Package substrate laser drilling method and package substrate

Abstract

The embodiment of the invention provides a packaging substrate laser drilling method and a packaging substrate, the packaging substrate comprises a first copper layer, a dielectric layer and a second copper layer which are stacked in sequence, and the method comprises the steps that first drilling operation is carried out with first laser energy, and an annular area is ablated on the first copper layer; second drilling operation is conducted through second laser energy, the copper cover in the middle of the annular area and part of the dielectric layer are removed, a blind hole is formed, and the second laser energy is smaller than the first laser energy; third drilling operation is carried out with third laser energy, the dielectric layer at the bottom of the blind hole is removed until the second copper layer is exposed out of the bottom of the blind hole, and the third laser energy is smaller than the second laser energy. According to the packaging substrate laser drilling method, on the premise that the laser drilling quality requirement is met, the laser drilling machining efficiency can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of packaging substrate processing, and in particular to a packaging substrate laser drilling method and a packaging substrate. Background Art

[0002] Liquid Crystal Polymer (LCP) resin is a high-performance high-frequency circuit substrate material widely used in packaging substrates for 5G communications, millimeter-wave radar, and high-speed data transmission. LCP resin has poor thermal conductivity and is prone to localized overheating. Its low melting point (less than 280°C) allows it to melt and flow easily. Laser drilling of LCP packaging substrates uses a nanosecond laser. The high peak power generates transient high temperatures within the resin, causing it to flow. This can lead to problems such as resin residue at the bottom of the blind vias and poor bonding strength of the solder ring at the bottom of the blind vias.

[0003] Currently, the industry's standard practice is to use low-energy laser drilling multiple times to avoid quality issues caused by instantaneous overheating of LCP resin. However, this processing method reduces laser drilling efficiency. Summary of the Invention

[0004] The embodiments of the present application provide a packaging substrate laser drilling method and a packaging substrate, which can avoid quality problems caused by instantaneous overheating of the dielectric layer of the packaging substrate and can improve the efficiency of laser drilling processing.

[0005] An embodiment of the present application provides a method for laser drilling a package substrate, wherein the package substrate includes a first copper layer, a dielectric layer, and a second copper layer stacked in sequence, and the method includes: performing a first drilling operation with a first laser energy to ablate an annular area on the first copper layer; performing a second drilling operation with a second laser energy to remove the copper cover in the middle of the annular area and a portion of the dielectric layer to form a blind hole, wherein the second laser energy is less than the first laser energy; A third drilling operation is performed with a third laser energy to remove the dielectric layer at the bottom of the blind hole until the second copper layer is exposed at the bottom of the blind hole, wherein the third laser energy is less than the second laser energy.

[0006] In some embodiments, the second copper layer is formed with a pad, and before performing the second drilling operation with the second laser energy, the method further includes: Determine the pad type at the bottom of the blind hole to be processed; The second laser energy and the third laser energy corresponding to the pad type are determined.

[0007] In some embodiments, the pad types include independent pads, non-independent pads, pad combinations, and large copper pads; The independent pad is surrounded by a closed etching area, and the etching area has no circuit connection; The non-independent pad is connected to a circuit extending outward; The pad combination includes a plurality of pads connected in sequence; The copper surface area of ​​the large copper surface pad is greater than k times the area of ​​the blind hole, where k is greater than or equal to 30.

[0008] In some embodiments, the second laser energy corresponding to the independent pad is less than the second laser energy corresponding to the non-independent pad, the second laser energy corresponding to the non-independent pad is less than the second laser energy corresponding to the pad combination, and the second laser energy corresponding to the pad combination is less than the second laser energy corresponding to the large copper surface pad.

[0009] In some embodiments, the third laser energy corresponding to the independent pad is less than the third laser energy corresponding to the non-independent pad, the third laser energy corresponding to the non-independent pad is less than the third laser energy corresponding to the pad combination, and the third laser energy corresponding to the pad combination is less than the third laser energy corresponding to the large copper surface pad.

[0010] In some embodiments, the laser scanning speed of the first drilling operation is lower than the laser scanning speed of the second drilling operation, and the laser scanning speed of the second drilling operation is lower than the laser scanning speed of the third drilling operation.

