HK1113012A - Method and apparatus for connecting metal structures on opposing sides of a circuit - Google Patents

Description

Method and apparatus for connecting metal structures on opposite sides of a circuit

RELATED APPLICATIONS

This p.c.t application claims priority from U.S. provisional application No.60/547,439,2004, filed on 26.02/2004, U.S. application No.10/860,163, filed on 06/02/06.

Technical Field

The present invention relates to a method and apparatus for manufacturing electronic components. More particularly, the present invention relates to providing electrical connections between opposing conductive layers with one or more insulating layers therebetween.

Background

Hard disk drives are common information storage devices that primarily include a series of rotating disks that are accessed by magnetic reading and writing elements. These data transducing elements (known as transducers) are typically carried by and embedded in a slider body which is positioned in opposed proximity to discrete data tracks on the disk for reading and writing. To properly position the transducer relative to the disk surface, an Air Bearing Surface (ABS) formed on the slider body is traversed by flowing air, providing sufficient lift to "fly" the slider body and transducer above the data tracks. The high speed rotation of the magnetic disk generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow combines with the ABS of the slider body, causing the slider body to fly above the rotating disk. In effect, the suspended slider body is physically separated from the disk surface by this self-controlled air bearing. The ABS of the slider body is generally formed on the slider body surface facing the rotating disk and has a large effect on the ability of the slider body to fly above the disk under various conditions.

The transducer is built on a substrate called a wafer, made of a conductive material such as AlTiC, using a process similar to that of semiconductor devices. The gold pads on the outer surface of the recording head are electrically connected to the recording device through internal electrical paths established during wafer level processing. The wafer is then cut into rectangular pieces, each having a separate recording head attached to a substrate called a slider. The slider is then mounted on a suspension. This assembly head is referred to as a head gimbal assembly, or HGA. The slider is then glued to the suspension with glue, which may be a conductive glue, to form an electrical connection between the substrate and the stainless steel component of the suspension. Some additional electrical connections are made between the gold pads on the recording head and the metal lines on the suspension by ultrasonic welding or soldering. The HGA is finally assembled into a hard disk drive with the suspension wires connected to other electrical components (typically a preamplifier) and the stainless steel components of the suspension connected to the drive ground.

HGAs are generally of two types-wired and wireless. In a tape head gimbal assembly (HSA), a flexible circuit of a HSA and a read/write head are connected by a single lead. In a wireless HGA, the conductive paths are integral to the flexure and provide conduction between the HSA flex circuit and the slider read/write head. There are generally two types of wireless suspensions in the art. In the first category (e.g., trace suspension assemblies TAS and circuit integrated suspension CIS), traces are built on stainless steel flexures by subtractive processes (e.g., etching operations) or additive processes (e.g., coating or deposition processes), with an insulating layer between the traces and the flexures. After the traces are in place, the flexures may be soldered to other components of the suspension. In the second category, such as Flexible Suspension Assemblies (FSAs) and Flexures On Suspensions (FOS), the traces are built on an insulating layer and then covered with another insulating layer to form a flex circuit. The circuit is then secured to the suspension by adhesive. An additional metal layer called the ground plane can also be attached to the flex circuit before it is glued to the suspension. In FSA, the flexures are integrated for communication with the load beam and the mounting plate along with integrated traces.

As shown in FIG. 1, an ABS structure such as a conventional catamaran slider 5 may be comprised of a pair of parallel rails 2 and 4 that extend along the outer edge of the slider surface facing the disk. Other ABS configurations have also been developed, including three or more additional rails, which vary in surface area and geometry. The two rails 2 and 4 generally extend along at least a portion of the slider body length from the leading edge 6 to the trailing edge 8. By leading edge 6 is meant the edge of the slider that the rotating disk passes before walking the length of the slider 5 towards the trailing edge 8. As shown, the leading edge 6 may be made to taper, but its machining process typically has undesirably large tolerances. As shown in fig. 1, the transducer, i.e., the magnetic element 7, is typically mounted at some location along the trailing edge 8 of the slider. The rails 2 and 4 form a pair of air bearings on which the slider flies and provides the necessary lift when in contact with the air flow generated by the rotating disk. As the disk rotates, the resulting wind, i.e., air flow, flows along and between the underside of the catamaran slider tracks 2 and 4. As the air flow passes under the tracks 2 and 4, the air pressure between the tracks and the disk increases, providing positive pressure and lift. Catamaran sliders generally generate sufficient lift, or positive load, force to suspend the slider at an appropriate height above the rotating disk. Without the rails 2 and 4, the large surface area of the slider body 5 would create an excessive air bearing surface area. In general, as the air bearing surface area increases, the lift generated also increases. The slider would fly too far from the rotating disk, provided there is no track, so that all the advantages of the above low flying height are lost.

