Non-destructive unsealing method suitable for copper bonding wire of advanced packaging plastic packaging device

Abstract

The invention discloses a lossless unsealing method suitable for a copper bonding wire of an advanced packaging plastic package device. The lossless unsealing method comprises the following steps: step 1, positioning: positioning a chip bonding area; step 2, laser pretreatment: after positioning, carrying out rapid laser rough etching until the solder ball is exposed; step 3, after the solder balls are exposed, reversely selecting an outer area of the chip, and etching until two solder joints are exposed; step 4, performing reactive plasma first-stage etching according to a gas proportion 1; step 5, after the first stage of plasma etching is carried out, the device is interrupted and taken out for inspection, if the chip bonding pad is not exposed, the step 4 is repeated, and otherwise, the step 6 is carried out; step 6, performing reactive plasma second-stage etching according to a gas ratio 2; step 7, cleaning and drying; and 8, carrying out subsequent bonding detection and analysis.

Description

Technical Field

[0001] This invention belongs to the field of component reliability research, and in particular relates to a non-destructive method for opening copper bonding wires of advanced packaged plastic devices. Background Technology

[0002] As the performance and cost requirements of integrated circuit devices increase, copper wire bonding is gradually replacing gold wire bonding and becoming the mainstream packaging technology due to its advantages such as low resistivity, high thermal conductivity, high mechanical strength, and low cost. However, copper wire bonding has a narrow process window, is prone to oxidation, and its high hardness leads to stress concentration. Furthermore, it is susceptible to the effects of impurities such as halides in the packaging material, resulting in significant reliability issues. Because of these characteristics, copper wire bonding and gold wire bonding differ significantly in their failure mechanisms and models. However, the industry still widely uses gold wire bonding standards, leading to biases in the reliability assessment of copper wire bonding devices.

[0003] In reliability studies and failure analysis of copper leads, unpacking is a crucial step in obtaining accurate failure information. Differences in packaging materials and structures mean there is no fixed unpacking method; improper process selection can cause secondary damage to the copper bonding wires, interfering with subsequent characterization and data accuracy. Therefore, employing scientific, controllable, and verifiable unpacking methods is fundamental for the reliability assessment, failure mechanism analysis, and lifetime prediction of advanced packaged copper bonding wires.

[0004] (1) Patent CN107680919A A method for unpacking plastic-encapsulated copper bonding wire integrated circuits Key points of the method: Laser is used to thin the molding compound to reduce the contact time between the acid and the copper bonding wire during wet etching; by heating the back of the device, adjusting the mixed acid ratio, and developing a special cleaning procedure, the molding compound is removed while the morphology of the copper wire is preserved.

[0005] Technical Analysis: This solution optimizes the conditions of wet etching, which can mitigate the direct corrosion of copper by acid to some extent. However, it still relies on highly reactive oxidizing acids for chemical etching. The high temperature / strong oxidizing environment inevitably alters the chemical state of the copper surface and may damage the bonding structure and mechanical properties. Furthermore, acid treatment places high demands on safety, environmental protection, and waste disposal.

[0006] (2) Patent CN114814542A: A method for opening a plastic-encapsulated copper bonding lead semiconductor device Key points of the method: First, X-ray positioning is used, and the molding compound is thinned using a laser. Then, a prepared mixed solution of concentrated sulfuric acid / concentrated nitric acid / benzotriazole is added dropwise to the unsealed area after heating for a short time until the chip and bonding wire are exposed. Ultrasonic cleaning is then performed. Benzotriazole is used to inhibit copper corrosion.

[0007] Technical Analysis: This method is more standardized in terms of operation procedures and chemical solution formulation, and the addition of corrosion inhibitors can improve the protective effect. However, it is still essentially a strong acid chemical desealing process, which carries the risk of high-temperature short-term corrosion, complex operation, high equipment and consumable costs, and the safety and environmental burden of acid treatment. It is still difficult to avoid irreversible changes to the copper bonding wire.

