JP4645212B2 - Wiring circuit board built-in resistance element - Google Patents

Description

  The present invention relates to a substrate built-in resistor incorporated in a printed circuit board.

  Electronic devices are becoming smaller, higher density, and higher performance. And the demand for miniaturization, high density, and high speed is increasing for the wiring circuit board incorporated in the electronic device, and a wiring circuit board that satisfies these requirements is demanded.

  Conventionally, components such as a semiconductor chip, a resistor, a capacitor, and an inductor are surface-mounted on a wiring circuit board, and the components to be mounted are miniaturized to reduce the size and density of the wiring circuit board.

  However, there is a limit to surface mounting alone, and further improvement in component mounting density is required, and development of wiring circuit boards with built-in components that incorporate components such as resistors, capacitors, and inductors is underway.

  As a method for forming a resistor inside a printed circuit board, a method is used in which an electrode is formed by copper wiring on an insulating substrate, and a resistance paste formed by mixing a carbon filler and a resin is printed and fired between the electrodes. Is reported in Patent Document 1.

  However, in the conventional resistance paste element, the resistance element is formed with a resistance paste containing a resin on the surface of the insulating resin base material and adjusted to within a design value ± 1% by various trimmings. There was a problem that the resistance value increased due to moisture absorption of the resin constituting the resistor.

  Therefore, Patent Documents 2 and 3 report a method of coating a resistor with an insulating material as a method of suppressing resistance value fluctuation due to moisture absorption of the resistor.

However, in coating with an epoxy resin or the like, the coating material itself is an organic material and absorbs moisture, so that the moisture-proofing effect is insufficient. When an inorganic material such as SiO ₂ is used as the coating material, moisture absorption from the resistor surface can be suppressed.

However, moisture absorption occurs not only from the surface of the resistor but also from the insulating base material on which the element is formed, that is, from the lower surface, so that there is a problem that the resistance value fluctuates only by the overcoat on the surface.
Japanese Patent No. 2835451 Japanese Patent Laid-Open No. 02-309692 Japanese Patent Laid-Open No. 11-4056

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a resistance element with a built-in substrate in which a resistance value variation due to moisture absorption is small.

In order to solve the above-mentioned problems in the present invention, the invention according to claim 1 is a resistance element built in a wiring circuit board, and is provided between a resistor made of a resistance paste containing carbon black and resin and an insulating substrate. And a water vapor barrier layer made of electroless nickel / phosphorus / iron alloy plating .

  The invention according to claim 2 is characterized in that the resistance value of the portion of the water vapor barrier layer that overlaps the resistor is 100 times or more the resistance value of the resistor. did.

The invention according to claim 3 is the resistance element according to claim 1 or 2, wherein the surface of the resistor is covered with an overcoat layer .

The invention according to claim 4 is the resistance element according to claim 3 , wherein the overcoat layer is an inorganic material .

The invention according to claim 5 is a printed circuit board in which the resistance element according to any one of claims 1 to 4 is incorporated .

  The invention according to claim 6 is the resistance element according to any one of claims 1 to 5, wherein the conductive substance is carbon black.

  The invention according to claim 7 is a printed circuit board in which the resistance element according to any one of claims 1 to 6 is incorporated.

  In the present invention, it is possible to prevent moisture absorption from the substrate of the resistor by providing the water vapor barrier layer between the insulating base material and the resistor. In addition, moisture absorption of the entire resistor can be suppressed by sandwiching the upper and lower sides of the resistor between the water vapor barrier layer and the overcoat layer, and a highly reliable wiring board without an increase in the resistance value of the resistor element can be obtained. .

  Embodiments of the present invention will be described below.

  FIG. 1 is a cross-sectional view showing an example of a substrate having a resistance element composed of a resistor, a metal oxide film, an overcoat and an electrode of the present invention. There is a copper wiring 32 on the insulating substrate 11, and a silver paste 51 is present between the copper wirings 32. There is a resistor 52 between the silver paste 51, the water vapor barrier layer 21 under the resistor 52, and the overcoat layer 22 over the resistor 52. The water vapor barrier layer 21 and the overcoat layer 22 only need to cover at least the resistor 52. An arbitrary number of wiring layers can be formed above and below the resistor 52. In the present invention, when the insulating base material is a resin, the effect becomes remarkable.

