JP7645958B2 - Bonding tool for connecting print head units to FPCs - Google Patents

Description

The present invention relates to a bonding tool for bonding a flexible printed circuit to a print head unit and a method for bonding a flexible printed circuit to a print head unit.

Bonding tools are commonly applied to connect chips to flexible printed circuits (FPCs). Both the chip and the FPC contain one or more rows of numerous bond pads and/or tracks, and the bond pads of the chip must be individually connected to the tracks on the FPC to establish the electrical connections required to control the chip. A printhead unit may contain exceptionally long rows of bond pads due to the large number of nozzles provided on a single printhead unit. Also, the density of bond pads is typically high as a result of the high nozzle density (dots per inch, DPI) of the printhead unit. A bonding tool for a printhead unit includes a support surface for supporting the printhead unit and a bond head including an elongated contact surface extending in a first direction. The first direction is the direction in which the one or more rows of nozzles and/or bond pads extend. The contact surface is configured to press the flexible printed circuit onto the printhead unit. Both are pressed together with a predetermined force. After bonding the FPC and printhead unit together, it was discovered that not all of the bond pads produced actually made proper electrical contact with the individual tracks.

The object of the present invention is to improve the yield of the process of bonding together an FPC and a print head unit.

According to the invention there is provided a bonding tool as claimed in claim 1 and a method as claimed in claim 10.
A bonding tool for bonding a flexible printed circuit to a printhead unit by adhesive provided at a contact area between the flexible printed circuit and the printhead unit, comprising:
a support surface configured to support a printhead unit;
a bond head including a contact surface configured to press a flexible printed circuit onto a print head unit on a support surface;
a hinge mechanism configured to movably support the bond head.
The bonding tool is characterized in that the hinge mechanism has a structure that limits the movement of the contact surface of the bond head such that the contact surface moves around a rotation axis located within the intended location of the contact area between the print head unit and the flexible printed circuit. The rotation axis is preferably a so-called "virtual" rotation axis located inside the contact area where the layer of adhesive is located, and allows the FPC and the print head unit to be rotated relative to each other until both are parallel to each other. The rotational movement of the contact surface (which may be limited to a predetermined range) inhibits any translation between the bond pads on the print head unit relative to the tracks on the FPC. However, the rotational movement allows the print head unit and the FPC to be made parallel to each other without the risk of the bond pads on the print head unit translating relative to the tracks on the FPC. The rotational axis counters the initial non-parallelism between the support surface and the contact surface when both are positioned and pressed together. This results in a substantially constant pressure distribution over all bond pads, regardless of the initial relative angle between the FPC and the print head unit. As a result, all bond pads are subjected to a full and equal pressing force. The pivot further keeps the pressing force or pressure substantially constant when the distance between the printhead unit and the FPC is adjusted. Rotational movement about the pivot allows opposing rows of bond pads and tracks to be parallelized, thereby establishing a highly reliable connection, thereby achieving the object of the present invention.

More specific optional features of the present invention are set out in the dependent claims.

In one embodiment, the contact surface is elongated and extends in a first direction, and the structure restricts the movement of the contact surface to rotation about a rotation axis. Due to the relatively long row of nozzles, the corresponding row of contact pads is effectively a line structure that must be aligned with the corresponding track. The rows extend in the first direction. To ensure proper contact, the rows of tracks must be parallel to the rows of contact pads. This is achieved by allowing rotation about an axis perpendicular to the first direction, the rotation axis being located in the contact area between the rows of contact pads and the rows of tracks. The hinge mechanism is configured to locate the rotation axis in the contact area, preferably without having any physical components in the contact area. Thus, the rotation axis is a virtual rotation axis formed by the rod mechanism structure of the hinge mechanism.