[0008] (3) Literature report: “Research on the opening method of electrolytically encapsulated copper wire bonding device” (Electronics & Packaging, October 2018) Key points of the method: The molding compound is removed by electrolysis. Selective peeling of the molding compound is achieved by controlling parameters such as electrolyte ratio and current density, with the aim of minimizing chemical damage to the copper bonding wires.

[0009] Technical Analysis: Electrolysis removes molding compound through electrochemical reactions, which can significantly reduce chemical corrosion of copper bonding wires and has the potential for lower cost. However, it is highly sensitive to electric field and current density, and is prone to local over-etching and "tunneling effect", resulting in uneven coating removal and difficult-to-remove residues. At the same time, it requires modification of test benches and fixtures, increasing process complexity and promotion difficulty.

[0010] The current industry standard employs a combined process of "laser rough removal + strong oxidizing wet refining." First, a laser is used to rapidly remove large pieces of molding compound, then a mixed acid is used to briefly dissolve residual carbon deposits and organic matrix. This improves demolding efficiency and facilitates subsequent reliability testing and bonding wire inspection. While this process is highly efficient, the strong acid has a significant oxidizing and dissolving effect on copper, easily altering the surface chemical state of the bonding wire and weakening its mechanical strength, thus failing to obtain accurate data on the copper bonding wire. Summary of the Invention

[0011] The purpose of this invention is to provide a non-destructive method for opening copper bonding wires in advanced encapsulated plastic devices, characterized by the following steps: Step 1, Positioning: Position the chip bonding area; Step 2, Laser pretreatment: After positioning, rapid laser coarse etching is performed until the solder balls are exposed; Step 3: After the solder balls are exposed, etch the outer area of ​​the chip until the two solder joints are exposed; Step 4: Perform reactive plasma first-stage etching with a gas ratio of 1. Step 5: After the first stage of plasma etching, interrupt the process and remove the device for inspection. If the chip pads are not yet exposed, repeat step 4; otherwise, proceed to step 6. Step 6: Perform reactive plasma second-stage etching at gas ratio 2; Step 7, washing and drying; Step 8: Subsequent bonding detection and analysis.

[0012] Preferably, step 1 includes: using an X-ray imaging device to accurately locate the chip body, inner solder joints, bonding wire routing, and the position of the outer solder joints of the lead frame.

[0013] Preferably, step 2 includes: laser pretreatment using a short-wavelength laser to remove the molding compound on the device surface layer by layer. First, a high-frequency laser above 50kHz is used to quickly remove the large volume of molding compound on the device surface. When the bonding wires are gradually exposed, the frequency is switched to 10kHz and the scanning speed is slowed down until the bonding wires and solder balls are completely exposed, so as to avoid damage to the chip surface caused by excessive laser etching.

[0014] Preferably, step 4 includes: etching with a mixture of O2 and CF4 gas, wherein the gas ratio of O2 to CF4 is 10:3, the oxygen flow rate is 100 sccm, the CF4 flow rate is 30 sccm, and the etching time is adjusted according to the residual thickness and surface morphology of the molding compound to achieve efficient removal of the molding compound.

[0015] Preferably, step 6 includes: if the pads are exposed, adjusting the gas ratio of the reactive plasma etching machine, adding Ar gas, and the ratio of O2, CF4 and Ar is 10:1:5; performing a short etching process until the bonding wires on the chip surface are completely exposed.

[0016] Preferably, step 7 includes: after reactive plasma etching, stirring and rinsing the residual ashed molding compound with isopropyl alcohol (IPA) or acetone, avoiding ultrasonic cleaning, and then using nitrogen gas through a micro-nozzle for low-pressure purging to dry the device surface.

[0017] Preferably, step 8 includes: performing electrical performance testing and bonding wire reliability testing on the device within 24 hours after unpacking; and verifying that there is no obvious corrosion or mechanical damage on the surface of the copper bonding wire inside the device, which meets the requirements for non-destructive unpacking.

