JP4752281B2 - Printed wiring board with built-in resistor - Google Patents

Description

  The present invention relates to a resistance element built-in printed wiring board in which a resistance element is formed in advance on a printed wiring board.

In recent years, in order to meet the demands for higher speed, higher functionality, smaller size, and lighter weight of electronic devices, technology for creating passive elements in substrates used in electrical devices and increasing the density will be widely deployed. It is said.
A resistive element which is one of such passive elements is also desired to be smaller in order to be incorporated in a printed wiring board. As a kind of resistance element incorporated in the printed circuit board, a resin-based resistance paste is partially formed by screen printing or the like between a pair of electrodes, and a resistance element is formed on one electrode and a metal film having a high resistance value and There is a method of forming an inorganic material by plating, sputtering, or the like. The former has the advantage that it can be manufactured at low cost with fewer steps.

However, when the resistance element is formed by the printing method described above, as shown in FIG. 1, the electrode 12 made of the copper wiring 10 and the resistor 11 made of the resistance paste provided on the insulating substrate 13 are in direct contact. The influence of the contact resistance at the interface is large. For example, it has been reported that the resistance value greatly increases due to the corrosion of the interface under high temperature and high humidity conditions (temperature = 85 ° C., relative humidity = 85%) (non-patent document). 1).
In order to solve this problem, as shown in FIG. 2, a silver paste 24 having excellent electrical connectivity is sandwiched between a copper electrode portion 22 provided on an insulating substrate 23 and a resistor 21 made of a resistance paste, and the interface A resistance element 22 having a structure with reduced contact resistance and a resistance element in which the copper electrode portion 22 is subjected to silver plating have been reported (see, for example, Non-Patent Document 1, Patent Document 1 and Patent Document 2).
However, since the resistor 21 is formed on the above-described silver paste 24 by screen printing, it is difficult to control the printing conditions, and the resistor 21 printed on the silver paste 24 is faint and printing such as blurring. Defects were easy to occur. For this reason, there has been a problem in that the resistance value varies greatly between products of the printed wiring board with a built-in resistance element.

In addition, there is a problem that electromigration occurs between the silver paste-wiring layer and the silver paste-silver paste, and the resistance value of the resistance element decreases. Electromigration is a phenomenon in which when a DC voltage is applied to a printed wiring board with a built-in resistance element, metal atoms move due to collision of electrons, and problems such as short-circuiting with adjacent wiring and silver paste patterns occur. Further, in the surface roughening treatment of the wiring layer performed before the insulating resin lamination, the etching rate of the copper wiring becomes abnormally fast due to the local battery action at the boundary between the silver paste or silver plating forming region and the copper wiring, and disconnection occurs. There is a problem.
The object of the present invention is to provide a resistance value which is excellent in accuracy of resistance value by screen printing of a resistor, has a small fluctuation in resistance value even in a high-temperature and high-humidity test, and does not cause a short circuit and disconnection due to electromigration in an insulation reliability test. An element-embedded printed wiring board is provided.

Japanese Patent Laid-Open No. 11-340633 Japanese Patent Laid-Open No. 11-4056 Isao Shioka: “Polymer Resistors Used for Embedded Passive Device Technology” Journal of Japan Institute of Electronics Packaging, Vol. 6, No4, p. 294-299, 2003

