KR20080043202A - Method of laser-trimming for resistor-embedded printed circuit board - Google Patents

Abstract

A method of laser-trimming for a resistor-embedded printed circuit board is provided to implement management of resistance tolerance of less than ±1% regardless of resistor material by offsetting a resistance measurement error due to heat generated in a laser process of a resistor. A method of laser-trimming for a resistor-embedded printed circuit board includes the step of: finely controlling a resistance by forming a rectangular resistor(20) by printing the resistor with predetermined length and width with carbon paste on a screen between a pair of copper clad electrode pads(10) and then locally removing the carbon paste by irradiating laser beams on a surface of the resistor, wherein a trim process is performed by irradiating the laser beam with measuring the resistance in real time through probes(40) in contact with the both copper clad electrodes and heat of a region of the resistor with a trim(100) is discharged to cool the resistor by locally injecting air on the surface of the resistor on which the trim process is performed through an air nozzle(80).

Description

METHOD OF LASER-TRIMMING FOR RESISTOR-EMBEDDED PRINTED CIRCUIT BOARD}

1 is a view showing a process of proceeding a laser trim in accordance with a preferred embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

10: resistor electrode pad

20: carbon resistor

30: resistance meter

40: Probe

70: compressed air tank

80: air nozzle

90: laser device

100: laser trimmed resistor site

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistor-embedded printed circuit board, and more particularly, to a technique for precisely controlling resistance values by applying a laser trim in the process of manufacturing a resistor on a substrate. will be.

In order to improve the portability and function of electronic devices, embedded PCB technology has been introduced in the art to embed active or passive components in a substrate. When the active component or the passive component is embedded in the substrate, the substrate can be miniaturized, the mounting density of the component is increased, and the high frequency characteristics of the mounting circuit are improved. Currently, in the printed circuit board industry, development is mainly focused on a technology for embedding passive components due to the nature of the embedded substrate manufacturing process. Embedded substrate manufacturing technology may be classified into a technology of inserting an existing chip-shaped component into the substrate, and a technology of manufacturing embedded components by applying thin film or thick film technology. Typical embedded board passive components include resistors, capacitors and inductor coils.

The technology for manufacturing a resistor embedded in a printed circuit board is disclosed in Korean Patent No. 639,063 filed by the applicant of the present invention to paste a carbon resistor. Korean Patent No. 639,063 discloses a technique of carbon printing by determining a horizontal length and a vertical length of a carbon resistor using a photosensitive resist instead of an emulsion printing technique.

In addition, Patent Nos. 486,750 and 585,203 of the applicant of the present invention disclose a carbon paste resistor manufacturing technique. In the prior art disclosed in the document, an electrode pad is formed on a substrate and a carbon resistor is pasted on the electrode pad. After the printing process to form the resistor, manufacturing tolerances generally occur, so that the process of adjusting the target resistance value through the laser trim process is subsequently performed.

That is, manufacturing tolerances of about 10 to 20% for thin film resistive materials and about 15 to 30% for thick film resistive materials occur, and these tolerances may be due to variations in sheet resistance of the resistor material itself or PCB manufacturing. It occurs in the resistance size tolerance, etc. generated in the process.

Therefore, in the art, the resistance value is tuned through the laser trim to control the tolerance of the internal resistor within 5 to 10%. The laser trim connects the probe connected to the resistance measuring device to both electrodes of the built-in resistor, which has a resistance value of about 20 to 50% lower than the specified target resistance value, and measures the resistance value in real time while processing the resistor part with a laser. It is a method of matching the target resistance value. In this case, a fixed jig method or a moving probe method is used as the resistance measurement probe.

However, in the above-described laser trimming process, the laser beam irradiates the surface of the resistor to process the resistor to generate heat of more than several hundred degrees Celsius in the resistor portion, and the generated heat increases the resistance value of the thin film resistor as the temperature increases. There is a problem of causing an error in measuring the resistance of the resistor by lowering or lowering the resistance. That is, in general, an alloy-type thin film resistor has a higher resistance value as the temperature increases, and a carbon polymer-type thick film resistor has a tendency to decrease its resistance value with increasing temperature. As a result, even if the resistance processing tolerance of the equipment is set to ± 1% due to the heat generated during the laser trim processing, there is a problem that the resistance value after the actual processing is about 3%.

This technical problem is that the smaller the size of the built-in resistor, the greater the influence of heat distribution, which makes precise resistance tolerance management more and more difficult. In addition, the resistance value of the embedded resistor is subjected to high temperature thermal shock during reflow soldering in a component assembly process after the PCB manufacturing is completed, and when the resistance value is changed, the resistance range is about 2 to 3%.