The water vapor barrier layer 21 in the present invention is not particularly limited as long as the resistance value of the portion overlapping the resistor 52 is 100 times or more the resistance value of the resistor 52. If the resistance value under the resistor of the water vapor barrier layer is 100 times or more compared to the resistance value of the resistor, the resistance value of the designed resistor is not affected. Specific examples of the water vapor barrier layer include metal compounds such as metal oxides and ceramic films such as SiO ₂ . The method for forming these water vapor barrier layers is not particularly limited, and various conventionally known thin film forming techniques, coating / coating film forming techniques, and the like can be appropriately used. Thin film formation techniques include vacuum deposition, sputter deposition, ion plating, physical competing growth (PVD), chemical vapor deposition (CVD), vacuum coating, spin coating, and dip coating. And a method of performing in air such as a roll coating method, a spray coating method and a plating method. The film thickness of the water vapor barrier layer is preferably 0.02 μm or more. In the case of 0.02 μm or less, sufficient water vapor barrier performance cannot be obtained. In consideration of the film thickness and cost of the water vapor barrier layer, a method of forming the water vapor barrier layer using an electroless plating method is preferable. The plating solution is preferably nickel / phosphorus, and specifically nickel / phosphorus / iron, nickel / phosphorus / tungsten, nickel / phosphorus / molybdenum, nickel / phosphorus / rhenium / nickel / phosphorus / chromium can be used.

  In the resistor 52 made of a resin paste having a conductive substance, the conductive substance is preferably an inexpensive carbon black such as acetylene black, furnace black, thermal black, or graphite. Examples of the resin component include an epoxy resin, a phenol resin, and a polyimide resin, but are not particularly limited thereto. In addition to the conductive filler, an inorganic filler may be added in order to improve printability and stability. In addition, as a method for forming the resistor, various printing methods may be mentioned, and among these, screen printing is preferable.

  As the overcoat layer 22, a material having a low water vapor transmission rate and a high insulating property is preferable, and a polysilazane material, particularly a polysilazane material curable at a low temperature, for example, 260 ° C. or less is preferable. As the overcoat forming method, various thin film forming techniques and various coating / coating film forming techniques can be used as appropriate.

  Next, the manufacturing method of the resistor built-in wiring circuit board of this invention is demonstrated. FIG. 2 shows a first embodiment as an example of a method for manufacturing a resistance element built-in wiring circuit board according to the present invention.

First, an appropriate pretreatment is performed on one surface of the insulating base material 11, electroless nickel / phosphorus / iron alloy plating is performed, and water vapor is obtained by adjusting the film thickness so that soft etching is performed with an ammonium persulfate aqueous solution and the resistance becomes sufficiently high. A barrier layer 21 is formed (see FIG. 2A).
Subsequently, an appropriate pretreatment is performed to form a thin film conductor layer by electroless copper plating (not shown). Using this thin film conductor layer as a cathode, a conductor layer 31 is formed by electrolytic copper plating (see FIG. 2B). A photosensitive layer (resist) is formed on the conductor layer 31 by a method such as bonding a dry film, and a series of patterning processes such as exposure and development are performed to form a resist pattern 41 (see FIG. 2C). ). Next, using the resist pattern 41 as a mask, the conductor layer 31 is etched, and the resist pattern 41 is removed with a special stripping solution to form a copper wiring 32 on the insulating substrate 11 (FIG. 2D). reference).

  Thereafter, a resist pattern 42 is formed again in addition to the portion where the resistance element is formed (see FIG. 2E), and a solution for selectively etching copper (alkali etching solution) is used for the resistance element portion. Copper is removed (see FIG. 2 (f)).

  A resistor paste is screen-printed and fired so as to connect between the copper electrodes 33 to the resistor portion to form the resistor 52. At this time, it is desirable to sandwich the silver paste 51 or silver plating in order to reduce the contact resistance between the resistance paste and the copper electrode (see FIGS. 2G and 2H). The overcoat layer 22 is coated on the surface of the resistor thus formed. The substrate built-in resistor element 60 of the present invention can be formed by these steps (see FIG. 2 (i)). Further, the insulating resin 12 is laminated thereon, and a normal printed wiring board multilayering process such as drilling by leather processing is performed to obtain the resistance element built-in wiring circuit board 100 of the present invention (FIG. 2 ( j)).

  FIG. 3 shows a second embodiment as an example of a method of manufacturing a resistor built-in wiring circuit board according to the present invention. First, a photosensitive layer (resist) is formed on a copper-clad laminate 13 (see FIG. 3A) composed of an insulating base material 11 and a conductor layer 31 by a method such as bonding a dry film, and exposure, development, etc. The resist pattern 41 is formed by performing a series of patterning processes. (See FIG. 3B.) Next, using the resist pattern 41 as a mask, the conductor layer 31 is etched, the resist pattern 41 is removed with a special stripping solution, and the copper wiring 32 and A copper electrode 33 is formed. (See Fig. 3 (c))

  Thereafter, a resist pattern 42 is formed again other than the portion where the resistance element is formed (see FIG. 3D), and the water vapor barrier layer 21 is formed. (See FIG. 3E) The resist pattern 42 is removed with a special stripping solution. (See Fig. 3 (f))

