Packaging method for improving yield of packaging substrate

Abstract

The invention provides a packaging method for improving the yield of a packaging substrate. The packaging method comprises the following steps: S1, removing a solder mask layer covering the surface of a golden finger of a substrate by adopting a laser ablation method; s2, the substrate is cleaned, and the cleaned substrate is dried; and S3, packaging the substrate. According to the invention, the solder mask layer covering the golden finger is ablated by using laser, so that the golden finger is exposed, and the yield of the packaging substrate is improved. According to the method, the windowing area of the solder mask does not need to be increased, the exposed copper sheet area cannot be increased, and compared with an existing method, the yield of the packaging substrate can be improved on the premise that the reliability of the packaging substrate is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor integrated circuit packaging and testing, and relates to a packaging method for improving the yield of a packaging substrate. Background Art

[0002] The surface of the package substrate is coated with a solder mask, which can effectively prevent the copper layer from oxidizing and reduce the probability of delamination between the plastic packaging material and the substrate during packaging. However, during the substrate manufacturing process, the solder mask often shifts and covers the gold finger area, resulting in a reduction in the gold finger area, making it difficult to bond during packaging, resulting in the scrapping of the substrate and a reduction in yield.

[0003] At present, the method to solve this problem in the industry is to increase the window area of ​​the solder mask layer during the substrate design stage to maintain a sufficient distance between the gold finger and the solder mask layer. Even if the solder mask layer is severely offset, the solder mask layer will not cover the gold finger area.

[0004] The above method can effectively prevent the solder mask from covering the gold fingers, but the solder mask can prevent the copper layer from oxidizing in contact with the air. After increasing the opening of the solder mask, the exposed copper area will increase, the copper will be easily oxidized, and the reliability of the package substrate will be reduced. Summary of the invention

[0005] In order to solve the above-mentioned problems of the prior art, the present invention provides a packaging method for improving the yield of a packaging substrate, which can effectively eliminate the solder mask layer covering the gold finger, thereby improving the yield of the packaging substrate and providing a new solution for opening windows on the packaging substrate.

[0006] The present invention is achieved through the following technical solutions: A packaging method for improving the yield of a packaging substrate comprises the following steps: S1, removing the solder resist layer covering the surface of the gold finger of the substrate by laser ablation; S2, cleaning the substrate and drying the cleaned substrate; S3, packaging the substrate.

[0007] Preferably, S1 specifically includes: Measure the size of the area of ​​the substrate's gold finger covered by the solder mask; A marking pattern is drawn on a laser marking machine according to the area size, and the laser marking machine laser ablates the solder resist layer covering the surface of the gold finger of the substrate according to the marking pattern.

[0008] Furthermore, the size of the area of ​​the gold finger of the substrate covered by the solder mask layer is measured under a microscope.

[0009] Preferably, in S1, when the thickness of the solder resist layer is 15-30 μm, the laser density used in laser ablation is 0.040-0.050.

[0010] Preferably, in S1, the laser power used for laser ablation is 33.36%-42.76%.

[0011] Preferably, in S1, the laser frequency used for laser ablation is 200 KHz.

[0012] Preferably, in S1, the processing speed is 400-500 mm / s.

[0013] Preferably, in S2, a plasma cleaning machine is used to clean the substrate.

[0014] Preferably, S2 further includes: measuring the cleaning effect of the surface of the cleaned substrate using a water drop angle tester until the cleaning effect meets the requirements, and then drying the cleaned substrate.

[0015] Preferably, S3 specifically includes: mounting the chip on the substrate, bonding the gold finger to the chip, and plastic-sealing the substrate to obtain a packaged substrate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a packaging method for improving the yield of a packaging substrate, using a laser to ablate the solder mask layer covering the gold finger to expose the gold finger, thereby improving the yield of the packaging substrate. The method does not need to increase the window area of ​​the solder mask layer, and does not increase the exposed copper area. Compared with the existing method, the yield of the packaging substrate can be improved while ensuring the reliability of the packaging substrate.

[0017] Furthermore, the present invention first measures the size of the area of ​​the gold finger of the substrate covered by the solder resist layer; according to the area size, the solder resist layer covering the surface of the gold finger of the substrate can be accurately laser ablated.

