JP3543731B2 - Laser trimming method and laser trimming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser trimming method and apparatus for trimming a microresistive chip and the like, and in particular, by changing the pause time between laser pulse irradiation periods optimally in association with the progress of the trimming process, thereby achieving high speed and high accuracy. The present invention relates to a laser trimming method and apparatus capable of laser trimming.
[0002]
[Prior art]
Conventionally, tracking trimming that performs laser trimming of these resistors while measuring the resistance value or DC voltage of the resistors in real time is one method of adjusting the electrical resistance values of resistors such as printing resistors by laser trimming. There is a method called. In this method, high speed and processing stability are required in the first stage of the trimming process, and electrical characteristics are required to be adjusted with high accuracy in the final stage of the trimming process.
[0003]
Recently, with the demand for cost reduction and miniaturization of electronic components, high speed and high accuracy are also required in laser trimming. Therefore, the size of the chip resistor is changing from 1005 size to 0603 size. However, even if the chip size is reduced, the film thickness of the resistor is determined by the material of the resistance paste, so it is the same as before, and the continuous laser pulse determined by the processing speed and the pause time between the laser pulse irradiation periods The laser trimming conditions such as the distance between the irradiation positions (hereinafter referred to as byte size) are basically unchanged. When the size of the resistor is reduced, the resistance change rate per byte size is increased, and it is difficult to control the trimming accuracy with high accuracy.
[0004]
An example of a conventional trimming method is shown below. FIG. 4 shows the relationship between the timing of laser pulse irradiation and the change in the electrical resistance value of the resistor in the conventional laser trimming method. In the conventional laser trimming method, as shown in FIG. 4, the rest time T during the laser pulse irradiation period is constant, and the irradiation position of the laser pulse 45 is scanned on the resistor at a constant speed by a beam scanner. As a result, as shown in FIG. 5, the irradiation positions 52 of the laser pulses on the resistor are arranged at a constant interval L. That is, the byte size is constant. Then, when a measured value such as an electric resistance value exceeds a preset target value Rf, the laser pulse irradiation is stopped and the trimming is finished.
[0005]
Here, when the resistor is a thick film resistor formed by screen printing, the film thickness is about 10 to 20 μm. The laser beam diameter is 30 to 50 μm. The bite size is set to 5 to 10 μm in order to make the processing state of the laser processing groove formed by the laser pulse good. When the laser beam diameter is 30 μm and the bite size is 5 μm, the number of overlapping laser pulses at an arbitrary position of the laser processing groove is six. If the number of overlaps is too large, the laser processed groove is damaged and deteriorates.
[0006]
However, this conventional method has the following two problems. The first problem is that the error of the electric resistance value after trimming is increased. In the conventional method, the byte size is constant, and trimming is completed when the measured value of the electrical resistance value exceeds a preset target value Rf. In this case, if the amount of change in the electric resistance measurement value that changes with one laser pulse irradiation is ΔR, the electric resistance value after trimming varies in the range of Rf to Rf + ΔR as shown in FIG. For example, in FIG. 4, a line 43 is a line indicating a change in the electric resistance value of the resistor R6. The electric resistance value of the resistor R6 is an electric resistance value slightly smaller than the target value Rf after the n−1th pulse irradiation. However, in the conventional method, the same n-th pulse irradiation as the (n-1) th pulse irradiation is performed, so that the electric resistance value of the resistor R6 increases to an electric resistance value slightly smaller than Rf + ΔR. That is, the electric resistance value of the resistor R6 overshoots exceeding the target value Rf.
[0007]
The second problem is that it is difficult to increase the processing speed. In order to increase the speed of laser trimming, it is necessary to increase the processing speed by increasing the scanning speed of the laser pulse and shortening the pause time during the laser pulse irradiation period. However, when the machining speed is increased, there is a problem that the measurement of the electric resistance value of the resistor cannot follow the change in the electric resistance value, the error of the electric resistance measurement value becomes large, and the trimming accuracy is lowered. Therefore, conventionally, when performing high-accuracy trimming, if the machining speed is sufficiently reduced or the machining speed is increased, trimming is paused every time a certain distance is machined, and the electrical resistance value is measured accurately. The method of restarting trimming from the beginning is adopted. However, these methods all reduce the processing efficiency.
