NL2033279B1

NL2033279B1 - Bonding tool for connecting a printhead unit to an FPC

Info

Publication number: NL2033279B1
Application number: NL2033279A
Authority: NL
Inventors: H W Lamers Norbert
Original assignee: Canon Kk
Priority date: 2022-10-11
Filing date: 2022-10-11
Publication date: 2024-04-26
Also published as: JP2024056639A

Abstract

A bonding tool for bonding a flexible printed circuit (10) to a printhead unit (1) defining a contact region (16) where an adhesive (15) is to applied for bonding the printhead unit (1) to the flexible printed circuit (10), comprising : - a support surface (21) configured to support the printhead unit (1); - a bond head (22) comprising a contact surface (23) configured to press the flexible printed circuit (10) onto printhead unit (1) on the support surface (21); - a hinge mechanism (40) configured to movably support the bond head (22); characterized in that the hinge mechanism (40) has a structure which restricts movement ofthe contact surface (23) ofthe bond head (22), such that the contact surface (23) moves about a rotational axis (55) positioned within an intended location of the contact region (16) between the printhead unit (1) and the flexible printed circuit (1).

Description

11012665NL01 1

Bonding tool for connecting a printhead unit to an FPC

BACKGROUND OF THE INVENTION

1.Field of the invention

The invention relates to a bonding tool for bonding a flexible printed circuit to a printhead unit and to a method of bonding of a flexible printed circuit to a printhead unit. 2. Description of Background Art

Bonding tools are generally applied to connect a chip to a flexible printed circuit (FPC).

Both the chip and the FPC comprise one or more rows of a large number of bond pads and/or tracks, wherein the bond pads of the chip have to be individually connected to tracks on the FPC to establish the electrical connection required for controlling the chip.

Printhead units may comprise exceptionally long rows of bond pads due to the large number of nozzles provided on a single printhead unit. The density of the bond pads is also generally high, as a result of the high nozzle density (dots per inch, DPI) of the printhead unit. A bonding tool for printhead units comprises a support surface for supporting the printhead unit and a bond head comprising a longitudinal contact surface extending in a first direction. The first direction is the direction wherein the one or more rows of nozzles and/or bond pads extend. The contact surface is configured for pressing the flexible printed circuit onto printhead unit. The two are pressed together with a predetermined force. It was found that in practice not all produced bond pads are in proper electrical contact with their respective track after bonding the FPC and the printhead unit together.

SUMMARY OF THE INVENTION

It is an object of the invention to improve the yield of a process of bonding together an

FPC and a printhead unit.

In accordance with the present invention, a bonding tool according to claim 1 and a method according to claim 10 are provided.

The bonding tool for bonding a flexible printed circuit to a printhead unit by means of an adhesive provided in a contact region between the flexible printed circuit and the printhead unit comprises :

11012665NL01 2 - a support surface configured to support the printhead unit; - a bond head comprising a contact surface, configured for pressing the flexible printed circuit onto printhead unit on the support surface, and - a hinge mechanism configured to movably support the bond head.

The bonding tool is characterized in that the hinge mechanism has a structure which which restricts movement of the contact surface of the bond head, such that the contact surface moves about a rotational axis positioned within an intended location of the contact region between the printhead unit and the flexible printed circuit. The rotational axis is is a preferably a so-called “virtual” rotational axis positioned inside the contact region where the layer of adhesive is to be positioned, allowing the FPC and the printhead unit to be rotated with respect to one another until both are parallel to one another. The rotational motion (which may be restricted to a predetermined range) of the contact surface prevents any translation between the bond pads on the printhead unit with respect to tracks on the FPC. The rotational motion however does allow the printhead unit and the FPC to be brought parallel to one another without the risk of any translation of the bond pads on the printhead unit with respect to the tracks on the FPC.

The rotational axis counteracts any initial non-parallelism between the support surface and the contact surface, when the two are being positioned and pressed together. This results in a substantially constant pressure distribution across all bond pads, regardless of the initial relative angles between the FPC and the printhead unit. In consequence, every bond pad experiences sufficient and the same pressing force. The rotational axis further keeps the pressing force or pressure to substantially constant when the distance between the printhead unit and the FPC is adjusted. By bringing the opposing rows of bond pads and tracks parallel by a rotational movement around this rotational axis a highly reliable connection can be established. Thereby the object of the present invention has been achieved.

