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Semiconductor laser and ceramic substrate

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What is a semiconductor laser?
        A semiconductor laser, also known as a semiconductor laser diode (LD), refers to a type of laser that uses a semiconductor material as a working substance. The process of laser generation is quite special. Commonly used materials are gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), and zinc sulfide (ZnS). According to the incentive method, there are three types: electric injection, electron beam excitation and optical pumping. According to the structure classification, semiconductor laser devices can be divided into homojunctions, single heterojunctions, and double heterojunctions. The three major elements of semiconductor laser operation are: gain greater than or equal to loss, cavity and laser radiation.
        Semiconductor lasers have the advantages of small size, long life, easy integration, high photoelectric conversion efficiency, etc. in laser communication, laser display, laser drilling, laser cutting, laser welding, laser indication, laser printing, laser marking, laser ranging, laser Medical and other aspects have a very wide range of applications.

Structure of semiconductor laser

The simplest semiconductor laser consists of a thin active layer, a P-type, and an N-type confinement layer. The active layer is between the P-type and the N-type, and the resulting PN heterojunction is forward biased by an ohmic contact, and current is injected over a larger area covering the entire laser chip.
Taking GaAs laser as an example, the heat dissipation and point contact parts have certain requirements on the material selection. The ceramic circuit board metal-based substrate has good thermal and electrical properties, and is an excellent material for power LED packaging, laser and ultraviolet. It is especially suitable for package structure of multi-chip package (MCM) and substrate direct bond chip (COB); it can also be used as heat dissipation circuit substrate for other high-power power semiconductor modules, antenna for high-current switch, relay, communication industry, and filtering. , solar inverters, etc. At present, GaAs lasers are basically made of ceramic circuit boards, and ceramic circuit boards are most commonly used with aluminum oxide and aluminum nitride ceramic circuit boards.

Semiconductor laser packaging process
       The semiconductor laser packaging process is roughly divided into the following processes: cleaning, evaporation, eutectic patching, sintering, gold wire, ball bonding, soldering leads, visual inspection, pre-aging testing, aging, post-aging testing, capping, Packaging and storage.
1. The cleaning function mainly includes the cleaning of heat sink, pipe socket, ceramic chip and chip box, including daily cleaning of some instruments, such as: full glass steel fume hood, ultra pure water machine, oven, ultrasonic cleaning machine, etc.
2. The evaporation is mainly used for the heat sinking of the solder, and the ceramic sheet is vapor-deposited with the metal electrode. Soft solder requires small welding stress, mainly refers to heat sink material with large difference between thermal expansion coefficient and chip; hard solder requires large welding stress, good fatigue resistance and thermal conductivity, mainly refers to the difference between thermal expansion coefficient and chip. Small heat sink material. Heat sink requires high thermal conductivity, is not easy to be contaminated, easy to process, easy to weld, thermal expansion coefficient and chip matching.
3. The eutectic patch or sintering mainly functions to realize the chip and the socket or the heat sink eutectic patch through the preformed soldering piece, and the chip, the TO socket, the soldering piece and the like are involved.
4. The main function of gold wire ball bonding is to electrically connect the LD chip, the PD chip and the ceramic metal or the stem.
5. Soldering leads are mainly used to connect the C-mount tube leads. The process materials involved are electric soldering iron, copper lead, solder wire, flux, C-mount, etc.
6. The main function of the visual inspection is to observe and measure the patch, bonding, capping, etc. through the stereo microscope and the metallographic microscope to complete the abnormal analysis of the appearance of the defective product.
7. Reliability testing and analysis at different temperatures after laser encapsulation by DC stabilized power supply, chiller, and aging station to meet the aging test requirements.
8. After the package and test meet the requirements, you can use the capping machine to cap the different types of TO tube caps.

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