Apparatus and photosensitive ink for preparing PCB products having high density conductors

Abstract

An improved system for printed circuit board (PCB) manufacturing based on inkjet of liquid photoresist materials is provided. [Solution] The apparatus includes a common stage (112) characterized by including a light-scattering PCB substrate support surface, and a laser light generator (180) that causes laser light to impinge on the PCB substrate support surface, where the laser light that reaches the PCB substrate support surface through a via through-hole is scattered, and then impinges on the sidewall of the via through-hole, thereby causing polymerization of the photoresist inside the via through-hole.

Description

[Technical field]

[0001] The present invention relates to printed circuit board (PCB) manufacturing based on inkjet of liquid photoresist materials. [Background technology]

[0002] Various systems and methods for manufacturing PCBs are known in the art. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2018 / 0192521 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention seeks to provide an improved system and method for printed circuit board (PCB) manufacturing based on inkjet of liquid photoresist materials. [Means for solving the problem]

[0005] Therefore, according to a preferred embodiment of the present invention, there is provided a method for preparing a PCB product having high density conductors, the method including: providing a PCB substrate including a conductive layer; using an inkjet printer to selectively print an unexposed photosensitive pattern on the PCB substrate, the unexposed photosensitive pattern having a thickness of less than 5 μm; exposing the photosensitive pattern to radiation to define an exposure pattern, the exposure pattern having a pitch of less than 20 μm; and wet etching the conductive layer according to the pattern defined by the exposure pattern to define high density conductors having a pitch of less than 30 μm.

[0006] Preferably, the high density conductors have a pitch of less than 25 μm, more preferably, the high density conductors have a pitch of less than 20 μm.

[0007] According to a preferred embodiment of the present invention, the conductive layer is a copper layer.

[0008] According to a preferred embodiment of the present invention, the method also includes using an inkjet printer to selectively print an oxygen-impermeable pattern before exposing the photosensitive pattern after utilizing an inkjet printer to selectively print an unexposed photosensitive pattern. In addition, the oxygen-impermeable pattern has a height of less than 3 μm. In addition or alternatively, the oxygen-impermeable pattern is transparent to radiation. Preferably, printing the oxygen-impermeable pattern does not increase the pitch of the exposed pattern.

[0009] In accordance with a preferred embodiment of the present invention, the method also includes inspecting at least one of the unexposed photosensitive pattern and the non-oxygen-permeable pattern prior to exposing the unexposed photosensitive pattern and the non-oxygen-permeable pattern to radiation.

[0010] In accordance with a preferred embodiment of the present invention, the method also includes registration of the PCB substrate prior to utilizing the inkjet printer to selectively print the unexposed photosensitive pattern.

[0011] Preferably, the unexposed photosensitive pattern is printed with a photosensitive ink comprising: a photoresist constituting 33-64% by weight of the photosensitive ink; a solvent constituting 19.99-59.99% by weight of the photosensitive ink; a humectant constituting 1-10% by weight of the photosensitive ink; a surfactant constituting 0.01-0.1% by weight of the photosensitive ink; an adhesion promoter constituting 1-3% by weight of the photosensitive ink, the adhesion promoter having a molecular weight of 1700-70000 Da; and a basic solution constituting 2-3% by weight of the photosensitive ink, the adhesion promoter being dissolved in the basic solution.

[0012] According to a preferred embodiment of the present invention, the adhesion promoter acts to increase the anisotropy of the wet etching process of the copper component onto which the photosensitive ink is printed. Additionally or alternatively, the photosensitive ink has a surface tension of less than 30 dyn / cm.

[0013] According to a preferred embodiment of the present invention, the oxygen-impermeable pattern is printed with an oxygen-impermeable ink comprising a polymer constituting 10-15% by weight of the oxygen-impermeable ink, the polymer having a minimum molecular weight of 7000 Da, one or more solvents constituting a total of 63.9-68.99% by weight of the oxygen-impermeable ink, a thickener solvent constituting 20% ​​by weight of the oxygen-impermeable ink, a humectant constituting 1% by weight of the oxygen-impermeable ink, and a surfactant constituting 0.01-0.1% by weight of the oxygen-impermeable ink.

[0014] Preferably, the oxygen-impermeable ink is transparent to light having a wavelength of 355 to 460 nm. Additionally or alternatively, the oxygen-impermeable ink has a surface tension of less than 30 dyn / cm.

[0015] Also, according to another preferred embodiment of the present invention, there is provided an apparatus for use in preparing a PCB product having high density conductors, the apparatus comprising: a common chassis; an inkjet printer mounted on the common chassis and operative to selectively print an unexposed photosensitive pattern on a PCB substrate, the unexposed photosensitive pattern having a thickness of less than 5 μm; and a pattern exposure machine mounted on the common chassis and operative to expose the photosensitive pattern to radiation to define an exposure pattern, the exposure pattern having a pitch of less than 20 μm.

[0016] According to a preferred embodiment of the present invention, the inkjet printer includes a first inkjet head operative to print an unexposed photosensitive pattern of a photosensitive ink, and a second inkjet head operative to print an oxygen-impermeable pattern of an oxygen-impermeable ink, and a nozzle plate of the inkjet head operative to be heated to 40-60°C to obtain optimal viscosities of the photosensitive ink and the oxygen-impermeable ink.

[0017] In accordance with a preferred embodiment of the present invention, the apparatus includes a hood at least partially enclosing a common chassis, an inkjet printer, and a pattern exposure machine, wherein the environment within the hood is additionally characterized by an inert gas flow that acts to prevent oxidation of the unexposed photosensitive pattern during exposure by the pattern exposure machine.

[0018] Preferably, the apparatus also includes at least a first ink dryer operative to dry the unexposed photosensitive pattern. In addition, the first inkjet head, the at least first ink dryer, and the second inkjet head are arranged such that a step-wise advancement of the PCB substrate along the common chassis allows the unexposed photosensitive pattern to be dried by the at least first ink dryer before the second inkjet head prints the oxygen-impermeable pattern.

[0019] Preferably, the apparatus also includes a camera operative to inspect at least one of the unexposed photosensitive pattern and the oxygen-impermeable pattern.

[0020] According to a preferred embodiment of the present invention, the pattern exposure machine includes at least one light source that emits light in the range of 355 to 460 nm. Preferably, the pattern exposure machine is a laser direct imaging exposure machine. Alternatively, the pattern exposure machine is an LED exposure machine.

[0021] In accordance with a preferred embodiment of the present invention, the apparatus also includes a camera which serves to register the PCB board.

[0022] In accordance with a preferred embodiment of the present invention, the apparatus also includes a common stage, which is additionally heated to a maximum temperature of 80° C. to aid in drying at least one of the photosensitive ink and the oxygen-impermeable ink.

