PROTECTIVE FILM PEELING MACHINE FOR PRINTED CIRCUIT BOARDS

Abstract: A machine peels a protective film (18) off a surface of a photoresist film laminated onto the surface of a printed circuit board (12), being the motion of the boards through the machine continuous. Such a condition is obtained in an effective manner by employing mechanical devices (2) for preventively degrading the adhesion along an edge zone of the laminated board (12) that, instead of acting onto the leading edge thereof substantially normal to the direction of advancement, act along two opposite lateral edges of the protective film (18), substantially parallel to the direction of advancement of the board through the machine, and are themselves a functional part of the board advancement system (conveyor). The mechanical devices (2) for degrading the adhesion along the two lateral edges of the protective film, eventually on both faces of the board, may be common knurls that act along the side edges of the protective film when the board passes at a substantially constant speed through the machine. According to the preferred embodiment, nozzles, (9, 10) suitable to blow air a relatively low pressure may be present in the separation gaps between two adjacent knurling wheels.

Description: "PROTECTIVE FILM PEELING MACHINE FOR PRINTED CIRCUIT BOARDS" The present invention relates to a technique for peeling a protective film off a surface of a laminate and more particularly a protective film of a layer of a photoresist (dry film) hot laminated onto one or most likely both faces of a printed circuit board being fabricated. Modern fabrication techniques of printed circuit boards contemplate the lamination of a photoresist film onto the surface of the superficial copper sheet of the board to be patterned. Most often, such a photoresist film is a so-called "dry film" that is conveniently produced in rolls in the form of a laminate comprising a peelable film of support plastic material, a second peelable film of protective plastic material, typically of Mylar®. The first support film is removed before hot laminating the photoresist film onto the copper face of the board. The successive exposition phases of the photoresist layer to define the printed circuit are carried out advantageously with the photoresist film protected by the second protective film of Mylar®. Only when the board is going to be subjected to the steps of photolithographic patterning (etching) of the copper layer, the protective film must be removed. In order to increase productivity, the fabrication process of the printed circuit boards should be fully automatized and thus also the peeling off of the protective film must be carried out by automatic mechanical means able to handle in a continuous manner a stream of boards being processed. There are apparatuses and machines specially proposed and developed for this purposes. Attempts of peeling off the protective film by vacuum means (suction bells and similar) have proven themselves unreliable so as mechanisms for pulling off the protective film by using strong adhesives. The only technique that so far has proven itself suitable for peeling the protective film off the surface of a hot laminated photoresist layer on a board consists in mechanically indenting (chewing) an edge of the laminate photoresist - protective film. In this way, an encroachment of air at the interface between the two materials is promoted even if only in a narrow edge strip of few millimeters from the trimming edge of the laminate. This preliminary locally provoked disruption of the existing adhesion between the two films permits to approximate catching means, for example strong adhesive ribbons, to lift off gradually the protective film starting from the narrow edge zone of so compromised adliereiice caused by tl e mechanical lαiurling treatment and to pull it completely off the surface of tl e photoresist layer. According to the known techniques, the mechanical action of degradation of the adhesion of the protective film (typically of Mylar®) to tl e surface of the photoresist film is carried out by means of knurls, scrapers or scratch-brashes. They work essentially on the whole or on parts of tl e front or leading edge of the board advancing through the machine towards the device for catching and pulling the protective film. Commonly known machines carry out such a mechanical action on the front or leading edge of the board, in a distinct processing station. Such a processing station precedes a station equipped with air jets and with appropriate organs for lifting and for catching tl e lifted leading edge of the protective film that eventually effect the peeling action. The document US-A-4,867,836 discloses a peeling machine wherein in a first station, rotating wire brushes (4) act on the leading edges of the board lifting the edges of the protective film by one or few millimeters from the trimming edge, on both faces of the board. In the successive station, air streams oriented towards the leading edges of the advanced laminated board, on both faces of the board, lift the leading