Patent Publication Number: US-2002001159-A1

Title: Magnetic head device having resin stop structure preventive of flowing and scattering of insulating resin

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a magnetic head device for use on a helical-scan magnetic recording/reproducing apparatus and, more particularly, to a magnetic head device for use in a video-tape recorder (VTR) or in a magnetic recording/reproducing apparatus for recording and/or reproducing images handled by computers.  
       [0003] 2. Description of the Related Art  
       [0004]FIGS. 5 and 6 show a conventional magnetic head device known as a “combination-type” magnetic head. The magnetic head device, denoted by  31 , is of an induction-coil type, and has a pair of head chips  34   a ,  34   b  which are also collectively denoted by  34  and which are responsible for writing and reading information, respectively. These head chips  34  are fixed to corresponding protrusions on a head base  33  which is made of brass and which serves as a base member of the magnetic head device  31 , by means of an insulating resin  40  serving as an adhesive, such as, for example, an acrylic resin, epoxy resin, or the like. These head chips  34   a  and  34   b  respectively have ferrite cores  34   a ′ and  34   b ′ on which are wound lead lines  36  to form coils. Lead lines  36  are extended from both ends of each coil, so as to serve as conductor lines. A wiring board  32  is bonded by heat and pressure to the surface of the head base  33  opposite to the surface carrying the head chips  34 .  
       [0005] Four first electrode pads  34   a ,  34   b ,  35   c  and  35   d  (collectively denoted by  35 ) and four second electrode pads  38   a ,  38   b ,  38   c  and  38   d  (collectively denoted by  38 ) are formed on the surface of the wiring board  32 . The first electrode pads are electrically connected to corresponding second electrode pads through conductors laid on the wiring board  32 . Two lead lines  36  are laid to extend from each of the head chips  34   a ,  34   b  via a channel  41  formed between the pair of head bases  33 , so as to be connected to the first electrode pads  35  by soldering as at  35   e . More specifically, the pair of lead wires  36  leading from one  34   a  of the head chips are connected are connected to the first electrode pads  35   a  and  34   b , while the pair of lead wires  36  leading from the other head chip  34   b  are connected to the first electrode pads  35   c  and  35   d . The areas on the printed wiring board  32  other than the regions where the electrode pads are formed is coated with an insulating resin such as an epoxy resin. An insulating resin  37  such as an epoxy resin covers the lead wires  36  extending from the head chips  34  to the first electrode pads  35 , inclusive of the soldered portions  35   e , so as to protect these lead wires  36 . The insulating resin  37  is applied by means of a dispenser or the like and is then cured.  
       [0006] The second electrode pads  38  are to be connected to an internal wiring (not shown) of a rotary cylinder head of a helical-scan magnetic recording/reproducing apparatus which is used on a computer and which incorporates the magnetic head  31 . The magnetic head  31  is fixed in the rotary cylinder head by means of, for example, a screw which is driven through a hole  39  formed in the head base  33 .  
       [0007] The current trend towards miniaturization of magnetic recording/reproducing apparatuses has given a rise to the demand for smaller rotary cylinders and smaller magnetic head devices. This naturally leads to smaller surface area of the printed wiring board and, hence, a smaller distance between the first electrode pads  35  and the second electrode pads  38  on the printed wiring board  32 .  
       [0008] The small distance between the first electrode pads  35  and the second electrode pads  38  poses a problem. To be ore specific, the insulating resin, which is applied to cover the lead wires  36  between the first electrode pads  35  and the head chips  34  and soldered portions  35   e , undesirably flows during the application thereof, or is scattered by inadequate manner of application work. The flowing or scattered resin is deposited on the second electrode pads  38 , thus causing impediment to the electrical connection between the second electrode pads  38  and the external lead wires (not shown).  
       SUMMARY OF THE INVENTION  
       [0009] Accordingly, it is an object of the present invention to provide a highly reliable magnetic head device in which, despite a diminished surface area of a printed wiring board, lead wires between head chips and first electrode pads and soldered portions are satisfactorily covered and protected by an insulating resin, without allowing undesirable deposition of the insulating resin on the second electrode pads.  