[0023] According to a preferred embodiment of the present invention, the unexposed photosensitive pattern is printed by a photosensitive ink, the photosensitive ink including a photoresist constituting 33-64% by weight of the photosensitive ink, a solvent constituting 19.99-59.99% by weight of the photosensitive ink, a wetting agent constituting 1-10% by weight of the photosensitive ink, a surfactant constituting 0.01-0.1% by weight of the photosensitive ink, an adhesion promoter constituting 1-3% by weight of the photosensitive ink, the adhesion promoter having a molecular weight of 1700-70000 Da, and a basic solution constituting 2-3% by weight of the photosensitive ink, the adhesion promoter being dissolved in the basic solution.

[0024] According to a preferred embodiment of the present invention, the adhesion promoter acts to increase the anisotropy of the wet etching process of the copper component onto which the photosensitive ink is printed. Additionally or alternatively, the photosensitive ink has a surface tension of less than 30 dyn / cm.

[0025] According to a preferred embodiment of the present invention, the oxygen-impermeable pattern is printed with an oxygen-impermeable ink comprising a polymer constituting 10-15% by weight of the oxygen-impermeable ink, the polymer having a minimum molecular weight of 7000 Da, one or more solvents constituting a total of 63.9-68.99% by weight of the oxygen-impermeable ink, a thickener solvent constituting 20% ​​by weight of the oxygen-impermeable ink, a humectant constituting 1% by weight of the oxygen-impermeable ink, and a surfactant constituting 0.01-0.1% by weight of the oxygen-impermeable ink.

[0026] Preferably, the oxygen-impermeable ink is transparent to light having a wavelength of 355 to 460 nm. Additionally or alternatively, the oxygen-impermeable ink has a surface tension of less than 30 dyn / cm.

[0027] According to yet another preferred embodiment of the present invention, there is further provided an apparatus for use in preparing a PCB product having high density conductors, the apparatus including: a common stage; an inkjet printer operative to selectively print an unexposed pattern on a PCB substrate on the stage, the unexposed pattern having a thickness of less than 8 μm; and a pattern exposure machine operative to expose the pattern on the PCB substrate on the stage to radiation to define an exposure pattern, the exposure pattern having a pitch of less than 20 μm.

[0028] According to a preferred embodiment of the present invention, the inkjet printer includes a first inkjet head operative to print an unexposed photosensitive pattern of a photosensitive ink, and a second inkjet head operative to print an oxygen-impermeable pattern of an oxygen-impermeable ink, and a nozzle plate of the inkjet head operative to be heated to 40-60°C to obtain optimal viscosities of the photosensitive ink and the oxygen-impermeable ink.

[0029] Preferably, the apparatus also includes a hood at least partially enclosing the common stage, the inkjet printer, and the patterned exposure machine, and in addition, the environment within the hood is characterized by a flow of inert gas that acts to prevent oxidation of the unexposed photosensitive pattern during exposure by the patterned exposure machine.

[0030] According to a preferred embodiment of the present invention, the apparatus also includes at least a first ink dryer acting to dry the unexposed photosensitive pattern. In addition, the first inkjet head, the at least first ink dryer, and the second inkjet head are arranged such that a step-by-step advance of the PCB substrate by the common stage allows the unexposed photosensitive pattern to be dried by the at least first ink dryer before the second inkjet head prints the oxygen-impermeable pattern.

[0031] Preferably, the apparatus also includes a camera operative to inspect at least one of the unexposed photosensitive pattern and the oxygen-impermeable pattern.

[0032] According to a preferred embodiment of the present invention, the pattern exposure machine includes at least one light source that emits light in the range of 355 to 460 nm. Preferably, the pattern exposure machine is a laser direct imaging exposure machine. Alternatively, the pattern exposure machine is an LED exposure machine.

[0033] In accordance with a preferred embodiment of the present invention, the apparatus also includes a camera which serves to register the PCB board.

[0034] Preferably, the apparatus also includes a common chassis.

[0035] In accordance with a preferred embodiment of the present invention, the common stage is heated to a maximum temperature of 80° C. to aid in drying at least one of the unexposed photosensitive ink and the oxygen-impermeable ink.

[0036] According to a preferred embodiment of the present invention, the unexposed photosensitive pattern is printed by a photosensitive ink, the photosensitive ink including a photoresist constituting 33-64% by weight of the photosensitive ink, a solvent constituting 19.99-59.99% by weight of the photosensitive ink, a wetting agent constituting 1-10% by weight of the photosensitive ink, a surfactant constituting 0.01-0.1% by weight of the photosensitive ink, an adhesion promoter constituting 1-3% by weight of the photosensitive ink, the adhesion promoter having a molecular weight of 1700-70000 Da, and a basic solution constituting 2-3% by weight of the photosensitive ink, the adhesion promoter being dissolved in the basic solution.

[0037] Preferably, the adhesion promoter acts to increase the anisotropy of the wet etching process of the copper component onto which the photosensitive ink is printed. Additionally or alternatively, the photosensitive ink has a surface tension of less than 30 dyn / cm.

[0038] According to a preferred embodiment of the present invention, the oxygen-impermeable pattern is printed with an oxygen-impermeable ink comprising a polymer constituting 10-15% by weight of the oxygen-impermeable ink, the polymer having a minimum molecular weight of 7000 Da, one or more solvents constituting a total of 63.9-68.99% by weight of the oxygen-impermeable ink, a thickener solvent constituting 20% ​​by weight of the oxygen-impermeable ink, a humectant constituting 1% by weight of the oxygen-impermeable ink, and a surfactant constituting 0.01-0.1% by weight of the oxygen-impermeable ink.

[0039] Preferably, the oxygen-impermeable ink is transparent to light having a wavelength of 355 to 460 nm. Additionally or alternatively, the oxygen-impermeable ink has a surface tension of less than 30 dyn / cm.

[0040] According to yet another preferred embodiment of the present invention, there is still further provided a photosensitive ink for use in an inkjet printer, the photosensitive ink comprising a photoresist constituting 33-64% by weight of the photosensitive ink, a solvent constituting 19.99-59.99% by weight of the photosensitive ink, a humectant constituting 1-10% by weight of the photosensitive ink, a surfactant constituting 0.01-0.1% by weight of the photosensitive ink, an adhesion promoter constituting 1-3% by weight of the photosensitive ink, the adhesion promoter having a molecular weight of 1700-70000 Da, and a basic solution constituting 2-3% by weight of the photosensitive ink, the adhesion promoter being dissolved in the basic solution.

[0041] Preferably, the adhesion promoter acts to increase the anisotropy of the wet etching process of the copper component onto which the photosensitive ink is printed. Additionally or alternatively, the photosensitive ink has a surface tension of less than 30 dyn / cm.

[0042] In accordance with a preferred embodiment of the present invention, the photosensitive ink is operative to produce printed features having a height of less than 5 μm.

[0043] According to another preferred embodiment of the present invention there is still further provided an oxygen-permeable ink for use in an ink jet printer comprising a polymer constituting 10-15% by weight of the oxygen-permeable ink, the polymer having a minimum molecular weight of 7000 Da, one or more solvents constituting a total of 63.9-68.99% by weight of the oxygen-permeable ink, a thickener solvent constituting 20% ​​by weight of the oxygen-permeable ink, a humectant constituting 1% by weight of the oxygen-permeable ink, and a surfactant constituting 0.01-0.1% by weight of the oxygen-permeable ink.