It will be appreciated that the virtual rotation axis described above creates a rotational movement between the support surface and the bond head. Preferably, one of the support surface and the bond head is kept stationary during pressing, while the other moves towards it. The virtual rotation axis therein may be configured to rotate either of the contact surfaces on the bond head while the support surface moves towards the bond head, or vice versa. Alternatively, the virtual rotation axis may be provided on a moving member, e.g. the bond head is movable towards the support surface, and the virtual rotation axis ensures that the contact surface on the bond head is rotatable. Similarly, the support surface may be movable and rotatable. Also, either the FPC or the print head unit may be provided on the bond head, as well as on the support surface.

In one embodiment, the imaginary axis of rotation is parallel to the support surface, and the movement of the contact surface is fully rotational, at least within the intended range of motion. The rows of bond pads extend in a first direction, as do the tracks. To make the rows of bond pads on the print head unit parallel to the rows of tracks on the FPC, the print head unit may be rotated about an imaginary axis of rotation located between the FPC and the print head unit. The imaginary axis of rotation is more preferably parallel to the support surface. The contact surface is limited to only rotational motion to constrain translational movement of the rows of bond pads relative to the tracks on the FPC. The movement of the contact surface is rotational within the working range in which the FPC and the print head unit are pressed together. The rotational movement of the contact surface results in each point on the contact surface moving in a circle around the imaginary axis of rotation. The displacement of each point on the contact surface in the first direction is accompanied by a proportional displacement in height, and the ratio between these displacements is determined by the individual angle of the point relative to the imaginary axis of rotation.

In another embodiment, the bond head, and specifically the contact surface, is rigid compared to a flexible printed circuit. The FPC is deformable and has a certain compliance that allows it to be reshaped while being pressed against the print head unit. The bond head is relatively non-deformable.

In one embodiment, the print head unit and the FPC comprise conductive tracks, each of which comprises an electrical contact element or area at its end, and the electrical contact elements or areas on each of the print head unit and the FPC are sized and/or positioned such that each electrical contact element and/or area on one is in electrical contact with a corresponding electrical contact element and/or area on the other. Essentially, each track on the print head unit is connected to a track on the FPC so that together they form a single electrical connection between the actuator and the controller. The corresponding electrical contact elements and/or areas may simply be formed as the ends of the respective tracks, or alternative structures such as bond pads may be applied to the ends of the tracks of one or both of the print head unit and the FPC. The contact areas are preferably defined to be located between the electrical contact elements of the FPC on one side and the electrical contact elements of the print head unit on the other side.

In one embodiment, the hinge mechanism comprises at least four hinges, two of which are each connected to the bond head via a respective rigid arm and another respective hinge. The hinge mechanism defines a virtual axis of rotation located at the adhesive-containing contact area between the FPC and the print head unit. The hinge mechanism is a simple, low-cost method for creating the virtual axis of rotation without interfering with the bonding process. Preferably, the hinge mechanism is located on the opposite side of the contact surface from the virtual axis of rotation.

In one embodiment, the hinges can be arranged mirror-symmetrically with respect to a mirror plane extending perpendicular to a plane extending through the axis of the hinge attached to the main structure. The mirror plane is further arranged in the middle between the hinges and thus equidistantly spaced from both of the hinges. In at least one of its positions, the hinge mechanism is mirror-symmetric with respect to the mirror plane. During rotation, the hinge mechanism can move out of this symmetric state, but can be brought back to it by repositioning the angle of the contact surface when the hinge mechanism is in its symmetric state. The symmetric hinge mechanism contributes to restricting the contact surface to a pure rotational movement. With respect to the mirror plane, the corresponding hinges have the same position, but are mirror planes, and the individual connecting arms have the same dimensions, specifically lengths. After bonding, the mirror plane is further perpendicular to the first direction.

In one embodiment, the main structure includes a positioning means for adjusting the position of the hinge mechanism relative to the support surface. The main structure of the hinge mechanism is attached to the positioning means. The positioning means is configured to generally move the hinge mechanism with the bond head relative to the support surface. Thereby, the hinge mechanism and the bond head can be moved apart to allow the printhead unit to be positioned on the support surface. The positioning means may further be used to press the printhead unit and the FPC together. The positioning means may include a guide and/or a drive. The positioning means may also further form or include a pressing means for pressing the printhead unit and the FPC together with a predetermined force.

