Thick-layer PCB drilling method based on liquid nitrogen cooling drilling processing system and PCB

Abstract

The invention provides a thick-layer PCB drilling method based on a liquid nitrogen cooling drilling processing system. The method comprises the steps that a pressed PCB is acquired; drilling operation is carried out on the pressed PCB, so that a drilled PCB can be formed; the drilling instantaneous temperature of the drill point is obtained; detecting whether the borehole instantaneous temperature is greater than or equal to the critical borehole heat temperature; and if the drilling instantaneous temperature is larger than or equal to the critical drilling heat temperature, liquid nitrogen cooling operation is conducted on the drill point. When drilling is carried out for a long time, heat is generated by friction between a drill pin and a PCB, the drill pin has a high temperature, the temperature is transmitted to resin in the PCB, the resin is melted, and the overall quality problem is caused, a liquid nitrogen cooling mode is adopted in the scheme, and when drilling is carried out on the PCB through the drill pin, if the instantaneous temperature, collected by a system, of the drill pin is higher than a preset value, the drill pin is cooled; and liquid nitrogen cooling operation is carried out, accelerated abrasion caused by continuous heating of the drill point is prevented, and rapid melting of resin in a drill hole and rapid oxidation of a copper layer are prevented.

Description

Technical Field

[0001] This disclosure relates to the technical field of PCB manufacturing, and in particular to a drilling method for thick PCBs based on a liquid nitrogen cooling drilling system and the PCB itself. Background Technology

[0002] As electronic devices become smaller and denser, PCBs with 30 or fewer layers and a thickness of 4 mm or less are increasingly used in high-end fields such as communications and aerospace. The through-hole diameter of such PCBs is generally greater than or equal to 0.25 mm.

[0003] 0.25mm is the minimum diameter for a through hole, requiring an extremely small drill bit diameter. During drilling, the drill bit's rigidity decreases significantly, making it prone to bending or even breakage. Simultaneously, due to the small hole diameter, the chip removal channel is narrow, making chip removal more difficult and easily causing blockage within the hole. This can lead to problems such as scratches on the hole wall and diameter deviations. Traditional drilling methods struggle to guarantee drilling accuracy and hole wall quality when machining such small-diameter through holes, often resulting in defects such as excessive hole position misalignment, rough hole walls, and excessive burrs at the hole opening. These defects severely impact the electrical performance and reliability of the PCB (Printed Circuit Board).

[0004] In addition, some PCBs have a large number of layers (such as 42 or 48 layers) and a large thickness, and the drilling depth can reach 5-6mm. The drill bit generates a lot of heat during long-term drilling. Since the diameter of the drill bit is extremely small, it is easy to accumulate heat, making the drill bit prone to wear. The heat of the drill bit itself can also be conducted to the inside of the PCB, causing the resin to melt, the copper layer to oxidize, and causing quality problems such as board delamination, reducing the reliability of PCB drilling. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a drilling method and PCB board based on a liquid nitrogen cooling drilling system to effectively reduce the temperature of the drill bit during long-term drilling and reduce the melting of resin and oxidation of copper layer inside the PCB board caused by long-term drilling.

[0006] The purpose of this disclosure is achieved through the following technical solution:

[0007] A method for drilling thick PCB boards based on a liquid nitrogen-cooled drilling system is disclosed. The system comprises a processing table, a drilling mechanism, and a sensing and cooling mechanism. The processing table holds the laminated PCB board. The drilling mechanism includes a drilling head, a spindle, and a drill bit. The spindle is retractably mounted on the drive end of the drilling head, and the drill bit is detachably mounted on the spindle. The sensing and cooling mechanism includes a liquid nitrogen cooling pipe and a temperature sensor. The liquid nitrogen cooling pipe is connected to a liquid nitrogen pump. The temperature sensor is located on the drilling head, and its acquisition end is used to acquire the instantaneous drilling temperature of the drill bit. The outlet of the liquid nitrogen cooling pipe is directed towards the drill bit and the PCB board during drilling operations, so that the liquid nitrogen pump activates cooling when the instantaneous drilling temperature of the drill bit, as acquired by the temperature sensor, reaches a predetermined value.

[0008] The drilling method for thick-layer PCB boards includes the following steps:

[0009] S101. Obtain the laminated PCB board;

[0010] S103. Drill holes in the laminated PCB board to form a drilled PCB board.

[0011] When executing S103, the following steps are also included:

[0012] S105. Obtain the instantaneous drilling temperature of the drill bit;

[0013] S107. Detect whether the instantaneous temperature of the borehole is greater than or equal to the critical borehole thermal temperature;

[0014] S109. If the instantaneous temperature of the borehole is greater than or equal to the critical borehole thermal temperature, the drill bit shall be cooled with liquid nitrogen.

[0015] In one embodiment, after S107 is executed, the following step is further included: if the instantaneous temperature of the borehole is less than the critical borehole thermal temperature, then no cooling operation is performed.

[0016] In one embodiment, before performing S103, the following steps are included: pre-drilling the already laminated PCB board.

[0017] In one embodiment, when performing S103, the following steps are specifically included: performing segmented drilling on the laminated PCB board to form a drilled PCB board.

