Patent Publication Number: US-6705505-B2

Title: Paste providing method, soldering method and apparatus and system therefor

Description:
The present application is a continuation of application Ser. No. 09/733,096, filed Dec. 11, 2000; now U.S. Pat. No. 6,533,162 which is a divisional application of application Ser. No. 09/102,212, filed Jun. 22, 1998, now U.S. Pat. No. 6,193,144, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a method, apparatus and system for filling through holes made in a printed circuit board or the like with paste-like substance, and a method, apparatus and system for soldering the printed circuit board or the like filled with the paste-like substance. More particularly this invention relates to a method, apparatus and system for filling the through holes with paste-like substance using a roller with adding power for rotating the roller. 
     Various methods for printing solder paste on a surface mounting land of a printed circuit board have been disclosed up to now. 
     In the solder paste printing, usually a mask having openings corresponding to predetermined positions of the printed circuit board is used. By sweeping (dragging) a squeegee, solder paste suitable for the openings is supplied to the printed circuit board through a mask. 
     In a printed circuit board substrate in which the surface mounting parts land and through holes coexist, as well known, according to one prior method, the solder paste is supplied to the surface mounting part land, and after surface mounting parts are loaded thereon, reflowing is carried out. After that, a lead of each lead provided insertion part is inserted into a through hole coated with flux and soldering is carried out using wave solder. This method requires at least two processes, that is, a process for soldering surface mounting parts by reflowing and a process for soldering lead provided insertion parts with wave solder. 
     According to this method, a number of reflow frequencies is increased in some types of printed circuit boards loaded with parts and therefore thermal shock to the substrate increases, so that the reliability of the substrate drops. Further, floating of chip parts and the necessary steps for masking with tape or the like cause the increase of the number of steps for mounting process. 
     According to the prior method, it is impossible to complete soldering with a single reflow by supplying solder paste to the surface mounting land and through holes at the same time, of a substrate in which the surface mounting parts and lead provided insertion parts coexist. 
     Further because solder volume is reduced about half after the solder is melted, solder paste more than twice a volume of a through hole needs to be supplied to the through hole. Further as the aspect ratio (ratio between a through hole diameter and substrate thickness) increases, it is more difficult to fill with solder paste. 
     Another prior art method is described in Japanese patent laid open number H05-33742. The document discloses a filling device for filling viscous tungsten paste into a through hole formed on a green sheet. The filling device has a roller squeegee and scrapers for scraping the paste. However the roller squeegee must be forced to rotate. Further the filling device can not supply enough of the paste to the through holes. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method, apparatus and system for supplying solder paste sufficiently to through holes of lead provided parts of a printed circuit board or the like. 
     Another object of the present invention is to provide a method, apparatus and system for supplying solder paste sufficiently to surface mounting part land and lead provided through holes on a circuit board having a large thickness in which surface mounting parts and lead provided insertion parts coexist at a time. 
     Still another object of the present invention is to provide a method, apparatus and system for soldering parts with a single reflow to a printed circuit board having a large thickness in which the surface mounting parts and lead provided insertion parts coexist. 
     To achieve the above objects, according to the present invention, there is provided a paste filling method, apparatus and system for supplying paste-like substance to any through holes formed in an article. The invention provides first, setting a printing mask, which has predetermined openings corresponding to the through holes on the article. Then providing the paste-like substance on the printing mask, and dragging a roller, which is forced to rotate independent of dragging motion, along a surface of the printing mask. After that, removing the printing mask from the article. 
     According to a further embodiment, the rotation of the roller is carried out so that a peripheral velocity of the roller rotation is a different speed with respect to the roller dragging speed. Preferably the rotation of the roller is carried out so that the peripheral velocity of the roller is faster than the roller sweeping speed. 
     The invention can be used on articles wherein surface mounting part lands are provided on the article in addition to the through holes so that the paste-like substance is supplied to the through holes and the surface mounting part lands. 
     According to another aspect of the present invention, there is provided a paste filling method, apparatus and system for supplying paste-like substance to through holes and surface mounting part lands provided arbitrarily on an article, including the steps of matching a printing mask having predetermined openings for through holes and surface mounting part lands therewith in the article and sweeping a roller by rotating the roller independent of the sweeping motion and further sweeping a follow-up squeegee so as to supply the paste-like substance to the through holes. A paste receiving plate is disposed corresponding to the through holes and the surface mounting part lands. 