[0011] In some embodiments, the number of laser ring cuttings in the first drilling operation is less than or equal to the number of laser ring cuttings in the second drilling operation, and the number of laser ring cuttings in the second drilling operation is less than the number of laser ring cuttings in the third drilling operation.

[0012] In some embodiments, the laser frequency of the first drilling operation, the laser frequency of the second drilling operation, and the laser frequency of the third drilling operation are all the same.

[0013] In some embodiments, the dielectric layer is made of liquid crystal polymer resin.

[0014] An embodiment of the present application also provides a packaging substrate, comprising a first copper layer, a dielectric layer, and a second copper layer stacked in sequence, wherein a blind hole is formed on the packaging substrate, wherein the opening of the blind hole is located in the first copper layer, and the bottom of the blind hole exposes the second copper layer, and the blind hole is formed by any of the methods described above.

[0015] In the laser drilling method for a package substrate according to the embodiment of the present application, the high temperature generated by the first drilling operation can be quickly conducted and dissipated by the first copper layer. Therefore, the first drilling operation can use a higher-energy laser pulse to improve the efficiency of the laser drilling process. The high temperature generated by the second and third drilling operations is mainly conducted and dissipated by the second copper layer at the bottom of the blind hole. Since the second copper layer is located inside the package substrate, its heat dissipation performance is not as good as that of the first copper layer. Therefore, a lower-energy laser pulse is used to avoid the resin in the dielectric layer from generating local high temperature and causing rheology. This can avoid quality problems caused by instantaneous overheating of the dielectric layer of the package substrate. Therefore, the laser drilling method for a package substrate according to the embodiment of the present application can improve the efficiency of the laser drilling process while meeting the quality requirements of the laser drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0017] Figure 1 This is a schematic diagram of the first structure of the packaging substrate of an embodiment of the present application.

[0018] Figure 2 This is a schematic diagram of the second structure of the packaging substrate of an embodiment of the present application.

[0019] Figure 3 This is a schematic diagram of a first process of the laser drilling method for a package substrate according to an embodiment of the present application.

[0020] Figure 4 This is a schematic diagram of the packaging substrate structure after the first drilling operation in an embodiment of the present application.

[0021] Figure 5 Schematic diagram of the annular area formed by the first drilling operation in an embodiment of the present application.

[0022] Figure 6 This is a schematic diagram of the packaging substrate structure after the second drilling operation in an embodiment of the present application.

[0023] Figure 7 This is a schematic diagram of the packaging substrate structure after the third drilling operation in an embodiment of the present application.

[0024] Figure 8 This is a second flow chart of the laser drilling method for a package substrate according to an embodiment of the present application.

[0025] Figure 9 Schematic diagram of independent pads of the package substrate according to an embodiment of the present application.

[0026] Figure 10 Schematic diagram of the non-independent pads of the package substrate according to an embodiment of the present application.

[0027] Figure 11 Schematic diagram of the pad combination of the package substrate according to an embodiment of the present application.

[0028] Figure 12 Schematic diagram of the large copper pad of the package substrate of an embodiment of the present application. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making any creative work are within the scope of protection of this application.

[0030] The present application provides a packaging substrate. In some embodiments, the packaging substrate may be a flexible packaging substrate. Figure 1 , Figure 1 This is a schematic diagram of the first structure of the packaging substrate 100 according to an embodiment of the present application.

[0031] Package substrate 100 includes a first copper layer 10, a dielectric layer 20, and a second copper layer 30, stacked in sequence. Dielectric layer 20 is made of resin. In some embodiments, dielectric layer 20 is made of liquid crystal polymer (LCP) resin. In practical applications, LCP resin has poor thermal conductivity and is prone to local overheating. Furthermore, it has a low melting point (less than 280°C), making it easy to melt into a liquid and flow.

[0032] The second copper layer 30 is formed with a plurality of pads 31 . In some embodiments, the first copper layer 10 may not form a circuit pattern, and the second copper layer 30 forms a circuit pattern, which may include the pads 31 .

