A processing method for removing silica gel on a chip surface of a ceramic hermetic packaging product

Abstract

This invention discloses a method for removing silicone from the surface of ceramic hermetic packaging products. The method involves heating 98% concentrated sulfuric acid at high temperature, and removing the pressure-resistant insulating silicone from the hermetic package by controlling the temperature of the etching solution and the etching time. Because concentrated sulfuric acid at high temperatures is highly corrosive to organic materials but relatively weakly corrosive to aluminum, controlling the etching time effectively reduces the corrosion rate on the aluminum layer and the polyimide layer beneath the silicone on the chip, preventing damage to the wire bonding and allowing for further electrical testing and observation of the integrity of the wire bonding joints.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for removing silicone from the surface of ceramic hermetic packaging products. Background Technology

[0002] Semiconductor packaging technology can be broadly categorized into hermetic and non-hermetic packaging based on the degree of sealing. Non-hermetic packaging primarily uses resin materials for sealing, employing various methods such as coating, heating, immersion, and casting. Hermetic sealing technologies mainly include solder sealing, low-melting-point glass sealing, seam welding, and laser sealing. These two packaging technologies are used in different environments due to differences in packaging costs and reliability requirements. For example, non-hermetic packaging, with its lower cost, is often used in consumer products, but its moisture resistance is inferior to hermetic packaging, making it unsuitable for high-reliability environments. The device analyzed in this study utilizes solder sealing, a type of hermetic packaging, where a metal cap is soldered onto a ceramic substrate to achieve a hermetic seal for the semiconductor device.

[0003] Multiple chips are mounted on this ceramic substrate, and their signal terminals are led out to the substrate via gold wires using a wire bonding method. Some chips have silicone and polyimide layers on their surfaces to protect the internal metal bonding wires from external impact damage and to provide insulation. Silicone is used because current semiconductor plastic-based encapsulation materials include epoxy molding compound (EMC), silicone encapsulation materials, and polyimide. Silicone has good heat resistance, corrosion resistance, and insulation, so it is used in semiconductor chip coatings and LED encapsulation adhesives. Silicone can also adhere to the polyimide layer on the chip surface. Therefore, when both silicone and polyimide are present in the device encapsulation process, chemical etching in failure analysis presents a challenge. Because silicone has poor fluidity, manufacturers often add different colors to it to improve conductivity and dielectric constant, resulting in poor light transmittance and making it impossible to observe the chip surface. Chemical etching is the only way to treat it. However, silicone becomes very hard after curing, making it difficult to remove during the chemical etching process in failure analysis.

[0004] Chemical etching is a crucial component of failure analysis techniques. By performing processes such as opening the device, planar and cross-sectional etching, and peeling, it is possible to observe the internal electrical interconnections, chip surface damage, burns, and other conditions. It can also serve as preliminary processing for subsequent failure analysis projects.

[0005] Current semiconductor failure analysis utilizes the following chemical methods to treat silicone:

[0006] 1. After removing the metal cap, immerse the device in an organic solvent such as acetone or alcohol until the silicone softens, then wipe it clean with a cotton swab or a lint-free cloth.

[0007] 2. After removing the metal cap, immerse the device in fuming nitric acid while it is heating to corrode it, and then clean it with water.

[0008] Both of the above methods have obvious drawbacks:

[0009] 1. Soaking in organic solvents will soften the silicone, but it takes a long time, more than 2 hours. In addition, the gold wires are very easy to break during the subsequent cleaning and wiping process, which will make it impossible to carry out other tests.

[0010] 2. Fuming nitric acid treatment can corrode silicone, but it will also corrode other organic material layers on the chip, such as polyimide, which will cause the gold wires on the chip to fall off without the protection of the polyimide layer. Summary of the Invention

[0011] The technical problem to be solved by this invention is, on the one hand, to shorten the processing time of chemicals and silicone, improve work efficiency, and reduce time costs; on the other hand, when there are two organic materials, silicone and polyimide, on the chip, the reaction time between the chemicals and the polyimide layer can be reduced, ensuring the integrity of wire bonding and the metal layer on the chip, and facilitating subsequent testing of the device and observation of the chip.

[0012] This invention rapidly etches the silicone layer on a chip using chemical treatment, while simultaneously protecting the wire bonding and other organic layers on the chip, ensuring that the device's function is unaffected and facilitating further analysis. The specific steps are as follows:

[0013] (1) Grind around the metal cap of the ceramic hermetic packaging product, thin the sealing area around the metal cap, expose one corner, and then use antistatic metal tweezers to open the metal cap.