[0044] According to a preferred embodiment of the present invention, the oxygen-impermeable ink is transparent to light having a wavelength of 355 to 460 nm. Additionally or alternatively, the oxygen-impermeable ink has a surface tension of less than 30 dyn / cm.

[0045] Preferably, the oxygen-non-permeable ink is operative to produce printed features having a height of less than 3 μm.

[0046] According to yet another preferred embodiment of the present invention, a method for preparing a PCB product is also provided, the method comprising: providing a PCB substrate including a conductive layer; using an inkjet printer for selectively printing an unexposed photosensitive pattern on the PCB substrate; and exposing the photosensitive pattern to radiation to define an exposure pattern, characterized in that printing the unexposed photosensitive pattern comprises printing and drying multiple layers layer by layer, such that a layer is dried before printing its subsequent layer, thereby reducing or eliminating the generation of pinholes.

[0047] According to yet another preferred embodiment of the present invention, there is further provided a method for preparing a PCB product, the method including: providing a PCB substrate including a conductive layer; wiping the conductive layer with a liquid photoresist ink solvent; and then using an inkjet printer to selectively print an unexposed photosensitive pattern onto the PCB substrate.

[0048] According to yet another preferred embodiment of the present invention, there is still further provided a method for preparing a PCB product, the method comprising: providing a PCB substrate including a conductive layer; and using an inkjet printer to selectively print a through-hole via fill material ink at selected locations on the PCB substrate.

[0049] According to yet another preferred embodiment of the present invention, an apparatus for use in preparing a PCB product including a via through-hole is also provided, the apparatus including a common stage characterized by including a light scattering PCB substrate support surface, and a laser light generator for impinging laser light onto the PCB substrate support surface where the laser light passing through the via through-hole and reaching the PCB substrate support surface is scattered, thereby impinging further onto the sidewall of the via through-hole, thereby causing polymerization of the photoresist inside the via through-hole.

[0050] Preferably, the PCB substrate support surface is laser light diffusing. The present invention will be more fully understood and appreciated from the following detailed description taken in conjunction with the following drawings, in which: [Brief description of the drawings]

[0051] [Figure 1A] 1 is a simplified schematic diagram of two alternative embodiments of a Computer Controlled Product Preparation Mini-Environment (CCPPME) constructed and operative in accordance with a preferred embodiment of the present invention; [Figure 1B] 1 is a simplified schematic diagram of two alternative embodiments of a Computer Controlled Product Preparation Mini-Environment (CCPPME) constructed and operative in accordance with a preferred embodiment of the present invention; [Figure 2A] FIG. 2 is a simplified diagram of a printed circuit board (PCB) product prepared by the CCPPME of FIG. 1, showing various stages of preparation. [Figure 2B] FIG. 2 is a simplified diagram of a printed circuit board (PCB) product prepared by the CCPPME of FIG. 1, showing various stages of preparation. [Figure 2C] FIG. 2 is a simplified diagram of a printed circuit board (PCB) product prepared by the CCPPME of FIG. 1, showing various stages of preparation. [Diagram 3] FIG. 1B is a simplified flow chart showing an exemplary printing and exposure preparation method useful in preparing the PCB product of FIGS. 2A-2C using the CCPPME of FIG. 1A or FIG. 1B. [Figure 4A]2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4B] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4C] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4D] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4E] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4F] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4G] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 4H] 2A-2C are images of the PCB products of FIGS. 2A-2C taken by an optical microscope. [Figure 5A] FIG. 1C is a simplified diagram of a method for preparing a PCB product with through-hole vias, which may be prepared using the CCPPME of FIG. 1B. [Figure 5B] FIG. 1C is a simplified diagram of a method for preparing a PCB product with through-hole vias, which may be prepared using the CCPPME of FIG. 1B. [Figure 5C] FIG. 1C is a simplified diagram of a method for preparing a PCB product with through-hole vias, which may be prepared using the CCPPME of FIG. 1B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Reference is now made to FIG. 1A, which is a simplified schematic diagram of a computer-controlled product preparation mini-environment (CCPPME) 100 constructed and operative in accordance with a preferred embodiment of the present invention. It is noted that FIG. 1A is not to scale, and dashed lines are drawn around subsystems that are present only in some embodiments of the present invention. It is further noted that the CCPPME 100 operates to print and expose photosensitive features on a variety of substrates, including flexible plates, porous plates, and roll-to-roll, among others. The CCPPME 100 preferably includes a roll-to-roll processing system (not shown), such as the roll-to-roll processing systems described in U.S. Patent Application Publication No. 2017 / 0225447 or 2018 / 0229516, the disclosures of which are incorporated herein by reference.

[0053] As seen in Figure 1A, the CCPPME 100 preferably includes a hood 102 mounted over a common chassis 110 having a common stage 112. The common stage 112 serves to advance a substrate, typically a printed circuit board (PCB) substrate 114, through various subsystems 116 of the CCPPME 100, which are shown and described below with reference to Figures 2A-2C. An exemplary common stage 112 is constructed and serves as described in Assignee's U.S. Patent No. 8,770,563, the disclosure of which is incorporated herein by reference.

[0054] Preferably, the common stage 112 has a high degree of flatness, e.g., a gradient of less than 50 μm over a length of 800 mm. Furthermore, the vacuum generated inside the stage 112 is preferably strong enough to hold a PCB substrate having a thickness of 0.05 mm to 10 mm.

[0055] Preferably, the first subsystem 116 of the CCPPME 100 includes a camera 118, such as a TTDCMOS 120, commercially available from TechnoTeam Bildverarbeitung GmbH, Ilmenau, Germany. The camera 118 serves to register the PCB substrate 114 prior to further processing by the CCPPME 100. The common stage 112 advances the PCB substrate 114 in a constant manner, such that after registration of the PCB substrate 114 by the camera 118, no further registration is necessary while the PCB substrate 114 is supported by the common stage 112. Additionally, the common stage 112 is preferably heated to a maximum temperature of preferably 100° C. to aid in drying of the ink once it is printed. More preferably, the common stage 112 is heated to a maximum temperature of 80° C. to aid in drying of the ink once it is printed. More preferably, the common stage 112 is heated to a maximum temperature of 50° C. to aid in drying the ink once it is printed.

[0056] Preferably, another subsystem 116 of the CCPPME 100 includes a high throughput piezoelectric inkjet printer (HTPIJ) 120 including at least one first high throughput bidirectional piezoelectric inkjet head (HTBPIH) 130 operative to print a photosensitive ink and at least one first ink dryer 140 operative to dry the photosensitive ink printed by the first HTBPIH 130 onto the PCB substrate 114. The HTPIJ 120 may optionally include a second HTBPIH 150, which may be identical to the first HTBPIH 130 operative to print an oxygen-impermeable ink, and a second ink dryer 160 operative to dry the oxygen-impermeable ink printed by the second HTBPIH 150 onto the PCB substrate 114.