edges of the protective films as much as sufficient to catch them between respective pairs of ribbons running onto a system of pulleys (6A-6C, 6A-6B) and definitively pull them off the faces of the photoresist films laminated onto the two sides of the board. The advancement motion of the boards in succession through the processing line is generally discontinuous. The various processing stations operate with different advancement speeds of the boards and often contemplate a temporary stop of the motion of the board, for example, in order to carry out the mechanical operation of preventive degradation of tl e adhesion in a determined limited zone of the leading edge of the dry film laminated onto the copper face of the board. Eventual differences among respective intervention times are customarily managed by a control system and/or by the use of proximity sensors and similar automation devices. OBJECT AND SUMMARY OF THE INVENTION Object of the present invention is a machine for peeling a protective film off a surface of a photoresist film laminated onto the surface of a printed circuit board in which the motion of the boards tlirough the machine is continuous. Such a condition is obtained in an outstandingly effective manner by employing mechanical devices for preventively degrading the adhesion along an edge zone of the laminated board that, instead of acting onto the leading edge thereof substantially normal to the direction of advancement, act along two opposite lateral edges of the protective film, substantially parallel to the direction of advancement of tl e board through the machine, and are themselves a functional part of the board advancement system (conveyor). The mechanical devices for degrading the adhesion along the two lateral edges of the protective film, eventually on both faces of the board, may be common knurls that act along the side edges of the protective film when the board passes at a substantially constant speed through the machine. According to a preferred embodiment, nozzles suitable to blow air at a relatively low pressure may be present in the separation gaps between two adjacent knurling wheels. The purpose of this optional feature, is not yet that of lifting the protective film pinched by the teeth of the knurling wheels, but more simply to favour an encroachment of air at the interface between the protective film pinched by the teeth of the knurling wheels and the laminated photoresist layer. At the output of the knurling zone, along opposite lateral edges of each protective film parallel to the advancement direction of the board tlirough the machine, two arrays of firsts nozzles placed on transversal supports that during the phase of operation translates together with the advancing board, direct jets of air that are individually oriented, on the respective plane of the laminate on one and on the other face of tl e board, towards the longitudinal center axis thereof, activating themselves according to a temporal sequence, starting first from the two extreme lateral jets and progressing to the central jet that, differently from the other ones is oriented along the longitudinal center axis. These sequentially activated strong air jets last only for a short pre-established time interval, which may be of about half a second, and determine a progressive detachment and lifting of the whole leading edge of the protective film, even if the knurling had taken place along the two lateral edges of the protective film. The leading edge of tlie protective film of the respective face of the laminate, so lifted by the sequentially activated strong jets of compressed air, stalling from the two corners and progressively across the whole edge, for a depth of few centimeters, is sustained by continuous parallel air jets longitudinally oriented of relatively moderate intensity ejected by array of secondary nozzles that translate together with tlie board and the arrays of the first or primary oriented nozzles against tlie surface of a motor driven end multipulley roll of a respective articulated arm of a conveyor device and on tlie plurality of belts running in a respective throats of the mull pulley roll. The two opposed, articulated arms of these conveyor devices, whose motor driven end pulley-roll is pivotally mounted on side plates shifted by a cylinder, besides advancing the board pinched between the two end pulley-rolls, orderly support the lifted front edge of the respective protective film. The two articulated aπn conveyor devices form an integral part of the overall system of conveying the boards and the two end pulley-rolls elastically biased one against the other eventually press on the surfaces of the respective protective film adhering onto the respective face of an incoming laminated board in its advancing tlirough the machine. The card roll pressed on the surface prevents the encroachment of air in the adhesion interface of the protective film beyond the line of abutment of the end roll of the articulated arm on the face of the laminate. The leading edge portion of the protective film so lifted and orderly