[0018] Furthermore, the present invention optimizes a suitable laser density according to the thickness of the solder resist layer, which can ensure that the solder resist layer is completely ablated without affecting the copper layer below the solder resist layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 Schematic diagram of a substrate with no solder mask shift.

[0021] Figure 2Schematic diagram of a substrate with solder mask offset.

[0022] Figure 3 This is a schematic diagram of the substrate after the solder mask is ablated using a laser marking machine.

[0023] Figure 4 Schematic diagram of high-density laser energy of laser marking machine.

[0024] Figure 5 Schematic diagram of low-density laser energy for laser marking machine.

[0025] Figure 6 This is a picture of the gold finger after the solder mask layer is ablated in Example 1.

[0026] Figure 7 This is a picture of the product after plastic packaging of Example 1. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0029] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0030] Figure 1 This is a schematic diagram of a substrate with no solder mask shift. The yellow area in the figure is the gold finger, which is used for wire bonding. The white area is not covered with copper and is a reserved safety distance. The green area is the solder mask. In this figure, the solder mask has not shifted and does not cover the gold finger.

[0031] Figure 2The schematic diagram of the substrate with solder mask shifted. The yellow area in the figure is the gold finger, which is used for wire bonding. The white area is not covered with copper and is a reserved safety distance. The green area is the solder mask. In this figure, the solder mask shifted to the right, causing part of the gold finger area to be covered, making it difficult to perform wire bonding during packaging.

[0032] Considering that the main component of the solder resist layer is resin, the packaging method of the present invention for improving the yield of the packaging substrate mainly uses a laser marking machine to burn off the solder resist layer covering the gold finger to expose the gold finger, and then uses a plasma cleaning machine to clean off the burnt residue, and then performs the wire bonding and plastic sealing processes.

[0033] Figure 3 This is a schematic diagram of the substrate after the solder mask is ablated using a laser marking machine. The solder mask covering the gold finger is ablated using a laser marking machine to expose the gold finger so that wire bonding can be performed during packaging.

[0034] Specifically, the technical concept of the present invention is embodied in the following aspects: (1) The ablation spot diameter of the laser marking machine is only 7-12μm, which can achieve precise ablation, and the ablation area can be flexibly selected according to the actual situation. The method proposed by the present invention first uses a measuring microscope to observe and measure the size of the solder mask layer covering the gold finger area, and then adjusts the solder mask layer area to be ablated by the laser marking machine according to the data, and then uses the laser marking machine to accurately ablate the solder mask layer on the gold finger in a small range without affecting the solder mask layer in other areas, which is better than the current existing technology.

[0035] (2) The thickness of the solder mask layer varies from 15 to 30 μm. The thickness of the solder mask layer should be fully considered when adjusting the parameters of the laser marking machine. When the laser density is too high, the solder mask layer will be burned, and the copper layer under the solder mask layer will also appear uneven, making it difficult to perform wire bonding; when the laser density is too low, the copper layer is difficult to ablate. The preferred laser density is 0.040-0.050.

[0036] Figure 4 This is a schematic diagram of high-density laser energy for laser marking machines. Figure 5 This is a schematic diagram of low-density laser energy for laser marking machines. Set the laser density according to the thickness of the solder mask. When the solder mask thickness is above 30μm, the laser density should be increased. When the solder mask thickness is below 20μm, reduce the laser density to avoid ablation of the copper layer under the solder mask.

[0037] (3) The particles generated after ablating the solder mask may cover the gold fingers, which may cause unqualified ball pushing and wire pulling during wire bonding. To avoid this risk, after ablating the solder mask, a plasma cleaner should be used to clean the substrate surface to remove the particles, and then a water drop angle tester should be used to measure the cleanliness of the substrate surface.

[0038] Based on the above concept, the packaging method for improving the yield of the packaging substrate according to the present invention comprises the following steps: S1, removing the solder resist layer covering the surface of the gold finger of the substrate by laser ablation; S2, cleaning the substrate; S3, packaging the substrate.

[0039] In order to accurately remove the solder mask layer covering the surface of the gold finger of the substrate, specifically, the present invention S1 includes: Measure the size of the area of ​​the substrate's gold finger covered by the solder mask under a microscope; A marking pattern is drawn on a laser marking machine according to the area size, and a solder resist layer covering the surface of the gold finger of the substrate is laser ablated according to the marking pattern.

