JP6135815B1 - Printed wiring boards and electronic devices - Google Patents

Abstract

Provided is a printed wiring board in which foaming hardly occurs even after a reflow process, a conductive adhesive layer and a metal reinforcing plate have a good adhesive force, and a conductive property between a ground circuit and a metal plate is good. With the goal. A wiring circuit board, a conductive adhesive layer, and a metal reinforcing plate are provided, and the conductive adhesive layer is bonded to the wiring circuit board and the metal reinforcing plate, respectively. A protective layer is provided on the surface of the metal plate, the metal plate is a stainless steel plate, the protective layer is formed of a noble metal and an alloy thereof, and the atomic concentration of chromium on the surface of the protective layer is 1 to 20%. This is solved by a printed wiring board. [Selection] Figure 1

Description

  The present invention relates to a printed wiring board including a metal reinforcing plate and an electronic apparatus including the printed wiring board.

  Electronic devices such as mobile phones and smartphones are generally provided with an electromagnetic shielding layer to prevent malfunction caused by electromagnetic noise generated by electronic components mounted inside or electromagnetic noise entering from the outside. is there. Also, printed wiring boards mounted inside electronic devices, especially flexible printed wiring boards, are flexible, so when mounting electronic components on the surface, be sure to place them on the other side of the flexible printed wiring board facing the electronic component mounting surface. A metal plate is attached and reinforced with a conductive adhesive. Patent Document 1 discloses a printed wiring board reinforced with a conductive adhesive and a nickel-plated stainless steel plate.

  Further, Patent Document 2 discloses a printed wiring board in which the surface of a metal plate is plated with gold in order to efficiently remove electromagnetic waves from an electronic component to improve conductivity.

JP 2013-41869 A International Publication No. 2014/132951

However, the printed wiring board described in Patent Document 1 has a problem that the connection resistance value with the conductive adhesive deteriorates due to insufficient resistance value due to oxidation of nickel plating.
Further, the printed wiring board described in Patent Document 2 is gold-plated on the entire surface of the metal plate, and the polarity of the surface of the metal plate is remarkably low, so that the adhesive force with the conductive adhesive layer is low, and the reflow process There was a problem of foaming.

  In the present invention, the conductive adhesive layer and the metal reinforcing plate have a good adhesive force, hardly foam after the reflow process, and the electrical conductivity between the ground circuit and the metal plate is good even after aging. The purpose is to provide a printed wiring board.

The printed wiring board of the present invention includes a wiring circuit board, a conductive adhesive layer, and a metal reinforcing plate, and the conductive adhesive layer is bonded to the wiring circuit board and the metal reinforcing plate, respectively, and the metal The reinforcing plate has a protective layer on the surface of the metal plate, the metal plate is a stainless steel plate,
The protective layer is made of a noble metal or an alloy thereof, and has a chromium atom concentration of 1 to 20% on the surface of the protective layer.

  According to this invention, it is excellent in adhesiveness compared with the case where the noble metal layer which covers the whole surface of a metal plate is provided, and it can integrate with sufficient adhesive force. Further, foaming during the reflow process is suppressed, and the connection resistance value between the protective layer and the conductive adhesive layer is improved. In addition, it is possible to maintain a stable conductivity over a long period of time, and to obtain a printed wiring board excellent in mechanical strength and conductivity.

It is sectional drawing which shows the structure of the printed wiring board of this invention.

  Hereinafter, the printed wiring board of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a cross-sectional view showing the configuration of the printed wiring board of the present invention. In the following, for convenience of explanation, the upper side in FIG. 1 is “upper” and the lower side is “lower”.

<Printed wiring board>
As shown in FIG. 1, the printed wiring board 1 of the present invention includes a conductive adhesive layer 3 that bonds a wiring board 6 and a metal reinforcing plate 2. The metal reinforcing plate 2 has a protective layer 2b on the surface of the stainless steel plate 2a.
The protective layer 2b has a chromium atom concentration of 1 to 20% on the surface of the protective layer.

