JPH03280565A - Semiconductor device - Google Patents

Abstract

PURPOSE:To judge whether solderability is perfect, only by observing whether an outer lead is colored or not, by a method wherein the solder-plated surface of an outer lead is coated with material whose hue is different to that of the solder-plating. CONSTITUTION:One end portion 1a of an outer lead 1 which portion is buried in sealing material 2 is connected with the surface electrode of a semiconductor element 3 by using a metal thin wire 4. The other end portion 1b exposed from the sealing material 2 is coated with solder-plating 5. Thereon a thin film 6 is formed by copper-plating or gold-plating, and then lead cutting and bending process are performed, thereby forming a semiconductor device. The outer lead 1 exhibits the hue of red-brown or gold which is quite different to silver-white, the hue of solder. The copper-plated red-brown-colored thin film 6 or the gold-plated gold-colored thin film 6 is heated when a device is mounted on a printed wiring board 8. In the state where the solder plated on the outer lead is fused, the thin film 6 is gradually diffused into the fused solder. In the period required for soldering, however, the thin film 6 is not completely diffused but exhibits the hue of red-brown or gold.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a semiconductor device, Regarding external leads.

[Conventional technology]

In particular, some semiconductor devices use plastic, metal, or ceramic as their sealing material, and all of them are equipped with a plurality of external leads made of metal. FIG. 2 is a sectional view of a conventional semiconductor device. External lead 1
A portion 1a embedded in the encapsulant 2 is connected to an electrode of the semiconductor element 3 by a thin metal wire 4, and a portion 1b of the external lead 1 exposed from the encapsulant 2 is connected to a printed wiring board as shown in FIG. Connected to 8th grade. This connection is made using a tin-lead based eutectic alloy. In order to facilitate the connection, the exposed portions of the external leads 1 have already been plated with tin-lead solder.

[Problem to be solved by the invention]

The above-described conventional semiconductor device is temporarily fixed at a predetermined position on a printed wiring board, and passed through a molten solder tank as it is to solder the external leads 1 of the semiconductor device and the conductor pattern 9 provided on the printed wiring board 8. (Figure 3).

Another method is to print a solder paste at a predetermined location on the conductive pattern described above, place the external lead of the semiconductor device on the solder paste, and heat it as it is to solder the external lead and the conductive pattern. In either case, it is necessary to check the connection between the external lead and the conductor pattern to confirm the quality of the soldering.

By the way, recently, because high-density packaging is easy, SOP
The usage of surface-mountable semiconductor devices such as , SOJ, etc. is increasing. However, as shown in FIG. 3, since the lower surface of the external lead 1 and the upper surface of the conductor pattern 9 on the upper surface of the printed wiring board 8 are connected by soldering, it is not possible to visually observe the connection part. The quality of the soldering was determined by observing the color tone of the sides and the shape of the solder bulges. However, this method has the disadvantage that it takes an enormous amount of time for visual observation and also causes many erroneous determinations.

[Means to solve the problem]

The present invention is characterized in that, in a semiconductor device having solder-plated external leads, the surface of the solder-plated external leads is further coated with a substance completely different in hue from the solder plating. A substance that is completely different in hue from solder plating is an electrolytic or electroless copper plating thin film or a gold plating thin film. Further, an organic compound film having an infrared absorption function or a simple dye film can also be applied.

〔Example〕

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

FIG. 1 is a longitudinal sectional view of a first embodiment of the invention. One end part (la) of the external lead 1 that is embedded in the sealing material 2 is connected to the surface electrode of the semiconductor element 3 and the thin metal wire 4, and the other part (lb) which is exposed from the sealing material 2 is solder plated. Further, the surface of the solder plating 5 is coated with a copper plating thin film 6.

In an external lead processing process for a semiconductor device, after applying 5 to 20 microns of solder plating as in the conventional method, copper plating with a thickness of 0.01 to 0.1 micron is deposited using an electrolytic copper plating bath. The copper plating bath used may be a copper birophosphate bath, a copper sulfacate bath, or the like, and is not particularly limited. If you do not want oxidation discoloration of the copper plating itself, use an electrolytic gold plating bath.
Gold plating of about 01 to 0.05μ may be deposited.

After forming a plating thin film 6 of copper, gold, etc. on the solder plating 5 of the external lead 1 in this manner, the leads are cut and bent to produce a semiconductor device. This method has the disadvantage that the cut surface of the external lead cannot be colored because it is cut after plating.

