Apparatus and method for printing a viscous substance by means of laser induced forward transfer on a product

Abstract

Apparatus for printing a viscous substance by means of Laser Induced Forward Transfer on a product, the apparatus comprising: • - a substrate handler (4) arranged for holding a substrate (5) and positioning a first surface (7) of the substrate (5) into a coating position (9) and a printing position (11), wherein, in the printing position (11), the first surface (7) of the substrate (5) is at a predetermined position relative to the product (3) for printing the viscous substance (2) on the product (3); • - a support (13) for positioning the product (3) in relation to the first surface (7) of the substrate (5) in the printing position (11) of the substrate (5); • - a coater (15) arranged for providing a layer (17) of the viscous substance (2) on the first surface (7) of the substrate (5) in the coating position (9) of the substrate (5); • - a printing device (19) comprising a first emitter unit (21) arranged for transmitting a beam of electromagnetic radiation (23) for printing, in the printing position (11) of the substrate (5), the viscous substance (2) on the product (3); • - a scanning device (25) arranged for scanning the beam of electromagnetic radiation (23) across the first surface (7) of the substrate (5) for printing a selective layer-part (27) of the viscous substance (2); and • - a heating device (29) arranged for heating the selective layer- part (27) of the viscous substance (2) on the substrate (5) to a first predetermined temperature range for reducing the viscosity of the viscous substance (2) of the selective layer-part (27) before printing the selective layer-part (27) of the viscous substance (2) on the product (3). A method for printing viscous substance by means of Laser Induced Forward Transfer on a product using the apparatus.

Description

[0001] Title: Apparatus and method for printing a viscous substance by means of Laser Induced Forward Transfer on a product

[0002] Description:

[0003] According to a first aspect of the present disclosure, the disclosure relates to an apparatus for printing viscous substance by means of Laser Induced Forward Transfer on a product.

[0004] According to a second aspect of the present disclosure, the disclosure relates to a method for printing viscous substance by means of Laser Induced Forward Transfer on a product using an apparatus according to the first aspect of the present disclosure.

[0005] A known method for applying a viscous substance such as solder paste to a product, such as a Printed Circuit Board (PCB), relies on stencil printing or dispensing. Stencil printing is a deposition method requiring direct contact with the PCB. Stencil printing is a non- digital method, where a stencil, also referred to as a mask, is used to define the printing pattern. It also limits the freedom to achieve small volumes for small components while allowing relatively large volumes of the viscous substance such as the solder paste to be applied for the larger components which are also still present on new PCBs.

[0006] Dispensing is a nozzle based deposition technology requiring the control of a gap that is present between the end of the nozzle and the PCB. The gap between the end of the nozzle and the PCB is either actively measured and compensated or calibrated according to a pre-mapping. A drawback of dispensing is the relatively low speed of applying the viscous substance. It is noted that a relatively high speed of applying viscous substance is in particular relevant for high volume production. A further drawback of dispensing is the relative frequent clogging of nozzles of the dispenser resulting in missed shots, thereby avoiding, or at least partly avoiding, application of viscous substance. A further method for applying a viscous substance on a product, such as solder interconnects in a three-dimensional Integrated Circuit (IC), also referred to as 3D interconnects, 3D chip stacking, 3D stacking or 3D packaging may comprise placing preformed solder balls in deposits of a Ball Grid Array (BGA) socket. A drawback of this placement technique is the relatively expensive equipment required. In addition, the size of the solder balls that may be placed is relatively large.

[0007] A known technique for printing solder paste on a product is presented in US11779955B1 , which relates to systems and methods for collecting residual material that remains on a donor substrate after laser-assisted deposition of the material from the donor substrate to a receiving substrate, allowing for immediate reuse of the collected residual material. The patent does not focus on improving printing quality of the solder paste on the product.

[0008] WO2021 / 171100A1 discloses systems and methods for printing solder paste on electronic components from a coated film and placing the electronic components onto a substrate with the solder paste therebetween. It focusses on printing without causing defects in a final assembly by means of jetting of solder paste directly on the electronic component.

[0009] In US2022 / 009247A1 , which uses Laser Induced Forward Transfer (LIFT), the focus lies on improving high resolution in LIFT over substantially large transfer distances. The presented solution creates a very narrow jet-on-jet by using a first large spot size pulse and subsequently a second small spot size laser pulse. However, the laser pulse only provides a very local effect.