       [0010] To this end, according to the present invention, there is provided a magnetic head device, comprising: a head chip; a head base carrying the head chip; a wiring board fixed to the head base and having first electrode pads and second electrode pads formed thereon, the first electrode pads being electrically connected to the head chip via lead wires extending from the head chip, the second electrode pads being electrically connected to the first electrode pads and being arranged for external connection; an insulating resin covering the lead wires connected to the first electrode pads; and a resin-flow stopping structure disposed between the first electrode pads and the second electrode pads.  
       [0011] With these features of the present invention, when the insulating resin is applied, excessive resin flowing on the wiring board is prevented by the resin-flow stopping structure from reaching the second electrode pads, whereby undesirable deposition of the insulating resin on the second electrode pads is prevented.  
       [0012] In addition, the risk of deposition of the insulating resin on the second electrode pads, which may occur due to inferior resin applying work, is greatly suppressed by virture of the feature that the second electrode pads are spaced apart from the first electrode pads by a distance large enough to prevent such undesirable deposition.  
       [0013] In the magnetic head device according to the present invention, the wiring board may further has third electrode pads for use in an inspection and electrically connected to the first and second electrode pads, and the resin-flow stopping structure may be disposed between the first electrode pads and the third electrode pads.  
       [0014] These features prevent undesirable deposition of the insulating resin on the third electrode pads, thus allowing the inspection to be performed smoothly and without delay.  
       [0015] The third electrode pads may be positioned between the first electrode pads and the second electrode pads.  
       [0016] This arrangement permits an efficient use of the limited area on the wiring board, thus eliminating the necessity for the use of a greater wiring board.  
       [0017] In the magnetic head device of the present invention, the wiring board may further have a fourth electrode pad for use in an inspection, the fourth electrode pad being electrically connected to a first electrode pad other than the first electrode pads that are connected to the third electrode pads, and the resin-flow stopping structure may be disposed between the first electrode pads and the fourth electrode pad.  
       [0018] These features effectively prevent deposition of the insulating resin on the fourth electrode pads, thus contributing to improvement in the reliability of the magnetic head device.  
       [0019] The head chip may comprise a magnetoresistive element having electrode layers and a magnetic shield layer. When the magnetoresistive element is used, the third electrode pads are electrically connected to the electrode layers of the magnetoresistive element, and the fourth electrode pad are electrically connected to the magnetic shield layer of the magnetoresistive element.  
       [0020] These features enable an inspection for confirming the state of smear which occurs in the course of a tape lapping process, thus offering high performance and reliability of the magnetic head device.  
       [0021] In the magnetic head device of the present invention, the resin-flow stopping structure may comprise an aperture formed in the wiring board.  
       [0022] This feature permits the resin-flow stopping structure to be easily implemented.  
       [0023] These and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments when the same is read in conjunction with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0024]FIG. 1 is a plan view of a magnetic head device embodying the present invention;  
     [0025]FIG. 2 is a side elevational view of the magnetic head device shown in FIG. 1;  
     [0026]FIG. 3 is an illustration of a head chip which is used in the magnetic head device of the present invention and which employs a magnetoresistive element;  
     [0027]FIG. 4 is an illustration of a tape lapping process performed on the magnetoresistive element used in the magnetic head device of the present invention;  
     [0028]FIG. 5 is a plan view of a known magnetic head device; and  
     [0029]FIG. 6 is a side elevational view of the magnetic head device shown in FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0030] An embodiment of the magnetic head device in accordance with the present invention will be described with reference to FIGS.  1  to  4 .  
     [0031] Referring first to FIGS. 1 and 2, a magnetic head device  1 , which is of a so-called combination type, has information reading head chips denoted respectively y  4   a  and  4   b  and collectively designated at  4 . The magnetic head device  1  also has a head base  3  and a wiring board  2  which is coated by an insulating resin or adhesive denoted by  10 . The insulating resin  10  is a transparent, electrically insulating resin such as, for example, an acrylic resin or an epoxy resin.  
     [0032] The head base  3  serves as a substrate of the magnetic head device  1 , and is made of brass. A fixing hole  13  is formed in the center of the head base  3  and is used when the magnetic head device  1  is mounted in the rotary head. A pair of protrusions  14 , on which the head chips are to be mounted, are formed on the upper edge of the head base  3 . These protrusions are separated from each other by a channel  15 . Lead wires  6  lead from the head chips  4  for electrical connection.  