supported onto the end pulley-roll and belts of tlie articulated arm of the conveying device that advances carrying along with the board eventually is clamped, in a conventional manner, against a cooperating fixed belt conveyor device. At that pomt the motor driven end pulley roll of the ailiculated arm belt conveyor device starts to rotate and so does the cooperating fixed belt conveyor device and the protective film held between the two belt conveyor devices is progressively peeled off from the advancing board, transferred and discarded into a container. In practice the operation for peeling-off, lifting and blocking the protective film takes place wliile the board continues to move without interruption tlirough tl e machine. The different aspects and advantages of the device of the invention will become even more evident tlirough a detailed description of an embodiment and by referring to the attached drawings, wherein: Figures 1 and 2 are schematic plan and elevation views, respectively, of the machine of the invention wliile waiting a new board; Figures 3 and 4 are a partial and simplified plan view and elevation view, respectively, of the machine in a successive phase of the advancement motion of a board tlirough the machine; Figures from 5 to 8 are elevation views that illustrate the remaining operating phases of the machine. Referring to the figures in which the same numbers are used to indicate the same functional parts of the device, the film peeling machine of the invention includes a common conveyor system using a plurality of motor driven rolls 1 for conveying the boards 12. The conveyor system customarily includes feeding rolls and output rolls. The input roll conveyor is provided with centering devices 13 for ensuring that each board 12 be positioned exactly along the center line of the roll conveyor and the lateral edges of the protective films on the laminated photoresist layer over the two faces of the board 12 be perfectly aligned with the knurling wheels 2. The rolls 1 of the input and output roll conveyors are rotated by an electrical motor at a speed that may be comprised between about 1 and 6 meters/minute (tangential speed of the rolls or advancement speed of the board 12, also referred to as machine speed). The trains of knurling wheels 2, that in the example each comprises three pairs of wheels functionally opposed to one another, are positioned by the hand- wheel 16 in order to be suitably aligned with the lateral trimming edges of the protective films 18 (Mylar) of the photoresist films laminated onto the opposite faces of the board 12. The knurling wheels 2 are motor driven at a tangential speed equal to that of the rolls 1 of the input and output conveyors. Therefore they act as devices for advancing the board 12 as well as pinching knurls working the two lateral edges of the protective film 18 (Mylar) on the photoresist film to cause a substantial degradation of adhesion therealong. The machine ftulher comprises a pair of counteropposed articulated arms of respective belt conveyor devices, each constituted by at least three pulley-rolls 3, 5a and 6a on which a plurality of belts 7 runs constituting an articulated arm. Wliile the rolls 5a and 6a of each of said pair of articulated arm belt conveyor device are pivoted onto fixed side plates, the end roll 3 is pivoted on side plates 15 that are longitudinally translated by suitable actuating cylinders 14. Suitable tensioning rolls 8 ensure maintenance of a correct tension of the belts 7 running in respective grooves of tlie rolls 3 and 5a during tlie reciprocating motion of the articulated arm. During a stand-by phase while waiting for a new board to arrive, as depicted in Figs. 1 and 2, the two ailiculated arms, each constituted by a linearly shifted end roll 3, a fixed roll 5a and by the belts 7 running in their grooves, are closed the one against the other by a spring system (not depicted in the figures) such to engage the respective faces of a board 12 when it reaches die position of the rolls 3, as it will be described in a greater detail later. A fixed belt conveyor device is associated to each of the articulated arm belt conveyor device, each constituted by a three rolls 4, 5b and 6b and the relative belts 7 running in respective grooves of the pulley-rolls. The machine further comprises two arrays of first nozzles 9, sequentially and momentarily ejecting high intensity jets of compressed air oriented, on the respective plane of the laminated, towards the longitudinal center axis of the board 12, and two arrays of second nozzles 10 continuously ejecting jets of air parallel among them and to the advancement axis of the board 12 of relatively small intensity than the strong convergently oriented jets of nozzles 9. The secondary parallel air streams are suited to keep the leading or front edge portion of the protective film 18 (Mylar), detatched and lifted by the strong impulses of compressed air sequentially delivered by the first array of nozzles 9, against the end pulley-roll 3 of the relative articulated and linearly advancing arm of the belt conveyor