[0057] Preferably, both the first HTBPIH 130 and the second HTBPIH 150 are formed from a material that is not soluble in the solvent used in the ink of the present invention described below. Each of the first HTBPIH 130 and the second HTBPIH 150 preferably operates at a frequency of 5-100 kHz and includes a plurality of nozzles, each having a volume of 6-60 pL, and a nozzle plate that is preferably operative to determine the optimum viscosity of the photosensitive ink and the oxygen non-permeable ink and is heated to a temperature of 25-80° C. More preferably, the nozzle plate of the inkjet head is operative to determine the optimum viscosity of the photosensitive ink and the oxygen non-permeable ink and is heated to a temperature of 40-60° C. Alternatively, the nozzle plate of the inkjet head is operative to determine the optimum viscosity of the photosensitive ink and the oxygen non-permeable ink and is heated to a temperature of 25-50° C.

[0058] The HTPIJ 120 may be constructed and operated as described in US Pat. Nos. 7,757,628, 9,085,157, and 9,221,265, the disclosures of which are incorporated herein by reference.

[0059] A unique feature of one embodiment of the present invention is that the first HTBPIH 130, the first ink dryer 140, and the second HTBPIH 150 are arranged such that the photosensitive ink printed by the first HTBPIH 130 is dried by the first ink dryer 140 before being overprinted by the second HTBPIH 150 by stepwise advancement of the PCB substrate 114.

[0060] Printing and drying layer by layer helps to avoid pinhole formation, which is otherwise found to occur due to the difference in evaporation rates of the various ink components. Typically, the high vapor pressure solvent in the ink evaporates first, increasing the viscosity of the ink and thus can lead to the formation of a thin polymer film. The lower vapor pressure solvent that evaporates subsequently can generate pinholes as the evaporated gas passes through the thin polymer layer. The step of drying the previously printed photosensitive ink layer before printing the subsequent oxygen-impermeable ink layer prevents the formation of a thin polymer film and thus pinholes.

[0061] The first ink dryer 140 and the second ink dryer 160 may each be any suitable dryer, such as an airflow dryer, a linear IR lamp, a scanning IR lamp, a flash lamp, a vacuum dryer, a heated stage dryer, or any combination thereof. By varying the print settings and inks used, the HTPIJ 120 provides printing of features having length and width dimensions as small as 50 μm, and heights between 0.5 and 5 μm.

[0062] Further optional subsystems 116 of the CCPPME 100 include a second camera 170, such as the TTDCMOS 120, commercially available from TechnoTeam Bildverarbeitung GmbH, Ilmenau, Germany. The second camera 170 serves to inspect print features.

[0063] In some embodiments, the environment within the CCPPME 100, and particularly within its hood 102, includes an inert gas flow 172, such as flowing N2, which acts to prevent oxidation of the printed features during exposure. It is noted that the pressure within the CCPPME 100 remains at ambient pressure, regardless of whether the inert gas flow 172 is included within the CCPPME 100 or whether the inert gas flow 172 is not included.

[0064] In some embodiments, the environment within the CCPPME 100, specifically within its hood 102, contains clean air to provide a clean environment, eg, class <100,000, at positive pressure.

[0065] Further subsystems 116 of the CCPPME 100 include a pattern exposer 180, preferably a laser direct write (LDI) subsystem, which operates to selectively expose portions of the photosensitive ink printed by the first HTBPIH 130. The pattern exposer 180 operates to expose the photosensitive print pattern to laser radiation, defining an exposure pattern having lines / spaces (L / S) as small as 5 / 5 μm. A typical pattern exposer 180 includes at least one light source that emits light in the range of 355-460 nm, and may be constructed and operated as described in U.S. Patent No. 8,531,751, the disclosure of which is incorporated herein by reference.

[0066] It can be seen that the sum of the two values ​​of an L / S measurement equals the pitch of the repeating pattern. Thus, an L / S of 5 / 5 μm equals a pitch of 10 μm. The first value of the L / S measurement represents the regular length or width dimension of the repeating features, and the second value of the L / S measurement represents the regular length or width dimension of the spaces between the repeating features.

[0067] Alternatively, the patterned exposure machine 180 may be another suitable exposure system, such as an LED exposure machine. An exemplary LED exposure machine that may be applied for such exposure is the Orbotech Diamond™ 8, commercially available from Orbotech, Yavne, Israel.

[0068] Referring now to Figure 1B, which shows an alternative to the embodiment of Figure 1A, including all of its elements as described above. As seen in Figure 1B, an additional HTBPIH 190 is provided and operative to print a through-hole via fill material ink. An additional ink curing device 191 is provided and operative to cure the through-hole via fill material ink deposited by the additional HTBPIH 190 inside the through-hole vias of the PCB substrate.

[0069] Preferably, the common stage 112 is coated with a light diffusing layer or otherwise treated to be light scattering, for example, by scrubbing or chemical roughening. Laser light impinging on the light diffusing layer through the via through-holes in this manner is scattered to also impinge on the sidewalls of the via through-holes. This scattered laser light causes polymerization of the photoresist inside the via through-holes. In particular, the scattered laser light causes polymerization of the photoresist on the sidewalls of the via through-holes that did not receive enough direct laser light to be polymerized.

[0070] Preferably, the light scattered inside the via-hole exposes the entire inner via-hole surface. As is well known, photoresist requires a certain exposure light energy to be fully polymerized, and since the via-hole inner surface may be larger than the via-hole circular area, it may be necessary to increase the exposure light intensity whenever the exposure light is impinging on the via-hole area. Another reason for increasing the exposure light intensity inside the via-hole may be due to the reflectivity reduction at the bottom of the via-hole, or non-uniform scattering from the surface. To increase the exposure intensity on the via-hole, the direct image light must be increased accordingly, for example, by increasing the modulated laser scanning spot power at the corresponding via-hole area.

[0071] It is understood that both negative and positive photoresists may be used in embodiments of the present invention.

[0072] A photosensitive ink suitable for use in conjunction with the first HTBPIH 130 of the CCPPME 100 preferably includes a photoresist to which a solvent, a wetting agent, a surfactant, and an adhesion promoter have been added. When using a photoresist that includes a surfactant, the use of an additional surfactant may be avoided. In some embodiments, a banking agent may be added to the photosensitive ink. Alternatively, the adhesion promoter may also function as a banking agent.

[0073] As mentioned above, the photosensitive ink preferably comprises a photoresist. Preferably, the photoresist used in the photosensitive ink of the present invention is a negative photoresist, which is either a radical polymerization photoresist, such as Diaetch 100 and DET 765.12, commercially available from HTP HiTech Photopolymere AG, Basel, Switzerland, or PHOTOPOSIT™ SN68H, commercially available from Dow Inc., USA, or a photodimerization polymerization photoresist, such as DET 539.72 and DET 539.21, commercially available from HTP HiTech Photopolymere AG, Basel, Switzerland. Alternatively, the photoresist used in the photosensitive ink of the present invention may be one of LP7609H, LP7803D1 and LP7901V, commercially available from Great Eastern Resins Industrial Co. Ltd., Taichung, Taiwan; Longlite®, commercially available from Chang Chun Group, Taiwan; PHOTRAK™, from Electra Polymers LTD, UK; and X-77, commercially available from Taiyo Ink, Japan.

[0074] As mentioned above, the photosensitive ink preferably includes a solvent. The solvent reduces the viscosity of the photosensitive ink, which is typically not suitable for ejection from a nozzle due to the viscosity of the photoresist, to a viscosity more suitable for ejection from a nozzle as required for inkjet printing. The viscosity of the photosensitive ink is preferably in the range of 5-15 cps at the printer operating temperature. Preferably, the solvent has a boiling point of 100° C. or less, which aids in fast drying of the photosensitive ink. In addition, the solvent is preferably of low risk to humans and the environment, having, among other things, relatively low toxicity, flammability, and reactivity properties. Exemplary solvents include n-propanol, 2-methoxy-2-propanol, isobutanol, propylene glycol monomethyl ether, and isopropyl alcohol.

[0075] As mentioned above, the photosensitive ink preferably includes a humectant, which prevents the photosensitive ink from solidifying on the nozzle plate prior to ejection from the first HTBPIH 130. Exemplary humectants include glycols such as glycerin (1-3 wt%), propylene glycol (5-10 wt%), dipropylene glycol (1-3 wt%), triethylene glycol (5-10 wt%), and glycol ethers such as diethylene glycol diethyl ether (5-10 wt%), diethylene glycol dimethyl ether (5-15 wt%), ethylene glycol monobutyl ether (5-10 wt%), dipropylene glycol dimethyl ether (2-6 wt%), dipropylene glycol monomethyl ether (2-6 wt%), and the like.

[0076] As mentioned above, the photosensitive ink preferably includes a surfactant. The surfactant adjusts the surface tension of the photosensitive ink, affecting both its droplet size and wettability. The surface tension of the photosensitive ink is preferably in the range of 20-30 dyn / cm. The droplet size of the photosensitive ink emitted by the first HTBPIH 130 is preferably in the range of 6-60 pL. The wettability is preferably such that the photosensitive ink droplets spread to form a flat deposit on the PCB substrate 114 with minimal doming. Exemplary surfactants include silicone polymers such as BYK-345 (0.1-0.3 wt%), BYK-310 (0.1-0.5 wt%), BYK-3760 (0.1-0.5 wt%), commercially available from BYK-Chemie GmbH, Wesel, Germany, and fluoropolymers such as Capstone™ 1157 (0.01-0.05 wt%), Capstone™ 1460 (0.05-0.1 wt%), Capstone™ 1475 (0.01-0.05 wt%), commercially available from DuPont Inc., USA.

[0077] As mentioned above, the photosensitive ink preferably includes an adhesion promoter. The adhesion promoter promotes the adhesion of the photosensitive ink to the PCB substrate 114, resulting in smoother printed features. It has been found that adhesion promoters, especially those with a high acid value, improve the solubility of the unexposed photopolymer under development and improve the stability of the features printed by the photosensitive ink during its etching, even for features with length and width dimensions as small as 5 μm. The molecular weight of the adhesion promoter is preferably in the range of 1000-70000 Da. Some polymer chains of the adhesion promoter, having a molecular weight in the range of 8000-70000 Da, may extend beyond the width of the printed photosensitive ink feature. In such a case, most of the extending polymer chains are removed by the pressure of the liquid etchant sprayed on the substrate during the etching step. The remaining extending polymer chains act as banking agents that adsorb to the sidewalls of the material to be etched and prevent undesired isotropic etching of it. Exemplary adhesion promoters have a high acid number and include Joncryl® 682, Joncryl® ECO 684, Joncryl® 680, Joncryl® ECO 675, Joncryl® 678, Joncryl® HPD 696, and Joncryl® HPD 671, which are commercially available from BASF, Ludwigshafen, Germany. The adhesion promoter is preferably dissolved in a basic solution, such as 2-amino-2-methyl 1-propanol (0.5-4 wt %), 2-dimethylaminoethanol (0.5-4 wt %), or ethanolamine.

[0078] The general procedure for preparing a photosensitive ink suitable for use in conjunction with CCPPME100's 1HTBPIH130 is as follows: In the first step, the solvent, base solution, and adhesion promoter are mixed together in a low shear mixer (<500 rpm) for preferably 10 minutes. In the second step, surfactants and wetting agents are added to the mixer and the solution is mixed for preferably an additional 5 minutes. In the final mixing step, the photoresist solution is added to the mixer and mixed for preferably an additional 10 minutes. The solution is then filtered through a membrane preferably having a pore size of about 0.2 μm. It is noted that the preparation of the photosensitive ink is carried out under yellow light conditions.

[0079] Photosensitive ink formulation example Tables 1-5 provide examples of photosensitive ink formulations suitable for use in conjunction with CCPPME100 No. 1HTBPIH130. [Table 1] [Table 2] [Table 3] [Table 4] [Table 5]

[0080] A non-oxygen permeable ink suitable for use in conjunction with the second HTBPIH 150 of the CCPPME 100 is transparent to the exposure of the pattern exposure machine 180 and preferably comprises a polymer having a minimum molecular weight of 7000 Da, a solvent, a thickener solvent, a wetting agent, and a surfactant.

[0081] The polymers in the oxygen-impermeable ink protect the photosensitive ink from oxygen during the exposure process. Protecting the photosensitive ink from oxygen prevents the polymerizing agent in the photosensitive ink from reacting with oxygen instead of polymerizing the photosensitive ink during its exposure. Typical polymers include poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), hemicellulose, and poly(butyl methacrylate-co-(2-dimethylaminoethyl) methacrylate-co-methyl methacrylate).

[0082] As mentioned above, the oxygen-impermeable ink preferably includes a solvent and a thickener solvent. The thickener solvent adjusts the viscosity of the oxygen-impermeable ink to a suitable viscosity for ejection from the nozzle as required for inkjet printing. The viscosity of the oxygen-impermeable ink is preferably in the range of 5-15 cps at the printer operating temperature. Preferably, the solvent aids in fast drying of the oxygen-impermeable ink having a boiling point of 100° C. or less. In addition, the solvent is preferably of low risk to humans and the environment, having, inter alia, relatively low toxicity, flammability, and reactivity properties. Exemplary solvents include water, n-propanol, 2-methoxy-2-propanol, and isobutanol. Exemplary thickener solvents include propylene glycol (10-20% by weight), dipropylene glycol (10-20% by weight), and triethylene glycol (10-20% by weight).

[0083] As noted above, the oxygen-non-permeable ink preferably includes a humectant, which prevents the oxygen-non-permeable ink from solidifying on the nozzle plate prior to ejection from the second HTBPIH 150. Typical humectants include glycols such as glycerin (1-3% by weight) and glycol ethers such as ethylene glycol monobutyl ether (5-10% by weight) and dipropylene glycol dimethyl ether (2-6% by weight).

