WO2001035703A1

WO2001035703A1 - Improvements in solder printers

Info

Publication number: WO2001035703A1
Application number: PCT/US2000/042003
Authority: WO
Inventors: Robert J. Balog; A. William Johnson; Augustus Ashton; Frank Marszalkowski
Original assignee: Speedline Technologies, Inc.
Priority date: 1999-11-08
Filing date: 2000-11-08
Publication date: 2001-05-17
Also published as: AU2751801A

Abstract

A printer for the deposition of electronic materials onto the surface of a printed circuit board is provided in a first embodiment with a drum arrangement with apertures formed through the drum which correspond to positions on the pads of a printed circuit board which will have electronic materials deposited thereon. Alternatively, a belt with apertures formed therein may also be utilized. An electronic materials dispensing station is located within the drum or belt and, upon activation, dispenses electronic materials through the apertures in the drum or belt onto a printed circuit board which has been moved from an entry station to a print station. At least one radio frequency tag may be incorporated in the belt or drum to identify particular formations of apertures which relate to specific printed circuit boards which are to be printed.

Description

IMPROVEMENTS IN SOLDER PRINTERS

Background of the Invention

In the electronics assembly industry, it is well known to utilize what is called a screen or stencil printer to print solder paste or other materials, such as adhesives (collectively "electronic materials"), onto the surface of electronic boards such as printed circuit boards (PCBs). One example of such a printer is disclosed in U.S. Patent Reissue No. 34,615 assigned to the assignee of the present invention. Such screen or stencil printer is organized in a "linear" or "in-line" fashion. Printed circuit boards which are to be printed upon with electronic materials are conveyed in line from a storage section to a printing section and thence to an exit section.

This conventional system utilizes, at the printing section, a stencil printing head. The printing head includes a stencil, usually made of a metal or other material which has holes or apertures formed therethrough. Such holes or apertures, when in contact with a surface of a PCB and when properly aligned, correspond to portions on the printed circuit board such as contacts or conductive pads onto which the solder or another electronic material is printed. In a conventional stencil printing head, on the surface of the stencil opposite to the surface the printed circuit board is placed into contact with, a squeegee pushes solder or other material across the stencil such that the solder is pushed through the holes or apertures in the stencil and onto the desired contact or pad on the printed circuit board. In such a conventional printer, once the squeegee has pushed the solder material across the holes, the stencil is moved out of contact from the printed circuit board and the printed circuit board is moved to the next, usually the exit, station.

Next, a new printed circuit board to be printed upon is placed in the printing section of the printer and the squeegee may either be returned to the start position, that is. the position prior to the printing of the first board or else the stencil is once again placed in contact with the new board to be printed upon and the squeegee reverses its direction and translates in a direction opposite to the first direction pushing before it, in a conventional manner, the solder which then, once again, is pushed through the holes in the stencil onto the second printed circuit board. Thus, the process of solder printing in this conventional system is what might be termed "batch^" printing in that boards are brought into a printing station, the stencil is brought down and comes into contact with the printed circuit board through its mounting in the print head, a squeegee pushing solder translates across the opposite surface of the stencil and then the board is removed once it has been printed with solder or other electronic material. While the printed circuit boards move in one direction into the printing area and out of the printing area, the squeegee is moved back and forth across the apertures in the stencil. The set of apertures which correspond to desired solder or other electronic material deposition contacts for a particular PCB is called an "image".

Additionally, it is desirable, if not necessary, that the surface of the stencil which comes into contact with the printed circuit board be kept free of any stray solder or other electronic materials because otherwise this would lead to the deposition of solder or other electronic materials on portions of the board where such deposition is not desired and even detrimental. Thus, in conventional screen printing machines, a cleaning device is incorporated. As desired by the user and as determined by the build-up of materials on the stencil, a cleaner station which may include an impregnated cloth or wiper or other material is passed under and against the bottom surface of the stencil (that is, the surface which comes into contact with the printed circuit board) and wipes any material from that stencil surface. This function is performed off-line, that is, the function of repetitive printing of printed circuit boards must be interrupted in order for the stencil surface to be cleaned. Obviously, this causes delays in the throughput of boards through the stencil printing machine and contributes to the already existing delay which is also inherent in the reciprocal back-and-forth motion of the solder squeegee across the apertures and the raising and lowering of the print head to alternatively contact the stencil with the PCB for printing and removal of the PCB from the printing station.

