A de-capping method for removing red glue plastic sealing material and completely retaining copper wire in integrated circuit failure analysis

Abstract

This invention provides a DECAP method for removing red adhesive molding compound while preserving the copper traces in integrated circuit failure analysis. After physically opening the intact plastic package, a mixed solution of sulfuric acid and nitric acid, along with anhydrous ethylenediamine, is used to alternately react with the red adhesive molding compound. This increases the reaction rate, shortens the decapsulation time, and reduces the corrosion of the copper traces by the mixed acid. The anhydrous ethylenediamine reacts with the phenolic compounds in the red adhesive, altering its dense structure and facilitating faster corrosion of the red adhesive by the mixed acid.

Description

Technical Field

[0001] This invention relates to the field of chip failure analysis, and specifically to a DECAP method for integrated circuit failure analysis that removes red adhesive molding compound while completely preserving copper wires. Background Technology

[0002] Failure analysis is a diagnostic process used to determine the cause of product failure. Failure analysis technology is now widely used in various industrial sectors, especially in the field of electronic components, where it holds particular importance. Failure analysis is a crucial component of semiconductor device reliability analysis, and failure analysis of packaged chips is one type of semiconductor device failure analysis. To perform failure analysis on packaged chips, the packaging on the surface of the chip must first be removed.

[0003] In the decapsulation process of red glue-encapsulated chips, the red glue encapsulant has a denser structure and higher hardness compared to conventional encapsulants. After reacting with mixed acid, it becomes a red liquid, while conventional encapsulants react with acid to form a black liquid. Currently, the conventional method for decapsulating red glue-encapsulated chips involves using a mixture of nitric and sulfuric acid to remove the encapsulant from the chip through a dripping acid process. However, the conventional mixed acid etching rate of red glue encapsulants is very slow. To completely remove the red glue encapsulant from the chip, the dripping time must be increased (requiring 3-4 hours). For red glue-encapsulated devices with copper wire bonding, prolonged etching time can easily corrode the copper wires, even breaking them, compromising the integrity of the copper bonding wires and hindering chip testing and analysis after decapsulation. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a chip decapsulation method for removing red adhesive molding compound. The main process involves physically opening the intact device, then alternating the reaction of the red adhesive molding compound with a mixed solution of sulfuric acid and nitric acid, along with anhydrous ethylenediamine. This increases the reaction rate, shortens the decapsulation time, and reduces the corrosion of copper wires by the mixed acid. The anhydrous ethylenediamine reacts with the phenolic compounds in the red adhesive, altering its dense structure and facilitating faster corrosion of the red adhesive by the mixed acid.

[0005] Specifically, the chip requiring analysis and testing undergoes laser encapsulation to create a concave window in the encapsulation material on the chip. A mixed acid is prepared using fuming nitric acid and concentrated sulfuric acid. Anhydrous ethylenediamine is poured into a beaker and heated. The laser-encapsulated device is placed on a heating platform for heating. A small amount of the mixed acid is dropped onto the laser-encapsulated area, and after the mixed acid reacts with the red adhesive encapsulation material, the reaction solution is rinsed clean. The rinsed device is then placed on the heating platform again for heating. At this time, an appropriate amount of anhydrous ethylenediamine is dropped onto the device surface using a dropper, allowing the anhydrous ethylenediamine to react with the red adhesive encapsulation material. The reaction solution is then rinsed clean. This process of alternating between mixed acid and anhydrous ethylenediamine with the red adhesive is repeated until the chip is exposed. This method can accelerate the dissolution of the red adhesive encapsulation material, shorten the contact time between the mixed acid and the copper wire, and ensure that the copper wire is not corroded and broken. Finally, the decapsulated device is cleaned.

