JPH04354399A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To prevent application of heat stress to a mold part which is mounted by heat rays when soldering a substrate and a lead of a mold part mounted thereon by using heat rays. CONSTITUTION:An over coat 6 whose color is easy to absorb heat rays is applied to an opposite surface of a part mounting surface of a substrate 1, heat rays 5 are irradiated to the surface, the substrate is heated and soldering is carried out by the heat conduction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mounting components on semiconductor devices.

0002

2. Description of the Related Art Conventionally, this type of semiconductor device has been manufactured as shown in FIG. An example of this will be explained below based on FIG. 2. Configuring a circuit on the board 1 as shown in FIG. 2a,
Electrodes 2 for attaching parts are applied. Next, as shown in FIG. 2b, a quantity of solder paste 3 is applied to a predetermined portion of the electrode 2 in order to solder the components. Note that solder paste is a paste made by mixing fine powder of solder with flux or solvent, and is generally applied to a predetermined area by a method such as printing. Next, as shown in FIG. 2c, a component to be mounted, in this case a molded IC 4, is placed at a predetermined location. Then, the object in this state is heated by applying a hot ray (generally infrared rays) 5 as shown in FIG. 2d. Then, the solder in the solder paste 3 on the electrode 2 melts, causing wetting on the electrode 2 and the leads 4a of the molded IC. Thereafter, the irradiation of the heat source 5 is stopped, and the solder is solidified by cooling, thereby performing so-called soldering. This process is usually called a tunnel furnace, in which a tunnel is provided in the middle of the belt conveyor.
Using a device equipped with a lamp that generates infrared rays in a tunnel, the products in the state shown in Figure 2c are placed on a belt conveyor that moves at a constant speed and soldered one after another. FIG. 2e is a structural diagram of the molded IC 4, in which an IC chip 4b is bonded to one of the frame leads 4a with a brazing material 4c, and this IC 4b and each lead 4a are connected with a wire 4d, and these are connected to the exterior. It is covered and molded with material 4e.

0003

[Problems to be Solved by the Invention] However, the heating method described above has a characteristic as shown in FIG. There have been problems such as the occurrence of oxidation, a decrease in density at the interface with the lead 4a, and deterioration of moisture resistance.

The present invention was made to solve the above-mentioned problems, and aims to alleviate thermal stress on mounted components and eliminate problems related to thermal stress.

[0005]

[Means for Solving the Problem] In the semiconductor device according to the present invention, an overcoat of a color that easily absorbs heat rays is applied to the part to be heated on the opposite side of the component mounting surface of the board, and the overcoat surface is irradiated with heat rays. This heats the substrate.

[0006]

[Operation] In this invention, the heat conduction route is from the board → electrode → solder paste (solder) → lead (component electrode part) → the component body, so the exterior of molded components etc. is rapidly heated. No heat stress occurs, improving quality and reliability.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1a, an electrode 2 is provided on a substrate 1 as in the conventional case, and in addition, an overcoat (hereinafter simply referred to as an overcoat) 6 of a color that easily absorbs heat rays is provided on the back surface of the electrode 2. In addition, as long as the material easily absorbs heat rays, as long as it does not impair the function of the product,
The color type doesn't matter. 1b and 1c are the same as the conventional method, in which solder paste 3 is applied to a predetermined position on the board 1 and a component 4 is placed. Next, in FIG. 1d, a hot wire 5 is applied to the surface of the overcoat 6 to heat the substrate 1, and the lead of the component 4 and the electrode 2 are soldered by the heat conduction. Note that the equipment used for this can be easily accommodated by changing the position of the lamp in the tunnel furnace described above.

In the present invention, first, the substrate 1 is heated, and the heat is transferred to the electrodes 2 applied thereon and the solder paste 3 applied thereon, and the solder is blended into the electrodes while being applied thereto. Since the leads of the parts that are in contact are heated to blend the solder, the electrodes and solder always blend first. Since the heat reaches the component body via the lead 4a, the temperature gradually rises, making it difficult to generate thermal stress, and it is also possible to control the tunnel so that it passes through the tunnel before it reaches a harmful temperature. . Also, regarding soldering, conventionally the component body → lead →
There is a relationship between the heating speed from the board to the electrode, and the solder is absorbed before the leads, so as shown in Figure 4, most of the solder 3 is absorbed by the leads 4a, making it possible to solder the leads 4a and the electrodes 2. However, in the present invention, wetting between the electrode 2 and the solder 3 always occurs, and the wetting between the lead 4a and the solder 3 begins, so that the above-mentioned problems can be avoided.

[0009]

[Effects of the Invention] As described above, according to the present invention, when soldering a board and a mounted component with a hot wire, the hot wire does not directly hit the component, and the problem arises due to thermal stress caused by the difference in the degree of absorption of the heat wire. Since the occurrence of can be avoided, it is possible to obtain an inexpensive and highly reliable semiconductor device.

[Brief explanation of the drawing]

FIG. 1: a to d are diagrams showing manufacturing steps according to an embodiment of the present invention.

[Fig. 2] a to e are diagrams showing the manufacturing process of a conventional semiconductor device.

[Figure 3] A graph showing an example of the temperature rise curve of the surface of the exterior material and the lead part of a molded IC when heated using a conventional method.

[Figure 4] Enlarged view showing an example of a problem with lead soldering using the conventional method

[Explanation of symbols]

1 Substrate 2 Electrode 3 Solder paste or solder 4
Mold IC 4a Lead or frame lead 5
Heat ray 6 overcoat

Claims (2)

[Claims] [Claim 1] A semiconductor device in which a board and leads of a molded component mounted thereon are heated with hot rays such as infrared rays, and the board and leads are soldered by solder reflow, the side of the board opposite to the side on which the component is mounted. A semiconductor device characterized by having an overcoat on its surface in a color that easily absorbs heat rays. [Claim 2] An overcoat of a color that easily absorbs heat rays is applied to the opposite side of the component mounting surface of the board, and the overcoated surface of the board is heated by irradiating heat rays to perform solder reflow. A method for manufacturing a semiconductor device.