In one embodiment, the hinge is a film hinge. Film hinges have little or no play, thus allowing precise positioning of the head support structure relative to the main structure. The minimal play also allows the rotational movement of the contact surface to be precisely maintained during movement, such that shifting of the bond pads relative to the tracks on the FPC outside of the circular orbit determined by the imaginary axis of rotation is avoided. A point on the contact surface may still move in a first direction, and/or vice versa, provided there is a corresponding displacement in the elevation direction, as determined by the circular orbit defined by the imaginary axis of rotation. Film hinges are also low cost and durable.

In one embodiment, a recess extending in a first direction is provided in the bond head adjacent to the contact surface. The recess faces the support surface. The recess is preferably located between the contact surface and a holding means for holding the FPC. At the contact surface, the FPC is preferably not actively held relative to the bond head to allow sufficient compliance during bonding. Generally, since the bond head is above the support surface, the holding means must ensure that the FPC does not lose its position relative to the bond head. The recess during pressing is located above the edge of the print head unit, thus suppressing excessive pressure on other areas of the print head unit other than the bond pad area. In particular, pressure on the edge of the print head unit is thus avoided, which ensures that the pressing force is directed entirely into the bond head, so that the pressing force can be precisely controlled. The recess allows a portion of the FPC at the contact surface to be at least a small amount of mobile in a second direction relative to the contact surface without falling off the bond head. This allows the tracks on the FPC to better conform to the printhead unit during bonding compared to being held fixed against the contact surface.

In one embodiment, the contact surface is provided with a curved surface that tapers toward the support surface when viewed in a first direction. The contact surface ideally forms a straight line in the first direction with a width comparable to the width of the bond pad. The curved contact surface allows for this linear pressing while still allowing the contact surface to rotate without affecting the bonding process. The curvature also allows the bond head to adjust to any differences in height or distance between the printhead unit and the FPC due to tolerances in manufacturing and/or processing. The curved contact surface follows the surface against which it is pressed, ensuring reliable bonding.

In one embodiment, the curved surface comprises an anti-stiction material, preferably a FOTS material. A coating is applied to inhibit or reduce adhesion of the adhesive to the bond head. The anti-stiction coating reduces bonding between the adhesive and the curved surface. FOTS material has been found to work well in this regard.

The present invention relates to a method of bonding a flexible printed circuit to a printhead unit, comprising the steps of:
- bonding the printhead unit to a flexible printed circuit board with an adhesive therebetween;
- pressing the bond pads and/or tracks of the printhead unit and the flexible printed circuit board together by means of a contact surface,
The method further relates to a method in which the contact surface rotates about an imaginary axis of rotation located at the contact area between the print head unit and the flexible printed circuit, the contact area being where the adhesive is applied, the rotation of the contact surface being preferably determined by a hinge mechanism as described above.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the 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.

The invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings, which are given by way of example only and therefore are not limiting of the invention.
FIG. 2 is a schematic cross-sectional view of a printhead unit bonded to a flexible printed circuit board by an adhesive. 1B is a schematic cross-sectional view of the contact interface along section C of the printhead unit of FIG. 1A. FIG. 2 is a perspective schematic diagram of a bonding tool for bonding a printhead unit to a flexible printed circuit board by adhesive. 3 is a perspective side view of the bonding tool of FIG. 2 attached to a pressing means; FIG. 2 is an enlarged perspective view of the bond head of the bonding tool of FIG. 2 attached to its hinge mechanism. FIG. 2 is another enlarged perspective view of the bond head of the bonding tool of FIG. 2 attached to its hinge mechanism. FIG. 3 is a side view of the bonding tool of FIG. 2 . FIG. 7 is an enlarged side view of the bond head of the bonding tool of FIGS. 2 and 6 . FIG. 8 is a front view of a hinge mechanism of the bonding tool in FIGS. FIG. 9 is a schematic diagram reflecting the hinge mechanism of FIG. 8 during the initial stages of pressing the FPC and printhead unit together. FIG. 10 is another schematic diagram reflecting the hinge mechanism, where the FPC has been rotated relative to FIG. 9 for initial contact with the FPC. FIG. 10 is another schematic diagram reflecting the hinge mechanism of FIG. 9, where the FPC has been rotated to a parallel orientation relative to the printhead unit.