     [0033] The head chips  4  are fixed to the protrusions  14  on the upper edge of the head base  3 , by means of an insulating resin or adhesive  11  such as an acrylic resin or an epoxy resin. The head chips  4  incorporate magnetoresistive elements.  
     [0034] The structure of each head chip  4  will be described with specific reference to FIG. 3 which is a sectional view of the head chip  4 . The head chip  4  has a base plate  17  on which is formed a magnetic shield layer  21 . A non-magnetic, non-conductive layer (not shown) is formed on the magnetic shield layer  21 . A bias layer  20  and a magnetoresistive element layer  18  are formed on the non-magnetic, nonconductive layer. The bias layer  20  is overlain by another non-magnetic, non-conductive layer (not shown) having a contact hole  43  which provides electrical connection between electrode layers  42  and the bias layer  20 . The bias layer  20  has a protuberance  19  which is formed in the course of the process for forming the magnetoresistive element layer  18 . The bias layer  20  serves to apply a magnetic bias to the magnetoresistive element layer  18 , while the magnetic shield layer  18  serves to magnetically shield the magnetoresistive element layer  18 . Although not shown, another magnetic shield layer is provided so as to cooperate with the magnetic shield layer in sandwiching therebetween the magnetoresistive element layer  18 . These two magnetic shield layers are connected to each other.  
     [0035] Three lead wires  6  (not shown in FIG. 3) are led from both electrode layers  42  and the magnetic shield layer  21 , and are extended towards the wiring board  2 .  
     [0036] The wiring board  2  has an inverse U-like shape so as to clear the fixing hole  13 . On the surface of the wiring board  2  are formed a first group of first electrode pads  5   a ,  5   b  and  5   c  and a second group of first electrode pads  5   d ,  5   e  and  5   f . These two groups of the first electrode pads, collectively denoted by  5 , are arranged in symmetry with respect to a center line which extends in the up and down direction as viewed in FIG. 1. Likewise, formed symmetrically on the surface of the wring board  2  are second electrode pads  7  ( 7   a ,  7   b ;  7   c ,  7   d ), third electrode pads  8 ( 8   a ,  8   b ;  8   c ,  8   d ), and fourth electrode pads  9  ( 9   a ;  9   b ). The first electrode pad  5   a  and the fourth electrode pad  9   a  are connected through an electrode line  16  laid on the wiring board  2 . Similarly, the first electrode pad  5   b , the third electrode pad  8   a  and the second electrode pad  7   a  are connected through electrode lines  16  laid on the wiring board  2 . Likewise, electrode lines  16  laid on the wiring board  2  provide electrical connections between the first electrode pad  5   c  and the second electrode pad  7   b  via the third electrode pad  8   b , between the first electrode pad  5   d  and the second electrode pad  7   c  via the third electrode pad  8   c , between the first electrode pad  5   e  and the second electrode pad  7   d  via the third electrode pad  8   d , and between the first electrode pad  5   f  and the fourth electrode pad  9   b.    
     [0037] Lead lines  6  coated with an insulating material extend through the channel  15  between the head chips  4  so as to be connected at their ends to the first electrode pads  5  by soldering at connecting portions  5   g  (see FIG. 2). The lead lines  6  inclusive of the connecting portions  5   g  are covered by a transparent insulating resin  10  so as to be protected from mechanical impact. The insulating resin  10  is, for example, a UV-curable acrylic resin or a thermosetting epoxy resin.  
     [0038] The second electrode pads  7   a  to  7   d , which are connected to the first electrode pads  5   b  to  5   e  by the electrode lines  16 , are connected to internal wiring (not shown) of a rotary cylinder head of a helical-scan magnetic recording/reproducing apparatus which is mounted in a computer and which incorporates the magnetic head device  1 . The magnetic head device  1  is fixed in the rotary cylinder head by means of, for example, a screw by using the fixing hole  13  formed in the head base  3 . Electrode portions inclusive of the electrode lines  16 , except for the electrode pads, are print-coated by an insulating resin such as an epoxy resin. Apertures  12  are formed in the printed wiring board  2  to separate the second electrode pads  7  and the first electrode pads  5  from each other, so as to serve as resin stopping portions. When the insulating resin  10  is applied to cover the lead lines  6  connected to the first electrode pads, the resin stopping portions constituted by the apertures  12  serve to prevent the insulating resin from spreading along the surface of the wiring board  2 , whereby the undesirable deposition of the insulating resin to the second electrode pads is avoided.  