[0033] Multiple blind vias 40 are formed on the package substrate 100. The openings of the blind vias 40 are located in the first copper layer 10, and the bottoms of the blind vias 40 expose the second copper layer 30. In practical applications, the blind vias 40 can be positioned directly opposite the pads 31. The blind vias 40 can undergo a metallization process such as copper plating to form plated holes, thereby achieving electrical connections between the pads 31 and other layers or electronic components.

[0034] In some embodiments, reference Figure 2 , Figure 2 This is a schematic diagram of a second structure of the packaging substrate 100 according to an embodiment of the present application.

[0035] The first copper layer 10, dielectric layer 20, and second copper layer 30 are sequentially stacked on both sides of the package substrate 100. A core layer 50 is disposed between the two inner second copper layers 30. In some embodiments, the core layer 50 can also be made of liquid crystal polymer (LCP). Blind vias 40 are formed on both sides of the package substrate 100.

[0036] The embodiment of the present application also provides a packaging substrate laser drilling method for forming the above-mentioned blind hole 40 on the packaging substrate 100. Figure 3 , Figure 3 This is a schematic diagram of a first process flow of a package substrate laser drilling method according to an embodiment of the present application. The package substrate laser drilling method includes the following steps: 210 , performing a first drilling operation with a first laser energy to ablate an annular area on the first copper layer; 220, performing a second drilling operation with a second laser energy to remove the copper cover and a portion of the dielectric layer in the middle of the annular area to form a blind hole, wherein the second laser energy is less than the first laser energy; 230 , performing a third drilling operation with a third laser energy to remove the dielectric layer at the bottom of the blind hole until the second copper layer is exposed at the bottom of the blind hole, wherein the third laser energy is less than the second laser energy.

[0037] For reference Figures 4 to 7 , Figure 4 This is a schematic diagram of the packaging substrate structure after the first drilling operation in an embodiment of the present application. Figure 5 This is a schematic diagram of the annular area formed by the first drilling operation in the embodiment of the present application. Figure 6 This is a schematic diagram of the packaging substrate structure after the second drilling operation in an embodiment of the present application. Figure 7 This is a schematic diagram of the packaging substrate structure after the third drilling operation in an embodiment of the present application.

[0038] Wherein, the first drilling operation is first performed with the first laser energy, such as Figure 4 and Figure 5 As shown, a ring-shaped area is ablated on the first copper layer 10. The first copper layer 10 forms a large copper surface, and the ring-shaped area can be called a copper ring. A copper cap is located in the center of the ring-shaped area, and beneath the copper cap is the resin of the dielectric layer 20. During the first drilling operation, the high temperature generated by the laser is quickly conducted and dissipated through the outer large copper surface (first copper layer 10), preventing localized high temperatures within the resin from causing rheological changes.

[0039] Subsequently, a second drilling operation is performed with a second laser energy, such as Figure 6As shown, the copper cap and part of the dielectric layer in the center of the annular area are removed to form a blind via. The second drilling operation removes the copper cap and some of the resin beneath it, but resin remains at the bottom of the blind via. Therefore, the second drilling operation does not burn through the dielectric layer 20. During the second drilling operation, the high temperature generated by the resin in the dielectric layer 20 absorbing the laser light is primarily dissipated through the copper layer at the bottom of the blind via (i.e., the second copper layer 30). The second laser energy is lower than the first laser energy.

[0040] Subsequently, a third drilling operation is performed with a third laser energy, such as Figure 7 As shown, the dielectric layer 20 at the bottom of the blind hole, specifically the residual resin at the bottom of the blind hole, is removed until the second copper layer 30 is exposed at the bottom of the blind hole. This completes the processing of the blind hole 40. During the third drilling operation, the high temperature generated by the resin in the dielectric layer 20 absorbing the laser light is primarily dissipated through the copper layer at the bottom of the blind hole (i.e., the second copper layer 30). The energy of the third laser is lower than that of the second laser.

