Abstract:
A magnetic head apparatus includes a slider with at least one magnetic head element, a suspension having one end portion, one surface and connection pads formed on the one surface, for supporting the slider at the one end portion, a head IC chip flip chip bonded on the connection pads, and an overcoat layer formed on the one surface of the suspension to cover at least a part of each of the connection pads, the overcoat layer with anti-running structures for controlling flow of solder while the IC chip is flip chip bonded.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a magnetic head apparatus which includes a slider with at least one thin-film magnetic head element, a resilient suspension for supporting the slider and a head IC chip. 
     DESCRIPTION OF THE RELATED ART 
     In such magnetic head apparatus, the thin-film magnetic head element for writing magnetic information into and/or reading magnetic information from a magnetic recording medium such as a magnetic disk is in general formed on the slider flying in operation above the magnetic recording medium. The slider is supported by the suspension made of a resilient thin metal plate extended from one end of a movable arm of a magnetic disk drive unit. 
     The head IC chip is used for amplifying writing current to the magnetic head element, for amplifying reading current from the head element and for controlling the writing and reading operations of the head element. The head IC chip had been mounted on the movable arm located in a rearward position of the suspension or on a flexible printed cable (FPC) at a rearward position of the suspension. However, if the IC chip is mounted on the movable arm or on the FPC, lead lines for electrically connecting the magnetic head element with the IC chip become long causing noises to be easily generated. Also, the long lead lines provide some delay in rising and falling times of pulse signals due to parasitic capacitance and inductance of these lead lines causing the high rate transfer of data to make difficult. 
     In order to suppress the generation of noises from the lead lines, Japanese patent unexamined publications nos. 53(1978)-69623, 55(1980)-150130 and 3(1991)-108120 propose a magnetic head apparatus wherein the length of the lead lines is shortened by mounting the head IC chip on the slider or on the suspension. 
     However, if the IC chip is mounted on the slider or on the suspension, the IC chip itself is heated to a high temperature due to the writing current flowing through the IC chip during recording operation. This causes reliability of the head IC chip to lower. Therefore, how dissipate the generated heat from the head IC chip becomes very important. 
     The head IC chip is in general connected to pads formed on the suspension by flip chip bonding and C.T.E. (Coefficient of Thermal Expansion) of the IC chip and of the suspension differ with each other. Thus, if the IC chip is heated to the high temperature, the stress that is generated due to C.T.E. difference will not be sufficiently absorbed at the soldered bonding portion causing the remaining stress to directly apply to the head IC chip. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a magnetic head apparatus, whereby stress generated due to increase in temperature of a head IC chip can be prevented from being applied to the head IC chip itself. 
     According to the present invention, a magnetic head apparatus includes a slider with at least one magnetic head element, a suspension having one end portion, one surface and connection pads formed on the one surface, for supporting the slider at the one end portion, a head IC chip flip chip bonded on the connection pads, and an overcoat layer formed on the one surface of the suspension to cover at least a part of each of the connection pads, the overcoat layer with anti-running structures for controlling flow of solder while the IC chip is flip chip bonded. 
     Since the overcoat layer with anti-running structures such as openings is formed on the suspension to cover a part of each of the connection pads, flow of the solder during flip chip bonding is controlled by the openings so as to prevent the solder from spreading out. Thus, the height and the shape of soldered bonding portions can be correctly controlled. In addition, since the overcoat layer with the openings is formed on the suspension to cover a part of each of the connection pads, the head IC chip disposed on the openings on the connection pads during the flip chip bonding is self-aligned due to the surface tension of the solder in liquid state. Namely, when the head IC chip is bonding, the surface tension of the solder in liquid state moves the head IC chip to the correct position so as to align the pads formed on the bottom of the head IC chip with the openings on the connection pads. Also, since the overcoat layer is formed on the suspension to cover a part of each of the connection pads, no shunt or no short-circuit problem of the connection pads on the suspension due to incorrect positioning of the pads of the head IC chip will occur. 
     As the height and the shape of soldered bonding portions are correctly controlled, the stress which is generated under high or low temperature due to C.T.E. difference between the head IC chip and the suspension can be sufficiently absorbed at the soldered bonding portions so as to prevent the stress to directly apply to the head IC chip. Also, since the height of the soldered bonding portions is correctly controlled, problems that the IC chip is mounted on the suspension at an angle and that the edge of the inclined head IC chip accidentally contacts with the conductors on the suspension can be prevented from occurring. Thus, correct and stable mounting of the head IC chip can be expected, and furthermore reliability for bonding by the soldered bonding portions extremely increases. 
     In addition, since outflow of solder from the bonding portions during the flip chip bonding is suppressed to ensure a sufficient height of the soldered bonding portions, a space is provided between the suspension and the head IC chip. Therefore, underfill with good heat conductivity (filler material with good heat conductivity) can be easily injected into the space so that heat generated from the IC chip can be easily dissipated through the underfill into the suspension to extremely improve heat radiation characteristics. 