[0008]
In order to solve the above-described problems, conventionally, the following methods have been proposed. Regarding the first problem, there is a method of reducing the byte size and reducing the trimming amount per laser pulse in order to improve the trimming accuracy. By this method, the value of ΔR can be reduced, and the error of the final electric resistance value is reduced.
[0009]
Further, as a method for solving the second problem, Japanese Patent Application Laid-Open No. 59-171103 has two or more resistance comparison circuits, in which the processing speed is increased in the initial stage of trimming and switched to a lower speed in the middle. Thus, a method for achieving both high processing efficiency and good trimming accuracy is disclosed.
[0010]
[Problems to be solved by the invention]
However, the above solution has the following problems. In the method of reducing the error by reducing the bite size, if the bite size is too small, the number of overlaps mentioned above will increase too much and damage the resistor and ceramics of the substrate material, and significantly reduce the reliability of the resistor. There is a problem. For example, if the beam diameter is 30 μm and the bite size is 1 μm, the number of overlaps is 30, so that the resistor and the substrate material are damaged and the resistor is deteriorated.
[0011]
On the other hand, according to the method disclosed in Japanese Patent Application Laid-Open No. 59-171103, the processing efficiency can be improved to some extent, but the first problem cannot be solved. Further, with respect to the improvement of the machining efficiency, in this method, although the machining speed is increased at the initial stage of the machining process, the machining speed is switched to a low speed in the middle, so there is a limit to the improvement of the machining efficiency. Furthermore, when switching the processing speed, it is necessary to move a beam positioner device that controls the beam path of the laser pulse. There are various types of beam positioner devices, such as galvanometer type and linear motor drive XY table type, but anyway, since it involves mechanical operation, until the processing speed actually changes after inputting the switching of the processing speed Will be delayed. In order to improve trimming accuracy, the machining speed must be low at the end of trimming, and it is necessary to change the beam positioner speed sufficiently early in anticipation of the fluctuation of the delay time described above, so that machining can be performed at high speed. The period will be more limited.
[0012]
The present invention has been invented in view of such problems, and it is intended to provide a laser trimming method and apparatus capable of improving trimming accuracy and performing high-speed and efficient processing without damaging a resistor. Objective.
[0013]
[Means for Solving the Problems]
The laser trimming method according to the present invention is a laser trimming method for trimming a resistor by intermittently irradiating a laser pulse while measuring an electric resistance value of the resistor. the difference between the target value and the measured value in the laser trimming and ΔRfm, 1 time the amount of change in the measured value of the electrical resistance value that changes by laser pulse irradiation and [Delta] R, the initial of the pause time of the laser pulse irradiation When T is a set value and Tend is a pause time from the last laser pulse irradiation to the next laser pulse irradiation when ΔRfm becomes equal to or less than ΔR, the Tend is determined by the following Equation 1. Laser trimming method.
[0014]
[Expression 1]
Tend = ΔRend / ΔR × T
[0017]
By this method , high-accuracy laser trimming can be realized by optimally changing the pause period between the laser pulse irradiation periods that has been conventionally constant as the trimming process proceeds. Further, it is possible to eliminate an overshoot error due to the last laser pulse irradiation that has been inevitably generated in the past, and to improve the trimming accuracy.
[0018]
Furthermore, it is preferable to use a Q-switched laser pulse as the laser pulse.