The present invention is described below with reference to the accompanying drawings, in which the same reference numerals are used throughout the several views to identify the same or similar elements.

1A illustrates a printhead unit 1. The printhead unit 1 includes an ink supply line 5 that supplies ink to a pressure chamber 3. A piezoelectric actuator 2 is disposed above the pressure chamber 3. By actuating the piezoelectric actuator 2, the upper wall of the pressure chamber 3 is deformed, which results in a pressure pulse in the pressure chamber 2. This causes a droplet of fluid to be ejected from the nozzle 4. The actuator 2 is connected to a controller (not shown) via conductive tracks 6. Each piezoelectric actuator 2 is connected to at least a drive electrode on one side and a ground electrode on the other side. Additional electrodes may be further applied to measure and/or improve the performance of the piezoelectric actuator 2. The printhead unit 1 includes a number of piezoelectric actuators 2 and corresponding nozzles 4 arranged in a row extending in a first direction X, as shown in FIG. 1B. The number of nozzles 4 is generally about several hundred, preferably more than 500. As a result, the printhead unit 1 is elongated in the first direction X. At least two tracks 6 are connected to each piezoelectric actuator 2, so that the number of tracks 6 is even greater than the number of nozzles 4. The ground tracks may be further connected to one or more common ground lines to conserve space.

All tracks 6 extend to the outer surface of the printhead unit 1 in the second direction Y. At one end, each of the tracks 6 is provided with an electrical contact element in the form of a bond pad 7 to facilitate electrical connection with a flexible printed circuit or FPC 10. The FPC 10 comprises a flexible planar carrier 11 on which electronically conductive tracks 12 are provided. The tracks 12 on the FPC 10 may be provided with respective bond pads, the electrical contact elements of which are formed as ends of the tracks 12 themselves throughout Figs. 1A and 1B. The bond pads 7 have increased dimensions, e.g. increased width and/or height, with respect to their connected tracks 6. The bond pads 7 and/or tracks 6 on the printhead unit 1 are arranged correspondingly to the tracks 12 on the FPC 10, e.g. by the same positioning and spacing. This allows electrical connection between the piezoelectric actuators 2 and a controller connected to an end of the FPC 10, not shown. To ensure that the connection remains established during long-term use, the FPC 10 is fixed to the printhead unit 1 by an adhesive 15. Adhesive 15 is present in the contact areas 16 between the carrier 11 of the FPC 10 and the outer surface of the printhead unit 1. In establishing a connection, the adhesive 15 is forced out of the space between the bond pads 7 and the tracks 12, preferably for the most part, so that they are in conductive contact. The adhesive 15 is a non-conductive adhesive, although a non-conductive adhesive with embedded conductive particles may also be applied.

Figure 1B shows a cross-sectional view of the interface between the printhead unit 1 and the flexible printer circuit 10 parallel to the XZ plane. The cross-sectional view shows the contact area 16 located between the printhead unit 1 and the FPC 10. To bond the two together, adhesive 15 is applied inside the contact area 16 between the contact elements, and then the tracks 12 are pressed onto the bond pads 7. As the adhesive is liquid, by pressing together the adhesive 15 flows out of the area between the opposing pairs of tracks 12 and bond pads 7. Thus, an electrical connection is established and at the same time a solid bond is formed between the printhead unit 1 and the flexible printer circuit 10.