More specific optional features of the invention are indicated in the dependent claims.

In an embodiment, the contact surface is longitudinal and extends in a first direction, and the structure limits movement of the contact surface to a rotation around the rotational axis. Due to the relatively long row of nozzles, the corresponding row of contact pads is effectively a line structure to be aligned with the corresponding tracks.

The row extends in the first direction. To ensure proper contact, the row of tracks must

11012665NL01 3 be parallel to the row of contact pads. This is achieved by allowing for a rotation around the axis perpendicular to the first direction, wherein the rotational axis is positioned in the contact region between row of contact pads and the row of tracks. The hinge mechanism is preferably configured to position the rotational axis in the contact region without having any physical components in the contact region. The rotational axis is thus a virtual rotational axis formed by the rod mechanism structure of the hinge mechanism.

It will appreciated that the above mentioned virtual rotational axis creates a rotational movement between the support surface and the bond head. Preferably, one of the support surface and the bond head is maintained stationary during pressing, while the other moves towards it. The virtual rotational axis may therein be configured for rotating either the contact surface on the bond head while support surface is moved towards the bond head or vice versa. The virtual rotational axis may alternatively be provided on the moving member, for example the bond head is movable towards the support surface, while the virtual rotational axis ensure that the contact surface on the bond head is rotatable. Similarly, the support surface may movable and rotatable. Also, either the

FPC or the printhead unit may be provided on the bond head, as well as on the support surface.

In an embodiment, the virtual rotational axis is parallel to the support surface and the movement of the contact surface fully rotational at least in an intended working range.

The rows of bond pads extend in the first direction, as do the tracks. To bring a row of bond pads on the printhead unit parallel to a row of tracks on the FPC, the printhead unit may be rotated around the virtual rotational axis positioned in between the FPC and the printhead unit. The virtual rotational axis is further preferably parallel to the support surface. The contact surface is limited to a solely rotational motion to prevent translational movement of the rows of bond pads with respect to the tracks on the FPC.

The movement of the contact surface is rotational in the working range wherein the FPC and the printhead unit are pressed together. The rotational movement of the contact surface results in each point on said contact surface travelling in a circle around the virtual rotational axis. The displacement of each point on the contact surface in the first direction is accompanied by proportional displacement in the height direction, wherein the ratios between these displacements are determined by the respective angle of said

11012665NL01 4 point with respect to the virtual rotational axis.

In another embodiment, the bond head, specifically the contact surface is rigid as compared to the flexible printed circuit. The FPC is deformable, having a certain compliance which allows it to be re-shaped while being pressed against the printhead unit. The bond head is relatively undeformable.

In an embodiment, the printhead unit and the FPC comprise electrically conductive tracks, each of which is provided with an electrical contact element or area at its end, wherein the electrical contact elements or areas on respectively the printhead unit and the FPC are dimensioned and/or positioned, such that each electrical contact element and/or area on the one is in electrical contact with a corresponding electrical contact element and/or area on the other. Basically, each track on the printhead unit is connected to a track on the FPC, such that they together form a single electrical connection between the actuator and the controller. The corresponding electrical contact element and/or area may be simply formed as end portions of the respective tracks or alternative structures, such as bond pads may be applied at the end of the tracks at one or both of the printhead unit and the FPC. The contact region is preferably defined as being positioned between the electrical contact elements of the FPC on one side and the electrical contact elements of the printhead unit on the other.

In an 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 the virtual rotational axis to lie in the contact region comprising the adhesive between the FPC and the printhead unit. The hinge mechanism is a simple and low-costs manner to create the virtual rotational axis without obstructing the bonding process. Preferably, the hinge mechanism is positioned on an opposite side of the contact surface as the virtual rotational axis.