[0019]
A laser trimming apparatus according to the present invention includes a laser oscillation unit that intermittently oscillates a laser pulse, an optical system control unit that controls a path of the laser pulse, and a workpiece to control the position of the workpiece. Connected to and controlling the transporting means, the measuring means for measuring the electrical resistance value of the resistor in the workpiece, the laser oscillation means, the optical system control means, the transporting means, and the measuring means. In the laser trimming apparatus, comprising an operation control means for performing an arbitrary trimming process on the resistor of the workpiece and adjusting an electric resistance value thereof, a final target value in the electric resistance value of the resistor The difference between the measured value during laser trimming and ΔRfm is ΔRfm, and the amount of change in the measured value of the electrical resistance value that is changed by one laser pulse irradiation is ΔR, and the laser When T is the initial setting value of the pulse irradiation pause time and Tend is the pause time from the immediately preceding laser pulse irradiation to when the ΔRfm is equal to or less than the ΔR, the Tend is the above formula. It has the calculating means determined by 1. It is characterized by the above-mentioned.
[0020]
In the laser trimming apparatus, the laser pulse is preferably a Q-switch laser pulse, and the arithmetic means is preferably a digital signal processor.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of the laser trimming apparatus in this embodiment. The laser trimming apparatus is provided with a laser light source 2 that oscillates a Q-switch pulse laser (hereinafter referred to as a QSW pulse laser). The output signal of the laser oscillation control circuit 16 for controlling the operation of the laser light source 2 is input to the laser light source 2.
[0022]
Further, on the output side of the laser light source 2, a galvanometer type laser beam scanner 3 for controlling the path of the QSW pulse laser 17 oscillated from the laser light source 2 is provided. The galvanometer type laser beam scanner 3 includes a beam expander 4 that spreads the QSW pulse laser 17 oscillated from the laser light source 2, a scanner mirror 7 that reflects the QSW pulse laser 17 that has passed the beam expander 4 in an arbitrary direction, and a scanner. A galvanometer 6 that controls the angle of the mirror 7, an f-θ lens 8 that converges the QSW pulse laser 17 reflected by the scanner mirror 7, and a QSW pulse laser 17 that passes through the f-θ lens 8 is reflected and applied to the workpiece 10. A beam scanner control circuit 5 for controlling the mirror 9 and the galvanometer 6 is provided. The signal output from the beam scanner control circuit 5 is input to the galvanometer 6, and the signal output from the galvanometer 6 is input to the scanner mirror 7.
[0023]
In addition, the workpiece 10 is placed on a mounting table 11, and the mounting table 11 is mounted on an XY table 14 for moving the mounting table 11 and the workpiece 10 in the XY directions.
[0024]
On the other hand, a probe 12 for measuring the electrical resistance value is connected to the workpiece 10. The signal detected by the probe 12 is input to the electrical resistance measuring device 13 through a probe up / down mechanism 18 that adjusts the position of the probe 12.
[0025]
The electrical resistance value of the workpiece 10 measured by the electrical resistance measuring device 13 is converted into an electrical signal and output, and the amount of change is calculated from the electrical resistance measurement value by calculating the rest time between the laser pulse irradiation periods. The measurement value change amount calculation / laser pulse interval control device 15 for determination is input. A signal output from the measured value variation calculation / laser pulse interval control device 15 is input to the operation control device 1.
[0026]
The operation control device 1 controls the operations of the laser oscillation control circuit 16, the beam scanner control circuit 5, the XY table 14, the electrical resistance measuring device 13, the probe up-and-down mechanism 18, and the measured value change calculation / laser pulse interval control device 15. It is a device for. A control signal output from the operation control device 1 is input to each of these devices.
[0027]
Next, the operation of the laser trimming apparatus shown in FIG. 1 will be described. A workpiece 10 such as an electronic component having a resistor is placed on a mounting table 11, the workpiece 10 and the loading table 11 are mounted on an XY table 14, and the probe 12 is resistance of the workpiece 10. Connect to the body. Here, a control signal is output by the operation control device 1 and input to the XY table 14 and the probe up-and-down mechanism 18, and the XY table 14 and the probe up-and-down mechanism 18 are driven to move the workpiece 10 to an optimal position. Further, the operation control device 1 outputs control signals and inputs them to the electric resistance measuring device 13 and the measured value change amount calculation / laser pulse interval control device 15 to operate them.