The atomic concentration of chromium on the surface of the protective layer is such that when the protective layer is a porous film having pores such as pinholes and cracks, stainless steel, which is a metal plate, is partially exposed on this surface and partially exposed on this surface. Derived from stainless steel, it is possible to control the surface atomic concentration of chromium. Chromium contained in stainless steel has a higher polarity than gold, etc., and adheres to a stainless steel plate with a conductive adhesive partly exposed through a hole. Will improve. As a result, the metal plate and the protective layer can be integrated with superior adhesion and sufficient adhesion as compared with the case where a noble metal layer covering the entire surface of the metal plate is provided.
Further, foaming during the reflow process is suppressed, and the connection resistance value between the protective layer and the conductive adhesive layer is improved. In addition, it is possible to maintain a stable conductivity over a long period of time, and to obtain a printed wiring board excellent in mechanical strength and conductivity.
Or the effect similar to the above is acquired also when a chromium atom contains as an alloy component in a protective layer.

  The embodiment of the printed wiring board 1 will be further described. The wiring board 6 has a strength required for the printed wiring board 1 by mounting the electronic component 10 on a surface that is in contact with the insulating base material 9 and that is opposed to the metal reinforcing plate 2. By providing the metal reinforcing plate 2, it is possible to prevent damage to the solder bonding site or the electronic component 10 when a force such as bending is applied to the printed wiring board 1. Moreover, the conductive adhesive layer 3 can shield electromagnetic waves from the upper direction to the lower direction of the printed wiring board.

<Metal reinforcement plate>
The metal reinforcing plate 2 of the present invention has a protective layer 2b as a surface protective layer on the surface of the stainless steel plate 2a.

[Stainless steel plate]
The stainless steel plate 2a is a metal plate that is highly corrosive and excellent in electrical conductivity, and has a strength as a metal reinforcing plate with a certain thickness or more. As the stainless steel plate, an austenitic stainless steel plate, a ferritic stainless steel plate, a two-phase stainless steel plate, a martensitic stainless steel plate, or a precipitation hardening stainless steel plate can be used. As an austenitic stainless steel plate, for example, SUS301, SUS301L, SUS301J1, SUS302B, SUS303, SUS304, SUS304Cu, SUS304L, SUS304N1, SUS304N2, SUS304LN, SUS304J1, SUS304J2, SUS3J, SUS3S3, SUS309S, SUS310S, SUS3L SUS316LN, SUS316Ti, SUS316J1, SUS316J1L, SUS317, SUS317L, SUS317LN, SUS317J1, SUS317J2, SUS836L, SUS890L, SUS321, SUS347, SUSXM7, SUSXM15J1. Examples of the ferritic stainless steel plate include SUS405, SUS410L, SUS429, SUS430, SUS430LX, SUS430J1L, SUS434, SUS436L, SUS436J1L, SUS445J1, SUS445J2, SUS444, SUS447J1, and SUS447M1. Examples of the duplex stainless steel plate include SUS329J1, SUS329J3L, and SUS329J4L. Examples of the martensitic stainless plate include SUS403, SUS410, SUS410S, SUS420J1, SUS420J2, and SUS440A. Examples of the precipitation hardening stainless steel plate include SUS630 and SUS631.
Among these, SUS301, SUS303, SUS304, SUS305, SUS316, and SUS316L are preferable in terms of strength, cost, and chemical stability as a metal reinforcing plate.
The thickness of the metal reinforcing plate 2a is preferably 0.04 to 1 mm.