[0041] As can be understood, the high temperature generated by the first drilling operation can be quickly dissipated by conduction through the large outer copper surface (first copper layer 10). Therefore, higher-energy laser pulses can be used for the first drilling operation to improve laser drilling efficiency. The high temperature generated by the second and third drilling operations is primarily dissipated by conduction through the copper layer at the bottom of the blind via (i.e., second copper layer 30). Because second copper layer 30 is located within the package substrate 100, its heat dissipation performance is inferior to that of first copper layer 10. Therefore, lower-energy laser pulses are required to prevent the resin in dielectric layer 20 from locally overheating and causing rheological changes. This can avoid quality issues caused by transient overheating of dielectric layer 20 of the package substrate.

[0042] Therefore, the package substrate laser drilling method according to the embodiment of the present application can improve the laser drilling processing efficiency while meeting the laser drilling quality requirements.

[0043] In some embodiments, the laser parameters for the first laser drilling can be set as follows: frequency 250 kHz, energy 8-12 uJ, scanning speed 50-150 mm / s, and number of circular cuts 1-2 times. The laser parameters for the second laser drilling can be set as follows: frequency 250 kHz, energy 4-6 uJ, scanning speed 100-200 mm / s, and number of circular cuts 1-2 times. The laser parameters for the third laser drilling can be set as follows: frequency 250 kHz, energy 2-4 uJ, scanning speed 150-250 mm / s, and number of circular cuts 2-3 times. Therefore, the second laser energy is less than the first laser energy, and the third laser energy is less than the second laser energy.

[0044] In some embodiments, reference Figure 8 , Figure 8This is a second flow diagram of the package substrate laser drilling method according to an embodiment of the present application. Prior to step 220, performing the second drilling operation with the second laser energy, the following steps are also included: 241, determining the pad type at the bottom of the blind hole to be processed; 242 , determining the corresponding second laser energy and third laser energy according to the pad type.

[0045] In actual applications, the second copper layer 30 is formed with multiple pads 31. The multiple pads 31 can have different pad types, and different pad types have different pad structures and pad areas. It can be understood that during the second and third drilling operations described above, the high temperature generated by the resin in the dielectric layer 20 absorbing the laser is mainly dissipated by the second copper layer 30 at the bottom of the blind hole 40. Since the bottom of the blind hole 40 is directly opposite the pad 31, the high temperature generated by the resin is mainly dissipated by the pad 31 at the bottom of the blind hole 40. Different types of pads have different heat dissipation efficiencies. For example, the larger the pad area, the faster its heat dissipation efficiency; the smaller the pad area, the slower its heat dissipation efficiency.

[0046] Therefore, before performing the second drilling operation, the type of pad at the bottom of the blind hole 40 to be processed can be determined first, and the corresponding second laser energy and third laser energy can be determined according to the pad type to ensure that when the second drilling operation is performed with the second laser energy and when the third drilling operation is performed with the third laser energy, the high temperature generated by the resin can be promptly conducted out through the pad 31 at the bottom of the blind hole, thereby avoiding local high temperature inside the resin and rheology.

[0047] In some embodiments, the pad type includes an independent pad, a non-independent pad, a pad combination, and a large copper pad. Figures 9 to 12 , Figure 9 Schematic diagram of independent pads of the package substrate of the embodiment of the present application. Figure 10 This is a schematic diagram of a non-independent pad of a package substrate according to an embodiment of the present application. Figure 11 Schematic diagram of the pad combination of the package substrate of the embodiment of the present application, Figure 12 Schematic diagram of the large copper pad of the package substrate of an embodiment of the present application.

[0048] Among them, such as Figure 9 As shown, the independent pad is surrounded by a closed etched area with no circuit connections. This means there are no copper traces around the pad that connect to it. Independent pads can be circular (or irregular) in shape. Independent pads have the lowest heat dissipation efficiency, and the resin above the pad is prone to melting during laser drilling, resulting in poor blind via quality.

[0049] like Figure 10As shown, a non-independent pad is connected to an outward-extending circuit, meaning that a connecting wire (copper circuit) extends from the pad. A non-independent pad is a non-independent circular (or irregular) pad. During laser drilling, the wire connected to the non-independent pad participates in conduction heat dissipation, resulting in higher heat dissipation efficiency than that of an independent pad. However, the overall heat dissipation efficiency is still lower. During laser drilling, the resin above the pad is more likely to melt at high temperatures, resulting in abnormal blind via quality.