     According to still another aspect of the present invention, there is provided a soldering method, apparatus and system for soldering parts on a printed circuit board having through holes and surface mounting part lands. The invention provides for first, matching a printing mask having predetermined openings for the through holes and surface mounting part lands with the printed circuit board. Then, sweeping a roller by rotating the roller and further sweeping a follow-up squeegee so as to supply solder paste to the through holes. A paste receiving plate is disposed corresponding to the through holes and the surface mounting part lands. After loading parts on the surface mounting part lands of the printed circuit board and inserting leads of the parts into the through holes, heating and melting solder paste with the printed circuit board and the paste receiving plate as a set, so as to carry out soldering. 
     According to the present invention, it is possible to supply paste-like substance to high aspect ratio through holes. It is also possible to supply paste-like substance to the surface and through holes of an article in a time. 
     Further, in mounting parts onto a printed circuit board according to the present invention, soldering can be carried out by supplying solder paste, loading parts and then melting the solder. As a result, in a printed circuit board in which lead provided parts having leads to be inserted into each through hole and surface mounting parts coexist, the number of steps for mounting process can be substantially reduced thereby contributing to improvement of the reliability of the printed circuit board. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The scope of the present invention will be apparent from the following detailed description, when taken in conjunction with the accompanying drawings, and such detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description, in which: 
     FIG. 1 is a diagram for explaining a method for filling a printed circuit board with paste, of the present invention; 
     FIG. 2 is a view illustrating an example of a state after a printed circuit board is filled with paste; 
     FIG. 3 is a view showing an example of a state with parts loaded (inserted) after paste is filled; 
     FIG. 4 is a diagram for explaining various roller forcible rotation methods of the present invention; 
     FIGS. 5A and 5B are diagrams for explaining paste filling property when the paste filling method of the present invention is actually applied; 
     FIG. 6 is a diagram illustrating an overall construction of a soldering system; and 
     FIG. 7 is a flow chart illustrating an operation of the soldering system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. 
     Referring to FIG. 1, reference numeral  1  shows a printed circuit board in which surface mounting part lands and lead provided insertion part through holes coexist and the aspect ratio is 4. Numeral  2  denotes a printing mask having predetermined masks and numeral  3  denotes a printing roller which is forcibly rotated. A shadow portion thereabove indicates a holder. Numeral  4  denotes a printing squeegee and a shadow portion thereabove indicates a holder. Numeral  5  denotes solder paste and numeral  6  denotes a high aspect ratio through hole having a minute opening. Numeral  7  denotes a surface mounting part land and numeral  8  denotes a paste receiving plate. 
     The printed circuit board  1  and printing mask  2  are fixed to a printer (not shown in FIG. 1) and a pattern of the printing mask is matched with the through holes and surface mounting part lands and set thereon. 
     After that, the solder paste  5  is supplied and then the printing roller  3  which is forcibly rotated is swept (dragged) in a printing direction indicated by an arrow so as to supply the solder paste  5  to the surface mounting part lands  7 , through holes  6  and paste receiving plate  8 . It is permissible to sweep the printing squeegee  4  after the printing roller  3  which is forcibly rotated. 
     The printed circuit board  1  may be a printed circuit board provided with only the lead provided insertion part through holes or a printed circuit board provided with only the surface mounting part lands. 
     As for the forcible rotation of the printing roller  3 , the peripheral velocity of the roller should be faster than the sweeping speed. It is more effective that to keep the peripheral velocity of the roller 4 to 10 times faster than the sweeping speed. When a shaft of roller is free from any power and the roller naturally rotates by sweeping movement, it provides an insufficient of paste. 
     According to this method, a sufficient amount of paste is loaded to the surface mounting part lands and through holes of the printed circuit board  1  in which the high aspect ratio through holes and surface mounting part lands coexist. At the same time, a sufficient amount of paste is also loaded onto the paste receiving plate  8  having a volume the same or larger than that of the through hole. The through hole and paste receiving plate can be loaded with solder paste more than twice the volume of the through hole. 
     The printing squeegee  4  supplies paste to the surface mounting part land  7  and sweeps so that no paste  5  remains on the printing mask  2 . 
     Although an attack angle (angle formed by the printing squeegee  4  and printing mask  2 ) is desired to be 60°, if it is intended to further supply paste to the through hole  6 , the attack angle is set to 45° or 30°. 