[Protective layer]
The protective layer 2b as the surface protective layer is a noble metal layer formed on the outermost surface of the metal reinforcing plate 2, the chromium atom concentration on the surface of the protective layer is 1 to 20%, preferably 3 to 17%, 15% is more preferable.
Here, the noble metal layer refers to a layer formed of at least one of a noble metal and an alloy containing the noble metal as a main component.
When the chromium atom concentration on the surface of the protective layer is 1 to 20%, a porous film in which holes such as pinholes are formed on the entire surface of the protective layer is obtained, and the stainless steel plate is partially exposed on the surface It becomes. Since the chromium component in the partially exposed part of the stainless steel plate and the conductive adhesive layer are firmly bonded, the adhesive strength of the conductive adhesive layer to the metal reinforcing plate can be improved and foaming during reflow can be suppressed. . Moreover, it becomes possible to maintain the electroconductivity stable over the long term, and the printed wiring board excellent in mechanical strength and electroconductivity can be obtained.

In the present invention, the protective layer is preferably formed on the entire interface in contact with the conductive adhesive layer.
When a protective layer is formed on the entire interface in contact with the conductive adhesive layer, micron or nano-sized pinholes are formed on the entire surface of the protective layer, rather than a form in which a protective layer is locally applied to a part of the stainless steel plate. By forming the above, the above-described effect can be obtained.
Moreover, the form which contains a chromium atom as an alloy component in a protective layer and makes the chromium atom density | concentration of a protective layer surface 1-20% can also acquire the effect similar to the above.
The area of the protective layer is preferably 80 or more and more preferably 90 or more with respect to the area 100 of the conductive adhesive layer to be bonded. By setting it as said range, foaming by a solder float test can be suppressed more and the connection reliability after a high temperature, high humidity test can be improved.

  By setting the atomic concentration of chromium on the surface of the protective layer to 1% or more, peeling strength and foaming during reflow can be suppressed. In addition, by setting the surface atomic concentration of chromium to the protective layer to 20% or less, the connection resistance value is good even after aging at a high temperature and high humidity of 85% relative humidity (RH) 85%, and connection reliability Can be increased.

Examples of noble metals that can be used to form the protective layer 2b include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), iridium (Ir), ruthenium (Ru), osmium (0s), and the like. And preferably any one of gold, silver, platinum, and palladium. Or it is also preferable to form from the alloy which has these noble metals as a main component.
These noble metals are preferable from the viewpoint of improving the stability of the connection resistance value after 85% relative humidity (RH) 85% since the resistance value hardly increases due to oxidation of the protective layer.

  Especially, when forming using gold | metal | money, it is preferable to form by soft gold plating, hard gold plating, and electroless plating. Among these, soft gold plating is preferable in terms of maintaining adhesion to the metal reinforcing plate 2 and high conductivity.

  The thickness of the protective layer 2b is preferably 0.005 μm to 1 μm, and more preferably 0.01 μm to 0.05 μm. By setting the thickness of the protective layer to 0.005 μm to 1 μm, the conductivity can be improved while suppressing the cost.

  The protective layer 2b preferably has a surface roughness Ra of 0.2 μm or more, more preferably 0.3 μm or more, and further preferably 0.4 μm or more. If the numerical value of the surface roughness Ra is large, the surface of the protective layer 2b becomes rough. Therefore, when the metal reinforcing plate 2 and the conductive adhesive layer 3 are thermocompression bonded, the conductive adhesive layer 3 is the protective layer 2b. It can penetrate into the recesses on the surface and strengthen the adhesive force between them.

  In this invention, the aspect which forms a protective layer directly on a stainless steel plate without a nickel layer etc. is preferable. When an intermediate layer such as a nickel layer is not provided, the cost can be reduced by simplifying the process, and the thickness of the protective layer can be reduced, so that the uneven shape on the surface of the stainless steel plate can be reliably transferred to the surface of the protective layer. That is, since Ra can be easily controlled, the adhesive force between the protective layer and the conductive adhesive can be improved.

  In addition, surface roughness Ra is the numerical value which measured the surface of the protective layer 2b based on JISB0601-2001 using the contact-type surface roughness meter.

As for the ratio of the thickness of the protective layer 2b to Ra, the thickness of the protective layer is preferably 0.001 to 0.5, and more preferably 0.01 to 0.3, relative to Ra 1. By setting the ratio of the thickness of the protective layer 2b to Ra to be 0.001 to 0.5, the peel strength and the connection resistance value can be improved.