A bonding tool for bonding the FPC 10 to the printhead unit 1 is shown in FIG. 2. The bonding tool comprises a holder having a support surface 21 on which the printhead unit 1 is placed during bonding. Preferably, the holder comprises holding means, such as a suction system, clamps, etc., to hold the printhead unit 1 securely in place. Then, adhesive 15 is applied to the bond pads 7 on the printhead unit 1 and/or the tracks 12 on the FPC 10 in what are to be the contact areas 16. The FPC 10 is placed on top of the printhead 1. In FIG. 2, the bonding tool 20 comprises a holding surface 26 configured to releasably hold a portion of the FPC 10. For example, an opening may be provided in the holding surface 26, through which a negative pressure (i.e. a pressure negative with respect to the environment) is applied to the FPC 10 to pull it against the holding surface 26. This allows the FPC 10 to be accurately positioned with respect to the printhead unit 1, with the bond pads 7 and the tracks 12 overlapping when viewed in the vertical direction Z.

The bonding tool further comprises a bond head 24 for pressing the FPC 10 against the print head unit 1. A recess 24 is provided between the bond head 22 and the holding surface 26 to allow some (limited) movement at the end of the FPC 10 including the bond pads 12. The bond head 22 is configured to press the FPC 10 against the support surface 21 with a predetermined force. This force is preferably relatively small, for example around 160 N, to avoid damage to the fine electrical tracks 6, 12 and the bond pads 7, 12, as well as to reduce or prevent excessive force in unintended areas. The pressing force is preferably provided via an arrangement and/or pressing means to which the bond head 22 is attached.

Figure 3 illustrates the bond head 22 attached to its pressing means 60 by a mount 62. The pressing means 60 includes an arm pivotable about a fixed pivot 61, thereby allowing the bond head 22 to move along the arc of the dashed line shown. The arm allows precise control of the pressing force with which the bond head 22 is pressed against the track 6. It will be understood that the arm is an exemplary embodiment and other pressing means such as linear drives, rack and pinion assemblies, screw-based devices may be applied as well.

Figures 4 and 5 illustrate the bond head 22 supported on its hinge mechanism 40. The structure of the hinge mechanism 40 will be described in detail with reference to Figures 8 to 11. The hinge mechanism 40 allows the bond head 22 to be rotated relative to the pressing means 60 so that the bond head 22 can be made parallel to the track 6. The hinge mechanism 40 is further attached to a mount 62.

Figure 6 illustrates a side view of the bonding tool in a first direction X. The bond head 22 is included in the end 20 mounted on a support frame 30 that is disposed on a support surface. The support frame 30 may include positioning means, such as a motor or guide, for adjusting the position of the end 20 relative to the support surface. Pressing means may also be provided on the support frame to press the bonding head 22 against the FPC 10 with a predetermined force.

The end 20 is shown diagrammatically in FIG. 7. FIG. 7 shows that the contact surface 23 of the bond head 22 is curved so as to taper towards the support surface 21. The curve ensures that the force is applied locally to the FPC 10 along the second direction Y. The contact surface 23 is further constant in the first direction X so as to form a straight line in the first direction X in contact with the FPC 10. Since the FPC 10 and its tracks 11 are compliant, it conforms itself to the bond head 22 and/or the print head unit 1. To form a virtual axis of rotation 55, a hinge mechanism (40 in FIG. 8) is provided on at least one side of the support frame 30. Preferably, the hinge mechanisms 40 are provided on two opposite sides of the support frame 30 such that the bond head 22 is located between the hinge mechanisms 40 when viewed from the vertical direction Z.

