JPH0682905B2 - Printed wiring board having connector function and connecting method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a printed wiring board having a connector function (connecting terminal part) having a fine pitch and having a connector function, and more specifically, a conductor of the connecting terminal part. Very small connection resistance and excellent insulation between adjacent conductors by contacting the conductor of the mating printed circuit board through the metal protrusions (dendrites) generated above to establish continuity and fixing with an adhesive The present invention relates to a printed wiring board having a connector function that can be connected with a property.

[Prior Art] Conventionally, when a lead wire is taken out from a rigid printed wiring board such as glass epoxy, paper phenol, a transparent electrode glass substrate, a ceramic circuit board, a metal circuit board by a flexible printed wiring board, etc., most commonly, Methods such as soldering and connection using a film or sheet-like anisotropic conductive film are used.

Anisotropic conductive film (film, sheet) is made into a film or sheet by dispersing conductive particles such as metal powder, plating powder, and carbon particles in a hot-melt type or thermosetting type adhesive. For example, as shown in FIG. 9, a glass substrate 5 having a circuit pattern of a conductor 6 such as an ITO (indium tin oxide) film and a polyimide film 1 having a circuit pattern of a conductor 2 such as copper are formed. When the anisotropic conductive film (film, sheet) is sandwiched between them and thermocompression-bonded, the conductive particles 11a present in the adhesive 4 adhere to each other because the space between the conductors 2 and 6 becomes narrow. Then, there is a continuity between the conductors 2 and 6,
It has conductivity in the thickness direction and insulation in the plane direction.

[Problems to be Solved by the Invention] However, any of the methods of soldering or using an anisotropic conductive film is a method used when the pitch interval between conductors is large, for example, when the pitch is 0.2 mm or more. However, if the pitch is narrower than this, there is a drawback that adjacent conductors are short-circuited, or even if they are not short-circuited, the insulation between the conductors is extremely deteriorated. Further referring to the anisotropic conductive film, as shown in FIG. 9, the conductive particles 11b are present between adjacent circuit patterns (gap portions), which deteriorates the insulating property. 11
Since there is conduction due to the contact between a, it also has the drawback of high contact resistance and low reliability.

In view of such problems of the conventional example, it is an object of the present invention to provide a printed wiring board having a connector function with excellent insulation between adjacent conductors and extremely low connection resistance.

[Means and Actions for Solving Problems] In order to achieve the above object, the present invention provides a single-sided or double-sided printed wiring board having a connector function, which includes a connection terminal portion connected to a printed circuit board. A needle-shaped or lump-shaped metal projection is formed on the surface of the conductor portion of the terminal portion by electrodeposition, that is, electroplating, and an adhesive is applied to the connection surface of the connection terminal portion including the projection, or the projection is An adhesive layer is interposed between the connection terminal portion including the connection terminal portion and the connection terminal portion on the printed circuit side, and the connection is made by hot pressing.

The present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view schematically illustrating a part of the connection terminal portion of the printed wiring board of the present invention. In the figure, 1 is a film or sheet-like film that is a base material of a printed wiring board, 2 is a conductor that constitutes a circuit pattern formed on the film 1, and 3 is a metal projection formed on the conductor 2. Reference numeral 4 denotes an adhesive filled in the gap region between the conductors 2 and between the metal protrusions 3.

A polyimide film, a cured adhesive, or the like can be used as the film 1, but a rigid substrate may be used.

As the material of the conductor 2, copper, zinc, nickel or the like can be used. A circuit pattern is formed by laminating such a conductor material on one side or both sides of the film 1 and etching.

The needle-shaped or lump-shaped metal projections 3 are needle-shaped or lump-shaped dendrites formed on the conductor 2 by electrodeposition. As a material for the dendrite, a metal such as copper, nickel, zinc, gold or silver is suitable. It is also possible to further apply gold plating, platinum plating, or the like on the dendrite of copper, nickel, or the like, which is preferable from the viewpoint of improving the adhesion with the conductor on the other side. The height of the metal protrusion 3 is 0.1μ
It is preferably m or more, and if it is too small, the thickness of the adhesive cannot be removed, resulting in poor contact.

The dendrites are formed by performing bump plating by electrodeposition using the conductor 2 as a cathode, that is, plating in which a lump of dendrites is attached by using electrode 2 as a cathode in a plating bath suitable for producing dendrites.