<Conductive adhesive layer>
The conductive adhesive layer 3 is bonded to the printed circuit board and the metal reinforcing plate, respectively. Further, it is formed using an isotropic conductive adhesive or an anisotropic conductive adhesive containing a thermosetting resin and a conductive component. Here, the isotropic conductivity is a property of conducting in the three-dimensional direction of the X axis (left and right direction in FIG. 1), Y axis (depth direction in FIG. 1), and Z axis (up and down direction in FIG. 1). The anisotropic conductivity is a property of conducting only in the Z axis. These electrical conductivity can be suitably selected according to the usage mode of a printed wiring board.

  The thermosetting resin preferably has at least one of a hydroxyl group and a carboxyl group. Specific examples include acrylic resins, epoxy resins, polyester resins, urethane resins, urethane urea resins, silicone resins, amide resins, imide resins, amideimide resins, elastomer resins, and rubber resins. The above resins can be used alone or in combination of two or more.

The thermosetting resin is preferably cured using a curing agent. The curing agent is not limited as long as it is a compound having at least one functional group capable of reacting with the crosslinkable functional group of the thermosetting resin. When the crosslinkable functional group is a carboxyl group, the curing agent is preferably an epoxy compound, an alidiline compound, an isocyanate compound, a polyol compound, an amine compound, a melamine compound, a silane-based, carbodiimide-based compound, a metal chelate compound, or the like.
When the crosslinkable functional group is a hydroxyl group, the curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, or a metal chelate compound. When the crosslinkable functional group is an amino group, the curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, or a metal chelate compound. These curing agents can be used alone or in combination of two or more.

  The conductive component can be appropriately selected from conductive fine particles, conductive fibers, carbon nanotubes, and the like. Examples of the conductive fine particles include metals such as gold, silver, copper, iron, nickel, and aluminum, alloys thereof, and inorganic materials such as carbon black, fullerene, and graphite. Moreover, the silver coating copper fine particle which coat | covered the surface of the copper particle with silver is also mentioned.

  The conductive adhesive layer further includes a tackifying resin, an ion scavenger, an inorganic filler, a metal deactivator, a flame retardant, a photopolymerization initiator, an antistatic agent, an antioxidant, and the like as appropriate. be able to. The thickness of the conductive adhesive layer is usually about 10 to 80 μm.

<Wiring circuit board>
The printed circuit board 6 includes insulating layers 4a and 4b, adhesive layers 5a and 5b, a ground wiring circuit 7, a wiring circuit 8, and an insulating substrate 9. The printed circuit board 6 has a cylindrical or mortar-shaped hole called a via 11 (Via) on the ground wiring circuit 7.

  The insulating layers 4a and 4b are also called cover lay films and contain at least a resin. Examples of the resin include acrylic resins, epoxy resins, polyester resins, urethane resins, ethane urethane resins, silicone resins, polyamide resins, polyimide resins, amideimide resins, and phenol resins. The resin can be appropriately selected from a thermoplastic resin, a thermosetting resin, and an ultraviolet curable resin, and is preferably a thermosetting resin in terms of heat resistance. These resins can be used alone or in combination of two or more. The thickness of the insulating layers 4a and 4b is usually about 5 to 50 μm.

  Examples of the adhesive layers 5a and 5b include thermosetting resins such as acrylic resins, epoxy resins, polyester resins, urethane resins, silicone resins, and amide resins. Examples of the curing agent used for the thermosetting resin include an epoxy curing agent, an isocyanate curing agent, and an alidiline curing agent. The adhesive layers 5a and 5b are used for bonding the insulating layers 4a and 4b to the insulating substrate 9 including the ground wiring circuit 7 and the wiring circuit 8, and have insulating properties. The thickness of the adhesive layers 5a and 5b is usually about 1 to 20 μm.