[0040] The particles generated after ablating the solder mask layer may cover the gold finger, so it needs to be cleaned. In S2 of the present invention, a plasma cleaning machine is preferably used to clean the surface of the substrate to remove the particles.

[0041] The cleaned substrate is dried and then the conventional packaging process can be carried out, including: The chip is mounted on the substrate, the gold finger is bonded to the chip, and the substrate is plastic-sealed to obtain a packaged substrate.

[0042] Embodiment 1: This embodiment will improve the yield of a substrate with a solder mask thickness of 25 μm, a gold finger size of 80×180 μm, and a solder mask offset of 30 μm, and package the ablated substrate. The specific steps are as follows: Step 1: Measure the area of ​​the gold finger covered by the solder mask layer under a microscope, and the size of the covered area is measured to be 20×30μm.

[0043] Step 2: Draw a 20×30μm rectangle on the laser marking machine, and adjust the laser parameters to: filling density is 0.040, laser power is 33.36%, laser frequency is 200KHz, processing speed is 500mm / s, and use laser to ablate the solder mask layer with a thickness of 25μm and a size of 20×30μm covering the gold finger.

[0044] Step 3: Use a plasma cleaner to clean the substrate to remove the ablated materials on the surface of the substrate, and then use a water drop angle tester to measure the cleaning effect of the substrate surface until the cleaning effect meets the requirements.

[0045] Step 4: Use an oven to bake the laser ablated substrate at 125°C for 2 h.

[0046] Step 5: Use a thinner to thin the 12-inch wafer with an initial thickness of 750μm and a chip size of 4.6mm×4.6mm to 120μm.

[0047] Step 6: Use a dicing machine to dice the 12-inch wafer to obtain 4.6 mm × 4.6 mm chips.

[0048] Step 7: Use a die bonding machine to squeeze S220 conductive adhesive onto the substrate, and then mount the 4.6mm×4.6mm chip on the substrate.

[0049] Step 8: Use an oven to bake the conductive adhesive at 175°C for 90 minutes to cure the conductive adhesive.

[0050] Step 9: Use a bonding machine to bond a 20μm diameter gold wire to the ablated gold finger and the chip pad to interconnect the gold finger and chip signals.

[0051] Step 10: Use a plastic encapsulation system with a Mold Cap of 0.7 mm to encapsulate the substrate.

[0052] The gold finger picture after the solder mask layer is ablated in this embodiment is as follows Figure 6 As shown, the product picture after plastic sealing is as follows Figure 7 It can be seen that the present invention solves the problem of the solder mask covering the gold finger, and the rationality of the method is verified during use, achieving the purpose of improving the yield rate of the packaging substrate.

[0053] Embodiment 2: This embodiment will improve the yield of a substrate with a solder mask thickness of 35 μm, a gold finger size of 70×150 μm, and a solder mask offset of 25 μm, and package the ablated substrate. The specific steps are as follows: Step 1: Measure the area of ​​the gold finger covered by the solder mask layer under a microscope, and the size of the covered area is measured to be 25×25μm.

[0054] Step 2: Draw a 25×25μm rectangle on the laser marking machine, and adjust the laser parameters to: filling density 0.050, laser power 42.76%, laser frequency 200KHz, processing speed 400mm / s, and use laser to ablate the solder mask with a thickness of 35μm and a size of 25×25μm covering the gold finger.

[0055] Step 3: Use a plasma cleaner to clean the substrate to remove the ablated materials on the surface of the substrate, and then use a water drop angle tester to measure the cleaning effect of the substrate surface until the cleaning effect meets the requirements.

[0056] Step 4: Use an oven to bake the laser ablated substrate at 125°C for 2 h.

[0057] Step 5: Use a thinner to thin the 12-inch wafer with an initial thickness of 670 μm and a chip size of 8.76 mm × 9.70 mm to 250 μm.

[0058] Step 6: Use a dicing machine to dice the 12-inch wafer to obtain 4.6 mm × 4.6 mm chips.

[0059] Step 7: Use a die bonding machine to squeeze S220 conductive adhesive onto the substrate, and then mount the 4.6mm×4.6mm chip on the substrate.