Figure 8 illustrates the structure of the hinge mechanism 40 included in the support frame 30. The hinge mechanism 40 includes a main structure 42 rigidly connected to the support frame 30. The main structure 42 is preferably attached to a positioning means so that the contact surface 23 can be positioned in a working position to press the FPC 10 with an intended predetermined force. The head support structure 48 is movably connected to the main structure 42 via film hinges 50-53. The head support structure 48 holds the bond head 22 such that the movement of the contact surface 23 relative to the main structure 42 is entirely determined by the hinge mechanism 40 when the main structure 42 is held stationary. The position of the main structure 42 can be fixed by the positioning means. The head support structure 48 is connected to the main structure 42 by two rigid arms 44, 46. Each arm 44, 46 is connected at either end to one of the main structure 42 and the head support structure 48 via a film hinge 50-53. Each film hinge 50-53 allows a respective arm 44, 46 to pivot about an axis parallel to the second direction Y. The rotational movement of the contact surface 23 as defined by the hinge mechanism 40 is illustrated in FIG. 9.

First, the bond head 22 is brought into its operating position by placing the main structure 42 against the support surface 21 on which the print head unit 1 is supported. In the example of FIG. 9, the print head unit 1 is on the lower support surface 21 and the FPC 10 is held against the bond head 22. Since the adhesive 15 has been applied, the adhesive 15 is in the contact area 16 between the print head unit 1 and the FPC 10 so that they are pressed together. By placing the bond head 22 in its operating position, the FPC 10 is pressed towards the print head unit 1. In FIG. 9, the contact pads 7 and the tracks 12 are not yet in contact because the FPC 10 and the print head 1 are spaced apart. Preferably, one or more alignment markers are provided on the print head unit 1 and/or on the FPC 10 so that the bond pads 12 on the FPC 10 can be accurately aligned to the bond pads 7 on the print head unit 1 using a placement means. After this alignment is achieved, the main structure 42 may be fixed in position such that it is fixed relative to the support surface 21. In FIG. 9, the FPC 10 is presented at an oblique angle to the printhead unit 10. In FIG. 9, the FPC 10 is moved downward in the vertical direction Z toward the printhead unit 1. In FIG. 9, the contact area 16 between the FPC 10 and the printhead unit 1 is relatively large and decreases in size as the FPC 10 and the printhead unit are pressed together, as shown in FIG. 10.

10 illustrates the rotation of the FPC 10 around a virtual axis of rotation 55 upon initial contact between the tracks 12 and the contact pads 7. The adhesive 15 is forced out from between the individual contact pads 7 and the tracks 12 that contact each other in FIG. 10. This contact results in a force that causes the hinge mechanism 40 to rotate the FPC 10 around the virtual axis of rotation 55 in FIG. 10 to reduce the skew angle between the FPC 10 and the print head unit 1. The hinge mechanism 40 defines a virtual axis of rotation 55 for the contact surface 23, which is located inside the contact area 16 after alignment. The upper film hinges 50, 53 each allow their respective rigid arms 44, 46 to pivot relative to the main structure 42, as shown by the dashed lines. This allows the lower film hinges 51, 52 to pivot or rotate around their respective upper film hinges 50, 53. Furthermore, the lower film hinges 51, 52 are rigidly coupled by the head support structure 48. This restricts the movement of the head support structure 48 to rotation about a virtual axis of rotation 55. While the main structure 42 is fixed in position, the head support structure 48 is constrained from translational movement relative to the support surface and the print head unit 1 thereon. The hinge mechanism 40 reduces the degrees of freedom of the head support structure to rotation only. Any point on the lower surface of the track 12 is restricted to move in a circular motion, as shown by the dashed circle. Note that a point on the track 12 may be displaced downwards by a distance ΔZ in the height direction Z, and/or vice versa, provided that it is accompanied by a corresponding horizontal displacement ΔX in a first direction X determined by the dashed circular path. In the example of FIG. 10, the individual horizontal displacement ΔX is (almost) zero due to the (almost) vertical direction of the tangent of the dashed circle at this point. The risk of misalignment of the bond pads 7, 12 is minimized because the head support structure 48 is constrained from translating relative to the support surface. Moreover, only the rotational movement of the contact surface 23 allows the contact surface 23 to be parallel to the support surface without translation of the bond pads 7, 12 (as shown in FIG. 11 ). This allows the FPC 10 to be brought into parallel alignment with the print head unit 1 without affecting the relative placement of the bond pads 7, 12. Even if the bonding tool is used on a non-flat table, it allows the pressing force to be applied evenly along the entire length of the print head unit 1 in the first direction X. This allows a reliable electrical connection despite the relatively long length of the rows of bond pads 7, 12.