[0084] As mentioned above, the oxygen-impermeable ink preferably includes a surfactant. The surfactant adjusts the surface tension of the oxygen-impermeable ink, which affects both the droplet size and its wettability. The surface tension of the oxygen-impermeable ink is preferably in the range of 20-30 dyn / cm. The droplet size of the oxygen-impermeable ink emitted by the second HTBPIH 150 is preferably in the range of 6-60 pL. The wettability is preferably such that the oxygen-impermeable ink droplets spread to form a flat deposit on the PCB substrate 114 with minimal doming. Exemplary surfactants include silicone polymers such as BYK-345 (0.1-0.3 wt %), BYK-310 (0.1-0.5 wt %), and BYK-3760 (0.1-0.5 wt %), commercially available from BYK-Chemie GmbH, Wesel, Germany, and fluoropolymers such as Capstone™ 1157 (0.01-0.05 wt %), Capstone™ 1460 (0.05-0.1 wt %), and Capstone™ 1475 (0.01-0.05 wt %), commercially available from DuPont, Inc., USA.

[0085] The general procedure for preparing an oxygen-impermeable ink suitable for use in conjunction with CCPPME100 No. 2HTBPIH150 is as follows: In a first step, the solvent, thickener solvent, humectant, and surfactant are mixed together in a low shear mixer (<500 rpm), preferably for 5 minutes, then the mixing shear is increased and the polymer is added at low speed, then mixed for preferably an additional 30 minutes. Afterwards, the solution is filtered through a membrane, preferably having a pore size of about 0.2 μm.

[0086] Example of non-oxygen permeable ink formulation Tables 6-7 provide examples of non-oxygen permeable ink formulations suitable for use in conjunction with CCPPME100 No. 2HTBPIH150. [Table 6] [Table 7]

[0087] Through-hole via filling material inks suitable for use in conjunction with the additional HTBPIH 190 of the CCPPME 100 of FIG. 1B are preferably characterized in that they are stable during growth and etching and removable by stripping. Curing of the through-hole via filling material ink may be performed by thermal curing or chemical fixation. The through-hole via filling material ink may be, for example, a positive photoresist such as NOVOLAC®, or a polyimide formulation that is thermally curable. Furthermore, through-hole via filling may be accomplished by utilizing a high acid value acrylic polymer, preferably a propionate or butyrate, that is stable at pH<10 and selectively removable at pH=14.

[0088] In PCB manufacturing, there are various types of vias, such as through-hole vias and microvias, that need to be coated and protected during the etching process. Although the through-hole vias may be coated with a liquid photoresist, in the exposure process, the central region of the via's sidewall may not be polymerized by the illumination. As a result, the through-hole area may remain unprotected and may be washed away during the etching process. To solve this problem, a through-hole via fill material ink may be directly and selectively deposited inside the through-hole via, followed by its curing.

[0089] A through-hole via fill material ink suitable for use in conjunction with the additional HTBPIH190 of the CCPPME100 of FIG. 1B preferably includes a solvent and a thickener solvent, as well as a wetting agent and a surfactant. The thickener solvent adjusts the viscosity of the through-hole via fill material ink to a viscosity suitable for ejection from a nozzle, as required for inkjet printing. The viscosity of the through-hole via fill material ink is preferably in the range of 5-15 cps at the printer operating temperature. Preferably, the solvent has a boiling point of 100° C. or less, which aids in fast drying of the through-hole via fill material ink. In addition, the solvent is preferably of low risk to humans and the environment, having, inter alia, relatively low toxicity, flammability, and reactivity properties. Post-curing of the through-hole via fill material ink preferably occurs at a temperature of 200° C. or less. Exemplary solvents include water, n-propanol, 2-methoxy-2-propanol, and isobutanol. Typical thickener solvents include propylene glycol (10-20% by weight), dipropylene glycol (10-20% by weight), and triethylene glycol (10-20% by weight).

[0090] As mentioned above, the through-hole via fill material ink preferably includes a humectant, which prevents the through-hole via fill material ink from solidifying on the nozzle plate prior to ejection from the additional HTBPIH 190. Exemplary humectants include glycols such as glycerin (1-3 wt%) and glycol ethers such as ethylene glycol monobutyl ether (5-10 wt%) and dipropylene glycol dimethyl ether (2-6 wt%).

[0091] As mentioned above, the through-hole via filling material ink preferably includes a surfactant. The surfactant adjusts the surface tension of the through-hole via filling material ink, which affects both the droplet size and its wettability. The surface tension of the through-hole via filling material ink is preferably in the range of 20-30 dyn / cm. The droplet size of the through-hole via filling material ink emitted by the additional HTBPIH190 is preferably in the range of 6-60 pL. Exemplary surfactants include silicone polymers such as BYK-345 (0.1-0.3 wt%), BYK-310 (0.1-0.5 wt%), and BYK-3760 (0.1-0.5 wt%), commercially available from BYK-Chemie GmbH, Wesel, Germany, and fluoropolymers such as Capstone™ 1157 (0.01-0.05 wt%), Capstone™ 1460 (0.05-0.1 wt%), and Capstone™ 1475 (0.01-0.05 wt%), commercially available from DuPont Inc., USA.

[0092] Reference is now made to Figures 2A-2C, which are simplified diagrams of a PCB product 200 prepared by CCPPME 100 (Figure 1), showing various stages of preparation. It is noted that Figures 2A-2C are not to scale. Figure 2A shows the PCB product 200, which includes a PCB substrate 114 formed with a copper layer 210 covering its upper surface, the copper layer 210 typically having a thickness of 0.2-36 μm. The PCB product 200 shown in Figure 2A also includes at least one printed pattern 212 printed on the copper layer 210 selectively by the first HTBPIH 130, and optionally by the second HTBPIH 150. It is noted that the printed pattern 212 has length and width dimensions as small as 50 μm, as indicated by a pair of arrows 214 and 216.

[0093] The printed pattern 212 includes a photosensitive printed pattern printed by the first HTBPIH 130, having a typical thickness of 0.5-5 μm, and optionally includes an oxygen-non-permeable printed pattern printed by the second HTBPIH 150, having a thickness of 0.1-3 μm. As described above, the optional oxygen-non-permeable printed pattern is printed over the photosensitive printed pattern.

[0094] 2B shows PCB product 200 with printed pattern 212 after being selectively exposed by pattern exposure machine 180 to produce exposure patterns 220 and 222. As can be seen in FIG. 2B, the width of exposure pattern 220 is an order of magnitude different from that of exposure pattern 222. It is noted that exposure pattern 222 has an L / S as small as 5 / 5 μm, as indicated by arrow 224.

[0095] 2C shows the PCB product 200 after the growth of the printed pattern 212 and the exposed patterns 220 and 222, and after the subsequent etching of the copper layer 210. It is noted that after the etching of the copper layer 210, the exposed pattern 222 has an L / S, as indicated by the arrow 230, as small as 10 / 10 μm.

