Liquid jet recording head unit, method of making same and liquid jet recording apparatus incorporating same
This application is a continuation of application Ser. No. 251,971 filed Sept. 26, 1988, now abandoned, which in turn is a continuation of application Ser. No. 935,092, filed Nov. 24, 1986, now abandoned, which in turn is a continuation of application Ser. No. 739,715, May 31, 1985, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid jet recording head for jetting liquid to form flying droplets to make a record. 
     2. Description of the Prior Art 
     A liquid jet recorder makes a record by discharging liquid such as ink from a nozzle of a recording head. This type of recorder has been warranted attention in that the noise generated during recording is negligible, it attains high speed recording and the record can be made on a plain paper without special treatment. 
     Among others, liquid jet recording methods disclosed in Japanese Patent Application Laid-Open No. 51875/1979 and West Germany DOLS No. 2843064 are unique compared with other liquid jet recording methods because thermal energy is applied to the liquid to produce a motive force for discharging droplets. 
     In the disclosed recording method, the liquid acted by the thermal energy causes a change of state with a rapid increase of volume, liquid is discharged from an orifice at an end of a recording head by a force due to the change of state to form flying droplets and the droplets are deposited on a record medium to form a record. 
     The liquid jet recording method disclosed in the West Germany DOLS No. 2843064, is not only effectively applied to a drop-on demand recording method but also allows easy implementation of a full-line type, high density multi-orifice recording head and hence it enables rapid formation of a high resolution and high quality image. 
     The recording head used in the above recording method comprises a liquid discharge unit including an orifice for discharging liquid and a liquid flow path having a heating unit by which a thermal energy for discharging droplets is applied to the liquid, and an electro-thermal converter for generating the thermal energy. 
     In the prior art recorder having a liquid jet recording head, wiring of the recording head extends on a substrate to a flexible wiring cable connected to a drive circuit which produces an electrical signal to drive the electro-thermal converter of the recording head. The connecting pads of the flexible cable for applying the electrical signal to the recording head have been connected to the wiring pads of the recording head by press-contact method, wire bonding method, soldering or thermal press-contact method, and thereafter the flexible cable is fixed to the recording head. 
     The substrate of the liquid jet recording head has one of different wiring and heat generating resistor patterns depending on an end product such as eight lines with 2.5 lines/mm for a desk top calculator printer or sixteen lines with 4 lines/mm for a facsimile machine. 
     FIG. 1 shows a structure of a prior art liquid jet recording head. Numeral 1 denotes a substrate, numeral 2 denotes electrodes through which electrical signals are supplied, numeral 3 denotes heat generating resistors which are electrothermal converters, numeral 4 denotes an area of a protection film which protects the electrodes and the heat generating resistors from liquid, and numeral 5 denotes a flexible cable for connecting the substrate to a drive circuit. 
     In the prior art liquid jet recording head, the wiring area 6 is large and hence the amount of the substrate material required for each head is large. Since the substrate is made of an expensive material such as Si, the increase of the cost of the recording head by the substrate is not negligible. 
     The increase of the size of the substrate by the unnecessary area causes the reduction of throughput in etching, sputtering or vapor deposition process and impedes mass-production. 
     Further, because the mask changes from product to product, the etching, sputtering or vapor deposition process is complex and yield is lowered due to misoperation. 
     Even in the unnecessary area, short-circuits and bridging of the wiring occur at the same probability as that in the necessary area. Thus, the unnecessary area causes the reduction of the yield. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an inexpensive liquid jet recording head which uses a minimum of expensive substrate material. 
     It is another object of the present invention to provide a liquid jet recording head which allows a high manufacturing yield and has a high reliability in manufacture. 
     It is another object of the present invention to provide a recording head which can be assembled by sub-elements and is applicable for mass-production of a multi-orifice type recording head. 
     It is another object of the present invention to provide a recording head which allows a large freedom of in taking out wiring from the recording head and in designing a head shape. 