[0028]
Next, the operation control device 1 outputs a control signal and inputs it to the laser oscillation control circuit 16 to operate the laser oscillation control circuit 16. The signal output therefrom is input to the laser light source 2, and a QSW pulse is applied to the laser light source 2. The laser 17 is oscillated. On the other hand, the beam scanner control circuit 5 is operated by the operation control device 1, and the control signal output from the beam scanner control circuit 5 is input to the galvanometer 6 to operate it. The galvanometer 6 controls the angle of the scanner mirror 7 and the irradiation position of the QSW pulse laser 17.
[0029]
The QSW pulse laser 17 oscillated from the laser light source 2 is expanded in beam diameter by the beam expander 4, reflected in a predetermined direction by the scanner mirror 7, converged by the f-θ lens 8, and then reflected by the mirror 9. Irradiate the resistor of the workpiece 10.
[0030]
In the resistor of the workpiece 10, the resistor is evaporated at a portion irradiated with the QSW pulse laser 17. Thereby, trimming is performed.
[0031]
On the other hand, the electrical resistance value of the resistor is detected by the probe 12, and this detection signal is input to the electrical resistance measuring device 13 to calculate the electrical resistance value of the resistor. The electrical resistance measuring device 13 sends the electrical resistance value as an electrical signal to the measured value change amount calculation / laser pulse interval control device 15 where the change amount of the electrical resistance value before and after the laser pulse irradiation and the laser pulse irradiation period. The optimum pause time is calculated, and this result is output and input to the operation control device 1. In response to this result, the operation control device sends a control signal to the laser oscillation control circuit and reflects it in the timing when the next laser pulse is irradiated.
[0032]
Next, the laser trimming method in the present embodiment will be described. The laser trimming apparatus used in this embodiment is the apparatus shown in FIG. In the laser trimming method of the present embodiment, until one pulse before the end of trimming, the beam scanner is scanned with a constant byte size as before, and trimming is performed by irradiating the resistor with laser pulses. At this time, the change amount ΔR of the electrical resistance value before and after the laser pulse irradiation and the difference ΔRfm between the target value and the measured value of the electrical resistance value are calculated for each laser pulse, and the final laser pulse is reached when ΔRfm becomes equal to or less than ΔR. The timing to irradiate is changed. However, ΔRfm is a value obtained by subtracting the measured value from the target value, and ΔR is a value obtained by subtracting the measured value before the laser pulse from the measured value after the laser pulse.
[0033]
The initial setting value of the pause time during the laser pulse irradiation period is T, the value of ΔRfm when ΔRfm is less than or equal to ΔR is ΔRend, and the pause time from the immediately preceding laser pulse irradiation to the next laser pulse irradiation When Tend is set, Tend is determined by Equation 1 above.
[0034]
In this case, since the time required for calculating the ΔR needs to be less than the Tend, a high-speed arithmetic device may be used for calculating the ΔR. In the laser trimming apparatus shown in FIG. 1, ΔR is calculated by the measurement value change amount calculation / laser pulse interval control device 15. The measurement value change amount calculation / laser pulse interval control device 15 is a digital device capable of high-speed calculation. It is preferable to use a signal processor.
[0035]
Next, the effect of the present embodiment will be described. FIG. 2 is a diagram illustrating the relationship between the timing of laser pulse irradiation and the change in the electrical resistance value of the resistor in the laser trimming method of the present embodiment. In FIG. 2, the values of ΔRend in the resistors R1, R2, and R3 are denoted as ΔRend1, ΔRend2, and ΔRend3, respectively, and the values of Tend in the resistors R1, R2, and R3 are denoted as Tend1, Tend2, and Tend3, respectively. FIG. 4 is a diagram showing the relationship between the timing of laser pulse irradiation and the change in the electrical resistance value of the resistor in the conventional laser trimming method. As shown in FIGS. 2 and 4, in the method of this embodiment, when the resistors R1, R2 and R3 having different initial electric resistance values are subjected to laser trimming, the initial electric resistance values are also different from each other by the conventional method. Compared with the case where the resistors R4, R5, and R6 are subjected to laser trimming, the final variation in electric resistance value is extremely small, and a value substantially equal to the target value can be realized.
