JP2016201167A - Suspension substrate, suspension, suspension with head, hard disc drive, and manufacturing method for suspension substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a suspension substrate which allows improved surface flatness of an insulator layer between laminated wiring layers and stable impedance in the wiring layers.SOLUTION: In a hard disc drive, a suspension substrate mounting a magnetic head slider comprises: a metal substrate 20; a first insulator layer 22 provided on the metal substrate 20; a first wiring layer 10 provided on the first insulator layer 22; a second insulator layer 24 provided on the first insulator layer 22 and the first wiring layer 10; and a second wiring layer 12 provided on the second insulator layer 24. The second wiring layer 12 is covered with a protective layer 26. The suspension substrate satisfies T1-T2<4.5 μm, when T1 represents the sum of thickness of the first wiring layer 10 and thickness of the second insulator layer 24 on the first wiring layer 10, and T2 represents thickness of the second insulator layer 24 in a position where a surface of the second insulator layer 24 becomes flat at a predetermined distance away from the first wiring layer 10.SELECTED DRAWING: Figure 22

Description

  The present invention relates to a suspension substrate, a suspension, a suspension with a head, a hard disk drive, and a method for manufacturing a suspension substrate, and more particularly to a suspension substrate having improved surface flatness of an insulating layer between laminated wiring layers. The present invention relates to a suspension, a suspension with a head, a hard disk drive, and a method for manufacturing a suspension substrate.

  In general, a hard disk drive (HDD) includes a suspension board on which a magnetic head slider for writing and reading data to and from a disk storing data is mounted. The suspension substrate has a plurality of wiring layers and a plurality of wiring pads provided in the vicinity of the mounting area on which the magnetic head slider is mounted, and each wiring pad is connected to the wiring layer. By connecting these wiring pads to the slider pads of the magnetic head slider, data is transferred to the magnetic head slider.

  In recent years, with the increase in capacity of HDDs and the increase in information transmission speed, it has been required to increase the number of wirings in a suspension substrate, to make them finer, and to stack them. For example, in order to suppress the occurrence of crosstalk, a metal substrate, a first insulating layer formed on the metal substrate, a pair of first wiring layers formed on the first insulating layer at a predetermined interval, There has been proposed a suspension substrate including a second insulating layer formed so as to cover the first wiring layer and a pair of second wiring layers formed on the second insulating layer at a predetermined interval (for example, (See Patent Documents 1 and 2).

  However, in the suspension substrate having such a conventional laminated wiring, since the second insulating layer is formed on the first insulating layer and the first wiring layer, the surface of the first insulating layer and the first wiring are formed. The shape follows the step generated by the surface of the layer, and unevenness is generated on the surface of the second insulating layer. When the second wiring layer is formed on the uneven surface of the second insulating layer, the second wiring layer may be misaligned or a pattern defect of the second wiring layer may occur. As a result, there is a problem that the impedance in the first wiring layer and the second wiring layer becomes unstable.

JP 2009-188379 A JP 2004-133888 A

  The present invention provides a suspension substrate, a suspension, a suspension with a head, a hard disk drive, and a suspension substrate capable of improving the flatness of the surface of the insulating layer between the laminated wiring layers and stabilizing the impedance in the wiring layer. An object is to provide a manufacturing method.

  The suspension substrate according to the present invention includes a metal substrate, a first insulating layer provided on the metal substrate, a first wiring layer provided on the first insulating layer, the first insulating layer, and the first insulating layer. A second insulating layer provided on one wiring layer; and a second wiring layer provided on the second insulating layer; and a thickness of the first wiring layer and the first wiring layer on the first wiring layer. When the total thickness of the second insulating layer is T1, and the thickness of the second insulating layer at a position where the surface of the second insulating layer is flat at a predetermined distance from the first wiring layer is T2, T1 -T2 <4.5 μm is satisfied.

  In the suspension substrate according to the present invention, T2 is the minimum thickness of the second insulating layer at a position away from the first wiring layer by a predetermined distance and the surface of the second insulating layer is flat.

  In the suspension substrate according to the present invention, the thickness of the first wiring layer is not less than 3 μm and not more than 7 μm.

  In the suspension substrate according to the present invention, when the pair of first wiring layers is provided on the first insulating layer, and the thickness of the second insulating layer located between the pair of first wiring layers is T3, T1-T3 <4.5 μm is satisfied.

  In the suspension substrate according to the present invention, the second wiring layer includes a first portion provided on the same plane as the first wiring layer and a second portion provided on the second insulating layer. The second portion is non-parallel on a plane with respect to the first wiring layer and straddles the first wiring layer via the second insulating layer.