  The ground wiring circuit 7 and the wiring circuit 8 are generally formed by etching a conductive metal layer such as copper or by printing a conductive paste. Although not shown, the printed circuit board 6 can have a plurality of ground wiring circuits 7 and wiring circuits 8. The ground wiring circuit 7 is a circuit that maintains a ground potential, and the wiring circuit 8 is a circuit that transmits an electrical signal to an electronic component or the like. The thicknesses of the ground wiring circuit 7 and the wiring circuit 8 are usually about 5 to 50 μm, respectively.

  The insulating substrate 9 is a film having insulating properties such as polyimide, polyamideimide, polyferene sulfide, polyethylene terephthalate, and polyethylene naphthalate, and is a base material for the printed circuit board 6. The insulating substrate 9 is preferably polyferene sulfide and polyimide when the reflow process is performed, and is preferably polyethylene terephthalate when the reflow process is not performed. The thickness of the insulating substrate 9 is usually about 5 to 100 μm.

  The via 11 is formed by etching, laser, or the like in order to expose a part of the circuit pattern appropriately selected from the ground wiring circuit 7 and the wiring circuit 8. According to FIG. 1, a part of the ground wiring circuit 7 is exposed by the via 11, and the ground wiring circuit 7 and the metal reinforcing plate 2 are electrically connected through the conductive adhesive layer 3. The diameter of the via 11 is usually about 0.5 to 2 μm.

  The printed wiring board 1 usually includes an electromagnetic wave shield sheet. The electromagnetic wave shielding sheet generally includes an insulating layer 101, a metal film 102, and a conductive adhesive layer 103, and is particularly preferable when an electrical signal flowing through the wiring circuit 8 is a high frequency. On the other hand, although not shown, when the electric signal flowing through the wiring circuit 8 has a relatively low frequency, the electromagnetic wave shielding sheet only needs to include at least the insulating layer 101 and the conductive adhesive layer 103.

  For the insulating layer 101, in addition to using the insulating film described in the insulating substrate 9, a thermosetting resin such as an acrylic resin, an epoxy resin, a polyester resin, a urethane resin, a silicone resin, and an amide resin is appropriately selected. It can also be formed. The thickness of the insulating layer 101 is usually preferably about 2 to 20 μm.

  The metal film 102 is preferably a film formed of a conductive metal such as gold, silver, copper, aluminum, and iron, and an alloy thereof, and copper is more preferable from the viewpoint of cost. The metal film 102 can be appropriately selected from a rolled metal foil, an electrolytic metal foil, a sputtered film, and a deposited film, but a rolled metal foil is preferable and a rolled copper foil is more preferable from the viewpoint of cost. The thickness of the metal film 102 is preferably about 0.1 to 20 μm in the case of a metal foil, about 0.05 to 5.0 μm in the case of a sputtered film, and preferably about 10 to 500 nm in the case of a deposited film. In addition, when forming a sputtered film, it is preferable to use ITO (indium tin oxide) or ATO (antimony trioxide), and when forming a vapor deposition film, gold, silver, copper, aluminum, or nickel is used. It is preferable.

  The conductive adhesive layer 103 preferably includes the raw materials described in the conductive adhesive layer 3. The thickness of the conductive adhesive layer 103 is preferably about 2 to 20 μm.

<Method for manufacturing printed wiring board>
The method for producing a printed wiring board of the present invention needs to include a step of crimping at least the printed circuit board 6, the conductive adhesive layer 3, and the metal reinforcing plate 2. Examples of the crimping include a method in which after the printed circuit board 6 and the electromagnetic wave shielding sheet are crimped, the conductive adhesive layer 3 and the metal reinforcing plate 2 are laminated and crimped, and then an electronic component is mounted. Is not limited. In this invention, what is necessary is just to provide the process of crimping | bonding the wiring circuit board 6, the conductive adhesive layer 3, and the metal reinforcement board 2, and another process can be suitably changed according to the structure thru | or use aspect of a printed wiring board. .
In the case where the conductive adhesive layer 3 contains a thermosetting resin, the pressure bonding is particularly preferably performed simultaneously from the viewpoint of acceleration of curing. On the other hand, even when the conductive adhesive layer 3 includes a thermoplastic resin, it is preferable to heat the adhesive adhesive layer 3 because adhesion is likely to be strong. The heating is preferably about 150 to 180 ° C., and the pressure bonding is preferably about 3 to 30 kg / cm ² . As the crimping apparatus, a flat plate crimping machine or a roll crimping machine can be used. However, when a flat plate crimping machine is used, it is preferable because a certain pressure can be applied for a certain period of time. The crimping time is not particularly limited as long as the printed circuit board 6, the conductive adhesive layer 3, and the metal reinforcing plate 2 are sufficiently adhered to each other, but is usually about 1 minute to 2 hours.