[0018] In one embodiment, when performing S109, the following steps are specifically included: if the instantaneous temperature of the borehole is greater than or equal to the critical borehole thermal temperature, liquid nitrogen is sprayed to cool the drill bit that is drilling.

[0019] In one embodiment, the drill bit being drilled is cooled by liquid nitrogen injection at a pressure of 0.25-0.3 MPa.

[0020] In one embodiment, after performing S103, the following steps are included: deburring the drilled PCB board.

[0021] In one embodiment, the deburring operation on the drilled PCB board specifically includes the following steps:

[0022] Perform high-pressure hole cleaning operation on the drilled PCB board;

[0023] The drilled PCB board is subjected to surface deburring.

[0024] In one embodiment, the angle formed by the drill bit and the extension direction of the liquid nitrogen cooling pipe outlet is in the range of 15°-20°.

[0025] A PCB board is manufactured using the thick-layer PCB board drilling method based on a liquid nitrogen cooling drilling system as described in any of the above embodiments.

[0026] Compared with the prior art, this disclosure has at least the following advantages:

[0027] During prolonged drilling, friction between the drill bit and the PCB board generates heat. The drill bit reaches a high temperature, which can transfer to the resin inside the PCB board, causing it to melt and leading to overall quality issues. This solution employs liquid nitrogen cooling. When drilling into the PCB board, if the instantaneous temperature of the drill bit detected by the system exceeds a predetermined value, liquid nitrogen cooling is performed to effectively cool the drill bit and the drill hole. This prevents accelerated wear caused by continued heating of the drill bit, and also prevents rapid melting of the resin inside the drill hole and rapid oxidation of the copper layer, ensuring the reliability of the PCB board drilling and effectively guaranteeing the accuracy and quality of the drilling. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of a thick PCB board drilling method based on a liquid nitrogen cooling drilling system in one embodiment;

[0030] Figure 2 for Figure 1The flowchart shown is a process for executing S103 in the thick PCB board drilling method based on a liquid nitrogen cooling drilling system.

[0031] Figure 3 This is a schematic diagram of a liquid nitrogen-cooled drilling system in one embodiment.

[0032] Reference numerals: 10A, PCB board; 100, processing table; 101, platform through hole; 200, drilling mechanism; 210, drilling head; 220, spindle; 230, drill bit; 300, sensing and cooling mechanism; 310, liquid nitrogen cooling pipe; 320, temperature sensor; 400, constant pressure pump; 500, constant pressure through pipe; 600, air pressure sensor. Detailed Implementation

[0033] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0034] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments:

[0037] Please see Figures 1 to 3 This is an embodiment of the present invention of a drilling method for thick PCB boards based on a liquid nitrogen cooling drilling system. The drilling method is performed using a liquid nitrogen cooling drilling system. The thick PCB board refers to a PCB board with a large thickness, such as a 42-layer circuit board or a 48-layer circuit board.

[0038] like Figure 3As shown, the liquid nitrogen-cooled drilling system includes a processing table 100, a drilling mechanism 200, and a sensing and cooling mechanism 300. The processing table 100 is used to place the laminated PCB board 10A. The drilling mechanism 200 includes a drilling head 210, a spindle 220, and a drill bit 230. The spindle 220 is telescopically mounted on the drive end of the drilling head 210, so that the system controls the vertical movement of the spindle 220, thereby driving the drill bit 230 to move. The drill bit 230 is detachably mounted on the spindle 220. The sensing and cooling mechanism 300 includes a liquid nitrogen cooling pipe 310 and a temperature sensor 320. The liquid nitrogen cooling pipe 310 is used to connect to a liquid nitrogen pressure pump, and the temperature sensor 320 is used to connect to the liquid nitrogen pressure pump. Sensor 320 is located on the drill head 210, and the acquisition end of temperature sensor 320 is used to obtain the instantaneous drilling temperature of drill bit 230. The outlet of liquid nitrogen cooling pipe 310 is used to face the drill bit and the PCB board during drilling operations on the laminated PCB board, so that the liquid nitrogen pump starts cooling when the instantaneous drilling temperature of drill bit 230 collected by temperature sensor 320 reaches a predetermined value. That is, during the drilling process, when the instantaneous drilling temperature of drill bit 230 collected by temperature sensor 320 reaches the critical drilling thermal temperature, the liquid nitrogen pump is activated, so that liquid nitrogen rushes out from liquid nitrogen cooling pipe 310 to cool drill bit 230 and through hole. It can be understood that temperature sensor 320 can be an infrared sensor, thermocouple sensor, etc.

[0039] In this embodiment, the acquisition feedback terminal of the temperature sensor 320 is used to be electrically connected to the system host so that the system host can drive the liquid nitrogen pressure pump to start or not based on the temperature data acquired by the temperature sensor 320.

[0040] like Figure 1 As shown, the drilling method for thick-layer PCB boards includes the following steps:

[0041] S101. Obtain the laminated PCB board; it can be understood that the laminated PCB board refers to the PCB board that has undergone the lamination process. Specifically, it is a laminated PCB board made by laminating the prepreg, substrate and copper foil together. The lamination method can be selected according to production needs. After the PCB board is laminated, it is prepared for the next step of drilling.