  In the suspension substrate according to the present invention, the second wiring layer is parallel to the first wiring layer and is provided above the first wiring layer.

  The present invention is a suspension having a suspension substrate.

  The present invention is a suspension with a head including a suspension and a slider mounted on the suspension.

  The present invention is a hard disk drive having a suspension with a head.

  The method for manufacturing a suspension substrate according to the present invention includes a step of forming a first insulating layer on a metal substrate, a step of forming a plurality of first wiring layers on the first insulating layer, the first insulating layer, Forming a second insulating layer by applying and drying a first resin material having a first viscosity on the plurality of first wiring layers; and forming a second wiring layer on the second insulating layer And a step of forming a protective layer by applying and drying a second resin material having a second viscosity lower than the first viscosity on the second insulating layer and the second wiring layer. It is to be prepared.

  In the manufacturing method of the suspension substrate according to the present invention, the total of the thickness of the first wiring layer and the thickness of the second insulating layer on the first wiring layer is T1, and a predetermined distance from the first wiring layer. When the thickness of the second insulating layer at a position where the surface of the second insulating layer is flat apart is T2, T1−T2 <4.5 μm is satisfied.

  In the method for manufacturing a suspension substrate according to the present invention, when a pair of the first wiring layers are formed and the thickness of the second insulating layer positioned between the pair of first wiring layers is T3, T1−T3 < It satisfies 4.5 μm.

  In the method for manufacturing a suspension substrate according to the present invention, the plurality of first wiring layers are not parallel to each other on a plane, and straddle the plurality of first wiring layers via the second insulating layer. The second wiring layer is formed on the first insulating layer and the second insulating layer.

  In the manufacturing method of the suspension substrate according to the present invention, the second wiring layer is formed in parallel to the first wiring layer and above the first wiring layer.

  In the method for manufacturing a suspension substrate according to the present invention, the first resin material is a polyimide precursor varnish, and the first viscosity is 2000 cP or more and 5000 cP or less.

  According to the present invention, the flatness of the surface of the insulating layer can be improved by forming the insulating layer between the laminated wiring layers with a highly viscous material. Further, by improving the flatness of the surface of the insulating layer, the displacement of the wiring layer on the insulating layer can be prevented and the impedance of the wiring can be stabilized.

1 is a plan view of a suspension substrate according to a first embodiment of the present invention. 2 is a cross-sectional view of the suspension substrate according to the first embodiment. FIG. It is a graph which shows the relationship between the level | step difference of a 2nd insulating layer, and the quality of the shape of a 2nd wiring layer. 2 is a plan view of a suspension substrate according to the first embodiment. FIG. 2 is a cross-sectional view of the suspension substrate according to the first embodiment. FIG. It is a top view which shows an example of the suspension in the said 1st Embodiment. It is a top view which shows an example of the suspension with a head in the said 1st Embodiment. It is a top view which shows an example of the hard-disk drive in the same 1st Embodiment. It is process sectional drawing explaining the manufacturing method of the board | substrate for suspensions concerning the said 1st Embodiment. FIG. 10 is a process cross-sectional view subsequent to FIG. 9. It is process sectional drawing following FIG. FIG. 12 is a process cross-sectional view subsequent to FIG. 11. FIG. 13 is a process cross-sectional view subsequent to FIG. 12. FIG. 14 is a process cross-sectional view subsequent to FIG. 13. FIG. 15 is a process cross-sectional view subsequent to FIG. 14. FIG. 16 is a process cross-sectional view subsequent to FIG. 15; FIG. 17 is a process cross-sectional view subsequent to FIG. 16. FIG. 18 is a process cross-sectional view subsequent to FIG. 17. FIG. 19 is a process cross-sectional view subsequent to FIG. 18. FIG. 20 is a process cross-sectional view subsequent to FIG. 19. FIG. 21 is a process cross-sectional view subsequent to FIG. 20. It is sectional drawing of the board | substrate for suspensions concerning the 2nd Embodiment of this invention. It is a graph which shows the relationship between the level | step difference of a 2nd insulating layer, and the quality of the shape of a 2nd wiring layer. It is a SEM photograph of the resist pattern formed on the 2nd insulating layer. It is sectional drawing of the board | substrate for suspension which combined the 1st Embodiment and 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  (First Embodiment) FIG. 1 is a plan view of a suspension substrate 1 according to a first embodiment of the present invention. As shown in FIG. 1, the suspension substrate 1 includes a mounting region 2 on which a slider (not shown) is mounted as viewed from above, an electrode pad 3, and a plurality of wiring layers that connect the mounting region 2 and the electrode pad 3. (First wiring layer 10 and second wiring layer 12). FIG. 1 is a simplified plan view showing a suspension substrate 1. In FIG. 1, a plurality of wiring layers are indicated by a single line. Although two electrode pads 3 are shown in FIG. 1, the number of electrode pads 3 corresponding to the wiring layer is actually provided. The electrode pad 3 is used for connection between the suspension substrate 1 and an external circuit.