     For the surface mounting part land  7 , an opening and thickness of the printing mask  2 , corresponding to a required amount of paste are considered. The through hole  6  is formed so as to be equal to the diameter of the opening or as large as possible in such an extent that no bridge or short occurs between the lands. 
     Next, an example of the soldering method after the solder paste is supplied will be described below. 
     As shown in FIG. 2, the solder paste is printed on the printed circuit board  1  and paste receiving plate  8 . Then, mounting parts  9  are loaded on the printed circuit board  1  and paste receiving plate  8  as shown in FIG.  3 . That is, the surface mounting parts are mounted on the surface mounting part lands  7  and the lead provided insertion parts are inserted into the through holes  6 . Then, the printed circuit board  1  and paste receiving plate  8  are set and solder melting procedure is carried out. 
     After that, the printed circuit board  1  and paste receiving plate  8  are separated from each other. As a result, the surface mounting parts and lead provided parts can be soldered to the printed circuit board  1  by a single soldering procedure. 
     According to the above described soldering method, the number of processes and working time are substantially reduced and frequency of thermal hysteresis is also reduced so that the reliability of the printed circuit board is improved. Meanwhile, the paste receiving plate  8  is formed of a material having a property of blocking solder from adhering and high-temperature resistance because solder is melted thereon. 
     The forcible rotation methods for the roller illustrated in FIG. 4 will be described in detail. 
     There are various methods available for forcible rotation of the roller. Reference numeral  10  indicates motor contained type. The motor cause a shaft  11  of the roller to be rotated. According to methods  12 ,  13 ,  14 , a driving system is placed at a location other than the shaft and the roller is rotated forcibly by power transmission. The methods  12 ,  13 ,  14  indicate gear type, belt type and contact type in which another roller is provided to rotate the roller, respectively. 
     Next, solder paste filling property of the printing roller  3  will be described with reference to FIGS.  5 (A) and (B). 
     FIG.  5 (A) shows conditions of solder filling tests and the tests results. The tests were practiced by 4 types of squeegees, one method using a flat squeegee and three methods using rollers A-C subject to various factors. Conditions of the tests, excluding roller peripheral velocity, are quite same. Printing frequency is one time (item 1). Printing speed is five mm/s (item 2). Roller diameter of each of the three rollers is  42 F (item 4). The load (pressure) given to the each of the squeegee and the rollers is also same. Each of the squeegee and rollers is given 50 g/mm per unit length of the squeegee or roller (FIG.  5 (B)). The same paste is used for each squeegee and roller. 
     A shaft of Roller A is forced to rotate independent with Roller sweeping motion. Roller peripheral velocity of Roller A is 20 mm/s. It is four times as fast as the printing speed. A shaft of Roller B freely rotates. Roller peripheral velocity of Roller B is 5 mm/s. It is same speed with the printing speed. And Roller C is no rotation. A shaft of Roller C is fixed. 
     On conditions mentioned above, when the volume of the through hole is expressed as “1”, the filling ratio by flat squeegee is around “0.4” (item 5). In the same way, the filling ratio by Roller C is around “0.85” and the filling ratio by Roller B is around “1.13”. Each of them causes insufficiency of the application of paste. On the other hand, the filling ratio by Roller A becomes “2.5” and we can fill paste to the through holes sufficiently. 
     FIG.  5 (B) visually illustrates the results. A horizontal axis shows the load given to each squeegee. A vertical axis shows paste filing ratio. V 1  is the volume of through holes in the printed circuit board. The volume of each through hole is (F 0.75×t3.1). V 2  is the volume of holes in the receiving jig. The volume of each hole in the receiving jig is (F 1.35×t1.3). Each hole in the receiving jig has about 1.25 times the volume in each through hole in the printed circuit board. Only Roller A could fill a sufficient amount of paste for the through holes and holes in the receiving jig. 
     As compared to the known squeegee, the printing roller of the present invention that is forced to rotate is capable of filling paste more sufficiently. The rotation speed of the printing roller is desired to be 4-10 times the sweeping speed so as to ensure low speed sweeping. 
     Further, this printing method is also available for filling a green sheet used upon production of a ceramic substrate. 
     FIG. 6 is a diagram illustrating an overall construction of a soldering system. In FIG. 6,  603  denotes a keyboard for inputting data and command for controlling the soldering system.  602  denotes a controller for controlling the whole soldering system according to information from the keyboard or other elements.  601  denotes a display for displaying various information from the controller  602 . The information includes guidance for inputting data or commands. 