[0042] S103. Drilling operation is performed on the laminated PCB board to form a drilled PCB board. It can be understood that after the laminated PCB board is completed, the drilling operation can be performed by a liquid nitrogen cooling drilling system. That is, the drilled PCB board is placed on the processing table 100, and then the drilling head 210 is controlled by the system host to make the drill bit 230 drill the drilled PCB board.

[0043] like Figure 2 As shown, when executing S103, the following steps are also included:

[0044] S105. Obtain the instantaneous drilling temperature of the drill bit. Specifically, the instantaneous drilling temperature is the instantaneous temperature of the drill bit 230 when drilling the PCB board.

[0045] S107. Check whether the instantaneous borehole temperature is greater than or equal to the critical borehole thermal temperature;

[0046] S109. If the instantaneous drilling temperature is greater than or equal to the critical drilling thermal temperature, liquid nitrogen cooling is applied to the drill bit. The critical drilling thermal temperature is the temperature at which the liquid nitrogen pump is activated during drilling. During drilling, when the temperature sensor 320 detects that the instantaneous drilling temperature of the drill bit 230 reaches the critical drilling thermal temperature, the liquid nitrogen pump is activated, causing liquid nitrogen to flow from the liquid nitrogen cooling pipe 310 to cool the drill bit 230 and the borehole. This way, if the drill bit 230 overheats due to prolonged operation, the liquid nitrogen pump can be activated for liquid nitrogen cooling, preventing accelerated wear or even breakage caused by prolonged high temperatures during drilling. For example, the critical drilling thermal temperature is 400℃-500℃.

[0047] In this embodiment, a drill bit 230 with a diameter of 0.25 mm and a needle length of 7.2 mm is used to drill through the laminated PCB board to ensure that the hole can be drilled through.

[0048] In the above embodiments, during prolonged drilling, the friction between the drill bit 230 and the PCB board generates heat. At this time, the drill bit 230 has a high temperature, which will be transferred to the resin inside the PCB board, causing the resin to melt and causing overall quality problems. This solution uses liquid nitrogen cooling. When the drill bit 230 drills into the PCB board, if the instantaneous temperature of the drill bit 230 collected by the system is higher than a predetermined value, liquid nitrogen cooling is performed to effectively cool the drill bit 230 and the drill hole, prevent the drill bit 230 from continuing to heat up and causing accelerated wear, and prevent the resin inside the drill hole from melting rapidly and the copper layer from oxidizing rapidly, ensuring the reliability of the PCB board drilling and effectively ensuring the accuracy and quality of the drilling. It is understandable that liquid nitrogen vaporizes and expands when it encounters the high-temperature drill bit 230 and PCB board, so that the vaporized nitrogen gas covers the PCB board, thereby achieving a cooling effect. At the same time, the nitrogen gas formed by the vaporization of liquid nitrogen after being heated is chemically inert under normal conditions and does not react with other substances. After the liquid nitrogen vaporizes and expands after being heated, it reduces the oxygen concentration in the drilling environment of the PCB board. On the one hand, the copper layer of the PCB board is effectively cooled by liquid nitrogen. On the other hand, liquid nitrogen prevents the copper layer from contacting oxygen, thereby inhibiting the oxidation of the copper layer and preventing the reduction of electrical performance caused by the oxidation of the copper layer.

[0049] In one embodiment, during step S109, the liquid nitrogen flow rate is negatively correlated with the instantaneous drilling temperature. In this embodiment, the liquid nitrogen flow rate can be adjusted according to the current temperature of the drill bit 230. A higher liquid nitrogen flow rate results in a faster temperature drop for both the drill bit 230 and the PCB board, i.e., a faster cooling rate. The liquid nitrogen flow rate can be adjusted according to production needs to effectively cool the drill bit 230 and the drilled holes on the PCB board, preventing the resin on the PCB board from melting at excessively high temperatures or the copper layer from oxidizing at excessively high temperatures. For example, when the temperature of the drill bit 230 is 400°C, with the same cooling time, adjusting the liquid nitrogen flow rate to 1.2 L / min results in a more significant cooling effect than adjusting it to 1.0 L / min; that is, the instantaneous drilling temperature obtained at a liquid nitrogen flow rate of 1.2 L / min is lower.

[0050] In one embodiment, after executing S107, the following step is further included: if the instantaneous drilling temperature is less than the critical drilling thermal temperature, then no cooling operation is performed. It can be understood that when the temperature sensor 320 detects that the instantaneous drilling temperature of the drill bit 230 has not reached the critical drilling thermal temperature, the cooling step is not performed. Since this solution uses liquid nitrogen cooling, manufacturing liquid nitrogen incurs certain costs. Therefore, when the instantaneous drilling temperature of the drill bit 230 is not found to have reached the critical drilling thermal temperature, for example, if the current temperature is 110°C, then no cooling operation is performed, reducing unnecessary liquid nitrogen cooling steps. Furthermore, drilling operations on PCB boards are relatively short; for example, drilling a 0.25mm diameter through hole only takes a few seconds. During this short time, the temperature of the drill bit 230 will not increase significantly. Thus, the liquid nitrogen pump determines whether to start based on the temperature detected by the temperature sensor 230, thereby reducing unnecessary cooling costs.

