JP5077090B2 - Circuit board - Google Patents

Description

  The present invention relates to a circuit board on which a chip is mounted, and more particularly to a circuit board that performs function adjustment by laser trimming.

  In recent years, laser trimming is used for adjusting the resistance value by cutting a printed and fired resistor with a laser to adjust the current and voltage of an electronic circuit. When trimming a resistor with a laser, if the laser is incident on the chip, a semiconductor element constituting the chip is excited by the laser to generate an electromotive force, and the circuit may malfunction.

  Although not a laser, as a method for preventing light from entering the chip, a method of providing a light shielding film on the front and back surfaces of the chip has been proposed (see, for example, Patent Document 1). Also, a method of preventing light incident on the chip by providing a light-shielding film on the surface of the chip and the glass substrate so that vertical light traveling perpendicular to the chip and oblique light incident obliquely on the glass substrate and reflected inside the glass substrate are incident on the chip. Has been proposed (see, for example, Patent Document 2).

  However, in the method of providing a light shielding film on the front surface and the back surface of the chip described in Patent Document 1 and the method of providing the light shielding film on the surface of the chip and a glass substrate described in Patent Document 2, a process for manufacturing the chip However, there is a problem that the structural difficulty and cost increase.

In addition, when trimming with a laser, the chip is covered with a light shielding cover or a resistor is placed away from the chip to prevent the laser from entering the chip, so the component mounting density around the chip is low. There was a problem.
Japanese Patent No. 3547940 Japanese Patent Laid-Open No. 9-5770

  An object of the present invention is to provide a circuit board capable of preventing a laser from entering a chip when trimming with a laser.

According to one aspect of the present invention, in a circuit board that performs function adjustment by laser trimming,
A substrate provided with wiring on the surface, a chip that is electrically connected to the wiring by solder bumps and mounted on the substrate, and a gap formed immediately below the chip on the substrate and formed by solder bumps A first light-shielding film having a light-shielding property with respect to laser light used for laser trimming, and a second light-shielding film having a light-shielding property with respect to the laser light used for laser trimming, disposed on the periphery of the chip on the substrate and wiring And a circuit board comprising

  ADVANTAGE OF THE INVENTION According to this invention, when trimming with a laser, the circuit board which can prevent that a laser injects into a chip | tip can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(Embodiment)
As shown in FIG. 1 and FIG. 2, the circuit board according to the embodiment of the present invention is a circuit board whose function is adjusted by laser trimming. A chip 40 connected to the substrate 10 and mounted on the substrate 10, the first light-shielding film 20 disposed immediately below the chip 40 on the substrate 10 and the wiring 30, and having a light-shielding property against laser light used for laser trimming; A second light shielding film 22 is provided on the substrate 10 and the wiring 30 in the periphery of the chip 40 and has a light shielding property against laser light used for laser trimming. As a laser used for laser trimming, a laser that can cut the printed and fired resistance provided on the substrate 10 and does not damage or harm the substrate 10 is used. As a laser used for laser trimming, for example, a YAG laser (1056 nm) can be used.

  The substrate 10 may be a ceramic substrate that is transparent to laser light used for laser trimming, a resin substrate such as glass epoxy, or the like. The substrate 10 is transparent to the laser light used for laser trimming, thereby preventing the laser from being damaged and damaged. The wiring 30 provided on the substrate 10 is a conductor pattern designed on the surface of the substrate 10. The thickness of the wiring 30 is about 15 μm. Solder bumps 50 for electrically connecting the wiring 30 and the chip 40 are provided on the wiring 30.

  The chip 40 is a semiconductor chip such as a monolithic integrated circuit (MIC) chip and a transistor chip. The chip 40 is formed into a flip chip. The chip 40 is electrically connected to the wiring 30 by solder bumps 50. The height of the solder bump at that time is about 40 to 50 μm.

  The first light shielding film 20 and the second light shielding film 22 have a function of absorbing a laser used for laser trimming. The first light-shielding film 20 and the second light-shielding film 22 absorb the laser, thereby substantially shielding the laser that has reached the first light-shielding film 20 and the second light-shielding film 22. Moreover, the 1st light shielding film 20 and the 2nd light shielding film 22 have insulation. Since the first light-shielding film 20 and the second light-shielding film 22 are insulative, a short circuit between the wirings 30 can be prevented even when arranged on the wirings 30. The first light shielding film 20 and the second light shielding film 22 are formed of, for example, insulating magnetic ink, glass or the like, and the thickness of the first light shielding film 20 and the second light shielding film 22 is about 20 μm.

  The first light shielding film 20 prevents the laser from entering the chip 40 from the substrate 10 side. The first light shielding film 20 is preferably disposed on the entire surface immediately below the chip 40 on the substrate 10. By disposing the first light shielding film 20 on the entire surface directly below the chip 40, it is possible to completely shield the laser incident on the chip 40 from the substrate 10 side.

  The second light shielding film 22 prevents the laser reflected from the periphery of the chip 40 from entering the side surface of the chip 40. The second light shielding film 22 is preferably disposed on the entire periphery of the chip 40 on the substrate 10 and the wiring 30. By disposing the second light shielding film 22 over the entire periphery of the chip 40, the laser incident on the side surface of the chip 40 can be completely shielded.

