JP2820115B2 - Method for highly reliable connection and mounting of electronic components on printed circuit board and electronic components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to connection to a printed circuit board, and more particularly to a method for connecting and mounting a surface mount electronic component with high reliability and an electronic component used in the method.

[0002]

2. Description of the Related Art In recent years, miniaturization of portable electronic devices and the like has been realized along with the development of LSIs in electronic circuits. On the other hand, with the progress of multimedia, the functions of the devices have been enhanced and the convenience of carrying has been improved. Due to the demand, it is necessary to mount many components at high density. For this reason, mounting on a printed circuit board is often based on a surface mounting technology called SMT, and the tendency is that LSI packages have a finer connection lead pitch, and other so-called SMD surfaces. The mounting components have been further downsized. Conventionally, the connection of these LSIs and SMD parts to the printed circuit board is mostly done by soldering, but in some cases the LSI is mounted on the printed circuit board with a bare chip, and the connection is made by wire bonding or flip chip. In some cases, this is done in combination with a connection called

[0003] In soldering, various conditions such as the amount of solder, the oxidized state of the connection portion, the deformation of the connection lead, the finish of the surface of the printed circuit board, and the flux to be used are involved, and the structure of the connection portion becomes fine. However, it is necessary to control the conditions severely and to reduce the variation. However, since there is variation due to manufacturing, the quality of the connection generally deteriorates as the density increases.

For example, Japanese Patent Application Laid-Open No. 63-070597 relates to a method of soldering a surface mount component, since silver-palladium is used for the SMD electrode, so-called electrode erosion (electrode diffuses into the solder and is scraped off by the solder). phenomenon)
There is disclosed a device for preventing the occurrence of. Here, we do not mention when the surface mount components are very small or when the lead pitch is very fine, but phenomena occur regardless of the size of the components, so if small components are used, It is easily presumed that the influence of soldering on the connection part increases.

[0005] Generally, when the lead pitch of a QFP type LSI is about 0.5 mm, the connection quality (the number of connection failure points for the total number of connection points of a printed circuit board) is as follows.
It is said that the connection quality is 50 to 100 PPM, but when it is 0.4 mm, the connection quality is said to be 500 to 1000 PPM, and the difficulty of the connection is exposed at a stretch. Although miniaturization of equipment requires miniaturization of components, miniaturization may be hindered for such reasons. On the other hand, wire bonding is a technology that connects to the pads of the bare chip,
At present, a connection pitch of 100 μm can be easily connected, and the connection quality is said to be 1 to 2 PPM. Therefore, it can be said that the quality is one to two digits better than that of soldering. Therefore, it can be said that wire bonding is a connection method that can sufficiently withstand miniaturization to which soldering cannot be applied.

[0006]

In the conventional connection of electric and electronic parts to a printed circuit board by soldering, the quality of the connection gradually increases as the size of the parts becomes smaller as the size of the equipment becomes smaller and the connection parts become smaller. There is a problem of getting worse.

[0007] In order to maintain the quality of the connection, during production, the appearance of the connection portion, an electrical connection test, and the like are checked to ensure that there are no defects. Man-hours and capital investment for that affect the production cost. I have. In addition, appearance inspections are performed by humans or machines, but they are not complete.
Even if the solder is not connected, it is connected because the lead part of the component is pressed by the contact, and it operates electrically and is not judged to be defective, so it can not be found in production It can happen that it is shipped.

[0008] More recently, it has been reported that lead contained in solder has an adverse effect on the human body, and some solders that do not use lead have begun to appear. However, the temperature required for soldering is high and unknown parts are still unknown. It is a situation that is not often used.

An object of the present invention is to provide an electronic component which can securely connect a printed circuit board to an LSI or a surface mount component without using soldering, can increase the reliability of equipment, and can increase productivity. An object of the present invention is to provide a connection mounting method to a printed circuit board.

[0010]

SUMMARY OF THE INVENTION The present invention provides at least one
The two electronic components are fixed to the printed circuit board using a conductive adhesive, the connection between the electronic component and the printed circuit board is performed by the above-described conductive adhesive, and the further connection is performed double by wire bonding.

Forming a component pad on the printed circuit board, the component pad being connected to the wiring pattern and mounting the connection terminal of the electronic component, and applying a conductive adhesive on the component pad;
The connection terminal may be placed on the component pad on which the conductive adhesive is formed, and the conductive adhesive may be cured.

A conductive adhesive may be applied on the component pad by printing or dispensing.

[0013] The conductive adhesive may be cured by ultraviolet irradiation or heating.

A bonding stitch is arranged on the wiring pattern at a position adjacent to the component pad, gold plating is applied to the connection terminal portion and the bonding stitch, and a gold wire is used between the gold plated connection terminal portion and the bonding stitch. Wire bonding.

After the wire bonding, the bonding portion or the surface of the printed circuit board including the bonding portion may be coated.

Further, the facilities of the gold in at least a portion of the connection terminals of the electronic component is surface mounted on a printed circuit board
Preferably .

[0017]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an external perspective view showing an example of connection and mounting of an electronic component on a printed circuit board according to the present invention, and FIG. 2 is a sectional view of a main part thereof.

FIG. 1 shows a state in which a chip component 6 as a surface mount component and a QFP type LSI 7 are connected and mounted on a part of the printed circuit board 1, and FIG.
The cross section including SI7 is shown.