     It is preferred that each of the anti-running structures of the overcoat layer is an opening formed at each of the connection pads. In this case, preferably, shape of the connection pad is a circle, and shape of the opening of the overcoat layer is a circle. 
     It is also preferred that the head IC chip has solder bumps, and that a diameter of the opening of the overcoat layer is larger than a diameter of each of the solder bumps. More preferably, the diameter of the opening of the overcoat layer is 120-150% of the diameter of each of the solder bumps. 
     It is preferred that the overcoat layer has a thickness of 5 μm or less. Thus, adequate flexibility for the suspension can be ensured. Also, the overcoat layer is preferably made of polyimide resin or high temperature endurance coating or film material. 
     It is also preferred that the apparatus further includes a resin layer with high heat conductivity filled between the suspension and the head IC chip. 
     By thus filling the high heat conductivity resin, heat generated from the IC chip can be easily dissipated through the resin layer into the suspension to extremely improve heat radiation characteristics. In addition, the filled resin layer improves not only mechanical strength of this portion but also reliability of the IC chip because the resin layer covers the bottom surface of the IC chip. 
     Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a plane view, seen from a slider-attached surface side, of a preferred embodiment of a magnetic head apparatus according to the present invention; 
     FIG. 2 shows a sectional view seen from A—A line of FIG. 1; 
     FIG. 3 shows a sectional view seen from B—B line of FIG. 1; and 
     FIG. 4 shows a plane view illustrating a soldered bonding portion in the embodiment of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a slider-attached surface of a magnetic head apparatus as a preferred embodiment of the present invention, and FIG. 2 illustrates an A—A line section of the apparatus. 
     In these figures, reference numeral  10  denotes a head-suspension assembly corresponding to the magnetic head apparatus according to the present invention. The head-suspension assembly is assembled by fixing a slider  12  having a magnetic head element to a top end portion of a suspension  11 , and by mounting a head IC chip  13  on a middle portion of this suspension  11 . The slider  12  and the head IC chip  13  are fixed on a surface of the suspension  11 , which opposes to the magnetic disk surface. This surface of the suspension is called hereinafter as a slider-attached surface. 
     As shown in FIG. 1, the suspension  11  is substantially constituted by a resilient flexure  14  which carries the slider  12  at its tang located near its top end portion and supports the head IC chip  13  at its middle portion, a load beam  15  which supports and fixes the flexure  14 , and a base plate  16  formed at a base end portion of the load beam  15 . 
     The flexure  14  is made of in this embodiment a stainless steel plate (for example SUS304TA) with a thickness of about 25 μm. 
     A conductor layer of a thin-film pattern  17  that constitutes necessary number of lead lines is formed on the flexure  14  along its length. One end of the conductor layer  17  (the base plate  16  side) is connected to connection terminals  18  connected to external circuits, and the other end of the conductor layer  17  is connected to connection terminals  19  formed at the top end portion of the flexure  14 . 
     The thin-film conductive pattern can be formed by a well-known method similar to the patterning method of forming a printed circuit board on a thin metal plate. Namely, as shown in FIG. 2, the conductive pattern is formed by sequentially depositing a first insulation material layer  20  made of a resin such as polyimide with a thickness of about 5 μm, a patterned Cu layer (conductive layer)  17  with a thickness of about 4 μm, and a second insulation material layer  21  made of a resin such as polyimide with a thickness of about 5 μm on the flexure  14  in this order. Within the regions of the connection terminals  18  and  19 , a Ni layer and an Au layer are sequentially deposited on the Cu layer and there is no second insulation material layer  21 . In order to easily understand the structure, the conductor layer  17  is indicated by solid lines in FIG.  1 . 
     The load beam  15  is made of in this embodiment a stainless steel plate with a thickness of about 70-75 μm and supports the flexure  14  along its whole length. This load beam  15  has a shape with a width that narrows with approaching to its top end. Fixing of the flexure  14  to the load beam  15  is achieved by means of a plurality of welded spots. 
     The base plate  16  is made of a stainless steel or iron and is fixed to the base end portion of the load beam  15  by means of welded spots. The suspension  11  is attached to a movable arm (not shown) by fixing an attachment part of the base plate  16  to the movable arm. In modification, the head-suspension assembly may be formed in a two-pieces structure with a base plate and a flexure-load beam instead of the three-pieces structure with the flexure  14 , the load beam  15  and the base plate  16 . 
     As aforementioned, the slider  12  with the magnetic head element is mounted on the flexure  14  at the top end portion of the suspension  11 . The conductor layer  17  which constitutes the necessary number of lead lines passes both sides of the slider  12  and turns back at the top end portion of the flexure  14  to the connection terminals  19  so as to electrically connect with input/output electrodes of the slider  12 . The conductor layer  17  is covered by the insulation material layer made of the resin. In modification, a dimple may be formed between the load beam  15  and the flexure  14  at a position on which the slider  12  is mounted. 
