JPH0640563B2 - Laser trimming method for membrane resistor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for trimming a film resistor with a laser beam, and more particularly to a laser trimming method for preventing damage to a base insulating film of the film resistor.

[Technical background of the invention and its problems]

Recently, electronic devices have been remarkably reduced in size and thickness, and accordingly, demands for miniaturization of various electronic components have been increased. In order to meet this demand, for example, regarding resistors, chip components are becoming widespread in place of axial lead type elements, and ruthenium oxide-based or carbon-based thick film printing resistors are also widely used. Contributes significantly to thin mounting.

By the way, since it is difficult to accurately form a film resistor such as these thick film printed resistors to a target resistance value,
After printing and firing, a trimming process is required to remove a part of the resistor and adjust it to a predetermined resistance value. As the trimming method, there are a sandblast method in which alumina powder of a resistor is sprayed to scrape the resistor, and a laser trimming method in which a part of the resistor is removed by irradiation with a laser beam. The latter laser trimming method has been particularly popular recently because it is easy to control by computer and has a large processing capability, and is often applied to a ruthenium oxide resistor formed on an alumina substrate.

However, since the laser trimming method irradiates a resistor with a laser beam having a considerably large power as a minute spot, there is almost no problem when the base material is an inorganic material such as alumina. When a material is used, there is a problem that the laser beam reaches the resin below the resistor to damage it. In particular, on a metal core printed wiring board that requires high heat dissipation using a metal substrate having a resin-based insulating film formed on the surface, damage to the resin under the resistor lowers the withstand voltage of the insulating film. It becomes a fatal defect.

[Object of the Invention]

The present invention has been made in view of such problems, and an object thereof is to irradiate a film resistor formed on a resin-based insulating film with a laser beam for trimming, and to perform insulation film under the film resistor. It is to provide a laser trimming method that does not damage the laser.

[Outline of Invention]

To achieve this object, the present invention forms a resin-based insulating film containing a white pigment in advance in the lower layer portion of the film resistor, and in that state, the film resistor is irradiated with a laser beam to perform trimming. Characterize.

〔The invention's effect〕

According to the present invention, since the resin-based insulating film under the film resistor contains the white pigment and has light reflectivity, the laser beam applied to the film resistor during trimming is reflected by the insulating film. It Therefore, there is no risk of the laser trimine damaging the resin-based insulating film below the film resistor, and it is possible to prevent the deterioration of the electrical characteristics, especially the decrease in the body voltage of the insulating film.

Example of Invention

An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

First, as shown in FIG. 1A, a resin-based insulating film 2 containing a white pigment is applied / formed as a base layer on a base material 1. The base material 1 may be a metal substrate, an insulating substrate, a printed wiring board, or the like.

As the resin component serving as a base in the insulating film 2, for example, at least one selected from polybutadiene resin, epoxy resin, polyimide resin, phenoxy resin, bismaliimide resin acrylic resin, and phenol resin can be used. Of these, 1,2 polybutadiene resin is particularly suitable because it has a low degree of yellowing, is less likely to be damaged by laser beam irradiation, and has excellent heat resistance and electrical characteristics as a circuit yellow plate material. On the other hand, as the white pigment, at least one selected from titanium oxide, zinc oxide, basic lead carbonate, barium sulfate, zinc sulfide, basic lead sulfate, antimony oxide, silica, and alumina can be used.
The resin-based insulating film 2 is formed by coating the above resin by kneading and preparing it on the base material 1 to a thickness of, for example, about 5 μm to 200 μm. Among the white pigments listed above, titanium oxide is particularly suitable because it has a high reflectance with respect to the YAG laser output of 1.06 μm wavelength light and is excellent in heat resistance and electrical characteristics. Is.

Here, the content of the white pigment in the resin-based insulating film 2 is 1w.
t. % -60 wt. % Is desirable. This has a white pigment content of 1 wt. If it is less than%, almost no effect can be expected in achieving the purpose, and 60 wt. If it exceeds%, the dielectric constant of the insulating film 2 is excessively increased, and as a result, problems such as a large amount of crosstalk noise in the circuit and a signal delay occur. Further, it is perfectly acceptable to add a solvent, a thixotropic agent or the like to the resin-based insulating film 2 for the purpose of improving the coating property and workability. As a resin coating method for forming the resin insulating film 2, any method such as a screen printing method, a spinner coating method, or a dipping method may be used. Furthermore, the resin-based insulating film 2 may be applied / formed on the entire surface of the substrate 1, or may be selectively formed only in the region where the film resistor is formed or in the vicinity thereof.

Next, as shown in FIG. 1B, the film resistor 3 and the electrode 4 are formed to produce a resistance element. The film resistor 3 is a thick film printed resistor or a thin film resistor. As the thick film printed resistor, for example, a carbon printed resistor can be used, and as the thin film resistor, for example, RuO ₂ , TaN, Ta _{2 is used.}
Sputtered film resistance such as O ₃ or NiCr, or Ni plating resistance can be used.

Next, as shown in FIG. 1C, a laser beam 5 is irradiated onto the film resistor 3 to perform laser trimming. For the laser trimmer, for example, YAG laser (wavelength 1.06 μm)
Can be used, and it may be performed in the same manner as the laser trimming that is conventionally performed on the RuO ₂ resistor directly formed on the alumina ceramic substrate. The trimming form may be single cut, double cut, L cut, serpentine cut, or the like.

