JP2005199628A - Screen printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system which rapidly makes appropriate screen printing conditions ensuing from the switching of the model of a circuit board and the change of a solder paste, when the solder paste is screen-printed to the circuit board in an actual production. <P>SOLUTION: In this screen printing method, the actual results of printing to a production substrate are accumulated as templates and the templates are used or the results of test printing are analyzed using a test substrate, a test screen mask and a test paste, and the analytical results are registered as the templates; and the printing conditions are set up based on the template data, when the actual production is started. Refer to Fig.10 and step 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a screen printing method for printing a solder paste and a conductive adhesive or a printing paste such as an electronic circuit forming paste on an electronic circuit forming substrate such as a printed circuit board through a screen mask. It is.

  Screen printing is a technique for transferring a solder paste onto a screen mask, for example, onto a circuit board by a squeegee operation. In the case of the solder paste to be transferred, it is a mixed material of metal particles, which is a conductive material, and a flux. The main component of the flux is alcohol, but its components are complex and have many types for various purposes such as the electrical joining function of electrodes, the temporary fixing function of electronic parts, and the storage performance. Sophisticated knowledge and experience are required to quickly deal with such solder paste in response to setup changes involving various types of printed circuit boards. In general, in the case of solder paste, the factors that determine the quality of screen printing are not only the selection of the squeegee device of the screen printing device itself but also its operation method, the solder paste characteristics, the quality of the screen mask, and the requirements of the printed circuit board. Accuracy is deeply involved. As another factor on the printing apparatus side, a method of detaching the screen mask from the circuit board is also important. With respect to circuit boards to be printed, with the recent development of electronic devices, the reduction in size and weight, miniaturization, and enhancement of functions are progressing. Improvements in the functions and quality of screen masks and solder pastes are always lagging against the evolution of electronic components and circuit boards, and screen printing devices and their operation methods are sufficiently addressing the evolution of electronic devices. I can't say that.

Production engineers and operators in the screen printing process will not only improve the production of circuit boards and improve the quality of solder paste, but also the proper operation of printing equipment in order to quickly respond to the start-up of circuit board production and model changes. Despite spending a lot of effort and time, it has not yet come out of the situation where it is necessary to rely on the capabilities of the individual operator. In addition, as circuit boards built into electronic devices are becoming more and more miniaturized and miniaturized as described above, the reliability of the solder paste printing process is improved in the subsequent electronic component mounting process and reflow process. This will have an increasing impact on productivity and reliability. Naturally, the function required for the screen printing process will gradually become more sophisticated, and it will not be overlooked that it will occupy a more important position than the electronic component mounting process in the entire circuit board production process.

One solution in this background is to use information recording media such as barcodes on circuit boards, screen masks, and solder pastes, and collect these information by sucking up information necessary for the printing process. Attempts have been made to reduce the time for changing the circuit board model. However, by simply using a limited information medium such as a barcode, it is difficult to realize highly reliable printing that can sufficiently cope with variation factors associated with model changes and paste material variations. This is because simply extracting individual factor element information such as the characteristics of screen masks and solder paste from the bar code information only absorbs variable element information and does not satisfy the overall appropriate conditions of screen printing itself. Because.

Japanese Laid-Open Patent Publication No. 06-262749 Japanese Laid-Open Patent Publication No. 11-151797 JP 11-320823 A

  The material handled in the screen printing process is composed of various chemical substances such as the size and shape of metal particles in the case of solder paste, and the presence or absence of rosin and the solvent used in the flux component. For this reason, not only the printing characteristics differ depending on the type of paste, but also qualitative changes over time are significant and environmental dependence is high. In addition, since a plurality of factors that determine the success or failure of screen printing are intricately intertwined with each other, it is extremely difficult to quickly optimize printing conditions for different required specifications for each production circuit board. It is a problem to be solved by the present invention to efficiently operate the screen printing process by easily and quickly carrying out the optimization of the printing conditions without depending on the operator's personal skill and experience.

  In the present invention, the actual production circuit board is changed by recording / accumulating the print data on the actual production circuit board by the corresponding screen printer or the analysis result data of the pretest printing using the destination board. Even when the operator is changed, or when the paste to be used is changed, it is possible to derive appropriate printing conditions in each case, as in the case of accurate judgment by a skilled operator. This can greatly reduce the time and cost of trial and error in screen printing devices due to model switching, introduction of new equipment, and operator fluctuations, and the effect on the entire electronic circuit board production line is immeasurable.

  In screen printing on circuit boards, test printing is performed prior to printing on actual production boards, and the test result data is recorded as template data. Based on this template data, model changes and paste changes are made. Quickly select the proper printing conditions to accompany.

  A basic function of a general screen printing machine is shown in FIG. The squeegee 1 is a double squeegee type, and is a pair. The squeegee operation 5 can be printed twice for each reciprocation. In FIG. 1, the paste 15 is filled in the opening 23 of the screen mask 10 by moving from the left to the right, and transferred to the circuit board 11. The squeegee holder 3 has a function of pressing the squeegee 1 against the screen mask with a predetermined force, and is connected and held by the squeegee grip 2 so that the angle 4 of the squeegee with respect to the mask can be changed. As an example, the squeegee vertical movement drive device 6 uses a step motor 6. The squeegee head 16 is provided with a nut of the ball screw 8 and is connected to a drive motor 7 that moves the squeegee head 16. When the drive motor 7 rotates, the squeegee head 16 moves via the ball screw 8 and simultaneously the printing operation of the squeegee 1 is performed.

  A circuit board 11 is held by a substrate backup device 14 below the screen mask 10. If there are electronic components previously mounted on the back surface of the circuit board 11, support pins (not shown) are often set. In this embodiment, the lifting drive 13 of the backup device 14 is a servo motor. Thereby, in order to detach the circuit board 11 from the screen mask 10 after the screen printing operation is completed, a predetermined detachment speed, acceleration, and stroke can be set.

Although not shown because it is not deeply related to the subject matter of the present invention, an image capturing camera for aligning the pattern opening of the screen mask and the pattern of the circuit board, and the above-described image based on the captured image. A position correcting device for precisely aligning the opening of the screen mask and the pattern of the circuit board is required. Similarly, although not shown because it is not deeply related to the subject matter of the present invention, a circuit board to be screen-printed is generally discharged out of the printing press and loaded with a new circuit board when printing is finished. There is a need. For this purpose, a circuit board transfer device for carrying in and discharging the circuit board is necessary.

  An example of the printing factor-specific template T1 is shown in FIG. The screen mask type (M), the squeegee type (S), the base type (P), the variation factors (A to H), and the evaluation value (V) are sequentially arranged on the vertical axis of FIG. The horizontal axis in FIG. 2 records the printing result data for the hardware items (M, S, P), the printing software items (A to H), and the evaluation value (V) among the printing factors. If this print result data is obtained by printing an actual production circuit board, a good one is selected from the past data and recorded. When the print result data uses a test screen mask, a test substrate, or a test paste, the analysis result of the test print data is recorded as will be described later. Therefore, optimization of printing conditions in actual screen printing can be completed by searching for and selecting the optimum template (T1) shown in FIG. The evaluation value V is an evaluation of the printing result based on the factor variation data described in the column. For example, if the perfect score is 10, a numerical value from 1 to 10 is applied to facilitate the search for an appropriate printing condition.

  A paste function auxiliary template (T2) is shown in FIG. In this example, solder paste is taken up. As described above, the solder paste has various properties related to printing characteristics such as adhesion of electronic components to the circuit board, flux characteristics, environmental conservation, and various physical properties. It is not possible to cover all functions and properties here. Accordingly, although eight items were selected for properties that are considered to be relatively deeply related to solder paste printing, of course, the present invention is not limited to this range. There may be variations for each hardware and software of the screen printing apparatus. This template (T2) is linked to the paste type (P) in the template (T1).

  Also, the fluctuation factors (A to H) in FIG. 2 have the same meaning as the fluctuation factors (A to H) in FIG. 4, the factors (A to H) in FIG. 5, and the fluctuation factors (A to H) in FIG. 6. Have. 4 to 6 are tables for explaining a procedure for proceeding with optimization of printing conditions by test printing. FIGS. 10 and 11 are flowcharts of a procedure for proceeding with optimization by test printing.

  An example of a procedure for obtaining template data (An to Hn) for each variable in FIG. 2 will be described. Template data (An to Hn) when an actual production substrate is used only needs to be registered by evaluating the printing status of the paste transferred to the production substrate. However, precise evaluation in actual production is not easy and complicated, and therefore, oversight often occurs in the investigation of defective print locations. For this countermeasure, it is desirable to continuously correct the registered template data. In this way, if a lot of printing condition data on the actual production board is accumulated as templates (T1, T2), the choices of good printing conditions are increased accordingly.