  FIG. 2 shows a cross section taken along line AA of FIG. That is, in the AA sectional view of FIG. 1 shown in FIG. 2, the suspension substrate 1 is provided on the metal substrate 20, the first insulating layer 22 provided on the metal substrate 20, and the first insulating layer 22. First wiring layer 10 (10R, 10W), second insulating layer 24 provided on first insulating layer 22 and first wiring layer 10, and second wiring provided on second insulating layer 24 The layer 12 (12R, 12W) and the protective layer 26 provided on the second insulating layer 24 and the second wiring layer 12 are included.

  A plurality of first wiring layers 10 are provided at predetermined intervals, and similarly, a plurality of second wiring layers 12 are also provided at predetermined intervals. In FIG. 2, a pair of first wiring layers 10 and a pair of second wiring layers 12 are shown. Each second wiring layer 12 is provided above the corresponding first wiring layer 10, and each second wiring layer 12 extends in parallel to the corresponding first wiring layer 10. For example, when the first wiring layer 10R is a reading wiring, the first wiring layer 10W is a writing wiring, the second wiring layer 12R is a writing wiring, and the second wiring layer 12W is a reading wiring, crosstalk is reduced. Transmitted signal can be transmitted.

  As shown in FIG. 2, in the suspension substrate 1, the sum of the thickness of the first wiring layer 10 and the thickness of the second insulating layer 24 on the first wiring layer 10 is T1, and the pair of first wiring layers 10. When the thickness of the second insulating layer 24 positioned therebetween is T3, T1−T3 <4.5 μm is satisfied, and the surface of the second insulating layer 24 has a small level difference. For example, T1 is the sum of the thickness of the first wiring layer 10 and the maximum thickness of the second insulating layer 24 on the first wiring layer 10. For example, T3 is the minimum thickness of the second insulating layer 24 located between the pair of first wiring layers 10.

  FIG. 3 shows the relationship between the step (T1-T3) formed in the second insulating layer 24 and the result of whether or not the second wiring layer 12 is formed in a desired shape. In FIG. 3, a circle indicates that the second wiring layer 12 is formed in a desired shape, that is, a normal pattern, and a cross indicates that the second wiring layer cannot be formed in a desired shape, that is, a defective pattern. It shows that it was. The horizontal axis of the graph in FIG. 3 indicates the thickness of the first wiring layer 10. As can be seen from FIG. 3, if T1-T3 is less than 4.5 μm, the second wiring layer 12 can be formed in a desired shape.

  As described above, T1 and T3 are determined as described above, and the step on the surface of the second insulating layer 24 is reduced, so that the formation position of the second wiring layer 12 is not shifted, and the second wiring layer 12 is formed in the second wiring layer 12. The wiring layer 10 can be provided at a desired position above the wiring layer 10 so as to have a desired shape. Therefore, the second wiring layer 12 can be stably formed, and a desired wiring impedance can be obtained.

  In FIG. 2, the distance L1 between the pair of first wiring layers 10 is, for example, 5 μm or more and 100 μm or less. The thickness of the 1st wiring layer 10 should just be the thickness which can fully transmit a signal, for example, is 3 micrometers or more and 12 micrometers or less, More preferably, they are 3 micrometers or more and 7 micrometers or less. The width of the first wiring layer 10 and the second wiring layer 12 is, for example, 5 μm or more and 100 μm or less. The thickness of the second insulating layer 24 on the first wiring layer 10 may be a thickness that can control the impedance of the first wiring layer 10 and the second wiring layer 12, and is, for example, 3 μm or more and 15 μm or less.

  FIG. 4 is a plan view showing wiring layers (first wiring layer 10 and second wiring layer 12) in region B of FIG. As shown in FIG. 4, in the region B, the second wiring layer 12 is provided so as to straddle the pair of first wiring layers 10 so as to be non-parallel on the plane with respect to the pair of first wiring layers 10. It has been.