In an embodiment, the hinges are mirror symmetrically positionable with respect to a mirror plane extending perpendicular to the plane extending through axes of the hinges mounted at the main structure. The mirror plane is further positioned centrally between said hinges, thus at an equidistant spacing with respect to both said hinges. In at least one of its positions, the hinge mechanism is mirror symmetric with respect to the mirror

11012665NL01 plane. While rotating, the hinge mechanism may move out of this symmetric state, but can be returned to it by repositioning the contact surface at the angle it had when the hinge mechanism was in its symmetric state. The symmetrical hinge mechanism contributes to restricting the contact surface to a purely rotational motion. With respect 5 to the mirror plane corresponding hinges have the same positions but mirrored and the respective connecting arms have the same dimensions, specifically lengths. After bonding, the mirror plane is further perpendicular to the first direction.

In an embodiment, the main structure comprises positioning means for adjusting a position of the hinge mechanism with respect to the support surface. The main structure of the hinge mechanism is mounted on the positioning means. The positioning means are configured to move the hinge mechanism with the bond head in its entirety with respect to the support surface. The hinge mechanism and bond head may thereby be moved away to allow the printhead unit to be placed 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 drives. The positioning means may further form or include the pressing means for pressing the printhead unit and FPC together with a predetermined force.

In an embodiment, the hinges are film hinges. Film hinges have little to no play and thus allow for an accurate positioning of the head support structure with respect to the main structure. Minimal play also allows the rotational movement of the contact surface to be accurately maintained during motion, such that shifting of the bond pads with respect to the tracks on the FPC outside of the circular trajectory determined by the virtual rotational axis is avoided. Points on the contact surface may still move in the first direction if accompanied by a corresponding displacement in the heigh direction as determined by the circular trajectory defined by the virtual rotational axis, and/or vice versa. Film hinges are further low-costs and durable.

In an embodiment, a recess extending in the first direction is provided in the bond head adjacent the contact surface. The recess faces the support surface. The recess is preferably positioned between the contact surface and holding means for holding the

FPC. At the contact surface the FPC is preferably not actively held against the bond head to allow it sufficient compliance while bonding. Generally the bond head is above

11012665NL01 6 the support surface, so holding means are require to prevent the FPC from losing its position with respect to the bond head. The recess during pressing is positioned over an edge of the printhead unit, thus preventing excess pressure on other areas of the printhead unit besides the bond pad area. Specifically, pressure on the edges of the printhead unit is avoided in this manner, which ensures that the pressing force is entirely directed into the bond head, such that the pressing force can be accurately controlled.

The recess allows a portion of the FPC at the contact surface a small amount of mobility in at least the second direction with respect to the contact surface without falling off the bond head. This allows the tracks on the FPC to better conform to the printhead unit while bonding, as compared to when it would be held secured against the contact surface.

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

In an embodiment, the curved surface comprises a non-stiction material, preferably a

FOTS material. To prevent or reduce adhesive from adhering to the bond head, a coating is applied. A non-stiction coating reduces the bonding between the adhesive and the curved surface. FOTS materials were found to work well in this regard.

The present invention further relates to a method for bonding a flexible printed circuit to a printhead unit, comprising the steps of: - bonding the printhead unit to the flexible printed circuit by means of adhesive between the two; - pressing bond pads and/or tracks on respectively the printhead unit and the flexible printed circuit together by means of a contact surface, wherein the contact surface rotating around a virtual rotational axis positioned in a

11012665NL01 7 contact region between the printhead unit and the flexible printed circuit. The contact region is where the adhesive is to be applied. The rotation of the contact surface is preferably determined by the hinge mechanism as described above.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

Fig. 1A is a schematic, cross-sectional view of a printhead unit bonded to a flexible printed circuit by means of an adhesive;

Fig. 1B is a schematic, cross-sectional view of the contact interface along the cross- section C of the printhead unit in Fig. 1A;

Fig.2 is a perspective schematic view of a bonding tool for bonding a printhead unit to a flexible printed circuit by means of an adhesive;

Fig. 3 is a perspective side of the bonding tool in Fig. 2 mounted on its pressing means;

Fig. 4 Fig. 2 is a close-up, perspective view of the bond head of the bonding tool in

Fig. 2 mounted on its hinge mechanism;

Fig. 5 Fig. 2 is another close-up, perspective view of the bond head of the bonding tool in Fig. 2 mounted on its hinge mechanism;

Fig. 6. is a side view of the bonding tool in Fig. 2;

Fig. 7 is an enlarged, side view of a bond head of the bonding tool in Figs. 2 and 6;

Fig. 8 is a front view of the hinge mechanism of the bonding tool in Figs. 2 to 7;

Fig. 9 is a schematic diagram reflecting the hinge mechanism in Fig. 8 during the initial stage of pressing the FPC and printhead unit together;

Fig. 10 is another schematic diagram reflecting the hinge mechanism, wherein the FPC has rotated with respect to Fig. 9 due to initial contact with the FPC;

11012665NL01 8

Fig. 11 is another schematic diagram reflecting the hinge mechanism in Fig. 9, wherein the FPC has been rotated into a parallel orientation with respect to the printhead unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views.

Fig. 1A illustrates a printhead unit 1. The printhead unit 1 comprises an ink supply line 5, which supplies ink to the pressure chamber 3. A piezo-actuator 2 is positioned over the pressure chamber 3. By actuating the piezo-actuator 2 the top wall of the pressure chamber 3 is deformed, resulting in a pressure pulse in the pressure chamber 2.

Thereby, a droplet of fluid is ejected from the nozzle 4. The actuator 2 is connected to a controller (not shown) via electrically conductive tracks 6. Each piezo-actuator 2 is connected to at least a driving electrode on one side and a ground electrode on an opposing side. Further electrodes for measuring and/or improving the performance of the piezo-actuator 2 may further be applied. The printhead unit 1 comprises a large number of piezo-actuators 2 and corresponding nozzles 4 positioned in a row extending in the first direction X, as shown in Fig. 1B. The number of nozzles 4 is generally around a several hundred, preferably greater than 500. In consequence, the printhead unit 1 is longitudinal in the first direction X. The number of tracks 6 is even greater than the number of nozzles 4 as at least two tracks 6 are connected to each piezo-actuator 2.

Ground tracks may further be connected to one or more common ground lines to save space.

All tracks 6 extend to an outer surface of the printhead unit 1 in the second direction Y.

The tracks 6 at one end are each provided with an electrical contact element in the form of a bond pad 7 to facilitate an electrical connection with the flexible printed circuit or

FPC 10. The FPC 10 comprises a flexible, planar carrier 11 upon which electronically conductive tracks 12 are provided. The tracks 12 on the FPC 10 may be provided with their respective bond pads, though in Fig. 1A, 1B the electrical contact elements of the tracks 12 are formed as the end portions of the tracks 12 themselves. The bond pads 7 have increased dimensions with respect to their connected tracks 6, for example an

11012665NL01 8 increased width and/or height. The bond pads 7 and/or the tracks 6 on the printhead unit 1 are positioned corresponding to the tracks 12 on the FPC 10, by e.g. the same positioning and spacings. This allows for an easy electrical connection between the piezo-actuators 2 and the controller connected to the not shown end of the FPC 10. To ensure the connection remains established during prolonged use, the FPC 10 is secured to the printhead unit 1 by means of an adhesive 15. The adhesive 15 is present in a contact region 16 between the carrier 11 of the FPC 10 and the outer surface of the printhead unit 1. When establishing the connection the adhesive 15 is preferably for the most part pressed out of the space between the bond pads 7 and the tracks 12, such that these are in electrically conductive contact. The adhesive 15 is a non-conducting adhesive, though a non-conducting adhesive with embedded conductive particles may be applied as well.

Fig. 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 region 16 being positioned between the printhead unit 1 and the FPC 10. To bond the two together, the adhesive 15 is applied inside the contact region 16 between the contact elements and the tracks 12 are then pressed onto the bond pads 7. As the adhesive is liquid, the pressing together forces the adhesive 15 to flow out of the areas between opposing pairs of tracks 12 and bond pads 7. Thus, an electrical connection is established, while at the same time forming a solid bond between the printhead unit 1 and the flexible printer circuit 10.

The bonding tool for bonding the FPC 10 to the printhead unit 1 is shown in Fig. 2. The bonding comprises a holder with a support surface 21 upon which the printhead unit 1 is positioned during bonding. Preferably, the holder is provided with holdings means, such a suction system, clamps, etc. to securely hold the printhead unit 1 in position. The adhesive 15 is then applied in what is to be the contact region 16, to the bond pads 7 on the printhead unit 1 and/or the tracks 12 on the FPC 10. The FPC 10 is positioned over 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, openings may be provided in the holding surface 26 through which an underpressure (i.e. a negative pressure with respect to the ambient) is applied to the FPC 10 to draw it against the holding surface 26. This allows accurately positioning the FPC 10 with respect to the printhead unit 1, so

11012665NL01 10 that the bond pads 7 and tracks 12 overlap when viewed in the vertical direction Z.

The bonding tool further comprises a bond head 24 for pressing the FPC 10 against the printhead unit 1. A recess 24 is provided between the bond head 22 and the holding surface 26 to allow a (limited) degree of movement to the end of the FPC 10 comprising the bond pads 12. The bond head 22 is configured for pressing the FPC 10 towards the support surface 21 with a predetermined force. This force is preferably relatively small, e.g. around 160 N, to avoid damaging the fine electrical tracks 6, as well as to reduce or prevent excessive force in unintended areas. 12 and bond pads 7, 12. The pressing force is preferably provided via the positioning and/or pressing means upon which the bond head 22 is mounted.

Fig. 3 illustrates the bond head 22 as mounted on its pressing means 60 by means of the mount 62. The pressing means 60 comprise an arm pivotable around a fixed pivot axis 61. Thereby, the bond head 22 is movable along the indicated dashed arc. The arm allows for accurate control of the pressing force by which the bond head 22 is pressed on the tracks 6. It will be appreciate that the arm is an exemplary embodiment, and that other pressing means, such as linear drives, rack and pinion assemblies, screw-based devices, may be applied as well.

Figs. 4 and 5 show the bond head 22 supported on its hinge mechanism 40. The structure of the hinge mechanism 40 will be discussed in detail with regard to Figs. 8 to 11. The hinge mechanism 40 allows the bond head 22 to be rotated with respect to the pressing means 60, such that the bond head 22 can be brought parallel to the tracks 6.

The hinge mechanism 40 is further mounted on the mount 62.

Fig. 6 illustrates a side view of the bonding tool in the first direction X. The bond head 22 is comprised in the end portion 20, which is mounted on a support frame 30, which is positioned over the support surface. The support frame 30 may include positioning means for adjusting the position of the end portion 20 with respect to the support surface, such as motors or guides. Pressing means may also be provided on the support frame to press the bond head 22 with a predetermined force onto the FPC 10.

The end portion 20 is shown in schematically in Fig. 7. Fig. 7 shows that the contact

11012665NL01 11 surface 23 of the bond head 22 is curved, such that it tapers towards the support surface 21. The curvature 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, such that it forms a straight line in the first direction X where it contacts the FPC 10.

Since the FPC 10 and its tracks 11 are compliant, it will conform itself to the bond head 22 and/or the printhead unit 1. To form the virtual rotational axis 55, the hinge mechanism (40 in Fig. 8) is provided on at least one side of the support frame 30.

Preferably, a hinge mechanism 40 is provided on two opposite sides of the support frame 30, such that the bond head 22 is positioned in between the hinge mechanisms 40 when viewed in the vertical direction Z.

Fig. 8 illustrates the structure of the hinge mechanism 40 which is comprised in the support frame 30. The hinge mechanism 40 comprises a main structure 42, which is rigidly connected to the support frame 30. The main structure 42 is preferably mounted on the positioning means, such that the contact surface 23 can be positioned into its working position, where it presses onto the FPC 10 with the intended predetermined force. A 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 movement of the contact surface 23 with respect to the main structure 42 is determined entirely by the hinge mechanism 40, when the main structure 42 is kept stationary. The position of the main structure 42 can be fixed by means of the positioning means. The head support structure 48 is connected to the main structure 42 by means of 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 the respective arm 44, 46 to pivot around an axis parallel to the second direction Y. The rotational motion of the contact surface 23 as defined by the hinge mechanism 40 is illustrated in Fig. 9.