  The level (L) in FIG. 4 is a standard value (2) that is generally considered appropriate for each of the variation factors (A to H), and the test data has a width ( By having 1) and (3), the purpose is to actively investigate the direction of each variation factor. Here, the input value is changed in three stages. In FIG. 5, the variation factors are arranged on the horizontal axis, and the variation level (L) for each variation factor is assigned to the vertical axis. In this case, the number of test prints was assigned as 18 patterns. The number of intersections between the variable factors assigned to the horizontal axis and the number of tests on the vertical axis is the above-mentioned level (L: 1 to 3), and this arrangement has long been established as an experimental design (later developed and quality engineering). What is necessary is just to implement mechanically according to the "orthogonal table".

  Next, the SN ratio η for each test in FIG. The SN ratio η is the ratio of the mean or bias squared to the square of variation, and the higher the numerical value, the better the overall evaluation. In addition, Sm described in Formula 1 is a change in average value, and Ve is an error variance. Further, n is the number of tests, and since these are known matters in the quality engineering, the detailed description is omitted here.

FIG. 6 shows the average of the SN ratio η by variation level. The SN ratio η for each printing factor (A to H) and each level (L) is calculated based on the values of η ₁ to η ₁₈ calculated in FIG. These calculation methods are also publicly known matters, and dedicated calculation software is also commercially available, and detailed description thereof is omitted here. In the series of test print analysis, the highest SN ratio η among the three levels (L) may be selected for the variation factors (A to H) in FIG. The analyzed data is registered as recommended data (An to Hn) for each variation factor as the template (T1) in FIG. The above is an example of a method for creating template data by test printing.

  An example of a test screen mask is shown in FIG. The test mask 20 is compatible with an actual production circuit board screen mask in terms of its usage. The openings 23 of the mask corresponding to the pattern are formed in a plurality of locations of the screen mask 10 in different sizes or shapes assuming the pattern of the circuit board to be printed in the printable area of the mask 10. In this case, it is desirable that the openings 23 of the same size are combined with a single row arrangement, a double row arrangement, an orthogonal row arrangement, or the like in order to facilitate evaluation of printing performance. The test substrate on which the paste is printed is not shown here, but a substrate color that makes the contrast with the paste clear is desirable in order to facilitate the evaluation of the printing performance of the printed paste. Of course, an electronic circuit wiring pattern is not necessary. This makes it possible to accurately recognize the print state of the test-printed paste and to easily evaluate the print result.

  FIG. 11 is a flowchart showing a template creation procedure for paste printing conditions by the test printing. First, a test screen mask and a test substrate are determined and set in the printing machine 101. In 101, the temperature or humidity of the printing environment is measured and recorded. Select a test paste 102. It is desirable to select a variety and type of paste that will be used in the near future. These are recorded 103 in the paste function auxiliary template. A variation factor is selected 104 based on the characteristics of the corresponding paste. The level for each variable factor is determined 105. The variable factors and test order are assigned 106 to the orthogonal table. Test printing is performed 107 in the test order of the orthogonal table. The SN ratio is calculated 108 in the order of test numbers. An average is calculated 109 for each variation level of the signal-to-noise ratio. The highest signal-to-noise ratio is selected 110 for each variation level. Finally, the optimum printing conditions for the applied paste and the variation factors are recorded in the template T1.

    However, in the case of a printed circuit board on which electronic components are actually mounted, an electronic circuit wiring pattern exists unlike a test board. This circuit pattern often forms minute irregularities on the surface of the circuit board. In some cases, through holes are formed to electrically connect the circuits on the front and back of the double-sided circuit board. Such unevenness on the surface of the circuit board becomes an obstacle for uniform printing of the paste when the circuit board is set on the circuit board by vacuum. That is, the vacuum pressure is transmitted through the unevenness of the circuit board and the through hole, and the paste in the printing pattern portion near the through hole is also evacuated, so that the printed shape of the paste transferred to the board is deteriorated. . In order to reduce this obstacle, it is desirable to provide a predetermined through hole in the test board. In this sense, it is difficult to determine the print result, but it can be said that it is meaningful to use the production substrate itself as a test substrate.