Summary of the Present Invention

What would be desirable, then, is an electronics material stencil printer which can work in a continuous mode to print on printed circuit boards in a manner which is faster than the known conventional batch process solder printers but which also has the ability to perform a cleaning operation on the stencil in a continuous, rather than an off-line manner. The printer of the present invention performs these functions by integrating or replacing the conventional flat stencil with a stencil in either a drum or belt form which moves in one direction with a solder head being held stationary within the drum or belt. In this manner, the drum or belt may be moved in one direction and the printed circuit boards may be moved beneath the moving belt or drum to eliminate the back-and-forth motion of the solder squeegee and improve speed. In addition, a continuous operation cleaning station may be incorporated into the drum or belt printer such that, as the drum passes the cleaning station, the cleaning station can engage the belt or drum and remove materials that may have been deposited on them. Further, the nature of the contact between the moving drum and a moving board support may eliminate the need to raise and lower the print head. The foregoing result in the ability to have a continuous printing and cleaning operation without the inherent delays which occur in conventional screen printers.

Brief Description of the Drawings Fig. 1 illustrates a drum printer embodiment according to the present invention.

Fig. 2 illustrates a belt printer embodiment according to the present invention.

Fig. 3 illustrates an alternative printed circuit board support to be utilized with the embodiments of Figs. 1 and 2.

Fig. 4 illustrates a drum or belt with images according to the present invention.

Detailed Description Turning now to Fig. 1, Fig. 1 shows a drum printer embodiment of the present invention.

This embodiment includes a stencil print drum 2 which, as shown in Fig. 1. which comprises a thin metal or other resilient material having a series of apertures forming an image formed through the drum surface from one drum surface 4 through to the other inner drum surface 6. It is expected that a plurality of images could be made on the stencil print drum.

As the drum 2 rotates in direction 8 shown in Fig. 1 and depending on the number of images formed on the drum, a fresh image is presented to each circuit board as it arrives in the print station. A stationary rheopump 10 is a solder or other material gathering and dispensing head and may be in the form of a rheometric pump such as that shown in Serial No. 08/966.057. filed November 7, 1997 and assigned to the assignee of the present invention, the disclosure of which is herein incorporated by reference. The rheopump head 10 is open at its bottom surface 12, through which solder is pushed out and onto the inner drum surface 6 under pressure out of the head. Thus, as can be seen, as the stencil print drum is rotated in a direction 8 and with the rheopump 10 held in a fixed position, solder paste or other electronic material under pressure, when encountering one of the images, will be pushed through the apertures and out the other side 4 of the stencil print drum and. in operation, onto a waiting PCB. An example of another electronic material which may be used in rheopump 10 is an epoxy material which is conventionally used to affix electronic devices on PCBs.

Also as shown in Fig. 1. a raw board 12 is placed on a stage 14 which holds the board at its entry, printing and post-print stations. The stage 14 moves the unprinted raw board 12 from its position 16 as shown in Fig. 1 to its position 18 of Fig. 1. As the board 12 moves while mounted on stage 14 from position 16 to position 18, the drum rotates in direction 8. The timing of the arrival of the printed circuit board and the timing of the rotation of the stencil print drum are controlled such that, as the apertures forming the image in the stencil come below the open bottom surface 12 of the rheopump, the appropriate contacts or pads on the printed circuit board present themselves aligned with such holes. Thus, as the stage moves from position 16 to position 18, the action of the rheopump 10 pushes solder through holes formed in the print drum 2 onto the appropriate contacts or pads on the still-moving board 12. Printing board position 20 shown in Fig. 1 illustrates the PCB while being printed upon and exiting from under drum 2 while being carried by stage 14. It is to be understood that the term PCB and/or circuit board is meant to encompass any of a variety of flat surfaces onto which electronic elements may be affixed.

Once the board has been printed, it proceeds to post-print station 22 and the printed board 24 exits from the printer. The stage 14 which holds the board then moves from station 22 through an intermediate station 26 and back to station 16, ready to take another PCB through the printing process. While the drum is rotating to print another board, and depending upon the number of images which are formed on the drum, the already printed apertures may come into contact with drum wash station 28 which contains cleaning fluid and/or materials to wipe any residue from either the outside surface 4 or the inside surface 6, or both, of the print drum 2. Such cleaning stations are well known in the art pertaining to conventional solder screen printers. An example of such stencil cleaning station is one which is incorporated into the ULTRAPRINT 3000 printer distributed by Speedline Technologies, Inc. of Franklin, MA. the assignee of the present application.