As a result, when the resistance tolerance range generated in the laser trim process and the resistance change generated in the component assembly process are combined, the resistance tolerance is about ± 5% or more. Considering that the tolerance of the built-in resistance required in the art is ± 5%, a technique for managing resistance measurement error within ± 1% during laser trimming is needed.

Accordingly, an object of the present invention is to provide a laser trim process technology capable of managing resistance tolerances of less than ± 1% in manufacturing a resistor-embedded printed circuit board.

In order to achieve the above object, the present invention provides a method for forming a built-in resistor on a printed circuit board, the resistor is formed by screen printing a rectangular resistor having a predetermined length and width with a pair of copper foil electrode pads therebetween with carbon paste. After the formation, the surface of the rectangular carbon paste resistor is irradiated with a laser beam to locally remove the carbon paste to finely adjust the resistance value, while measuring the resistance value in real time by contacting both copper foil electrodes of the resistor with a probe. The printed circuit board is irradiated with the laser beam to perform a trimming process and by spraying air to the surface of the resistor to which the trim proceeds through an air nozzle to radiate and cool the heat of a portion of the resistor to be trimmed. It provides a method of manufacturing a built-in resistor.

Hereinafter, with reference to the accompanying drawings Figure 1 will be described in detail a preferred embodiment of the present invention.

1 is a view showing a process of proceeding a laser trim in accordance with a preferred embodiment of the present invention. Referring to Figure 1, the present invention is characterized in that the cooling device for cooling the substrate is mounted, the cooling device according to a preferred embodiment of the present invention, through a pipe connected to the general compressed air tank 70, the laser Air is sprayed on the surface of the substrate where the trim is in progress with the air nozzle 80 to radially cool the temperature of the surface of the resistor. In this case, the air injected may be used, and a cooling device may be mounted between the compressed air tank 70 and the nozzle 80 to inject air lower than room temperature.

As a preferred embodiment of the present invention, the pressure of the compressed air can be maintained at 100 Pa to 100 MPa. The laser beam spot size used in the laser trimming process is usually 100 μm or less, and the heat distribution area generated by the resistor is also limited to a small area of up to several hundred micros. This local heat can be easily cooled in the same manner as air injection. It can dissipate heat.

The air jet cooling technology according to the present invention can be applied to both a moving probe type as well as a fixed jig type resistance measuring system through a method of mounting an air nozzle to a probe module portion of a resistance measuring device.

Referring again to FIG. 1, a carbon resistor 20 pasted by silk screen printing is formed on an electrode pad 10 of a substrate, and an electrode pad 40 contacted with a probe 40 with a resistance meter 30. The trim 100 is formed by irradiating a laser beam with the laser apparatus 90, measuring the resistance value between them. At this time, the air nozzle 80 lowers the temperature by locally injecting air to the trim 100 to radiate heat.

The foregoing has outlined rather broadly the features and technical advantages of the present invention to better understand the claims of the invention which will be described later. Additional features and advantages that make up the claims of the present invention will be described below. It should be appreciated by those skilled in the art that the conception and specific embodiments of the invention disclosed may be readily used as a basis for designing or modifying other structures for carrying out similar purposes to the invention.

In addition, the inventive concepts and embodiments disclosed herein may be used by those skilled in the art as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. In addition, such modifications or altered equivalent structures by those skilled in the art may be variously evolved, substituted and changed without departing from the spirit or scope of the invention described in the claims.

As described above, the present invention reduces the resistance measurement error due to heat generated during laser processing of the resistance by using the laser trim equipment adopting the cooling device, thereby reducing the laser trim tolerance to less than ± 1% regardless of the resistive material. Provided is a method for manufacturing a register-embedded substrate that enables management.

Claims (1)

A method of forming a built-in resistor in a printed circuit board, wherein the rectangular carbon paste resistor is formed by screen printing a rectangular resistor having a predetermined length and width with a pair of copper foil electrode pads therebetween with carbon paste to form a resistor. The laser beam is irradiated on the surface of the surface to remove the carbon paste locally to finely adjust the resistance value. However, the trimming process is performed by irradiating the laser beam while measuring the resistance value in real time by contacting both copper foil electrodes of the resistor with a probe. A method of manufacturing an embedded resistor of a printed circuit board, characterized by radiating and cooling heat of a portion of a resistor to be trimmed by locally injecting air through an air nozzle onto a surface of the resistor to which the trim is advanced.

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