[0060] Step 8: Use an oven to bake the conductive adhesive at 175°C for 90 minutes to cure the conductive adhesive.

[0061] Step 9: Use a bonding machine to bond gold wires with a diameter of 18 μm to the ablated gold fingers and chip pads to interconnect the gold fingers and chip signals.

[0062] Step 10: Use a plastic encapsulation system with a Mold Cap of 0.75 mm to encapsulate the substrate.

[0063] This embodiment solves the problem of the solder mask covering the gold finger, verifies the rationality of the method, and achieves the purpose of improving the yield rate of the substrate.

[0064] Embodiment 3: This embodiment will improve the yield of a substrate with a solder mask thickness of 15 μm, a gold finger size of 70×150 μm, and a solder mask offset of 20 μm, and package the ablated substrate. The specific steps are as follows: Step 1: Measure the area of ​​the gold finger covered by the solder mask layer under a microscope, and the size of the covered area is measured to be 20×20μm.

[0065] Step 2: Draw a 20×20μm rectangle on the laser marking machine, and adjust the laser parameters to: filling density of 0.025, laser power of 27.64%, laser frequency of 200KHz, processing speed of 150mm / s, and use laser to ablate the solder mask layer with a thickness of 15μm and a size of 20×20μm covering the gold finger.

[0066] Step 3: Use a plasma cleaner to clean the substrate to remove the ablated materials on the surface of the substrate, and then use a water drop angle tester to measure the cleaning effect of the substrate surface until the cleaning effect meets the requirements.

[0067] Step 4: Use an oven to bake the laser ablated substrate at 125°C for 2 h.

[0068] Step 5: Use a thinner to thin the 12-inch wafer with an initial thickness of 889 μm and a chip size of 9.12 mm × 5.98 mm to 150 μm.

[0069] Step 6: Use a dicing machine to dice the 12-inch wafer to obtain 9.12mm×5.98mm chips.

[0070] Step 7: Use a die bonding machine to squeeze S220 conductive adhesive onto the substrate, and then mount the 9.12mm×5.98mm chip on the substrate.

[0071] Step 8: Use an oven to bake the conductive adhesive at 175°C for 90 minutes to cure the conductive adhesive.

[0072] Step 9: Use a bonding machine to bond a 20μm diameter gold wire to the ablated gold finger and the chip pad to interconnect the gold finger and chip signals.

[0073] Step 10: Use a plastic encapsulation system with a Mold Cap of 0.85 mm to encapsulate the substrate.

[0074] This embodiment solves the problem of the solder mask covering the gold finger, verifies the rationality of the method, and achieves the purpose of improving the yield rate of the substrate.

Claims

1. A packaging method for improving the yield of a packaging substrate, characterized in that: The steps include: S1, removing the solder resist layer covering the surface of the gold finger of the substrate by laser ablation; S2, cleaning the substrate and drying the cleaned substrate; S3, packaging the substrate.

2. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: S1 specifically includes: Measure the size of the area of ​​the substrate's gold finger covered by the solder mask; A marking pattern is drawn on a laser marking machine according to the area size, and the laser marking machine laser ablates the solder resist layer covering the surface of the gold finger of the substrate according to the marking pattern.

3. The packaging method for improving the yield of packaging substrate according to claim 2, characterized in that: Measure the size of the area of ​​the substrate's gold finger covered by the solder mask under a microscope.

4. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: In S1, when the thickness of the solder mask layer is 15-30 μm, the laser density used for laser ablation is 0.040-0.

050.

5. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: In S1, the laser power used for laser ablation was 33.36%-42.76%.

6. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: In S1, the laser frequency used for laser ablation is 200 KHz.

7. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: In S1, the processing speed is 400-500 mm / s.

8. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: In S2, a plasma cleaning machine is used to clean the substrate.

9. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: S2 also includes: using a water drop angle tester to measure the cleaning effect of the surface of the cleaned substrate until the cleaning effect meets the requirements, and then drying the cleaned substrate.

10. The packaging method for improving the yield of packaging substrate according to claim 1, characterized in that: S3 specifically includes: mounting the chip on the substrate, bonding the gold finger to the chip, and plastic-sealing the substrate to obtain a packaged substrate.

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