CN116546746B

CN116546746B - Precise mounting control method and device for PCB chip mounter

Info

Publication number: CN116546746B
Application number: CN202310821286.9A
Authority: CN
Inventors: 余耀国; 杨建军
Original assignee: Shenzhen Eton Automation Equipment Co ltd
Current assignee: Shenzhen Eton Automation Equipment Co ltd
Priority date: 2023-07-06
Filing date: 2023-07-06
Publication date: 2023-09-15
Anticipated expiration: 2043-07-06
Also published as: CN116546746A

Abstract

The invention discloses a precise mounting control method and a precise mounting control device for a PCB chip mounter, wherein in the method, when a suction nozzle drives a workpiece to descend at a first speed, and the suction nozzle is detected to reach a preset position, the descending speed is adjusted to a second speed; the second speed is lower than the first speed, and the suction nozzle is driven by the first motor to realize lifting; when the current change value of the first motor is detected to exceed the preset current range in the process that the suction nozzle drives the workpiece to continuously descend at the second speed, a motor stop instruction is sent to the first motor; wherein the motor stop command is used for controlling the rotor of the first motor to stop rotating. The invention utilizes the semi-solid solder paste to buffer the descending chip, and controls the buffer time of the chip or the component in the semi-solid solder paste to reach the millisecond level through software, although the suction nozzle generates the overshoot problem at the microsecond level, the impulse generated by microsecond level overshoot is absorbed and buffered by the semi-solid solder paste, and the damage to the chip or the component caused by the overshoot is reduced.

Description

Precise mounting control method and device for PCB chip mounter

Technical Field

The invention relates to the technical field of semiconductor manufacturing, in particular to a precise mounting control method and device of a PCB chip mounter.

Background

The full-automatic production line scheme of the chip mounter is that, as shown in fig. 1, a PCB sequentially passes through three processing stations of dispensing (printing solder paste), chip mounting and reflow soldering, and the scheme of full-automatic chip mounting for the PCB is completed. In the prior art, a PCB board is transported in each processing station by a conveyor belt or a manipulator. Generally, no matter when the PCB processed by the dispensing station is transferred to the pasting station through a conveyor belt or a mechanical arm, the PCB is considered to be transferred to a position appointed by the pasting station, then the PCB is fixed on the position, and the pasting device controls an air cylinder or a motor of the pasting device to act on XY coordinates according to the coordinates of each target point to be pasted on the PCB, which are acquired in advance (if deviation exists in the fixed position of the PCB, rotation and coordinate compensation operation are also required to be executed), so that a chip or an element can be sent to each target point on the PCB to realize pasting.

In the process of pasting, a suction nozzle of the pasting device picks up the chip through negative pressure and moves to the position right above the target point according to the XY coordinates of the target point, and then the suction nozzle is controlled to descend so that the chip or the element is pressed into the solder paste on the bonding pad. In order to monitor the pressure applied to the chip or the component during the chip mounting process, the pressure detection module of reference 1 detects the current change of the motor, and when the current of the motor is greater than a preset value, determines that the pressure change of the die attach suction nozzle reaches a set value. The principle of the method for detecting pressure is that when the bottom of a chip or an element collides with a PCB and is blocked by the PCB, the PID controller of the motor increases the current to increase the torque so as to overcome the blocking of the chip or the element when detecting the speed feedback reduction of a speed loop in order to reach a target value, so that the pressure of the chip or the element can be judged by detecting whether the current reaches a preset value or not by utilizing the proportional relation between the torque of the motor and the current.

However, as described in reference 2, the time period (i.e., response speed) of a general servo motor is in the order of microseconds (referring to fig. 11 and taking a kolmorgin (kollmorgin) type servo driver as an example, the current loop time period is 0.67 microseconds, the speed loop is 62.5 microseconds, the position loop is 250 microseconds, and the response speed from the current loop, the speed loop to the position loop is sequentially slow). It is known that if the above-mentioned scheme of judging the pressure to which the chip or the element is subjected by detecting whether the current reaches the preset value is adopted in reference 1, overshoot is liable to be caused (in this context, overshoot means that the signal or the function exceeds the expected value, for example, the pressure to which the chip or the element is subjected exceeds the set value). There is a risk of damage to the chip or component. In this regard, the core of the solution of reference 2 is to solve the overshoot problem from the hardware level, i.e. the hardware of the patch device is improved to achieve a response at the nanosecond level by using a pressure sensor with ultra-high sampling frequency and a matched mechanical structure.

However, the solution shown in reference 2 is only applicable to chip mounters with specific mechanical structures, and the hardware improvement is not friendly for the fully automatic production line of the chip mounters which are already in use and have the shaped mechanical structures. In addition, in the process of pasting, the coordinate compensation of the distorted PCB is also a problem to be solved.

Reference 1, grant bulletin number: CN113571429B patent name: die bonding method and die bonder publication date: 2021-10-29.

Reference 2, application publication No.: CN115116898A patent name: high-precision low-pressure controlled ZR shaft patch device publication date: 2022-09-27.

Disclosure of Invention

The invention aims to at least solve one of the technical problems in the prior art, and provides a precise mounting control method and device for a PCB (printed circuit board) chip mounter, which can reduce damage to chips or elements caused by overshoot problem in the mounting process through a software scheme, and is suitable for a fully-automatic production line of the chip mounter with a fixed mechanical structure.

The invention is characterized in that: the semi-solid solder paste is utilized to buffer the descending chip, and the buffer time (namely the travelling time length) of the chip or the component in the semi-solid solder paste is controlled by software to reach the millisecond level, and although the suction nozzle generates an overshoot problem at the microsecond level, the impulse generated by the microsecond level overshoot is absorbed and buffered by the semi-solid solder paste, so that the damage caused by the overshoot to the chip or the component (hereinafter referred to as a workpiece) is reduced.

The technical scheme of the invention is as follows:

In a first aspect, the present invention provides a precise mounting control method for a PCB mounter, including:

when the suction nozzle detects that the suction nozzle reaches a preset position in the process of driving the workpiece to descend at the first speed, the descending speed is adjusted to be the second speed; the second speed is lower than the first speed, and the suction nozzle is driven by the first motor to realize lifting;

when the current change value of the first motor is detected to exceed the preset current range in the process that the suction nozzle drives the workpiece to continuously descend at the second speed, a motor stop instruction is sent to the first motor; wherein the motor stop command is used for controlling the rotor of the first motor to stop rotating.

In a second aspect, the present invention provides an electronic device comprising: the precise mounting control method of the PCB chip mounter comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, wherein the processor realizes the precise mounting control method of the PCB chip mounter when executing the program.

In a third aspect, the present invention provides a computer-readable storage medium storing computer-executable instructions for causing a computer to perform a precision mounting control method of a PCB mounter as described above.

The precise mounting control method and device for the PCB chip mounter provided by the invention have the following beneficial effects:

1. chip mounter among the prior art generally includes high-speed paster mode and slow paster mode, and whole invariable high-speed or slow paster of whole journey is to fragile chip of material or component, generally adopts slow paster mode, reduces the risk of damage when chip striking PCB board, but whole invariable slow speed can lead to paster efficiency to reduce. Compared with the prior art, the invention only needs to decelerate when reaching the preset position (namely when approaching to the solder paste position) in the descending process, combines the high-speed mode and the low-speed mode, and reduces the loss of the patch efficiency.

2. In the present invention, when the lower end of the chip or the component contacts the semi-solid solder paste, the suction nozzle receives the resistance of the semi-solid solder paste, after a response time (such as a speed loop, a total time of 500 microseconds for current sampling, calculation, etc.), the current of the first motor changes (i.e. increases) in response to the resistance, and when the current change value exceeds the preset current range, the first motor is controlled to stop rotating. In an ideal situation, the chip should stop moving immediately when contacting the semisolid solder paste, but the overshoot problem is caused by the delay response of the servo system, namely, the chip moves in the semisolid solder paste for a microsecond time, and in the invention, the kinetic energy of the semisolid solder paste is absorbed and buffered by the semisolid solder paste due to the impulse generated by the overshoot of the suction nozzle in the microsecond time, so that the damage to the chip or the component (hereinafter referred to as a workpiece) caused by the overshoot can be reduced.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The invention is further described below with reference to the drawings and examples;

fig. 1 is an application environment diagram of a precise mounting control method of a PCB mounter in one embodiment.

Fig. 2 is a flow chart of a precise mounting control method of the PCB mounter in one embodiment.

Fig. 3 is a flow chart of a precise mounting control method of the PCB mounter in one embodiment.

Fig. 4 is a flow chart of a precise mounting control method of the PCB mounter in one embodiment.

Fig. 5 is a flow chart of a precise mounting control method of the PCB mounter in one embodiment.

Fig. 6 is a flow chart of a precise mounting control method of the PCB mounter in one embodiment.

Fig. 7 is a schematic diagram of a servo motor cylinder used in one embodiment.

Fig. 8 is a schematic diagram of the 4-point reference Mark point compensation principle.

Fig. 9 is a schematic diagram of the 4-point reference Mark point compensation principle.

Fig. 10 is a schematic diagram of inapplicability in the 4-point reference Mark point compensation calculation process.

FIG. 11 is a schematic diagram of a prior art servo motor control system.

Reference numerals:

10. a production line; 11. full-automatic plate sucking and conveying machine; 12. a dispensing machine; 13. a docking station; 14. a manipulator; 15. a chip mounter; 16. reflow soldering equipment; 17. full-automatic plate collecting machine; 20. a servo electric cylinder; 21. a first motor; 22. a speed reducer; 23. a ball screw pair; 24. the front end joint of the telescopic tube.

Detailed Description

Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the accompanying drawings are used to supplement the description of the written description so that one can intuitively and intuitively understand each technical feature and overall technical scheme of the present invention, but not to limit the scope of the present invention.

Fig. 1 is an application environment diagram of a precise mounting control method of a PCB mounter in one embodiment. Referring to fig. 1, the precise mounting control method of the PCB mounter is applicable to a full-automatic production line 10 of the mounter. The scheme of the full-automatic production line 10 of the chip mounter sequentially comprises a full-automatic board sucking and conveying machine 11, a dispensing machine 12, a connection table 13, a manipulator 14, a chip mounter 15, another connection table, reflow soldering equipment 16 and a full-automatic board collecting machine 17 according to the working procedures, and various hardware equipment in the production line 10 can be connected and are widely applied in the field, and the description is omitted here. It should be noted that, fig. 1 shows only one full-automatic production line scheme of the chip mounter, and for other full-automatic production line schemes of the chip mounter, those skilled in the art can understand that after implementing all or part of the processes in the method in the embodiment, the method provided by the invention is suitable for other full-automatic production line schemes of the chip mounter without performing creative labor, so that the method provided by the invention falls within the protection scope of the invention when applied to other full-automatic production line schemes of the chip mounter.

In order to facilitate understanding of the present invention, it is necessary to make a brief description of the background of the invention again. Reference 2 discloses a technical route for solving the process problem by hardware, and the core is to solve the overshoot problem from the hardware level, namely, the pressure sensor with ultra-high sampling frequency and the matched mechanical structure are adopted to improve the hardware of the patch device to realize the response in nanosecond level. However, the hardware improvement is not friendly to the fully automatic chip mounter production line 10 which is already in use and has a fixed mechanical structure, and has the problems of high labor input in the reconstruction engineering, high cost of purchasing hardware equipment, long time for hardware reconstruction and the like, and the finding of the problems in communication with users becomes an important factor for preventing the users from improving the scheme of the fully automatic chip mounter production line 10.

