JPS628530A - Method of mounting electronic device - Google Patents

Abstract

PURPOSE:To seal an element chip with resin in a simple way and at a low cost, by depositing a thermosetting powder resin on a circuit board including the element chip so as to form a uniformly thick layer and selectively heating the powder resin on the regions of the circuit board to be sealed for melting and curing the resin. CONSTITUTION:A semiconductor element chip 2 is secured onto an insulating circuit board 1, and the chip 2 is electrically connected to a thin metallic film 3 on the circuit board 1 by means of metallic wires 4. Liquid resin 5 is dropped thereon. Further, powder resin 6 is deposited on the whole circuit board 1 and irradiated with laser beams 7 only in the region to be sealed. The powder resin 5 is thereby selectively heated and melted, while the melted liquid resin 8 is prevented from being overspread, by the non-heated powder resin 6. After the resin 8 is cured, the residual powder resin 6 is removed. Finally, the structure is heated so that the element is completely sealed with the cured resin 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of mounting an electronic device, and particularly to a method of resin-sealing a semiconductor element chip.

[Conventional technology]

Conventionally, as a method for mounting semiconductor element chips such as integrated circuit devices on circuit boards, after fixing the element chips to the circuit board and making electrical connections, the element chips, etc. are directly set in molding, and transfer molding is performed. A resin sealing method, or a similar method in which the element chip is fixed and electrically connected, a sealing frame is attached to surround the chip, and then a thermosetting resin is dripped into the sealing frame and cured. A bofting method, a method of screen printing resin, etc. are used.

However, with the former transfer molding method, the sealing shape can be made small, so it has been used as a sealing method for small electronic devices, but it requires special equipment such as a transfer molding machine and a mold, and the This method requires many man-hours for loading and unloading the circuit board, and also requires a deburring process after molding, resulting in a large number of man-hours and a high price.

Also, the last screen printing method (Japanese Unexamined Patent Publication No. 58-2076
No. 43), there is a problem in that the thin metal wires making electrical connections are cut or short-circuited due to the pressure during screen printing, and the reliability of the electronic device is reduced, such as damage to the element chips.

For this reason, the frame potting method, which does not require special equipment and does not reduce the reliability of electronic devices, is used for inexpensive and small-sized electronic devices. For example, FIGS. 2(a) to 2(c) are examples of conventional methods of this kind. First, as shown in FIG. 2(a), a semiconductor element chip 22 is fixed on the surface of a circuit board 21, and then the circuit board is The metal thin film wiring 23 provided on the surface of the element chip 21 and the element chip 22 are electrically connected by a thin metal wire 24. After precoating the element chip 22 and the like with the liquid resin 25, a sealing frame 26 is attached so as to surround the element chip 22 and the like.

Then, as shown in the figure (b), liquid resin 27 for sealing is dripped into the sealing frame 26, and the surrounding area is regulated by the sealing frame 26 as shown in the figure (c). Sealing is completed by curing the liquid resin.

[Problems to be Solved by the Invention] The conventional frame potting method described above has the advantage of not requiring any special equipment and is easy to perform as described above, but it is difficult to attach the sealing frame to the circuit board. Since a space is required for the sealing, the sealing size becomes large as a whole, and there is a problem in that it is not suitable for sealing an electronic device that particularly requires miniaturization, such as an electronic wristwatch.

[Means for solving problems]

The method for encapsulating an electronic device of the present invention is to apply thermosetting powder resin to a uniform thickness on a circuit board containing an element chip in order to make the encapsulation shape small and to perform simple and inexpensive resin encapsulation. The method includes the steps of: depositing the powder resin on the circuit board portion to be sealed; selectively heating the powder resin on the circuit board portion to be sealed to melt and harden it; and removing the remaining powder resin.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) to 1(C) are cross-sectional views explaining one embodiment of the method of the present invention in the order of steps. First, as shown in FIG. 1(a),
A semiconductor element chip 2 is fixed onto an insulating circuit board 1 made of ceramic, epoxy, etc., and the element chip 2 is electrically connected to a metal thin film wiring 3 provided on the surface of the circuit board 1 using a thin metal wire 4 made of aluminum, gold, etc. do. And these elements,
Drop the liquid resin 5 so as to cover the pipe 2 and the thin metal wire 4,
It forms a so-called precoat. On top of that, circuit board 1
Powdered resin 6 is deposited on the upper surface of the substrate to a uniform thickness of 300 to 2000 μm. The powder resin 6 can mainly be an epoxy detection resin, which is a thermosetting resin that melts at around 150 to 200° C. and then becomes solid and hardens when cooled.

Next, as shown in FIG. 2B, laser beams, infrared rays, etc. 7 are selectively irradiated onto the area to be sealed, that is, the narrowest possible area including the element chip 2. As a result, the powder resin 6 is selectively heated and melted. At this time, the molten liquid resin 8 tries to spread to the surrounding area, but since the resin 6 is kept in a powder state in the parts that have not been heated in the previous process, the powder at the boundary with the molten part The resin acts as a sealing frame to prevent it from spreading.

After that, wait for the resin 8 to harden and remove the remaining powder resin 5.
is removed and finishing heating is performed to complete the sealing with the hardened resin 9, as shown in FIG. 9(c).

Therefore, in this method, the powder resin 6 has the function of a sealing frame to restrict the spread of the liquid thermosetting resin 8 to the periphery, so a separate member is sealed around the element chip. There is no need to attach a frame, and the process and space on the circuit board 1 for this purpose are unnecessary. In addition, the sealing frame can be constructed in a self-aligning manner simply by selectively heating the powder resin 6 by selectively irradiating it with light, etc., and since it is only necessary to drop the liquid resin, special equipment is required. There is no need for it.

Thereby, small electronic devices can be easily and inexpensively sealed.

Here, in the above embodiment, a case was explained in which one element chip was mounted, but when a circuit board mounted with multiple IC chips, resistors, capacitors, coils, etc., such as a hybrid RC, is sealed with resin. The same can be applied to

〔Effect of the invention〕

As explained above, the present invention includes a step of depositing powder resin to a uniform thickness on a circuit board including an element chip, and selectively heating the powder resin on a portion of the circuit board to be sealed. This method includes a step of melting and hardening the resin, and a step of removing the remaining powder resin, so the sealing frame function of the powder resin prevents the liquid resin from spreading to the surrounding area without the need for a special sealing frame. It is possible to easily perform resin sealing in a small number of steps without requiring any special equipment, and electronic devices can be sealed in a small size and at low cost.

[Brief explanation of drawings]

FIGS. 1(a) to (c) are sectional views for explaining the method of the present invention in the order of steps, and FIGS. 2(a) to (C) are sectional views for explaining the conventional method in the order of steps. 1.21... Circuit board, 2.22... Semiconductor element chip, 3, 23... Metal thin film wiring, 4, 24... Metal thin wire, 5, 25... Precoat, 6... Thermosetting powder resin, 7... Laser beam, 8... Molten liquid resin, 9... Hardened resin, 26... Sealing frame, 2
7...Liquid resin Figure 1 (a) Figure 1 (C)

Claims (1)

[Claims] 1. In an electronic device mounting method in which a semiconductor element chip is fixed on a circuit board, predetermined electrical connections are made, and the element chip etc. is sealed with a resin, thermosetting is applied onto the circuit board containing the element chip. a step of depositing a uniform thickness of powdered resin, a step of selectively heating and melting the powdered resin on the portion of the circuit board to be sealed, and a step of removing the remaining powdered resin. A method for mounting an electronic device, comprising the steps of: