Paste providing method, soldering method and apparatus and system therefor

An improved soldering system which reduces the numbers of steps for paste supply and soldering in soldering lead provided parts and surface mounting parts onto a printed circuit board. A printed circuit board has through holes through which a lead of each lead provided part is to be inserted and lands for surface mounting parts. A printing mask is matched with the through holes and lands and a paste receiving plate having holes to which solder paste is to be supplied corresponding to each of the through holes is disposed. A printing roller is swept by forcibly rotating it so as to fill with solder paste, then a printing squeegee is swept following that printing roller so as to further fill with solder paste. Parts are loaded on the through holes and lands of the printed circuit board loaded with solder paste and reflowing is carried out on the printed circuit board and paste receiving plate at the same time, so that the lead provided parts and surface mounting parts are soldered to the printed circuit board at the same time.

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.

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.degree., if it is intended to further
 supply paste to the through hole 6, the attack angle is set to 45.degree.
 or 30.degree..
 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 FIG. 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.PHI.
 (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. V1
 is the volume of through holes in the printed circuit board. The volume of
 each through hole is (.PHI.0.75.times.t3.1). V2 is the volume of holes in
 the receiving jig. The volume of each hole in the receiving jig is
 (.PHI.1.35.times.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.