     The head IC chip  13  is mounted on the slider-attached surface at the middle length portion of the suspension  11 . The head IC chip  13  has preferably a lightweight of 1 mg or less. Thanks to the lightweight of the IC chip, even if the IC chip  13  is mounted on the suspension  11 , it can be expected to produce little ill effect to mechanical resonance characteristics of this suspension  11 . 
     The head IC chip  13  in this embodiment is formed by a bear chip and mounted on and connected to, by the flip chip bonding, the conductor layer  17  which is formed on the flexure  14  of the suspension  11  via the first insulation material layer  20 . 
     FIG. 3 illustrates a B—B line section of the apparatus FIG. 1, and FIG. 4 illustrates a soldered bonding portion in the head IC chip  13 . 
     As shown in FIG. 3, on connection pads  23  which are a part of the conductor layer  17  formed on the first insulation material layer  20 , an overcoat layer  24  made of a resin such as polyimide or high temperature endurance coating or film material with a thickness of about 1-5 μm are multi-layered. The overcoat layer  24  has openings  24   a  at positions corresponding to soldering bumps  25  (FIG. 4) for the head IC chip  13 . 
     As shown in FIG. 4, the diameter of each opening  24   a  is larger than, preferably 120-150% of, the diameter of the soldering bump  25 . For example, in case of about 81 μm of the soldering bump diameter, the diameter of the opening  24   a  is about 120 μm. The opening  24   a  is preferred to shape in a circle as shown in FIG. 4 because the shape of the soldering bump  25  is sphere. However, the opening  24   a  can be made in another shape such as a polygon or an oblong. Also, The connection pad  23  is preferred to shape in a circle as shown in FIG.  4 . However, the connection pad  23  can be made in another shape such as a polygon or an oblong. 
     Since the overcoat layer  24  with the openings  24   a  at positions of the soldering bumps  25  for the IC chip  13  is formed on the connection pads  23 , flow of the solder during flip chip bonding is controlled by the openings  24   a  so as to prevent the solder from spreading out. Thus, the height and the shape of soldered bonding portions  26  can be correctly controlled. 
     In addition, since the overcoat layer  24  with the openings  24   a  is formed on the connection pads  23 , the head IC chip  13  disposed on the openings  24   a  during the flip chip bonding is self-aligned due to the surface tension of the solder in liquid state. Namely, when the head IC chip  13  is bonding, the surface tension of the solder in liquid state moves the head IC chip  13  to the correct position so as to align pads formed on the bottom of the head IC chip  13  with the openings  24   a  on the connection pads  23 . Also, since the overcoat layer  24  is formed on the suspension  11  to cover a part of each of the connection pads  23 , no shunt or no short-circuit problem of the connection pads  23  on the suspension  11  due to incorrect positioning of the pads of the head IC chip  13  will occur. 
     Because the height and the shape of soldered bonding portions  26  are correctly controlled, the stress which is generated under high or low temperature due to C.T.E. difference between the head IC chip  13  and the suspension  11  can be sufficiently absorbed at the soldered bonding portions  26  so as to prevent the stress to directly apply to the head IC chip  13 . Also, since the height of the soldered bonding portions  26  is correctly controlled, problems that the IC chip  13  is mounted on the suspension  11  at an angle and that the edge of the inclined head IC chip  13  accidentally contacts with the conductors on the suspension  11  can be prevented from occurring. Thus, correct and stable mounting of the head IC chip can be expected, and furthermore reliability for bonding by the soldered bonding portions  26  extremely increases. In addition, since the thickness of the overcoat layer  24  is 5 μm or less, adequate flexibility for the suspension can be ensured. 
     Since outflow of solder from the bonding portions  26  during the flip chip bonding is suppressed to ensure a sufficient height of the soldered bonding portions  26 , for example about 50 μm, a space is provided between the first insulation material layer  20  on the flexure  14  and the bottom surface of the head IC chip  13 . Therefore, an underfill (filler material) with good heat conductivity can be easily injected into the space to form an underfill layer  27 . The underfill layer  27  will be made of mixture of a resin such as polyimide and insulation material with good heat conductivity. The underfill with good heat conductivity may be for example a resin containing fused silica (heat conductivity ratio of about 12×10 −4  cal/cm sec degrees), a resin containing alumina (heat conductivity ratio of about 40×10 −4  cal/cm sec degrees), a resin containing crystal silica (heat conductivity ratio of about 35×10 −4  cal/cm sec degrees), or a resin containing aluminum nitride (heat conductivity ratio of about 40×10 −4  cal/cm sec degrees). 
     By thus filling the underfill of a high heat conductivity resin, heat generated from the IC chip  13  can be easily dissipated through the filler material layer into the suspension  11  to extremely improve heat radiation characteristics. In addition, the underfill layer  27  improves not only mechanical strength of this portion but also reliability of the IC chip  13  because the layer  27  covers the bottom surface thereof. 
     Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.