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5ТЕХНИЧЕСКИЕ НАУКИ (TECHNICAL SCIENCE) УДК 62-213.1
Isayev K.
Master degree student National Nuclear Research University "MEPHI" (Russia, Moscow)
Huseynzada K.
National Nuclear Research Center (Azerbaijan, Baku)
Heydarov N.
Institute of Radiation Problems (Azerbaijan, Baku)
METHOD OF HOUSING OF HIGH-SENSITIVITY PHOTODIODES
Abstract: the paper presents a new method ofpackaging photodiodes. This technology uses textolite, which is technologically dielectric, insensitive to temperature changes and is not deformed. For better contact with the photodiode, the soldering areas are covered with gold plating. The casing substrate has a matrix type for better wedge soldering in accordance with uniform settings of ultrasonic micro-welding, which contributes to high performance and quality. The matrix is coated with optical epoxy resin in order to increase the resistance to mechanical stress and contamination of the sensitive part of the photo detector.
Key words: MAPD, photodiode, SiPM, matrix.
To date, the development of photometric instruments is one of the priority areas. Modern photon detectors have different designs and varieties and consist mainly of silicon materials [1-7]. It is known that silicon is a technologically simple and flexible material for the production of silicon photodiodes with internal amplification
more than 105 times. Such photodiodes have sufficiently small currents and capacitances, measured in nA and pF, respectively. They also strongly depend on the external temperature, with the increase in which the operating parameters deteriorate. Photodiodes are used in many high-energy physics experiments, medicine, and optical transmission of information. For use in certain areas, geometrically versatile samples are required. It is proposed to develop a method for packaging photodiodes with protection against the transfer of thermal energy, protected from mechanical effects and minimal changes in the characteristics of the original measurement. Because of the small sensitive area of photodiodes (~ 3x3 ^m), we have to use arrays based on them. This fact should be taken into account where it will be possible to combine singleelement elements in a matrix with the required number of elements with a minimum loss of the geometric parameter of the obtained device.
The paper presents the process of manufacturing photodiode housings and their installation. The main material was a textolite FR 4 which is a dielectric based and have several layers of glass cloth impregnated with epoxy resin and having a burning degree equal to 0. The thermal conductivity of this textolite is <0.5 W / m * K. The milling of the photodiode planting cells was carried out on the LPKF63 ProtoMat installation, after which end-to-end metallization was performed. Copper contacts with thickness of 35um were covered with a gold layer for better contact with the photodiode (Figure 1).
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Figure 1. Back (right) and front (left) side of the housing matrix.
The housing matrix has 64 elements, each of which has 3 contact pads. The photodiodes were mounted with a dielectric epoxy resin at a temperature of 60 ° C, gluing the photodiode with the base of the textolite. Afterwards, in order to output the photo signal and provide voltage (<100V), the photodiodes were connected to the contact areas of the casings by a gold wire with a diameter of 25 microns. The process of micro-welding was carried out by an ultrasonic method using TPT HB05 equipment. Ultrasonic energy frees the surface from impurities, provides a metal-metal compound, and stimulates free electrons at external valence levels to interact with free electrons of adjacent molecules. This leads to the formation of a series of covalent bonds and the formation of a bimetal on the surface of the compound of two metals. The metal temporarily becomes ductile and soft under the influence of only ultrasonic energy, which disrupts its crystal structure and allows the metal to deform even with a low pressing force. The heat released becomes a by-product, which makes it possible not to use additional thermal energy to form a compound. Also, due to the deformation, all impurities are naturally removed from the weld area. In order to reduce the possibility of contact overlap, which can lead to a short circuit and thus lead to malfunction of the photodiode, a wedge type of micro-welding was chosen. In the case of a wedge-welded wire, the wire receives minimal deformation and can be welded to a fairly narrow contact pad; it can also conduct micro-welding in deep cavities and shells. To check the reliability of the contacts, each element is tested for the process of leakage currents and measurements of the dark current of the photodiodes. The test was carried out at the probe control station TS200, which has the ability to apply the contact to a metal pad of 5 micron. The equipment is completely isolated from the influence of external factors, such as light, electromagnetic waves, vibrations, etc.
The next step is to cover the photodiodes with a transparent dielectric, in order to ensure the durability of the instruments. For this, a transparent EPOXY 301 epoxy resin with optical transmission of 99% of visible wavelengths was chosen. Epoxy resin is coated with a thickness of no more than 0.5 mm and dries at a temperature of 80 ° C. The further process is the cutting of single elements from the housing matrix (Figure
2). For this purpose, on disk cutting equipment, which has a disk section of 70 ^m and a diamond coating with a grain of 5 ^m. Prepared single photodiodes differ from the initial photodiode parameters by not more than 1%.
Figure 2. Cut out single-element photodiodes Acknowledgment
This work was supported by the SOCAR Science Foundation.
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