JPH0468778B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a laser welding method, and more particularly to a laser welding method for mounting an IC chip on a flexible printed circuit board.

[Conventional technology]

In the past, this type of work generally required advanced technology, and ICs were mounted on flexible printed circuit boards (FPC) made of polyimide film, etc.
In order to connect substrates with high density and high precision, it is necessary to obtain sufficient reliability. Also, IC
As the number of electrodes on a chip increases, it is necessary to save labor and achieve uniformity, and a connection method that can be automated must be developed.

In other words, to put the above in more detail, it is important that the electrical and mechanical reliability of the connection parts is maintained, and it is not desirable for the connection to fail immediately even when a light load is applied. . Furthermore, it is necessary to miniaturize the space required for connection as much as possible in connection with how to reduce the area of the electrodes in the fine wiring and how to keep the gap between the electrodes as short as possible. Furthermore, it is desirable to simplify the connection method and thereby enable continuous and rapid operation, and it is also necessary to reduce costs through such automation.

Figures 4-6 illustrate the method of implementation using conventional welding techniques. That is, FIG. 4 shows soldering by the wire bonding method, FIG. 5 shows the soldering by the beam lead wire method, and FIG. 6 shows the case of soldering by the reflow method. In Figure 4, 1
is the FPC placed on the reinforcing plate 2, and 3 is the pad provided on the electrode part on the FPC 1. In this case, first, the IC chip 4 is glued to a predetermined position on the FPC 1, and then the IC chip 4 is glued on the IC chip 4. The solder bumps 5 and the pads 3 on the FPC 1 are connected by bonding wires 6, so-called bonding.

Further, in FIG. 5, 7 is a beam-shaped lead wire formed in the electrode part of the IC chip 4.
8 is the conductor pattern of FPC1, and this example is an IC
In this method, the conductive pattern 8 and the beam-shaped lead wire 7 are aligned by slightly moving the chip 4, and then they are bonded by thermocompression.

Furthermore, in FIG. 6, 9 is the IC chip 4.
Solder bump provided on the side of , 10 is FPC1
In this case, after fixing the solder bumps 9 of the IC chip 4 on the paste solder 10 so as to match them, the entire component is placed in a high temperature atmosphere 11.
It is heated inside and melted and connected.

[Problem that the invention seeks to solve]

However, in the wire bonding method shown in FIG. 4, the mechanical structure of the bonding wire 6 itself is weak, so this method is not suitable for use in places where the characteristics of the flexible FPC 1 can be utilized. It is unsuitable to implement what has been obtained, and in that respect it lacks reliability.

Furthermore, in the method shown in FIG. 5, the beam-shaped lead wire 7 must be precisely arranged on the IC chip 4, and the process is complicated and time-consuming, which is economically disadvantageous. Since the FPC 1 is sometimes exposed to high temperatures, it is easily deformed.

Furthermore, since the method shown in Figure 6 heats the entire electronic component in a high-temperature atmosphere such as a furnace, FPC1
Of course, the electrical and mechanical properties of other electronic components may be impaired.

Therefore, an object of the present invention is to focus on the above-mentioned problems, and to solve the problems, it is possible to quickly and easily perform soldering between the solder bumps of an IC chip and an FPC electrode by local heating, and at a high cost. The purpose of this invention is to propose a laser welding method that guarantees reliability.

[Means for solving problems]

In order to achieve such an object, the present invention, when mounting an IC chip on a flexible printed circuit board, stores the IC chip having solder bumps in the positioning part of the base plate, and places the flexible circuit board on the base plate with its electrodes. Position the electrode so that it is facing the solder bump, and position the pressing plate with a masked glass at the position facing the positioning part of the base plate overlapping the flexible board, press the electrode against the solder bump, and press the mask. It is characterized by irradiating a laser beam through a light-transmitting window of the attached glass to heat only the solder bump and electrode, thereby welding them together.

[Effect]

According to the laser welding method of the present invention, an IC chip is positioned at the positioning part of the base plate, and then the FPC is
are placed one on top of the other, and while keeping them in pressure contact with each other using a holding plate with a masked glass, the laser beam is projected only onto the welded area through the transparent window of the masked glass, so that the laser beam does not reach the solder bumps. Since laser irradiation is concentrated and a good soldering condition is obtained, and other parts are blocked from laser irradiation by a mask, it is particularly effective in protecting FPCs with low heat capacity from burning out.

〔Example〕

Embodiments of the present invention will be described in detail and specifically below based on the drawings.

FIG. 1A shows an example of an FPC to which the present invention is applied, and FIG. 1B shows an example of a welding jig for implementing the present invention. As shown in FIG. 1A, a solder-plated conductor pattern 12 is provided on the FPC 1, and a pin hole 13 for positioning is bored in the blank space. Furthermore, in FIG. 1B, 14 is a base plate on which a positioning pin 15 is erected, and the center part of the base plate 14 is provided with a positioning pin 15 as will be described later.
A recess 16 is provided to accommodate and hold an IC chip.

