JPH027482Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a printed circuit board in which a chip resistor is installed between terminals formed in a wiring pattern of the printed circuit board and then cut and trimmed with a laser beam.

(Background of the Idea) In recent years, chip resistors 1 without lead wires, as illustrated in FIGS. 1 and 2, have been increasingly used as elements constituting electric circuits.

That is, the chip resistor 1 is made of ceramic plate 1.
Internal electrodes 12, 12 are formed by plating so as to cover both ends of the internal electrodes 12, 12, respectively.
A resistor 13 is attached to the surface of the ceramic plate 11 across the gap, and a glass coat protective film 14 is applied on the resistor 13.
An external electrode 15 is printed on the external electrode 15, and one of its features is that the resistance value can be easily and reliably adjusted by cutting and trimming with a laser beam.

When it is necessary to adjust the resistance value in many places in an electric circuit, the resistances to be adjusted are gathered in one place to form a resistance block, and variable resistors and semi-fixed resistors with sliding resistance are concentrated in one place. In some cases, the resistance can be adjusted in one place, simplifying the adjustment work. Forming resistor blocks in this way has many other advantages, such as matching temperature characteristics and being able to share power lines, but on the other hand, it also means that resistors are collected from various parts of the electrical circuit. Therefore, the wiring on the board (usually an FPC (flexible printed circuit)) becomes complicated, making pattern design and manufacturing difficult, which increases costs, and in the case of poor adjustment, resistor blocks are used. The disadvantage is that the entire process has to be discarded, resulting in waste.

Therefore, after considering the advantages and disadvantages of the entire electric circuit, the resistor blocks are abolished or reduced in size, and chip resistors 1 as described above are arranged in each part of the circuit.
It has been proposed to adjust the resistance by cutting and trimming the resistor 13 of the chip resistor 1 using a laser beam.

Aside from resistance adjustment, which can only be done after the board is mounted on the device, this proposal is suitable when adjusting the resistors to equalize variations in the characteristics of elements such as ICs that make up the circuit. ing.

As shown in FIGS. 3 and 4, the chip resistor 1 is installed between terminals 31, 31 formed on a wiring pattern 3 attached to a circuit board 2, and external electrodes 15, 15 on both sides are connected to each other. They are fixed and attached to terminals 31, 31, respectively, with solder 32. Note that conductive adhesive may be used instead of solder.

When trimming the resistor 13 of the chip resistor 1, the substrate 2 on which the chip resistor 1 is mounted is placed on the bed 4 of the pallet as shown in FIG. As shown in , the laser beam starts scanning from a starting position a a little away from the side end 16 of the chip resistor 1, passes through a run-up section a1, reaches the side end 16, and passes through the resistor 13 and the glass from there. Trimming to cut the coat protective film 14 is started.

The reason why the run-up section a1 is required in this way is
The width of the terminal 31 is the external electrode 15 of the chip resistor 1.
Although it is easy to install because it is wider than the width of the solder 32, the attitude and position of the chip resistor 1 tends to vary due to the surface tension of the solder 32, and this error must be tolerated, and cutting starts from the side end 16. Otherwise, it will not be electrically stable.

However, when the resistor 13 and glass coat protective film 14 of the chip resistor 1 are actually being cut, the laser beam will not hit the substrate 2 because the ceramic plate 11 is underneath it. However, in the run-up section a1, the laser beam hits the substrate 2. The substrate 2 is usually a rigid substrate such as glass epoxy resin or an FPC made of polyimide resin, and when it is hit by a laser beam, it is burned by the energy and a large amount of gas is generated, which may adhere to other parts of the circuit. There is a risk of problems such as loss of insulation and poor contact, and in order to prevent these problems from occurring, cleaning may even be necessary after trimming. Also, the board 2
There is a problem in that when the burnout occurs and strength-reduced portions 21 such as grooves are formed, the strength may decrease or cracks may occur.

(Purpose of the invention) The present invention has been made by paying attention to such conventional problems, and aims to provide a printed circuit board in which the laser beam does not burn out the board during trimming.

(Summary of the invention) In order to achieve the above object, the present invention provides a printed circuit board characterized by providing a burnout prevention part on the board along the scanning line of the laser beam, and the board is protected by the burnout prevention part. This protection prevents the generation of gas and the formation of parts with reduced strength, thereby preventing the above-mentioned problems from occurring.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. Note that the same parts as in each of the previous figures are given the same reference numerals, and redundant explanation will be omitted.

5 and 6 show the fifth embodiment. Generally, when soldering chip components to a board, the chip components are temporarily fixed with adhesive to prevent them from shifting from the terminals of the wiring pattern. The present embodiment utilizes this.

That is, the burnout prevention portion is formed by extending the adhesive 5 from both ends of the chip resistor 1 to the starting position a by the length of the run-up section a1. In other words, the area where the adhesive is applied is the entire range from the laser scanning start point outside the chip resistor 1 to the laser scanning locus.

In this embodiment, the laser beam is applied to the run-up section a1.
When scanning, it hits the adhesive 5, loses energy there, and does not damage the substrate 2. Needless to say, the adhesive 5 should be made of a material that is difficult to burn out and does not generate harmful gases.

(Effects of the invention) According to the printed circuit board according to the invention, when trimming, the laser beam does not attack the board, so no harmful gases are generated, and problems such as poor insulation do not occur. There is no need for subsequent cleaning. Furthermore, since the strength of the substrate does not decrease, durability is also improved.

[Brief explanation of the drawing]

Figure 1 is a plan view showing an example of a chip resistor;
FIG. 2 is a longitudinal sectional view, FIGS. 3 and 4 show a conventional example, FIG. 3 is a plan view of a board equipped with a chip resistor, and FIG. 4 is a sectional view of FIG. 5 and 6 show a first embodiment of the present invention,
Figure 5 is a plan view of a board equipped with chip resistors;
FIG. 6 is a sectional view of FIG. 5. DESCRIPTION OF SYMBOLS 1... Chip type resistor, 11... Ceramic plate, 12... Internal electrode, 13... Resistor, 14...
...Glass coat protective film, 15...External electrode, 2...
... Board, 3 ... Wiring pattern, 31 ... Terminal, 3
2...Solder, 4...Bed, a...Start position,
a1... Run-up section, 5... Adhesive (burnout prevention part).

Claims (1)

[Claims for Utility Model Registration] The resistance value of the chip resistor can be adjusted by scanning a laser toward the chip resistor from outside the chip resistor and laser-trimming the resistor of the chip resistor. In a flexible printed circuit board in which a chip resistor is installed between terminals formed in a wiring pattern of the flexible printed circuit board, when installing the chip resistor between the terminals by soldering, the chip resistor is An adhesive for temporarily fixing is applied on the flexible printed circuit board between the terminals, and an area where the adhesive is applied extends from the laser scanning start point outside the chip resistor to the laser scanning starting point. A printed circuit board characterized by having a full range including a locus.