Since it is important that the apertures formed in the images in the stencil print drum 2 match precisely with the contacts or pads on the board, an alignment system is included to allow adjustment of PCB position if it is determined that such alignment is not sufficiently precise. Alignment systems for printed circuit boards are illustrated, for example, in the previously mentioned U.S. Patent Reissue No. 34,615, as well as U.S. Patent No. 5, 060.063 also assigned to the assignee of the present invention, the disclosures of which are herein incorporated by reference. As shown in Fig. 1, a line scan camera 30 views the raw board 12 as it moves on stage 14 from station 16 past the camera. Any lack of alignment is corrected by moving the stage 14 in X, Y and theta (that is, orthogonal and rotative directions) as the stage arrives at print station 18. It is understood that, alternatively, the drum may be adjusted to match board position and orientation. Further, it may be desirable, depending on PCB size, thickness and other factors to move the drum vertically in directions shown by arrow 34. The stages on which the PCBs are mounted may be of a type in which the stage supports a movable table on which the PCB is mounted but remains movable in X, Y and theta directions.

A further feature of the present invention is the inclusion of a post-inspection station 32. The post-inspection station 32 views the board which has been printed upon to determine that the printing has occurred only on those positions or pads which were designed to have solder or other electronic materials printed upon them.

Turning now to Fig. 2. Fig. 2 shows another embodiment of the present invention. In the embodiment of Fig. 2, the stencil print drum 2 is replaced with a stencil print belt 100. The stencil print belt 100 is. like the drum, made of a relatively thin, resilient material with a number of images having apertures formed therethrough. The foregoing discussion with respect to the stencil print drum applies equally to the embodiment of Fig. 2 except as follows. The stencil print belt 100 of Fig. 2 includes at least two stencil print belt rollers 102 and 104 as well as enter roller 106 and exit roller 108. The rollers 102. 104, 106 and 108 act to hold the stencil print belt in position at the print stage 18 to allow for solid and uniform contact between the stencil print belt 100 and the board 110 at the print station 18. Depending on PCB size, thickness and other factors, it may be desirable to provide for movement of the rheopump 1 12 and/or roller 106 and/or roller 108, as shown by arrows 114. The operation, structure and sequencing of print processing occurs as with the drum print embodiment of Fig. 1.

A further embodiment of the present invention is shown in Fig. 3 which illustrates an alternative staging mechanism. In the alternative staging system of Fig. 3. a stencil print drum 200 contains, like the stencil print drum 2 of Fig. 1, a number of images containing apertures formed through the drum. Further, an unprinted printed circuit board 202 is mounted on a conveyor belt 204. The conveyor belt 204 is mounted on rollers 206 and 208 and a conventional motor drive rotates the rollers in direction 210 as shown in Fig. 3. The direction 210 of the rollers is opposite to that direction of the rotation of the stencil print drum.

In operation, the board 202 moves on conveyor 204 from a station 212 to a station 214 under the drum and the movement of the conveyor moves the printed circuit board 202 under the moving drum 200. The print head 216, in the same manner as described in Figs. 1 and 2, then pushes solder paste or other materials through the images in drum 200 onto the selected positions on the selected portions or contacts or pads on printed circuit board 202. The then printed board moves along conveyor belt 204 to position 218. at which time it may be subjected to inspection as previously described.

In each of the embodiments of Figs. 1 and 2 (discussed above) and Fig. 3 (to be discussed below), a computer control system of the conventional variety is utilized. The computer control systems 40 (Fig. 1). 150 (Fig. 2) and 240 (Fig. 3) are operatively connected with line scan cameras 30. and 140 and post-inspection stations 32 and 142. as well as RF tag readers 36, 136 and 236. As is conventionally known in the art. when the line scan camera detects a misaligned board, it sends a signal to the computer which then, again in a conventional manner, causes the circuit board mounting mechanism to translate and/or rotate into an aligned position such that the apertures in the drum 2 or belt 100 are aligned with pads or other places on the PCB on which it is desired to deposit an electronic material such as solder paste. The computer is also operatively connected with post-inspection stations 32 and 142. such that inspection of a PCB in the exit stage is initiated and appropriate action, such as rejection if there was an inadequate print operation, is instituted, again in the conventional manner.

Computers 40, 150 and 240 are also operatively connected to RF tag readers 36. 136 and 236. RF tag readers can be used to query one or more RF tags 310, 312 and/or 314, etc. to determine, for example, the identity of the particular set of apertures 302, 304 and/or 306. etc., as discussed below. The information provided by the RF tag to the RF tag reader is communicated to one of the computers 40. 150 or 240, and such computer can then coordinate operation of the pump to dispense materials or merely be used to identify and verify that the particular set of apertures identified by the RF tag reader corresponds to the particular type or set of circuit boards to be printed upon.

