Optical semiconductor device lead frame and manufacturing method thereof

Abstract

The present invention provides a lead frame for an optical semiconductor device and a manufacturing method thereof. In this lead frame, a pure silver layer made of pure silver is formed on the substrate. The arithmetic mean height Ra of the pure silver layer is 0.001-0.2 μm, and an average film made of a metal material with excellent corrosion resistance is formed on the surface. A film with a thickness of not less than 0.001 μm and not more than 0.2 μm. The lead frame for an optical semiconductor device has excellent reflection properties in the visible light region and excellent corrosion resistance.

Description

technical field [0001] The present invention relates to a lead frame for an optical semiconductor device and a manufacturing method thereof. Background technique [0002] Lead frames for optical semiconductor devices are currently widely used as various display and illumination light sources using LED elements and the like as light sources. In this optical semiconductor device, for example, a lead frame is arranged on a substrate, and after a light-emitting element is mounted on the lead frame, the light source is encapsulated with a sealing resin to prevent deterioration of the light source or its surrounding parts caused by heat, moisture, oxidation, etc. and its surroundings are sealed. [0003] In addition, directly below the light source, a layer of silver or a silver alloy having excellent light reflection characteristics is often formed. There is a content that the reflection characteristics are improved by setting the crystal grain size of the silver or silver allo...

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Problems solved by technology

[0005] However, in the case of simply forming a film of silver or its alloy as in the technology disclosed in Patent Document 1, it is unavoidable that the wavelength in the ultraviolet region is greatly reduced, and the reflectance in the visible region from around 400nm to around 300nm is unavoidable.

[0006] In addition, if the crystal grain size is formed to be 0.5 μm or more as in the technology disclosed in Patent Document 2, the reflectance in the visible light region is definitely slightly improved, but the wavelength of 400 nm or less appears to be the same as that disclosed in Patent Document 1. The same phenomenon as the technology, the decrease in reflectance in the ultraviolet region cannot be avoided

In addition, if the crystal grain size is adjusted to the above-mentioned by heat treatment, it is presumed that silver is oxidized due to the influence of residual oxygen, and the reflectance decreases instead, so that a sufficient effect of improving the reflectance cannot be obtained.

[0007] Furthermore, Patent Document 2 discloses that the maximum height Ry of the base material of the surface layer silver film is set to be 0.5 μm or more in surface roughness, but the factor that constitutes the reflection phenomenon of light is not the roughness of the base portion, but the surface layer near the outermost layer. The thickness of the

Therefore, a silver film is formed on the substrate or substrate plating by electroplating or vapor deposition to form a reflective layer, so it may be meaningless even to define the roughness of the substrate.

In addition, Ry refers to the difference between the maximum value and the minimum value of the roughness, and it is likely to indicate only the unevenness of a specific part of the surface, such as the numerical value of a small part such as a scratch formed in a line, and does not indicate the overall value that depends on reflection. The thickness of the range, so Ry is sometimes not suitable as a parameter to represent the characteristics of the reflective layer

[0008] Furthermore, when the lead frame produced by the technique disclosed in the above document is used for an LED, the luminance decreases over time.

As a result of the investigation, it was found that the silver on the surface of the lead frame is sulfurized due to the small amount of sulfur contained in the sealing resin, so the silver turns black and the brightness decreases.

In addition, sterling silver is prone to migration

[0009] In addition, in the lead frame disclosed in Patent Document 3, compared with silver, rhodium reduces the reflection characteristics important for optical semiconductor devices, especially the reflectance including the visible light region, such as the wavelength 400 to 800 nm, by 20%. As mentioned above, if only thin rhodium is simply coated, blue or white optical semiconductor devices cannot meet the required characteristics of reflectance.

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