  FIG. 5 shows a cross section taken along the line CC of FIG. The suspension substrate 1 includes a metal substrate 20, a first insulating layer 22 provided on the metal substrate 20, a first wiring layer 10 provided on the first insulating layer 22, a first insulating layer 22, and a first insulating layer 22. A second insulating layer 24 provided on one wiring layer 10; a second wiring layer 12 provided on the second insulating layer 24; and a protective layer 26 provided so as to cover the second wiring layer 12. Have.

  The second wiring layer 12 is provided so as to straddle the pair of first wiring layers 10 via the second insulating layer 24. The second wiring layer 12 was provided on the second insulating layer 24 so as to straddle the portion provided on the first insulating layer 22 (on the same plane as the first wiring layer 10) and the first wiring layer 10. Part.

  As described above, in the suspension substrate 1, the sum of the thickness of the first wiring layer 10 and the thickness of the second insulating layer 24 on the first wiring layer 10 is defined as T 1 and between the pair of first wiring layers 10. When the thickness of the second insulating layer 24 positioned is T3, T1−T3 <4.5 μm is satisfied, and the upper surface of the second insulating layer 24 has a small step. The result of whether or not the step (T1-T3) formed in the second insulating layer 24 and the second wiring layer 12 straddling the first wiring layer 10 was formed in a desired shape was the same as in FIG. That is, if T1-T3 is less than 4.5 μm, the second wiring layer 12 straddling the first wiring layer 10 can be formed in a desired shape.

  For this reason, the level | step difference and unevenness | corrugation of the upper surface of the 2nd insulating layer 24 can be made small, the 2nd wiring layer 12 straddling the 1st wiring layer 10 can be formed stably, and the reliability of the 2nd wiring layer 12 is improved. Can be made. As a result, the arrangement of the wiring patterns can be changed stably without disconnection, and the degree of freedom of wiring can be improved.

  In FIG. 4, the distance L2 between the pair of first wiring layers 10 is, for example, 5 μm or more and 100 μm or less. The thickness of the first wiring layer 10 shown in FIG. 5 may be a thickness that can sufficiently transmit a signal, and is, for example, 3 μm or more and 12 μm or less, more preferably 3 μm or more and 7 μm or less. The width of the first wiring layer 10 and the second wiring layer 12 is, for example, 5 μm or more and 100 μm or less. The thickness of the second insulating layer 24 on the first wiring layer 10 may be a thickness that can control the impedance of the first wiring layer 10 and the second wiring layer 12, and is, for example, 3 μm or more and 15 μm or less.

  Next, each component of the suspension substrate 1 will be described.

  The electrode pad 3 includes, for example, a nickel (Ni) plating layer formed on the wiring layers 10 and 12 and a gold (Au) plating layer formed on the Ni plating layer.

  The material of the metal substrate 20 is not particularly limited as long as it has desired conductivity, elasticity, and strength. For example, stainless steel, aluminum, beryllium copper, or other copper alloys are used. It is preferable to use stainless steel.

  The material of the first wiring layer 10 and the second wiring layer 12 is not particularly limited as long as the material has desired conductivity, but it is preferable to use copper (Cu). In addition to copper, any material having electrical characteristics similar to pure copper can be used.

  The material of the first insulating layer 22 and the second insulating layer 24 is not particularly limited as long as it has a desired insulating property. For example, it is preferable to use polyimide (PI).

  As a material of the protective layer 26, it is preferable to use a resin material, for example, polyimide (PI). The material of the protective layer 26 can be a photosensitive material or a non-photosensitive material.

  Next, the suspension 41 in the present embodiment will be described with reference to FIG. A suspension 41 shown in FIG. 6 is provided on the surface (lower surface) opposite to the suspension substrate 1 and the mounting region 2 of the suspension substrate 1 described above, and a slider 52 (see FIG. And a load beam 42 for holding (see FIG. 8).

  Next, referring to FIG. 7, the suspension with head 51 in the present embodiment will be described. A suspension 51 with a head shown in FIG. 7 has the above-described suspension 41 and a slider 52 mounted on the mounting region 2 of the suspension substrate 1 and provided with a plurality of slider pads on the back surface.