17 is a pin hole 18 that matches the positioning pin 15
The press plate 17 has a through window 19 in the center thereof at a position facing the recess 16 of the base plate 14.
is bored, and the stepped portion 19 of this through window 19
A masked glass 20 is fitted into A.
The mask of the masked glass 20 is shown in FIG.
As shown in Figure D, the light-transmitting window 23 of the masked glass 20 allows laser light to be selectively and intensively irradiated only on the conductor pattern 12 during laser light irradiation, which will be described later. Something,
The mask 22 is made of a material with high reflectance so that the laser beam is not absorbed by the mask 22 itself.

Next, referring to FIG. 2, the welding method according to the present invention will be explained together with its implementation process. Here, in the masked glass 20, the mask 22 is an FPC
1 side, thereby suppressing the influence of the laser beam by refraction within the glass and further diffraction at the edge of the mask 22. Now, first fit the flip-chip IC chip 4 into the recess 16 of the base plate of such a jig, position it so that its solder bumps 9 protrude from the base plate, and then place the FPC 1 on top of it. The solder-plated conductor patterns 12 are positioned so as to face the solder bumps 9, respectively. Note that such positioning can be achieved by passing the positioning pins of the base plate 14 through the pin holes 13 of the FPC 1.

Next, the pressing plate 17 is similarly positioned by the positioning pins 15 of the base plate 14 while pressing the FPC.
1 and a pressing force is applied via a pressing plate 17. In addition, the pressing force in this case is the pressing force of the pressing plate 17.
This may be due to its own weight, or it may be a force applied separately from the outside of the press plate 17. Thus, solder bump 9 and conductor pattern 1
2, while maintaining the state in which they are in pressure contact with each other, the through window 19
When the laser beam 21 is irradiated downward from above, the welded area is irradiated with the laser beam 21 through the light-transmitting window 23 of the masked glass 20, so parts other than the welded area are affected by the laser beam 21 . Therefore, there is no risk of burnout. Further, since the welded portion is maintained in a press-contact state as described above, the heat of the laser beam 21 is efficiently transmitted to the solder bump 9, and good soldering can be performed.

FIG. 3 shows another embodiment of the invention. In this example, a plurality of recesses 16 are formed on a base plate 14, IC chips 4 are fitted into each recess, and the chips are successively mounted on the FPC 1 using a laser beam 21 . Therefore, the through window 19 and the masked glass 20 must also have an area large enough to cover such a wide area. Note that the procedure of the welding method is the same as that shown in FIG. 2.

In addition, in the examples shown in Figs. 2 and 3, the laser beam is irradiated from above, but depending on the holding structure of the optical fiber transmission section, etc., the state shown in Figs. 2 and 3 may be changed. It goes without saying that the light may be irradiated from below while the light is held vertically.

〔Effect of the invention〕

As explained above, according to the present invention, the IC chip and the FPC are held between the base plate and the pressing plate in a mutually positioned state, so that the solder bumps on the IC chip and the FPC are overlapped. The solder electrode is kept in pressure contact with the solder electrode. Then, a glass mask provided on the press plate is positioned above the solder bump and solder electrode which are kept in pressure contact, and a laser beam is applied only to the pressure contact area through the transparent window of the mask glass. irradiate. Due to the melting of the solder at this time,
Since the IC chip is welded onto the FPC, it is possible to perform good soldering while protecting the FPC from burnout due to heat. Moreover, by using the base plate and the pressing plate as jigs, the position of the FPC and IC chip can be The alignment can be carried out very easily.

[Brief explanation of the drawing]

FIG. 1A is a plan view showing an example of the configuration of a flexible printed circuit board (FPC) for implementing the present invention, FIG. 1B is a sectional view showing an example of the configuration of a jig for implementing the present invention, and FIG. 1C is a plan view showing an example of the configuration of a flexible printed circuit board (FPC) for implementing the present invention. FIG. 1D is a plan view of the glass with a mask, FIG. 1D is a side view of the same, FIG. The explanatory diagrams of the embodiment, FIGS. 4 to 6, relate to the prior art. FIG. 4 is a wire bonding method, FIG. 5 is a beam lead wire method, and FIG. 6 is a reflow welding method. be. 1...FPC, 4...IC chip, 9...solder bump,
12... Conductor pattern, 13... Pin hole, 14... Base plate, 15... Positioning pin, 16... Recess, 17... Press plate, 18... Pin hole, 19... Penetration window, 19A... Stepped part, 20... Glass with mask , 21...Laser light, 22...Mask, 23...Transparent window.

Claims (1)

[Claims] 1. When mounting an IC chip on a flexible printed circuit board, the IC chip having solder bumps is stored in a positioning section of a base plate, and the flexible circuit board is mounted on the base plate so that its electrodes are connected to the solder. The electrodes are positioned so as to face the bumps, and the electrodes are pressed against the solder bumps while a pressing plate having a glass with a mask is superposed and positioned on the flexible substrate at a position facing the positioning portion of the base plate. and irradiating a laser beam through a transparent window of the masked glass to heat only the solder bump and the electrode to weld them together.