[0010] Another laser printing method is disclosed in US2018 / 110127A1 , which requires the use of two lasers; a first laser for heating a solid metal donor thin film and a second laser for jetting the melted metal on the receiver substrate.

[0011] It is an object of the present disclosure to provide an apparatus and a method that at least partly overcomes a drawback of the known methods of applying a viscous substance to a product. The apparatus according to the first aspect of the present disclosure comprises: a substrate handler arranged for holding a substrate and positioning a first surface of the substrate into a coating position and a printing position, wherein, in the printing position, the first surface of the substrate is at a predetermined position relative to the product for printing the viscous substance, by means of Laser Induced Forward Transfer (LIFT), on the product; a support for positioning the product in relation to the first surface of the substrate in the printing position of the substrate; a coater arranged for providing a layer of the viscous substance on the first surface of the substrate in the coating position of the substrate; a printing device comprising a first emitter unit arranged for transmitting a beam of electromagnetic radiation for printing, in the printing position of the substrate, the viscous substance, by means of Laser Induced Forward Transfer (LIFT), on the product; a scanning device arranged for scanning the beam of electromagnetic radiation across the first surface of the substrate for printing a selective layer-part of the viscous substance, by means of Laser Induced Forward Transfer (LIFT).

[0012] Laser Induced Forward Transfer (LIFT) is a direct-write technique that was first reported by Bohandy, Kim, and Adrian in 1986 for the deposition of Cu patterns on Si and fused silica substrates under high vacuum conditions. In this technique, a pulsed laser is used to induce the transfer of the material from a donor substrate to a receiver substrate, usually placed at a short distance or in contact with each other. Donor substrates are usually laser transparent and coated with a thin film of the material of interest. As the laser beam passes through the transparent substrate, it is being absorbed by the film, which is subsequently propelled toward the receiver substrate, above a certain laser energy threshold.

[0013] Providing the apparatus with the substrate handler and the support, a substrate may be positioned relative to the product. In addition, the functionality of the substrate handler to hold the substrate and positioning the substrate in a coating position and a printing position allows the substrate to be coated in a position wherein the risk of damaging the product during the coating, by the coater, for instance by spilling of viscous substance may be prevented.

[0014] The coater is used to apply a layer of viscous substance on the substrate, which can be relatively small compared to the product. This coated substrate is then positioned relative to the product using the substrate handler and the support, as explained above, such that the viscous substance may be transferred to the product by means of the LIFT process.

[0015] The beam of electromagnetic radiation originating from the first emitter unit is arranged for locally removing the viscous substance from the substrate at the location of impingement of the beam of electromagnetic radiation at the surface of the viscous substance.

[0016] In this regard, the beam of electromagnetic radiation is arranged for locally heating the layer of viscous substance up to a temperature causing rapid vaporization of part of the viscous substance. Due to the rapid vaporization, a gas bubble is formed that locally pushes the viscous substance away from the substrate.

[0017] By positioning the product relative to the substrate in a predetermined position, the viscous substance that is pushed away from the substrate may be directed to predetermined positions of the product and thereby providing the product with viscous substance at the predetermined positions.

[0018] The scanner device allows for scanning the beam of electromagnetic radiation along the surface of the viscous substance and thereby allowing to transfer a predetermined pattern of the viscous substance and thereby printing viscous substance onto the product according to the predetermined pattern.

[0019] The apparatus further comprises a heating device arranged for heating the selective layer-part of the viscous substance on the substrate to a first predetermined temperature range for reducing the viscosity of the viscous substance of the selective layer-part before printing the selective layer-part of the viscous substance, by means of Laser Induced Forward Transfer (LIFT), on the product.

[0020] The invention according to the present disclosure relies at least partly on the insight that the printability of viscous substance can be improved by temporarily, after providing a layer of the viscous substance on the first surface of the substrate, but before printing the viscous substance on the product, lowering the viscosity of the viscous substance to be printed by heating up the selective layer-part of the viscous substance. The temporary lower viscosity of the viscous substance increases the subsequent flow of the viscous substance upon the induced vapor bubble push during printing of viscous substance in order to achieve higher quality volume printing.

[0021] In addition, by pre-heating (pre-heating because it is done before printing the viscous substance on the product) the selective layer-part of the viscous substance, the printing process may be relatively stable for smaller volumes of the viscous substance.