[0051] In one embodiment, when performing S109, the following steps are also included:

[0052] Obtain the liquid nitrogen cooling time value;

[0053] Check whether the liquid nitrogen cooling time value is greater than or equal to the critical cooling time value;

[0054] If the liquid nitrogen cooling time is greater than or equal to the critical cooling time, then the liquid nitrogen pressure pump is turned off.

[0055] In this embodiment, when the temperature sensor 320 detects that the instantaneous drilling temperature of the drill bit 230 is greater than or equal to the critical drilling temperature, the liquid nitrogen pump is activated to spray liquid nitrogen. The liquid nitrogen expands upon heating, forming a nitrogen cooling space. However, continuous liquid nitrogen cooling, due to the instantaneous vaporization temperature of liquid nitrogen being far below room temperature, not only wastes resources but also causes the PCB board to cool rapidly, leading to "freezing" and resulting in structural brittleness, fracture, or delamination. Therefore, it is necessary to control the duration of liquid nitrogen cooling. At this time, when liquid nitrogen cooling of the drill bit 230 and the PCB board begins, the liquid nitrogen cooling time value is recorded, i.e., the liquid nitrogen cooling time value is obtained. Then, it is detected whether the time value exceeds the critical cooling time value, i.e., whether the liquid nitrogen cooling time value is greater than or equal to the critical cooling time value. If the liquid nitrogen cooling time value is greater than or equal to the critical cooling time value, it indicates that the liquid nitrogen cooling time is too long, and the liquid nitrogen pump needs to be turned off to stop its operation, thereby controlling the amount of liquid nitrogen sprayed and thus controlling the time and cost of liquid nitrogen cooling. Furthermore, the critical cooling time value can be set to 5 seconds.

[0056] In another embodiment, if the liquid nitrogen cooling time is less than the critical cooling time, the instantaneous drilling temperature is checked to see if it is less than or equal to the critical drilling cold temperature. If the instantaneous drilling temperature is less than or equal to the critical drilling cold temperature, the liquid nitrogen pump is shut down. It can be understood that during liquid nitrogen cooling, the cooling time is timed, and during this period, the instantaneous drilling temperature of the drill bit 230, collected by the temperature sensor 320, is checked to see if it drops to the critical temperature for shutting down the liquid nitrogen pump. That is, the instantaneous drilling temperature is checked to see if it is less than or equal to the critical drilling cold temperature. If, within the critical cooling time, the instantaneous drilling temperature is no higher than the critical drilling cold temperature, the liquid nitrogen pump is shut down to save on liquid nitrogen cooling costs and prevent the PCB board from becoming brittle due to a rapid drop in temperature. The critical drilling cold temperature is the critical temperature at which the liquid nitrogen pump is shut down during liquid nitrogen cooling.

[0057] Furthermore, the critical cold drilling temperature is less than the critical hot drilling temperature. That is, the critical temperature at which the liquid nitrogen pump is shut down during liquid nitrogen cooling is less than the critical temperature at which the liquid nitrogen pump is started during drill bit drilling. For example, the critical cold drilling temperature is 250°C and the critical hot drilling temperature is 400°C.

[0058] In another embodiment, if the instantaneous drilling temperature is greater than the critical drilling cold temperature, the liquid nitrogen cooling time value is continuously acquired until the instantaneous drilling temperature of the drill bit 230 collected by the sensor 320 is not higher than the critical temperature for shutting down the liquid nitrogen pump, or the liquid nitrogen cooling time value exceeds the upper limit. Then, the liquid nitrogen pump is shut down to avoid excessive liquid nitrogen cooling of the drill bit 230 and the PCB board.

[0059] In one embodiment, before executing S103, the following steps are included: pre-drilling the laminated PCB board. It can be understood that pre-drilling the laminated PCB board before the actual drilling is performed. For example, for a 6mm thick PCB board, a 0.6-0.7mm hole is drilled first. On the one hand, pre-drilling the PCB board can guide subsequent drilling, helping the drill bit 230 to be positioned and preventing unnecessary material damage caused by drilling deviation during subsequent drilling. On the other hand, subsequent drilling is based on the pre-drilled hole to reduce alignment deviations caused by long-term drilling, reducing the risk of subsequent process failures. Simultaneously, pre-drilling can slow down the temperature rise caused by the drill bit during drilling, thus reducing the wear of the drill bit and further ensuring the quality and reliability of the drilling. In this embodiment, before executing S103, a drill bit 230 with a diameter of 0.25mm and a length of 3.0mm will be used to pre-drill the laminated PCB board.