  In FIG. 8, the printing device control device 40 includes an input device 41, a communication device 42, a storage device 43, a circuit board transport device 30, a circuit board backup device 31, a screen correction device 51, a squeegee driving device 55, and a screen cleaning device 52. And an output device 44 are connected. The input device 41 is operated by an operator to input commands and data necessary for screen printing of the circuit board. The communication device 42 communicates with other devices and is connected to the host computer 70 via the LAN 85 shown in FIG. The storage device 43 is a system program for controlling the entire screen printing apparatus, a control program for individually controlling each element function of the apparatus on the system program, a production program and a circuit board for the screen printing apparatus transmitted from the host computer 70 The backup information is stored. The output device 44 outputs the production information, warnings, or newly created and corrected printing condition template information of the screen printing device to the electronic component mounting device 90 in the downstream process via the LAN 85 via the host computer 70. The information is communicated.

  The host computer 70 of the present control system is mainly intended for control related to template creation. If the control scale related to template creation is not so large, it can of course be incorporated in the control device 40 of the printing apparatus. In general, a screen printing process is often configured as a part of a plurality of processes in a circuit board production line rather than being operated as a single process. In such a case, it is desirable to control all or some of the plurality of processes collectively. If the host computer 70 and the production management computer (not shown) of the entire factory constitute a network using the LAN 85, the load on a specific control device such as a printing machine can be reduced, and basic data for circuit boards can be shared. By sharing production information, efficient operation of not only the printing process but the entire production line becomes possible.

In the case where production information of the screen printing apparatus is transmitted to the electronic component mounting apparatus 90 in FIG. 9 via the communication unit 72, the communication line LAN 85 may be used. Also, the circuit board data generated by the circuit board design CAD 95 can be used to generate a circuit pattern of a test board (not shown) to be used in the screen printing machine via the LAN 85. is there. The production support device 60 is connected to the host computer 70 via a LAN 85. If the control scale is not so large, the production support apparatus 60 may be incorporated in the control apparatus 40 of the printing apparatus. In FIG. 9, an input unit 73, a communication unit 72, a production program unit 76, a printing condition optimization unit 78, and a circuit board backup optimization unit 80 are data processing steps using data of a control device other than the printing device. is there. The display unit 74, the image processing unit 75, and the storage unit 79 are processes for storing processed data. However, the image processing unit 75 may perform reference mark recognition of the production substrate and screen mask, recognition of actually printed paste, and data analysis.

The procedure for setting the printing conditions of the production circuit board in actual production will be described with reference to the flowchart of FIG. First, the corresponding production circuit board is input, and the step of searching for the corresponding screen mask type M and squeegee type S from the template T1 stored in the storage unit 79 of the control unit 71 is S0. Next, S1 is a step of inputting paste type information to be used in actual production and searching for an approximate function and property from the paste function auxiliary template T2. If it is a past paste with a past record, or if there is an approximate one in the template T1, the process advances to an automatic setting step S8 of the printing conditions. If there is no past record corresponding to the template T1, the paste information is checked again. Step S2 for investigating whether the RFID tag information is present in the paste container. If the wireless tag is not attached, the specification is manually input to the auxiliary template T2 from the manual of the paste, and the search is performed again in step S6. If the wireless tag is attached, it is read in step S5. Next, a search for approximate printing conditions is performed in step S6. If printing conditions that are approximate as a result of the search are found, the data is set (step S8). If an appropriate printing condition approximated by the automatic search in step S6 cannot be found, provisional setting of a printing condition considered to be more appropriate from the list of templates T1 and T2 is manually performed in step S7. Step S9 of adding the temporary setting result to the templates T1 and T2. When the printing conditions are determined, the automatic operation step S10 is executed. When the actual operation is confirmed and the printing result is valid, the selected printing condition is properly registered in the template T1 as a formal one. If not, it is determined whether to perform test printing again or to try provisional setting again in step S11. In the case of the test printing step S12, the work is separately performed according to the flowchart of FIG. If the temporary setting is made again, the process returns to step S7.