[0014] (2) Preheat the heating platform to 320℃;

[0015] (3) Place 98% concentrated sulfuric acid on a heating platform and heat it until a clear white mist can be seen with the naked eye;

[0016] (4) Immerse the sample in the concentrated sulfuric acid for 20 seconds;

[0017] (5) After 20 seconds, remove the sample and slowly rinse it with pure water for the first time.

[0018] (6) Place the cleaned sample into a container of pure water and clean it a second time with ultrasound.

[0019] (7) The cleaned sample does not need to be dried. It can be placed directly into acetone and ultrasonically cleaned for the third time.

[0020] (8) Take out the cleaned sample and let it stand to air dry.

[0021] Because concentrated sulfuric acid at high temperatures is highly corrosive to organic materials, but less corrosive to aluminum, by controlling the corrosion time, the corrosion rate of the aluminum metal layer and the polyimide layer under the silicone on the chip can be effectively reduced, so that the wire bonding on the chip is not damaged, and further electrical testing and observation of the integrity of the wire bonding joints can be performed. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention.

[0023] Figure 2 This is a photograph of the ceramic hermetic encapsulation product in the embodiment before the adhesive is removed using the process of the present invention.

[0024] Figure 3 yes Figure 2 A photograph of a ceramic hermetic encapsulation product after adhesive removal using the process of this invention. Detailed Implementation

[0025] The preferred embodiments of the present invention are given below with reference to the accompanying drawings to illustrate the technical solution of the present invention in detail.

[0026] Example

[0027] like Figure 1 The process shown describes the hermetic encapsulation of ceramic products ( Figure 2 (As shown) Use an electric grinder to grind around the metal cover to thin the sealed area around the metal cover and expose one corner. Then use anti-static metal tweezers to remove the metal cover and observe the silicone of the chip inside the device to determine the metal layer on the chip surface, the material of the wire bonding, and whether there are other organic materials, etc.

[0028] Wear EHS protective equipment, clean other chemicals from the acid and alkali resistant ventilation table, turn on the heating platform, set the temperature to 320℃, and heat for 5 minutes. The preheating time can be adjusted according to the model and heating speed of the heating platform.

[0029] Depending on the size of the experimental sample, the procedure should be performed in an acid- and alkali-resistant fume hood. Pour 30 ml of 98% concentrated sulfuric acid into a glass beaker, then place the glass beaker on a heating platform at 320°C and heat for 30 minutes until a noticeable white mist (water absorption and heat release) is visible to the naked eye.

[0030] Turn on the timer and set the duration to 30 seconds;

[0031] Hold the sample encapsulation substrate at both ends with antistatic metal tweezers. When there are 20 seconds left on the timer, put the sample into heated concentrated sulfuric acid. At this time, it is observed that the silica gel is reacting rapidly, and a grayish-colored reaction substance emerges. The color of the reaction substance varies depending on the type and color of the silica gel.

[0032] When the timer goes off, take out the sample. Because the concentrated sulfuric acid on the sample is at a high temperature and releases heat when it comes into contact with water, the operator needs to slowly put the sample into pure water and gently shake it back and forth to clean it for the first time.

[0033] Place the cleaned sample into a glass containing pure water, place it in an ultrasonic cleaner, and clean it with the ultrasonic cleaner for 30 seconds.

[0034] The cleaned sample does not need to be dried. It can be placed directly into a glass containing acetone and then cleaned with an ultrasonic cleaner for about 30 seconds.

[0035] Remove the cleaned sample and let it air dry on the sample processing table.

[0036] After air drying, it can be observed under an optical microscope, such as... Figure 3 As shown, the silicone has been completely removed, and the polyimide layer beneath the silicone is preserved to the maximum extent, completing the wire bonding process. This method is suitable for ceramic packaging products where the chip surface is coated with silicone and polyimide layers, and the silicone contains wires that can be made of gold, copper, aluminum, or other materials.

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for removing silicone from the surface of a chip in a ceramic hermetic encapsulation product, wherein the chip surface of the ceramic hermetic encapsulation product is coated with a silicone and a polyimide layer, and the silicone contains wire bonding, characterized in that... Includes the following steps: (1) Grind around the metal cap of the ceramic hermetic packaging product, thin the sealing area around the metal cap, expose one corner, and then use antistatic metal tweezers to open the metal cap. (2) Preheat the heating platform to 320℃; (3) Place 98% concentrated sulfuric acid on a heating platform and heat it until a clear white mist can be seen with the naked eye; (4) Immerse the sample in the concentrated sulfuric acid for 20 seconds; (5) After 20 seconds, remove the sample and slowly rinse it with pure water for the first time. (6) Place the cleaned sample into a container of pure water and clean it a second time with ultrasound. (7) The cleaned sample does not need to be dried. It can be placed directly into acetone and ultrasonically cleaned for the third time. (8) Take out the cleaned sample and let it stand to air dry.

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