     [0039] The third electrode pads  8  are used for setting thereon an inspection probe which inspects the degree of lapping achieved in a tape-lapping process which will be described later. The third electrode pads  8  are also used in the final inspection. The apertures  12  also lie between the third electrode pads  8  and the first electrode pads. When the insulating resin  10  is applied to cover the lead lines  6  connected to the first electrode pads, the apertures  12  serve to prevent the insulating resin from spreading along the surface of the wiring board  2 , whereby the undesirable deposition of the insulating resin to the third electrode pads is avoided.  
     [0040] The third electrode pads are positioned between the first electrode pads  5  and the second electrode pads  7 . This is because the first electrode pads  5  are essentially provided on an upper portion of the wiring board  2  for the convenience of the electrical connection to the head chips  4 , while the second electrode pads  7  are disposed in a lower portion of the wiring board  2  due to requirement concerning the internal structure of the rotary cylinder in which the magnetic head device  1  is to be mounted.  
     [0041] Thus, in order to save the space by making efficient use of the limited area, it is preferred feasible to dispose the third electrode pads  8  in the region between the first electrode pads  5  and the second electrode pads  8 .  
     [0042] When a tape lapping is conducted on the sliding surfaces  22  of the head chips  4  of the magnetic head device  1 , the materials of the magnetic shield layer  21  and the electrode layers  42  are spread over the take sliding surfaces  22  of the head chips  4 , due to plasticity f these materials. This phenomenon is generally known as “smear”. The fourth electrode pads  9  are used for the purpose of electrical inspection to determine the state of such smear. More specifically, the fourth electrode pads  9   a  and  9   b  are connected to the magnetic shield layers  21  of the head chips  4  of the magnetic head device  1 , via the first electrode pads  5   a  and  5   f . The third electrode pads  8  are connected to two electrode layers  42  associated with the magnetoresistive layers  18  of each head chip  4 . It is therefore possible to know the state of any short-circuiting between the magnetoresistive element layer  18  and the associated electrode layer  42 , by measuring the electrical resistance between the third electrode pad  8  and the fourth electrode pad  9 . Thus, the fourth electrode pads  9  are electrically isolated from the second electrode pads  7  and the third electrode pads  8  on the wiring board  2 .  
     [0043] The apertures  12  intervene the fourth electrode pads  9  and the first electrode pads  5  on the wiring board  2 , thereby preventing the insulating resin  10  from flowing and spreading on the wiring board  2 , thereby preventing deposition of this insulating resin on the fourth electrode pads, when the insulating resin  10  is applied to cover the lead wires  6  leading from the first electrode pads.  
     [0044] More specifically, the first electrode pads  5  are separated from other electrode pads, i.e., the second electrode pads  7 , third electrode pads  8  and the fourth electrode pads  9 , by the apertures  12  which are elongated and which are formed in the wiring board  2 . When the connecting portions  5   a  at which the lead wires  6  are soldered to the first electrode pads  5  are covered by the insulating resin (adhesive) applied by, for example, a dispenser, there is a risk that excess insulating resin flows along the surface of the wiring board  2 . In this embodiment, however, the flowing resin cannot reach the second, third and fourth electrode pads, because the flowing resin falls into the apertures  12 , whereby deposition of the insulating resin on these electrode pads is avoided.  
     [0045] There is also a risk that the insulating resin is attached to an area around the target position, due to inferior resin applying work. Such wrong application of the insulating resin, however, does not cause contamination of the second, third and fourth electrode pads with the insulating resin, because these electrode pads are sufficiently spaced apart from the first electrode pads by the intervening apertures  12 .  