[0096] Reference is now made to Figure 3, which is a simplified flow chart illustrating an exemplary print and expose preparation method 300 useful in preparing PCB product 200 (Figures 2A-2C) using CCPPME 100 (Figure 1). CCPPME 100 is preferably used in conjunction with another tool as part of a larger manufacturing process. It is noted that print and expose preparation method 300 is particularly suited to being part of a subtractive manufacturing process, but is not limited to use therewith.

[0097] The following embodiment description describes the printing and exposure preparation method 300 being used to prepare a PCB product 200 including a PCB substrate 114 formed with a copper layer 210 on its upper surface, the copper layer 210 typically having a thickness of 0.5-36 μm, although it will be appreciated that the printing and exposure preparation method 300 may also be performed with substrates having conductive or non-conductive upper layers of different materials and / or thicknesses. Typically, when the PCB substrate 114 includes a temporary protective layer, such as a chromate protective layer, the protective layer is removed as part of processing prior to the printing and exposure preparation method 300.

[0098] It is found that the use of liquid photoresist coatings preferably eliminates the need for microetching processes, which are required to increase surface roughness and thus physical adhesion between the copper layer and the dry photoresist film, since the liquid photoresist coatings are chemically bonded to the copper layer. The liquid photoresist coatings are preferably printed on relatively smooth surfaces. The use of liquid photoresist coatings may be beneficial in reducing processing steps and material waste. Furthermore, the use of liquid photoresists is beneficial when working with smooth surfaces, such as one or more flexible materials used in high frequency applications.

[0099] Preferably, the copper surface is wiped with a wipe dipped in the ink solvent to increase ink wetting and coating quality. Removing the protective chromate layer from the copper surface by oxidation provides a highly reactive and hydrophobic copper surface while allowing a suitable solvent to be applied to this reactive surface which typically takes a few seconds to evaporate, and leaves the copper surface less reactive and more compatible with the liquid photoresist ink.

[0100] 3, in a first step 308, a user uploads a suitably formatted computer-aided manufacturing (CAM) file to the CCPPME 100, containing instructions for the desired printing and exposure of the PCB board 114 to be processed. In a next step 310, the PCB board 114 to be processed is placed on the stage 112 of the CCPPME 100 and advanced to the camera 118 for registration of the PCB board 114, as seen in a registration step 311. Thankfully, by advancing the PCB board 114 in an unchanged manner by the common stage 112, it can be seen that following registration of the PCB board 114 by the camera 118 in step 311, no further registration is required while the PCB board 114 is supported by the common stage 112 during the print and expose preparation method 300.

[0101] 1B, the method 300 checks the CAM file for reference if through-hole vias need to be printed. Preferably, when printing through-hole vias, the CAM file contains the coordinates for the exact via location and size, as well as instructions for the desired printing and exposure of the vias.

[0102] If through-hole vias need to be printed, the PCB substrate 114 is advanced to the HTBPIH 190 for printing of the via-fill ink, as seen in step 313. The PCB substrate 114 is then advanced by the stage 112 to an ink curing step 314, where the via-fill ink is made impervious to downstream growth and etching processes.

[0103] 1A following the registration step 311, or following step 312 when no through-hole vias need to be printed, or following ink curing step 314 when no through-hole vias need to be printed, the portion of the PCB substrate 114 being processed is generally advanced to the first HTBPIH 130 for selective printing of photosensitive ink, as seen in photosensitive ink printing step 315. It is noted that the first HTBPIH 130 prints photosensitive ink to form a printed pattern, such as printed pattern 212, that covers all areas of the PCB substrate 114 that contain material that will be retained during the etching step that follows the printing and exposure preparation method 300. The portion of the PCB substrate 114 being processed is then advanced by stage 112 to the first ink dryer 140 where the solvent present in the photosensitive ink is evaporated as seen in the first drying step 316. Following solvent evaporation in the first drying step 316, by varying the print settings and inks used, the length and width dimensions of the features printed in the photosensitive ink printing step 315 may be as small as 50 μm, and the height of the features printed in the photosensitive ink printing step 315 is in the range of 0.5 to 5 μm.

[0104] As seen in steps 318, 320, and 322, in some embodiments of the present invention, the features printed in the photosensitive ink printing step 315 require coating with an oxygen-impermeable coating. An oxygen-impermeable coating for the photosensitive ink is necessary when the photosensitive ink includes a photoresist that utilizes radical polymerization and the photosensitive ink is exposed in the presence of oxygen.

[0105] When an oxygen-impermeable coating is required, the portion of the PCB substrate 114 being processed is advanced to the second HTBPIH 150 for selective printing of an oxygen-impermeable ink, as seen in an oxygen-impermeable ink printing step 320. It is noted that the oxygen-impermeable ink is preferably printed over all of the printed pattern 212 and not on other areas of the PCB product 200.

[0106] When an oxygen-impermeable coating is required, the portion of the PCB substrate 114 being processed is then advanced to a second ink dryer 160 to evaporate the solvent present in the oxygen-impermeable ink, as seen in a second drying step 322. Following the second drying step 322, by modifying the printing settings and inks used, the length and width dimensions of the features printed in the oxygen-impermeable ink printing step 320 may range from 50 μm up to the maximum dimension of the PCB substrate 114, and the height of the features printed in the oxygen-impermeable ink printing step 320 is in the range of 0.1-3 μm.

[0107] It can be seen that during steps 315-322, the PCB product 200 preferably corresponds to Fig. 2A. A particular feature of an embodiment of the present invention is that the oxygen-impermeable ink printed in the oxygen-impermeable ink printing step 320 is printed on top of the photosensitive ink and acts to protect the photosensitive ink from oxidation during exposure, but the oxygen-impermeable ink printed in the oxygen-impermeable ink printing step 320 does not increase the minimum length and width dimensions of the exposure pattern 220.

[0108] The process continues with either a first drying step 316 when an oxygen-impermeable coating is not required, or a second drying step 322 when an oxygen-impermeable coating is required, followed by an optional inspection step, as seen in steps 324 and 326. If inspection is required, the portion of the PCB substrate 114 being processed is advanced to the camera 170, and the PCB substrate 114 is inspected to ensure that there are minimal pinholes in the printed pattern, as seen in step 326. It can be seen that the liquid composition of the printed ink, along with the height of the printed pattern 212, promotes adhesion of the ink to the PCB substrate 114.

[0109] The process continues with the next step 328, in which the portion of the PCB substrate 114 being processed is advanced to the pattern exposure machine 180, and the printed pattern 212 is selectively exposed to form the exposed pattern 220. After step 328, the PCB product 200 is seen to preferably correspond to FIG. 2B. The exposed pattern 220 is characterized by a L / S as small as 5 / 5 μm. It is noted that the printed pattern 212 is selectively exposed to form the exposed pattern 220 that overlies the material, which will be retained during the etching step that follows the printing and exposure preparation method 300. After step 328, the PCB substrate 114 is ready for further processing following the printing and exposure preparation method 300.