FIG. 2 shows the film resistor 3 after the laser trimming is performed in this way, and in the example of the figure, L-cut laser trimming is performed as indicated by symbol 6. Next, more specific examples and comparative examples of the present invention will be described.

Example A hard aluminum (JIS A-2017) plate (thickness: 2 mm) was prepared as a substrate, and after blasting the surface, trichlene washing was performed and an insulating resin having the following composition was screen-printed on the substrate surface.

Then, after drying at 180 ° C. for 15 minutes, the product is dried in a nitrogen atmosphere at 37
Heated and cured at 0 ° C for 15 minutes, thickness 140 μm
To obtain a white resin-based insulating film. A carbon printed resistor was formed as a film resistor on the insulating film by screen printing, dried at 130 ° C. for 15 minutes, and an electrode was printed / formed using a resin-based copper paste.
Firing was performed at 0 ° C. for 15 minutes to obtain a film resistance substrate. Between the electrode on this membrane resistance substrate and the aluminum substrate 5
A withstand voltage test of [KV] × 10 [sec] was performed, and a laser trimmer (LA manufactured by Toshiba
Y-711) was used to perform L-cut trimming under conditions of an output of 6 W, a beam diameter of 50 μm, and a scan speed of 30 mm / sec. When the periphery of the film resistor after the laser trimming was observed with a microscope, it was confirmed that only the film resistor was cut without any damage on the surface of the resin-based insulating film.

Also, for the same film resistance substrate, 5 [KV] × 10 [sec
], No damage was found in the resin-based insulating film even in the result of testing 50 samples.

Comparative Example 1 A stainless steel plate having a thickness of 0.5 mm was used as a base material, and a polybutadiene resin was spinner-coated, followed by heating and curing at 370 ° C. for 10 minutes in a nitrogen atmosphere to obtain a film thickness of 100.
A transparent resin-based insulating film of μm was obtained. Next, a carbon printing resistor and a copper paste were sequentially screen-printed on the insulating film, and baked at 370 ° C. for 5 minutes in a nitrogen atmosphere.
Then, when L-cut trimming was performed under the same apparatus and conditions as in Example and the surface was observed, there was no scratch on the surface of the resin-based insulating film, but a groove-like scratch was found on the stainless steel plate as the base material. Moreover, it was confirmed that many cracks were generated at the boundary between the insulating film and the stainless steel plate. Also, 5 [K
When a withstand voltage test of V] × 10 [sec] was performed, it was 5
A defect occurred in 41 out of 0 samples.

Comparative Example 2 The same aluminum hard plate as in the example was used as the base material,
After performing the same pretreatment as in the example, an insulating resin having the following composition was screen-printed on the surface of the base material.

Then, after drying at 180 ° C. for 20 minutes, 37 in a nitrogen atmosphere
When it was heated and cured at 0 ° C. for 5 minutes, a brown-colored resin-based insulating film was obtained. A carbon printing resistor and a copper paste were sequentially screen-printed on this insulating film, and then heated at 370 ° C. for 5 minutes in a nitrogen atmosphere to be cured to obtain a film resistance substrate. A 5 [KV] × 10 [sec] withstand voltage test was performed between the electrode on the film resistance substrate and the aluminum base material, and the passed substrate was L-cut trimmed under the same apparatus and conditions as in the example. As a result of observing the periphery of the film resistor with a microscope after the trimming, it was confirmed that the resin-based insulating film also had cracks and kerfs, and that the laser trimming significantly damaged the insulating film. Further, as a result of performing the same withstand voltage test on 50 samples, 13 samples failed.

As is clear from the above Examples and Comparative Examples, according to the method of the present invention in which a resin-based insulating film containing a white pigment is previously formed in the lower layer of the film resistor, and laser trimming is performed in that state, As a result of the insulating film having the effect of reflecting the laser beam by the white pigment component contained therein, it is possible to perform laser trimming without damaging the insulating film and the underlying material. It is possible to contribute to the improvement of withstand voltage characteristics and the yield of the film resistor.

[Brief description of drawings]

FIG. 1 is a process diagram for explaining a laser trimming method for a film resistor according to an embodiment of the present invention, and FIG. 2 is a view showing the film resistor after the laser trimming process in the same embodiment. 1 ... Substrate, 2 ... Resin-based insulating film, 3 ... Membrane resistor, 4
... electrodes, 5 ... laser beam.

Claims (4)

[Claims] 1. A laser trimming method for irradiating a film resistor with a laser beam so as to obtain a predetermined resistance value, wherein a resin-based insulating film containing a white pigment is previously formed in a lower layer of the film resistor. A laser beam method for a film resistor, wherein laser trimming is performed in that state. 2. A patent using at least one selected from titanium oxide, zinc oxide, basic lead carbonate, barium sulfate, zinc sulfide, basic lead sulfate, antimony oxide, silica and alumina as the white pigment. A laser trimming method for a film resistor according to claim 1. 3. At least one selected from polybutadiene resin, epoxy resin, polyimide resin, phenoxy resin, bismaliimide resin acrylic resin, and phenol resin is used as a resin component in the resin-based insulating film containing the white pigment. A laser trimming method for a film resistor according to claim 1. 4. The content of the white pigment in the resin-based insulating film is 1 wt. % -60 wt. The laser trimming method for a film resistor according to claim 1, wherein the ratio is%.