Initially the bond head 22 is brought into its working position by positioning the main structure 42 with respect to the support surface 21 up which the printhead unit 1 is supported. In the example in Fig. 9, the printhead unit 1 is on the support surface 21 below, while the FPC 10 is held against the bond head 22. Adhesive 15 has been applied, so that the adhesive 15 is in the contact region 16 between the printhead unit 1 and the FPC 10 as these are pressed together. By positioning the bond head 22 in its

11012665NL01 12 working position, the FPC 10 is pressed towards the printhead unit 1. In Fig. 9, the FPC 10 and the printhead 1 are spaced apart, so that the contact pads 7 and the tracks 12 do not yet make contact. Preferably, one or more alignment markers are provided on the printhead unit 1 and/or on the FPC 10, so that the bond pads 12 on the FPC 10 can be accurately aligned with the bond pads 7 on the printhead unit 1 using the positioning means. After this alignment is achieved, the main structure 42 may be fixed in its position, so that it is fixed with respect to the support surface 21. In Fig. 9, the FPC 10 has been provided at a skewed angle with respect to the printhead unit 10. In Fig. 9, the

FPC 10 is moved downwards in the vertical direction Z towards the printhead unit 1. In

Fig. 9, the contact region 16 between the FPC 10 and the printhead unit 1 is relatively large and will decrease in size as the FPC 10 and printhead unit are pressed together, as shown in Fig. 10.

Fig. 10 illustrates the rotation of the FPC 10 around the virtual rotational axis 55 upon the initial contact between the tracks 12 and the contact pads 7. The adhesive 15 is pushed out from between the respective contact pad 7 and the track 12, which contact each other in Fig. 10. This contact results in a force, which in Fig. 10, causes the hinge mechanism 40 to rotate the FPC 10 around the virtual rotational axis 55 to reduce the skew angle between the FPC 10 and the printhead unit 1. The hinge mechanism 40 defines a virtual rotational axis 55 for the contact surface 23, which virtual rotational axis 55 is positioned inside the contact region 16 after alignment. The upper film hinges 50, 53 each allow their respective rigid arm 44, 46 to pivot with respect to the main structure 42, as indicated by the dashed lines. Thereby, the lower film hinges 51, 52 are set to pivot or rotate around their respective upper film hinge 50, 53. Additionally, the lower film hinges 51, 52 are rigidly coupled by the head support structure 48. This causes the movement of the head support structure 48 to be limited to a rotation around the virtual rotational axis 55. While the main structure 42 is fixed in its position, the head support structure 48 is prevented from translational movement with respect to the support surface and the printhead unit 1 thereon. The hinge mechanism 40 reduces the degrees of freedom of the head support structure to only a rotation. Any points on the lower surface of the tracks 12 are restricted to move in a circular motion, as indicated by the dashed circle. It is noted that a point on the track 12 may be displaced downward by a distance AZ in the height direction Z, if accompanied by a corresponding horizontal displacement AX in the first direction X as determined by the dashed circular path,

11012665NL01 13 and/or vice versa. In the example in Fig. 10, the respective horizontal displacement AX is (near) zero due to the (near) vertical direction of the tangent of the dashed circle at this point. Since the head support structure 48 is prevented from translating with respect to the support surface, the risk of misaligning the bond pads 7, 12 is minimized. Further, the solely rotational movement of the contact surface 23 allows the contact surface 23 to be brought parallel to the support surface without any translation of the bond pads 7, 12 (as shown in Fig. 11). The FPC 10 can thereby be brought into parallel alignment with the printhead unit 1 without affecting the relative positioning of the bond pads 7, 12.

Even when the bonding tool is used on a non-flat table, it allows the pressing force to be homogenously applied along the full length of the printhead unit 1 in the first direction X.

This allows for a reliable electrical connection, despite the relatively long length of the rows of bond pads 7, 12.

To improve the lifetime of the bonding tool limiters, such as stops, may be provided which restrict the angular range of the rotation around the virtual rotational axis 55 to e.g. less than 10°, preferable less than 5°, and very preferably less than 2°. Thereby, excessive bending and/or forces on the leaf hinges 50-53 can be avoided.