[0022] Furthermore, it is discovered that by pre-heating the selective layer-part of the viscous substance, a relatively stable printing process may be achieved for a relatively large range of print volumes.

[0023] Pre-heating the selective layer-part of the viscous substance may also allow for printing features of the viscous substance relatively close to each other. In other words, at a small pitch. A relatively low viscosity of the viscous substance at the location of the selective layer-part is beneficial for reducing the area of the locally removed viscous substance from the substrate during the printing process.

[0024] Corresponding embodiments disclosed below for the first aspect are also applicable to the method for printing viscous substance on a product using the apparatus according to the first aspect according to the present disclosure, unless stated otherwise. In an embodiment, the heating device is arranged for indirectly heating the selective layer-part of the viscous substance to the first predetermined temperature range by heating of the substrate. The heating device of this particular embodiment may comprise at least one of: a second emitter unit arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the substrate for heating the substrate; a direct heating member arranged to be in direct contact with a second surface of the substrate for heating the substrate via the second surface, wherein the second surface is provided at a side of the substrate facing away from the first surface; and a first gas heating member arranged for heating a gas and providing a flow of the heated gas along the second surface for heating the substrate via the second surface.

[0025] The heating of the selective layer-part of the viscous substance, optionally with the heating device comprising these additional components, is beneficial for the printability of the viscous substance on the product.

[0026] In another embodiment, the heating device is arranged for directly heating the selective layer-part of the viscous substance. For this, the heating device may comprise at least one of: a third emitter unit arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the viscous substance; and a second gas heating member arranged for heating a gas and providing a flow of gas along a surface of the layer of viscous substance facing away from the substrate.

[0027] These additional components even further improve the printability of the viscous substance.

[0028] In an embodiment, the heating device is arranged for heating the selective layer-part of the viscous substance to a predetermined temperature range in the range of 25 °C to 70 °C, preferably in the range of 30 °C to 50 °C, more preferably in the range of 30 °C to 40 °C. Below 25 °C, printing of the viscous substance onto the PCB becomes too difficult. Above 70 °C, there is a risk that part of the solder flux will start evaporating significantly. The heating device may be arranged for heating the complete layer of the viscous substance on the first surface of the substrate. This has the effect that the viscous substance has improved flowing behaviour during the printing process such that it is possible to print a broader range of the required specifications for the industry with regard to volumes, pitches, and patterns. Hence, it enables to print with an increased process window and with greater accuracy and reproducibility compared to when the viscous substance is not heated or only partly heated.

[0029] In an embodiment, the apparatus further comprises: a detector unit arranged for detecting a temperature of the selective layer-part of the viscous substance; and a control unit, communicatively coupled with the detector unit and the heating device, and arranged for controlling the heating device for bringing the selective layerpart of the viscous substance in the first predetermined temperature range.

[0030] This enables to improve control of the temperature of the (locally) heated viscous substance such that the viscosity of the viscous substance, especially of the selective layer-part of the viscous substance, can be lowered in a more controlled manner.

[0031] In another embodiment, the apparatus is arranged for providing the beam of electromagnetic radiation of the first emitter unit to the first surface via the substrate.

[0032] The method according to the second aspect of the present disclosure comprises the steps of: providing the substrate and the product; supporting, by the support, the product; holding the substrate, by the substrate handler; moving the substrate, by the substrate handler, to the coating position; providing, by the coater, the layer of viscous substance on the first surface of the substrate; moving, by the substrate handler, the substrate to the printing position; emitting, by the first emitter unit, the beam of electromagnetic radiation for printing the viscous substance, by means of Laser Induced Forward Transfer (LIFT), on the product; scanning, by the scanning device, the beam of electromagnetic radiation across the first surface of the substrate for printing the selective layer-part of the viscous substance, by means of Laser Induced Forward Transfer (LIFT); heating, by the heating device, the selective layer-part of the viscous substance on the substrate to the first predetermined temperature range for reducing the viscosity of the viscous substance of the selective layer-part, wherein the step of heating is performed before the step of emitting.

[0033] In the method, the steps of providing the layer of viscous substance, moving, heating, and emitting may be repeated for providing the viscous substance to predetermined positions on the product.

