JPS6027166B2 - Laser trimming method for resistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for laser trimming a resistor.

The conventional trimming method for resistors does not change the scanning speed of the laser beam on the resistor and the laser pulse irradiation frequency of the laser beam on the resistor from the beginning to the end of trimming. In other words, trimming was attempted while keeping the number of overlapping spots constant.

Therefore, when attempting to improve the accuracy of the adjusted value of the resistor, there is a drawback that trimming requires a long time. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for laser trimming a resistor that is devised to alleviate the drawbacks of the prior art described above and improve the accuracy of resistance value adjustment in resistor trimming.

That is, the present invention focuses on the fact that resistance value adjustment accuracy is determined by the number of overlapping spots, and is characterized in that the resistor is laser trimmed by changing the number of overlapping spots. The present invention will be specifically described below based on embodiments shown in the drawings.

FIG. 1 shows an outline of the laser trimming device.

1 is a laser oscillator that oscillates pulsed laser light 2;

3 is a mirror that directs the laser light 2 downward, 4 is the laser light 2
5 is a resistor for trimming, 6 is an XY table for sending the resistor 5, 7 is a circuit for driving the XY table, 8 is a resistance value measuring means for measuring the resistance value of the resistor 5 via a probe. , the resistance value measured by the resistance value measuring means and the preset target resistance value Ro or (Ro
-Q) (where Q is a preset resistance value) and determines whether Ro or (Ro-Q) has been reached. A resistance value determination circuit functions as a general control section for sending signals, and 9 is a laser oscillator control circuit that functions to control excitation input as well as ON/OFF control of laser oscillation of the laser oscillator 1. Laser trimming starts from a state where the resistance value Rx of the resistor 5 is 4 points less than the target resistance value Ro. When the start switch in the determination circuit 8 is pressed, a signal is sent to the drive circuit 7 and the XY table 6 starts moving. When the XY table 6 reaches a constant speed, the determination circuit 8 confirms this and sends a signal to the control circuit 9 to cause the oscillator 1 to oscillate the laser beam 2. The laser beam 2 is reflected downward by a mirror 3 and condensed by a lens 4 to process a resistor 5. Therefore, the resistance value Rx of the resistor 5 gradually increases to the target resistance value Ro.
approach. FIG. 2 shows the change in resistance value at this time. As shown in the figure, the resistance value digitally increases by ΔR ohm each time a laser pulse is irradiated at T=1, 2, and 3. At the moment when the resistance value exceeds a predetermined value (Ro-Q), the judgment circuit 8 sends a signal to the drive circuit 7 and the XY table 6
Slow down the feed speed. Since the pulse irradiation frequency is constant, the number of spot overlaps increases by the above operation. That is, the amount of resistance removed per irradiation pulse is reduced, and the amount of increase in resistance value is also reduced to Ay ohm (<ΔR ohm). After that, at the time T=6, the resistance value of the resistor 5 becomes the target resistance value R. The moment when the laser beam 2 is exceeded, the judgment circuit 8 sends a signal to the control circuit 9 and the laser beam 2
Cuts off the oscillation and finishes trimming. There is no pulse irradiation after T=7. An alternative method of controlling the pulse irradiation frequency is shown in FIGS. 1 and 3.

The first half of the operation is the same as the method described above. T in Figure 3
In steps 1, 2, and 3, each time a laser pulse is irradiated, the value is digitally increased by △R ohm, and the moment the resistance value exceeds a predetermined (Ro-Q) ohm, the judgment circuit 8 sends it to the control circuit 9. A signal is sent to increase the pulse irradiation frequency, and at the same time, the excitation input is controlled so that the peak value of the pulse becomes an appropriate value that matches the processing conditions. Since the feed speed of the XY table 6 is constant, the number of overlapping spots increases by the above operation, and the amount of increase in resistance value per irradiation pulse becomes small, Δy ohms. In this method, since the pulse irradiation frequency becomes high, the time interval between irradiation pulses is shortened from ΔT to Δt, and the trimming time is shorter by T time than in the previous method. In the laser trimming device shown in FIG. 1, the laser beam is fixed and the resistance moves, but the laser beam itself moves by mirror operation and the resistance is fixed. In the case of a trimming device, the above two methods can also be applied to the same device. As an extension of the method described above, if the XY table and pulse frequency are controlled simultaneously, the number of spot overlaps can be increased while the XY table feed speed is slowed and the pulse frequency is also low at the end of trimming. By widening the time interval and lengthening the cooling time, it is possible to reduce heat accumulation and reduce resistance errors due to the temperature coefficient of the resistor material, thereby improving resistance value adjustment accuracy. FIG. 4 shows a comparison diagram of the trimming time between the conventional method and the present invention when the resistance value adjustment accuracy is the same. A is a conventional method and B is according to the present invention. The trimming time of L time is shorter in the present invention. As a specific example, Ta
In trimming a 2N thin film resistor, the number of overlapping spots must be 35 or more in order to trim a resistor of 10 rudders Q with an accuracy of 0.01%. However, judging from the cutting characteristics, a spot overlap number of 3.5 is sufficient. Therefore, using the present invention, the trimming time is approximately 1'1
It will be shortened to 0. FIG. 6 shows the relationship between the number of spot overlaps and resistance value adjustment accuracy when trimming a Ta2N thin film resistor.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an apparatus for carrying out the laser trimming method according to the present invention, Fig. 2 is a diagram showing the change in resistance value when the feeding speed of the
Figure 4 shows the change in resistance value when the pulse irradiation frequency is changed. Figure 4 shows a comparison of the change in resistance value and trimming time between the present invention and the conventional method when the feed speed of the XY table is changed. FIG. 5 is a diagram showing the relationship between the number of overlapping spots and resistance adjustment accuracy. 1... Laser oscillator, 2... Laser light, 3
...Mihu, 4...Lens, 5...Resistance, 6...XY table, 8...Resistance value judgment circuit. 2 figures, 3 boxes, 4 figures, 5 figures

Claims (1)

[Claims] 1. A laser oscillator oscillates a pulsed laser beam at a predetermined frequency while relatively scanning a resistor and a laser beam using a scanning means, and the scanning speed at which the scanning means scans or the laser beam is scanned by the scanning means. The control means for changing the oscillation frequency of the pulsed laser light oscillated by the oscillator is adjusted to reduce the overlap of the laser light spots, and then laser trimming of the resistor is started, and the determination means also measures the resistance with the resistance measuring means. The resistance value Rx is a predetermined value (R_0-α) (however, R
_0 is the target resistance value. α is a preset resistance value. ), the control means is adjusted to increase the overlap of laser beams and laser trimming is performed, and the determination means also determines that the resistance value Rx measured by the resistance measuring means is equal to the target resistance. A method for laser trimming a resistor, characterized in that when it is determined that the value R_0 has been reached, oscillation of the pulsed laser beam of the laser oscillator is stopped to adjust the resistance value of the resistor to a target resistance value.