[0060] In one embodiment, when performing S103, the following steps are specifically included: performing segmented drilling on the laminated PCB board to form a drilled PCB board. It is understandable that this solution is designed for segmented drilling of thick PCBs. Due to the high thickness-to-diameter ratio of thick PCBs (e.g., 6mm thickness, 0.25mm hole diameter, and a thickness-to-diameter ratio of 24), if drilling is performed in one pass, the drill bit 230 needs to overcome more resistance, which makes it easier to generate heat and cause the drill bit 230 temperature to rise significantly, posing a risk of breakage, or causing the hole to be drilled off-center or the hole wall to be rough. Therefore, segmented drilling is necessary to reduce the risk of increased drill bit temperature. Furthermore, segmented drilling can reduce the burrs generated by single-pass drilling, which can lead to significant wear on the hole wall. In other words, segmented drilling can reduce the drilling depth, thereby reducing the burrs or drill chips generated during drilling, and can also reduce the resistance that needs to be overcome during drilling, thus slowing down the rate of temperature rise of the drill bit 230, extending the drill bit life, improving drilling accuracy, and reducing board defects. In this embodiment, the segmented drilling operation on the laminated PCB board will be carried out in five segments. Taking a 6mm thick PCB board as an example, the drilling depth of each segment is 1.0mm-1.2mm, so that the drill bit 230 drills in 5 steps. The drilling depth of the first 4 drilling steps gradually increases until the drill bit 230 drills through the hole in the 5th drilling step. This makes it less likely for the drill bit 230 to heat up rapidly during drilling, and also makes the temperature rise rate of the resin and copper layer of the PCB board slower, thereby reducing the cost of the liquid nitrogen cooling step.

[0061] In one embodiment, when executing S109, the following steps are specifically included: if the instantaneous drilling temperature is greater than or equal to the critical drilling thermal temperature, liquid nitrogen jet cooling is performed on the drill bit 230 that is drilling. In this embodiment, when the instantaneous drilling temperature collected by the temperature sensor 320 is greater than or equal to the critical drilling thermal temperature, it indicates that the temperature of the drill bit 230 is too high and exceeds the temperature critical value. A signal is then sent to enable the liquid nitrogen pump to start, performing liquid nitrogen jet cooling. That is, the specific cooling operation for the drill bit 230 is liquid nitrogen jet cooling. Because liquid nitrogen cooling is used, its pressure is greater than the standard gas pressure. When heated, it will absorb heat from the drill bit 230 and the through hole, and then vaporize. The liquid nitrogen sprayed from the liquid nitrogen cooling pipe 310 will diffuse from the drill bit 230 and the drilling location of the thick-layer PCB board. In other words, the gas expands after the liquid nitrogen vaporizes, achieving a better cooling effect. Furthermore, the liquid nitrogen jet cooling operation on the drill bit 230 during drilling is performed at a liquid nitrogen jet pressure of 0.25-0.3 MPa. By setting a reasonable liquid nitrogen injection pressure, the high-temperature drill bit 230 can be effectively and rapidly cooled. The vaporized liquid nitrogen expands in volume and diffuses into the thick-layer PCB board, thus rapidly cooling the through-holes and preventing accelerated melting of the resin within the through-holes. Furthermore, nitrogen is chemically inert under normal conditions and does not react with most substances, which also reduces the oxygen concentration in the drilling environment, preventing accelerated oxidation of the copper layer on the thick-layer PCB board and ensuring the drilling stability of the thick-layer PCB board. In this embodiment, the liquid nitrogen injection pressure is 0.3 MPa.

[0062] In one embodiment, after executing S103, the following steps are included: deburring the drilled PCB board to remove drill chips and burrs generated during drilling, so as to prevent drill chips and burrs from damaging the PCB board surface and through holes. Further, the deburring operation on the drilled PCB board specifically includes the following steps: first, performing a high-pressure hole cleaning operation on the drilled PCB board; then, performing a surface deburring operation on the drilled PCB board. In this embodiment, when drilling holes in the PCB board, the drill bit 230 acts on the PCB board, drilling through the copper foil and substrate resin to create through holes. Drilling generates drill chips and burrs. Some of these chips and burrs adhere to the area around the through holes, while others remain inside. The chips and burrs inside the through holes are more likely to scratch the hole walls, thus affecting subsequent processes (such as chemical copper plating or electroplating), leading to poor plating adhesion, short circuits, etc. Therefore, a high-pressure cleaning operation is first performed on the drilled PCB board. This involves using high-pressure water washing to remove the drill chips and burrs generated inside the through holes, flushing them away to ensure the PCB board remains undamaged. The through-holes on board B are cleaned and free of impurities. Then, a surface deburring operation is performed on the PCB board, which involves removing burrs from the PCB board surface using wet sanding. During the initial drilling, drill debris surrounds the through-holes, forming burrs. These burrs can scratch the PCB board surface, damaging the copper layer or circuitry. Wet sandpaper is then used to polish the edges of the through-holes to reduce frictional heat during polishing. This removes burrs, drill debris, and flash, resulting in a clean PCB board surface free of protrusions and ensuring its flatness. Furthermore, during the high-pressure cleaning operation, the water pressure is 100 kg / cm². 2 .

[0063] In one embodiment, the angle formed between the drill bit 230 and the extension direction of the liquid nitrogen cooling pipe 310 is in the range of 15°-20°. It can be understood that when a certain angle is formed between the drill bit 230 and the liquid nitrogen cooling pipe 310, both the drill bit 230 and the surrounding area of ​​the drill hole can be cooled. Furthermore, the expanding liquid nitrogen will diffuse into the drill hole. The 15°-20° angle between the drill bit 230 and the liquid nitrogen cooling pipe 310 allows more liquid nitrogen to penetrate into the drill hole, further cooling the resin and copper layers within the PCB board vias and preventing melting and oxidation caused by the resin and copper layers continuing to rise. In this embodiment, the angle formed between the drill bit 230 and the extension direction of the liquid nitrogen cooling pipe 310 is 15°.