[0034] In an embodiment of the method, the substrate is substantially transparent, preferably transparent, for the electromagnetic radiation emitted, by the first emitter unit, during the step of emitting. Preferably, the substrate is sufficiently absorbent for the electromagnetic radiation emitted by the second emitter. Having a substrate that is substantially transparent, preferably transparent, for the electromagnetic radiation emitted by the first emitter unit, and preferably sufficient absorbent for the electromagnetic radiation emitted by the second emitter, improves the efficiency of heating of the substrate.

[0035] The method may further comprise the step of: positioning, by at least one of the support and the substrate handler, the product relative to the first surface of the substrate in the printing position of the substrate.

[0036] In an embodiment of the method, the selective layer-part of the viscous substance is heated to a temperature in the range of 25 °C to 70 °C, preferably in the range of 30 °C to 50 °C, more preferably in the range of 30 °C to 40 °C.

[0037] Preferably the viscous substance comprises solder paste and wherein, during the step of heating, by the heating device, the viscosity of the solder paste is in the range of 0.5 to 200 Pa-s. In this regard, the viscosity of the solder paste may be determined according to the IPC-TM-650-2.4.34.2 Test Methods Manual and IPC-TM-650-2.4.34.3 Test Methods Manual depending on the viscosity of the solder paste.

[0038] In another embodiment of the method, during the steps of emitting and scanning, a distance between the surface of the layer of viscous substance facing away from the first surface and a surface of the product onto which the viscous substance is to be printed is at a predetermined distance in the range of 30 micrometres to 400 micrometres.

[0039] The present disclosure is hereinafter explained in more detail with reference to the accompanying drawings in which embodiments of the present disclosure are shown and in which like reference numbers indicate the same or similar elements. The present disclosure is by no means limited to the embodiments described therein.

[0040] Fig. 1 schematically shows a top view of an apparatus according to the present disclosure;

[0041] Fig. 2 and 3 schematically show side views of the apparatus of Fig. 1 ;

[0042] Fig. 4 schematically shows details of a heating device according to the present disclosure;

[0043] Fig. 5 schematically shows printing of viscous substance on the product;

[0044] Fig. 6 schematically shows a method according to the present disclosure.

[0045] In Fig. 1 , an apparatus 1 according to the present disclosure for printing viscous substance 2 by means of Laser Induced Forward Transfer on a product 3 is shown. The apparatus 1 comprises a substrate handler 4 arranged for holding a substrate 5 and positioning a first surface 7 of the substrate 5 into a coating position 9 and a printing position 11. In the printing position 11 , the first surface 7 of the substrate 5 is at a predetermined position relative to the product 3 for printing the viscous substance 2 on the product 3.

[0046] The apparatus 1 also comprises a support 13 for positioning the product 3 in relation to the first surface 7 of the substrate 5 in the printing position 11 of the substrate 5. In the shown top view of the apparatus 1 , the product 3, seen from an operator’s 53 position, moves from left to right as indicated by the black arrows.

[0047] Furthermore, the apparatus 1 comprises a coater 15 arranged for providing a layer 17 of viscous substance 2 on the first surface 7 of the substrate 5 in the coating position 9 of the substrate 5; a printing device 19 comprising a first emitter unit 21 arranged for transmitting a beam of electromagnetic radiation 23 for printing, in the printing position 11 of the substrate 5, the viscous substance 2 on the product 3; a scanning device 25 arranged for scanning the beam of electromagnetic radiation 23 across the first surface 7 of the substrate 5 for printing a selective layer-part 27 of the viscous substance 2; and a heating device 29 arranged for heating the selective layerpart 27 of the viscous substance 2 on the substrate 5 to a first predetermined temperature range for reducing the viscosity of the viscous substance 2 of the selective layer-part 27 before printing the selective layer-part 27 of the viscous substance 2 on the product 3.

[0048] Fig. 2 shows a side of the apparatus 1 view from the side facing towards the operator 53 (not shown in Fig. 2). This side view provides more details about how the apparatus 1 according to the present disclosure may be arranged; for example the first emitter unit 21 is clearly shown next to the heating device 29 and the printing device 19. The apparatus 1 shown in Fig. 2 further comprises a detector unit 47 arranged for detecting a temperature of the selective layer-part 27 of the viscous substance 2.

[0049] Fig. 3 shows the apparatus 1 of Fig. 1 from the side facing away from the operator 53 (not shown in Fig. 3). From this side it is seen that the apparatus 1 further comprises a control unit 49, communicatively coupled with the detector unit 47 and the heating device 29 for bringing the selective layer-part 27 of the viscous substance 27 in the first predetermined temperature range. The scanning device 25 is also clearly visible in this side view.

