1. Field of the Invention
The present invention relates to a semiconductor device such as an illuminator which includes an LED chip and a resin package for sealing the LED chip. The present invention also relates to a method of making such a semiconductor device.
2. Description of the Related Art
An example of semiconductor devices is an illuminator incorporating an LED chip. FIGS. 7 and 8 illustrate a typical prior art illuminator for use in a display of a mobile phone as a light source or in a photointerrupter for example. As shown in FIGS. 7 and 8, the illuminator 100 comprises a first lead 2 having an inner portion on which an LED chip 1 is mounted, a second lead 3 having an inner portion electrically connected to the LED chip 1 via a wire 4, and a transparent resin package 5 for sealing the LED chip 1 and the wire 4. In this illuminator 100, the LED chip 1 is surrounded by a shock absorber 107 within the resin package 5.
The LED chip 1 may be provided by forming a p-type semiconductor layer, a light emitting layer, and an n-type semiconductor layer by epitaxial growth on a semiconductor wafer, forming electrodes on the semiconductor wafer, and dividing the wafer into chips of a desired size by dicing.
The shock absorber 107 is formed before the formation of the resin package 5. The shock absorber 107 functions to protect the LED chip from breaking in forming the resin package 5. The shock absorber 107 maybe formed of a soft resin called JCR (Junction Coating Resin).
The resin package 5 is generally formed of a transparent epoxy resin which does not contain a filler, because such a resin is relatively inexpensive and is easily hardened by heating.
Specifically, for forming the resin package 5, the respective inner portions of the first lead 2 and the second lead 3 together with the LED chip 1 and the wire 4 are disposed in a cavity having a predetermined configuration defined by a mold. Then, an epoxy resin in a fluid state is injected into the cavity and heated for hardening. At this time, the epoxy resin tends to thermally expand in the cavity to compress the LED chip 1.
The LED chip 1, which is obtained by cutting a wafer, may suffer strains at the cut surfaces. Therefore, when the LED chip 1 is compressed by the epoxy resin, the LED chip may start breaking at the cut surfaces. Particularly, since a transparent epoxy resin, which has a greater coefficient of linear expansion as compared with a black epoxy resin, is used for forming the resin package 5, the possibility of breakage of the LED chip 1 due to the expansion of the resin is relatively high.
In the prior art device, however, the LED chip 1 is surrounded by the shock absorber 107 before the resin package 5 is formed. Therefore, in forming the resin package 5, the pressing force of the resin toward the LED chip 1 is absorbed by the resiliency of the shock absorber 107. In this way, the shock absorber 107 protects the LED chip 1.
The shock absorber 107 is generally formed of a soft resin such as a transparent silicone resin. However, since silicone resin is used in a gel state for forming the shock absorber 107, the thickness of the shock absorber 107 becomes relatively large. As a result, the shock absorber 107 may cause lens effect for refracting the light emitted from the LED chip 1.
Further, the shock absorber 107 is formed by surrounding the LED chip 1 by a silicone resin in a gel state and then heating the resin in a furnace for example for hardening. Such process steps are rather troublesome and hinder the efficient manufacturing of the light emitting diode 100.