Resistive paste 52 is screen-printed and fired so as to connect between the copper electrodes 33 to the resistor portion, thereby forming a resistance element. At this time, it is desirable to sandwich the silver paste 51 or silver plating in order to reduce the contact resistance between the resistor and the copper electrode. (See FIGS. 3G and 3H) The surface of the resistance element formed in this way is coated with an inorganic insulating film 22 such as SiO ₂ . The substrate built-in resistance element 60 of the present invention can be formed by these steps. (Refer to FIG. 3 (i)) Furthermore, the insulating resin 12 is laminated thereon, and a multilayered process of a normal printed wiring board such as drilling by leather processing is performed, whereby the resistance element built-in wiring circuit board 100 of the present invention is obtained. Obtainable. (See Fig. 3 (j))

Hereinafter, examples will be described in detail. First, the insulating base material is washed with a conditioning cleaner (Okuno Pharmaceutical Co., Ltd .: OPC-380 Condy Clean M), applied with a catalyst (Okuno Pharmaceutical Co., Ltd .: OPC-80 Catalyst), and activated (Okuno Pharmaceutical Co., Ltd .: OPC). -555 accelerator M) was pretreated. Next, it plated about 0.3 micrometer with the electroless nickel * phosphorus * iron alloy plating solution. Dip etching is performed with a 5 g / L ammonium persulfate aqueous solution for 20 minutes so that the resistance value of the plating film becomes sufficiently higher than the design value of the mounted resistor, and the film thickness of the electroless nickel / phosphorus / iron alloy plating is set to 0. Adjusted to 2 μm. In this way, a water vapor barrier layer was formed. Next, a thin-film conductor layer is formed by electroless copper plating (Shipley Far East CUPOSIT). At this time, the electroless copper plating thickness may be about 1 μm. Using this thin film conductor layer as a cathode, electrolytic copper plating was performed at 2 A / dm ² for 30 minutes to adjust the copper thickness to 15 μm. Subsequently, a laminate coating of 15 μm thick Hitachi Chemical dry film resist RY-3215 was performed at 110 ° C. and 3 kg / cm using a laminator. The resist pattern was formed by exposing with the exposure amount of 55 mJ, and developing with 1% sodium carbonate aqueous solution. Next, copper was etched using ferric chloride solution using the resist pattern as a mask, and then the resist pattern was removed with a 5% aqueous sodium hydroxide solution to form a wiring layer. Again, exposure and development were performed by a photolithography process to mask portions other than the resistor with a resist, and copper in the resistor portion was removed with an alkaline etching solution. Subsequently, the silver paste was screen printed so as to overlap the copper wiring and cured at 150 ° C. for 30 minutes. Resistive paste containing carbon particles and epoxy resin as a binder was screen-printed so that the end portion overlaps the silver paste electrode, and cured at 200 ° C. for 2 hours. After adjusting the resistance value by laser trimming, a polysilazane material made of Clariant was further dropped on the resistor by a quantitative coating machine and cured at 150 ° C. for 1 hour. Thus, the resistance element for incorporating a substrate of the present invention was formed.

  After forming the resistance elements, the resistance value between the resistance elements was 100.9 kΩ. Thereafter, the substrate with a built-in resistor element was left in a test chamber at a temperature of 85 ° C. and a humidity of 85% for 100 hours, and the resistance value between the resistor elements was measured again. As a result, it was 104.9 kΩ.

(Comparative Example 1)
A substrate built-in resistance element was formed in the same manner as in Example 1 except for the water vapor barrier layer forming step. After forming the resistance elements, the resistance value between the resistance elements was 100.3 kΩ. Thereafter, the resistance element-embedded substrate was left in a test chamber at a temperature of 85 ° C. and a humidity of 85% for 100 hours, and when the resistance value between the resistance elements was measured again, it was 112.3 kΩ.

It is sectional drawing which shows an example of the board | substrate built-in resistor of this invention. (A)-(j) is a schematic cross section which shows a part of manufacturing process of the resistor with a built-in substrate shown in 1st Embodiment of this invention. (A)-(j) is a schematic cross section which shows a part of manufacturing process of the resistor with a built-in board | substrate shown to 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Insulating base material 12 ... Insulating resin 13 ... Copper adhesion laminated board 21 ... Water vapor barrier layer 22 ... Overcoat layer 31 ... Conductor layer 32 ... Copper wiring 33 ... Copper electrode 41 ... Resist pattern 42 ... Resist pattern 51 ... Silver paste 52 ... Resistor 60 ... Built-in resistor element 100 ... Resistance element built-in wiring circuit board

Claims (5)

In a resistance element built in a wiring circuit board, a water vapor barrier layer made of electroless nickel / phosphorus / iron alloy plating is provided between a resistor made of a resistance paste containing carbon black and a resin and an insulating substrate. A resistance element.   The resistance element according to claim 1, wherein a resistance value of a portion of the water vapor barrier layer overlapping the resistor is 100 times or more of a resistance value of the resistor. The resistance element according to claim 1, wherein a surface of the resistor is covered with an overcoat layer . The resistance element according to claim 3 , wherein the overcoat layer is an inorganic material . A printed circuit board incorporating the resistance element according to claim 1.

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