Therefore, the inventor tries to open up a technical route for solving the process problem through software, and aims to reduce the damage to chips or elements caused by the overshoot problem in the process of mounting through a software scheme, so that the method is suitable for the fully-automatic production line of the chip mounter which is put into use and has a fixed mechanical structure. Based on the above objects, the invention adopts the following inventive concept: the semi-solid solder paste is utilized to buffer the descending chip, and the buffer time (namely the travelling time length) of the chip or the component in the semi-solid solder paste is controlled by software to reach the millisecond level, and although the suction nozzle generates an overshoot problem at the microsecond level, the impulse generated by the microsecond level overshoot is absorbed and buffered by the semi-solid solder paste, so that the damage caused by the overshoot to the chip or the component (hereinafter referred to as a workpiece) is reduced.

Based on the above-mentioned inventive concept, the following describes and describes in detail a precise mounting control method of a PCB mounter according to an embodiment of the present invention through several specific embodiments.

As shown in fig. 2, in one embodiment, a precise mounting control method of a PCB mounter is provided. The embodiment is mainly described by taking the chip mounter 15 in fig. 1 as an example.

Referring to fig. 2, the precise mounting control method of the PCB mounter specifically includes the steps of:

step S202, when the suction nozzle detects that the suction nozzle reaches a preset position in the process that the suction nozzle drives the workpiece to descend at a first speed, the descending speed is adjusted to a second speed; wherein the second speed is lower than the first speed, and the suction nozzle is driven by the first motor 21 to realize lifting.

It should be noted that the first speed may be a lowering speed originally programmed by the chip mounter 15, for example, 800mm/s, and when the suction nozzle reaches the preset position, for example, feedback from a servo motor encoder detects whether the suction nozzle reaches the preset position. Specifically, a specific value of the preset position may be set according to the initial position of each suction nozzle and the height of the workpiece, for example, the initial position of the suction nozzle is defined as 0, the distance between the suction nozzle and the PCB board at the initial position is 20cm, and the component or chip height corresponding to each suction nozzle, for example, 1cm, is obtained in advance. If the component or chip bottom is set to be 5cm from the PCB board, it is necessary to control the suction nozzle to reach a preset position when it is lowered to a distance of (20-5-1) =14 cm from the initial position, as an example, at which time the speed is adjusted from 800mm/s to 50mm/s. It will be appreciated that the calculated distance of the suction nozzle or chip bottom to the PCB is a rough estimate calculated from the height of the plane of the fixing base of the chip mounter 15 for fixing the PCB plus the thickness of the PCB. The precision error of the distance between the PCB and the bottom of the chip only needs to be controlled at the millimeter level or centimeter.

The purpose of the deceleration is to make the chip bottom contact point travel in the semisolid solder paste, and the same travel depth needs longer travel time length, so that more travel time length is provided, and the corresponding servo motor system in microsecond level can finish current detection and send out a motor stop instruction, so that the travel time length is aimed at millisecond level. In this example, the second speed was 50mm/s calculated by taking a solder paste thickness of 200 μm, and even if the second speed was not considered to be decreasing in the semi-solid solder paste, the chip could travel in the semi-solid solder paste for a period of time (200 μm/50 mm/s) =4 milliseconds.

Step S204, when detecting that the current variation value of the first motor 21 exceeds the preset current range in the process that the suction nozzle drives the workpiece to continuously descend at the second speed, sending a motor stop instruction to the first motor 21; wherein the motor stop command is for controlling the rotor of the first motor 21 to stop rotating.

In this embodiment, if the workpiece does not contact the semi-solid solder paste during the continuous lowering of the workpiece at the second speed by the suction nozzle, the current should be stable, but in consideration of the fluctuation of the electrical signal, there may be a slight fluctuation of the current, for example, the fluctuation range may be about 0.001A (the specific range depends on different circuit systems, and in practice, the range may be obtained by monitoring the fluctuation of the current when the workpiece does not contact the semi-solid solder paste during the continuous lowering of the workpiece at the second speed by the suction nozzle). In this example, taking the preset current range of 0.1A as an example, setting the preset current range can avoid misoperation caused by fluctuation of the system electrical signal.

The principle of this embodiment is that, by using the proportional relation between the torque and the current of the first motor, when the chip or the component is blocked by the PCB board, in order to reach the target value, when the PID controller of the motor detects that the speed fed back by the speed loop decreases, the current is increased to increase the torque so as to overcome the blocking of the chip or the component, so that the chip or the component can be judged to be contacted with the semisolid solder paste when the detected current variation value exceeds the preset current range, so as to immediately send out the motor stop command, and in cooperation with the second speed set in step S202, the time that the chip can travel in the semisolid solder paste is (200 μm/50 mm/S) =4 ms, which is longer than the response time of the microsecond level of the servo motor system, can send out the motor stop command before the bottom of the chip hits the PCB board (such as a bonding pad), and reduce the damage caused by overshoot to the chip or the component (hereinafter referred to as workpiece). It should be understood that in the present embodiment, it should be ensured that the current variation value of the first motor 21 caused by the semisolid solder paste resistance exceeds the preset current range, and specifically, the preset current range may be set according to the measurement result in the measurement stage.

In summary, compared with the prior art, the present embodiment has at least the following advantages:

2. In the present invention, when the lower end of the chip or the component contacts the semi-solid solder paste, the suction nozzle receives the resistance of the semi-solid solder paste, the current of the first motor 21 is changed (i.e. increased) in response to the resistance after the response time of microsecond level (such as the total time of speed loop, current sampling, calculation, etc. is 500 microseconds), and when the current change value exceeds the preset current range, the first motor 21 is controlled to stop rotating. In an ideal situation, the chip should stop moving immediately when contacting the semisolid solder paste, but the overshoot problem is caused by the delay response of the servo system, namely, the chip moves in the semisolid solder paste for a microsecond time, and in the invention, the kinetic energy of the semisolid solder paste is absorbed and buffered by the semisolid solder paste due to the impulse generated by the overshoot of the suction nozzle in the microsecond time, so that the damage to the chip or the component (hereinafter referred to as a workpiece) caused by the overshoot can be reduced.