To improve the life of the bonding tool, a limiter such as a stop may be provided that limits the angular range of rotation about the imaginary axis of rotation 55 to, for example, less than 10°, preferably less than 5°, and most preferably less than 2°. This may avoid excessive bending and/or forces on the leaf hinges 50-53.

The positions of the film hinges 50-51 and the dimensions of the arms 44, 46 are selected so that when the FPC 10 and the print head unit 1 are pressed together, a virtual axis of rotation 55 is located inside the contact area 16 where the adhesive 15 is applied. The hinge mechanism 40 is located on one side of the contact surface 23 and defines a virtual axis of rotation 55 located on the opposite side of the contact surface 23. Preferably, the arms 44, 46 have the same length. The film hinges 50-53 are further mounted mirror-symmetrically with respect to a mirror plane 58 extending perpendicular to the support surface 21 and/or the first direction X, at least when the head support structure 48 is parallel to the first direction X. The mirror plane 58 is always perpendicular to a plane extending through the axis of the upper hinges 50, 53 attached to the main support structure 42. The mirror plane 58 is located centrally between said hinges 50, 53. The mirror plane 58 is further parallel to said axis extending in the second direction Y. The location of the imaginary rotation axis 55 is selected taking into account the dimensions of the head support structure 48, the bond head 22, the FPC 10 and/or the print head unit 1, and the adhesive 15, so as to be located in the contact area 16 during pressing together of the print head unit 1 and the FPC 10. The imaginary rotation axis 55 is configured to be located below the contact surface 23 by a distance equal to the thickness of the FPC 10 in the height direction Z and the average height of the tracks 12 on the FPC 10. This places the imaginary rotation axis 55 in the contact area where the bond pads 7 contact the tracks 12. It will be understood that in practice the dimensions of the individual tracks 12 and bond pads 7 vary such that the contact area is not perfectly flat but is non-uniform. Adhesive residues may further affect the shape of the contact area.

In FIG. 8, hinges 50-53 of hinge mechanism 40 are configured as film hinges 50-53 because the film hinges have little or no play, resulting in accurate positioning of virtual rotation axis 55. It will be understood that different types of hinges may also be applied to the present invention. Also, the number of hinges may be more than the four hinges shown in FIG. 8 and FIG. 9.

Figure 11 illustrates the final state in which the FPC 10 has been rotated into parallel alignment with the printhead unit 1. Each track 12 contacts its respective contact pad 7. The contact area 16 has been reduced to a contact plane 16 that extends to the interface between the contact pad 7 and the track 12. Adhesive 15 has been extruded from this interface into the zone between the contact pad 7 and track 12 pairs. Although the contact plane 16 is shown in Figure 11 as a perfectly straight plane, in reality the contact surface 16 may be irregular due to differences in height and/or position of the tracks 12 and contact pads 7. The compliance of the FPC 10, which is held free against the contact surface 23, allows the FPC 10 to conform to such irregularities.

The contact surface 23 is further provided with a protective coating that reduces adhesion of the adhesive 15 to the contact surface 23. This coating is an anti-stiction coating, preferably comprising FOTS (fluoroctychlorosilane).