     [0046] A description will now be given of a process for producing the magnetic head device  1  of the present invention. The process begins with a step for preparing a structure composed of the head base  3  and the wiring board  2  which has the apertures  12  and which is bonded to the head base  3  by heat and pressure. Then, the head chips  4  each having the magnetoresistive element layer  18  are aligned with two protrusions  14  on the head base  3 , and are secured thereto by means of a UV-curable acrylic resin or a thermosetting epoxy resin. Then, the resin is cured or set by application of UV rays or heat, thereby fixing the head chips  4  to the protrusions  14  and, hence, to the head base  3 . Then, lead wires  6  are led from the fixed head chips  4   a  and  4   b  to the upper edge of the wiring board  2 , via the channel  15  formed between the protrusions  14 . The ends of these lead wires  6  are then soldered to corresponding first electrode pads  5   a ,  5   b ,  5   c ,  5   d ,  5   e  and  5   f . More specifically, the lead wires  6  led from the two electrode layers  42  of one  4   a  of the head chips are connected to the first electrode pads  5   b  and  5   c , and the lead wire  6  leading from the magnetic shield layer  21  of this head chip  4   a  is connected to the first electrode pad  5   a . Likewise, the lead wires  6  led from the two electrode layers  42  of the other  4   b  of the head chips are connected to the first electrode pads  5   d  and  5   e  and the lead wire  6  leading from the magnetic shield layer  21  of this head chip  4   b  is connected to the first electrode pad  5   f.    
     [0047] After the soldering of the ends of the lead wires  6  to the first electrode pads  5 , the portions of the lead wires  6  laid on the wiring board  2  and the head base  3 , inclusive of the soldered connecting portions  5   g , are coated with a UV-curable acrylic resin or a thermosetting epoxy resin. The resin is then hardened by application of UV rays or heat.  
     [0048] The magnetic head device  1  thus assembled is then subjected to a tape lapping process. As shown in FIG. 4, the lapping is performed by means of a lapping tape  23  which rubs the tape sliding surface  22  of the head chip  4  of the magnetic head device  1  which is fixed on a jig. More specifically, the lapping tape  23  rubs the tape sliding surface  22  in the directions perpendicular to the plane of the sheet of the drawing. The tape lapping process is conducted for the purpose of improving the affinity to a magnetic tape which is a recording medium. Another purpose of the tape lapping process is to achieve a predetermined resistivity of the magnetoresistive element layer  18 , by adjusting the breadth of this layer  18 , i.e., the height H of the magnetoresistive element. In order to optimize the resistivity of the magnetoresistive element layer  18 , the lapping with the lapping tape is executed while the resistance between the third electrode pads  8   a ,  8   b  and the third electrode pads  8   c ,  8   d  is monitored. The lapping is ceased when the resistance value monitored through the third electrode pads  8  has reached a predetermined value. Finally, the resistance values between the third electrode pads and the fourth electrode pads are measured and checked to confirm that there is no short-circuiting between the magnetic shield layer  21  and the electrode layer  19  attributable to any smear. Products of the magnetic head device  1  exhibiting any short-circuiting due to smear are discarded as being unacceptable goods.  
     [0049] While the invention has been described through illustration of an embodiment which is a combination-type magnetic head device having a couple of head chips, it is to be understood that the described embodiments is only illustrative and the invention may be carried out with a single head chip as well. The magnetic head device of the present invention can be implemented in the form of a device other than the described magnetoresistive magnetic head device, e.g., an induction-coil magnetic head device.  
     [0050] While in the illustrated embodiment the lead wires  6  having insulating coat thereon and led from the head chips  4  are connected to the first electrode pads  5  by soldering, this is only illustrative and the electrical connections between the head chips  4  and the first electrode pads  5  may be achieved by a tape-like FPC (Flexible Printed Circuit). The FPC when used may be connected to the head chips  4  and the first electrode pads  5  by ball bonding method.  
     [0051] While the resin-flow stopping structure has been described as being apertures formed in the wiring board  2 , any type of structure can be adopted equally well such as a recesses or protrusions that can receive or retain the flowing resin.  
     [0052] Although the invention has been described through its specific form, it is to be understood that the described embodiments are only illustrative and various changes and modifications may be imparted thereto without departing from the scope of the present invention which is limited solely by the appended claims.