[0050] like Figure 11 As shown, a pad assembly consists of multiple sequentially connected pads. For example, a pad assembly can be composed of 2 to 4 connected pads, each of which can be an independent circular (or irregular) pad. The pad assembly is surrounded by a closed etched area with no circuit connections. This pad assembly offers high heat dissipation efficiency, making it less likely that the resin above the pads will melt during laser drilling, leading to poor blind via quality.

[0051] like Figure 12 As shown, the large copper pad has a larger copper surface area. The pad at the bottom of the blind via is a large copper area, and its copper surface area is greater than k times the blind via area, where k is greater than or equal to 30. For example, in one example, k can be 30. Large copper pads have higher heat dissipation efficiency, and the resin above the pad is less likely to melt at high temperatures during laser drilling, resulting in abnormal blind via quality.

[0052] In some embodiments, to prevent localized high temperatures within the resin during laser drilling, which can cause rheological changes and lead to abnormal blind via quality, the second laser energy can be set as follows: the second laser energy for independent pads is lower than that for dependent pads, the second laser energy for dependent pads is lower than that for pad combinations, and the second laser energy for pad combinations is lower than that for pads with large copper surfaces. In other words, pad types with higher heat dissipation efficiency correspond to higher second laser energy.

[0053] In some embodiments, the third laser energy can be set as follows: the third laser energy corresponding to an independent pad is smaller than the third laser energy corresponding to a dependent pad, the third laser energy corresponding to a dependent pad is smaller than the third laser energy corresponding to a pad combination, and the third laser energy corresponding to a pad combination is smaller than the third laser energy corresponding to a large copper surface pad. In other words, the higher the heat dissipation efficiency of the pad type, the greater the corresponding third laser energy.

[0054] In some embodiments, the laser scanning speed of the first drilling operation is lower than the laser scanning speed of the second drilling operation, and the laser scanning speed of the second drilling operation is lower than the laser scanning speed of the third drilling operation. In one example, the laser scanning speed of the first drilling operation is 50-150 mm / s, for example, 150 mm / s; the laser scanning speed of the second drilling operation is 100-200 mm / s, for example, 200 mm / s; and the laser scanning speed of the third drilling operation is 150-250 mm / s, for example, 250 mm / s.

[0055] In some embodiments, the number of laser circumcisions in the first drilling operation is less than or equal to the number of laser circumcisions in the second drilling operation, and the number of laser circumcisions in the second drilling operation is less than the number of laser circumcisions in the third drilling operation. In one example, the number of laser circumcisions in the first drilling operation is 1 to 2 times, for example, 1 time; the number of laser circumcisions in the second drilling operation is 1 to 2 times, for example, 1 time; and the number of laser circumcisions in the third drilling operation is 2 to 3 times, for example, 2 times.

[0056] In some embodiments, the laser frequency of the first drilling operation, the laser frequency of the second drilling operation, and the laser frequency of the third drilling operation are all the same. For example, in one example, the frequencies may all be 250 kHz.

[0057] In a specific application example, the laser parameters corresponding to the second drilling operation and the third drilling operation can be set according to the following table: The remaining resin in the copper cover and blind vias is removed by laser using different laser parameters corresponding to the above four pad types. Four different tools need to be distinguished when making the drill belt. Multiple blind vias on the package substrate are laser processed according to the above-set laser parameters. This can improve laser processing efficiency while meeting the blind via quality requirements.

[0058] It is understandable that in actual applications, a packaging substrate will usually contain the above four types of pads at the same time. Compared with independent pads, non-independent pads can be laser processed with higher laser energy and faster scanning speed; compared with non-independent pads, pad combinations can be laser processed with higher laser energy and fewer ring cuts; compared with pad combinations, large copper surface pads can be laser processed with higher laser energy and faster scanning speed. Therefore, compared with the traditional laser processing method that uses low laser energy and multiple processing for all pads, the embodiment of the present application uses different laser parameters for different types of pads. Non-independent pads, pad combinations, and large copper surface pads can improve the laser processing efficiency to a certain extent. Therefore, for a large number of pads on the packaging substrate, the embodiment of the present application can greatly improve the overall laser processing efficiency of the packaging substrate. According to the comparison of experimental data, the laser drilling method of the embodiment of the present application can improve the laser processing efficiency of blind holes of the packaging substrate by 20%-30% compared with the traditional laser drilling method.