This bumpy plating varies depending on the type of metal electrodeposited as a dendrite, but for example, in the case of copper dendrite, the copper concentration is 5 to 10 g / l or less and the current density is 3 to 10 A / d.
The desired bumpy plating is achieved by electrolysis for a few minutes in a bath containing m ² , and optionally traces of additives such as arsenic compounds and β-naphthoquinoline. At this time, since the dendrite grows largely on the upper surface of the conductor 2 and hardly grows on the side surface, or because such bath composition and plating conditions are selected, even if the pitch interval between the conductors 2 is extremely short, a short circuit occurs. Extremely low risk. This is the reason why fine-pitch connection is possible, and the greatest advantage is that it does not short-circuit up to a pitch interval (60 μm pitch) that contains 8 to 16 conductors per 1 mm width, and maintains good insulation. It is possible to do.

As the adhesive 4, any of a hot-melt type, a thermosetting type, and a room temperature adhesive can be used. The adhesive 4 is filled so as to have a thickness equal to or less than the height of the metal projection 3 within a range that does not greatly exceed the height of the metal projection 3.
That is, it is desirable that the total thickness of the conductor 2 such as copper foil and the height of the metal protrusions 3 is not more than 10 and usually 10 or less.
~ 35 μm is desirable. However, as in the case of a conductive paste filled with metal powder or an anisotropic conductive film (film, sheet), even if the adhesive is thinly covered on the metal protrusions 3, or if the adhesive has a thickness of metal, Even if the height of the protrusion 3 is equal to or higher than that of the protrusion 3, good conduction can be obtained by pressure bonding with a press.

Such a printed wiring board of the present invention, as shown in FIG. 2, has a glass substrate 5 and a circuit pattern formed by a conductor 6 such as an ITO film on the glass substrate 5 on the other side of the printed circuit board. The connection terminal portions are connected to each other by pressure bonding and fixing with an adhesive 4.
The adhesive 4 is used, for example, by applying it to the connection terminal portion of the printed wiring board or by sandwiching the adhesive layer between both connection terminal portions.

Therefore, in comparison with the case where the conductive particles such as metal or carbon powder as in the conventional example shown in FIG.
The resistance is incomparably small because conduction is established via the metal protrusions 3 which are two metal lumps, and the insulating property is extremely excellent because there are no conductive particles between adjacent conductors, and reliability is improved. I am raising.

As described above, the most important feature of the present invention is that a fine anisotropic conductive film (film, sheet) having 8 or 16 conductor wires in a 1 mm interval is not possible. Suitable for pitch connection,
In addition, the connection resistance is 10 ⁻⁴ to 10 ⁻⁵ Ω, which is a value that is several orders of magnitude lower than that of the conventional anisotropic conductive film or conductive paste. And, in particular, the flexible printed wiring board according to the present invention,
It is effective for connection with transparent electrodes for display devices such as liquid crystal televisions, which are becoming finer in pitch in recent years, and connection with alumina heads used in printers and facsimiles where the number of dots is increasing. It can also be used as a simple connector.

[Examples] Examples of the present invention will be described below.

Example 1 18 μm on a 25 μm thick polyimide film (Kapton)
Flexible printed circuit board (250mm
After cleaning the copper surface of (330 mm), a photosensitive dry film of 25 μm thickness is laminated, and a 125 μm pitch (gap 60 μm is included so that 8 conductors are included per 1 mm).
m, conductor width 65 μm), exposed to light, developed with an alkaline solution, etched the copper layer with a ferric chloride solution, and stripped the resist of the dry film to obtain the fine pitch wiring board. It was

Next, after pickling the exposed copper conductor with acid, this was used as a cathode, and the current density was increased in an electrolytic solution containing copper concentration of 8 g / l, sulfuric acid concentration of 100 g / l and α-anthraquinoline of 20 mg / l. 6A / dm ²
As a result, electrolysis was carried out for about 8 minutes, and electroplating was performed to deposit and form a dendrite in the form of a block having a height of 2 to 3 μm and good adhesion.

In addition, a gold coating, which is generally performed in a neutral cyanide gold bath, is coated to a thickness of about 0.5 μm to prevent copper rusting, reduce contact resistance, and improve the adhesion of dendrites on the copper layer. It was Then, a thermosetting epoxy adhesive is applied to the gold-plated fine pattern wiring board with a roll coater in a dry state to a thickness of about 20 μm, and then dried.
It was stored in the β stage called epoxy system.