[0018] This invention proposes a non-destructive unpacking method for copper-containing bonding wires in molded devices based on a combination of laser pretreatment and reactive plasma etching. Compared with existing technologies, this invention has the following significant advantages: a) Fundamentally avoid chemical corrosion: Traditional mixed acid methods and their optimization schemes still rely mainly on chemical oxidation, which can easily change the surface chemical state of copper bonding wires; this invention uses reactive ion etching to replace the chemical etching process, fundamentally eliminating strong acid contact and significantly reducing the risk of chemical changes and mechanical damage to the copper surface.

[0019] b) Higher economic efficiency and laboratory scalability: Compared to alternative methods that require specific electrolysis equipment or complex chemical formulations (electrolysis, microwave-induced plasma, etc.), reactive plasma etching equipment is more common in semiconductor and failure analysis laboratories, and has lower process consumables and environmental treatment costs, making it easier to promote and repeat.

[0020] c) Preserving original microscopic and mechanical information is beneficial for failure analysis: The acid-free and low-disturbance process of this invention can preserve the surface morphology of the bonding wire, the metal oxidation state and the interfacial bonding characteristics to the maximum extent, thereby obtaining more realistic and reliable material and structural data, and avoiding the impact of artifacts introduced by the opening process on the judgment of failure mechanism and reliability assessment.

[0021] In summary, this invention achieves a balance between efficient coating removal and extremely low disturbance protection by combining laser pre-etching with precise reactive plasma etching, thus meeting the rigid requirement for obtaining accurate, repeatable, and low-interference copper bonding wire data in reliability testing and failure analysis. Based on the aforementioned technical differences and advantages, this invention has significant innovative points and application and promotion value. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the device etching area according to an embodiment of the present invention; Figure 3 This is an example diagram of the unpacking effect of the LQFP-80 packaged device in Embodiment 1 of the present invention; Figure 4 This is an example of the unpacking effect of the SOT-23 packaged device in Embodiment 2 of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] To achieve non-destructive opening of molded copper bonding wires, this invention proposes a composite opening process, comprising the following steps: Step 1: Locate the chip bonding area. Using X-ray imaging technology, accurately locate the chip position, inner solder joints, and outer solder joints of the leadframe to ensure the accuracy of subsequent processing.

[0025] Step 2: After positioning, rapid laser coarse etching is performed until the solder balls are exposed. Laser pretreatment uses a short-wavelength laser to remove the molding compound layer by layer from the device surface. First, a high-frequency laser above 50 kHz is used to rapidly remove the large volume of molding compound from the device surface. As the bonding wires are gradually exposed, the frequency is switched to a low 10 kHz and the scanning speed is slowed down until the bonding wires and solder balls are completely exposed. This avoids damage to the chip surface caused by excessive laser etching. Figure 2 As shown.

[0026] Step 3: After the solder balls are exposed, reverse the etching process on the outer area of ​​the chip until the two solder joints are exposed. Adjust the laser irradiation area to perform laser etching on the outer area of ​​the chip until the two solder joints of the lead frame are completely exposed.

[0027] Step 4: The first stage of reactive plasma etching is performed using a gas ratio of 1. During the reactive plasma etching stage, a mixture of O2 and CF4 gas is used, with an O2 to CF4 gas ratio of 10:3, an oxygen flow rate of 100 sccm, and a CF4 flow rate of 30 sccm. The etching time is adjusted according to the residual thickness and surface morphology of the molding compound to achieve efficient removal of the molding compound.

[0028] Step 5: After the first stage of plasma etching, interrupt the process and remove the device for inspection. If the chip pads are not yet exposed, repeat step 4; otherwise, proceed to step 6.

[0029] Step 6: Perform the second stage of reactive plasma etching using gas ratio 2. If the pads are already exposed, adjust the gas ratio of the reactive plasma etching machine, adding Ar gas, with the ratio of O2, CF4, and Ar being 10:1:5. Perform a brief etching process until the bonding wires on the chip surface are fully exposed.