[0006] Unlike conventional techniques that use a 3:1 ratio of fuming nitric acid to concentrated sulfuric acid and a reaction temperature of 160-180°C, this invention preferably uses a mixed acid of fuming nitric acid and concentrated sulfuric acid in a 2:1 (volume ratio) ratio and a reaction temperature of 230°C. Too low a concentration of fuming nitric acid will not corrode the red adhesive, while a temperature of 230°C will accelerate the reaction without damaging the chip due to excessive heat. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of an embodiment of a chip de-encapsulation method for removing red adhesive molding compound according to the present invention;

[0008] Figure 2 The chemical equation for the chemical reaction between anhydrous ethylenediamine and red glue is given in this invention.

[0009] Figure 3 The experimental results are shown in the figure below, which is obtained by mixing fuming nitric acid and concentrated sulfuric acid in a ratio of 3:1 with anhydrous ethylenediamine and heating at 230℃.

[0010] Figure 4 The experimental results are shown in the figure below, with a fuming nitric acid to concentrated sulfuric acid ratio of 3:1, without the use of anhydrous ethylenediamine, and a heating temperature of 230℃.

[0011] Figure 5 The experimental results are shown in the following figure: fuming nitric acid: concentrated sulfuric acid ratio 2:1, without anhydrous ethylenediamine, and heated at 230℃.

[0012] Figure 6 The experimental results are shown in the following figure: fuming nitric acid: concentrated sulfuric acid ratio 2:1, anhydrous ethylenediamine, and heating temperature 200℃.

[0013] Figure 7 The following is a set of experimental results under the conditions of fuming nitric acid: concentrated sulfuric acid ratio 2:1, anhydrous ethylenediamine, and heating temperature 230℃.

[0014] Figure 8 Another set of experimental results is shown under the conditions of fuming nitric acid: concentrated sulfuric acid ratio of 2:1, anhydrous ethylenediamine, and heating temperature of 230℃. Detailed Implementation

[0015] This invention provides a specific embodiment of a chip de-encapsulation method for removing red adhesive molding compound. The steps are as follows:

[0016] 1. Laser open the encapsulation of the chip that needs to be analyzed and tested, and laser engrave a concave window on the encapsulation material on the chip (do not directly laser the copper wires).

[0017] 2. Prepare a mixed acid by mixing fuming nitric acid and concentrated sulfuric acid in a 2:1 (volume ratio). If the proportion of fuming nitric acid is too high, it will easily corrode the copper wire. If the proportion of fuming nitric acid is too low, it will not effectively corrode the red glue. Through experiments, it was found that a 2:1 (volume ratio) of fuming nitric acid and concentrated sulfuric acid is more suitable.

[0018] 3. Pour anhydrous ethylenediamine into a beaker (20 mL) and place it on a heating platform. Heat to 100°C.

[0019] 4. Place the laser-etched device on a heating platform and heat it to 230℃;

[0020] 5. Use a dropper to take a small amount of mixed acid and drop it onto the laser opening area. After the mixed acid reacts with the red sealant (the reaction solution is red during the reaction), use acetone to rinse the device surface to remove the red reaction solution.

[0021] 6. Place the cleaned device back on the heating platform and heat to 230℃. At this point, use a dropper to apply an appropriate amount of anhydrous ethylenediamine to the device surface. The anhydrous ethylenediamine reacts with the red molding compound, also turning red. Rinse the device with pure water to remove the reaction liquid. (Anhydrous ethylenediamine mainly reacts with the phenolic resin in the molding compound, reducing the density of the red molding compound and facilitating further etching with mixed acid.)

[0022] Reaction mechanism: The reaction formula between anhydrous hexamethylenediamine and phenolic substances in red glue molding compound is as follows. Figure 2 As shown.

[0023] 7. Perform alternating tests according to steps 5 and 6 until the chip is exposed. This method can accelerate the dissolution of the red glue molding compound and shorten the contact time between the mixed acid and the copper wire (this method can complete the de-encapsulation in only 0.5 hours), ensuring that the copper wire will not be corroded and broken.