[0036]
The reason for this will be described. FIG. 3 is a plan view showing laser pulse irradiation positions in the resistors R1, R2 and R3 shown in FIG. By adjusting the Tend according to the value of the ΔRend, the byte size in the final laser pulse irradiation is adjusted. Thereby, the electric resistance value change ΔR due to the last laser pulse irradiation is optimally adjusted, and the electric resistance value after trimming is controlled to be substantially equal to the target value Rf.
[0037]
For example, for the resistor R2 shown in FIGS. 2 and 3, when the difference ΔRfm between the target value and the measured value of the electrical resistance value becomes a value ΔRend2 smaller than ΔR after the n−1th pulse irradiation, n− The pause time Tend2 from the first pulse irradiation to the n-th pulse irradiation is expressed as Tend2 = ΔRend2 / ΔR × T from Equation 1. Here, assuming that the trimming speed is V, the relationship between the pause time T and the byte size L during the laser pulse irradiation period is expressed by the following Equation 2.
[0038]
[Expression 2]
L = V × T
[0039]
Therefore, the final byte size Lend2 in the resistor 2 is given by the following formula 3.
[0040]
[Equation 3]
Lend2 = V × Tend2 = V × T × ΔRend2 / ΔR = L × ΔRend2 / ΔR
[0041]
Here, when the coefficient of the measured value change amount ΔR with respect to the byte size L is k, the following formula 4 is established.
[0042]
[Expression 4]
ΔR = k × L
[0043]
Therefore, the change amount ΔRn2 of the electrical resistance value of the resistor 2 due to the final pulse irradiation is given by the following formula 5.
[0044]
[Equation 5]
ΔRn2 = k × Lend2 = k × L × ΔRend2 / ΔR = ΔRend2
[0045]
As described above, the change amount ΔRn2 of the electrical resistance value of the resistor 2 due to the final pulse irradiation is equal to the difference ΔRend2 between the target value Rf of the electrical resistance value and the electrical resistance value before the final pulse irradiation. Therefore, the method of this embodiment can eliminate trimming overshoot and make the electric resistance value after trimming substantially coincide with the target value.
[0046]
By the way, the measured value change amount ΔR is not constant and increases as the trimming distance increases. The coefficient k of the electrical resistance value change amount ΔR with respect to the bite size L defined by Equation 4 is a function of the trimming distance. Therefore, the accuracy of laser trimming is calculated by calculating the coefficient k by a mathematical method such as moving average or least square method, and estimating the amount of change ΔRn of the resistance value of the resistor due to the final pulse irradiation before the final pulse irradiation. Can be further improved. In this case, Tend is given by Equation 6 below.
[0047]
[Formula 6]
Tend = ΔRend / (k × V)
[0048]
In the trimming method of the present embodiment, the final electrical resistance value is controlled by adjusting the pause time during the laser pulse irradiation period. Therefore, the trimming speed is constant until the end, and the efficiency is improved by reducing the trimming speed. There is no reduction. In addition, since the adjustment of the pause time does not involve a mechanical operation, a delay time associated with the mechanical operation does not occur.
[0049]
In this embodiment, since the digital signal processor is used to measure the amount of change in the electric resistance value of the resistor, the calculation speed is sufficiently fast, and it is impossible to follow the change in the electric resistance value. The problem that the error increases and the trimming accuracy decreases does not occur.
[0050]
Furthermore, according to the trimming method of the present embodiment, trimming can be performed with extremely high accuracy, so that it is not necessary to repeatedly perform laser pulse irradiation for final adjustment of the electric resistance value, and a laser processing groove in a good state can be formed. Can be formed.