[0030] Step 7, Cleaning and Drying. After reactive plasma etching, the residual ashed molding compound is rinsed with isopropanol (IPA) or acetone, avoiding ultrasonic cleaning. Then, nitrogen is used to purge the device surface at low pressure through a micro-nozzle to dry it.

[0031] Step 8: Subsequent bonding inspection and analysis. Once unpacking is complete, device inspection and bonding testing must be completed within 24 hours. Example

[0032] Taking an LQFP-80 packaged plastic device as an example, the composite unpacking process of this invention was used to perform non-destructive unpacking of its copper bonding wires, and the unpacking effect was as follows: Figure 3 As shown. Specifically: 1) Positioning: First, use industrial X-ray imaging equipment to scan the LQFP-80 device from multiple angles to obtain the precise positions of the chip body, inner solder joints, bonding wire direction, and outer solder joints of the lead frame, providing coordinate reference for subsequent laser and plasma processing.

[0033] 2) Laser pretreatment: A short-pulse solid-state laser with a wavelength of 355 nm was selected. First, a high-frequency, fast scanning mode of 50 kHz was used to remove the large volume of epoxy molding compound from the surface of the device in layers. After the bonding wires were gradually exposed, the frequency was switched to 10 kHz and the scanning speed was reduced to perform fine material removal until the outline of the bonding wires and solder balls was completely clear, in order to avoid thermal / mechanical damage to the chip surface caused by excessive laser.

[0034] 3) Outer area etching: Adjust the laser irradiation area according to the X-ray positioning results, and perform laser etching on the outer edge of the chip and around the lead frame to expose the two solder joints.

[0035] 4) Reactive plasma etching (first stage): O2 / CF4 mixed gas is used in a ratio of 10:3; O2 flow rate is 100 sccm, CF4 flow rate is 30 sccm; the etching time is adjusted according to the thickness of the residual molding layer and the surface morphology (about 15 min in this embodiment) to quickly remove the residual molding material.

[0036] 5) Inspection: After etching, pause the removal of the device and use an optical microscope to inspect the exposure of the internal bonding wire pads. If not fully exposed, repeat this etching stage for 3–5 minutes.

[0037] 6) Reactive plasma etching (second stage): After the pads have been basically exposed, adjust the etching gas ratio to O2:CF4:Ar = 10:1:5 and etch for 1–2 min to perform residual etching, so that the bonding wires on the chip surface are fully exposed.

[0038] 7) Cleaning and drying: After etching, place the device in a beaker, add isopropanol and stir to rinse away the residual ashing, then blow dry the device surface with nitrogen micro-nozzle at low pressure.

[0039] 8) Subsequent testing: Within 24 hours of unpacking, the device's electrical performance and bonding wire reliability were tested. Verification showed no significant corrosion or mechanical damage on the surface of the copper bonding wires inside the device, meeting the requirements for non-destructive unpacking. Example

[0040] Taking an SOT-23 packaged plastic-encapsulated device as an example, the composite unpacking process of this invention was used to perform non-destructive unpacking of its copper bonding wires, and the unpacking effect was as follows: Figure 4 As shown. Specifically: 1) Positioning: First, use X-ray imaging equipment to scan the device from multiple angles to obtain the chip, inner solder joints, bonding wire direction and the position of the outer solder joints of the lead frame, providing coordinate reference for subsequent laser and plasma processing.

[0041] 2) Laser pretreatment: A short-pulse solid-state laser with a wavelength of 355 nm was selected. First, a high-frequency, fast scanning mode of 50 kHz was used to remove the large volume of epoxy molding compound on the surface of the device in layers. Since the molding compound layer of the device is relatively thick, after the bonding wires are gradually exposed, the frequency was switched to 10 kHz and the scanning speed was reduced to perform fine material removal until the outline of the bonding wire solder balls is completely clear.

[0042] 3) Outer area etching: Adjust the laser irradiation area according to the X-ray positioning results, and perform laser etching on the outer edge of the chip and around the lead frame to expose the two solder joints.