     It is another object of the present invention to provide a liquid jet recording head for discharging record liquid from an orifice as flying droplets by applying a thermal energy to the record liquid by a heat generator arranged on a substrate, wherein a plurality of heat generators are formed on a continuous substrate and the substrate is divided to produce a number of heat generators. 
     It is another object of the present invention to provide a liquid jet recording head unit in which a recording head is formed by dividing a substrate on which a plurality of heat generators are mounted, major electrode leads of the recording head unit are arranged on a separate substrate member, the recording head is mounted on the separate substrate member, and the major electrode leads and the electrodes of are electrically connected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a prior art liquid jet recording head, 
     FIGS. 2(a) and 2(b) are plan views of recording head substrates of a recording head of the present invention, 
     FIGS. 3(a) and 3(b) are perspective view of recording heads of the present invention, 
     FIG. 4 is a perspective view of the recording head unit of the present invention, 
     FIGS. 5(a), 5(b), 6(a) and 6(b) are sectional views of other embodiments of the recording head unit of the present invention, and 
     FIG. 7 is a perspective view of other embodiment of the recording head unit of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2(a) and 2(b) show head substrates. In FIG. 2(a), electrodes are folded and in FIG. 2(b), electrodes are not folded. Numeral 21 denotes a support made of a metal such as Ci, Al, Cu or Fe or a semiconductor such as Si. In the present embodiment, an insulative layer made of an oxide such as SiO 2  or Al 2  O 3  is formed on the substrate to electrically isolate a heat generating element. The substrate may be made of an oxide such as SiO 2 , glass or Al 2  O 3 , a nitride such as AlN, Si 3  N 4  or BN or a carbide such as SiC or FeC. 
     A heat generator 23 and electrodes 22 for supplying a current thereto are formed on the substrate 21. A heat generating resistor of the heat generator is made of a boronide such HfB 2  or ZrB 2 , a nitride such as TaN, AlN, TiN, HFN, or ZrN, a carbide such as SiC, TaC, WC or TiC or a high melting point metal such as Ta, W, Mo or Ti. A protection layer 24 for protecting the electrodes 22 and the heat generator 23 from the liquid are coated thereon. The protection layer may be made of an oxide such as SiO 2 , Ta 2  O 5 , Al 2  O 3 , a nitride such as Si 3  N 4  or AlN, a carbide such as SiC or a diamond-shaped carbon. The electrodes 22 may be made of electrically conductive material such as Al, Au, Cu, Ta, W, Mo, Ag or Fe. Numeral 26 denotes scribe lines along which the substrate is divided. They may be formed by a dicing saw, a diamond cutter, a scribing machine or a laser beam. 
     A pattern on the recording head substrate is a repetitive pattern so that each section has the same pattern as that of other sections. For those products which have different numbers of nozzles and the same nozzle pitch, the patterns can be taken out from the substrates of the same batch by merely changing the dividing length. 
     FIGS. 3(a) and 3(b) show perspective views of a liquid jet recording head with nozzles and a liquid chamber mounted on a substrate. 
     FIG. 3(a) shows an edge shooter type recording head having a discharge plane formed on an edge of the recording head, and FIG. 3(b) shows a side shooter type recording head having a discharge plane formed on a side of the recording head. 
     Numeral 31 denotes a recording head, numeral 32 denotes a substrate of the recording head, and numeral 33 denotes a liquid supply port to which a supply tube 34 is mounted and through which liquid is supplied to the recording head. The supply tube 34 is coupled to a liquid tank (not shown). Numeral 35 denotes a top plate for sealing the record liquid having formed therein a liquid chamber 38 for temporarily storing the liquid in the recording head, flow paths 37 through which the liquid is supplied to the heat generating element and orifices 36 through which the droplets are discharged toward a record medium (not shown). 
     The top plate 35 may be made of a material which is not modified by immersion in the record liquid for a long period and which is easy to be machined. For example, glass or ceramics such as almina is etched or ground. An anti-corrosion metal such as Au, Cu, SuS, Ni may be etched or electroformed. An organic resin may be molded or etched. A photosensitive resin or ceramics may be photolithographed. 