Further, in one embodiment, the suction nozzle is driven by a lifting mechanism to realize lifting motion, the lifting mechanism includes a first motor 21, a transmission mechanism and a ball screw pair 23 that are sequentially in transmission connection, in the chip mounter 15, the lifting mechanism is generally implemented by using a servo electric cylinder 20, as shown in fig. 7, the servo electric cylinder 20 is generally formed by the ball screw pair 23, a servo motor (i.e. the first motor 21), a telescopic tube front end connector 24, and a transmission mechanism, and the transmission mechanism mostly adopts a structural mode of transmission of a planetary reducer 22, transmission of a synchronous belt, or a combination of the two. In this embodiment, the transmission mechanism adopts the speed reducer 22, and the inertia effect of the motor rotor when stopping rotating acts on the input end of the speed reducer 22, but because the speed reducer 22 has a braking effect, the output end of the speed reducer 22 is not affected, that is, the inertia shake of the motor at the stopping moment is not transmitted to the chip, so as to ensure the stop effect of the chip in the semisolid solder paste after the stopping rotating instruction is sent.

The method is applicable to the common lifting mechanism, and further comprises a first motor when the suction nozzle drives the workpiece to continuously descend at a second speed according to the following formula (1) 21 current of 21：

wherein ,resistance generated by semisolid solder paste to pressing into a workpiece, < >>For screw lead->For the first motor 21 speed, is->For the first motor 21 operating voltage, +.>Is the reduction ratio of the transmission mechanism, +.>For the transmission efficiency of the first motor 21 to the ball screw, -, a>The transmission efficiency of the ball screw is achieved.

In this embodiment, the current of the first motor 21 conforms to formula (1) when the suction nozzle drives the workpiece to descend at the second speed, so that the downward thrust of the ball screw to the workpiece is ensured to be larger than the resistance of the semisolid solder paste to the workpiece, and the contact point on the back of the chip can be ensured to be smoothly pressed into the semisolid solder paste to be fully contacted with the semisolid solder paste. It should be noted that it is necessary to set the current of the first motor 21 when the suction nozzle drives the workpiece to descend at the second speed according to the formula (1). Taking a kollmorgan (kollmorgan) servo driver as an example, the response time of the speed loop needs 62.5 microseconds, if the current of the first motor 21 is not set according to the formula (1) when the suction nozzle drives the workpiece to descend at the second speed, the downward thrust of the ball screw to the workpiece is possibly smaller than the resistance of the semi-solid solder paste to the workpiece, and because the speed loop and other time delays of the servo system are 500 microseconds, the workpiece is possibly subjected to the solder paste resistance and cannot be continuously pressed into the solder paste. Obviously, when the chip is subjected to resistance (namely when the chip contacts the semisolid solder paste), the motor stop command can be sent after 500 microseconds due to the micron-level delay; if the suction nozzle is not arranged according to the formula (1), the first motor 21 current is generated when the suction nozzle drives the workpiece to descend at the second speed, so that the contact point on the back surface of the chip cannot be smoothly pressed into the solder paste, and insufficient contact between the contact point and the solder paste may be caused. The formula (1) provided in this embodiment aims to solve the above-described problem.

Based on the above embodiment, in this embodiment, the method further includes determining the second speed according to the following formula (2)：

wherein ,is a depth coefficient, said->Is the thickness of semisolid solder paste +.>To determine the resulting delay period.

In this embodiment, in order to ensure that the contact point at the bottom of the chip is fully contacted with the solder paste, the depth coefficient m is set to 1/2, that is, the chip is pressed into 1/2 of the thickness of the semi-solid solder paste, and in this embodiment, if the thickness h=200 μm of the semi-solid solder paste is measured to obtain a delay time of 0.5ms, the second speed is calculated to be 1/2×200 μm/0.5 ms=200 mm/s. In this embodiment, the travelable duration is 1 millisecond.

As described above, the present embodiment provides a scheme for adjusting the depth of pressing the contact point of the workpiece (chip or component) into the semi-solid solder paste, so as to adjust the specific pressing depth according to different production scene requirements.

Specifically, as shown in FIG. 3, in one embodiment, a process for determining parameters is provided.

In the measurement flow, the delay time length is measured according to the following steps：

In step S302, during the process that the suction nozzle drives the workpiece to continue to descend at the second speed, the pressure sensor is used to monitor the change of the suction nozzle pressure, the instant of abrupt change of the value output by the pressure sensor is used as the first instant, and when the current change value of the first motor 21 is detected to exceed the preset current range, a motor stop instruction is sent to the first motor 21.

It should be noted that, when the delay time is measured, the signal transmission and processing delay of the servo system corresponding to the lifting mechanism is mainly measured, so that all the suction nozzles adopting the servo system of the same model on one chip mounter production line 10 can only measure a single suction nozzle, and in general, for consistency, the suction nozzles on the chip mounter production line 10 from the factory adopt the servo system of the same model. For the suction nozzle adopting different servo systems, the suction nozzle driven by each type of servo system can be measured respectively, for example, three types of servo systems exist, namely, motors in the corresponding servo systems can be defined as a first motor, a second motor and a third motor, and the measuring steps are executed for the first motor, the second motor and the third motor respectively. How to monitor the change of the suction nozzle pressure by using the pressure sensor belongs to the prior art, and reference may be made to reference 2 or other documents specifically, and details are not repeated here.

Step S304, after the first time, takes the time when the value output by the pressure sensor is stable as the second time.

It may be connected that when the first motor 21 stops rotating, the chip or element does not continue to travel any more, at which time the value output by the pressure sensor stabilizes.

Step S306, calculating the difference between the second time and the first time to obtain the delay time。

In this embodiment, when the workpiece touches the semi-solid solder paste, the pressure sensor with high sampling frequency can quickly detect the touch, for example, a pressure sensor with sampling frequency of 2Mhz is adopted, and the response time is 500 nanoseconds. The embodiment can accurately measure the delay time of the nanometer level error.

Based on the above embodiment, in the measurement process, the resistance of the semisolid solder paste to the pressing-in work piece is measured according to the following steps：

In determining the delay time periodIn the process of (1), the maximum value of the output of the pressure sensor is taken as the resistance of the semisolid solder paste to the pressing-in workpiece +.>。

In the embodiment, the maximum value of the output of the pressure sensor is taken as the resistance of the semisolid solder paste to the pressed workpieceUnder the condition of conforming to the formula (1), the thrust force can be ensured to be larger than the maximum resistance force when the solder paste moves, so that the moving speed in the solder paste is ensured not to drop too much, and the moving depth is ensured.

