Processing method of plastic package IC chip

Abstract

The invention relates to a processing method of a plastic package IC (integrated circuit) chip, which comprises the following steps: removing a plastic package material on the top surface of the plastic package IC chip by laser selective ablation to expose a gold thread as an end point indication; removing the residual plastic packaging material on the top surface of the plastic packaging IC chip and the plastic packaging material on the side surface and the bottom of the plastic packaging IC chip by using mixed acid of nitric acid and sulfuric acid so as to completely expose the IC chip; removing the polyimide passivation protection layer on the surface of the IC chip by using fuming sulfuric acid to expose a metal wiring layer of the IC chip; and cleaning and drying the IC chip. According to the processing method, through the synergistic effect of laser selective ablation and chemical corrosion, layered removal of the driving IC chip in the intelligent power module is achieved, the original appearance of a failure site is reserved to the maximum extent, reliable guarantee is provided for accurate positioning of a failure mode, and the reliability of the failure mode is improved. And the success rate and the accuracy of failure analysis of the high-end semiconductor device are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a method for processing plastic-encapsulated IC chips. Background Technology

[0002] In the field of semiconductor device failure analysis, decapsulation of packaged integrated circuit (IC) chips is a crucial preliminary step in locating the cause of failure. This is especially true for highly integrated power devices such as intelligent power modules (IPMs), which typically contain multiple insulated-gate bipolar transistors (IGBTs), fast recovery diodes (FRDs), and driver protection circuits (ICs), all encapsulated in epoxy resin. When an IPM module experiences electrical failure or reliability issues, decapsulation is essential to precisely expose the internal chips, gold wire bonding points, and metal wiring layers for subsequent electrical testing, microscopic observation, and accurate fault location.

[0003] Currently, the mainstream capping technologies for molded IC chips mainly fall into two categories. The first is the all-chemical capping method, which uses a single strong acid such as fuming nitric acid or concentrated sulfuric acid, or a mixed acid system of nitric and sulfuric acid, to chemically dissolve the molding compound. The process involves immersing the entire device in the acid solution, relying on the acid's penetration and decomposition of the epoxy molding compound to achieve capping. However, this method has significant drawbacks: the corrosion rate of the strong acid on the molding compound is difficult to control precisely, easily leading to over-corrosion, causing the melting of fine gold wires on the chip surface, bond point detachment, or erosion of the passivation layer and aluminum pads on the chip surface, thus destroying original evidence of failure. Furthermore, the isotropic nature of chemical corrosion makes it difficult to selectively remove specific areas when processing complex devices with densely packed chips, such as IPM modules, resulting in a narrow process window. The second type is the all-laser capping method, which uses a high-energy laser beam to directly ablate and vaporize the molding compound, rapidly removing the packaging material through layer-by-layer scanning. Its advantages lie in its high processing efficiency and precise positioning via optical systems. However, the laser ablation process is accompanied by intense thermal effects and mechanical impacts. The instantaneous high temperature can easily cause gold wire annealing and brittle fracture, cracking of the passivation layer on the chip surface, and even introduce thermal stress damage to the silicon chip itself, creating new defects and interfering with the determination of the true failure mechanism. At the same time, the energy distribution characteristics of the laser limit its ability to process the narrow area between the molding compound and the chip sidewalls. Once the laser penetrates the molding compound and reaches the chip surface, it will directly cause irreversible damage, resulting in a low process tolerance.

[0004] In summary, existing technologies face common technical challenges when addressing the capping requirements of IC chips in IPM modules: while all-chemical methods can gently remove material, they lack spatial selectivity and offer insufficient protection for delicate structures; all-laser methods, while possessing spatial precision, pose a high risk of thermal damage and do not fully cover complex three-dimensional structures. Therefore, the industry urgently needs a layered capping method that can synergistically leverage the advantages of laser and chemical etching to achieve step-by-step targeted removal. This method would efficiently remove large amounts of molding compound while preserving gold wires, chip surfaces, and microscopic failure characteristics without damage, thus meeting the requirements for high-reliability failure analysis. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of the prior art, and to this end, the following technical solution is adopted:

[0006] A method for processing a plastic-encapsulated IC chip is provided, comprising the following steps:

[0007] S0. Use a laser to selectively ablate and remove the molding material from the top surface of the molded IC chip to expose the gold wires as an endpoint indicator.

[0008] S1. Use a mixture of nitric acid and sulfuric acid to remove residual molding material from the top surface of the molded IC chip and the sides and bottom of the molded IC chip to fully expose the IC chip;

[0009] S2. Use fuming sulfuric acid to remove the polyimide passivation protective layer on the surface of the IC chip to expose the metal wiring layer of the IC chip;

[0010] S3. Clean and dry the IC chip.

[0011] Preferably, in the mixed acid, the volume ratio of nitric acid to sulfuric acid is (3-5):1.

[0012] Preferably, the reaction temperature in step S1 is 60℃-70℃.

[0013] Preferably, the reaction temperature in step S2 is 130℃-140℃.

[0014] Preferably, in step S3, the IC chip is cleaned using deionized water to neutralize and remove residual acid.

[0015] Preferably, in step S3, nitrogen gas is used to dry the IC chip.

[0016] Preferably, the encapsulated IC chip is a driver IC chip in a smart power module.

[0017] Preferably, the steps further include:

[0018] S4. Perform failure analysis on the IC chip.

