Method for improving reliability of plastic package transistor output type photoelectric coupler

Abstract

The invention relates to a method for improving the reliability of a plastic package transistor output type photoelectric coupler, which comprises the following steps of: before plastic package, covering a layer of transparent silica gel on the surface of a photosensitive transistor chip, then carrying out plastic package, and utilizing the flexibility of the silica gel to disperse the extrusion force generated by the expansion of a plastic package material on the surface of the photosensitive transistor chip so as to improve the reliability of the plastic package transistor output type photoelectric coupler. Therefore, the passivation layer on the surface of the photosensitive transistor chip is protected. The process for covering the transparent silica gel on the surface of the photosensitive transistor chip comprises the following steps of: (1) coating the transparent silica gel on the surface of the photosensitive transistor chip, completely wrapping the surface of the chip, controlling the thickness of the transparent silica gel at the highest point of the surface of the photosensitive transistor chip to be 0.5-2 times of the thickness of the photosensitive transistor chip, and completely wrapping the gold wire with the silica gel after curing; (2) curing at the temperature of 90 + / -5 DEG C for 10 + / -5 minutes; (3) curing for 2-2.5 hours under the condition of 150 + / -5 DEG C; and (4) after curing is completed, the next procedure is carried out. According to the invention, the transparent silica gel covers the surface of the chip to protect the passivation layer of the chip, so that the leakage current of the photoelectric coupler after high-temperature aging is prevented from being increased, and the reliability of the plastic package photoelectric coupler is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric couplers and relates to a method for improving the reliability of a plastic-sealed transistor output type photoelectric coupler. Background Art

[0002] Plastic-sealed photocouplers are widely used in communications, power, industrial control, medical equipment, automobiles, consumer electronics and other fields due to their low cost. At the same time, due to their light weight, they are also suitable for applications with strict load limits. However, compared with ceramic air-sealed photocouplers, due to differences in structure, the reliability of plastic-sealed photocouplers is somewhat different from that of ceramic air-sealed photocouplers.

[0003] Output leakage current I CEO It is an important indicator to measure the photoelectric coupler. It represents the output cutoff capability of the photoelectric coupler when the output is in the cutoff state. At room temperature, I CEO Usually less than tens of nA. CEO If it increases to more than tens of μA, it indicates that the output cutoff capability has deteriorated, which may cause the functional failure of the optocoupler.

[0004] In general plastic-encapsulated transistor output type photocouplers, the light-emitting diode chip (LED) and the photosensitive transistor chip (PD) are placed opposite each other. The light emitted by the LED directly illuminates the photosensitive surface of the PD chip to generate photocurrent. In order to form a light path, two injection moldings are used, one using white plastic molding compound (light path) and the other using black plastic molding compound. The white plastic molding compound is in direct contact with the chip after curing. Figure 1 shown.

[0005] For high-reliability plastic-sealed optocouplers, the output leakage current is prone to increase significantly after high-temperature aging. After analysis, it is found that under the action of temperature stress, the thermal expansion coefficients of the cured plastic sealing material inside the plastic-sealed optocoupler and the internal photosensitive transistor chip are different, causing the passivation layer on the chip surface to be squeezed and broken by the plastic sealing material; at the same time, chlorine-containing organic solvents are introduced into the chip manufacturing process, so chlorine-containing conductive ions will inevitably remain in the chip. The residual conductive ions inside the chip undergo ion migration under the action of electrical stress during the aging process, forming a leakage channel, which leads to an increase in the output leakage current. Summary of the invention

[0006] In view of this, the purpose of the present invention is to solve the problem of passivation layer being squeezed and broken by plastic packaging material, and to provide a method for improving the reliability of plastic-sealed transistor output type optocoupler, which can avoid the increase of leakage current of plastic-sealed optocoupler after high-temperature aging, thereby improving its reliability.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for improving the reliability of a plastic-sealed transistor output type photocoupler. Before plastic sealing, a layer of transparent silicone is first covered on the surface of a phototransistor chip, and then plastic sealing is performed. The flexibility of the silicone is used to disperse the squeezing force generated by the expansion of the plastic sealing material on the surface of the phototransistor chip, thereby protecting the passivation layer on the surface of the phototransistor chip.

[0009] Furthermore, the process of covering the surface of the phototransistor chip with transparent silicone is as follows:

[0010] (1) Apply transparent silicone on the surface of the phototransistor chip, requiring it to completely cover the chip surface. After curing, the silicone completely covers the gold wire;

[0011] (2) Curing at 90℃±5℃ for 10min±5min;

[0012] (3) Then cure at 150°C ± 5°C for 2 h to 2.5 h;

[0013] (4) After curing is completed, proceed to the next process.