  Laser trimming will be described with reference to FIG. As shown in FIG. 3A, resistors 60a to 60g are arranged on the circuit board. The resistors 60a to 60g are laser trimming resistors. The resistors 60a to 60g are covered with a protective coat (not shown) such as glass. Laser trimming is laser processing in which electrical characteristics are set to desired values by excising a part or all of the resistors 60a to 60g with a laser or causing the characteristics to change. As an example of laser trimming, as shown in FIG. 3B, a part of the resistors 60b, 60d, and 60f is cut with a laser to set the electrical characteristics to a desired value. The electrical characteristics are measured simultaneously with the measurement probe while performing laser trimming, and the trimming is terminated when the set value is reached.

  Of the lasers irradiated by laser trimming, lasers L1, L2, and L3 traveling in the vicinity of the chip 40 will be described with reference to FIG. The lasers L1, L2, and L3 are scattered light generated during laser processing (trimming), for example. The laser L <b> 1 is a laser incident on the substrate 10, and is a laser that obliquely repeats scattering and reflection in the substrate 10. The laser L 1 that has traveled through scattering and reflection in the substrate 10 reaches the first light shielding film 20, is absorbed by the first light shielding film 20, and disappears. The laser L <b> 2 is a laser that is directly incident on the second light shielding film 22. The laser L2 is absorbed by the second light shielding film 22 and disappears. The laser L3 is a laser that travels while being reflected by the wiring 30. The laser L3 reaches the second light shielding film 22, is absorbed by the second light shielding film 22, and disappears. Of the lasers that travel after being reflected by the wiring 30 such as the laser L3, lasers that do not reach the second light shielding film 22 are emitted to the atmosphere as they are. Therefore, the lasers L1, L2, and L3 traveling in the vicinity of the chip 40 are shielded by either the first light shielding film 20 or the second light shielding film 22, so that no laser reaches the chip 40.

  The circuit board according to the embodiment will be described below with reference to the process cross-sectional view of FIG.

  (A) First, as shown in FIG. 5A, a substrate 10 having transparency to a laser beam used for laser trimming is prepared. Here, for example, a ceramic substrate is prepared as the substrate 10.

  (B) Next, as shown in FIG. 5B, a desired circuit pattern (circuit design) is patterned on the surface of the substrate 10, and the wiring 30 is arranged by a known printing technique.

  (C) Next, as shown in FIG. 5C, a resistor 60, which is a laser trimming resistor, is disposed at a desired location by a known printing technique.

  (D) Next, as shown in FIG. 5D, a protective coat 70 is disposed on the resistor 60 by a known printing technique. The protective coat 70 is made of a material such as glass that is transparent to laser light used for laser trimming.

  (E) Next, as shown in FIG. 5E, a light-shielding material having a light-shielding property with respect to the laser light used for laser trimming is disposed at a desired location by a known printing technique, and the first light-shielding film 20 And the second light shielding film 22. The first light shielding film 20 and the second light shielding film 22 can be simultaneously formed by a single printing process.

  (F) Next, as shown in FIG. 5 (f), the chip 40 is mounted on the wiring 30 via the solder bumps 50.

  (G) Next, as shown in FIG. 5G, the resistor 60 is irradiated with a YAG laser or the like to perform laser trimming. In the laser trimming, the protective coating 70 where the laser beam hits becomes high temperature, melts and flows into the cut portion of the resistor 60 (not shown).

  Through the above steps, the circuit board according to the embodiment is formed.

  According to the circuit board according to the embodiment of the present invention, the first light shielding film 20 and the second light shielding film 22 can prevent the laser from entering the chip when trimming with the laser. Since the first light-shielding film 20 and the second light-shielding film 22 can prevent the laser from entering the chip, when trimming with the laser, the chip is covered with a light-shielding cover or the resistor is arranged away from the chip. Since this is not necessary, the component mounting density around the chip can be increased.

  In addition, according to the circuit board according to the embodiment of the present invention, the first light shielding film 20 and the second light shielding film 22 can be easily formed by a known printing technique, which increases the structural difficulty and cost. Nor.

(Other embodiments)
As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques should be apparent to those skilled in the art.

  For example, in the embodiment, it is described that laser trimming is laser processing that sets electrical characteristics to a desired value by cutting a part or all of a resistor with a laser or causing a characteristic change. However, laser trimming can be performed not only on resistors but also on capacitors, inductances, wirings, and the like.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

It is a typical sectional view of a circuit board concerning an embodiment of the invention. 1 is a schematic plan view of a circuit board according to an embodiment of the present invention. It is a figure for demonstrating laser trimming. It is a figure for demonstrating the behavior of the laser which advances in the chip | tip vicinity in the circuit board which concerns on embodiment of this invention. It is process sectional drawing which shows the method of forming the circuit board which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Board | substrate 20 ... 1st light shielding film 22 ... 2nd light shielding film 30 ... Wiring 40 ... Chip 50 ... Bump 60, 60a-60g ... Resistance 70 ... Protective coat L1, L2, L3 ... Laser

Claims (5)

In circuit boards that perform function adjustment by laser trimming,
A substrate with wiring on the surface;
A chip mounted on the substrate in electrical connection with the wiring and solder bumps ;
A first light-shielding film disposed on a gap directly below the chip on the substrate and formed by the solder bump and having a light-shielding property with respect to laser light used for laser trimming;
A circuit board comprising: a second light-shielding film disposed on a periphery of the chip on the substrate and the wiring and having a light-shielding property against laser light used for laser trimming.   The circuit board according to claim 1, wherein the board is transparent to laser light used for laser trimming.   The circuit board according to claim 1, wherein the first light shielding film has an insulating property.   The circuit board according to claim 1, wherein the second light shielding film has an insulating property.   The circuit board according to claim 1, wherein a laser used for laser trimming is a YAG laser.

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