In order to solve the above problems, the invention according to claim 1 is a printed wiring board comprising a multilayer printed wiring board comprising an insulating layer and a copper wiring layer, wherein at least one resistance element is built in at least one of the wiring layers. The resistive element includes an electrode part in which a part of the copper wiring layer is coated with substitutional electroless silver plating, a resistor disposed between the electrode parts, and a boundary part between the silver plating and the copper wiring. The thickness of the silver plating is 0.3 μm to 1 μm, and the resistor is formed of a resistance material in which a conductive filler is dispersed in a thermosetting resin. This is a printed wiring board with a built-in resistance element.
Thus, since the electrode part of the resistance element is formed by substitution silver plating, it became possible to suppress the resistance value fluctuation | variation accompanying the increase in the contact resistance in a resistor and an electrode part interface.
In addition, substitutional electroless silver plating formed on the electrode part of the resistive element can reduce the thickness of the electrode part compared to the case where the silver paste is formed on the electrode part. It has become possible to reduce printing defects such as blurring and blurring during printing.
Furthermore, since a silver plating film that easily generates electromigration is covered with a resistance paste (see FIG. 3), it becomes possible to prevent defects such as disconnection or short circuit due to electromigration.
In addition, by using a resistance material in which a conductive filler is dispersed in a thermosetting resin in this manner, resistor formation that generally requires high-temperature firing can be fired at a low temperature of 250 ° C. or less, Resistive elements can be formed on organic substrates with low heat resistance.
Furthermore, by increasing the thickness of the silver plating to 0.3 μm or more and 1 μm or less as described above, the contact resistance at the interface between the electrode portion and the resistance paste is increased even in the high temperature and high humidity test (85 ° C., 85%, 1000 h) Is suppressed, and the resistance value fluctuation can be minimized.
The invention according to claim 2 is a multilayer printed wiring board composed of an insulating layer and a copper wiring layer, wherein one or more resistance elements are incorporated in at least one of the wiring layers. A structure in which a part of the copper wiring layer is covered with substitutional electroless silver plating, a resistor is disposed between the electrode parts, and a boundary portion between the silver plating and the copper wiring is covered with a resistance paste layer The thickness of the silver plating is 0.3 μm to 1 μm, the insulating layer is formed from a build-up insulating resin film, and the resistor is formed of a resistance material in which a conductive filler is dispersed in a thermosetting resin. This is a printed wiring board with a built-in resistive element.
The invention according to claim 3 is the resistance element built-in printed wiring board according to claim 1 or 2 , wherein the resistor paste layer is continuous with a resistor formed between the electrodes.
Thus, since the resistor paste layer does not need to newly form a resistor paste formation pattern with respect to the boundary portion of the silver plating formation region, and the silver plating film is not exposed, an upper layer is formed after the resistor element is formed. It became possible to suppress resistance value fluctuations due to oxidation of the silver plating film during the process residence time until the lamination process.
Invention according to claim 4, wherein the resistor, to any one of claims 1 to 3 in which the resistive material maximum temperature, characterized in that the cured under temperature conditions such that the 180 ° C. or higher It is a printed wiring board with a built-in resistance element of description.
In this way, the resistance material is cured by curing the resistance material under a temperature condition in which the maximum temperature reaches 180 ° C. or more, that is, at a temperature higher than the curing temperature of a general multilayer printed wiring board insulating material. It became possible to reduce the resistance value change before and after.
The invention according to claim 5 is the resistor according to any one of claims 1 to 3 , wherein the resistor is formed by curing a resistance material under a temperature condition such that a maximum temperature reaches 180 ° C. or more. It is a printed wiring board with a built-in resistance element of description.
Thus, by making the thermal history in the insulating layer forming step on the built-in resistor element lower than the firing temperature of the resistor element, it becomes possible to suppress the resistance value fluctuation before and after the built-in resistor element.

According to the present invention, since a substitutional electroless silver plating film is formed at the interface between a resistor made of a resistance paste and a copper electrode, it has become possible to suppress a change in resistance value over time due to an increase in contact resistance. .
In addition, since the silver plating film formation region is covered with a resistance paste, ion migration of the silver plating film can be suppressed, and the plating formation region boundary on the copper wiring layer is covered with the resistance paste. It was possible to suppress the disconnection of the copper wiring part due to the local battery action in the wiring layer roughening process performed before the upper layer stacking process.

An example of an embodiment of the present invention will be described with reference to FIG.
FIG. 3A is a cross-sectional explanatory view showing the configuration of the resistive element in the printed wiring board with a built-in resistive element according to the present invention.
FIG.3 (b) is a top view of the resistive element structure in the printed wiring board with a built-in resistive element of this invention.

In the resistance element built-in printed wiring board 300a according to the present invention, the silver plating film 32 is formed on the copper electrode portion 34 of the resistance element, and the resistor 31 made of the resistance paste is electrically interposed between the resistance element electrode portions 34. The resistor paste layer 35 covers the boundary portion 36 of the silver plating formation region and is connected (see FIG. 3B).
That is, since the surface of the resistance element electrode portion 34 is covered with the silver plating film 32, the resistance value fluctuation can be suppressed by increasing the contact resistance due to the oxidation of the copper electrode portion surface. The conductor layer is broken due to local cell action at the conductor layer (copper) boundary where the silver plating film is formed in the surface roughening treatment of the conductor layer as a pre-lamination treatment after the resistor element is formed. Can be prevented.

