This invention relates to a light emitting apparatus for use in a head of an non-impact printer using an array-mode semiconductor light emitting device, and particularly to a light emitting device for emitting a radiant light in parallel to the surface of a substrate.
In a prior copying machine and a printer, the array-mode semiconductor light emitting device is used for a light source, and the method of emitting a light to a drum means linearly is disclosed in Japanese Pat. Publication No. 1964-25849.
However, in the known method, the light is emitted in vertical to the head substrate. Therefore, there has been some disadvantages that the head substrate of a printer should move to the direction of the emission and said substrate surface should be maintained in vertical to the direction of the emission, when controlling the space between a lens system and a light source system. Moreover, if a peripheral equipment is complex and narrow, namely, in case that the components such as a charger, a toner, and a copying machine are arranged toward a central axis on the photosensitive rum surface, or the space for inserting the light emitting apparatus is small, the conventional light emitting system are not easily attached and a larger space is required.
In FIG. 1 showing partially a perspective diagram of the prior light emitting apparatus, the emitting surface 2 of the array-mode light emitting device is arranged in parallel with the wiring surface 11 of the printer head substrate 6. Then, each chip of the array-mode light emitting devices (C1, C2, . . . ) is die-bonded on the head substrate (meaningfully the substrate). Thereafter, pads (P11, P21, . . . Pn1) of the light emitting device on each chip are connected with the wires (W11, W21, . . . ) on the head substrate 6 through a bonding wire 5. Said substrate 6 is in a mode of insulating plate such as a ceramic substrate, particularly of an alumina substrate, which may have a heat-sink on its back surface The wires (W11, W21, . . . ) are made of proper gold and copper pattern in single or multiple layer.
Then, a p-n junction is formed at the emitting surface 2 of a III or V family composite semiconductor such as GaAs or GaP substrate by a conventional method such as a diffusion or an epitaxial growth, so that a light emitting device chip (C1, C2, . . . ) are made.
Therefore, the light is emitted in vertical to the emitting portion 2, namely, in vertical to the surface of the head substrate 6. So, there occurs said difficulties in controlling the drum and lens system to be in order.
Besides, n case of using said method, a printer head comprises "m" number of chips and each chip comprises "n" number of light emitting elements Therefore, n x m times of wire bonding in total is necessary. In case of using a light-emitting head of 15 inches in its size having 400 DPI, it must meet a condition of n=128 dots/chip and m=48 chips/head. Moreover, 6144 times of wire bonding for the pad is required. So, a particular technique is needed for said wire bonding. In case of a high resolution printer above 400 DPI, said difficulties are more significant. Therefore, there is a problem in reliability in case of using said printer, because a short-circuit or a disconnection may be occurred frequently although wire bonding is possible.
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