[0043] 4) Reactive plasma etching (first stage): O2 / CF4 mixed gas is used in a ratio of 10:3; O2 flow rate is 100 sccm, CF4 flow rate is 30 sccm; the etching time is adjusted according to the thickness of the residual molding layer and the surface morphology, which is about 35 min in this embodiment to quickly remove the residual molding material.

[0044] 5) Inspection: After etching, pause the removal of the device and use an optical microscope to inspect the exposure of the internal bonding wire pads.

[0045] 6) Reactive plasma etching (second stage): After the pads have been basically exposed, adjust the etching gas ratio to O2:CF4:Ar = 10:1:5 and perform residual etching for 5 minutes to fully expose the bonding wires on the chip surface.

[0046] 7) Cleaning and drying: After etching, place the device in a beaker, add isopropanol and stir to rinse away the residual ashing, then blow dry the device surface with nitrogen micro-nozzle at low pressure.

[0047] 8) Subsequent testing: Within 24 hours of unpacking, the device's electrical performance and bonding wire reliability were tested. Verification showed that the surface of the copper bonding wires inside the SOT-23 device had no obvious corrosion or mechanical damage, meeting the requirements for non-destructive unpacking.

[0048] This invention utilizes a synergistic method of laser pretreatment and low-energy plasma etching to achieve efficient removal of coatings from molded copper bonding wires.

[0049] Laser etching principle: Short-wavelength, short-pulse lasers apply instantaneous high peak energy to the polymer surface, causing photochemical breakage of the molecular chains. This is accompanied by instantaneous vaporization and thermal decomposition effects, rapidly removing large volumes of molding compound and forming grooves in the treated area. Due to the extremely short pulse duration, heat diffusion within the material is limited, effectively reducing thermal damage to the underlying copper bonding wires and the chip, achieving efficient and controllable fine encapsulation removal.

[0050] Plasma etching and gas selection principle: Molding compounds are mainly composed of organic epoxy resin (approximately 10–30 wt%) and a large amount of silica filler (approximately 70–90 wt%). In low-bias, low-energy plasma, oxygen free radicals generated by O2 discharge preferentially oxidize and decompose the organic epoxy chains, breaking down the polymer into volatile small molecules (such as CO2 and H2O). Therefore, O2 is the main active agent for removing the organic matrix. However, using O2 etching alone can form a silicon-rich residue or filler agglomerates on the surface, hindering subsequent removal. After adding CF4, the fluorine free radicals generated can react with SiO2 to generate volatile fluorine-containing products (such as SiF4) or break down the filler structure. Combined with intermittent purging processes, efficient and controllable removal of molding compounds can be achieved, while ensuring that the underlying copper bonding wires and chips are not damaged.

[0051] This method is primarily applicable to SiP advanced packaged devices using epoxy molding, especially those using copper bonding wires or copper-plated wires. Applicable package types include QFP, BGA, TSOP, SOP, DFN, and power-PEM. This method can be widely used for rapid, low-damage decapsulation before failure analysis, effectively exposing the internal structure and ensuring the accuracy of the analysis results. Furthermore, in reverse engineering or chip surface characterization, this method enables non-destructive exposure while preserving as much chip and metal structure information as possible, meeting the high requirements for observing the internal structure and surface features of devices.

[0052] In practical applications, attention should be paid to the differences in the composition and structure of molding compounds. Epoxy molding encapsulation materials are mainly composed of a small amount of epoxy resin and a high proportion of silica filler. When the filler content is high, the dry etching rate may decrease significantly. It may be necessary to briefly add fluorine-containing gas during the etching process to etch the filler agglomerates, and combine this with physical purging to ensure the coating removal effect.

[0053] For bonding wires containing silver, nickel, or other special alloys, the chemical compatibility of the plasma process with the metal should be assessed in advance to avoid surface oxidation or fluorination caused by reactive oxygen species or fluorine radicals. If necessary, irreversible damage to the bonding wires can be prevented by adjusting the gas ratio and etching energy, or by taking protective / shielding measures.