In the resistance element of the present invention, a part of the copper wiring serves as an electrode, and a resistor is formed on the copper electrode via a substitutional electroless silver plating film. Contact resistance can be suppressed.
In addition, since the plating area is small as compared with the method of forming a silver plating film on the entire surface of the conductor layer, it is possible to reduce short-circuit defects due to electromigration and to suppress silver plating costs.
The thickness of the substitutional electroless silver plating film is 0. It is preferably 3 μm or more and 0.5 μm or less. In this case, the thickness of the silver plating film is 0. This is because if it does not reach 3 μm, the contact resistance between the resistor and the copper electrode cannot be lowered sufficiently, and if it exceeds 0.5 μm, there is almost no difference in the effect of reducing the contact resistance.

The resistor in the present invention is mainly composed of a thermosetting resin and a conductive filler.
Here, as the thermosetting resin, it is possible to use a thermosetting resin such as an epoxy resin, a phenol resin, a melamine resin, a polyimide resin, a resin obtained by modifying these, or a mixture of these resins and a thermoplastic resin. it can. Among these, it is preferable to use an epoxy resin from the viewpoints of adhesion to a substrate, chemical resistance, and cost.
As the conductive filler, it is preferable to use inexpensive carbon such as ketchelen black, acetylene black, graphite, activated carbon. In addition to the conductive filler, an inorganic filler such as silica may be added. Commercially available carbon paste can be used as it is.

  The resistive paste layer covering the silver plating formation region boundary on the copper wiring of the present invention has a structure composed of a part of a resistor pattern made of a resistive paste placed between the resistive element electrodes. A separate pattern is not required for covering the plating formation region boundary portion, and it can be prevented from being mistaken for a resistance element during inspection.

In the present invention, the insulating resin containing the passive element may be in the form of a prepreg, a resin-coated copper foil, an insulating resin film for a build-up substrate, or a varnish. Considering it, it is preferable to use a build-up insulating resin film.
In general, a thermosetting resin such as an epoxy resin tends to have a higher crosslinking density as the curing temperature becomes higher. For example, when a resistor that has been cured once is heated at a higher temperature, curing of the thermosetting resin proceeds, The resistance value tends to decrease.
Therefore, in order to reduce the change in resistance value before and after the incorporation of the resistance element, it is preferable that the maximum temperature reached in pressing, laminating, and curing the insulating resin is lower than the maximum temperature achieved in curing the resistance material.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited thereto.
In addition, about the printed wiring board with a built-in passive element which built in each Example and the comparative example, resistance value measurement, a high temperature / humidity test, and a thermal cycle test (TCT) are performed, and the characteristic of the built-in passive element Was evaluated.
<Resistance measurement>
The resistance value of 100 resistance elements manufactured in each of the examples and comparative examples was measured with a digital multimeter, and an average resistance value, standard deviation (σ), and 3σ values were calculated. The variation in resistance value was evaluated.
<High temperature and high humidity test>
About the passive element inner layer board | substrate manufactured by each Example and the comparative example, the high temperature high humidity test at 40 degreeC and 95% was done for 1000 hours, and resistance value change was computed from the resistance value before and behind a test.
<TCT>
About the printed wiring board with a built-in passive element manufactured in each Example and Comparative Example, 1000 cycles TCT was performed under conditions of a low temperature bath of −40 ° C., a high temperature bath of 125 ° C., and an exposure time of 30 minutes. An element having a value of 1000Ω or more was determined to be defective due to a crack.
Regarding the capacitor, an element having a capacitance value changed by ± 100% or more was determined to be defective. For each example and comparative example, 100 resistance elements having a design value of 100Ω and 100 capacitor elements having a design value of 10 pF were tested.

The following examples illustrate the invention in detail.
4 (a) to 4 (g) are explanatory views showing a part of the process in the printed wiring plate with a built-in passive element of the present invention in cross section.
First, an insulating layer 42 made of an insulating resin with double-sided copper foil (trade name: CCL-HL830, manufactured by Mitsubishi Gas Chemical) was prepared.
Next, a dry film resist (trade name: RY3215, manufactured by Hitachi Chemical Co., Ltd.) was thermocompression bonded with a roll laminator to obtain a conductor layer 41 of a wiring pattern by exposure and development using an affixed film mask (FIG. 4a).

  Next, dry film resist (trade name: RY3215, manufactured by Hitachi Chemical Co., Ltd.) 43 was attached by thermocompression bonding using a roll laminator, and an electrode pattern of a resistance element was obtained by exposure and development using a film mask. (Figure 4b).

  Next, acid cleaning is performed at 10 wt% -sulfuric acid aqueous solution, liquid temperature = 25 ° C. for 1 minute, and after washing with pure water, pre-dip (trade name: SSP-700P manufactured by Shikoku Kasei), liquid temperature = 40 ° C. Immersion for 40 seconds, substitution silver plating (trade name: SSP-700, manufactured by Shikoku Kasei), treatment at a liquid temperature of 40 ° C. for 5 minutes, stripping the dry film resist, A substitutional electroless silver plating film 44 having a thickness of 0.5 μm was formed. (Fig. 4c)

  Next, the dry film was immersed in a 5% aqueous sodium hydroxide solution to form a film. (Fig. 4d)

Next, a carbon paste (trade name: TU-100-8, manufactured by Asahi Chemical Research Laboratories) can be electrically connected between the pair of substituted silver plating electrodes using a stainless steel mesh plate of 200 mesh and wire diameter = 40 μm. Thus, the resistor 45 was formed by screen printing. At this time, simultaneously with the formation of the resistor, a resistor paste layer was provided so as to cover the boundary with the silver plating in a state continuous with the resistor.
The carbon paste of the resistor used for printing was about 700 dPa · s when the viscosity was measured with a rotational viscometer (trade name: manufactured by Viscotester VT-04 Lion).
The design value of the resistor sandwiched between the pair of electrodes was 0.5 mm in width and 0.67 mm in length. The substrate on which the resistor was printed in this way was dried at 90 ° C. for 30 minutes, and then fired at 200 ° C. for 1 hour. (Fig. 4e)

Using a prepreg (trade name: GEA-67N manufactured by Hitachi Chemical Co., Ltd.) 46 on the substrate on which the elements are formed as described above, a dielectric sheet on which a resistor is formed is pasted with a vacuum press to form a via hole. Then, plating, wiring formation, solder resist pattern 48 formation, and nickel-gold plating finish on the terminal portion were performed to produce a printed wiring board with built-in passive elements.
Table 1 shows the evaluation results of the printed circuit board with a built-in passive element manufactured by the above method.

(Comparative Example 1)
Stacked in order of prepreg / copper foil on the core substrate, laminated in a vacuum press machine, then formed via holes with CO2 laser, roughening treatment with alkaline permanganate, electroless copper plating, electricity by electrolytic copper plating The electrode of the resistance element and the wiring pattern were formed by etching.
Next, a silver paste pattern (form name: LS-504J, manufactured by Asahi Chemical Research Laboratories) was formed on the electrode of the resistance element by screen printing using a 200 mesh stainless steel mesh wire diameter = 40 μm.
After the substrate on which the silver paste pattern was formed in this manner was dried at 90 ° C. for 30 minutes and further baked at 150 ° C. for 30 minutes, the thickness of the cured silver paste was measured to be about 20 μm thick. Had.
Next, a carbon paste (trade name: TU-100-8 manufactured by Asahi Chemical Research Laboratories) is used with a 200 mesh, stainless steel mesh plate having a wire diameter of 40 μm so that the pair of silver paste electrodes can be electrically connected. Screen printed.
The viscosity of the carbon paste used for printing was about 700 dPa · s as measured with a rotational viscometer (trade name: manufactured by Viscotester VT-04 Lion).
The design value of the resistor sandwiched between the pair of electrodes was 0.5 mm in width and 0.67 mm in length.
The substrate on which the resistor was printed in this way was dried at 90 ° C. for 30 minutes, and further baked at 200 ° C. for 1 hour.
Next, a dielectric paste (trade name: CX-16 manufactured by Asahi Chemical Research Laboratories) was formed using a stainless mesh plate of 100 mesh and wire diameter = 50 μm so as to cover the lower electrode by screen printing.
The dielectric pattern thus obtained was dried at 90 ° C. for 30 minutes, and further baked at 150 ° C. for 30 minutes.
Next, a copper paste (trade name: manufactured by NF2000 Tatsuta System Electronics Co., Ltd.) was formed so as to straddle the dielectric pattern and the upper electrode lead-out wiring using a stainless mesh plate with 100 mesh and wire diameter = 50 μm.
The copper paste pattern was dried at 90 ° C. for 30 minutes, and then baked at 150 ° C. for 30 minutes to form a capacitor element.
A resistive element built-in printed wiring board was manufactured in the same manner as in Example 1 below.
Table 1 shows the evaluation results of the passive element built-in printed wiring board of Comparative Example 1.