  The printed wiring board of the present invention is mounted (provided) on an electronic device such as a mobile phone, a smartphone, a notebook PC, a digital camera, and a liquid crystal display, and also on a transportation device such as an automobile, a train, a ship, and an aircraft. It can be suitably mounted (equipped).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. “Part” means “part by mass”.

  The members used for the evaluation are as follows.

<Conductive adhesive sheet A>
100 parts of thermosetting polyamide resin (acid value = 10 mg KOH / g, manufactured by Toyochem), conductive fine particles (dendritic particles D50 using copper as the core and silver as the coating layer, average particle size = 12 μm, Fukuda Metal Foil) (Made by Kogyo Kogyo Co., Ltd.) was added to a 400-part container, and a mixed solvent of toluene: isopropyl alcohol (mass ratio = 2: 1) was added and mixed so that the nonvolatile content concentration was 40% by mass. Next, 40 parts of bisphenol A type epoxy resin (“JER828” (epoxy equivalent = 189 g / eq), manufactured by Mitsubishi Chemical Corporation) and 15 parts of amine type epoxy curing agent (“YN100” manufactured by Mitsubishi Chemical Corporation) were added, and 10 minutes with a disper. The conductive resin composition was produced by stirring. The obtained conductive resin composition was applied on the release-treated surface of the peelable film using a doctor blade so that the thickness after drying was 60 μm. The conductive adhesive sheet A was obtained by drying for minutes.

<Wiring circuit board>
Copper-clad laminate; Esperflex (8 μm thick copper foil / 38 μm thick polyimide manufactured by Sumitomo Metal Mining Co., Ltd.)

<Metal reinforcement plate>
A protective layer having a chromium atom concentration of 1 to 20% on the surface of the protective layer was formed on the commercially available stainless steel plate by various plating methods. A stainless steel plate (hereinafter simply referred to as “protective layer”) having a protective layer with a different thickness and surface roughness Ra, and adjusting the conditions of soft gold plating, hard gold plating, silver plating, palladium plating and platinum plating by a known method. SUS plates) 1 to 16 (SUS1 to 16) were obtained. Stainless steel plate 17 (SUS17) having only a nickel layer was obtained by performing only electrolytic nickel plating on the stainless steel plate surface without performing soft gold plating on the stainless steel plate surface. Separately, soft gold plating was formed on the stainless steel plate 17 (SUS17) to obtain a stainless steel plate 18 (SUS18). Each SUS plate was prepared as a test plate A having a thickness of 0.2 mm, a width of 30 mm, and a length of 150 mm, and a test plate B having a thickness of 0.2 mm, a width of 30 mm, and a length of 50 mm. An analytical test plate was prepared separately.

  About the obtained SUS board (SUS1-18), it analyzed by the method shown below, respectively. The results are shown in Table 1.