For example, assuming a delay time of 0.5 milliseconds, the pressure sensor employs a frequency of once every 5 microseconds, 200 times per millisecond, the maximum of 100 values may be selected as the resistance value Ensuring the smooth proceeding of the workpiece pressing.

As shown in fig. 4, in one embodiment, the method further comprises:

in step S402, a measurement temperature range and a measurement humidity range are obtained when resistance of the semisolid solder paste to pressing into the workpiece is measured.

For example, the temperature range is measured at 20-25℃and the humidity range is measured at 40% -60%.

And step S404, real-time adjustment of the on-site humidity in a measured temperature range is performed during the surface mounting, and real-time adjustment of the on-site humidity in a measured humidity range is performed.

In this embodiment, considering that the temperature and the humidity have a great influence on the hardness of the solder paste, the humidity and the temperature are adjusted in real time on the site of the patch, and the temperature and the humidity are kept within the range of the measurement, so that the control method is executed in the optimal environment to ensure the effect of the patch.

In some cases, if the content of the hardener in the lead-free solder paste is too high, the hardener reacts gradually at room temperature, resulting in gradual hardening of the solder paste, and the hardening speed increases with time. For example, for the production of some high-precision electronic products, lead-free solder paste with higher addition amount of hardening agent is adopted to improve the reliability and durability of the welding spots.

Therefore, it is also necessary to consider the influence of time on the hardness of solder paste for this type of the chip production line 10. The following examples are provided:

When the solder paste component is detected as the target component, the resistance of the semisolid solder paste to the pressed workpiece is measured for the first dispensing batch of PCB boardsAs shown in fig. 5, in this embodiment, the method further includes:

step S502, sequentially measuring the resistance of the semisolid solder paste to the pressed workpiece for the PCB board of the subsequent dispensing batchIs carried out by a method comprising the steps of.

In this embodiment, a piece of PCB board is clocked from the completion of dispensing (i.e. solder paste is applied to a pad of the PCB board), and the time period that it passes through transportation, defect detection (AOI detection or SPI detection), patch coordinate detection and compensation, and patch completion in order is counted as a waiting period T. After the waiting period T is obtained, dividing each PCB into corresponding batches according to the time elapsed by the distance between the PCBs and the dispensing time point. For example, when the time elapsed between the waiting period t=10 seconds and the time point of completing the dispensing of the four printed circuit boards A, B, C, D is 1 second, 12 seconds, 21 seconds, and 33 seconds, the dispensing batches of the four A, B, C, D printed circuit boards are the first dispensing batch, the second dispensing batch, the third dispensing batch, and the fourth dispensing batch in sequence, which are expressed as dispensing batches= [ T/10] +1 in terms of formulas, wherein [ ] is a whole-order symbol.

The PCB boards are divided according to the dispensing batch to determine the hardening condition of the semi-solid solder paste under different waiting time, because in the chip mounter production line 10 shown in fig. 1, the time consumed for dispensing is generally less than the time consumed for mounting, a large number of printed circuit boards with finished dispensing are accumulated on the docking station 13, and the longer the residence time (which is generally considered to be positively correlated with the waiting time) on the docking station 13, the lead-free solder paste with excessive hardener content will gradually react at room temperature, so that the solder paste gradually hardens, and the hardening speed will be accelerated with the time. When the semisolid solder paste hardens to a certain degree, the resistance of the semisolid solder paste to the pressed workpiece, which is measured in the measuring process, is causedNo longer applicable, therefore, the present embodiment requires determination of the resistance of the semi-solid solder paste to the pressing-in of the workpiece>Application range in latency.

In step S504, when it is detected that the resistance value exceeding the preset ratio is greater than the maximum resistance value measured by the first dispensing lot, the current dispensing lot value is set as the lot threshold a.

In one example, the delay time is 0.5 ms, the pressure sensor uses a frequency of once every 5 μs, 200 times every ms, and A, B, C, D, E, F four PCBs are taken as an example, and the maximum resistance (i.e., resistance) measured in the first dispensing lot (i.e., A board, first dispensing lot) ) 2N, the preset proportion is 20%, 5 values are more than 2N in the measuring process of the B plate and the second dispensing batch, and the proportion of more than 2N is 5%; in the measurement process of the C plate and the third dispensing batch, 8 values are more than 2N, and the proportion of more than 2N is 8%; 13 values are larger than 2N in the measuring process of the D plate and the fourth dispensing batch, and the proportion of the values larger than 2N is 13%; in the measurement process of the E plate and the fifth dispensing batch, 17 values are more than 2N, and the proportion of more than 2N is 17%; in the measurement process of the F plate and the sixth dispensing batch, 21 values are larger than 2N, the proportion of the values larger than 2N is 21% and the proportion is larger than 20% of the preset proportion; it is apparent that the sixth dispensing lot is eligible, with lot threshold A set to 6.

Step S506, monitoring the number of the PCB boards in a state of waiting for the pasting after the glue dispensing is completed during pasting.

The number of the PCB boards positioned on the connection table 13 can be counted by the connection table 13 between the dispensing equipment and the patch equipment, for example, the number of the PCB boards fed into and output from the connection table 13 can be counted by using an optical sensor, and the specific counting scheme belongs to the prior art and is not repeated here.

In step S508, when the number of the printed circuit boards in the state to be pasted after the dispensing has been completed reaches the preset number, the dispensing is paused.

Step S510, determining the preset number by the following formula (3) :

wherein ,the number of the patch stations in the current working state.

It should be noted that, in order to improve the production efficiency, there may be a plurality of mounting stations in one chip mounter 15, and each mounting station may independently complete the mounting operation of a PCB board.