  Next, the hard disk drive 61 in the present embodiment will be described with reference to FIG. A hard disk drive 61 shown in FIG. 8 is provided with a case 62, a disk 63 that is rotatably attached to the case 62, stores data, a spindle motor 64 that rotates the disk 63, and a desired flying height on the disk 63. And a suspension 51 with a head including a slider 52 for writing and reading data to and from the disk 63. Among them, the suspension with head 51 is attached to the case 62 so as to be movable, and the voice coil motor 65 for moving the slider 52 of the suspension with head 51 along the disk 63 is attached to the case 62. An arm 66 is connected between the suspension 51 with head and the voice coil motor 65.

  Next, a method for manufacturing the suspension substrate 1 according to the present embodiment will be described with reference to process cross-sectional views shown in FIGS. 9 to 21, (a) shows a cross section corresponding to FIG. 2, and (b) shows a cross section corresponding to FIG.

  First, as shown in FIG. 9, a metal substrate 20 on which polyimide as the first insulating layer 22 is laminated is prepared.

  Next, as shown in FIG. 10, a chromium (Cr) and copper (Cu) sputtering layer 30 is formed on the first insulating layer 22.

  Next, as shown in FIG. 11, resists 31 and 32 are formed on the upper surface of the sputtering layer 30 and the lower surface of the metal substrate 20. Then, the resist 31 is patterned into a pattern corresponding to the first wiring layer 10 by using a photolithography method.

  Next, as shown in FIG. 12, a metal film 33 made of copper is formed in the opening of the resist 31 by electrolytic copper plating.

  Next, as shown in FIG. 13, the resists 31 and 32 are removed.

  Next, as shown in FIG. 14, the exposed portion of the sputtering layer 30 is removed. Thereby, the first wiring layer 10 having the sputtering layer 30 and the metal film 33 is formed. Although a pair of wiring layers 10 is shown in FIG. 2, it is assumed here that a larger number of wiring layers 10 are formed.

  Next, as shown in FIG. 15, a resin material for forming an insulating layer is applied on the first insulating layer 22 and the first wiring layer 10 so as to cover the first wiring layer 10. The resin material is a polyimide precursor varnish. Then, the polyimide precursor varnish is thermally dried to form the second insulating layer 24.

  In addition, it is preferable that the polyimide precursor varnish apply | coated here has a high viscosity, for example, has a viscosity of 500 cP (centipoise) or more and 5000 cP or less, More preferably, 2000 cP or more and 5000 cP or less. When the viscosity is less than 2000 cP, coating variations are likely to occur after coating, making it difficult to obtain a desired film thickness. On the other hand, when the viscosity is greater than 5000 cP, the discharge amount of the apparatus for applying the resin material becomes non-uniform, making application difficult. Therefore, the viscosity of the resin material forming the second insulating layer 24 is preferably 2000 cP or more and 5000 cP or less.

  The polyimide precursor varnish is applied on the step formed by the surface of the first insulating layer 22 and the surface of the first wiring layer 10. However, since the polyimide precursor varnish applied in this step has a high viscosity, it does not have a shape that closely follows the steps. Therefore, the sum of the thickness of the first wiring layer 10 and the thickness of the second insulating layer 24 on the first wiring layer 10 is T1, and the thickness of the second insulating layer 24 located between the first wiring layers 10 is T3. Then, the second insulating layer 24 with a small step on the surface can be formed such that T1-T3 <4.5 μm.

  Next, as shown in FIG. 16, a sputtering layer 34 of chromium (Cr) and copper (Cu) is formed on the second insulating layer 24.

  Next, as shown in FIG. 17, resists 35 and 36 are formed on the upper surface of the sputtering layer 34 and the lower surface of the metal substrate 20. Then, the resist 35 is patterned into a pattern corresponding to the second wiring layer 12 using a photolithography method. In FIG. 17A, the resist 35 is patterned so as to form an opening parallel to the first wiring layer above the first wiring layer 10. In FIG. 17B, the resist 35 is patterned so as to form an opening that is orthogonal (non-parallel) to the first wiring layer 10 on a plane.

  Since the resist 35 is formed on the second insulating layer 24 with a small step on the surface, patterning is easy and an opening can be formed at a desired position.

  Next, as shown in FIG. 18, a metal film 37 made of copper is formed in the opening of the resist 35 by electrolytic copper plating.

  Next, as shown in FIG. 19, the resists 35 and 36 are removed.

  Next, as shown in FIG. 20, the exposed portion of the sputtering layer 34 is removed. Thereby, the second wiring layer 12 having the sputtering layer 34 and the metal film 37 is formed.

  Next, as shown in FIG. 21, a resin material for forming a protective layer is applied on the second insulating layer 24 and the second wiring layer 12 so as to cover the second wiring layer 12. The resin material is a polyimide precursor varnish. Then, the polyimide precursor varnish is thermally dried to form the protective layer 26.