The positions of the film hinges 50-51 and the dimensions of the arms 44, 46 are selected, such that the virtual rotational axis 55 is positioned inside the contact region 16 where the adhesive 15 is to be applied, when the FPC 10 and the printhead unit 1 have been pressed together. The hinge mechanism 40 is positioned on one side of the contact surface 23, while it defines the virtual rotational axis 55 to lie on the opposite side of the contact surface 23. Preferably, the arms 44, 46 have the same lengths. 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 at all times is perpendicular to a plane extending through the axes of upper hinges 50, 53 mounted at the main support structure 42. The mirror plane 58 lies in the middle between said hinges 50, 53. The mirror plane 58 is further parallel to said axes which extend in the second direction Y. The position of the virtual rotational axis 55 has been selected considering the dimensions of the head support structure 48, bond head 22, the FPC 10 and/or the printhead unit 1, and the adhesive 15, such that it lies in the contact region 16 during the pressing together of the printhead unit 1 and the FPC 10.

11012665NL01 14

The virtual rotational axis 55 is configured to be positioned below the contact surface 23 by a distance equal to a thickness of the FPC 10 in the height direction Z and an average height of the tracks 12 on the FPC 10. Thereby, the virtual rotational axis 55 is located at the contact area where the bond pads 7 will come into contact with the tracks 12. It will be appreciated that in practice the dimensions of individual tracks 12 and bond pads 7 will vary, such that the contact area is not a perfect plane, but uneven. Adhesive residue may further affect the shape of the contact area.

In Fig. 8 the hinges 50-53 of the hinge mechanism 40 are configured as film hinges 50- 53, since film hinges have little to no play, resulting in an accurate positioning of the virtual rotational axis 55. It will appreciate that different types of hinges may also be applied in the present invention. The number of hinges may also be greater than the four hinges shown in Figs. 8 and 9.

Fig. 11 illustrates the final state wherein the FPC 10 has been rotated into parallel alignment with the printhead unit 1. Each track 12 makes contact with its respective contact pad 7. The contact region 16 has been reduced to a contact plane 16 extending at the interface between the contact pads 7 and the tracks 12. The adhesive 15 has been pressed out of this interface into the zones between pairs of contact pads 7 and tracks 12. While in Fig. 11 the contact plane 16 is illustrated as a perfectly straight plane, in practice the contact plane 16 may be irregular due to height and/or positional differences in the tracks 12 and contact pads 7. The compliance of the FPC 10 which is freely held 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 which reduces the adhesion of the adhesive 15 to the contact surface 23. This coating is an anti-stiction coating, which comprising preferably FOTS (fluoroctatrichlorosilane).

Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and

11012665NL01 15 detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

It will also be appreciated that in this document the terms “comprise”, "comprising", "include", “including”, "contain", "containing", "have", "having", and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "a" and "an" used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.

The present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

11012665NL01 16

Embodiments 1. A bonding tool for bonding a flexible printed circuit (10) to a printhead unit (1) defining a contact region (16) where an adhesive (15) is to applied for bonding the printhead unit (1) to the flexible printed circuit (10), comprising : - a support surface (21) configured to supportthe printhead unit (1); - a bond head (22) comprising a contact surface (23) configured to press the flexible printed circuit (10) onto printhead unit (1) on the support surface (21); - a hinge mechanism (40) configured to movably support the bond head (22); characterized in that the hinge mechanism (40) has a structure which restricts movement of the contact surface (23) of the bond head (22), such that the contact surface (23) moves about a rotational axis (55) positioned within an intended location of the contact region (16) between the printhead unit (1) and the flexible printed circuit (1). 2. The bonding tool according to claim 1, wherein the contact surface (23) is longitudinal and extends in a first direction (X), and the rotational axis (55) extends perpendicular to the first direction (X). 3. The bonding tool according to any of the previous claims, wherein the rotational axis (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. 4. The bonding tool according to any of the previous claims, wherein the hinge mechanism (40) comprises at least four hinges (50-53), two of which each connect the bond head (22) via a respective rigid arm (44, 46) and another respective hinge (50, 53) to a main structure (42). 5. The bonding tool according to claim 4, wherein the hinges (50-53) are mirror symmetrically positionable with respect to a mirror plane (58) perpendicular to a plane extending through axes of the hinges (50, 53) mounted at the main structure (42) to the first direction (X) and positioned centrally between said hinges (50, 53) mounted at the main structure. 6. The bonding tool according to claim 4 or 5, wherein the main structure (42) comprises positioning means for adjusting a position of the hinge mechanism (40) with respect to the support surface (21).

