JPH0824218B2 - Wiring board - Google Patents

Description

The present invention relates to a wiring board, and more particularly to a wiring board suitable for trimming a mounted trimming element such as a chip resistor by a laser beam.

B. Conventional Technology When various circuit elements are mounted on a wiring board to form a target circuit, it is desirable that the characteristics and functions of the circuit can be adjusted with high accuracy from the outside.

Conventionally, as one method capable of realizing such circuit adjustment with high accuracy, as shown in FIG. 3, both ends of the rectangular chip resistor 3 are connected to the wiring patterns 2 and 2 formed on the wiring board 1 by soldering or the like. On the surface of this chip resistor 3,
By irradiating a YAG (yttrium-aluminum-garnet) laser beam, for example, on an inverted L-shaped pattern shown by reference numeral 4, trimming is performed to a preset resistance value.

By the way, the effective focal depth of the beam focusing lens used for the YAG laser is about 2 mm. Therefore, if the chip resistance is present within the depth of focus, even if the laser irradiation point of the chip resistance varies in the beam optical axis direction due to bending deformation of the wiring board, etc., there is no problem in laser trimming of the chip resistance. .

C. Problem to be Solved by the Invention However, since the effective depth of focus of the laser is about 2 mm, the thickness of the chip resistor is about 0.6 mm,
When the laser beam is focused on the surface of the chip resistor, the surface of the wiring board is also positioned within the effective depth of focus of the laser.

On the other hand, in the case where the inverted L-shaped trimming shown in FIG. 3 is formed on the surface of the chip resistor 3, the irradiation start point of the laser beam starts from the position P of the substrate surface which is separated from the edge of the chip resistor 3. Therefore, when trimming the mounted chip, the surface of the substrate is always irradiated with the laser beam to form a flaw 5 on the surface, and the depth of the flaw becomes 200 μ or more. Therefore, it is necessary not to provide a wiring pattern in the laser beam irradiation area.

Further, in the multilayer wiring board, there is an inner layer wiring pattern in addition to the surface wiring pattern, but it is necessary to take the same measure for this inner layer wiring pattern, which causes a problem that the wiring density decreases.

A technical problem of the present invention is to protect a substrate from a trimming laser beam and to improve quality and wiring density.

D. Means for Solving the Problem The present invention will be described with reference to FIG. 1 showing an embodiment. According to the present invention, wiring having one or more wiring patterns and capable of mounting a laser trimming element 17 is provided. Of the substrate surface which is applied to the substrate 10 and on which the laser trimming element 17 is mounted, the irradiation of the laser beam onto the substrate surface is protected in a predetermined area including at least the laser beam irradiation target area and the peripheral area of the laser trimming element 17. The above technical problems can be achieved by forming the white laser protect pattern 20.

E. Action When trimming the laser trimming element 17, the laser beam applied to the laser protect pattern 20 is reflected by the laser protect pattern 20, so the surface of the wiring board is protected from the laser beam.

It should be noted that, in the above-mentioned items D and E for explaining the configuration of the present invention, the drawings of the embodiments are used to make the present invention easy to understand, but the present invention is not limited to the embodiments.

F. Examples Hereinafter, examples of the present invention will be described with reference to the drawings.

1 and 2 show an embodiment of a wiring board according to the present invention. FIG. 1 is a partial plan view, and FIG. 2 is a sectional view taken along line II-II of FIG. is there.

In the figure, 10 is a wiring board having a wiring pattern of four layers, outer layer patterns 11 and 12 are formed on both sides of the wiring board, and inner layer patterns 13 and 14 are formed in two layers inside the board. Further, reference numerals 15 and 16 are solder resist layers formed on the outer surface of the wiring substrate 10 on which the outer layer patterns 11 and 12 are formed.

Reference numeral 17 denotes a chip resistor for laser trimming which is connected to one outer layer pattern 11 of the wiring board 10 by a soldering method or the like, and the back surface of the chip resistor 17 and the outer surface of the wiring board 10 corresponding to the left and right peripheral portions are A white pattern 20 for protecting the laser beam is formed by screen printing or the like so as to cover these areas. This white pattern 20
Is to prevent the laser beam from irradiating the surface of the wiring board when trimming the chip resistor 17.
The characters and symbols are printed at the same time as the screen printing on the wiring board 10.

