JP4661338B2 - Method for forming resistor - Google Patents

Description

  The present invention relates to a method of forming a resistor of a printed wiring board having a resistance element therein, and more particularly to a method of forming a pair of electrodes on an insulating substrate and a resistor disposed therebetween.

  In recent years, as devices such as mobile phones and digital cameras have been reduced in size and weight, there has been an increasing demand for elements to be mounted on a printed wiring board, such as miniaturization of elements and reduction in the distance between elements. On the other hand, it is difficult to cope with the conventional mounting technology, and there is an increasing expectation for a multilayer printed wiring board in which these elements are built in a printed wiring board. Passive elements (capacitors, resistors, inductors) can satisfy the characteristics required by device manufacturers relatively easily by embedding existing chip elements, but there is a problem that the substrate containing the elements becomes thick. . There is an urgent need to develop a method that can sufficiently satisfy characteristics with thin parts and thin film elements.

  As a method of creating a resistance element inside a printed wiring board, a method of forming a resistance layer with a metal thin film on a copper foil, a method of forming by plating on an insulating substrate, a method of printing a resistive thick film polymer, etc. is there. It is necessary to select a forming method according to the application from the resistance value, accuracy, shape, price, and the like. In the method of printing a thick film polymer, it is possible to form a high-resistance material, but it is difficult to form a fine size. The thin film type using a metal material is restricted to a low resistance range as compared with the thick film type, but can be formed with a small size and high accuracy.

Known documents are shown below.
JP-A-11-004056

  In the formation of a resistance element using a resistor paste, when an electrode is formed on a copper wiring layer and a resistance paste is formed directly on copper, the resistance value of the resistance element gradually increases due to copper oxidation. It was. In order to cope with this, recently, the resistance variation of the resistance element is reduced by applying noble metal plating such as gold plating or silver plating to the electrode portion on which the resistance paste is formed. (Refer to Fig. 1) When applying this noble metal plating, electroless plating is often used because it becomes independent wiring depending on the wiring pattern, but in electroless plating, the thickness of the noble metal plating is thin and the resistance value is stable It may be too thin to make. Moreover, when noble metal plating is performed by electrolytic plating, a plating lead for plating is required, and a wiring layout for that purpose is required, and it is necessary to cut this plating lead after plating.

The present invention has been made in view of the above-mentioned problems. The invention according to claim 1 of the present invention is a method of forming a resistor using a resistor paste built in a multilayer wiring board. A wiring layer having a wiring electrode for connecting the electrode and a plating lead for electrolytic plating of the wiring electrode is formed, and a noble metal plating of a metal having a smaller ionization tendency than copper is formed on the connection part of the wiring electrode and a part of the plating lead. A resistor is formed by using a resistance paste so as to cover the noble metal plating portion through the connection portion formed by electrolytic plating and noble metal plating between the wiring electrodes, and the copper wiring layer is roughened by CZ treatment or blackening treatment. The method of forming a resistor is characterized in that a part of the plated lead subjected to noble metal plating is cut by the action of a local battery .

In the above invention, when forming the resistor, noble metal plating can be formed on the wiring electrode portion by electrolytic plating without worrying about the wiring layout. If noble metal plating is applied to a part of the plating lead, the wiring layer is cut at the end of the noble metal by the action of the local battery during the roughening treatment of the wiring layer such as copper. The resistance element portion is also plated with noble metal, but this portion does not affect the copper wiring because the resistor is covered with the noble metal plating.

  According to a second aspect of the present invention, there is provided the resistor forming method according to the first aspect, wherein a metal containing silver, gold or palladium is used for the noble metal plating.

  In the said invention, the electroplating liquid containing metals, such as gold | metal | money, silver, and palladium which are generally marketed, can be used for noble metal plating.

  In the method of forming a resistor incorporated in a multilayer wiring board, the resistance value fluctuation of the resistance element is eliminated by passing noble metal plating by electrolytic plating at the interface between the resistor and the electrode wiring, and a highly accurate resistance element is placed in the substrate. It became possible to embed. Further, since the plating lead can be easily cut, it is possible to freely design a wiring layout for the plating lead at the time of electrolytic plating, and it is not necessary to consider an arrangement for cutting. Since electroless plating is difficult to manage the plating bath and has a short life, electrolytic plating can be employed, thereby reducing the cost of the substrate.

  A method of forming a resistor incorporated in the multilayer wiring board of the present invention will be described with reference to FIGS. 1, 2 and 3 are partial explanatory views of an example of a method of forming a resistor according to the present invention as seen in a plane (left side) and a cross section (right side). The method of forming a resistor of the resistor element-embedded substrate of this example forms a wiring electrode 10 for forming a resistor and a plating lead 11 for performing noble metal plating on the insulating substrate 1 as shown in FIG. Then, as shown in FIG. 1B, a resist 15 for partially precious metal plating is coated on the entire surface of the substrate and the wiring layer. However, the resist 15 is not shown in the figure seen from the plane of FIG. As shown in FIG. 1C, exposure and development are performed to form a resist pattern 15a having an exposed portion for precious metal plating. As shown in FIG. 2D, noble metal plating is performed, and noble metal plating 25 is performed on the opening of the resist. After removing the resist as shown in FIG. 2E, a resistor 30 is formed on the electrode 10 so as to cover the silver plating 25 as shown in FIG. In FIG. 3G, in order to improve the adhesion between the adhesive layer and the wiring layer in order to form the upper layer of the multilayer wiring layer, it is necessary to roughen the copper surface by CZ treatment or blackening treatment. The exposed precious metal plating portion is eroded and cut by the process. For this reason, it is not necessary to cut the plating lead as in the prior art, and it is possible to provide a method for forming a resistance element capable of plating a noble metal with an appropriate film thickness on the terminal portion of the resistance element.