[0050] A schematic figure of a heating device 29 is shown in Fig. 4 and further comprises a second emitter unit 31 arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the substrate 5 for heating the substrate 5; a direct heating member 33 arranged to be in direct contact with a second surface 35 of the substrate 5 for heating the substrate 5 via the second surface 35, wherein the second surface 35 is provided at a side of the substrate 5 facing away from the first surface 7; and a first gas emitting member 39 arranged for heating a gas and providing a flow of the heated gas along the second surface 35 for heating the substrate 5 via the second surface 35.

[0051] Hence, the heating device 29 of Fig. 4 is arranged for indirectly heating the selective layer-part 27 of the viscous substance 2 to the first predetermined temperature range by heating of the substrate 5 and also arranged for directly heating the selective layer-part 27 of the viscous substance 2. The heating device 29 may also be used for heating the complete layer 17 of the viscous substance 2 on the first surface 7 of the substrate 5.

[0052] The heating device 29 of Fig. 4 further comprises a third emitter unit 41 arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the viscous substance 2; and a second gas heating member 43 arranged for heating a gas and providing a flow of gas along a surface 45 of the layer of viscous substance facing away from the substrate 5.

[0053] The heating device 29 as shown in Fig. 1 , 2 and 4, which can be used during the step of heating 119 in the method 101 of the present disclosure, are arranged for heating the selective layer-part 27 of the viscous substance 2 to a predetermined temperature range in the range of 25 °C to 70 °C, and also in the narrower ranges of 30 °C to 50 °C and 30 °C to 40 °C.

[0054] Fig. 5 (a)-(d) shows a schematic of the printing of viscous substance on a product. In Fig. 5 (a), a product 3, having a surface 51 , and a substrate 5 that is transparent for the electromagnetic radiation 23 emitted by the first emitter unit 21 , e.g., a glass substrate, having a first surface 7 on which a layer 17 of viscous substance 2 has been applied, are positioned above each other in the printing position 11. By presenting the product 3 below the substrate 5 it can be used as a deposition method. The distance d between the surface 45 of the layer 17 of viscous substance 2 facing away from the first surface 7 and the surface 51 of the product 3 onto which the viscous substance 2 is to be printed is at a predetermined distance in the range of 30 micrometres to 400 micrometres.

[0055] A beam of electromagnetic radiation 23 is transmitted by a first emitter unit 12 (not shown) on the substrate 5. The apparatus 1 of the present disclosure is arranged for providing the beam of electromagnetic radiation 23 of the first emitter unit 21 to the first surface 7 of the substrate 5 via said substrate 5. The beam of electromagnetic radiation 23 locally heats the first surface 7 of the substrate 5 and a selective layerpart 27 of the layer 17 of viscous substance 2 causing vaporization within the layer 17 of the viscous substance 2 such that a gas bubble 55 is formed.

[0056] In Fig. 5 (b), the bubble 55 pushes the selective layer-part 27 of the layer 17 of the viscous substance 2 away from the substrate 5. Viscous substance 2 that is pushed away by the bubble 55 is deposited on the predetermined position on the surface 51 of the product 3. Subsequently in Fig. 5 (c), the substrate 5 is moved upwards (indicated by the black arrows) thereby creating a rupture position (indicated by the dashed circle) such that the selective layer-part 27 of the layer 17 of the viscous substance 2 is being separated from the layer 17 of viscous substance 2. As shown in Fig. 5 (d), the selective layer-part 27 of viscous substance 2 is deposited on the predetermined position on the product 3. Hence, the viscous substance 2 is printed on the printed circuit board 3.

[0057] A method 101 for printing viscous substance 2 on a product 3 using the apparatus 1 is shown in Fig. 6. The method 101 comprises the steps of providing 103 the substrate 5 and the product 3; supporting 105, by the support 13, the product 3; holding 107 the substrate 5, by the substrate handler 4; moving 109 the substrate 5, by the substrate handler 4, to the coating position 9; providing 111 , by the coater 15, the layer 17 of viscous substance 2 on the first surface 7 of the substrate 5; moving 113, by the substrate handler 4, the substrate 5 to the printing position 11 ; heating 119, by the heating device 29, the selective layer-part 27 of the viscous substance 2 on the substrate 5 to the first predetermined temperature range for reducing the viscosity of the viscous substance 2 of the selective layer-part 27; emitting 115, by the first emitter unit 21 , the beam of electromagnetic radiation 23 for printing the viscous substance 2 on the product 3; scanning 117, by the scanning device 25, the beam of electromagnetic radiation 23 across the first surface 7 of the substrate 5 for printing the selective layer-part 27 of the viscous substance 2; and the optional step of positioning 121 , by at least one of the support 13 and the support handler 4, the product 3 relative to the first surface 7 of the substrate 5 in the printing position 11 of the substrate 5.