Next, cut this wiring board to the required size,
Align the terminals of a rigid printed wiring board with a conductor-to-conductor pitch of / mm, and press for 3 minutes at 180 ° C and a press pressure of 20 kg / cm ² with a hot press to make connection resistance, insulation between wires, and adhesion. The force was measured. The results are shown in Table 1 in comparison with the case of the conventional anisotropic conductive film (film).

As shown in Table 1, the wiring board of this embodiment has a connection resistance,
It can be seen that both the line insulation and the adhesive force are superior to the conventional anisotropic conductive film (film).
It can also be seen that the conventional anisotropic conductive film is short-circuited in some places, whereas the wiring board of this embodiment does not have this.

In order to clarify the reason, the conventional anisotropic conductive film (film) and the connection terminal portion of the wiring board of this example were observed with an electron microscope. The results are shown as electron micrographs in FIGS. 3 and 4, respectively.

FIG. 3 is a photograph showing a grain structure when an anisotropic conductive film is connected to glass, and FIG. 4 (a) is a photograph showing a grain structure of a wiring board when a dendrite is attached in this example. . In the photograph of FIG. 3, the black dots are the conductive powder dispersed in the adhesive, which is also present in the gap between the conductors, which requires insulation. On the other hand, in the photograph of FIG. 4 (a), there is no material such as conductive particles that hinders the insulating property between the gaps other than the conductor. From this, it is understood that, in the case of the wiring board of the present embodiment, there is no risk of short-circuiting between adjacent circuits no matter how narrow the conductor spacing is. Also, the fourth
FIG. 4 (b) is a photograph showing a further enlarged grain structure of the conductor portion in FIG. 4 (a), which shows that dendrites are densely generated on the conductor surface. Further, FIG. 4 (c) is a photograph showing the particle structure of the dendrite when the contact situation with respect to the glass when the adhesive is filled and adhered to the glass is observed from the glass surface side. It is confirmed that the glass surface is surely in contact with the glass surface, and it can be seen that the electric conductivity can be surely achieved without impairing the conductivity.

Example 2 An ultra-thin copper layer obtained by laminating a copper film having a thickness of about 1 μm on a polyimide film having a thickness of about 25 μm by a sputtering method and electrodepositing copper to a thickness of 9 μm in a copper sulfate bath containing a slight amount of glue. Starting from a directly attached polyimide film substrate, apply a liquid photosensitive resist on this laminated copper surface,
After exposing and developing through a pattern of a negative film having 16 conductor lines with a width of 1 mm, the copper layer was etched in the same manner as in Example 1 and the resist was peeled off to obtain a super fine pitch printed wiring board. It was Next, after pickling the exposed copper conductor with acid, this was used as the cathode and nickel sulfate 10
In a weakly acidic electrolytic bath containing g / l, ammonium sulfate 5 g / l and potassium bromide 2 g / l, electrolysis was carried out by electrolysis for several minutes at a current density of 5 A / dm ² , a bath voltage of 6 V and a bath temperature of 40 ° C. By doing so, black dendrites of nickel lumps were deposited on the copper conductor.

FIG. 5 is a schematic cross-sectional view showing a part of the connection terminal portion of the printed wiring board thus obtained. When the surface of this printed wiring board was observed, as shown in the figure, the sputtered copper layer was sprinkled in a copper sulfate bath with a slight amount of glue added.
Irregularities of several μm in height of the electrodeposited copper layer 2b were confirmed on 2a, and nickel dendrite 3 was attached on the copper layer 2b. FIG. 6 is a photograph showing the grain structure of this dendrite portion. In addition, when an attempt was made to generate dendrites in the case of electrolytic conditions or bath compositions different from the above case, as shown in the photograph of the particle structure shown in FIG.
Needle-shaped dendrites were produced. However, in this case,
Copper concentration is 8 g / l, sulfuric acid concentration is 100 g / l, and in the electrolyte solution added with 50 ppm of β-naphthoquinoline, the cathode current density is 8 A /
Electrolysis was performed for 15 seconds as dm ² .

Next, after the dendrite electrodeposition is completed, the hot-melt type adhesive dissolved in a solvent is applied by screen printing to the terminal part of the wiring board and dried to evaporate the solvent, so that the adhesive is almost at the height of the dendrite. Was filled.

