Chip opening method and clamp for double-sided heat dissipation device with transfer molding and encapsulation

Abstract

The application relates to the technical field of semiconductor structure failure analysis, and discloses a chip opening method and clamp for a double-sided heat dissipation device with transfer molding and encapsulation, which comprises the following steps: adopting plane grinding on an upper lining plate until epoxy molding compound in the double-sided heat dissipation device with transfer molding and encapsulation appears; removing the epoxy molding compound in the double-sided heat dissipation device with transfer molding and encapsulation by adopting a laser etching gasification principle until bonding leads in the double-sided heat dissipation device with transfer molding and encapsulation appear; adopting a first mixed acid solution to perform chemical wet etching on the double-sided heat dissipation device with transfer molding and encapsulation until the bonding leads in the double-sided heat dissipation device with transfer molding and encapsulation are completely exposed; heating and remelting solder between a chip and a pad block, and removing the pad block; adopting a second mixed acid solution to perform chemical wet etching on the double-sided heat dissipation device with the removed pad block until the chip completely appears. The chip of the double-sided heat dissipation device with transfer molding and encapsulation is nondestructively opened, so that subsequent chip-level microscopic analysis is facilitated.

Description

Technical Field

[0001] This invention relates to the field of semiconductor structure failure analysis technology, and in particular to a chip unpacking method and fixture for a double-sided heat dissipation device using a transfer molding process. Background Technology

[0002] The double-sided heat dissipation device encapsulated by transfer molding forms the device shell through transfer molding. Its encapsulation structure mainly includes an upper substrate, a lower substrate, a chip, pads, a lead frame, and bonding wires. The lower surface of the chip is soldered to the lower substrate, and the upper surface is soldered to the upper substrate via pads. The circuit layout of the upper and lower substrates helps form the module circuit. The lead frame is soldered to the lower substrate to bring out the internal circuitry of the module. The upper and lower substrates consist of an insulating layer, a copper-clad layer, and a solder mask layer. The copper-clad layer on the front side has a circuit pattern, and the chips in the double-sided heat dissipation device are interconnected through this circuit pattern. The encapsulation material is primarily epoxy molding compound. Epoxy molding compound uses epoxy resin as the base resin, phenolic resin as the curing agent, and adds fillers such as fillers, flame retardants, colorants, coupling agents, and other trace components. Under the action of heat and the curing agent, the epoxy groups of the epoxy resin undergo ring-opening and chemical reaction with the phenolic resin, producing cross-linking curing and making it a thermosetting plastic. The type of epoxy resin and its proportion directly affect the flow characteristics, thermal properties, and electrical properties of epoxy molding compounds.

[0003] In current related technologies, the chip unpacking of double-sided heat dissipation devices using transfer molding is carried out by mixed acid heating. First, the transfer molding resin around the device is removed. Based on the high-frequency excitation in the vacuum, chemically active particles are generated and react with the molding material to produce volatile substances. Then, the solder of the substrate is melted by heating, and the upper substrate is removed with appropriate tools. After the epoxy resin inside the device is exposed, the remaining resin is etched away again using mixed acid.

[0004] However, in the process of implementing the technical solutions in the embodiments of this application, the inventors of this application discovered that the above technical solutions have at least the following technical problems:

[0005] (1) Due to the obstruction of the double-sided liner and the internal pad, the mixed acid cannot directly act on the epoxy resin inside the device, resulting in poor chemical corrosion uniformity and large differences in the degree of reaction at different locations, making it difficult to maintain the integrity of the sample structure.

[0006] (2) Due to the long reaction time, the chip is at risk of breaking;

[0007] (3) During the process of heating and removing the substrate, the solder on the substrate melts and overflows, causing the internal materials of the device to expand due to heat, which leads to chip damage. Summary of the Invention

[0008] The present invention aims to perform efficient and non-destructive unpacking of chips in double-sided heat dissipation devices using transfer molding, ensuring the integrity of the sample structure and the absence of chip damage, thereby improving chip unpacking efficiency and reducing chip unpacking costs.

[0009] The above-mentioned objectives are mainly achieved through the following technical solutions:

[0010] In a first aspect, a method for unpacking a chip of a transfer-molded double-sided heat dissipation device includes:

[0011] First, the upper backing plate is planar ground until the epoxy molding compound inside the double-sided heat sink is exposed, ensuring the flatness of the device. Then, laser etching vaporization is used to remove the epoxy molding compound inside the device until the bonding wires are exposed, preventing acid corrosion of the bonding wires. Next, a first mixed acid solution is used to perform chemical wet etching on the device to remove the epoxy molding compound remaining after laser etching until the bonding wires inside the device are completely exposed. The first mixed acid solution contains fuming nitric acid and concentrated sulfuric acid, effectively improving the success rate of chip unpacking for the double-sided heat sink. Then, the solder between the chip and the pad is heated and remelted, and the pad is removed. Finally, a second mixed acid solution containing methanesulfonic acid and nitric acid is used to perform chemical wet etching on the device after the pad has been removed until the chip is fully exposed. This second mixed acid solution removes residual solder from the chip surface, achieving non-destructive chip unpacking for the double-sided heat sink, facilitating subsequent chip-level microscopic analysis.