  Examples will be described in detail below with reference to FIGS.

  An embodiment of a method for forming a resistor of a resistance element built-in substrate according to the present invention is as follows.

  Using a 0.6 mm-thick BT resin substrate (Mitsubishi Gas Chemical Co., Ltd.) having a 12 μm copper foil on both sides of the wiring substrate 1, resistance is obtained by a photolithography process and etching in the same manner as a normal printed wiring substrate formation method. A wiring layer including the wiring electrode 10 and the plating lead 11 was formed in a portion where the element is to be formed (FIG. 1A).

In order to selectively perform plating on the wiring electrode 10 part forming the resistance element and the cut part of the plating lead 11, a 15 μm thick dry film resist (RY3315 manufactured by Hitachi Chemical Co., Ltd.) was laminated as a resist 15 using a laminator ( FIG. 1 (b)). Lamination conditions are 110 ° C., 3 MPa, and 0.5 m / sec. The resist pattern 15a can be formed as shown in FIG. 1C by exposing and developing with a pattern in which the electrode wiring in the plated portion is exposed. The exposure conditions were 60 mJ / cm ² , and the development was performed with a 1% sodium carbonate solution by spray development, and development was possible in about 15 seconds. After the resist pattern was formed, a plating process was performed using an electrolytic silver plating solution (Tempe resist silver plating solution, manufactured by Nippon High Purity Chemical Co., Ltd.) so that the plating film thickness was 0.5 μm or more (FIG. 2D). ). After plating, the dry film resist was removed with a 3% sodium hydroxide solution (FIG. 2 (e)). After washing and drying, a resistor paste was printed as a resistor 30 so as to cover the silver plating formed on the electrode wiring by screen printing (FIG. 2 (f)). After printing, this was baked at 80 ° C. for 30 minutes, and then baked at 180 ° C. for 2 hours. Next, in order to form an upper wiring layer, the wiring layer was roughened by the CZ process of MEC. By this CZ treatment, the wiring layer was cut at both ends of the exposed silver plating formed on the plating lead portion, and a wiring layer serving as a circuit in which the plating lead was disconnected was formed (FIG. 3G). By laminating a copper foil or the like on the adhesive layer via a prepreg, it is not necessary to cut the plating lead, and the next wiring layer can be formed. Moreover, since the thickness of the silver plating can be increased in a shorter time than that formed by electroless plating, the resistance does not fluctuate and the manufacturing time is shortened.

  Even when palladium plating is used for the noble metal plating, it is possible to form a multilayer wiring board having a built-in resistance element that does not require cutting of a plating lead having a stable resistance value, as in the first embodiment.

  Even when an independent circuit as shown in FIG. 4 exists, it is possible to arrange electrolytic plating plating leads without worrying about the wiring layout, and to form a wiring board with a built-in resistor that does not consider cutting of the plating leads Was possible. The detailed plating method and the like are the same as those in the first and second embodiments.

  The method for forming a resistance element for embedding a wired circuit board according to the present invention intends to incorporate a mounting component mounted on the wired circuit board inside the board. By incorporating the mounting component into the board, a space is created in the mounting area, and it becomes possible to mount a higher-performance component. In addition, it is possible to reduce the size of the conventional substrate, which is a driving force for promoting the reduction in the thickness and thickness of electronic devices.

It is the partial explanatory view which looked at an example of the formation method of the resistor of the present invention in the plane and the section. It is the partial explanatory view which looked at an example of the formation method of the resistor of the present invention in the plane and the section. It is the partial explanatory view which looked at an example of the formation method of the resistor of the present invention in the plane and the section. It is the partial explanatory view which looked at other examples of the formation method of the resistor of the present invention on the plane.

Explanation of symbols

1 ... Wiring board 10 ... Electrode wiring 11 ... Plating lead 11a ... Cut plating Lead 15 ... Plating resist 15a ... Patterned plating resist 25 ... Precious metal plating 30 by electrolytic plating ... ... Resistors

Claims (2)

In a method of forming a resistor using a resistor paste built in a multilayer wiring board, a copper wiring layer having a wiring electrode for connecting the resistor and a plating lead for electrolytic plating of the wiring electrode is formed on the insulating layer. The noble metal plating of metal having a smaller ionization tendency than copper is formed by electrolytic plating on the connection part of the wiring electrode and a part of the plating lead, and the noble metal plating part is covered through the connection part where the noble metal plating is provided between the wiring electrodes. A resistor is formed using a resistance paste, and the copper wiring layer is roughened by CZ treatment or blackening treatment, and a portion of the plating lead subjected to noble metal plating is cut by the action of a local battery. Body formation method. 2. The method of forming a resistor according to claim 1, wherein a metal containing silver, gold, or palladium is used for the noble metal plating.

Images