[0058] As becomes clear from the order of the steps as shown in Fig. 6, the order of execution of the steps may be different as compared to the order as disclosed in the claims. Hence, the method steps may be executed in different manners than the order as disclosed in the claims. For example, the step of heating 119 of the selective layerpart 27 of the viscous substance 2 on the substrate 5 may be done before or after the step of moving 113 the substrate 5.

[0059] Fig. 6 further shows that the steps of providing 111 the layer of viscous substance 2, moving 113, heating 119 and emitting 115 may be repeated for providing the viscous substance 2 to predetermined positions on the product 3.

[0060] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the present disclosure, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

[0061] The foregoing description provides embodiments of the present disclosure by way of example only. The scope of the present disclosure is defined by the appended claims. One or more of the objects of the present disclosure are achieved by the appended claims. CLAUSES

[0062] 1. Apparatus for printing solder paste on a printed circuit board, the apparatus comprising: a substrate handler arranged for holding a substrate and positioning a first surface of the substrate into a coating position and a printing position, wherein, in the printing position, the first surface of the substrate is at a predetermined position relative to the printed circuit board for printing the solder paste on the printed circuit board; a support for positioning the printed circuit board in relation to the first surface of the substrate in the printing position of the substrate; a coater arranged for providing a layer of solder paste on the first surface of the substrate in the coating position of the substrate; a printing device comprising a first emitter unit arranged for transmitting a beam of electromagnetic radiation for printing, in the printing position of the substrate, the solder paste on the printed circuit board; a scanning device arranged for scanning the beam of electromagnetic radiation across the first surface of the substrate for printing a selective layer-part of the solder paste; and a heating device arranged for heating the selective layer-part of the solder paste on the substrate to a first predetermined temperature range for reducing the viscosity of the solder paste of the selective layer-part before printing the selective layer-part of the solder paste on the printed circuit board.

[0063] 2. The apparatus according to clause 1 , wherein the heating device is arranged for indirectly heating the selective layer-part of the solder paste to the first predetermined temperature range by heating of the substrate.

[0064] 3. The apparatus according to clause 2, wherein the heating device comprises at least one of: a second emitter unit arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the substrate for heating the substrate; a direct heating member arranged to be in direct contact with a second surface of the substrate for heating the substrate via the second surface, wherein the second surface is provided at a side of the substrate facing away from the first surface; and a first gas heating member arranged for heating a gas and providing a flow of the heated gas along the second surface for heating the substrate via the second surface.

[0065] 4. The apparatus according to any one of the preceding clauses, wherein the heating device is arranged for directly heating the selective layer-part of the solder paste.

[0066] 5. The apparatus according to clause 4, wherein the heating device comprises at least one of: a third emitter unit arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the solder paste; and a second gas heating member arranged for heating a gas and providing a flow of gas along a surface of the layer of solder paste facing away from the substrate.

[0067] 6. The apparatus according to any one of the preceding clauses, wherein the heating device is arranged for heating the selective layer-part of the solder paste to a predetermined temperature range in the range of 25 °C to 70 °C, preferably in the range of 30 °C to 50 °C, more preferably in the range of 30 °C to 40 °C.

[0068] 7. The apparatus according to any one of the preceding clauses, wherein the heating device is arranged for heating the complete layer of the solder paste on the first surface of the substrate.

[0069] 8. The apparatus according to any one of the preceding clauses, wherein the apparatus further comprises: a detector unit arranged for detecting a temperature of the selective layer-part of the solder paste; and a control unit, communicatively coupled with the detector unit and the heating device, and arranged for controlling the heating device for bringing the selective layerpart of the solder paste in the first predetermined temperature range.

[0070] 9. The apparatus according to any one of the preceding clauses, wherein the apparatus is arranged for providing the beam of electromagnetic radiation of the first emitter unit to the first surface via the substrate.