[0110] It is noted that the printing and exposure preparation method 300 preferably forms part of a method for preparing a PCB product having a high density of conductors. Following the printing and exposure preparation method 300, the printing pattern 212 is developed and washed to remove the unexposed portions of the photosensitive printing pattern and all of the non-oxygen permeable printing pattern, if one is used, leaving only the exposure pattern 220 that masks the PCB substrate 114. A particular feature of the present invention is that the developed pattern is characterized by an L / S as small as 5 / 5 μm. A further feature of an embodiment of the present invention is that due to the height of the printing pattern 212 and therefore the height of the exposure pattern 220, as explained above with reference to FIGS. 2A-3, the printing pattern 212 created using the CCPPME 100 and the printing and exposure preparation method 300 may be developed and washed in a shorter time than would be the case for a similar pattern produced using a typical known photolithography method.

[0111] Reference is now made to Figures 4A-4H, which are images of a PCB product, such as PCB product 200 (Figures 2A-2C), taken with an optical microscope. The magnification of Figures 4A-4H is indicated by scale bar 410. It is noted that Figures 4A-4H are of exposed pattern 220 after it has been developed. It is further noted that exposed pattern 220 shown in Figures 4A-4D is formed from a photosensitive ink without an adhesion promoter, and exposed pattern 220 shown in Figures 4E-4H is formed from a photosensitive ink with an adhesion promoter.

[0112] Reference is now made to FIG. 5A, which includes two simplified cross-sectional images of a PCB board 500 including a through-hole via 502. FIG. 5A illustrates a problem that may arise during the formation of the through-hole via 502. As seen in FIG. 5A, both the PCB board 500 and the through-hole via 502 are coated with a thin copper layer 520 on a dielectric core 510. The PCB board 500 and the copper layer 520 are then coated with a photoresist ink 530, which covers the copper layer 520 over the entire board. The coated PCB board 500 including the copper layer 520 is then exposed using a pattern exposure machine, typically an LDI exposure machine, as indicated by arrow 540. During the exposure step, the photoresist ink 530 near the edges of the through-hole via 502 is photopolymerized, but not the center of the inner wall of the through-hole via 502. After the development process, the unpolymerized photoresist ink 530 is washed away, leaving portions of the underlying copper layer 520 unprotected for subsequent etching processes, which may result in non-conductive regions 503 within the through-hole vias 502.

[0113] Reference is now made to Figure 5B, which illustrates a first method for solving the problem described in Figure 5A. As seen in Figure 5B, printing a via fill ink 550 into the through-hole via 502 prior to applying a photoresist ink 530 and subsequent exposure 540 of the photoresist ink 530 provides a protective layer over the copper surface in the through-hole via during the developing and etching process.

[0114] Reference is now made to Figure 5C, which illustrates a second method for solving the problem described in Figure 5A. Figure 5C illustrates the creation of a PCB board on a stage that includes a diffusion layer 560. During the exposure process, the laser light that reaches the diffusion layer is backscattered as indicated by arrow 570, resulting in polymerization of the entire photoresist ink 530 inside the through-hole via 502, thus protecting the copper layer 520 during the etching process.

[0115] 3 above, the larger fabrication process proceeds after developing the printed pattern 212. Thankfully, the next step in the larger fabrication process described below is a copper surface wet etch step, while it will be appreciated that, as known to those skilled in the art, the next step in the larger fabrication process may be any suitable step following a lithography process including, among others, a dry etch step, a non-conductive surface etch step, or an ion implantation step.

[0116] The copper layer 210 may be etched using any suitable etching process, such as a wet etch. A typical etching solution suitable for wet etching includes one of the following components: a copper salt such as CuCl2, a ferric salt such as FeCl3, chromic sulfuric acid, a persulfate, sodium chlorite, and hydrogen peroxide. A typical etching process includes spraying the etching solution onto the copper layer 210.

[0117] It can be seen that after the etching step, the PCB product 200 preferably corresponds to Figure 2C. Due to the presence of a banking agent within the printed pattern as described above with respect to the photosensitive ink, as well as the thickness of the printed pattern 212 as described above with reference to Figures 2A-3, the anisotropy of the etch, and therefore the straightness of the conductors, is increased, allowing the conductors to be more closely spaced.

[0118] It is noted that the printing and exposure preparation method 300 of the present invention may be utilized to manufacture etched conductors having various dimensions. It is a specific feature of an embodiment of the present invention that an etched conductor having an L / S of 10 / 10 μm may be manufactured in conjunction with the printing and exposure preparation method 300 of the present invention. As an example, a copper layer having a height of 18 μm may be etched as described above to form a high density conductor having an L / S as small as 25 / 25 μm, while a copper layer having a height of 5 μm may be etched as described above to form a high density conductor having an L / S as small as 10 / 10 μm.

[0119] After etching the layer below the exposed pattern 220, the exposed pattern 220 may be optionally peeled off. Due to the thickness of the printed pattern 212, and therefore the thickness of the exposed pattern 220, the exposed pattern 220 created using the CCPPME 100 and printing and exposure preparation method 300, as described above with reference to Figures 2A-3, may be separated more easily and in less time than would be the case for a similar pattern created using a typical known photolithographic method. Furthermore, peeling of the exposed pattern 220 may be eliminated in some cases, and processing may proceed with the exposed pattern 220 in place.

[0120] Those skilled in the art will appreciate that the present invention is not limited to what has been specifically described and illustrated herein, but includes combinations and subcombinations of the features described herein and improvements thereon that are not within the prior art.

Claims

1. 1. A photosensitive ink for use in an inkjet printer to selectively print unexposed photosensitive patterns on a printed circuit board, said photosensitive ink comprising: a radical polymerization or photodimerization polymerization negative photoresist constituting 33 to 64% by weight of the photosensitive ink; a solvent comprising 19.99 to 59.99 weight percent of the photosensitive ink, the solvent reducing the viscosity of the photosensitive ink to a viscosity suitable for ejection from a nozzle of the inkjet printer, the solvent comprising one of n-propanol, 2-methoxy-2-propanol, isobutanol, propylene glycol monomethyl ether, and isopropyl alcohol; a humectant comprising 1-10% by weight of the photosensitive ink, the humectant comprising a glycol or glycol ether, which prevents the photosensitive ink from solidifying on the nozzle plate of the nozzle prior to ejection; a surfactant constituting 0.01 to 0.1% by weight of the photosensitive ink; an adhesion promoter constituting 1-3% by weight of the photosensitive ink to promote adhesion of the photosensitive ink to the printed circuit board, the adhesion promoter having a weight average molecular weight of 1,700-70,000 Da and acting as a banking agent to adsorb to the sidewalls of the material being etched to prevent undesired isotropic etching; a basic solution constituting 2-3% by weight of the photosensitive ink, the adhesion promoter being dissolved in the basic solution; A photosensitive ink comprising:

2. The photosensitive ink of claim 1 , wherein the adhesion promoter acts to increase the anisotropy of a wet etch process of a copper component onto which the photosensitive ink is printed.

3. The photosensitive ink of claim 1 , wherein the photosensitive ink has a surface tension of less than 30 dyn / cm.

4. The photosensitive ink of claim 1 , wherein the photosensitive ink is operative to produce printed features having a height of less than 5 μm.

Images