Although specific embodiments of the present invention are illustrated and described herein, it will be understood by those skilled in the art that various alternative and/or equivalent implementations exist. It should be understood that the exemplary embodiment or exemplary embodiments are merely examples and are not intended to limit the scope, applicability or configuration in any way. Rather, the foregoing summary and detailed description provide one skilled in the art with a convenient road map for implementing at least one exemplary embodiment, and it should be understood that various changes can be made in the function and arrangement of elements described in the exemplary embodiments without departing from the scope as set forth in the appended claims and their legal equivalents. In general, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

In this document, the terms "comprises," "comprises," "includes," "includes," "includes," "containing," "has," "having," and any variations thereof are intended to be understood in an inclusive (i.e., non-exclusive) sense, and it is understood that the processes, methods, devices, apparatuses, or systems described herein are not limited to those features or portions or elements or steps enumerated, and may include other elements, features, portions, or steps not expressly enumerated or inherent to such processes, methods, articles, or apparatus. Furthermore, the terms "a" and "an" as used herein are understood to mean one or more, unless expressly stated otherwise. Furthermore, terms such as "first," "second," "third," and the like are used merely as labels, and are not intended to impose or establish numerical requirements on a particular ranking of the importance of those objects.

The invention having thus been described, it will be apparent that the same may be modified in many ways. Such variations are not to be regarded as departures from the spirit and scope of the invention, and all such modifications which would be apparent to one skilled in the art are intended to be included within the scope of the following claims.

Claims (11)

A bonding tool for bonding a flexible printed circuit (10) to a printhead unit (1) defining contact areas (16) onto which an adhesive (15) is applied for bonding the printhead unit (1) to the flexible printed circuit (10), comprising:
a support surface (21) configured to support said printhead unit (1);
a bondhead (22) including a contact surface (23) configured to press said flexible printed circuit (10) against a printhead unit (1) on said support surface (21);
a hinge mechanism (40) configured to movably support said bond head (22),
The bonding tool is characterized in that the hinge mechanism (40) has a structure that limits movement of the contact surface (23) of the bond head (22) so that the contact surface (23) moves around a rotation axis (55) that is located within the intended position of the contact area (16) between the print head unit (1) and the flexible printed circuit (1). The bonding tool according to claim 1, wherein the contact surface (23) is elongated and extends in a first direction (X), and the rotation axis (55) extends perpendicular to the first direction (X). 2. The bonding tool of claim 1 , wherein the axis of rotation (55) is further parallel to the support surface (21) and the movement of the contact surface (23) is fully rotational at least in a predetermined working range. 3. The bonding tool of claim 2 , wherein the hinge mechanism (40) includes at least four hinges (50-53), two of which each connect the bond head (22) to a main structure (42) via a respective rigid arm (44, 46) and another respective hinge (50, 53). The bonding tool according to claim 4, wherein the hinges (50-53) can be arranged mirror-symmetrically with respect to a mirror plane (58) perpendicular to a plane extending in the first direction (X) through the axis of the hinges (50, 53) attached to the main structure (42) and centrally located between the hinges (50, 53) attached to the main structure. 5. The bonding tool of claim 4 , wherein the main structure (42) includes positioning means for adjusting the position of the hinge mechanism (40) relative to the support surface (21). The bonding tool of claim 4 , wherein the hinges (50-53) are film hinges. 3. A bonding tool as claimed in claim 2 , wherein a recess (24) extending in the first direction (X) is provided in the bond head (22) adjacent to the contact surface (23), the recess (24) facing the support surface (21). 3. A bonding tool as described in claim 2 , wherein the contact surface (23) is provided as a curved surface that tapers toward the support surface (21) when viewed from the first direction (X). 10. The bonding tool of claim 9 , wherein the curved surface comprises an anti-stiction material . A method for bonding a flexible printed circuit (10) to a printhead unit (1), comprising the steps of:
- bonding the printhead unit (1) to the flexible printed circuit (10) with an adhesive (15) between them;
- pressing the bond pads (7, 12) of said printhead unit (1) and said flexible printed circuit (10) together by means of a contact surface (23),
The method of claim 1, wherein the contact surface (23) rotates around an axis of rotation arranged in a contact area (16) for the adhesive (15) between the printhead unit (1) and the flexible printed circuit (10).