  In addition, the polyimide precursor varnish apply | coated here has a viscosity lower than the polyimide precursor varnish apply | coated at the process shown in FIG. Therefore, as shown in FIG. 21A, the protective layer 26 has a shape that follows the step generated by the surface of the second insulating layer 24 and the surface of the second wiring layer 12.

  Subsequent steps are not shown, but the end portions of the first wiring layer 10 and the second wiring layer 12 are exposed, Ni plating and Au plating are performed, and the electrode pad 3 and the mounting region 2 used for connection to an external circuit are provided. A wiring pad used for connection with a slider pad provided on the slider 52 is formed. Thereafter, a patterned resist is formed on the lower surface of the metal substrate 20, the metal substrate 20 is etched using a corrosive liquid such as a ferric chloride aqueous solution from the opening of the resist, and the resist is removed. The suspension substrate 1 is obtained.

  A load beam 42 is attached to the lower surface of the suspension substrate 1 obtained in this way, and the suspension 41 shown in FIG. 6 is obtained. A suspension 52 with a head shown in FIG. 7 is obtained by mounting a slider 52 having a plurality of slider pads on the back surface in the mounting area 2 of the suspension 41. In this case, the slider pad of the slider 52 is connected to the wiring pad provided at the end of each wiring layer 10, 12. Further, the suspension 51 with the head is attached to the case 62 of the hard disk drive 61 to obtain the hard disk drive 61 shown in FIG.

  When reading and writing data in the hard disk drive 61 shown in FIG. 8, the slider 52 of the suspension with head 51 is moved along the disk 63 by the voice coil motor 65, and the disk 63 rotated by the spindle motor 64 is moved. Keep close to the desired flying height. As a result, data is transferred between the slider 52 and the disk 63 via the slider pad and the wiring pad. During this time, electrical signals are transmitted by the wiring layers 10 and 12 connected between the wiring pads in the mounting region 2 of the suspension substrate 1 and the electrode pads 3.

  As described above, according to the first embodiment, the second insulating layer 24 of the suspension substrate 1 is formed of a highly viscous material, and the flatness of the surface of the second insulating layer 24 is improved. Since the resist 35 can be easily patterned on the second insulating layer 24 with a small step on the surface, the displacement of the second wiring layer 12 can be prevented. Therefore, the second wiring layer 12 can be stably formed on the second insulating layer 24, and a desired wiring impedance can be obtained. Further, the second wiring layer 12 straddling the first wiring layer 10 as shown in FIG. 4 can be easily formed.

  (Second Embodiment) FIG. 22 shows a cross section of a suspension substrate according to a second embodiment of the present invention. The cross section shown in FIG. 22 is a cross section along the AA line of FIG. In FIG. 22, the same parts as those of the first embodiment shown in FIG.

  As shown in FIG. 22, the suspension substrate 1 includes a metal substrate 20, a first insulating layer 22 provided on the metal substrate 20, a first wiring layer 10 provided on the first insulating layer 22, The second insulating layer 24 provided on the first insulating layer 22 and the first wiring layer 10, the second wiring layer 12 provided on the second insulating layer 24, the second insulating layer 24 and the second wiring layer 12 and a protective layer 26 provided on the substrate 12. Two or more first wiring layers 10 and second wiring layers 12 may be provided.

  In the suspension substrate 1, the sum of the thickness of the first wiring layer 10 and the thickness of the second insulating layer 24 on the first wiring layer 10 is T 1, a predetermined distance away from the first wiring layer 10, and the second insulating layer. When the thickness of the second insulating layer 24 at a position where the surface of 24 is flat is T2, T1−T2 <4.5 μm is satisfied, and the surface of the second insulating layer 24 is in a highly flat state. Yes. The position where the surface of the second insulating layer 24 becomes flat is, for example, the thickness of the second insulating layer 24 (the distance between the upper surface of the first insulating layer 22 and the upper surface of the second insulating layer 24) is minimized. Position. For example, T1 is the sum of the thickness of the first wiring layer 10 and the maximum thickness of the second insulating layer 24 on the first wiring layer 10.

When the second insulating layer 24 has a tapered shape or becomes thin in a step shape at the end in the left-right direction in FIG. 22, the thickness of the second insulating layer 24 is the minimum at the end. Become.
Therefore, in such a case, it is preferable that the minimum thickness of the second insulating layer 24 in the region excluding the end portion is T2. Further, the average value of the minimum thickness of the second insulating layer 24 in the left direction in FIG. 22 and the minimum thickness of the second insulating layer 24 in the right direction as viewed from the first wiring layer 10 may be T2.