(Comparative Example 2)
A resistance element built-in printed wiring board formed so as to electrically connect the conductor electrode pattern and the resistor pattern in the resistance element described in Comparative Example 1 was manufactured.
Table 1 shows the evaluation results of the passive element built-in printed wiring board of Comparative Example 2.

As is clear from Table 1, the printed wiring board with built-in passive elements of the embodiment has excellent resistance value creation accuracy by screen printing, has small resistance value fluctuations even in a high temperature and high humidity test, and also in an insulation reliability test. Short-circuiting and disconnection due to electromigration were not confirmed.
The printed circuit board with a built-in passive element of Comparative Example 1 has poor resistance element fabrication accuracy, and further has a large amount of variation in resistance value in a high-temperature and high-humidity test, and is used as a resistance element in line-to-line insulation reliability. The element which caused the silver paste to move due to electromigration and cause short circuit was confirmed.
It can be seen that the printed wiring board with a built-in passive element of Comparative Example 2 has a large variation in resistance value in a high-temperature and high-humidity test and has poor reliability.
From these results, it is clear that the passive element built-in printed wiring board having the structure of Example 1 is excellent in processing accuracy and reliability.

It is sectional explanatory drawing which shows an example of the printed wiring board which incorporated the conventional resistive element. It is sectional explanatory drawing which shows the other example of the printed wiring board incorporating the conventional resistive element. It is explanatory drawing of the resistive element which shows an example of the resistive element inner layer printed wiring board of this invention. It is explanatory drawing which shows the manufacturing process of the resistance element built-in printed wiring board of this invention.

Explanation of symbols

11, 21... Resistor 12, 22 ...... Copper electrode 13, 23 ...... Insulating layer 24 ...... Silver paste 300 a・ ・ ・ ・ ・ ・ ・ ・ Resistance element built-in printed wiring board 31 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Resistance paste 32 …… ・ ・ ・ ・ ・ Silver plating film 33 ・ ・ ・ ・ ・ ・ ・ ・.... Insulating resin 34 .... Conductor layer (lead-out wiring)
41 .... Conductor layer (copper)
42 ... Insulating layer 43 ... Resist 44 ... Silver plating film 45 ... Resistive paste 46 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Prepreg 47 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Via hole 48 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Solder resist

Claims (5)

In a printed wiring board comprising one or more resistance elements in at least one of the wiring layers of a multilayer printed wiring board comprising an insulating layer and a copper wiring layer, the resistance element replaces a part of the copper wiring layer A structure in which a resistor is disposed between the electrode parts covered by a type electroless silver plating, and a boundary between the silver plating and the copper wiring is covered with a resistance paste layer, and the thickness of the silver plating There 0.2μm or more and 0.5μm or less, wherein the resistor is resistance element embedded printed circuit board, characterized in that it is formed by a resistor material obtained by dispersing a conductive filler in a thermosetting resin. In a printed wiring board comprising one or more resistance elements in at least one of the wiring layers of a multilayer printed wiring board comprising an insulating layer and a copper wiring layer, the resistance element replaces a part of the copper wiring layer A structure in which a resistor is disposed between the electrode parts covered by a type electroless silver plating, and a boundary between the silver plating and the copper wiring is covered with a resistance paste layer, and the thickness of the silver plating 0.2 μm or more and 0.5 μm or less , the insulating layer is formed from a build-up insulating resin film, and the resistor is formed of a resistance material in which a conductive filler is dispersed in a thermosetting resin. A printed wiring board with a built-in resistance element. The resistance element-embedded printed wiring board according to claim 1, wherein the resistor paste layer is continuous with a resistor formed between the electrodes.   The resistance element-embedded printed wiring board according to any one of claims 1 to 3, wherein the resistor is formed by curing a resistance material under a temperature condition such that a maximum temperature reaches 180 ° C or higher. . 5. The resistance element built-in printed wiring according to claim 1, wherein the insulating layer is pressed, laminated, and cured at a temperature lower than a curing temperature of a resistance material constituting the resistor. Board.