[Chromium surface atom concentration (Cr concentration)]
A measurement sample was obtained by attaching a double-sided adhesive tape to a dedicated pedestal and fixing a SUS plate. The measurement sample was measured under the following conditions at three locations.
Apparatus: AXIS-HS (manufactured by Shimadzu Corporation / Kratos)
Vacuum degree in sample chamber: 1 × 10 ⁻⁸ Torr or less X-ray source: Dual (Al) 15 kV, 5 mA Pass energy 80 eV
Step: 0.1 eV / Step
Speed: 120 seconds / element Dell: 300, integration number: 5
Photoelectron extraction angle: 90 degrees with respect to the sample surface Binding energy: C1s main peak is 284.6 eV, shift correction Au (4f) peak region: 80-92 eV
Ag (3d) peak area: 376 to 362 eV
Pd (3d) peak area: 332-348 eV
Pt (4f) peak area: 69 to 82 eV
Ni (2p) peak region: 848-890 eV
Cr (2p) peak area: 572-583 eV

The peak that appeared in the peak region was smoothed, and a baseline was drawn by a linear method to determine the surface atomic concentration “Atomic Con” of noble metals and chromium.
With respect to the surface atom concentration of chromium in the total surface atom concentration of the obtained noble metal and chromium, the average value of three values was determined to determine the chromium atom concentration on the surface of the protective layer.

[Surface roughness (Ra)]
The surface roughness Ra was measured according to JISB0601: 2001 under the following conditions.
Ra refers to the arithmetic average roughness Ra, is a defined centerline average roughness, and refers to the centerline average roughness when the reference roughness is 1 mm. Using the contact type surface roughness meter ("SURFCOM 480A" manufactured by Tokyo Seimitsu Co., Ltd.), the above SUS plate was subjected to surface roughness under the conditions of a measurement speed of 0.03 mm / s, a measurement length of 2 mm, and a cutoff value of 0.8 mm. Ra was measured. Ra was an average value of 5 Ras obtained by changing the measurement location.

"Examples 1 to 14 and Comparative Examples 1 to 4"
<Preparation of test laminate>
The conductive adhesive sheet A was prepared to have a width of 25 mm and a length of 100 mm. Next, the exposed conductive adhesive layer on the peelable sheet is placed on the test plate A obtained from the metal reinforcing plate (SUS1-18) shown in Table 1, and a roll laminator (SA-1010 small tabletop test laminator tester industry). Ltd.) Temporarily fixed at 90 ° C., 3 kgf / cm ² , 1 m / min. Then, the peelable sheet was peeled off and placed on the exposed conductive adhesive layer so that the polyimide surface of the Esperflex of the copper clad laminate was in contact with the conductive adhesive layer, and temporarily fixed under the same roll laminating conditions as described above. And after crimping | bonding these on 170 degreeC, 2 Mpa, and the conditions for 5 minutes, the laminated body was obtained by heating for 60 minutes with a 160 degreeC electric oven.
Using the obtained laminate, the printed wiring board was evaluated by the following method.
However, Examples 1, 5, 6, and 7 are reference examples.

<Peel strength>
In order to measure the peel strength between the conductive adhesive layer and the test plate, the obtained laminate was subjected to a T-peel peel test at 23 ° C. and 50% relative humidity at a pulling rate of 50 mm / min. 23 ° C.) peel strength (N / cm) was measured. A small desktop testing machine (EZ-TEST, manufactured by Shimadzu Corporation) was used as the testing machine. Note that the peel strength is also referred to as adhesive strength.

The laminate obtained for measuring the peel strength after reflow was subjected to a reflow treatment using a small reflow machine (SOLSYS-62501RTP manufactured by Antom Co., Ltd.) at a peak temperature of 260 ° C. The laminate was allowed to stand for 1 hour in an atmosphere of 23 ° C. and 50% relative humidity, and then the peel strength (N / cm) after reflow was measured in the same manner as described above. The peel strength was evaluated according to the following criteria.

○: Peel strength is 6 N / cm or more Δ: Peel strength is 3 N / cm or more and less than 6 N / cm ×: Peel strength is less than 3 N / cm

<Solder float test>
The obtained laminate was floated on molten solder at 260 ° C. for 1 minute with the metal reinforcing plate down. Subsequently, about the laminated body immediately after taking out from molten solder, the external appearance of the electroconductive adhesive layer was confirmed visually from the side surface of the laminated body, and the following reference | standard evaluated. In addition, a square solder tank (POT100C manufactured by Taiyo Electric Industry Co., Ltd.) was used for the evaluation. Evaluation was performed 5 times per sample.
A good solder float test indicates that foaming during the reflow process is suppressed.