It can be understood that it is difficult to count the waiting time of the PCB board after each piece of dispensing is completed in the chip mounter production line 10, but the existing functions of the production line 10 are utilized to count the number of PCB boards on the docking station 13, so that the control of the waiting time of the PCB board after dispensing is completed can be achieved by fully utilizing the functions of the production line 10 by converting the relationship between the waiting time of the PCB board and the number of PCB boards on the docking station 13. The present embodiment is realized by the formula (3) in step S510.

Specifically, when a new Printed Circuit Board (PCB) with dispensing completed is sent to the docking station 13, the number of PCBs with dispensing completed in a state to be pasted is increased by one, the PCB newly sent to the docking station 13 is formed into a G board, and for the G board, since solder paste will harden to a condition that is not in compliance after a time of a×t passes, the longest time allowed to wait is (a-1) ×t (i.e., (a-1) cycles), and for the chip mounter 15 with k pasting stations, each cycle T can consume k PCBs from the docking station 13, so n= (a-1) k PCBs can be consumed after (a-1) cycles. Conversely, if the number of PCB boards on the docking station 13 is greater than n= (a-1) ×k PCB boards, the solder paste newly fed onto the PCB boards on the docking station 13 will harden to an unsatisfactory condition, so that the function of the production line 10 can be fully utilized to control the waiting time of the PCB boards after dispensing according to the formula (3), and the resistance of the semi-solid solder paste to the pressed workpiece measured in the measurement process is ensured Can be continuously applied to lead-free solder paste with excessive hardener content.

On the other hand, the prior art conveys the PCB board in various processing stations by means of a conveyor belt or robot 14. Generally, no matter when the PCB processed by the dispensing station is transferred to the pasting station by the conveyor belt or the manipulator 14, the PCB is considered to be transferred to a position designated by the pasting station, and then the PCB is fixed at the position, and the pasting device controls the cylinder or the motor of the pasting device to act on XYZ coordinates according to the coordinates of each target point to be pasted on the PCB obtained in advance, so that the component can be sent to each target point on the PCB to realize pasting.

However, in actual operation, when the patch device is controlled to perform the patch according to the preset target point coordinates, there is a deviation between the position where the component is sent to the PCB and the actual target point position on the PCB. The reason for this is as follows:

1. mechanical error: when the conveyor belt or the manipulator 14 transfers the PCB from the dispensing station to the placement station, the actual position of the PCB on the placement station may deviate from the preset position due to the accuracy limitation of the mechanical equipment. Furthermore, the movement of the patch device in the XYZ coordinate axes may also cause the element patch position to deviate from the target point due to mechanical errors.

Pcb board shape change: in the processing process, the PCB may have a shape change (e.g. bending, twisting, etc.) during the patch process due to various reasons (e.g. temperature change, elasticity of the material itself, etc.), which may shift the actual target point position during the patch, resulting in errors when the patch device patches according to the preset target point coordinates.

Therefore, in order to solve the problem that the position where the component is sent to the PCB is deviated from the actual target point position on the PCB, as shown in fig. 6, the following embodiment is provided:

in this embodiment, when the PCB board is transported to the bonding station, the method further includes:

step S602, obtaining a target image of the PCB on the surface mounting station.

Step S604, comparing the target image with corresponding Mark points on a preset template image to determine whether deviation exists; the template image is an image of a standard PCB, and the standard PCB is identical to the PCB on the surface mounting station in shape and size.

Step S606, if the deviation exists, calculating the displacement and the angular offset of each mounting point of the PCB on the mounting station relative to the standard position on the standard PCB.

And step S608, compensating the mounting coordinates and the rotation angle by using the displacement and the angular offset.

It should be noted that, there are two implementations of step S602 to step S608, the first is a 2-point reference Mark point compensation scheme as described in reference 3, which is a scheme commonly used in the prior art, and the specific implementation thereof may be referred to reference 3 and will not be described herein.

Reference 3: xu Yanjie the surface mounting technology experiment platform software system key technology research [ D ]. Western An university of electronic technology, 2015.

The second is the 4-point reference Mark point compensation scheme provided by the invention, and the effect of the four-point reference Mark point compensation scheme can be known by comparing with the 2-point reference Mark point compensation scheme.

As shown in table 1, the 2-point reference Mark point compensation is performed by performing 1-time planar rectangular coordinate transformation (parallel movement, expansion, contraction, rotation) using the image recognition result of the reference Mark of the 2-point substrate, and position compensation is obtained. I.e. the transformed coordinate system is still a planar rectangular coordinate. At this time, when the PCB is deformed, a problem occurs in the case of twisting (temperature change causes expansion and shrinkage of the PCB, twisting of the PCB during manufacturing, etc.), and the coordinate system on the PCB is not a planar rectangular coordinate system. Therefore, the coordinate transformation method of the 2-point reference Mark point cannot obtain normal high-precision position compensation when the PCB is distorted. At this time, in order to solve the above-described problem, a compensation scheme using the 4-point reference Mark point provided in the present embodiment may be considered. The compensation of the 4-point reference Mark point is to use any plane coordinate on the PCB to transform to any plane coordinate, and high-precision position compensation can still be obtained for the distorted PCB.

The detailed reference for the coordinate transformation is as follows:

4-point coordinate transformation

(1) Transformation method

Assume that:

theoretical coordinates of A, B, C, D-4 point reference Mark;

a, b, c, d-measured coordinates of point reference Mark;

theoretical coordinates of m— location of the mounting point;

m- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -isto be) a coordinate-converted.

As shown in figures 8 and 9 of the drawings,

(1) let the straight LINE connecting the arbitrary inner division points alpha (1-alpha) of the opposite sides AD, BC of the quadrilateral ABCD be LINE 1.

And M is a point on a LINE passing through LINE1, and α is calculated.

(2) The straight LINE connecting any inner division points beta (1-beta) of AB and DC is LINE 2.

LINE2 is also passing through point M to find β.

(3) Let the straight line connecting the arbitrary inner points alpha (1-alpha) of the opposite sides ad, bc of the quadrangle abcd be line 1.

(4) Similarly, the straight line connecting any inner points beta (1-beta) of the opposite sides ab, dc of the quadrilateral abcd is taken as line 2.