[0071] 10. A method for printing solder paste on a printed circuit board using an apparatus according to any one of the preceding clauses, the method comprising the steps of: providing the substrate and the printed circuit board; supporting, by the support, the printed circuit board; holding the substrate, by the substrate handler; moving the substrate, by the substrate handler, to the coating position; providing, by the coater, the layer of solder paste on the first surface of the substrate; moving, by the substrate handler, the substrate to the printing position; emitting, by the first emitter unit, the beam of electromagnetic radiation for printing the solder paste on the printed circuit board; scanning, by the scanning device, the beam of electromagnetic radiation across the first surface of the substrate for printing the selective layer-part of the solder paste; heating, by the heating device, the selective layer-part of the solder paste on the substrate to the first predetermined temperature range for reducing the viscosity of the solder paste of the selective layer-part, wherein the step of heating is performed before the step of emitting.

[0072] 11. The method according to clause 10, wherein the steps of providing the layer of solder paste, moving, emitting and heating are repeated for providing the solder paste to predetermined positions on the printed circuit board.

[0073] 12. The method according to clause 10 or 11 , wherein the substrate is substantially transparent, preferably transparent, for the electromagnetic radiation emitted, by the first emitter unit, during the step of emitting. 13. The method according to any one of the clauses 10 - 12, wherein the method further comprises the step of: positioning, by at least one of the support and the substrate handler, the printed circuit board relative to the first surface of the substrate in the printing position of the substrate.

[0074] 14. The method according to any one of the clauses 10 - 13, wherein, during the step of heating, the selective layer-part of the solder paste is heated to a temperature in the range of 25 °C to 70 °C, preferably in the range of 30 °C to 50 °C, more preferably in the range of 30 °C to 40 °C.

[0075] 15. The method according to any one of the clauses 10 - 14, wherein, during the steps of emitting and scanning, a distance (d) between the surface of the layer of solder paste facing away from the first surface and a surface of the printed circuit board onto which the solder paste is to be printed is at a predetermined distance in the range of 30 micrometres to 400 micrometres.

Claims

CLAIMS1. Apparatus (1) for printing a viscous substance (2), preferably solder paste or a conductive glue, by means of Laser Induced Forward Transfer (LIFT), on a product (3), the apparatus (1) comprising: a substrate handler (4) arranged for holding a substrate (5) and positioning a first surface (7) of the substrate (5) into a coating position (9) and a printing position (11), wherein, in the printing position (11), the first surface (7) of the substrate (5) is at a predetermined position relative to the product (3) for printing the viscous substance (2), by means of Laser Induced Forward Transfer (LIFT), on the product (3); a support (13) for positioning the product (3) in relation to the first surface (7) of the substrate (5) in the printing position (11) of the substrate (5); a coater (15) arranged for providing a layer (17) of the viscous substance (2) on the first surface (7) of the substrate (5) in the coating position (9) of the substrate (5); a printing device (19) comprising a first emitter unit (21) arranged for transmitting a beam of electromagnetic radiation (23) for printing, in the printing position (11) of the substrate (5), the viscous substance (2), by means of Laser Induced Forward Transfer (LIFT), on the product (3); a scanning device (25) arranged for scanning the beam of electromagnetic radiation (23) across the first surface (7) of the substrate (5) for printing a selective layer-part (27) of the viscous substance (2), by means of Laser Induced Forward Transfer (LIFT); and characterized in, that the apparatus (1) comprises: a heating device (29) arranged for heating the selective layer-part (27) of the viscous substance (2) on the substrate (5) to a first predetermined temperature range for reducing the viscosity of the viscous substance (2) of the selective layer-part (27) before printing the selective layer-part (27) of the viscous substance (2), by means of Laser Induced Forward Transfer (LIFT), on the product (3).

2. The apparatus (1) according to claim 1 , wherein the heating device (29) is arranged for indirectly heating the selective layer-part (27) of the viscous substance (2) to the first predetermined temperature range by heating of the substrate (5).

3. The apparatus (1) according to claim 2, wherein the heating device (29) comprises at least one of: a second emitter unit (31) arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the substrate (5) for heating the substrate (5); a direct heating member (33) arranged to be in direct contact with a second surface (35) of the substrate (5) for heating the substrate (5) via the second surface (35), wherein the second surface (35) is provided at a side of the substrate (5) facing away from the first surface (7); and a first gas heating member (39) arranged for heating a gas and providing a flow of the heated gas along the second surface (35) for heating the substrate (5) via the second surface (35).