device, as long as the lifted edge of the protective film is eventually caught between the end pulley-roll 3 advancing together with the board 12 and the fixed end pulley-roll 4 of the cooperating fixed belt conveyor device. All arrays of first nozzles 9 and of seconds nozzles 10 are carried by respective transversal members supported by moving side plates 15 and therefore they "back" away at the same advancement speed of the board through the film peeling machine, as may be observed in the plan views of figures 1 and 3. A pair of photoelectric cells 11 detect the incoming of the leading edge of a board 12 in the film stripping zone, commanding the sequential emission of strong jets of compressed air by the nozzles 9, respectively starting from the two most lateral jets and proceeding to activate sequentially the other pairs of nozzles up to the single central nozzle of the two arrays of nozzles 9, and simultaneously commanding also the advancement of all tlie arrays of nozzles 9 and 10 as well as of the end rolls 3 of the two articulated arms closed onto the board so that the board advances during this detachment phase of the front edge of the film(s) without any interruption of its motion tlirough the machine. The functioning, in a coordinate manner, of the various parts of the machine will be more recognizable tlirough the following description of each one of the main phases of the film peeling off process carried out by the machine of the invention making reference to figures from 1 to 8. Figure 1 and 2. The machine is waiting for a new board 12 advancing on tlie input train of conveying rolls 1 and being centered by tlie centering device 13. All rolls 1 of the input and output conveyors as well as tlie lαiurling wheels 2, the film stripping belt conveyors rolls 3, 4, 5a, 6a and 6b rotate at a uniform machine speed. Of course, tlie knurling wheels 2 will have been preliminarily positioned by means of tl e hand-wheel 16, in function of the width of the protective film 18 (Mylar). Figures 3 and 4. The board 12 is passing under the knurling wheels 2 that cause a pinching (knurled Mylar) along tlie two lateral edges of tlie protective film 18 without stopping tlie board 12, but letting it be pushed forward at a constant speed of advancement by tlie rotation of tlie motor driven pairs of knurling wheels 2. The board 12 is thus clamped between the end pulley-rolls 3 of the moving arms of the two belt conveyor devices 3, 5a, 6a, 7 and 8 that are rotating with the same tangential speed and thus they sustain and contribute in pushing d e board 12 forward. At the instant in wliich the photoelectric cells 11 detect the leading edge of d e advancing board 12 tlirough the machine, tlie rolls 3, 4, 5a, 5b, 6a and 6b stop rotating and the cylinder 14 advances the side plates 15 on wliich are pivoted tl e end rolls 3 and to which are fastened die transversal supports of the arrays of first nozzles 9 and of second nozzles 10, thus carrying forth the board 12 clamped between tlie end rolls 3 of the pair of opposed articulated arms as well as the nozzles 9 and 10. Figure 5. The detection of d e front or leading edge of the board by photoelectric cells 11 commands also d e sequential activation of tl e oriented ail- jets from tlie nozzles 9, starting respectively from d e two most lateral jets to die single central jet tiiat is oriented along the longitudinal central axis of d e board, for about half a second wliile the other sets of nozzles 10 continue to eject air streams of limited intensity. In tliis phase, while the knurling wheels 2 continue pinching the trailing portion of die two lateral edges of die protective films on die hot laminated photoresist layers applied on the two faces of the board 12, and to concur in die advancement of the board at a constant speed tlirough die machine, d e leading edges of the protective films 18, detactched by d e strong air stream 9 are kept subsided by die air jets continuously delivered by die nozzles 10 against die end rolls 3 and the belts 7 of the respective ailiculated arm. Both end rolls 3 as well as d e array of nozzles 9 and 10 advance linearly togedier widi the board 12, obviously at die same tangential speed of die rolls 1 of the input and output roll tains and of the knurling wheels 2. While die high speed air jets sequentially activated ejected by die nozzles 9 last about a fraction of a second, the weak parallel jets provided by the nozzles 10 keep the lifted front edge portion of the protective film orderly leaning over die respective roll 3 and d e relative belts that in d is phase do not rotate. Generally, the total linear travel driven by the cylinders 14 in this phase, may be of about 100 millimeters. Figure 6. The set of front views of d e upper face only of the board 12 and of the respective features d at detach and lift die front edge portion of protective film 18 laying on die face of the laminated board 12, illustrates how die progressive detaching of d e front edge portion of the protective film 18 takes places by sequentially activating impulses of oriented strong air jets from the