[0064] During the PCB drilling process, when the instantaneous drilling temperature collected by the temperature sensor 320 exceeds the limit value, the liquid nitrogen pump is activated. The liquid nitrogen is injected at a certain pressure, which is greater than the normal air pressure (approximately 1.013 kPa). This causes the liquid nitrogen to exert a certain pressure on the drill bit 230 and the drilling hole during cooling. When the entire drilling process adopts a closed drilling process, that is, the air inside the drilling hole is not connected to the external ambient air, the liquid nitrogen cooling operation will also make the drilling environment a positive pressure state, that is, the current air pressure is greater than the normal air pressure, causing the PCB board to deform inward. Furthermore, because the liquid nitrogen injection pressure is greater than the normal air pressure, the PCB board is more susceptible to force, which makes the drilling hole tend to be concave downward. Thus, the PCB board drilling process will be hindered.

[0065] To balance the air pressure on the PCB board, making it equivalent to the normal air pressure, in one embodiment, such as Figure 3 As shown, the liquid nitrogen cooling drilling system also includes a constant pressure pump 400 and a constant pressure pipe 500. The constant pressure pump 400 is located under the processing table 100. One end of the constant pressure pipe 500 is connected to the bottom of the processing table 100, and the other end of the constant pressure pipe 500 is connected to the pump port of the constant pressure pump 400. The processing table 100 has a platform through hole 101 so that the top of the processing table 100 is connected to the constant pressure pipe 500 through the platform through hole 101. The constant pressure pump 400 is used to start when the liquid nitrogen pump is started for the cooling step.

[0066] It is understandable that, since the PCB board is in a closed and atmospheric pressure environment, and the drilling process is carried out by the liquid nitrogen cooling drilling system, when the temperature sensor 320 detects that the temperature of the drill bit 230 exceeds the critical drilling thermal temperature, the liquid nitrogen pressure pump is started. At this time, when the liquid nitrogen is sprayed out, its pressure is greater than the normal air pressure. Because the drilling environment is a closed environment, the PCB board is in a positive pressure state, that is, the current air pressure is higher than the normal air pressure. This can lead to situations such as the PCB board structure warping, bending, or internal cracks. In order to balance the air pressure in the drilling environment and make it equal to the normal air pressure, the constant pressure pump 400 is started. When the constant pressure pump 400 is working, it will generate negative pressure. Since the platform through hole 101 is connected to the constant pressure through pipe 500 and the top of the processing table 100 respectively, the air pressure in the drilling environment is balanced. That is to say, the positive pressure generated when the liquid nitrogen pressure pump is working is balanced with the negative pressure generated when the constant pressure pump 400 is working, so as to prevent the PCB board from being deformed due to the change in air pressure in the drilling environment, thereby ensuring the smooth progress of the PCB board drilling process.

[0067] Furthermore, the execution of S109 also includes the following steps:

[0068] Obtain the ambient air pressure value during drilling;

[0069] Check whether the ambient air pressure in the borehole is greater than or equal to the reference air pressure.

[0070] If the ambient air pressure during drilling is greater than or equal to the reference air pressure, send the first constant pressure enable signal.

[0071] In this embodiment, when the temperature sensor 320 detects that the drill bit 230 temperature exceeds the critical drilling thermal temperature, the liquid nitrogen pressure pump is activated. At this time, the liquid nitrogen ejected has a certain pressure value, causing the internal drilling environment pressure to rise. That is, compared to atmospheric pressure, the PCB board is in a positive pressure environment. When the system detects that the drilling environment pressure is greater than or equal to the reference pressure value, it sends a first constant pressure enable signal to activate the constant pressure pump 400, which then performs a decompression step. The constant pressure pump 400 generates negative pressure to balance the current internal drilling environment pressure until it reaches atmospheric pressure. This prevents the PCB board from deforming inwards due to increased internal drilling pressure, thus ensuring the smooth progress of the PCB board drilling process. The drilling environment pressure value is the overall internal drilling environment pressure of the liquid nitrogen-cooled drilling system, while the reference pressure value is the pressure under normal conditions.

[0072] Furthermore, if the borehole ambient pressure is greater than the reference pressure, a first constant pressure enable signal is sent, followed by the following steps:

[0073] Get the current liquid nitrogen flow rate;

[0074] Detect whether the current liquid nitrogen flow rate is greater than the reference liquid nitrogen flow rate;

[0075] If the current liquid nitrogen flow rate is greater than the reference liquid nitrogen flow rate, increase the decompression rate.