       604  denotes a paste printer controller which controls a paste printer  607 . The Paste printer  607  includes following mechanisms. A board setting mechanism  610  sets a printed circuit board, a paste receiving board and a paste printing mask. A board setting mechanism  610  includes an adjuster for adjusting the position of the paste printing mask. A roller mechanism  611  moves a roller  3  from one end to another end on the printing mask adding a load which is a force applied to the printing mask  2  of the roller  11 , for filling holes in the printing mask paste. A roller mechanism  611  has a rotation mechanism for rotating a shaft of the roller  11  dependent with transfer movement. Various types of rotation mechanisms have already been shown in FIG.  4 . Paste provider  613  provides paste on the printing mask. The squeegee mechanism moves a squeegee  4  following the roller  3 . The squeegee mechanism  612  adjusts an attack angle of the squeegee. The attack angle is a contact angle between the squeegee  4  and the printing mask  2  in printing direction. The squeegee mechanism  612  also adjusts a load which is a force applied to the printing mask  2  of the squeegee. The squeegee mechanism  612  removes rest paste on the printing mask  2 . According to the attack angle, the squeegee further provides paste to the holes in the printing mask  2 . 
       605  denotes a parts mounter controller which controls a parts mounter  608 . The parts mounter  608  mounts electric parts on the printed circuit board  1 . The electric parts includes both surface mounting parts and parts having leads for inserting into the through holes. 
       606  denotes a heater controller which controls a heater  609 . The heater  609  heats and melts the paste printed on the printed circuit board  1  and fixes the parts to the printed circuit board  1 . 
     FIG. 7 is a flow chart illustrating an operation of the soldering system. 
     First, a controller  602  urges an operator to input initial numerals for accomplishing this soldering process by displaying guidance on the display  601 , and receives the numerals from the keyboard  603  ( 701 ). The numerals include roller transfer speed, roller rotation speed, roller pressure to the printing boards, squeegee transfer speed, squeegee pressure to the printing board, squeegee attack angle, and paste amount etc. 
     The controller  602  directs the paste printer controller  604  to set a paste receiving board, a printed circuit board, and a printing mask on the paste printer ( 702 ). The paste printer controller  604  sets a paste receiving board, a printed circuit board, and a printing mask on the paste printer  607  by controlling the board setting mechanism ( 703 ). A motion of the board setting mechanism includes to adjust the position of them. After they set, the paste printer controller  604  notifies completion to the controller  602 ( 703 ). 
     The controller  602  directs the paste printer controller  604  to print paste on the printing board( 704 ). The controller  602  gives various numerals input in the previous step  701 . For example, it gives the paste printer controller  604  roller rotation speed, roller transfer speed, squeegee transfer speed, squeegee attack angle etc. 
     The paste printer controller  604  performs paste printing by controlling the roller mechanism  611 , the squeegee mechanism  612  and the paste provider  613 ( 705 ). The paste printer controller  604  move them according to the numerals received from the controller  602 . After finishing the paste printing, the paste printer controller  604  remove the printing mask  2  from the printing board by controlling the board setting mechanism  610 . Then, the paste printer controller  604  notifies completion to the controller  602 ( 705 ). 
     The controller  602  moves the printed circuit board with paste printed thereon, to the mounter  608  by using a board path  614 . The controller  602  directs the mounter controller  605  to mount electric parts ( 706 ). 
     The part mounter controller  605  mounts the electric parts by controlling the part mounter  608 ( 707 ). The electric parts include both of surface mounting parts and parts having leads for inserting into the through holes. After all electric parts were set, the part mounter controller  605  notifies completion to the controller  602  ( 707 ). 
     The controller  602  moves the printing circuit board with parts mounted thereon, to the heater  609  by using the board path  614 . The controller  602  direct the heater controller  606  to fix the electric parts to the printed circuit board ( 708 ). 
     The heater controller  606  heats and melts the paste by controlling the heater, thereby fixes the electric parts to the printed circuit board. The heater controller  606  notifies completion to the controller  602 ( 709 ). 
     The controller moves the printed circuit board from the heater by controlling the board path and sets all soldering process. 
     While the present invention has been described in detail and pictorially in the accompanying drawings, it is not limited to such details since many changes and modification recognizable to these of ordinary skill in the art may be made to the invention without departing from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.