     The top plate 35, substrate 32 and supply tube 34 are bonded by adhesive material to form the liquid jet recording head. 
     The top plate 35 must be smaller than the substrate 32 so that an electrode take-out area 39, through which the recording head is electrically connected to an external circuit is exposed. Thus, when the substrate is to be divided, the size of the divided substrate must be larger than the total size of the top plate 35 and the electrode take-out area 39. The liquid chamber 38 must be in the area in which the electrodes are covered by the protection film. 
     FIG. 4 shows a perspective view of a recording head unit in which the liquid jet recording head shown in FIG. 3(b) is mounted on a separate substrate having separate wiring. Numeral 41 denotes the recording head unit which has the recording head 42 shown in FIG. 3(b) mounted on the substrate or support member 43 and which is electrically connected by electrode connection members 45. Numeral 46 denotes external electrodes to be connected to the external circuit in a printer. 
     The support member 43 may be made of an inorganic insulative substrate such as alumina, ceramics, SiC or glass, or a metal plate coated with an insulative material such as Denki-Kagaku Kogyo DENKA HITT plate, or Tokyo IC IMST substrate, or a printed circuit board or a flexible (polyester, glass epoxy, polyimide) substrate. 
     The electrodes 44 may be made of a highly conductive metal such as Au, Cu, Ag, Al, Fe or a conductive material such as conductive paste. It may be spin coated, vapor deposited, cladded and bonded, and then etched into a desired pattern, screen-printed and fired. 
     The members 45 for electrically connecting the recording head and the support member 43 are made of Al or Au and formed by wire bonding. 
     In this manner, the recording head unit of the present invention is formed. 
     The durability and reliability of the recording head of the present invention are improved by protecting the electrical connection area. FIGS. 5 and 6 show embodiments thereof. 
     FIG. 5 shows an embodiment of the edge shooter type recording head unit and FIG. 6 shows an embodiment of the side shooter type recording head unit. 
     In FIGS. 5(a) and 6(a), a sealing member 52 is bonded to a top of a recording head unit 51 by adhesive material 53. The sealing member may be made of plastic, metal or ceramics. 
     FIGS. 5(b) and 6(b) show recording head units in which wirings of the recording head are completely covered by sealing materials 54. The electrodes of the recording head are directly bonded to the external connection electrode members 46 and then the entire assembly is resin-sealed. 
     The sealing material used in the perfect sealing may be fluidic and curable insulative material such as epoxy resin, phenol resin or silicone resin. 
     As schematically depicted in FIG. 5(a), a recording head unit like those shown in FIGS. 5 and 6 is connected to an external circuit (comparable to the flexible circuit board 5 shown in FIG. 1) in a recording apparatus, when the recording head unit is mechanically and electrically connected to the apparatus by the external connection electrode members 46. 
     The present invention is applicable not only to a small liquid jet recording head unit used in a serial type printer but also to a full-multiple liquid jet recording head unit used in a line printer shown in FIG. 7. 
     In FIG. 7, numeral 71 denotes a recording head assembly having a plurality of recording heads 73 of the present invention parallelly arranged on a substrate 72 with common electrodes 75 and individual electrodes 74 being electrically connected by bonding wires 76. Numeral 77 denotes rectifier arrays for keeping the drive currents to the individual electrodes in one direction. The individual electrodes of the recording head assembly are overlapped to keep it compact, although they need not be overlapped. 
     The wiring may be done by a multi-layer wiring board for the purpose of compaction. The individual electrodes may be a separate member such as a flexible printed circuit board. 
     As described hereinabove in accordance with the present invention, the cost of the expensive substrate material is reduced and a number of substrates can be formed in a batch process. Accordingly, a facility cost, a material cost and a personnel cost are significantly reduced and an inexpensive recording head is provided. 
     Since the single substrate can be applied to various types of products, the process is unified and simplified, and mass-productivity and a manufacturing yield are improved. 
     Since no unnecessary wiring area is included, the reliability of the recording head is improved.