  Although the wireless tag 25 shown in FIG. 7 depends on the frequency band used for the tag IC, generally, it is an IC with a built-in RF function that can exchange information in a non-contact manner within a predetermined distance. It is a tag. This wireless tag 25 is used as a medium for bidirectional information exchange such as printed circuit board information, paste information, screen mask information, screen printing device components, squeegee information, and the like, which determines printability in screen printing. By reading at, efficient operation of the screen printing process can be performed. Some wireless tags 25 are affected by metal or water. In the case of this type, when the screen mask 20 is on the circuit board 11, it is difficult to read the RFID tag information attached to the upper part of the circuit board 11. It needs to be read while being transported to the screen printer. In addition, a wireless tag using a high frequency band generally has a long communication distance. In this case, data can be read by the wireless tag reader 26 installed outside the screen printer. The screen mask 20 is generally made of stainless steel or copper in the frame 21 made of a material mainly composed of aluminum and the mask 10 itself. Therefore, in the case of a general combination mask, the wireless tag is preferably attached to the mesh portion (FIG. 7). In the case of paste, it cannot be put into the material. In this case, it will be attached to the outside of the paste container. This is read by the reader 26 having a large communication distance. The squeegee is generally made of urethane, and in this case there is no problem with the communication function of the wireless tag. Care must be taken in the case of metal or composite materials such as metal and urethane. However, since wireless tags that are less susceptible to metal and moisture are being developed in the future, in this sense, the problem with the attached materials will gradually disappear.

As described above, the paste is sensitive to the effects of temperature and humidity. This is because the viscosity changes. When the viscosity changes, the fluidity of the paste changes, and the amount and speed of the paste passing through the opening of the screen mask change. This also changes the amount of paste transferred onto the circuit board. In particular, management of the environmental temperature is essential for a printing press. By arranging a means sensor 27 for measuring either the environmental temperature or the humidity inside the screen printing machine and further optimizing the printing conditions based on the template data based on the data obtained from this measuring device, A stable screen printing operation system can be constructed for a long time.
It is desirable that the temperature or humidity sensor directly measures the inside of the paste. However, it is difficult to realize. Therefore, it is realistic to measure while maintaining a certain distance. The sensor 27 is a directional sensor, and is installed inside the cover 28 that covers the entire screen printing apparatus so that the environmental temperature or humidity in the vicinity of the printed circuit board and the paste to be printed can be measured as accurately as possible. It is desirable that The inside of the cover 28 is preferably subjected to feedback control by a dedicated air conditioner in order to ensure certain printing conditions.

It is explanatory drawing which shows the basic function of the conventional type general screen printing apparatus. It is explanatory drawing of the data structure of the template according to printing factor. (Example 1) It is explanatory drawing of the structure of a paste function auxiliary | assistant template. (Example 1) It is explanatory drawing of the printing fluctuation factor of test printing, and its level. (Example 1) Explanatory drawing of the allocation of analysis factors of test printing and analysis results. (Example 1) It is explanatory drawing which shows the average according to the fluctuation | variation level of SN ratio. (Example 1) It is explanatory drawing of an example of the screen mask for test printing. (Example 1) Explanatory drawing of the control system structure of a screen printing apparatus. (Examples 1-3) It is explanatory drawing of the control system related to host computer and template data creation. (Examples 1-3) It is a printing condition setting flowchart in actual production. (Examples 1-3) It is explanatory drawing of the preparation procedure of the printing condition template data by test printing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printing squeegee 3 Squeegee holder 6 Squeegee raising / lowering drive device 7 Squeegee printing drive motor 10 Screen mask 11 Circuit board 13 Circuit board backup raising / lowering drive device 20 Screen mask 21 Screen mask frame 23 Test pattern opening 26 Wireless tag reader 27 Temperature or humidity measurement Sensor 28 Screen printer cover 40 Control device 70 Template creation computer configuration device

Claims (4)

In screen printing in which paste is filled in the opening of the screen mask with a squeegee and transferred onto the circuit board, the screen printing results on the circuit board in actual production are used as template data. A screen printing method comprising storing and optimizing screen printing conditions in actual production based on the stored template data. In screen printing in which paste is filled in the opening of the screen mask with a squeegee and transferred onto the circuit board, it is related to optimizing the screen printing conditions. Prior to printing on the circuit board for actual production, the test screen Based on the result of test printing of the paste using the mask and the test substrate, an appropriate printing condition for each paste is obtained, the obtained printing condition is stored as template data, and the stored A screen printing method characterized by optimizing printing conditions in actual production based on template data. The printing conditions are optimized based on the information recorded on the wireless tag attached to at least one of the actual production circuit board and the paste in the screen printing process and the template data. The screen printing method according to claim 1 or 2. Means for measuring at least one of the working environment temperature of the screen printing apparatus, the paste temperature used for actual production, or the working environment humidity, and the temperature or humidity data obtained by the measuring means; 4. The screen printing method according to claim 1, wherein the printing conditions are optimized based on the template data.

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