(5) Let the intersection of straight lines line1 and line2 be the coordinate of transformation point M of M coordinate, namely deformation, and the corresponding alpha, beta of each point in the transformation process of coordinate position before and after the distortion is unchanged.

(6) The difference of the inclination angles of the LINE1 and the difference of the inclination angles of the LINE2 and the LINE2 are respectively obtained, and the average value of the two differences is taken as the angle deviation of coordinate transformation.

(2) Actual calculation

(1) To simplify the coordinate calculation, the following conditions are satisfied for points a, B, C, D, and points a, B, C, D.

1) More than 3 points of the points A, B, C and D4 are not on the same straight line.

2) The order of points A, B, C, D4 should be such that a quadrilateral is defined. The situation as in fig. 10 (a) is not allowed, i.e. sides AD and BC are not crosswise.

3) Any interior angle of the quadrilateral ABCD cannot exceed 180 degrees. The case of fig. 10 (b) is not allowed, i.e. the internal angle ++abc is above 180 degrees.

4) The above 3 conditions are satisfied in the same way by the corresponding 4 points a, b, c, d.

(2) Solving for

In AD linesThe position coordinates of the inner points are ((1-)>)AX+/>DX, (1-/>)AY+/>DY), in BC lineThe position coordinates of the inner points are ((1-)>)BX+/>CX, (1-/>)BY+/>CY), the equation for LINE1 through this 2 point is: />

Let the straight LINE1 pass through the point M (MX, MY), substituting x=mx, y=my into the arrangement, and obtainingThe 2 nd order equation of (2):

wherein ,

A=(AY-DY)(AX-BX+CX-DX)-(AX-DX)(AY-BY+CY-DY)

B={(MY-AY)(AX-BX+CX-DX)-(AY-CY)(AX-BX)}-{(MX-AX)(AY-BY+CY-DY)-(AX-DX)(AY-BY)}

C=(MY-AY)(BX-AX)-(MX-AX)(BY-AY)

the above equation is not necessarily a real solution, but may be an imaginary solution.

In this case, the calculation is performed as a real solution. (the imaginary root considers that the effective range of the coordinate transformation is exceeded) the real solution of this equation is:

where AD BC, a=0, where α= -C/B. Also, since 1 of the solutions of 2 α is the intersection of the straight lines AD and BC, the solution needs to be deleted, which is often considered to be out of the effective range of the mounting compensation position. (3) Beta-finding

The calculation was performed in the same manner as in the case of the calculation of α. The results are shown below.

β={-B±√(B2-4AC)}/2A

wherein

A=(AY-BY)(AX-BX+CX-DX)-(AX-BX)(AY-BY+CY-DY)

B={(MY-AY)(AX-BX+CX-DX)-(AX-DX)(AY-BY)}-{(MX-AX)(AY-BY+CY-DY)-(AY-DY)(AX-BX)}

C=(MY-AY)(DX-AX)-(MX-AX)(DY-AY)

AB = -C/B at DC, a = 0, at which time β = -C/B.

Also, since 1 of the solutions for 2 α is the intersection of straight lines AB and DC, this solution needs to be deleted.

(4) Solving the coordinates of the point M (MX, MY) obtained by transforming the coordinates of the point M (MX, MY) by 4 points

The alpha and beta values obtained by (2) and (3) are used.

Let the straight line passing through the respective internal division points alpha (1-alpha) on ad, bc be line1,

the equation is:

(C-A)(Y-B)=(D-B)(X-A)

wherein ,

A=(1-α)ax+αdx, B=(1-α)ay+αdy, C=(1-α)bx+αcx, D=(1-α)by+αcy。

similarly, let ab, dc each inner division point beta (1-beta) straight line be line2,

the equation is:

(G-E)(Y-F)=(H-F)(X-E)

wherein ,

E=(1-β)ax+βbx,F=(1-β)ay+βby, G=(1-β)dx+βcx, H=(1-)dy+βcy 。

the intersection of line1 and line2 is m (mx, my),

substituting mx, my into the solution,

when (I) C-A is approximately equal to 0 and G-E is approximately equal to 0,

mx=(J*M-K*L)/(J-L), my=(M-K)/(J-L)，

wherein

J=(C-A)/(D-B), K=A-J*B, L=(G-E)/(H-F), M=E-L*F，

(II) when C-A is equal to 0 and G-E is equal to 0,

mx=(J*M+K)(1-J*L), my=(K*L+M)/(1-J*L)，

wherein

J=(C-A)/(D-B), K=A-J*B, L=(H-F)/(G-E), M=F-L*E，

(III) when C-A is equal to 0 and G-E is equal to 0,

mx=(K*L+M)(1-J*L), my=(J*M+K)/(1-J*L)，

wherein

J=(D-B)/(C-A), K=B-J*A, L=(G-E)/(H-F), M=E-L*F ，

(IV) when C-A is not equal to 0 and G-E is not equal to 0,

mx=(M-K)/(J-L), my=(J*M-K*L)/(J-L)。

wherein

J=(D-B)/(C-A), K=B-J*A, L=(H-F)/(G-E), M=F-L*E。

(5) Calculate the rotation angle of the coordinates of point m (mx, my)

Let LINE1 direction vector be L1

Let LINE2 direction vector be L2

Let the direction vector of line1 be l1

Let the direction vector of line2 be l2

LINE1 and LINE1 are at an angle θ1 and thus, COS (θ1) = (L1+L1)/(L1|l1|)

The angle of LINE2 and LINE2 is θ2 and thus, COS (θ2) = (L2+L2)/(|L2|l2|)

The rotation angle is set to be theta,

θ=(θ1+θ2)/2。

actual calculation:

θ=[sin-1{F/√(E2+F2)}-sin-1{B/√(A2+B2)}+cos-1{G/√(G2+H2)}– cos-1{C/√(C2+D2)}]/2.

