JP2725664B2 - Wiring board pin mounting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for assembling electronic components, and more particularly to a method for attaching pins to pads provided on one surface of a wiring board.

[0001]

2. Description of the Related Art Ceramic substrates are widely used as substrates for mounting electronic components such as integrated circuits. As one of the structures for connecting the internal wiring of the ceramic substrate and the external circuit, a pin standing on the ceramic substrate is known. With the high integration of components mounted on a ceramic substrate, finer pin intervals are required.

Referring to FIG. 8, in a conventional pin mounting method, a pin 27 is soldered to a pin connecting pad 22 provided on a lower surface of a ceramic substrate 21 by solder 20. At the time of brazing, the jig positions the pin 27 on the corresponding pin connection pad 22.

[0003]

In such a conventional method, there is a problem that the ceramic substrate 21 is easily broken. The occurrence of residual thermal stress in the ceramic at the connection portion of the pin 27 is the cause of this destruction. Residual thermal stress is generated due to a difference in thermal expansion coefficient between the pin 27, the solder 20, and the ceramic substrate 21.

[0004] In view of such problems of the prior art, an object of the present invention is to provide a method for connecting pins to a ceramic substrate which does not impair the reliability of the ceramic substrate. More specifically, a pin connection method that does not generate residual thermal stress on a ceramic substrate is provided.

[0005]

According to the present invention, there is provided a method of attaching pins to a wiring board, comprising the steps of: forming a pad on a first surface of the wiring board; and forming a main body and a head larger than the main body. A second step of preparing a pin having, and a third step of preparing an organic resin sheet, and perforating a through hole having a size through which the main body of the pin passes but does not pass through the head in the organic resin sheet. A third step of inserting the pins into the through-holes of the organic resin sheet, such that the heads of the pins face the pads of the wiring board,
A fourth step of positioning the wiring board and the organic resin sheet and thermocompression bonding the organic resin sheet to the wiring board.

In the first step, an organic resin layer that does not cover the pads is provided on the first surface of the wiring board, and in the fourth step, the organic resin sheet is formed of the organic resin layer of the wiring board. It may be thermocompression bonded to the layer.

[0007] The through hole of the organic resin sheet may be formed in a shape to accommodate a head of the pin. further,
The through-hole may be formed such that when the pin is accommodated in the through-hole of the organic resin sheet, the upper surface of the head of the pin substantially coincides with the upper surface of the organic resin sheet.

In the fourth step, a jig having a concave portion for accommodating the main body of the pin is prepared, and the organic resin sheet is placed on the jig so that the pin main body is accommodated in the concave portion. It may be placed.

[0009] The wiring substrate may be a ceramic wiring substrate. The organic resin sheet may include polyimide. Further, the organic resin layer may include polyimide.

[0010] Since no solder is used, residual thermal stress due to the difference between the coefficients of thermal expansion between the solder and the pins and between the solder and the wiring board is reduced.

Since the pins are not fixed to the pin connection pads, stress does not occur between the pins and the pads even if there is a difference in the coefficient of thermal expansion between the pins and the pads.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, in a first step, a ceramic substrate 1 is prepared.

The ceramic substrate 1 is a square having a side of about 100 mm. The thickness of the ceramic substrate 1 is about 2 mm. The main material of the ceramic substrate 1 is alumina. The ceramic substrate 1 is formed by laminating about 30 green sheets,
It is manufactured by firing these green sheets. A plurality of wiring layers are formed of a conductive material inside the ceramic substrate 1. The through hole in the ceramic substrate 1 is formed of tungsten and has a diameter of about 0.35 mm.
It is.

On the lower surface of the ceramic substrate 1, about 2000
The plurality of pin connection pads 2 are formed. The pin connection pads 2 are arranged in a lattice with a pitch of about 1.8 mm. The diameter of the pad 2 is about 1.2 mm. The pad 2 is formed of tungsten, and its surface is plated with gold.

An electronic component mounting pad 3 is provided on the upper surface of the ceramic substrate 1. Electronic component mounting pad 3
Are arranged at positions corresponding to the external terminals of the electronic component.