[0076] In this embodiment, when the obtained drilling environment pressure is higher than the normal atmospheric pressure, the liquid nitrogen pressure pump is started for cooling. Since the drilling environment of the PCB board is relatively enclosed, when the liquid nitrogen pressure pump is started to cool the PCB board, the extremely cold liquid nitrogen vaporizes and expands upon entering the drilling environment, resulting in a higher atmospheric pressure compared to the normal atmospheric pressure. At this time, the current liquid nitrogen flow rate is obtained and checked to see if it is greater than the reference liquid nitrogen flow rate, to determine whether to adjust the decompression rate of the constant pressure pump 400. If the current liquid nitrogen flow rate is greater than the reference liquid nitrogen flow rate, increasing the decompression rate indicates that the current liquid nitrogen flow rate is higher than the reference liquid nitrogen flow rate, resulting in a faster pressurization rate and a faster rise in the drilling environment pressure. Therefore, increasing the decompression rate of the constant pressure pump during operation balances the atmospheric pressure and prevents high atmospheric pressure from affecting the overall structure of the PCB board. Further, the reference liquid nitrogen flow rate is 1.0 L / min. The current liquid nitrogen flow rate is the real-time liquid nitrogen flow rate output by the liquid nitrogen pressure pump through the liquid nitrogen cooling pipe.

[0077] In another embodiment, if the current liquid nitrogen flow rate is less than the reference liquid nitrogen flow rate, the decompression rate is reduced. This maintains the pressurization rate of the liquid nitrogen pump and the decompression rate of the constant pressure pump, ensuring that the current borehole environment gas pressure is equal to the normal gas pressure, thus achieving a pressure balance.

[0078] In another embodiment, if the current liquid nitrogen flow rate is equal to the reference liquid nitrogen flow rate, the current decompression rate is maintained.

[0079] In another embodiment, if the drilling environment air pressure is lower than the reference air pressure, a second constant pressure enable signal is sent. In this embodiment, during the PCB drilling process, the system monitors the internal drilling environment air pressure in real time. When the internal drilling environment air pressure is lower than the normal air pressure, the internal pressure of the PCB is greater than the internal drilling environment air pressure, which poses a risk of the PCB expanding outward, i.e., there is a risk of surface deformation or even board bursting. At this time, the system detects that the drilling environment air pressure is lower than the reference air pressure and sends a second constant pressure enable signal to balance the drilling environment air pressure. Specifically, when the liquid nitrogen pump is working, if the drilling environment air pressure is lower than the reference air pressure, the second constant pressure enable signal is sent to keep the liquid nitrogen pump working until the drilling environment air pressure equals the reference air pressure. Then, the constant pressure pump is started, and the decompression rate of the constant pressure pump is equal to the liquid nitrogen flow rate to balance the drilling environment air pressure.

[0080] In one embodiment, if the borehole ambient pressure is equal to the reference pressure, a first constant pressure enable signal is sent, followed by the following steps:

[0081] Check whether the instantaneous borehole temperature is less than or equal to the critical borehole cold temperature;

[0082] If the instantaneous borehole temperature is less than or equal to the critical borehole cold temperature, then shut down the liquid nitrogen pressure pump and the constant pressure pump.

[0083] In this embodiment, when the drilling environment air pressure value is detected to be equal to the reference air pressure value, it indicates that the drilling environment air pressure value is at normal pressure. This step is performed in S109, which is the liquid nitrogen cooling step, and is performed in a closed environment. When the liquid nitrogen pump is started, the drilling environment air pressure value will be increased to be higher than the normal air pressure value. At this time, a first constant pressure enable signal needs to be sent at the same time as the liquid nitrogen pump is started to start the constant pressure pump 400. The constant pressure pump 400 generates negative pressure to balance the current internal drilling environment air pressure. At the same time, the temperature sensor obtains the instantaneous temperature of the drill bit during drilling and detects whether the instantaneous drilling temperature is less than or equal to the critical drilling cold temperature to determine whether to shut down the liquid nitrogen pump and the constant pressure pump at the same time. When the instantaneous drilling temperature obtained by the temperature sensor is less than or equal to the critical drilling cold temperature, it indicates that the drill bit and the drilling on the PCB board have cooled down and the temperature has reached the condition for shutting down the liquid nitrogen pump and the constant pressure pump. Then, the liquid nitrogen pump and the constant pressure pump are shut down to reduce unnecessary cooling steps and air pressure balancing steps.

[0084] In another embodiment, if the instantaneous drilling temperature is greater than the critical drilling cold temperature, the liquid nitrogen pressure pump and the constant pressure pump remain on, and the current liquid nitrogen flow rate and the current decompression rate are maintained. It can be understood that when executing S109, it has been determined that the instantaneous drilling temperature of the drill bit before cooling has reached the critical drilling hot temperature, i.e., the critical temperature at which the liquid nitrogen pressure pump is activated during drilling. Under this condition, the temperature sensor still detects the instantaneous drilling temperature. When the instantaneous drilling temperature is greater than the critical drilling cold temperature, and the drill bit on the surface and the drill hole on the PCB have not reached the critical temperature for shutting down the liquid nitrogen pressure pump, the liquid nitrogen pressure pump and the constant pressure pump remain on. Simultaneously, the liquid nitrogen flow rate during the operation of the liquid nitrogen pressure pump and the decompression rate during the operation of the constant pressure pump are maintained to ensure that the ambient air pressure during drilling is equal to the normal air pressure, thereby ensuring that the PCB will not deform due to changes in the ambient air pressure during drilling.