  FIG. 23 shows the relationship between the step (T1-T2) formed in the second insulating layer 24 and the result of whether or not the second wiring layer 12 is formed in a desired shape. In FIG. 23, a circle indicates that the second wiring layer 12 is formed in a desired shape, that is, a normal pattern, and a cross indicates that the second wiring layer cannot be formed in a desired shape, that is, a defective pattern. It shows that it was. The horizontal axis of the graph in FIG. 23 indicates the thickness of the first wiring layer 10. As can be seen from FIG. 23, if T1-T2 is less than 4.5 μm, the second wiring layer 12 can be formed in a desired shape.

  The quality of the pattern shape of the second wiring layer 12 is attributed to the shape of the resist pattern provided when the second wiring layer 12 is formed. As described in the first embodiment, the second wiring layer 12 is patterned by forming the sputtering layer 34 on the first insulating layer 24 (FIG. 16) and forming the resist 35 on the sputtering layer 34. (FIG. 17), a metal film 37 is formed by electrolytic copper plating on the opening of the resist 35 (FIG. 18), the resist 35 is removed (FIG. 19), and the portion of the sputtering layer 34 where the surface is exposed is exposed. It is formed by removing (FIG. 20). Further, a protective layer 26 is formed on the second wiring layer 12 (FIG. 21).

  If the step (T1-T2) formed in the second insulating layer 24 is large, the opening cannot be formed with high accuracy when the resist 35 is patterned. FIG. 24A shows an SEM photograph of the opening of the resist 35 when the thickness of the first wiring layer 10 is 13.5 μm and T1-T2 is 8.3 μm. As can be seen from FIG. 24A, when the step (T1-T2) formed in the second insulating layer 24 is large, the resist 35 remains in the opening where the sputtering layer 34 is exposed. This occurs because incident light that hardens the resist 35 is scattered by a step on the surface of the second insulating layer 24. When the metal film 37 is formed on the sputtering layer 34 with the resist 35 remaining in the opening, a shape defect of the second wiring layer 12 occurs.

  However, if the step (T1-T2) formed in the second insulating layer 24 is set to less than 4.5 μm and the surface flatness of the second insulating layer 24 is increased, the opening can be accurately formed when the resist 35 is patterned. Can be formed. FIG. 24B shows an SEM photograph of the opening of the resist 35 when the thickness of the first wiring layer 10 is 6.8 μm and T1-T2 is 3.8 μm. As can be seen from FIG. 24B, the opening of the resist 35 is formed with high precision, and when the metal film 37 is formed on the sputtering layer 34 exposed through such an opening, the first film having a desired shape is formed. Two wiring layers 12 are obtained.

  The suspension substrate according to the present embodiment can be manufactured by the same method as in the first embodiment. By setting the viscosity of the polyimide precursor varnish used to form the second insulating layer 24 to 500 cP or more and 5000 cP or less, more preferably 2000 cP or more and 5000 cP or less, the thickness of the first wiring layer 10 and the first wiring layer 10 When the total thickness of the second insulating layer 24 is T1, and the thickness of the second insulating layer 24 at a position where the surface is flat at a predetermined distance from the first wiring layer 10 is T2, T1-T2 < The second insulating layer 24 having a high surface flatness of 4.5 μm can be formed.

As can be seen from FIG. 23, the thickness of the first wiring layer 10 affects T1-T2.
In order to satisfy T1−T2 <4.5 μm, the thickness of the first wiring layer 10 is preferably 7 μm or less. The thickness of the first wiring layer 10 is preferably 3 μm or more so that signals can be sufficiently transmitted.

  Thus, according to the second embodiment, the flatness of the surface of the second insulating layer 24 is improved by forming the second insulating layer 24 of the suspension substrate 1 with a highly viscous material. Since the resist 35 can be easily patterned on the second insulating layer 24 having a high surface flatness, the second wiring layer 12 having a desired shape can be formed. Therefore, the second wiring layer 12 can be stably formed on the second insulating layer 24, and a desired wiring impedance can be obtained.