[0014] Furthermore, when applying the transparent silica gel, the thickness of the transparent silica gel at the highest point on the surface of the phototransistor chip is controlled to be 0.5 to 2 times the thickness of the phototransistor chip.

[0015] Furthermore, the transparent silicone is a single-component elastic silicone.

[0016] The beneficial effects of the present invention are:

[0017] The present invention adopts transparent silica gel covering the surface of the chip, and utilizes the squeezing force generated by the expansion of the plastic packaging material on the surface of the flexible dispersion sheet of silica gel to protect the chip passivation layer, avoid the leakage current of the photoelectric coupler from increasing after high temperature aging, and improve the reliability of the plastic-sealed photoelectric coupler.

[0018] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0020] Figure 1 It is a schematic diagram of the structure of an existing photoelectric coupler.

[0021] Figure 2It is a schematic diagram of the improved photoelectric coupler in the present invention. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and the features in the embodiments can be combined with each other without conflict.

[0023] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0024] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0025] See also Figure 2 , which is a method for improving the reliability of a plastic-encapsulated transistor output type photocoupler. Before plastic encapsulation, a layer of transparent silicone is first covered on the surface of a phototransistor chip, and then plastic encapsulation is performed. The flexibility of the silicone is used to disperse the squeezing force generated by the expansion of the plastic encapsulation material on the surface of the phototransistor chip, thereby protecting the passivation layer on the surface of the phototransistor chip.

[0026] Specifically, the process of covering the surface of the phototransistor chip with transparent silicone is as follows:

[0027] (1) Apply transparent silicone to the surface of the phototransistor chip, requiring it to completely cover the chip surface. The thickness of the highest point of the colloid is 0.5 to 2 times the thickness of the chip. After curing, the silicone completely covers the gold wire.

[0028] (2) Curing at 90℃±5℃ for 10min±5min;

[0029] (3) Then cure at 150°C ± 5°C for 2 h to 2.5 h;

[0030] (4) After curing is completed, the plastic sealing process begins.

[0031] The transparent silica gel in this embodiment is a single-component elastic silica gel, and its main parameters are shown in Table 1.

[0032] Table 1 Main parameters of transparent silicone

[0033]

[0034]

[0035] Table 2 shows the leakage current test results of the plastic-encapsulated photoelectric coupler before and after the present invention is used. The aging condition is V CC =10V, I F =10mA, R L =430Ω, T A =125℃, t=168h, before aging, the leakage current of all photocouplers is less than 0.1μA, and the abnormal condition criterion is the leakage current I CEO >1μA.

[0036] Table 2 Statistics of leakage current of plastic encapsulated optocouplers

[0037] Sample status Total quantity Abnormal leakage current after aging Abnormal leakage current test value range Photocoupler before using the present invention 100 23 5μA~360μA Photoelectric coupler using the present invention 100 0 -

[0038] It can be seen from the above comparative tests that the method of the present invention can prevent the leakage current of the photoelectric coupler from increasing after high-temperature aging, thereby improving the reliability of the plastic-sealed photoelectric coupler.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for improving the reliability of a plastic-encapsulated transistor output type photocoupler, characterized in that: Before plastic encapsulation, a layer of transparent silicone is first covered on the surface of the phototransistor chip, and then plastic encapsulation is performed. The flexibility of the silicone is used to disperse the extrusion force generated by the expansion of the plastic encapsulation material on the surface of the phototransistor chip, thereby protecting the passivation layer on the surface of the phototransistor chip.

2. The method for improving the reliability of a plastic-encapsulated transistor output type photocoupler according to claim 1, characterized in that: The process of covering the surface of the phototransistor chip with transparent silicone is as follows: (1) Apply transparent silicone on the surface of the phototransistor chip, requiring it to completely cover the chip surface. After curing, the silicone completely covers the gold wire; (2) Curing at 90℃±5℃ for 10min±5min; (3) Then cure at 150°C ± 5°C for 2 h to 2.5 h; (4) After curing is completed, proceed to the next process.

3. The method for improving the reliability of a plastic-encapsulated transistor output type photocoupler according to claim 2, characterized in that: When applying the transparent silicone, the thickness of the transparent silicone at the highest point on the surface of the phototransistor chip is controlled to be 0.5 to 2 times the thickness of the phototransistor chip.

4. The method for improving the reliability of a plastic-encapsulated transistor output type photocoupler according to claim 1, characterized in that: The transparent silica gel is a single-component elastic silica gel.

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