[0051]
【The invention's effect】
As described above in detail, according to the present invention, it has conventionally occurred inevitably without causing a decrease in machining efficiency due to a reduction in machining speed and without causing damage to the resistor due to excessive pulse irradiation. The overshoot error due to the last laser pulse irradiation can be eliminated, and the trimming accuracy can be improved. Therefore, for example, in a small component such as a microresistive chip, high-precision laser trimming is realized while maintaining the processing speed at a high speed, and a great effect is exhibited in improving productivity.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a laser trimming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating the relationship between the timing of laser pulse irradiation and the change in the electrical resistance value of a resistor in the laser trimming method of the embodiment.
FIG. 3 is a plan view showing laser pulse irradiation positions on resistors R1, R2 and R3 in the laser trimming method of the embodiment.
FIG. 4 is a diagram showing a relationship between a laser pulse irradiation timing and a change in electric resistance value of a resistor in a conventional laser trimming method.
FIG. 5 is a plan view showing laser pulse irradiation positions on resistors R4, R5 and R6 in a conventional laser trimming method.
[Explanation of symbols]
1; operation control device 2; laser light source 3; galvanometer type laser beam scanner 4; beam expander 5; beam scanner control circuit 6; galvanometer 7; scanner mirror 8; Mounting table 12; Probe 13; Electrical resistance measuring instrument 14; XY table 15; Measurement value variation calculation / laser pulse interval control device 16; Laser oscillation control circuit 17; QSW pulse laser 18; The electrical resistance value 22 of the resistor R2; the electrical resistance value 24 of the resistor R3; the power 25 of the laser that irradiates the resistor R1; the power 26 of the laser that irradiates the resistor R2; the resistor R3 Laser power to be irradiated 27; laser pulse 31; laser trimming groove 32 in resistor R1; The trimming groove 33; the laser trimming groove 34 in the resistor R3; the irradiation position 41 of the pulse laser; the electric resistance value 42 of the resistor R4; the electric resistance value 43 of the resistor R5; the electric resistance value 44 of the resistor R6; Laser power 45 for irradiating the resistors R4, R5 and R6; laser pulse 46; variation in electric resistance value 51 after trimming; laser trimming groove 52 in the resistors R4, R5 and R6; irradiation position of the pulse laser

Claims (4)

In a laser trimming method for trimming the resistor by intermittently irradiating a laser pulse while measuring an electrical resistance value of the resistor, a final target value of the electrical resistance value of the resistor and a measured value during laser trimming difference and ΔRfm of a, the variation of the measured value of one said electrical resistance value that changes by laser pulse irradiation of the [Delta] R, the initial set value of the pause time of the laser pulse irradiation is T, the ΔRfm is A laser trimming method , wherein Tend is determined by the following equation, where Tend is a pause time from the immediately preceding laser pulse irradiation to the next laser pulse irradiation when ΔR or less .
Tend = ΔRfm / ΔR × T The laser trimming method according to claim 1 , wherein a Q-switched laser pulse is used as the laser pulse. Laser oscillation means for intermittently oscillating a laser pulse, optical system control means for controlling the path of the laser pulse, transport means for mounting a workpiece and controlling the position of the workpiece, and the workpiece Measuring means for measuring the electrical resistance value of the resistor in the inside, connected to the laser oscillation means, the optical system control means, the transport means and the measuring means, and by controlling them, the resistance of the workpiece In a laser trimming apparatus comprising an operation control means for performing an arbitrary trimming process and adjusting an electrical resistance value, a final target value of an electrical resistance value of the resistor and a measured value during laser trimming Let ΔRfm be the difference, ΔR be the amount of change in the measured value of the electrical resistance value that changes with a single laser pulse irradiation, and T And calculating means for determining Tend according to the following formula, when Tend is a pause time from the immediately preceding laser pulse irradiation to the next laser pulse irradiation when ΔRfm becomes equal to or less than ΔR. Laser trimming device.
Tend = ΔRfm / ΔR × T The laser trimming apparatus according to claim 3 , wherein the laser pulse is a Q-switched laser pulse.

Images