Referring to FIG. 2, in a second step, a polyimide layer 4 is formed on the lower surface of the ceramic substrate 1. The thickness of the polyimide layer 4 is about 0.01 mm. The polyimide layer 4 has been removed from above the pad 2 for pin connection. Therefore, the pin connection pads 2 are exposed without being covered by the polyimide layer 4.

The polyimide layer 4 is formed by three steps. In the first step, a polyimide precursor varnish is applied to the lower surface of the ceramic substrate 1 and dried. In the second step, the polyimide precursor varnish is removed from above the pin connection pad 2 by exposing and developing the polyimide precursor varnish. In the third step, curing is performed and the polyimide precursor varnish is thermally cured.
Thereby, the polyimide layer 4 is formed.

Referring to FIG. 3, in a third step, a polyimide sheet 5 is prepared. The size of the polyimide sheet 5 is preferably slightly smaller than that of the ceramic substrate 1. In this embodiment, the polyimide sheet 5 is a square having a side of about 90 mm. The polyimide sheet 5
It has a uniform thickness of about 0.1 mm.

Referring to FIG. 4, holes 6 are drilled in the polyimide sheet 5. The diameter of the hole 6 is about 1.
2 mm and about 0.35 mm on the lower surface. Hole 6
It is provided at a position corresponding to the pad 2 for pin connection. The sectional shape of the hole 6 is machined so as to have an inclination in accordance with the head of the pin 7 described later. The hole 6 is drilled by laser processing. The taper of the hole 6 can be formed by using a condensing lens for forming the taper.

Referring to FIG. 5, a pin 7 is inserted into the hole 6 in a fifth step. The head of the pin 7 has a taper. When a head having a taper is used, the stress of the ceramic substrate 1 can be effectively reduced. The diameter of the head of the pin 7 is about 1 mm. The diameter of the body of the pin 7 is about 0.35 mm. The pins 7 are held in the polyimide sheet 5 by the heads of the pins 7 being housed in the holes 6. When the head of the pin 7 is received in the hole 6, the upper surface of the head of the pin 7 substantially coincides with the upper surface of the polyimide sheet 5. The pins 7 are formed of a metal having substantially the same coefficient of thermal expansion as the ceramic substrate 1. Specifically, gold-plated Kovar is preferable.

Referring to FIG. 6, in a sixth step, lower mold 9 is prepared. At a position corresponding to each pin 7 of the lower mold 9, a recess 10
Is provided.

In a seventh step, the polyimide sheet 5 is placed on the lower mold 9. At this time, the lower part of the pin 7 is housed in the recess 10 of the lower mold 9.

In the eighth step, the lower mold 9 is positioned so that each pin 7 is located immediately below the corresponding pin connection pad 2.

In the ninth step, the ceramic substrate 1 and the polyimide sheet 5 are sandwiched between the upper die 8 and the lower die 9 and are thermocompression-bonded. At this time, the heating temperature is
When the temperature is set to be equal to or higher than the glass transition point of the polyimide resin, very strong adhesion can be obtained. Specifically, the temperature is about 350 degrees,
Thermocompression bonding is performed under the condition of a pressure of 15 kg / cm 2.

At the time of thermocompression bonding, air bubbles between the polyimide layer 4 and the polyimide sheet 5 must be avoided. This is because if air bubbles are mixed, the adhesion reliability between the polyimide layer 4 and the polyimide sheet 5 and the contact reliability between the pin connection pad 2 and the pin 7 are impaired. Therefore, thermocompression bonding is 1
It is performed in a vacuum state of about 0-2 torr. Specifically, an autoclave type vacuum press is used. Nitrogen is used as the pressurized gas.

Referring to FIG. 7, in a tenth step, upper mold 8 and lower mold 9 are removed. By thermocompression bonding, the polyimide layer 4 and the polyimide sheet 5 are integrated, and the polyimide layer 11 is formed. Thus, the pin 7 is connected to the pin connection pad 2 by contact. The pin 7 is not fixed to the pad 2 for pin connection. Therefore, the pin 7
Even if the coefficient of thermal expansion of the pin connection pad 2 differs from that of the pin connection pad 2, stress does not occur between the pin connection pad 2 and the pin 7.