[0024] 8. Cleaning: Place the device after desealment into a beaker containing acetone and vibrate it with ultrasound (70W) for 10 seconds. Then, take it out and place it into a beaker containing clean water and vibrate it with ultrasound for 5 seconds. Remove the chip and gently rinse the entire package and chip surface with acetone. After completing the above steps, allow the device to air dry naturally.

[0025] This method, by controlling the mixed acid ratio, adding anhydrous ethylenediamine, and selecting an appropriate temperature, decapsulates the copper wire bonding agent using red glue. This improves the reaction rate of the red glue and prevents excessive corrosion and wire breakage during acid etching. It increases the success rate of decapsulation for this type of device, providing better scientific assurance for subsequent testing. The decapsulation time for one device using this method is approximately 0.5 hours, which is about 2.5 hours shorter than conventional methods, making it more efficient.

[0026] The 2:1 mixed acid ratio and the reaction temperature of 230℃ in this method are also the optimal parameter selections after research.

[0027] The applicant used the de-encapsulation method of this invention to conduct 6 sets of experiments under 5 different experimental conditions, namely:

[0028] 1. Fuming nitric acid: concentrated sulfuric acid in a 3:1 ratio, mixed with anhydrous ethylenediamine, heated to 230℃;

[0029] 2. Fuming nitric acid: concentrated sulfuric acid ratio 3:1, anhydrous ethylenediamine not used, heating temperature 230℃;

[0030] 3. Fuming nitric acid: concentrated sulfuric acid ratio 2:1, anhydrous ethylenediamine not used, heating temperature 230℃;

[0031] 4. Fuming nitric acid: concentrated sulfuric acid ratio 2:1, using anhydrous ethylenediamine, heating temperature 200℃;

[0032] 5. Fuming nitric acid: concentrated sulfuric acid ratio 2:1, using anhydrous ethylenediamine, heating temperature 230℃;

[0033] 6. Fuming nitric acid: concentrated sulfuric acid ratio 2:1, using anhydrous ethylenediamine, heating temperature 230℃;

[0034] The experimental results correspond to Figures 3-8 Except for two groups of experiments conducted under the same experimental conditions of the present invention (Group 5 and Group 6), the copper wires of the other four groups of chips showed varying degrees of breakage.

Claims

1. A method for removing red adhesive molding compound while completely preserving copper traces in integrated circuit failure analysis, characterized in that... a. Physically open the chip that needs to be analyzed and tested, and etch a concave window into the plastic encapsulation material on the chip; b. Prepare a mixed acid by mixing fuming nitric acid and concentrated sulfuric acid; c. Place the physically opened device on a heating platform and heat it; drip the mixed acid into the concave window, and after the mixed acid reacts with the red glue sealant, rinse the surface of the device clean; d. Place the cleaned device on the heating platform again and heat it; drop anhydrous ethylenediamine onto the device surface, react with the red glue molding compound, and then rinse the device surface clean; heat the anhydrous ethylenediamine to 100°C before adding it; the anhydrous ethylenediamine reacts with the phenolic substances in the red glue, changing the dense structure of the red glue; e. Alternate between steps c and d until the chip is exposed; The mixed acid ratio in step b is selected as fuming nitric acid and concentrated sulfuric acid in a volume ratio of 2:1; the heating temperature in steps c and d is 230℃.

2. The de-encapsulation method of claim 1, wherein, The physical opening method in step a is laser opening.

3. The de-encapsulation method of claim 1, wherein, In step c, the object is cleaned with acetone.

4. The de-encapsulation method of claim 1, wherein, In step d, the washing is performed with pure water.

5. The de-encapsulation method of claim 1, wherein, After step e is completed, the device that has been depackaged is placed in a beaker containing acetone and vibrated with 70W ultrasound for 10 seconds. Then, it is taken out and placed in a beaker containing water and vibrated with ultrasound for 5 seconds. The chip is then removed and the entire package and chip surface are rinsed with acetone and allowed to air dry naturally.

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