4. The apparatus (1) according to any one of the preceding claims, wherein the heating device (29) is arranged for directly heating the selective layer-part (27) of the viscous substance (2).

5. The apparatus (1) according to claim 4, wherein the heating device (29) comprises at least one of: a third emitter unit (41) arranged for emitting electromagnetic radiation at a wavelength that is absorbable by the viscous substance (2); and a second gas heating member (43) arranged for heating a gas and providing a flow of gas along a surface (45) of the layer (17) of viscous substance (2) facing away from the substrate (5).

6. The apparatus (1) according to any one of the preceding claims, wherein the heating device (29) is arranged for heating the selective layer-part (27) of the viscous substance (2) to a predetermined temperature range in the range of 25 °C to 70 °C, preferably in the range of 30 °C to 50 °C, more preferably in the range of 30 °C to 40 o / ^7. The apparatus (1) according to any one of the preceding claims, wherein heating device (29) is arranged for heating the complete layer (17) of the viscous substance (2) on the first surface (7) of the substrate (5).

8. The apparatus (1) according to any one of the preceding claims, wherein the apparatus (1) further comprises: a detector unit (47) arranged for detecting a temperature of the selective layerpart (27) of the viscous substance (2); and a control unit (49), communicatively coupled with the detector unit (47) and the heating device (29), and arranged for controlling the heating device (29) for bringing the selective layer-part (27) of the viscous substance (2) in the first predetermined temperature range.

9. The apparatus (1) according to any one of the preceding claims, wherein the apparatus (1) is arranged for providing the beam of electromagnetic radiation (23) of the first emitter unit (21) to the first surface (7) via the substrate (5).

10. A method (101) for printing a viscous substance (2) by means of Laser Induced Forward Transfer (LIFT) on a product (3) using an apparatus (1) according to any one of the preceding claims, the method (101) comprising the steps of: providing (103) the substrate (5) and the product (3); supporting (105), by the support (13), the product (3); holding (107) the substrate (5), by the substrate handler (4); moving (109) the substrate (5), by the substrate handler (4), to the coating position (9); providing (111), by the coater (15), the layer (17) of viscous substance (2) on the first surface (7) of the substrate (5); moving (113), by the substrate handler (4), the substrate (5) to the printing position (11); emitting (115), by the first emitter unit (21), the beam of electromagnetic radiation (23) for printing the viscous substance (2), by means of Laser Induced Forward Transfer (LIFT), on the product (3);scanning (117), by the scanning device (25), the beam of electromagnetic radiation (23) across the first surface (7) of the substrate (5) for printing the selective layer-part (27) of the viscous substance (2), by means of Laser Induced Forward Transfer (LIFT); and characterized in, that the method (101) comprises the step of: heating (119), by the heating device (29), the selective layer-part (27) of the viscous substance (2) on the substrate (5) to the first predetermined temperature range for reducing the viscosity of the viscous substance (2) of the selective layer-part (27), wherein the step of heating (119) is performed before the step of emitting (115).

11. The method (101) according to claim 10, wherein the steps of providing (111) the layer (17) of viscous substance (2), moving (113), heating (119), and emitting (115) are repeated for providing the viscous substance (2) to predetermined positions on the product (3).

12. The method (101) according to claim 10 or 11 , wherein the substrate (5) is substantially transparent, preferably transparent, for the electromagnetic radiation emitted (23), by the first emitter unit (21), during the step of emitting (115).

13. The method (101) according to any one of the claims 10 - 12, wherein the method (101) further comprises the step of: positioning (121), by at least one of the support (13) and the substrate handler (4), the product (3) relative to the first surface (7) of the substrate (5) in the printing position (11) of the substrate (5).

14. The method (101) according to any one of the claims 10 - 13, wherein, during the step of heating (119), the selective layer-part (27) of the viscous substance (2) is heated to a temperature in the range of 25 °C to 70 °C, preferably in the range of 30 °C to 50 °C, more preferably in the range of 30 °C to 40 °C.

15. The method (101) according to any one of the claims 10 - 14, wherein, during the steps of emitting (115) and scanning (117), a distance (d) between the surfaceand a surface (51) of the product (3) onto which the viscous substance (2) is to be printed is at a predetermined distance in the range of 30 micrometres to 400 micrometres.

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