wherein ,

A=(1-α)BX +αCX - ((1-α)AX +αDX),

B=(1-α)BY +αCY - ((1-α)AY +αDY),

C=(1-β)DX +βCX - ((1-β)AX +βBX),

D=(1-β)DY +βCY - ((1-β)AY +βBY),

E=(1-α)bx +αcx - ((1-α)ax +αdx),

F=(1-α)by +αcy - ((1-α)ay +αdy),

G=(1-β)dx +βcx - ((1-β)ax +βbx),

H=(1-β)dy +βcy - ((1-β)ay +βby)。

in summary, according to the compensation scheme of the 4-point reference Mark point provided by the embodiment, the rotation angle θ to be compensated for each mounting point and the coordinate M (MX, MY) after the compensation for each mounting point can be calculated, for example, the coordinates of the mounting point on the standard PCB board are M (MX, MY), and after the compensation for the M point is completed by using the compensation scheme of the 4-point reference Mark point, the suction nozzle is controlled to move to the coordinate M (MX, MY) and rotate for mounting by the angle θ. The scheme provided by the embodiment can be suitable for coordinate compensation of the distorted PCB.

In one embodiment, there is provided an electronic device including: the precise mounting control method of the PCB chip mounter comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, wherein the processor executes the steps of the precise mounting control method of the PCB chip mounter when executing the program. The step of the precise mounting control method of the PCB mounter may be the step of the precise mounting control method of the PCB mounter of the above-described respective embodiments.

In one embodiment, a computer-readable storage medium is provided, where the computer-readable storage medium stores computer-executable instructions for causing a computer to perform the steps of the precision mounting control method of the PCB mounter. The step of the precise mounting control method of the PCB mounter may be the step of the precise mounting control method of the PCB mounter of the above-described respective embodiments.

Those skilled in the art will appreciate that all or part of the processes in the methods of the above embodiments may be implemented by a computer program for instructing relevant hardware, where the program may be stored in a non-volatile computer readable storage medium, and where the program, when executed, may include processes in the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include non-volatile and/or volatile memory. The nonvolatile memory can include Read Only Memory (ROM), programmable ROM (PROM), electrically Programmable ROM (EPROM), electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRA), memory bus direct RAM (RDRA), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), among others.

The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

Claims

1. The precise mounting control method of the PCB chip mounter is characterized by comprising the following steps of:

when the current change value of the first motor is detected to exceed the preset current range in the process that the suction nozzle drives the workpiece to continuously descend at the second speed, a motor stop instruction is sent to the first motor; wherein the motor stop instruction is used for controlling the rotor of the first motor to stop rotating;

the suction nozzle is driven by a lifting mechanism to realize lifting movement, and the lifting mechanism comprises a first motor, a transmission mechanism and a ball screw pair which are sequentially connected in a transmission way; the method further comprises determining the current of the first motor when the suction nozzle drives the workpiece to continuously descend at the second speed according to the following formula (1) ：

wherein ,resistance generated by semisolid solder paste to pressing into a workpiece, < >>For screw lead->For the first motor speed,/->For the first motor operating voltage, < >>Is the reduction ratio of the transmission mechanism, +.>For the transmission efficiency of the first motor to the ball screw, < >>The transmission efficiency of the ball screw is achieved.

2. The precise mounting control method of a PCB mounter according to claim 1, wherein said method further includes determining said second speed according to the following formula (2):

3. The precise mounting control method of a PCB mounter according to claim 2, further comprising a measurement process in which said delay period is measured according to:

monitoring the change of the pressure of the suction nozzle by using a pressure sensor in the process that the suction nozzle drives the workpiece to continuously descend at a second speed, taking the moment of abrupt change of the numerical value output by the pressure sensor as a first moment, and sending a motor stopping instruction to the first motor when detecting that the current change value of the first motor exceeds a preset current range;

After the first moment, taking the moment when the value output by the pressure sensor is stable as a second moment;

calculating the difference between the second time and the first time to obtain the delay time length。

4. The precise mounting control method of a PCB mounter according to claim 3, further comprising a measurement process in which resistance of the semisolid solder paste to the pressed work piece is measured according to:

5. The precise mounting control method of a PCB mounter according to claim 4, wherein said method further comprises:

obtaining and measuring the resistance of the semisolid solder paste to the workpiece pressingA measurement temperature range and a measurement humidity range;

and when the patch is attached, the on-site humidity is adjusted in real time to be in a measured temperature range, and the on-site humidity is adjusted in real time to be in a measured humidity range.

6. The method according to claim 4, wherein after detecting the solder paste composition as a target composition and completing the step of measuring the resistance of the semi-solid solder paste to the pressed workpiece for the first dispensing lot of PCB boards, the method further comprises:

Sequentially measuring resistance of semisolid solder paste to pressed workpieces on PCB boards of subsequent dispensing batchesIs carried out by the steps of (a);

when the resistance value exceeding the preset proportion is detected to be larger than the maximum resistance value measured by the first dispensing batch, setting the value of the current dispensing batch as a batch threshold A;

during the pasting, monitoring the number of the PCBs in a state of pasting after finishing the pasting;

when the number of the PCBs in the state of being stuck after the dispensing is finished reaches a preset number, the dispensing is stopped;

the preset number is determined by the following formula (3):

wherein ,the number of the patch stations in the current working state.

7. The precise placement control method of a PCB placement machine of claim 4, further comprising, when transferring the PCB to a placement station:

acquiring a target image of a PCB on a patch station;

comparing the target image with a Mark point corresponding to a preset template image to determine whether deviation exists; the template image is an image of a standard PCB, and the standard PCB is identical to the PCB on the surface mounting station in shape and size;

if deviation exists, calculating displacement and angular offset of each to-be-mounted point of the PCB on the surface mounting station relative to a standard position on a standard PCB;

And compensating the mounting coordinates and the rotation angle by using the displacement and the angle offset.

8. An electronic device, comprising: a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements a precision mounting control method of a PCB mounter according to any one of claims 1 to 7 when executing the program.

9. A computer-readable storage medium storing computer-executable instructions for causing a computer to execute a precision mounting control method of a PCB mounter according to any one of claims 1 to 7.