The embodiment of Fig. 3 provides a continuous movement of the drum and the belt to increase throughput of the printing process. An inspection camera 220 may be positioned at or around station 212 to align the board on the belt prior to its entering into station 214 for printing to assure alignment. It is also to be understood that the embodiment of Fig. 3 may incorporate, instead of the stencil print drum 200, a stencil print belt such as that shown in Fig. 2.

A further advantage of the present invention is that a single drum or belt may be mounted on the printer but contain a number of different images corresponding to different PCBs. In some conventional printers, a single image is formed on a stencil and must be changed when a different image is to be printed. This consumes time and requires realignment of the stencil in its mounting.

Fig. 4 illustrates a drum or belt of the type described in connection with the embodiments of Figs. 1 and 2. only shown in Fig. 4 as cut and flattened for illustration purposes only. In Fig. 4, a number of different images 302, 304 and 306 are shown formed on the drum or belt 300 to allow for printing different images on different PCBs. In operation, the operator determines which image 302. 304 or 306 is to be utilized, depending on the PCB selected. The operator then adjusts the operation of the rheopump 10 such that it will activate (and thus dispense solder or other electronic material) only when the selected image comes below the opening 12 of the rheopump 10.

For example, if image 304 is selected, the rheopump 10 is pressurized and activated as image 304 comes into printing station 18, but is deactivated as the drum 2 or belt 100 further moves and images 302 and 306 move into station 18.

While three images 302. 304 and 306 are shown, it is to be understood that any number as practical may be formed on drum 2 or belt 100. Further, the same image may be formed a multiple of times on the drum 2 or belt 100, depending on board size, processing speed desired, etc.

If a number of different images are formed on the drum or belt 300, in order to ascertain where each image 302, 304 or 306 is located on the drum or belt so that the correct one of the images is printed, the drum or belt may have an RF tag of a well known type, such as tags 310, 312 and 314, fixed to the drum or belt, adjacent to the correlated images 302, 304 and 306 to identify the image and its characteristics. The RF tag may be as illustrated in U.S. Patent No. 6,123,024, the disclosure of which is herein incorporated by reference. The RF tags affixed to the belt or drum may be located on the interior side of the drum (6 in Fig. 1) or belt so as not to interfere with the print operation. Thus, an RF reader (not shown) may read the identity of the particular image and, when there is a correlation between the image desired to be printed and the location of that imager adjacent rheopump 112. the pump is turned on and dispenses solder or other electronic material onto a PCB positioned to receive the solder or other electronic material.

While the present invention has been illustrated by the description of a preferred embodiment, and while the embodiment has been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broadest aspects is therefore not limited to the specific details, representative apparatus and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.

Claims

Wi at is claimed is:CLAIMS

1. A printer for the continuous printing of electronic materials onto circuit boards, comprising: a printer table horizontally disposed; a drum rotatably mounted about its horizontal axis over the printer table; images formed through the drum body in the form of apertures, the apertures corresponding to positions through which electronic material will be dispensed; an electronic materials dispenser mounted within the drum which can dispense electronic materials through the apertures; a circuit board mounting and moving system which moves circuit boards to be printed from an entry station to a print station to an exit station; and wherein the electronic materials dispenser dispenses electronic materials through the apertures onto a circuit board when the circuit board and the apertures are aligned.

2. A printer of claim 1 additionally comprising an inspection camera to assess non- alignment of a circuit board on the circuit board mounting and moving system, mounted at the entry station to inspect circuit boards prior to the movement of such circuit boards into the printing station and wherein the inspection camera, upon detection of an out-of-alignment circuit board sends a signal to a mechanism to move the circuit board in X, Y and theta directions until the circuit board is aligned with the apertures.

3. A printer of claim 1, further comprising a drum wash station in contact with the drum surface for cleaning the drum and removing excess electronic materials formed on the drum.

4. A printer of claim 1, further comprising a post-inspection station which optically inspects a circuit board at the exit station.

5. A printer according to claim 1 , further comprising a circuit board mounting stage which holds a circuit board through the entry, print and exit stations and then disengages from the printed circuit board at the exit station and returns to the entry station to mount an additional circuit board.

6. A printer according to claim 1 wherein the drum rotates in a direction which is the same as the translational movement of the circuit board from the entry station to the print station to the exit station.