[0059] In the description of this application, it should be understood that terms such as "first" and "second" are only used to distinguish similar objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0060] The above describes in detail the package substrate laser drilling method and package substrate provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is intended only to facilitate understanding of the present application. Furthermore, those skilled in the art will appreciate that variations in the specific implementation methods and scope of application may occur based on the concepts of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. A laser drilling method for a package substrate, characterized in that: The package substrate includes a first copper layer, a dielectric layer, and a second copper layer stacked in sequence, and the method includes: performing a first drilling operation with a first laser energy to ablate an annular area on the first copper layer; performing a second drilling operation with a second laser energy to remove the copper cover in the middle of the annular area and a portion of the dielectric layer to form a blind hole, wherein the second laser energy is less than the first laser energy; A third drilling operation is performed with a third laser energy to remove the dielectric layer at the bottom of the blind hole until the second copper layer is exposed at the bottom of the blind hole, wherein the third laser energy is less than the second laser energy.

2. The packaging substrate laser drilling method according to claim 1, wherein: The second copper layer is formed with a pad, and before the second drilling operation is performed with the second laser energy, the method further includes: Determine the pad type at the bottom of the blind hole to be processed; The second laser energy and the third laser energy corresponding to the pad type are determined.

3. The packaging substrate laser drilling method according to claim 2, wherein: The pad types include independent pads, non-independent pads, pad combinations, and large copper pads; The independent pad is surrounded by a closed etching area, and the etching area has no circuit connection; The non-independent pad is connected to a circuit extending outward; The pad combination includes a plurality of pads connected in sequence; The copper surface area of ​​the large copper surface pad is greater than k times the area of ​​the blind hole, where k is greater than or equal to 30.

4. The packaging substrate laser drilling method according to claim 3, wherein: The second laser energy corresponding to the independent pad is less than the second laser energy corresponding to the non-independent pad, the second laser energy corresponding to the non-independent pad is less than the second laser energy corresponding to the pad combination, and the second laser energy corresponding to the pad combination is less than the second laser energy corresponding to the large copper surface pad.

5. The packaging substrate laser drilling method according to claim 3, wherein: The third laser energy corresponding to the independent pad is less than the third laser energy corresponding to the non-independent pad, the third laser energy corresponding to the non-independent pad is less than the third laser energy corresponding to the pad combination, and the third laser energy corresponding to the pad combination is less than the third laser energy corresponding to the large copper surface pad.

6. The packaging substrate laser drilling method according to any one of claims 1 to 5, characterized in that: The laser scanning speed of the first drilling operation is lower than the laser scanning speed of the second drilling operation, and the laser scanning speed of the second drilling operation is lower than the laser scanning speed of the third drilling operation.

7. The packaging substrate laser drilling method according to any one of claims 1 to 5, characterized in that: The number of laser ring cuttings in the first drilling operation is less than or equal to the number of laser ring cuttings in the second drilling operation, and the number of laser ring cuttings in the second drilling operation is less than the number of laser ring cuttings in the third drilling operation.

8. The packaging substrate laser drilling method according to any one of claims 1 to 5, characterized in that: The laser frequency of the first drilling operation, the laser frequency of the second drilling operation, and the laser frequency of the third drilling operation are all the same.

9. The laser drilling method for a package substrate according to any one of claims 1 to 5, wherein: The material of the dielectric layer is liquid crystal polymer resin.

10. A packaging substrate, characterized in that: It comprises a first copper layer, a dielectric layer, and a second copper layer stacked in sequence, a blind hole is formed on the packaging substrate, the opening of the blind hole is located in the first copper layer, the bottom of the blind hole exposes the second copper layer, and the blind hole is formed by the method described in any one of claims 1 to 9.

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