As shown in FIG. 2, the HGA 40 often provides multiple degrees of freedom to the slider, such as longitudinal spacing, or pitch and roll angles, the latter of which is used to describe the flying height of the slider. As shown in FIG. 2, the suspension 74 holds the HGA 40 above a moving disk 76, the moving disk 76 having an edge 70 and moving in the direction of arrow 80. In operation of the disk drive shown in FIG. 2, actuator 72 moves the HGA along arc 75 over disk 76 by different diameters (i.e., Inner Diameter (ID), Middle Diameter (MD), and Outer Diameter (OD)).

In disk drives and other technologies, conductive material such as metal may be placed on both sides of the intermediate material. For example, a printed circuit board may be made of an insulating material having a metal layer on each side. As shown in fig. 3, a first metal layer 33 may be provided on one side of the insulating layer 31 and a second metal layer 35 may be provided on the other side. To conductively connect the first and second metal layers 33, 35, a via or hole may be formed through the insulating material and then plated (e.g., electroplated) with a conductive material. Conductive via 37 is a common method of joining two opposing metal layers together. One problem with establishing such a conductive connection is that it can be expensive to drill a hole in the insulating layer 31 (e.g., when a single laser is used to form the hole).

Another common method of establishing such a conductive connection is shown in fig. 4. Also, the insulating material 41 serves as an intermediate material between the first metal layer 43 and the second metal layer 45. In this method, a "blind via" is made through the first metal layer 43 and the insulating layer 41 and filled with a conductive epoxy 47. A cover coat 49 of an insulating material covers and protects the epoxy in the blind hole from contamination and oxidation. The conductive epoxy is made from a conductive metal (e.g., silver) powder suspended in a non-conductive medium. The conductive path of the epoxy is formed by means of a contact chain between the metal powders. Thus, the conductive epoxy 47 provides a relatively poor conductive connection between the metal layer 43 and the metal layer 45. In addition, the use of the covercoat 49 may increase the overhead of the process of establishing such a connection.

Accordingly, there is a need for improved methods and apparatus for making conductive connections between opposing metal layers.

Disclosure of Invention

One embodiment of the present invention provides an improved method and system. In one embodiment, a structure is provided that includes first and second metal layers separated by an intermediate insulating layer. A conductive ball (e.g., made of gold or gold-plated conductor, etc.) is inserted through two or all three of the openings in the layers and then pressed into the hole (if necessary) to establish a conductive connection between the metal layers. The conductive balls may also be made in the form of smaller particles or smaller balls. In this case, the conductor may melt within the blind hole to establish a metal connection.

Drawings

FIG. 1 is a perspective view of a suspended slider having a read and write element assembly with a conventional tapered catamaran air bearing slider structure.

FIG. 2 is a plan view of an air bearing slider mounted over a moving magnetic storage medium.

Fig. 3 is a cross-sectional view of a workpiece containing a conductive connection within the industry.

Figure 4 is another cross-sectional view of a workpiece containing a conductive connection within the industry.

Fig. 5a-b are cross-sectional views of a workpiece showing the conductive connection of two metal layers, according to one embodiment of the invention.

Fig. 6 is a flow chart of a method of establishing the conductive connection shown in fig. 5a-b according to one embodiment of the present invention.

Fig. 7a-b are cross-sectional views of a workpiece showing conductive connection of two metal layers according to another embodiment of the invention.

Fig. 8 is a flow chart of a method of establishing the conductive connection shown in fig. 7a-b in accordance with one embodiment of the present invention.

Figure 9 is a cross-sectional view of a slider suspension showing a ground pad and metal suspension in one embodiment of the invention.

Fig. 10a-b are plan views of a portion of a suspension having a metal path attached to the metal suspension in accordance with the present invention.

