will be a coarse adjustment and the last a fine adjustment. The slots (3, 5) are introduced only on one side of the resistance surface (1) and they run parallel to each other. When three slots are used, the two outer slots (3, 6) are used for the coarse adjustment and the third slot (5) is placed half way between the two and used for fine adjustment. The slots are introduced by an automated system.

Description

The invention relates to a method for balancing flat electrical resistances Setpoint by cutting at least two non-conductive separating grooves perpendicular to the direction of current flow, of which not all have the same length and of which at least the first does the coarse adjustment and the last one causes the fine adjustment. Such a method is shown in DT-OS 19 50 771.

The areas of the resistors to be balanced in thin-film, thick-film and hybrid circuits are for miniaturization reasons and especially for applications in high-frequency technology for reasons of runtime very small, so that usually only a very small area is available for adjustment Cutting into a separating groove then increases even at the lowest feed speed of the separating device the resistance value increases so quickly that the required tight tolerances are not maintained can. The limit for this is due to the switching time of the automatic switch-off device and the Given the accuracy of the mechanical guidance. It also increases at a constant feed rate of the separating tool, the relative change in resistance per unit of time increases if the length of the separating groove is no longer small compared to the resistance range

Due to the "Funk-Technik" 1971, No. 1, p. 23/24, it is already a device for subsequent adjustment known from planar resistances by means of a laser beam, in which the focused laser beam strikes the resistive layer and in the process cuts out a trench by removing part of the Layer evaporates. The so-called L-cut is recommended for precise adjustment processes. Here is the resistance is first trimmed perpendicular to the direction of current flow. The resistance value changes a lot fast. If the desired value is reached within predetermined limits, then in the direction of de: Current flow trimmed, i.e. perpendicular to the first trimming direction. Since now the resistance is in spite of If the same laser power changes only slowly, the required value can be accurate to about 0.1%

compare. . . .

Matching procedure with at least two: non-conductive Separating grooves that are cut from one side, if not exclusively, as well as run parallel to each other, both the DT-AS 1106 893, in particular Fig. 1 and the DT-OS show 14 65 400. in particular F i g. 4th

The invention has set itself the task of

The above-mentioned method continues to this effect

ίο develop that the Trennut shortly before and when reaching

of the setpoint in an area with the lowest possible

Streamline density is moved.

This object is achieved in that the separating grooves exclusively from one side of the

Be cut parallel to each other.

This results in the advantages that only a relative simple balancing device is needed that with

can be worked at great speed and

that the last separating groove, which takes care of the fine adjustment and runs in an area of reduced current density, is a causes increased calibration accuracy.

Two separating grooves from one side into the resistance surface are advantageous for the coarse adjustment incised, while a third groove for fine adjustment <; approximately symmetrically between the first two is placed. The first two separating grooves are preferably of the same length. Herewith there are advantages over the use of only two separating grooves that the resistance layer is less and more evenly loaded and that the streamline density between the first two separating grooves is very small and thus allows closer tolerances to be observed.

The calibration process is preferably measured tracked and controlled.

The invention is to be explained in more detail with the aid of the drawing.

F i g. 1 shows a known adjustment method for an areal electrical resistance, consisting of from an approximately rectangular resistance area 1 and two contact areas 2. To compare values, use one Side of the resistance surface 1 cut a separating groove 3 transversely to the direction of current flow. It results the course of the electrical streamlines marked with 4. It is easy to see that with increasing Length of the Trennut the electric streamlines are more and more crowded together, so that the electric Resistance increases sharply with increasing length of the separating groove. You can also see that through the known so-called L-cut, in which the fine adjustment is effected by a separating groove in the direction of current flow is, the fine adjustment is made in an area of relatively high current density, so that none particularly high accuracies can be achieved.

2 shows the method according to the invention using two separating grooves. From one side of the Resistance surface 1 from a first longer separating groove 3 is first cut for the rough adjustment, until the resistance setpoint is approximated to a certain percentage. Then it is parallel for this purpose, a second separating groove 5 is cut from the same side of the resistance layer 1, which enables the fine adjustment concerned. By comparison with the one shown in FIG. 1 drawn streamlines one recognizes that the Fine adjustment in an area with very little

Current density is made. The second separating groove 5 Hert in the "shadow" of the first Trennut 3, so to speak.

FIG. 3 shows the calibration procedure according to the invention with the use of a total of three separating grooves. Initially JwS «tiTrennut3 cut into the resistance stand. Then a second separating groove is made. The length of the two separating grooves 13 6 is selected through preliminary tests so that, with the two separating grooves being approximately the same length, the desired resistance value is approximated up to a predetermined process. Subsequently, the FeUiabglekh with the help of a symmetrically introduced between the first separating grooves 3, 6 separating groove 5. By the length and spacing of the two Sn separation grooves 3, 6, the current density can _be set between the two separation grooves lying flat area and thus affects the accuracy of the adjustment.

The variant of the method according to the invention shown in FIG. 3 should also be based on a numerical example be clarified. A resistor 1 mm long and 1.7 mm wide was adjusted. The first Separation groove 3 was drawn at a distance of 0.2 mm from the left interconnect. After a line length of 0.5 mm there was a Resistance of 5% below the target value achieved. The second separating groove 6 was at a distance of 0.2 mm pulled from the right contact surface. After a length of 0.4 mm, the resistance setpoint was on 0.2% approximate. For fine adjustment, groove 5 was placed in the middle between separating groove 3 and Trer.nut 6. she reached a length of 0.2 mm, with the resistance setpoint having a tolerance of less than ± 0.01% could be achieved. Of course, more than three separating grooves could also be cut will. It has been found, however, that the improvement in accuracy that can be achieved in this way reduces the effort not justified.

The cutting of the separating grooves can be done in various ways. Are common Micro sandblasting blower, laser beams, electron beams, Spark erosion, etc. With advantage you will use a method in which one to the Resistance connected measuring device is not influenced and also easily is controllable.

1 sheet of drawings

Claims (4)

Patent claims: 1. Procedure for adjusting extensive electrical resistances to the nominal value Cutting of at least two non-conductive separating grooves transversely to the direction of current flow, of which not all have the same length and of which at least the first is the coarse adjustment and the last causes fine adjustment, characterized in that that the separating grooves (3,5) exclusively from one side of the resistance surface (1) cut parallel to each other. 2. The method according to claim 1, characterized that two separating grooves (3, 6) are cut for the coarse adjustment and that for the Fine adjustment a third groove (5) is placed approximately symmetrically between the first two (FIG. 3). 3. The method according to claim 2, characterized in that the first two separating grooves (3, 6) be carried out for the same length of time. 4. The method according to claim 1 to 3, characterized in that the calibration process measuring is tracked and controlled.