The external board 1 of the semiconductor device manufactured in this way has a reddish-brown and golden hue that is completely different from the silvery-white hue of the solder. This reddish-brown or gold-colored copper or gold-plated thin film 6 is heated when it is mounted on a printed wiring board 8 as shown in FIG. However, it does not completely diffuse in the time required for soldering.
It has a reddish-brown to golden hue. On the other hand, the solder 10 supplied from the outside, especially the solder in a jet state, is easily entangled and melted, and loses its reddish-brown or golden hue. That is, when the jet solder 10 supplied from the outside comes into contact with the external lead 1 and wetting begins, the hue disappears. In this case as well, the cut end face of the lead, which is the drawback described above, has the potential to cause an erroneous judgment in the visual judgment described below since there is no change in hue at all. To avoid this problem, there is a method of performing coloring plating after cutting and bending the external leads. In this case, electroless steel or gold plating using a reducing agent such as sodium hypophosphite can be used as the plating.

FIG. 4 is a longitudinal sectional view of a second embodiment of the invention. The solder plating 5 on the portion 1b of the external lead 1 exposed from the sealing material 2 is coated with an infrared absorber 7 having the structural formula shown in FIG. 0.0 as infrared absorber 7. Pigments exhibiting a dark green color with an absorption wavelength in the micrometer range (λ□8 is 0.71 μm), such as monoazo dyes (the structural formula is shown in Figure 5)
can be used. The external leads 1 can be coated by dissolving the infrared absorber 7 in a solvent, immersing the semiconductor device in the solution, taking it out, and drying it.

When the above-mentioned infrared absorber 7 is heated to a temperature around 250'C, it rapidly decomposes and loses its infrared absorbing function.

Chemical substances other than the dyes shown in FIG. 5 can be similarly treated as long as they have absorption wavelengths in the near-infrared region and decompose at high temperatures of 200° C. or higher. Further, although the effect is somewhat insufficient, a certain degree of effect can be obtained if the compound is thermally decomposable and has an absorption wavelength in the visible light region.

〔Effect of the invention〕

As described above, the external leads of the semiconductor device of the present invention are covered with a metal thin film of a different hue from solder plating or a compound thin film of dark green or other hue. When such a semiconductor device of the present invention is soldered and mounted on a printed wiring board, an external supply is applied between and around the external leads of the semiconductor device placed at a predetermined location on the printed wiring board and the conductor pattern of the board. When the molten solder reaches the external lead surface and the solder contacts the surface of the external lead, the metal thin film is caught up in the molten solder and melts, causing the color of the metal thin film to disappear. or,
When an infrared absorber or the like comes into contact with molten solder, it rapidly decomposes and its hue disappears. Therefore, the coloring of the external leads covered with the molten solder supplied from the outside disappears, and the coloring of the external leads not covered with the molten solder remains as is.

In the visual inspection after soldering and mounting, it is possible to determine whether the soldering is good or not by simply checking whether the external leads are colored or not. This allows the visual inspection to be completed in a short time.
The ability to detect pass/fail can be significantly improved.

Furthermore, if an infrared absorber or the like is used, it is easy to automate the visual inspection using a corresponding light source and a mechanism that irradiates a spectroscopic specific wavelength and detects its reflection coefficient. Furthermore, if a laser beam having the same wavelength as the infrared absorber is used as a light source, only the defective soldering area can be reheated, and the defective area can be easily regenerated.

As described above, the present invention greatly contributes to improving mounting reliability and reducing mounting costs by improving surface-mounted semiconductor devices.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of the first embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of a conventional example, FIG. 3 is a cross-sectional view showing a state in which a semiconductor device is mounted, and FIG. FIG. 5, a vertical cross-sectional view showing the second example, shows the structural formula of the chemical substance used in the second example. DESCRIPTION OF SYMBOLS 1... External lead, 2... Sealing material, 3... Semiconductor element, 4... Metal thin wire, 5... Solder plating, 6...
- Metal thin film, 7... Infrared absorber, 8... Printed wiring board, 9... Conductor pattern, 10... Solder.

Claims (2)

[Claims] 1. 1. A semiconductor device having solder-plated external leads, characterized in that a metal thin film made of copper or gold plating is provided on the solder-plated surface of the external leads. 2. 1. A semiconductor device having solder-plated external leads, characterized in that a compound coating having an absorption wavelength in the visible and near-infrared light region is provided on the solder-plated surface of the external leads.