Furthermore, after aligning the terminals of the ultra-fine-pitch flexible printed wiring board thus obtained and the ultra-fine terminals of the rigid circuit board formed by etching the transparent ITO film on the glass substrate, hot With the press, first, temporary pressure bonding was performed at 80 ° C. to 100 ° C. and pressure of 1 to ² kg / cm ² for 3 seconds, and then main pressure bonding was performed at 150 ° C. for 10 seconds. FIG. 8 is a side view schematically showing the flexible printed wiring board and the rigid circuit board thus connected, 7 is the above-mentioned fine pitch flexible printed wiring board, and 8 is copper on the polyimide film 1 Copper conductor circuit composed of layers, 9 is a rigid circuit board on the other side,
Reference numeral 10 is an ITO film circuit formed on the glass substrate 5.

Next, when the conduction resistance between the terminal of the copper conductor circuit 8 of the flexible printed wiring board thus connected and the transparent electrode terminal of the ITO film circuit 10 of the rigid circuit board was measured, it was 10 ⁻⁵ Ω, which was extremely high. The insulation resistance between the adjacent conductors which is small and which constitutes the circuit 8 is 10 ¹² to 10 ¹³ Ω, and the connection with extremely high reliability was confirmed.

[Effects of the Invention] As described above, according to the present invention, in a printed wiring board having a connector function, electrical continuity with a conductor of a mating rigid circuit board is provided through a metal projection formed on a conductor of a connection terminal portion. As a result, a very small connection resistance is realized and the insulation between adjacent conductors is improved,
It is possible to make a connection suitable for highly reliable fine pitch.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically illustrating a part of a connection terminal portion of a printed wiring board of the present invention, and FIG. 2 shows a printed wiring board of the present invention connected to a mating printed circuit board. Sectional drawing which illustrates typically a part of connection terminal part, FIG. 3 is a photograph of the particle structure by an electron microscope when the connection terminal part of the conventional anisotropic conductive film (film) is adhered to glass, FIG. 4 is a photograph of a particle structure of a connection terminal portion of a flexible printed wiring board according to an embodiment of the present invention, taken by an electron microscope. FIG. 4 (a) shows particles when dendrite is attached to a conductor portion. A photograph of the structure, (b) of the figure is a photograph of the particle structure when the conductor portion in (a) is further enlarged, and (c) of the figure is the tip of a dendrite that is filled with an adhesive and adhered to glass. A photograph of the particle structure showing how particles are in contact with the glass surface FIG. 5 is a sectional view schematically showing a part of a connection terminal portion of an ultrafine pitch printed wiring board according to another embodiment of the present invention, and FIG. 6 is an ultrafine pitch print of FIG. A photograph of the particle structure of the dendrite formed on the conductor of the wiring board is shown in FIG. 7. FIG. 7 is a photograph of the particle structure of the dendrite formed under other electrolytic conditions and bath compositions according to one embodiment of the present invention. 5 is a side view schematically showing a state in which the printed wiring board of FIG. 5 is connected to another circuit board, and FIG. 9 is a connection terminal of a wiring board using an anisotropic conductive film according to a conventional example. It is sectional drawing which shows a part of part typically. 1: Base film, 2: Conductor, 2a: Sputtered copper layer, 2b: Electrodeposited copper layer, 3: Metal protrusion (dendrites), 4: Adhesive, 5: Glass substrate, 6: ITO film conductor , 7: Printed wiring board, 8: Copper conductor circuit, 9: Rigid circuit board, 10: ITO film circuit, 11, 11a, 11b: Conductive particles.

Claims (3)

[Claims] 1. A single-sided or double-sided printed wiring board having a connector function, which is connected to a printed circuit board, and has needle-like or needle-like shape generated by electrodeposition on the surface of the conductor portion of the connection terminal section. A printed wiring board having a connector function, which has a block-shaped metal projection, and a surface of the needle-shaped or block-shaped metal projection is coated with an adhesive. 2. A method for connecting a printed wiring board having one or both sides having a connector function to a printed circuit board, which comprises a connecting terminal portion to be connected to the printed circuit board. Of a printed wiring board having a connector function, which is characterized in that needle-like or lump-shaped metal projections are formed by adhesion, and an adhesive is applied to the connection surface of the connection terminal portion including the projections and the connection is made by hot pressing. How to connect. 3. A method of connecting a single-sided or double-sided printed wiring board having a connector function to a printed circuit board, comprising a connection terminal portion connected to the printed circuit board, wherein an electric power is applied to the surface of the conductor portion of the connection terminal portion. The method is characterized in that a needle-shaped or lump-shaped metal projection is generated by adhesion, and an adhesive layer is interposed between the connection terminal portion including the projection and the connection terminal portion on the printed circuit side for connection by hot pressing. A method for connecting a printed wiring board having a connector function.