[0054] This invention proposes a non-destructive unpacking method for copper bonding wires in molded devices, based on a combination of laser pretreatment and reactive plasma etching. This method achieves efficient and non-destructive removal of molding compound from copper bonding wires in advanced packaging devices. Short-wavelength, short-pulse lasers can rapidly remove large volumes of molding compound and form a controllable thin layer. Subsequently, plasma etching effectively removes residual molding compound while preserving the surface morphology and interface features of the bonding wires to the greatest extent possible.

[0055] Compared with existing chemical etching or electrolytic methods, this method avoids strong acid corrosion and high-temperature treatment, reducing the risk of chemical and mechanical damage to the copper bonding wires. The process is simple, safe, and readily applicable. Example verification shows that this method can quickly expose internal solder joints and bonding wires while maintaining the integrity of the chip and metal structure, providing reliable data for failure analysis, mechanical testing, and reverse engineering.

[0056] In summary, this invention provides an efficient, controllable, and repeatable non-destructive method for opening copper bonding wires, which has significant technological innovation and application promotion value.

[0057] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for non-destructive unpackaging of copper wirebonds of advanced package plastic encapsulated devices, characterized in that, The method comprises the following steps: Step 1, positioning: positioning the chip bonding area; Step 2, laser pretreatment: after positioning, fast laser rough etching until the soldering ball is exposed; Step 3, after the soldering ball is exposed, the reverse selection of the chip outer area is etched until the second soldering point is exposed; Step 4, gas ratio 1 is used for reactive plasma first-stage etching; Step 5, after the first-stage plasma etching, the device is taken out for inspection, if the chip pad is not exposed, step 4 is repeated, otherwise, step 6 is entered; Step 6, gas ratio 2 is used for reactive plasma second-stage etching; Step 7, cleaning and drying; Step 8, subsequent bonding detection and analysis.

2. The method of claim 1, wherein, The step 1 comprises: using an X-ray imaging device to accurately position the positions of the chip body, the inner soldering point, the bonding wire direction and the outer soldering point of the lead frame.

3. The method of claim 1, wherein, The step 2 comprises: the laser pretreatment adopts a short-wavelength laser to remove the device surface plastic sealing material layer by layer, first, a high-frequency laser with a frequency higher than 50 kHz is used to quickly remove the large-volume plastic sealing material on the device surface, when the bonding wire is gradually exposed, the scanning speed is slowed down to 10 kHz and the low-frequency laser is used until the bonding wire soldering ball is completely exposed, so that the damage of the chip surface caused by the too strong laser etching is avoided.

4. The method of claim 1, wherein, The step 4 comprises: using O2 and CF4 mixed gas for etching, wherein the gas ratio of O2 to CF4 is 10:3, the oxygen flow is 100 sccm, the CF4 flow is 30 sccm, and the etching time is adjusted according to the residual thickness and surface topography of the plastic sealing material, so as to realize the efficient removal of the plastic sealing material.

5. The method of claim 1, wherein, The step 6 comprises: if the pad is exposed, the gas ratio of the reactive ion etching machine is adjusted, Ar gas is added, and the ratio of O2, CF4 and Ar is 10:1:5; after short etching, the chip surface bonding wire is completely exposed.

6. The method of claim 1, wherein, The step 7 comprises: after the reactive plasma etching is completed, isopropyl alcohol (IPA) or acetone is used for stirring and flushing of the residual ashed plastic sealing material, ultrasonic cleaning is avoided, and then nitrogen is used to blow dry the device surface through a micro nozzle.

7. The method of claim 1, wherein, The step 8 comprises: after the opening is completed, the device is detected for electrical performance and bonding wire reliability within 24 hours; It is verified that the surface of the internal copper bonding wire of the device has no obvious corrosion or mechanical damage, and meets the lossless opening requirement.

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