When trimming the chip resistor 17 mounted on the wiring board 10 with a laser beam such as a YAG laser, the wiring board 10
By operating an XY table (not shown) on which is mounted a laser beam, a point P on the white pattern 20 which is separated from one side edge of the chip resistor 17 by a predetermined distance is irradiated with a laser beam as shown in FIG. Set the start position.

By doing so, the time from the start of the laser source to the stabilization of the laser output is secured, and the trimming start point for the chip resistor 17 is stabilized.

If the irradiation start position of the laser beam is determined at the point P, the laser source is started and at the same time, X-
The Y table is moved to feed the wiring board 10 to operate. As a result, the surface of the chip resistor 17 is irradiated with a laser beam in the shape of an inverted L shown by reference numeral 19 for trimming. A laser beam having an effective depth of focus of about 2 mm is used at this time.

The resistance value of the chip resistor 17 at the time of trimming is monitored by a measuring device (not shown).

On the other hand, when the laser beam is irradiated on the white pattern 20, a slight scratch 20a is generated on the white pattern 20, but since a part of the laser beam is reflected by the white pattern 20, it penetrates the white pattern 20. The amount of laser beam reaching the surface of the wiring board 10 is greatly reduced, and as a result, the wiring board
The damage that occurs on the surface of 10 is smaller than in the conventional case.

As described above, in the present embodiment, when the chip resistor 17 is laser-trimmed, the laser beam applied to the substrate surface is blocked by the copper pattern 18, so that the wiring substrate 10 may be damaged by the trimming laser beam. Disappear. Along with this, the inner layer pattern can be freely routed inside the substrate regardless of the laser irradiation area, the wiring density can be improved, and the quality of the wiring board can be improved. Also,
The influence of the laser can be ignored regardless of the material, thickness, etc. of the base material (paper, glass, etc.) that constitutes the wiring board and its binder (phenol resin, epoxy resin, etc.).

Incidentally, according to the experimental results, when the surface of the wiring board 10 was directly irradiated with a YAG laser beam having an output suitable for trimming, the depth of scratches generated on the surface of the wiring board 10 was 200 μ or more. In contrast, through the white pattern 20
It was confirmed that the depth of the scratch generated on the surface of the wiring substrate 10 when irradiated with the YAG laser beam was 100 μm or less.

Therefore, the inner layer pattern inside the substrate is not affected by the trimming laser at all, and the inner layer pattern can be freely routed.

Further, when the chip resistor 17 is pattern-recognized and laser trimming is automatically performed, the white pattern 20 facilitates recognition of the trimming resistor, and attempts to replace the chip resistor with a new chip resistor due to failure in trimming the chip resistor or the like. At this time, the white pattern 20 serves as a mark of the resistor which is not properly trimmed, so that the resistor can be easily identified.

The present invention can be applied not only to resistors but also to trimming capacitors, inductors and the like.

The area where the laser protect pattern is formed is not limited to the area shown in FIG.

G. Effect of the Invention According to the present invention, since the laser protect pattern is formed in the laser beam irradiation target area of the substrate surface on which the laser trimming element is mounted, the surface of the wiring board is trimmed by the reflection action of the laser protect pattern. It is possible to protect from the laser beam for use and to improve the quality of the substrate and the wiring density. In addition, since the white laser protect pattern is formed up to the peripheral area of the laser trimming element, when the laser trimming element is pattern-recognized and laser trimming is automatically performed, the laser trimming element can be easily recognized. When a trimming element is replaced with a new trimming element due to a failure in trimming or the like, the laser protect pattern serves as a mark of the trimming element, which facilitates identification.

[Brief description of drawings]

1 is a plan view of a part of a wiring board showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line II-II of FIG. FIG. 3 is a partial plan view showing a conventional wiring board. 10: Wiring board, 11, 12: Outer layer pattern 13, 14: Inner layer pattern, 17: Chip resistor 20: White pattern

Claims (1)

[Claims] 1. A wiring board having a wiring pattern of one or more layers and capable of mounting a laser trimming element, wherein at least a laser beam irradiation target area and the laser trimming are provided on a substrate surface on which the laser trimming element is mounted. A wiring board, characterized in that a white-based laser protection pattern is formed in a predetermined area including a peripheral area of the element to protect the surface of the board from irradiation with a laser beam.