○: During 5 evaluations, no abnormality was observed in all samples. Excellent Δ: During 5 evaluations, bubbles were generated in 1 or 2 evaluations. Practical use ×: During 5 evaluations, bubbles were generated more than 3 evaluations. Impractical

<Connection resistance value>
Except for changing the size of the conductive adhesive sheet A used in <Preparation of test laminate> to a size of 10 mm in width and 50 mm in length and changing it to test plate B prepared in the same manner as test plate A The laminate was obtained in the same manner as in <Preparation of test laminate>. About the obtained laminated body, the connection resistance value was measured by a two-terminal method using a resistivity meter (Lorestar GP MCP-T600 manufactured by Mitsubishi Chemical Corporation). Thereafter, the sample was put into an oven at 85 ° C. and a relative humidity of 85%, and the resistance value after 500 hours was measured. The connection resistance value was evaluated according to the following criteria.
If the connection resistance value after 500 hours is good, it indicates that the conductivity can be maintained for a long time.

○: Connection resistance value is less than 20 mΩ / □ Δ: Connection resistance value is 20 mΩ / □ or more, less than 40 mΩ / □ ×: Connection resistance value is 40 mΩ / □ or more

From the result of Tables 1-3, it has a metal plate which is a stainless steel plate, and a protective layer, and the protective layer is formed of a noble metal and its alloy, and the chromium atom concentration on the surface of the protective layer is 1 to 20%. The printed wiring board of the present invention having a metal reinforcing plate is less likely to generate bubbles even after the reflow process, and the conductive adhesive layer and the metal plate have a good adhesive force. The conductivity was good.
On the other hand, the printed wiring board of the comparative example could not satisfy all of the electrical conductivity, peel strength, and solder floatability between the ground circuit and the metal reinforcing plate.

For this reason, the electronic device including the printed wiring board having excellent mechanical strength and conductivity according to the present invention has a long-term malfunction caused by electromagnetic noise generated by an electronic component mounted inside or electromagnetic noise entering from the outside. It is possible to prevent it stably and stably.
In addition, since the printed wiring board has a good adhesive strength between the conductive adhesive layer and the metal plate, electronic devices using the printed wiring board are resistant to vibration and dropping, and maintain stable operation over a long period of time. Can do.

DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 Metal reinforcement board 2a Metal board 2b Protective layer 3 Conductive adhesive layer 4a Insulating layer 4b Insulating layer 5a Adhesive layer 5b Adhesive layer 6 Wiring circuit board 7 Ground wiring circuit 8 Wiring circuit 9 Insulating base material 10 Electronic component 11 Via 101 Insulating layer 102 Metal film 103 Conductive adhesive layer

Claims (5)

A wiring circuit board, a conductive adhesive layer, and a metal reinforcing plate, wherein the conductive adhesive layer is bonded to the wiring circuit board and the metal reinforcing plate,
The metal reinforcing plate has a protective layer on the surface of the metal plate,
The metal plate is a stainless steel plate,
The protective layer is formed of a noble metal or an alloy thereof, and the chromium atom concentration on the surface of the protective layer is 3 to 17 % ,
Furthermore, the surface roughness Ra of the protective layer is 0.2 μm or more,
The printed wiring board , wherein the thickness ratio of the protective layer when the surface roughness Ra is 1 is 0.001 to 0.3 . The printed wiring board according to claim 1, wherein the protective layer is formed on the entire interface in contact with the conductive adhesive layer.   3. The printed wiring board according to claim 1, wherein the protective layer is formed of a single material made of any one of gold, silver, platinum, and palladium, or an alloy thereof.   The printed wiring board according to claim 1, wherein the protective layer is soft gold plating. The electronic device provided with the printed wiring board of any one of Claims 1-4.