[0012] Preferably, a grinding machine is used to perform planar grinding on the upper liner plate. The grinding machine includes a power head. During the grinding process, a diamond suspension is sprayed to lubricate the contact surface between the power head and the upper liner plate. The diamond suspension is embedded in the surface of the polishing cloth, which can effectively reduce deformation and damage to the surface of the device while ensuring accurate removal of the upper liner plate.

[0013] Preferably, a laser beam is used to ablate the device layer by layer according to the packaging structure, carbonizing the epoxy molding compound inside the device to remove the epoxy molding compound. At the same time, the energy and scanning speed of the laser beam are controlled, which can effectively improve the accuracy and reliability of chip unpacking and avoid acid corrosion of bonding wires.

[0014] Preferably, the device after chemical wet etching with the first mixed acid solution is cleaned to reduce impurities adhering to the device surface, fully preserve the internal circuit structure of the device, and prevent the chip from being damaged by stress.

[0015] In a second aspect, a fixture is provided for securing a transfer molded double-sided heat sink device to open the chip of the device using any of the chip opening methods for transfer molded double-sided heat sink devices described in the first aspect.

[0016] The fixture has a slot inside, and the bottom of the slot has several air holes;

[0017] The device is placed in the slot, and the vacuum pump and the air hole are used to adsorb the device into the slot, so as to fix the device.

[0018] This invention addresses the technical problem of chip unpacking via manual clamping due to the thinness of double-sided heat dissipation devices encapsulated in molded plastic packaging. A fixture was designed with a slot size matching the device size, allowing the device to be placed within the slot. A vacuum pump and air vents are then used to adhere the device to the slot, securing it in place. The fixture is then mounted on the power head of a grinding machine to perform chip unpacking, accurately removing the fixed-thickness upper liner from the device surface.

[0019] Compared to the benefits of existing technologies:

[0020] (1) The upper liner of the double-sided heat dissipation device of the molded plastic encapsulation is ground by a grinding machine to accurately control the opening depth. The diamond suspension used for lubrication is embedded in the surface of the polishing cloth to effectively reduce the deformation and damage of the device surface. Then, the device is ablated layer by layer according to the encapsulation structure by a laser beam to carbonize the epoxy molding compound inside the device and remove the epoxy molding compound. Then, chemical wet etching is performed using a mixed acid solution to prevent the chip from being damaged during opening. After opening, the internal circuit structure of the device can be completely preserved.

[0021] (2) The overall unpacking process is based on the packaging structure of the double-sided heat dissipation device in the molded plastic packaging and different packaging materials in each layer. The process involves sequentially using planar grinding, laser etching, and acid reaction to achieve the unpacking effect layer by layer. This avoids damage to the integrity of the device caused by destructive physical analysis methods, effectively reduces the risk of stress damage to the chip during the unpacking process, and ensures the chip is undamaged.

[0022] (3) After the plane grinding and laser etching are applied in sequence, the acid reaction is then applied. No longer restricted by the double-sided backing plate and the internal pad, the mixed acid solution can directly act on the epoxy resin inside the device. Therefore, the chemical corrosion uniformity is good and the reaction degree of different positions is small, which is conducive to ensuring the integrity of the internal structure of the sample device. Attached Figure Description

[0023] Figure 1 A schematic flowchart of a chip unpacking method for a double-sided heat dissipation device using a transfer molding process according to the present invention is shown.

[0024] Figure 2 A schematic diagram of the structure of a clamp according to the present invention is shown. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0026] Example 1

[0027] This invention provides a chip unpacking method for a double-sided heat dissipation device encapsulated by a transfer molding process, such as... Figure 1 As shown, it includes the following steps:

[0028] Step 1: Grind the upper liner plate with a flat surface until the epoxy molding compound inside the double-sided heat dissipation device is visible.

[0029] A grinding machine is used to grind the upper liner plate. The grinding machine includes a power head. During the grinding process, a diamond suspension is sprayed to lubricate the contact surface between the power head and the upper liner plate. The diamond suspension is embedded in the surface of the polishing cloth, which can effectively reduce deformation and damage to the surface of the device while ensuring accurate removal of the upper liner plate.