[0085] In another embodiment, such as Figure 3 As shown, the liquid nitrogen cooling drilling system also includes a pressure sensor 600, which is located on the drilling head 210. The pressure sensor 600 is used to obtain the current air pressure in the drilling environment, that is, to obtain the drilling environment air pressure value, so as to facilitate the subsequent drilling environment air pressure value detection operation.

[0086] In this embodiment, the acquisition feedback terminal of the air pressure sensor 600 is used to electrically connect to the system host, so that the system host drives the constant pressure pump 500 to start or not based on the internal drilling environment air pressure data obtained by the air pressure sensor 600.

[0087] This disclosure also provides a PCB board manufactured using any of the thick-layer PCB board drilling methods based on a liquid nitrogen cooling drilling system described in the above embodiments. It is understood that during prolonged drilling, heat is generated through friction between the drill bit 230 and the PCB board. At this time, the drill bit 230 has a high temperature, which is transferred to the resin inside the PCB board, causing the resin to melt and leading to overall quality problems. This solution uses liquid nitrogen cooling, which can effectively cool the drill bit 230 when its temperature is detected to be too high, preventing accelerated wear due to excessively high drill bit temperature, and preventing rapid melting of the resin or rapid oxidation of the copper layer due to excessively high drilling temperature.

[0088] Compared with the prior art, this disclosure has at least the following advantages:

[0089] During prolonged drilling, the friction between the drill bit 230 and the PCB board generates heat. At this time, the drill bit 230 has a high temperature, which will be transferred to the resin inside the PCB board, causing the resin to melt and leading to overall quality problems. This solution uses liquid nitrogen cooling. When the drill bit 230 drills into the PCB board, if the instantaneous temperature of the drill bit 230 collected by the system is higher than the predetermined value, liquid nitrogen cooling is performed to effectively cool the drill bit 230 and the drill hole, prevent the drill bit 230 from continuing to heat up and causing accelerated wear, and prevent the resin inside the drill hole from melting rapidly and the copper layer from oxidizing rapidly, ensuring the reliability of the PCB board drilling and effectively ensuring the accuracy and quality of the drilling.

[0090] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A drilling method for thick-layer PCB boards based on a liquid nitrogen-cooled drilling system, characterized in that, The drilling process employs a liquid nitrogen-cooled drilling system, which includes a processing table, a drilling mechanism, and a sensing and cooling mechanism. The processing table is used to place the laminated PCB board. The drilling mechanism includes a drilling head, a spindle, and a drill bit. The spindle is telescopically mounted on the drive end of the drilling head, and the drill bit is detachably mounted on the spindle. The sensing and cooling mechanism includes a liquid nitrogen cooling pipe and a temperature sensor. The liquid nitrogen cooling pipe is connected to a liquid nitrogen pump, and the temperature sensor is located on the drilling head. The sensor's acquisition end is used to obtain the instantaneous drilling temperature of the drill bit. The outlet of the liquid nitrogen cooling pipe is directed towards the drill bit and the PCB board during drilling operations, so that the liquid nitrogen pump starts cooling when the instantaneous drilling temperature of the drill bit, as measured by the temperature sensor, reaches a predetermined value. The drilling method for thick-layer PCB boards includes the following steps: S101. Obtain the laminated PCB board; S103. Drill holes in the laminated PCB board to form a drilled PCB board. When executing S103, the following steps are also included: S105. Obtain the instantaneous drilling temperature of the drill bit; S107. Detect whether the instantaneous temperature of the borehole is greater than or equal to the critical borehole thermal temperature; S109. If the instantaneous temperature of the borehole is greater than or equal to the critical borehole thermal temperature, the drill bit shall be cooled with liquid nitrogen.

2. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 1, characterized in that, After executing S107, the following steps are also included: If the instantaneous borehole temperature is less than the critical borehole thermal temperature, no cooling operation is performed.

3. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 1, characterized in that, Before executing S103, the following steps are included: Pre-drilling is performed on the already laminated PCB board.

4. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 1, characterized in that, The execution of S103 includes the following steps: The laminated PCB board is subjected to segmented drilling to form a drilled PCB board.

5. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 1, characterized in that, The specific steps involved in executing S109 are as follows: If the instantaneous temperature of the borehole is greater than or equal to the critical borehole thermal temperature, liquid nitrogen is sprayed to cool the drill bit that is drilling.

6. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 5, characterized in that, The process involves cooling the drill bit with liquid nitrogen injection at a pressure of 0.25-0.3 MPa.

7. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 1, characterized in that, After executing S103, the following steps are included: The drilled PCB board is deburred.

8. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 7, characterized in that, The deburring operation on the drilled PCB board specifically includes the following steps: Perform high-pressure hole cleaning operation on the drilled PCB board; The drilled PCB board is subjected to surface deburring.

9. The thick-layer PCB drilling method based on a liquid nitrogen-cooled drilling system according to claim 1, characterized in that, The angle between the drill bit and the extension direction of the liquid nitrogen cooling pipe outlet is in the range of 15°-20°.

10. A PCB board, characterized in that, The thick-layer PCB board is manufactured using the drilling method based on the liquid nitrogen cooling drilling system as described in any one of claims 1-9.

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