nozzles 9. The figures shows the end pulley-roll 3 and die relative belts 7 of die moving arm that in tiiis phase is being linearly shifted togedier witii die board 12 and die transversal members carrying the nozzles. In this phase of linear advancement, rotation of the motorized end pulley- roll 3 and thus also of d e odier pulley-rolls of the belt conveyor devices is stopped. The end roll 3 and die relative belts 7 bear on die respective face of the board 12 preventing the sequentially activated strong air jets produced by the nozzles 9 from lifting die protective film 18 beyond the abutment line of the end roll of die moving arm of the articulated belt conveyor device. The sequence of illustrations of Fig. 6 shows how die activation of d ese short lasting strong air jets for detaching and lining die front portion of d e protective film 18 takes place in sequential manner, starting from d e two most lateral jets and continuing in activating progressively more and more inner pairs of jets until the single central jet tiiat is oriented along the longitudinal central axis of the board 12 while progressing tiirough the machine. The two extreme lateral jets that are activated first impinge on die two comers of die front or leading edge of the protective film 18, respectively, whose lateral edges have been pinched by die knurling wheels 2 (emphasized in the figures by a saw-toothing thereof caused by die knurling wheels). The lifting die two corners of the front edge portion of die protective film 18 favoured by the preliminarily adliesion disruptive effect caused by die lαiurling wheels, is sufficient to permit detachment and lifting of the whole front edge of the protective film 18 by die progressive sequential activation of die odier inner jets. The parallel air streams continuously ejected by d e nozzles 10 (not depicted in Fig. 6) push the so lifted front edge of die sheet 18 against the end roll 3 and die belts 7 of the moving ami of the belt conveyor device, preventing it from falling back onto the surface of d e photoresist layer laminated onto die surface of die board. Figure 7. The cylinders 14 have completed d e sliifting of die two articulated aims and of d e relative end rolls 3 togetiier witi die board 12 clamped therebetween and die nozzles 9 and 10 and die end rolls 3 finally abut against the fixed rolls 4 of the cooperating respective fixed belt conveyor device 4, 5b and 6b, dius clamping die so lifted portion of the protective film 18 between die two end rolls 3 and 4. As soon as the contact between die advancing end roll 3 of d e articulated arm and die respective fixed end roll 4 of the cooperating fixed belt conveyor device is established, die rolls 3 and 4 start rotating again at machine speed as well as die o ier rolls 5a, 5b, 6a and 6b of d e pair of belt conveyor devices. The board 12 continues to move forward and the two sheets of protective film 18 (Mylar) are progressively stripped off die respective faces of die advancing board and transported by die belts 7 running on die rolls and eventually fall in the respective recovery containers 17. Figure 8. When die leading edge of die protective film 18 being stripped off die surface reaches the space between the two rolls 5a and 5b, coincident witii the pivoting point of the respective articulated arm that are always elastically held one against the other, the cylinder 14 (see Fig. 3) rapidly shift back to their start position both pairs of side plates 15 as well as the end rolls 3 and die arrays of nozzles 9 and 10. During this return phase of d e side plates 15, d e end rolls 3 and the rods 4, 5a, 5b, 6a and 6b w l have an effective "tangential speed" given by die sum of die rotating speed of the rolls (constant machine speed) and d e linear speed of translation of the side plate assemblies imposed by die cylinders 14. The result is that die board 12 being output from the peeling station retains a constant advancement speed witiioul any variation wliile d e film is stripped off its surface at a higher speed. Preferably, dedicated motors drive the end pulley-rolls 3 wliile die pulley-rolls 4, 5a, 5b, 6a and 6b are rotated by common transmission organs of die motion of ti eir respective end roll 3, thus avoiding formation of areas on the protective film because of speed disunifoimities. A new board 12 may then be engaged by d e first pair of lαiurling wheels 2 and successively become clamped between the pair of end rolls 3 of d e two articulated arm belt conveyor devices. As schematically depicted in d e plan view of figures 1 and 3, third nozzles 19 may be installed in the separation spaces between two adjacent knurling wheels in order to provide air jets of relatively low intensity impinging on the sides of the laminated layers to favour encroachment of air at die interface between the protective film 18 being pinched by the teeth of the knurling wheels 2 and the laminated photoresist film, in order to enhance deposition of the adhesion along the two lateral sides of the protective film 18, parallel to the advancement direction of the board through the machine.

