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(11) | EP 1 080 907 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Manufacturing printheads |
| (57) A method for fabricating thin-film ink-jet printheads includes a step (14) of electroforming
individualized orifice plates (16) on a surface of a mandrel (6). After the orifice
plates are formed, the mandrel is aligned with a wafer (24) to allow the orifice plates
to be aligned with their corresponding printhead dies (26) concurrently. After that,
polymeric adhesive (28) on the printheads dies is cured to allow the orifice plates
to be adhered to the corresponding printhead dies. The mandrel is then separated (36)
from the orifice plates. The printhead dies on the wafer is finally singulated (38)
to produce individual thin-film ink-jet printheads. |
[0001] This invention relates to a method for manufacturing printheads and in particular thin-film ink-jet printheads for use in pens for ink-jet printers. More particularly, this invention relates to a method for simultaneously attaching orifice plates to a wafer containing printhead dies.
[0002] A prior-art method of manufacturing thin film ink-jet printheads requires orifice plates to be individually attached to printhead dies. The method includes a step of electroforming a single sheet of nickel containing a number of orifice plates using a mandrel. The mandrel has a substrate of glass, plastic or a polished silicon wafer. A thin-film layer of conductive material is deposited on this substrate. The conductive material is typically of chrome and stainless steel. Next, a layer of dielectric is deposited on the conductive layer. This dielectric layer is of a nonconductive material such as silicon carbide. Patterns on the dielectric layer are lithographically formed using conventional masking, ultraviolet exposure and etching techniques to dimensionally define a mold for molding orifices in orifice plates. U.S. Patent 4,773,971 discloses a method of making such a mandrel.
[0003] The orifice plates are formed using an electroforming process. The orifice plates thus formed are all on a single sheet. Breaking tabs which are also electroformed on the sheet defines the boundaries of each orifice plate. In the manufacturing of printheads, the sheet of orifice plates is attached to a mounting tape , for example, the Nitto Denko Elep Holder type V-8T available from Nitto Denko Corporation, Tokyo, Japan,. The orifice plates are next singulated into individual orifice plates by breaking the sheet along the breaking tabs. The mounting tape holds the singulated orifice plates for further processing. A machine next picks and places each orifice plate over a corresponding printhead die on a wafer containing many such dies. The wafer and attached orifice plates are put through a "stake and bake" process to cause the orifice plates to adhere to the dies. After the "stake and bake" process, each printhead consisting of a die and an orifice plate is singulated using dice sawing. Each complete pair of orifice plate and printhead die is then ready for attaching to a pen body to complete the fabrication of an ink-jet pen. This pen body typically contains an ink reservoir which supplies ink to the printhead.
[0004] The prior art method of manufacturing printheads has several disadvantages. Firstly, the step of attaching orifice plates to the dies on the wafer is a sequential process and is therefore very time consuming. The process of attaching orifice plates is carried out one orifice plate at a time. The total time taken to attach orifice plates on all dies on a single wafer is the total number of dies multiplied by the time taken to attach a single orifice plate to a die. Secondly, there are extraneous steps in such a manufacturing process. Such extraneous steps include the steps of manually separating the orifice plates from the mandrel, attaching the separated orifice plates to the mounting tape and the subsequent singulating of the orifice plates. These extraneous step demand that the orifice plates be of a minimum thickness to withstand the rigors of separation from the mandrel and singulation of the orifice plates. This minimum thickness translates to an achievable minimum size of orifices, thus limiting the orifice count on each orifice plate. A thinner orifice plate will allow a larger numbers of orifices to be packed into a given area, since the orifices will be relatively smaller. A third disadvantage associated with this prior art method is the difficulty to correctly align a singulated orifice plate with a printhead die. A vision system is typically used to align the singlulated orifice plate with the die. The aligned orifice plate and the die is then put through a "stake and bake" process where heat and pressure is used to cure a thin layer of glue or adhesive on the die to secure the orifice plate to the die. The "stake and bake" process will nonetheless affect this alignment of the small singulated orifice plate with the printhead die.
[0005] The problems associated with the foregoing process therefore create the need for a faster and more reliable method of manufacturing thin-film ink-jet printheads.
[0006] In one aspect of the present invention, a preferred method of fabricating and attaching orifice plates to a wafer of printhead dies includes a step of electroforming individualized orifice plates. These orifice plates are formed in a predetermined pattern on a surface of a mandrel. This predetermined pattern corresponds to the arrangement of printhead dies on the wafer. The method also includes a step of aligning the mandrel with the wafer to allow the orifice plates to be aligned with their corresponding printhead dies concurrently. A polymeric layer on the printhead dies is then cured to allow the orifice plates to be adhered to their corresponding printhead dies.
[0007] In another aspect of the present invention, a preferred method of manufacturing thin-film ink-jet printheads includes the steps described above for the fabrication and attaching of orifice plates to a wafer of printhead dies. The preferred method further includes separating the mandrel from the attached orifice plates. After the mandrel is separated, the printhead dies are singulated.
[0008] In yet another aspect of the present invention, a thin-film ink-jet printhead has a printhead die including a polymeric barrier layer and an orifice plate. The orifice plate is separately electroformed and attached to the printhead die using the above-described method for manufacturing thin-film ink-jet printheads.
[0009] In yet another aspect, a mandrel for electroforming individualized orifice plates includes a substrate and a metallic layer residing on the substrate. The mandrel further includes a dielectric layer. This dielectric layer is photolithographically patterned and etched to produce dielectric buttons and boundary strips on the metallic layer. The buttons are for defining orifices during the electroforming of the orifice plates. The boundary strips ensures that the orifice plates are individually formed. The metallic layer, buttons and boundary strips form the molding surfaces of the mandrel.
[0011] Figure 1 is a block diagram showing a sequence of steps in a process of manufacturing thin-film ink-jet printheads according to the present invention.
[0012] Figure 2 is an enlarged isometric view of an illustrative mandrel used in the process of Figure 1.
[0013] Figure 3 is a further enlarged cross-sectional view of a mandrel of Figure 2 taken along a line A-A. This view is shown with orifice plates electroformed on the mandrel.
[0014] Figure 4 is an enlarged and exploded isometric view of the mandrel of Figure 2 in alignment with a wafer of printhead dies for attaching orifice plates on the mandrel onto the printhead dies on the wafer.
[0015] The method of manufacturing thin-film ink-jet printheads according to the present invention is described with the aid of Figure 1. Figure 1 is a block diagram showing a typical sequence 2 of process steps for manufacturing thin-film ink-jet printheads according to the invention. The sequence 2 starts in a CREATE MANDREL step 4, where a mandrel is created for electroforming orifice plates. Figure 2 shows an illustrative mandrel 6 which is created in this CREATE MANDREL step 4. This mandrel in Figure 2 is shown to be able to form only four orifice plates. It is well known to those skilled in the art that given the size of each orifice plate and the surface area of a silicon wafer, many orifice plates can be formed on a single silicon wafer. Once the mandrel 6 is created, it is reusable. The process of creating such a mandrel 6 is only briefly described here because such a process is well known to those skilled in the art. U.S. Patent 4,773,971 discloses such a process in detail. However, important design constraints will be emphasized. The steps of making such a mandrel 6 starts with a polished silicon wafer substrate 8. Other suitable materials with a smooth and non-conducting surface such as a glass substrate, an unpolished silicon wafer or a plastic wafer can also be used. Next, a layer of conductive thin film 10 such as chrome and stainless steel is deposited on the surface of the substrate 8. Other conductive materials may also be used. The conductive layer 10 forms a mold for creating an orifice plate. Next, a dielectric layer 12 is deposited over the conductive layer 10. In this preferred embodiment, the dielectric is of silicon carbide. Other dielectric materials are equally applicable to the present invention. This dielectric layer 12 is lithographically formed with known photoresist, making and etching processes in the art to define dielectric buttons 12 and boundary strips 13 on the conductive layer 10. Holes 14 are etched through the conductive layer 10 and the substrate 8 for subsequent aligning of the mandrel 6 with another wafer on which printhead dies are formed.
[0016] The sequence next proceeds to an ELECTROFORM ORIFICE PLATES step 14. Figure 3 shows an enlarged cross-sectional view of the mandrel 6 taken along a line A-A of Figure 2. The figure also shows a cross-section of two orifice plates 16 electroformed on the mandrel 6. In electroforming the orifice plates, the mandrel 6 is inserted into an electroforming bath to form a cathode. A metal source material which supplies the electroforming material is made an anode. In a preferred embodiment of the invention, the source material plate is composed of a non-ink-corrosive metal such as a nickel alloy. During the electroforming process, the metal is transferred from the anode metal plate to the cathode mandrel 6. The metal attaches to the conductive layer 10 of the cathode mandrel 6 and not the substrate 8, the buttons 12 or the boundary strips 13. This attraction of metal to the conductive layer 12 and away from the boundary strips 13 results in individualized orifice plates being formed. The attraction of metal away from the buttons 12 also result in the creation of orifices 18 in the orifice plates. The electroforming process is continued until a desired thickness of the electroformed orifice plates is achieved. Such an electroforming process is well known to those skilled in the art. Those skilled in the art are familiar with the profile of accumulation of metal on the mandrel 6. While the orifice plates are formed, a separate process is used to prepare thin-film printhead dies on a separate wafer. The process of making these printhead dies is well known to those skilled in the art and does not need to be described here. Any prior art process for making such printhead dies are equally applicable to the present invention. Figure 4 is an enlarged and exploded isometric view of a mandrel 6, electroformed orifice plates 16 in alignment with and a wafer 24 of printhead dies 26. It is well known that a barrier layer 28, made of a polymeric material is used to define ink channels and chambers in the printhead dies 26. Alignment markings 30 which correspond to those etched holes 14 on the mandrel 6 are made on the wafer 24.
[0017] The sequence 2 of manufacturing printheads next proceeds to an ALIGN MANDREL WITH DIE WAFER step 32. In this step 32, the mandrel 6 with the electroformed orifice plates 16 are aligned with the wafer 24 of printhead dies 26 with the orifice plates 16 facing the dies 26. The two wafers are aligned with the aid of a vision system. The vision system locates the alignment markings 30 through the alignment holes 14 on the mandrel 6 to align the two to a typical tolerance of less than or equal to one micron. Other alignment methods can also be used. After being aligned, pressure is applied to the mandrel 6 to hold the mandrel 6 and wafer 24 together.
[0018] The sequence 2 next proceeds to a BAKE MANDREL AND WAFER step 34, where the mandrel 6 and the wafer 24 are put in an oven which is heated to a temperature of approximately 200 degree Celsius. The mandrel 6 and wafer 24 are left in the oven for a period of approximately 15 minutes. The pressure and heat will cause the polymeric layer 28 to cure and adhere to the orifice plates.
[0019] After the BAKE MANDREL AND WAFER step 34, the sequence proceeds to a SEPARATE MANDREL step 36, where the mandrel 6 is separated from the wafer 24 to leave the orifice plates 16 attached to their respective printhead dies 26. Finally, the completed printheads of die and orifice plates are singulated using a dicing saw in a SINGULATE PRINTHEADS step 38. Each singulated printhead can then be attached to pen body to produce an ink-jet pen which is ready for use in an ink-jet printer. The separated mandrel 6 can be reused to make another set of orifice plates 16.
[0020] It is clear from the description that the extraneous steps found in the prior art method are eliminated from the process according to the present invention. The process therefore results in a significant saving in time. Since the orifice plates 16 are not required to be separated from the mandrel 6 prior to being attached to the printhead dies 26, they can be electroformed to be thinner than those available in the prior art. These thinner orifice plates result in smaller orifices, and therefore a larger orifice count is achievable.
1. A method of fabricating and attaching orifice plates (16) to printhead dies (26) which
are built in a first predetermined pattern on a wafer (24), the method comprising:
electroforming individualized orifice plates (16) in a second predetermined pattern on a surface of a mandrel (6);
aligning the mandrel (6) with the wafer (24) to allow the orifice plates (16) to be aligned with their corresponding printhead dies (26) concurrently; and
curing polymeric layers on the printheads dies to allow the orifice plates to be adhered to the corresponding printhead dies.
2. A method according to Claim 1, further comprising:
fabricating a mandrel having:
fabricating a mandrel having:
a substrate;
a conductive layer on the substrate having a molding surface to allow the electroforming of orifice plates; and
dielectric areas on the molding surface of the conductive layer to allow electroforming of individualized orifice plates and to define orifices on the orifice plates.
3. A method according to Claim 2, wherein each orifice plate is electroformed to have
a substantially flat surface facing the molding surface of the mandrel.
4. A method of fabricating thin-film ink-jet printheads given printhead dies which are
arranged in a first predetermined pattern on a wafer, the method comprising:
electroforming individualized orifice plates in a second predetermined pattern on a surface of a mandrel;
aligning the mandrel with the wafer to allow the orifice plates to be aligned with their corresponding printhead dies concurrently;
curing polymeric layers on the printheads dies to allow the orifice plates to be adhered to the corresponding printhead dies;
separating the mandrel from the orifice plates; and
singulating the printhead dies to produce individual thin-film ink-jet printheads.
5. A method according to Claim 4, further comprising:
fabricating a mandrel having:
fabricating a mandrel having:
a substrate;
a conductive layer on the substrate having a molding surface to allow the electroforming of orifice plates; and
dielectric areas on the molding surface of the conductive layer to allow electroforming of individualized orifice plates and to define orifices on the orifice plates.
6. A method according to Claim 5, wherein each orifice plate is electroformed to have
a substantially flat surface facing the molding surface of the mandrel.
7. A thin-film ink-jet printhead comprising:
a printhead die including a polymeric barrier layer; and
an orifice plate which is separately electroformed and attached to the printhead die in a process comprising:
electroforming individualized orifice plates in a predetermined pattern on a surface of a mandrel;
aligning the mandrel with the wafer to allow the orifice plates to be aligned with their corresponding printhead dies concurrently;
curing polymeric layers on the printheads dies to allow the orifice plates to adhere to the corresponding printhead dies;
separating the mandrel from the orifice plates; and
singulating the printhead dies to produce individual thin-film ink-jet printheads.
8. A mandrel for electroforming orifice plates comprising:
a substrate;
a metallic layer on the substrate having a molding surface for electroforming orifice plates; and
a dielectric layer which is photolithographically patterned and etched to produce dielectric areas on the metallic layer for electroforming individualized orifice plates and for defining orifices in the individualized orifice plates;
wherein the metallic layer and dielectric areas form the molding surfaces of the mandrel.