[0019] Compared with the prior art, the beneficial effects of this invention are reflected in:

[0020] The processing method of this invention achieves the layered removal of the molding material, passivation protective layer, etc. of the driver IC chip in the intelligent power module through the synergistic effect of laser selective ablation and chemical corrosion. It preserves the original appearance of the failure site to the greatest extent, including complete gold wire bonding points, chip surface morphology and micro-failure features. It provides a reliable guarantee for the accurate location of failure modes such as electromigration, dielectric breakdown and mechanical cracks. It is especially suitable for intelligent power modules with complex internal structures and dense chip arrangement, and effectively improves the success rate and accuracy of failure analysis of high-end semiconductor devices. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the processing after step S0 in the processing method of this embodiment of the invention;

[0022] Figure 2 This is a schematic diagram of the processing after step S1 in the processing method of this embodiment of the invention;

[0023] Figure 3 This is a schematic diagram of the processing after step S2 in the processing method of this embodiment of the invention. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below.

[0025] Unless otherwise defined, the technical or scientific terms used in the claims and description shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0026] The word "comprising" or similar terms used in the specification and claims of this patent application mean that the objects preceding "comprising" include the objects listed after "comprising" or their equivalents, and do not exclude other objects.

[0027] Example

[0028] This embodiment provides a method for processing a plastic-encapsulated IC chip, the steps of which include:

[0029] S0. Use a laser to selectively ablate the top surface of the molded IC chip to remove the molding compound, exposing the gold wires as an endpoint indicator, such as... Figure 1 As shown;

[0030] By utilizing the characteristics of laser ablation to quickly remove most of the top plastic encapsulation material, and using gold wire as a natural endpoint indicator, the opening depth is precisely controlled by real-time monitoring of laser reflection signals. This effectively avoids the problems of gold wire melting, chip surface damage and aluminum pad corrosion caused by the difficulty in controlling the corrosion rate in traditional chemical methods. At the same time, it solves the defects of chip passivation layer cracking and body thermal stress damage caused by thermal effects and mechanical impact in the all-laser method.

[0031] S1. Using a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 4:1, remove the residual molding material from the top surface of the molded IC chip, as well as the molding material from the sides and bottom of the molded IC chip, at 60℃-70℃ to completely expose the IC chip. Figure 2 As shown;

[0032] Based on laser decapsulation, a mixed acid of nitric acid and sulfuric acid is used to selectively corrode the residual molding material on the sides and bottom of the molded IC chip. This mixed acid has a high corrosion rate on epoxy molding material, but a very low corrosion rate on silicon chip and gold wire, thus achieving effective cleaning of complex three-dimensional structures and overcoming the technical bottlenecks of lasers being unable to reach narrow areas and chemical methods being unable to control large-area removal.

[0033] S2. Using fuming sulfuric acid at 130℃-140℃, remove the polyimide passivation protective layer on the surface of the IC chip to expose the metal wiring layer of the IC chip, such as... Figure 3 As shown;

[0034] For the polyimide passivation protective layer on the surface of IC chips, fuming sulfuric acid is used for removal. The strong sulfonation and dehydration effect of free sulfur trioxide destroys the conjugated structure and intermolecular forces of polyimide molecules, causing it to decompose into a brittle byproduct layer that is easy to peel off. Compared with the traditional mixed acid system, this mechanism shows better kinetic balance at the target temperature, has better selectivity for gold wire and aluminum wire frame, and completely avoids the generation of toxic nitrogen oxide gas, significantly improving the safety of the working environment and reducing the cost of exhaust gas treatment.

[0035] S3. Clean the IC chip with deionized water to neutralize and remove residual acid, and dry the IC chip with nitrogen.

[0036] S4. Perform failure analysis on the IC chip.

[0037] In some preferred embodiments, the encapsulated IC chip is a driver IC chip in a smart power module.

[0038] In summary, the processing method of this invention achieves the layered removal of the molding material, passivation protective layer, etc. of the driver IC chip in the intelligent power module through the synergistic effect of laser selective ablation and chemical corrosion. This preserves the original appearance of the failure site to the greatest extent, including complete gold wire bonding points, chip surface morphology, and microscopic failure features. It provides a reliable guarantee for the accurate location of failure modes such as electromigration, dielectric breakdown, and mechanical cracks. It is especially suitable for intelligent power modules with complex internal structures and dense chip arrangement, effectively improving the success rate and accuracy of failure analysis of high-end semiconductor devices.

[0039] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for processing a plastic-encapsulated IC chip, comprising the following steps: S0. Use a laser to selectively ablate and remove the molding material from the top surface of the molded IC chip to expose the gold wires as an endpoint indicator. The feature is that the steps further include: S1. Use a mixture of nitric acid and sulfuric acid to remove residual molding material from the top surface of the molded IC chip and the sides and bottom of the molded IC chip to fully expose the IC chip; S2. Use fuming sulfuric acid to remove the polyimide passivation protective layer on the surface of the IC chip to expose the metal wiring layer of the IC chip; S3. Clean and dry the IC chip.

2. The processing method according to claim 1, characterized in that, In the mixed acid, the volume ratio of nitric acid to sulfuric acid is (3-5):

1.

3. The processing method according to claim 1, characterized in that, The reaction temperature in step S1 is 60℃-70℃.

4. The processing method according to claim 1, characterized in that, The reaction temperature in step S2 is 130℃-140℃.

5. The processing method according to claim 1, characterized in that, In step S3, the IC chip is cleaned using deionized water to neutralize and remove residual acid.

6. The processing method according to claim 1, characterized in that, In step S3, nitrogen gas is used to dry the IC chip.

7. The processing method according to claim 1, characterized in that, The plastic-encapsulated IC chip is the driver IC chip in the intelligent power module.

8. The processing method according to any one of claims 1-7, characterized in that, The steps also include: S4. Perform failure analysis on the IC chip.

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