11012665NL01 17 7. The bonding tool according to any of the claims 4 to 6, wherein the hinges (50- 53) are film hinges. 8. The bonding tool according to any of the previous claims, wherein a recess (24) extending in the first direction (X) is provided in bond head (22) adjacent the contact surface (23), the recess (24) facing the support surface (21).

9. The bonding tool according to any of the previous claims, wherein the contact surface (23) is provided on a curved surface which tapers towards the support surface (21) when viewed in the first direction (X). 10. The bonding tool according to claim 8, wherein said curved surface comprises a non-stiction material, preferably a FOTS material. 11. 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) by means of adhesive (15) between the two;

- pressing bond pads (7, 12) on respectively the printhead unit (1) and the flexible printed circuit (10) together by means of a contact surface (23),

characterized by the contact surface (23) rotating around a rotational axis positioned in a contact region (16) for the adhesive (15) between the printhead unit (1) and the flexible printed circuit (10).

Claims

11012665EN01 18 Conclusions

1. Connection device for connecting a flexible printed circuit (10) to a printhead unit (1) defining a contact zone (16) where an adhesive (15) is provided to bond the printhead unit (1) to the flexible printed circuit (10) to be connected, comprising: - a supporting surface (21) designed to support the print head unit (1); - a connecting head (22) with a contact surface (23), wherein the contact surface (23) is designed for printing the flexible printed circuit (10) on the print head unit (1) on the supporting surface (21); -a hinge mechanism (40) designed to movably support the connecting head (22), characterized in that the hinge mechanism (40) comprises a structure that controls the movement of the contact surface (23) of the connecting head (22) in such a way limited, that the contact surface (23) moves about a rotational axis (55) located in a designated location within the contact zone (16) between the print head unit (1) and the flexible printed circuit

(1).

Connecting device according to claim 1, wherein the contact surface (23) is elongated and extends in a first direction (X), and the rotation axis (55) is perpendicular to the first direction (X).

Connecting device according to any one of the preceding claims, 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 operating range.

Connecting device according to any one of the preceding claims, wherein the hinge mechanism (40) comprises at least four hinges (50-53), two of which each connect the connecting head (22) via a respective, rigid arm (44, 46) and a further, respectively connect hinge (50, 53) to a main structure (42).

Connecting device according to claim 4, wherein the hinges (50-53) are mirror-symmetrically positionable with respect to a mirror plane (58) perpendicular to a plane extending through axes of the hinges (50, 53) on the main structure (42 ) and which mirror surface (58) is centrally between the hinges in question

11012665EN01 19 (50, 53) is located on the main structure (42).

Connecting device according to claim 4 or 5, wherein the main structure (42) comprises positioning means for adjusting a position of the hinge mechanism (40) relative to the support surface (21).

Connecting device according to any one of claims 4 to 6, wherein the hinges (50-53) are leaf hinges.

Connecting device according to any one of the preceding claims, wherein a recess (24) extending in the first direction (X) is provided in the connecting head (22) near the contact surface (23), the recess facing the supporting surface (21) is.

Connecting device according to any one of the preceding claims, wherein the contact surface (23) is provided on a curved surface that narrows towards the support surface (21) when viewed in the first direction (X).

10. Connecting device according to claim 9, wherein the curved surface in question comprises an anti-adhesion material, preferably a FOTS material.

11. Method of connecting a flexible printed circuit (10) to a print head unit (1), comprising the steps of: - connecting the print head unit (1) to the flexible printed circuit (10) by providing an adhesive (15) between the two; - pressing contact blocks (7, 12) against each other on the print head unit (1) and the flexible printed circuit (10) respectively by a contact surface (23), characterized by rotating the contact surface (23) around a rotation axis located in a contact zone (16) intended for the adhesive (15) between the print head unit (1) and the flexible printed circuit (10).