Each of the chip component 6 and the QFP type LSI 7 has its connection terminal portions 8 and 9 fixed on a component pad 3 provided on the printed circuit board 1 by a conductive adhesive 11, and each component pad has a bonding stitch 4. It is connected to the circuit pattern 2 of the printed circuit board 1 with it interposed therebetween. Reference numeral 5 denotes a solder resist. Therefore, chip component 6
The LSI 7 is fixed to the printed circuit board 1 by the conductive adhesive 11 and is connected to the circuit pattern 2 of the printed circuit board 1.

The connection terminals 8 and 9 of the chip component 6 and the LSI 7 are connected to the bonding stitch 4 by bonding wires 10. Therefore, the chip component 6 and the LSI 7 are connected to the circuit pattern 2 of the printed circuit board 1 via the conductive adhesive 11 and the bonding wires 10 at the same time.

Next, the mounting will be described in order. A conductive adhesive 11 on the printed circuit board 1 and also for fixing and connecting the components is formed on the component pads 3 by printing in substantially the same area. This can be done in the same way as cream solder printing for soldering. Next, electronic components (chip component 6, LSI 7, etc.) to be mounted on the printed circuit board 1 are mounted on the component pad 3 whose connection terminals 8, 9 are determined. This may also be a so-called SMT component mounting method. Thereafter, reflow is performed to cure the conductive adhesive 11. In the case of an ultraviolet curing type, ultraviolet rays are irradiated, and in the case of a type cured by heat, curing is performed by applying heat such as infrared rays. Next, each of the electronic components 6, 7
The bonding wire 10 is bonded between the connection portions 8 and 9 of the printed circuit board and the bonding stitch 4 of the printed circuit board 1. If this is performed with as low a loop as possible, deformation due to handling or the like can be avoided. This completes the mounting, but if sealing is further performed with, for example, silicon (not shown), the connection portion is reinforced as a whole, and the vibration resistance can be increased. In order to perform wire bonding with gold wires, gold plating is applied to connection terminal portions such as chip component terminal portions and LSI lead portions, and gold plating is also applied to bonding stitch portions of a printed circuit board. A component in which the connection terminal portion is already plated with gold may be used.

It is conceivable that the pitch of the leads of a QFP type LSI becomes extremely fine, making it impossible to print a conductive adhesive on each lead. Used only for fixing the body,
It is unavoidable that the connection is made only by bonding.

[0023]

As described above, according to the present invention, the connection terminals of electronic components mounted on a printed circuit board are adhered to designated positions on the printed circuit board using a conductive adhesive, and the electronic components are printed. At the same time as fixing to the board, circuit connection between these electronic components and the printed board is performed, and furthermore, the connection terminals and the bonding stitches on the board are connected by wire bonding, and the connection between the components and the board is duplicated. This has the effect of significantly improving the reliability of the connection.

The connection quality using the conductive adhesive is considered to be 100 PPM, which is the same as the connection by soldering. Even if the quality of wire bonding is considered as 2 PPM, which is worse, the total connection quality is 0.0002 PPM. At this level, inspections for connection in production can be completely omitted, and significant labor can be reduced when rework is included. In addition, portable devices are generally harsh to use, but have a dual connection and are unlikely to fail. Furthermore, there is an effect that connection without using solder, which is a concern for environmental problems, can be performed, and since it can be manufactured at a relatively low temperature, there is also an effect that the heat resistant temperature of components can be reduced to about 200 ° C. .

[Brief description of the drawings]

FIG. 1 is an external perspective view showing an example of connection and mounting of an electronic component on a printed circuit board according to the present invention.

FIG. 2 is a sectional view of a main part of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 printed circuit board 2 printed circuit board pattern 3 component pad 4 bonding stitch 5 solder resist 6 chip component 7 QFP type LSI 8 chip component connection terminal 9 LSI lead connection terminal 10 bonding wire 11 conductive adhesive

Claims (7)

(57) [Claims] 1. A method of connecting and mounting an electronic component to a printed circuit board, wherein at least one electronic component is fixed to the printed circuit board using a conductive adhesive, and a connection between the electronic component and the printed circuit board is made by the conductive material. A method of connecting and mounting electronic components, wherein the method is performed by a conductive adhesive, and the connection is performed double by wire bonding. 2. A component pad connected to a wiring pattern and on which a connection terminal portion of an electronic component is mounted is formed on a printed circuit board, and the conductive adhesive is applied and formed on the component pad. 2. The method of connecting and mounting an electronic component according to claim 1, wherein the connection terminal portion is placed on the component pad on which an agent is formed, and the conductive adhesive is cured. 3. 3. The method according to claim 2, wherein the conductive adhesive is formed on the component pad by printing or dispensing.
The connection mounting method of the electronic component described in. 4. The method according to claim 2, wherein the conductive adhesive is cured by irradiating ultraviolet rays or heating. 5. A bonding stitch is arranged on the wiring pattern at a position adjacent to the component pad, gold plating is performed on the connection terminal portion and the bonding stitch, and the gold-plated connection terminal portion and the bonding stitch are provided. The method according to any one of claims 2 to 4, wherein wire bonding is performed between the bonding stitches using a gold wire. 6. The method for connecting and mounting electronic components according to claim 1, wherein after the wire bonding, a bonding portion or a surface of a printed circuit board including the bonding portion is coated. 7. any one of claims 2 to 6, characterized in that are gold plated to at least a portion of the connecting terminal portion of the electronic component to be surface-mounted on the printed circuit board 1
Connection implementation method described in section .