7. A printer according to claim 1 in which the drum is constructed of a thin, resilient metallic material.

8. A printer for the continuous printing of electronic materials onto circuit boards, comprising: a printer table horizontally disposed; a belt rotatably mounted about its horizontal axis over the printer table; images formed through the belt body in the form of apertures, the apertures corresponding to positions through which electronic material will be dispensed; an electronic materials dispenser mounted within the belt which can dispense electronic materials through the apertures; a circuit board mounting and moving system which moves circuit boards to be printed from an entry station to a print station to an exit station; and wherein the electronic materials dispenser dispenses electronic materials through the apertures onto a circuit board when the circuit board and the apertures are aligned.

9. A printer of claim 8 additionally comprising an inspection camera to assess non- alignment of a circuit board on the circuit board mounting and moving system, mounted at the entry station to inspect circuit boards prior to the movement of such circuit boards into the printing station and wherein the inspection camera, upon detection of an out-of-alignment circuit board sends a signal to a mechanism to move the circuit board in X, Y and theta directions until the circuit board is aligned with the apertures.

10. A printer of claim 8, further comprising a belt wash station in contact with the belt surface for cleaning the belt and removing excess electronic materials formed on the belt.

1 1. A printer of claim 8, further comprising a post-inspection station which optically inspects a circuit board at the exit station.

12. A printer according to claim 8, further comprising a circuit board mounting stage which holds a circuit board through the entry, print and exit stations and then disengages from the printed circuit board at the exit station and returns to the entry station to mount an addition circuit board.

13. A printer according to claim 8 wherein the belt rotates in a direction which is the same as the translational movement of the circuit board from the entry station to the print system to the exit station.

14. A printer according to claim 8 in which the belt is constructed of a thin, resilient metallic material.

15. A printer in accordance with claim 8, further comprising at least one roller in the vicinity of the electronic materials dispenser and in which the roller presses the belt against a circuit board in the print station.

16. A printer in accordance with either claim 1 or claim 8 in which the electronic material dispensed comprises a solder.

17. A printer in accordance with either claim 1 or claim 8 in which the electronic material dispensed comprises an epoxy material.

18. A printer in accordance with claim 1 and in which the circuit board mounting system comprises a continuous belt which transports the circuit boards from the entry station to the print station and to the exit station and in which the direction of movement is the same as the direction of rotation of the drum.

19. A printer in accordance with claim 8 and in which the circuit board mounting system comprises a second belt which transports the circuit boards from the entry station to the print station and to the exit station and in which the direction of movement is the same as the direction of rotation of the first belt.

20. A printer in accordance with either claim 18 or claim 19 in which the circuit board is mounted on the belt, the circuit board being movable in the X, Y and theta directions upon detection of misalignment by an alignment camera at the entry station.

21. A printer in accordance with claim 1 and further comprising a radio frequency tag associated with at least one of the images formed on the drum, the radio frequency tag identifying the location or other characteristic of the at least one set of apertures formed on the drum and a radio frequency tag reader mounted in the vicinity of the drum to detect and read such identifying location or other characteristic from the radio frequency tag.

22. A printer in accordance with claim 1 and further comprising a radio frequency tag associated with at least one of the images formed on the belt, the radio frequency tag identifying the location or other characteristic of the at least one set of apertures formed on the belt and a radio frequency tag reader mounted in the vicinity of the drum to detect and read such identifying location or other characteristic from the radio frequency tag.

23. A printer in accordance with either claim 21 or claim 22 further comprising a plurality of images formed on the drum, radio frequency tags fixed to the drum and associated with each of the images, wherein, upon detection of a specific image and radio frequency tag, the detector signals the electronic materials dispenser to dispense electronic materials through the apertures of the image.

24. A process for the continuous printing of electronic materials onto circuit boards comprising: providing a printing table on which a drum is rotatably mounted about its horizontal axis; forming images through the surface of the drum with the images forming apertures corresponding to places in which electronic material may be dispensed therethrough; providing an electronic materials dispenser mounted within the drum to dispense electronic materials through the apertures formed in the drum; providing a circuit board mounting system which moves circuit boards from an entry station to a print station to an exit station; and rotating the drum while moving the circuit board from the entry station to the printing station and activating the electronic materials dispenser when a circuit board is located in the printing station.

25. A process for the continuous printing of electronic materials onto circuit boards comprising: providing a printing table on which a belt is rotatably mounted about its horizontal axis; forming images through the surface of the belt with the images forming apertures corresponding to places in which electronic material may be dispensed therethrough; providing an electronic materials dispenser mounted within the belt to dispense electronic materials through the apertures in the belt; providing a circuit board mounting system which moves circuit boards from an entry station to a print station to an exit station; and rotating the belt while moving the circuit board from the entry station to the printing station and activating the electronic materials dispenser when a circuit board is located in the printing station.