It is desirable that the resin material used for bonding and the substrate material have the same coefficient of thermal expansion as much as possible. If there is a large difference in the coefficient of thermal expansion between these materials, the stress generated at the time of thermocompression bonding increases, and the bonding reliability is impaired.

Next, another embodiment of the present invention will be described.

In this embodiment, polyimide is used as the organic resin on the bonding surface, but the scope of the present invention is not limited to this. For example, a melt-thermosetting maleide resin or a melt-type fluorine-based film can be used. One example of the melt-type fluorine-based film is a copolymer of ethylene fluoride and perfluoroalkylolovinyl ether.

In this embodiment, an alumina ceramic substrate is used as the wiring substrate, but the scope of the present invention is not limited to this. For example, the present invention can be applied to an organic resin molded substrate such as a polyimide substrate or a glass ceramic substrate.

[0032]

Since no solder is used, the residual thermal stress due to the difference in the coefficient of thermal expansion between the solder and the pin and the difference in the coefficient of thermal expansion between the solder and the wiring board is reduced.

Since the pins are not fixed to the pin connection pads, no stress is generated between the pins and the pads even if there is a difference in the coefficient of thermal expansion between the pins and the pads.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first step of an embodiment of the present invention.

FIG. 2 is a diagram showing a second step of the embodiment of the present invention.

FIG. 3 is a diagram showing a third step of the embodiment of the present invention.

FIG. 4 is a view showing a fourth step of the embodiment of the present invention.

FIG. 5 is a diagram showing a fifth step of the embodiment of the present invention.

FIG. 6 is a view showing sixth to ninth steps of one embodiment of the present invention.

FIG. 7 is a view showing a tenth step of the embodiment of the present invention.

FIG. 8 shows a ceramic substrate 21 according to a conventional connection method.
FIG. 4 is a diagram showing a connection structure between a pin and a pin 27;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic board 2 Pin connection pad 3 Electronic component mounting pad 4 Polyimide layer 5 Polyimide sheet 6 Hole 7 Pin 8 Upper die 9 Lower die 10 Depression 1 11 Polyimide layer 20 Solder 21 Ceramic substrate 22 Pin connection pad 23 Electronics Component mounting pad 27 pins

Claims (8)

(57) [Claims] 1. A method for attaching pins to a wiring board, comprising: a first step of forming pads on a first surface of the wiring board; and a second step of preparing a pin having a main body and a head larger than the main body. And a third step of preparing an organic resin sheet, and perforating a through hole having a size that allows the main body of the pin to pass through the organic resin sheet but does not allow the head to pass therethrough; A third step of inserting the pin into the through-hole; positioning the wiring board and the organic resin sheet so that the head of the pin faces the pad of the wiring board; And a fourth step of thermocompression bonding to the board. 2. In the first step, an organic resin layer that does not cover the pad is provided on the first surface of the wiring board, and in the fourth step, the organic resin sheet is provided on the first surface of the wiring board. 2. The method according to claim 1, wherein the pin is thermocompression-bonded to the organic resin layer. 3. The method according to claim 1, wherein the through hole of the organic resin sheet is formed in a shape to accommodate a head of the pin. 4. The organic resin sheet according to claim 3, wherein when the pin is accommodated in the through hole of the organic resin sheet, an upper surface of the head of the pin substantially coincides with an upper surface of the organic resin sheet. Pin mounting method of wiring board. 5. A jig having a concave portion for accommodating the main body of the pin is provided in the fourth step,
2. The method according to claim 1, wherein the organic resin sheet is placed on the jig such that the pin body is accommodated in the recess. 6. The method according to claim 1, wherein the wiring board is a ceramic wiring board. 7. The method according to claim 1, wherein the organic resin sheet contains polyimide. 8. The method according to claim 2, wherein the organic resin layer contains polyimide.