[0030] Because the double-sided heat sink in a transfer molded package is relatively thin, it is impossible to perform DCB (Direct Bonding Copper) grinding for thinning by manual clamping. Therefore, a fixture is designed to fix the double-sided heat sink in the transfer molded package. Figure 2 The fixture 200 has a slot 210 inside, and the bottom of the slot 210 has several air holes 220. The size of the slot 210 is consistent with the size of the device. The device can be placed in the slot 210, and the device can be attracted into the slot by the vacuum pump and the air holes 220 to fix the device. Then the fixture is installed on the power head of the grinding machine to perform chip unpacking operation; and the upper liner plate of fixed thickness on the surface of the device can be accurately removed.

[0031] It should be noted that the opening depth can be precisely controlled during the grinding process of the upper liner plate. The specific implementation method is as follows:

[0032] A diamond grinding disc with a particle size of 3–30 μm is used. The speed of the chassis of the precision grinding machine is adjusted to 100–300 r / min, the rotation speed of the power head of the grinding machine is adjusted to 10–300 r / min, and the grinding pressure is adjusted to 0.1–20 MPa.

[0033] A diamond suspension with a particle size of 3–30 μm is used for lubrication. During the grinding process, the diamond abrasive particles pass over the sample surface with high stress, and the material is removed in the form of abrasive debris. The sprayed diamond suspension is embedded in the surface of the polishing cloth. While ensuring accurate removal of the DBC (i.e., the upper liner) of a fixed thickness, it can effectively reduce the deformation and damage to the surface of the device as a sample.

[0034] By using planar grinding, the epoxy molding compound inside the sample is exposed, effectively ensuring the flatness of the sample. Alternatively, by controlling the parameters of the grinding machine and calculating the grinding time based on the set parameters and the thickness of the DCB on the sample surface, the grinding machine can be automatically controlled to continuously grind the DCB on the sample surface for the specified time, thus achieving complete exposure of the epoxy molding compound inside the device through planar grinding of the upper liner plate.

[0035] Throughout the entire process of planar grinding, the sample device surface is subjected to uniform force and is not subjected to additional stress damage, thus maximizing the flatness of the device surface and achieving edge protection.

[0036] Step 2: The epoxy molding compound inside the device is removed using the principle of laser etching vaporization until the bonding wires inside the device are exposed.

[0037] The specific implementation method may be as follows:

[0038] After step 1, a laser beam is used to ablate the device layer by layer according to the packaging structure, carbonizing the epoxy molding compound inside the device into fine particles, thereby removing the epoxy molding compound. The ablation process is monitored in real time until the bonding wires inside the device are completely exposed, accurately removing a fixed thickness of the epoxy molding compound inside the device.

[0039] It should be noted that during the laser etching process, the energy and scanning speed of the laser beam can be controlled. For example, the laser power can be set to 3-20W, the scanning speed to 100-1000mm / s, and the laser pulse width to 50-300ns.

[0040] It can effectively improve the accuracy and reliability of chip unpacking and avoid acid corrosion of bonding wires.

[0041] Step 3: Use the first mixed acid solution to perform chemical wet etching on the device to remove the epoxy molding compound remaining after laser etching until the bonding wires inside the device are completely exposed.

[0042] The specific implementation method may be as follows:

[0043] The device processed in step 2 is subjected to chemical wet etching using the first mixed acid solution to remove the epoxy molding compound remaining after laser etching.

[0044] For example, a first mixed acid solution consisting of 98% fuming nitric acid and 98% concentrated sulfuric acid is used, and the first mixed acid solution is heated to 150°C.

[0045] The residual epoxy molding compound after laser etching is removed using a heated first mixed acid solution until the bonding wires inside the device are completely exposed. This effectively improves the success rate of chip unpacking for double-sided heat dissipation devices encapsulated in transfer molding, facilitating subsequent chip-level microscopic analysis.

[0046] Step 4: Clean the device after the treatment in Step 3.

[0047] The device after the acid reaction is cleaned to reduce impurities adhering to the device surface, thus preserving the internal circuit structure of the device intact, while the chip is not subjected to stress damage.

[0048] Step 5: Heat and remelt the solder between the chip and the pad, and then remove the pad.

[0049] A specific implementation method may be: heating the temperature to 250°C to remelt the solder between the chip and the pad, and then removing the pad.

[0050] Step 6: Use a second mixed acid solution to perform chemical wet etching on the device after the pad has been removed until the chip is fully exposed.

[0051] The specific implementation method may be as follows:

[0052] For example, a second mixed acid solution composed of methanesulfonic acid and 65% nitric acid is heated to 150°C. This heated solution is then used to perform a chemical wet etching process on the device treated in step 5 until no solder residue remains on the chip surface. Alternatively, the heated second mixed acid solution can be used to perform a chemical wet etching process on the device treated in step 5 for 10 minutes. This removes residual solder from the chip surface, enabling non-destructive unpacking of the transfer-molded double-sided heat dissipation device, facilitating subsequent chip-level microscopic analysis.