  The first embodiment and the second embodiment may be combined. That is, as shown in FIG. 25, the sum of the thickness of the first wiring layer 10 and the thickness of the second insulating layer 24 on the first wiring layer 10 is T1 and the first wiring layer 10 positioned between the pair of first wiring layers 10. When the thickness of the second insulating layer 24 is T3 and the thickness of the second insulating layer 24 at a position where the surface of the second insulating layer 24 is flat at a predetermined distance from the first wiring layer 10 is T2, T1-T3 <4. .5 μm and T1−T2 <4.5 μm. With such a configuration, the second wiring layer 12 can be more stably formed on the second insulating layer 24, and a desired wiring impedance can be obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 1 Suspension board | substrate 2 Mounting area | region 3 Electrode pad 10 1st wiring layer 12 2nd wiring layer 20 Metal substrate 22 1st insulating layer 24 2nd insulating layer 26 Protective layer 30 Sputtering layers 31 and 32, Resist 33 Metal film 34 Sputtering layer 35, 36 Resist 37 Metal film 41 Suspension 42 Load beam 51 Suspension with head 52 Slider 61 Hard disk drive 62 Case 63 Disk 64 Spindle motor 65 Voice coil motor 66 Arm

Claims (15)

A metal substrate;
A first insulating layer provided on the metal substrate;
A first wiring layer provided on the first insulating layer;
A second insulating layer provided on the first insulating layer and the first wiring layer;
A second wiring layer provided on the second insulating layer;
With
The sum of the thickness of the first wiring layer and the thickness of the second insulating layer on the first wiring layer is T1, and the surface of the second insulating layer is flat at a predetermined distance from the first wiring layer. A suspension substrate characterized by satisfying T1−T2 <4.5 μm, where T2 is the thickness of the second insulating layer at the position.   2. The suspension according to claim 1, wherein T <b> 2 is a minimum thickness of the second insulating layer at a position where the surface of the second insulating layer is flat at a predetermined distance from the first wiring layer. substrate.   The suspension substrate according to claim 1 or 2, wherein the first wiring layer has a thickness of 3 µm to 7 µm. A pair of the first wiring layers is provided on the first insulating layer;
4. The structure according to claim 1, wherein T <b> 1 − T <b> 3 <4.5 μm is satisfied, where T <b> 3 is a thickness of the second insulating layer positioned between the pair of first wiring layers. 5. Suspension substrate.   The second wiring layer includes a first portion provided on the same plane as the first wiring layer and a second portion provided on the second insulating layer, and the second portion includes the first portion. 5. The suspension substrate according to claim 1, wherein the suspension substrate is not parallel to one wiring layer and straddles the first wiring layer via the second insulating layer. 6.   The suspension according to any one of claims 1 to 4, wherein the second wiring layer is provided parallel to the first wiring layer and provided above the first wiring layer. Substrate.   A suspension comprising the suspension substrate according to any one of claims 1 to 6.   A suspension with a head comprising the suspension according to claim 7 and a slider mounted on the suspension.   A hard disk drive comprising the suspension with a head according to claim 8. Forming a first insulating layer on a metal substrate;
Forming a plurality of first wiring layers on the first insulating layer;
Forming a second insulating layer by applying and drying a first resin material having a first viscosity on the first insulating layer and the plurality of first wiring layers;
Forming a second wiring layer on the second insulating layer;
Forming a protective layer by applying and drying a second resin material having a second viscosity lower than the first viscosity on the second insulating layer and the second wiring layer; and
A method for manufacturing a suspension substrate comprising:   The sum of the thickness of the first wiring layer and the thickness of the second insulating layer on the first wiring layer is T1, and the surface of the second insulating layer is flat at a predetermined distance from the first wiring layer. 11. The method for manufacturing a suspension substrate according to claim 10, wherein T <b> 1 − T <b> 2 <4.5 μm is satisfied, where T <b> 2 is a thickness of the second insulating layer at a certain position. Forming a pair of the first wiring layers;
12. The method of manufacturing a suspension substrate according to claim 11, wherein T1-T3 <4.5 [mu] m is satisfied, where T3 is a thickness of the second insulating layer positioned between the pair of first wiring layers.   On the first insulating layer and the second insulating layer so as to be non-parallel on a plane with respect to the plurality of first wiring layers and straddle the plurality of first wiring layers via the second insulating layer The method for manufacturing a suspension substrate according to claim 10, wherein the second wiring layer is formed on the suspension wiring.   13. The suspension substrate according to claim 10, wherein the second wiring layer is formed in parallel to the first wiring layer and above the first wiring layer. Manufacturing method.   The method for manufacturing a suspension substrate according to any one of claims 10 to 14, wherein the first resin material is a polyimide precursor varnish, and the first viscosity is 2000 cP or more and 5000 cP or less.