Claims: C L A I M S 1. A machine for peeling a protective film (18) off the surface of a photoresist layer laminated on at least a face of a printed circuit board (12), comprising mechanical means (2) for preventively degrading d e adhesion along a limited edge zone of said protective film (18) to said photoresist layer, a plurality of nozzles (9, 10) directing air jets to impinge along a perimetral segment of the interface plane between said protective film and said photoresist layer in said limited zone, and means (3, 4, 5a, 5b, 6a, 6b) for catching an edge portion of the protective fihn lifted by the air jets and for stripping said protective fihn (18) off the whole surface of d e laminated photoresist layer, characterized in that said mechanical means (2) for preventively degrading the adhesion are constituted by at least two pairs of motorized knurling wheels (2) acting respectively along die two lateral sides of said protective film (18) parallel to the direction of advancement of the board (12) tlirough the machine; said nozzles (9, 10) are installed on supports that are shifted during a phase of activation of the nozzles, in the same direction and at the same advancement speed of the board; first nozzles (9) directing air jets oriented, on the respective lamination plane of the board (12), toward its longitudinal center axis, in sequence starting from the two most lateral jets and progressing tiirough inner and inner pairs of jets until a central jet or jets oriented along said longitudinal center axis; said means for catching the lifted front or leading edge of said protective film and for stripping it comprise a first pair of belt conveyor devices (3, 5a, 6a, 7), each having an ailiculated moveable arm elastically held against the articulated and moveable arm of the other device, the end pulley-roll (3) of each arm being pivoted on longitudinally moveable side plates (15) carrying also the supports of said nozzles (9, 10); at least a cylinder (14) moving said side plates (15) at the advancement speed of a board (12) clamped between the end pulley-rolls (3) of said pair of elastically held articulated arms; each articulated arm belt conveyor device of said pair cooperating with a fixed belt conveyor device (4, 5b, 6b, 7) against an end pulley-roll of which (4) the linear advancement shift of said end pulley-roll (3) of the relative moving arm stops. 2. The machine according to claim 1, characterized in that said first nozzles (9), except the central nozzle, are oriented on the respective lamination plane of the board (12) with and angle of convergence comprised between 35° and 25° toward said longitudinal center axis and have an incidence angle of the impinging air jets onto said plane comprised between 10° and 20°. 3. The machine according to claim 1, characterized in that it comprises second nozzles (10) installed on supports that are shifted at the same advancement speed of the board (12) during a phase of operation and directing continuous air jets parallel to said longitudinal center axis, of intensity sufficient to keep the front edge portion of the protective film, detached and lifted by relatively intense short duration air jets sequentially issued by said first oriented nozzles (9). 4. The machine according to any of the preceding claims, characterized in that it comprises tiiird nozzles (19) directing ah jets to impinge orthogonally onto said two lateral sides of die protective film (18) fitted in the separation spaces between a pair of opposed knurling wheels and an another pair adjacent thereto.

Inventors: CANDORE AMEDEO, CANDORE, AMEDEO
Applicants: CANDORE AMEDEO, CANDORE, AMEDEO
Application year: 2001
Main classification: B29C63
IPC codes: B29C63, G03F7