[0053] Compared to the benefits of existing technologies:

[0054] (1) The upper liner of the double-sided heat dissipation device of the molded plastic encapsulation is ground by a grinding machine to accurately control the opening depth. The diamond suspension used for lubrication is embedded in the surface of the polishing cloth to effectively reduce the deformation and damage of the device surface. Then, the device is ablated layer by layer according to the encapsulation structure by a laser beam to carbonize the epoxy molding compound inside the device and remove the epoxy molding compound. Then, chemical wet etching is performed using a mixed acid solution to prevent the chip from being damaged during opening. After opening, the internal circuit structure of the device can be completely preserved.

[0055] (2) The overall unpacking process is based on the packaging structure of the double-sided heat dissipation device in the molded plastic packaging and different packaging materials in each layer. The process involves sequentially using planar grinding, laser etching, and acid reaction to achieve the unpacking effect layer by layer. This avoids damage to the integrity of the device caused by destructive physical analysis methods, effectively reduces the risk of stress damage to the chip during the unpacking process, and ensures the chip is undamaged.

[0056] (3) After the plane grinding and laser etching are applied in sequence, the acid reaction is then applied. No longer restricted by the double-sided backing plate and the internal pad, the mixed acid solution can directly act on the epoxy resin inside the device. Therefore, the chemical corrosion uniformity is good and the reaction degree of different positions is small, which is conducive to ensuring the integrity of the internal structure of the sample device.

[0057] In summary, the chip unpacking method for a double-sided heat dissipation device using a transfer molding process provided by this invention is reliable, easy to implement, and low in cost. It ensures uniform stress on the sample device surface and prevents chip damage during the unpacking process, while also greatly improving unpacking efficiency.

[0058] Example 2

[0059] like Figure 2 As shown, this invention provides a clamp 200 with a slot 210 inside. The bottom of the slot 210 has several air holes 220. The size of the slot 210 is consistent with the size of the device. The device can be placed in the slot 210, and a vacuum pump and the air holes 220 are used to adhere the device to the slot, thus fixing the device. Then, the clamp is mounted on the power head of a grinding machine for chip unpacking. This accurately removes the upper liner of a fixed thickness from the device surface. This solves the technical problem that double-sided heat dissipation devices encapsulated by mold are too thin to be manually unpacked.

[0060] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for unpacking a chip of a double-sided heat dissipation device using a transfer molding process, characterized in that, include: The upper liner plate is subjected to planar grinding until the epoxy molding compound inside the double-sided heat dissipation device is exposed. The planar grinding of the upper liner plate includes: using a diamond grinding disc and a grinding machine to perform planar grinding on the upper liner plate. The grinding machine includes a power head. During the grinding process, a diamond suspension is sprayed to lubricate the contact surface between the power head and the upper liner plate. The diamond suspension is embedded in the surface of the polishing cloth, ensuring that the removal of the upper liner plate of a fixed thickness is achieved while reducing deformation and damage to the device surface. The grinding time is calculated based on the set parameters of the grinding machine and the thickness of the upper liner plate, and the grinding machine is automatically controlled to continuously perform planar grinding on the upper liner plate for the specified grinding time. The epoxy molding compound inside the device is removed by laser etching vaporization until the bonding wires inside the device are exposed. The device is chemically wet-etched using a first mixed acid solution until the bonding wires inside the device are completely exposed. Heat and remelt the solder between the chip and the pad, then remove the pad; The device with the pad removed was subjected to chemical wet etching using a second mixed acid solution until the chip was fully exposed.

2. The chip unpacking method for a double-sided heat dissipation device using a transfer molding process as described in claim 1, characterized in that, The epoxy molding compound inside the device is removed using the principle of laser etching vaporization, including: The device is ablated layer by layer according to the packaging structure using a laser beam to carbonize the epoxy molding compound inside the device, thereby removing the epoxy molding compound.

3. The chip unpacking method for a double-sided heat dissipation device using a transfer molding process as described in claim 1, characterized in that... The first mixed acid solution contains fuming nitric acid and concentrated sulfuric acid.

4. The chip unpacking method for a double-sided heat dissipation device using a transfer molding process as described in claim 1, characterized in that, Before heating and remelting the solder between the chip and the pad, the process also includes: The device, after being chemically etched using the first mixed acid solution, was cleaned.

5. The chip unpacking method for a double-sided heat dissipation device using a transfer molding process as described in claim 1, characterized in that, The second mixed acid solution contains methanesulfonic acid and nitric acid.

6. A clamp, characterized in that, Used to fix a double-sided heat dissipation device for molding, so as to open the chip of the device using a chip opening method for a double-sided heat dissipation device for molding as described in any one of claims 1 to 5; The fixture has a slot inside, and the bottom of the slot has several air holes; The device is placed in the slot, and the vacuum pump and the air hole are used to adsorb the device into the slot, so as to fix the device.

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