Detailed Description

Referring to fig. 5a-b, there is shown a cross-sectional view of an electrically conductive connection between two metal layers according to the invention. In this embodiment, a structure is provided that includes a first metal layer 51, a second metal layer 53, and an intermediate insulating layer 55. It is desirable to make electrical connection between the first and second metal layers 51, 53, so that holes or vias are opened through these layers. The vias may be made by any method known in the art, including using a laser, IC chip processing (e.g., wafer etching), etc. Conductive balls 57 made of gold or gold plating are embedded in the vias. The balls are then pressed into the vias, forming contact between the first and second metal layers 51, 53. In this embodiment, the workpiece comprising metal layers 51, 53 and insulating layer 55 is placed on chuck support 59 to facilitate expansion of ball 57 within the via. For example, chuck support 59 may provide a hollow outer region, thereby creating a space between the bottom of the workpiece and the top of support 59. This improves the spreading of the balls into contact with the second metal layer 53. For example, when gold or gold-plated balls are used, the electrical connection can be improved by ultrasonic welding.

Fig. 6 is a flow chart of a method of establishing an electrical connection. At block 61, a workpiece is provided having an insulating layer with first and second metal layers on opposite sides of the workpiece. At block 62, a via is formed through the two metal layers that are required to make an electrical connection. After the workpiece is placed on chuck support 59 (block 63), metal balls are provided in the via at block 64. At block 65, a metal ball is pressed into the via to form a connection between the two metal layers.

Referring to fig. 7a and b, a second embodiment of the invention is shown. In this embodiment, rather than placing vias in two metal layers, a "blind via" is formed through one metal layer and an insulating layer. As can be seen from fig. 7a and b, underneath the first metal layer 71 is a polyimide insulating layer 78. In this embodiment, the first metal layer is made of stainless steel. In this embodiment, the second metal layer 73 is made of gold-plated copper. Metal balls 77 are placed in the blind holes. As shown in fig. 7b, metal balls 77 are pressed into the blind holes, thereby establishing an electrically conductive connection between the first and second metal layers 71, 73. As in the example shown in fig. 5a and b, a seat fixture may be provided below the blind hole for performing the pressing operation. The conductive balls may also be in the form of smaller particles or balls. In this case the conductive material can melt to wet the blind hole shown in figure 7b to form an electrical connection.

A flow chart of the apparatus shown in fig. 7a-b is shown in fig. 8. At block 81, a workpiece is provided having an insulating layer with first and second metal layers on opposite sides of the workpiece. Blind vias are formed through the first metal layer and the insulating layer where connections are desired, block 82. After the workpiece is placed in the fixture mount 59 (block 83), metal balls are provided in the blind holes at block 84. At block 85, a metal ball is pressed into the blind hole, thereby establishing a connection between the two metal layers.

The above-described methods and apparatus may be used in a variety of technical fields. In one example, forming an electrical connection between two metal layers may be used to fabricate a Head Suspension Assembly (HSA) for a disk drive. Referring to fig. 9, this is a cross-sectional view of the assembly. In this embodiment, the slider 91 has a ground pad 92 in addition to pads for transferring read and write signals. Copper traces can be formed on the assembly in various ways known in the art, including lands 93 for connecting to ground pads 92 of slider 91, such as by solder ball bonding. In this embodiment, the suspension includes an insulating layer 94 and a stainless steel base 95. The copper wire may be formed as part of a Flexible Suspension Assembly (FSA) that includes an insulating layer and is connected to a stainless steel base 95. In this embodiment, the stainless steel base 95 is connected to ground. The copper wire can be connected with the suspension by adopting the method and the device.

Referring to fig. 10a-b, there is shown a portion of a suspension comprising a stainless steel base 101, an insulating layer 102 of polyimide on top of this base, and copper traces 103, the latter being connected to ground pads of a slider (not shown in fig. 10 a). As shown in fig. 10b, via 105 is made through a stainless steel base and an insulating layer made of polyimide (via 106). Since the vias 105, 106 pass through the stainless steel base and the insulating layer of polyimide, the conductive balls can be pressed into the vias as was done above for the blind via embodiment. In addition, the vias 107 may also be made by copper traces. In this case, the connection may be made by pressing a metal ball into the three passages 105 and 107 (preferably with a clip support below the passages). Once all connections are made, the slider's ground pad is effectively connected to ground through the suspension's stainless steel base and metal traces.

While the invention has been described with reference to the foregoing application examples, the description of the preferred embodiments does not imply that the invention is limited thereto. It is to be understood that the invention in all its forms is not limited to the specific details, construction and dimensions set forth herein, which are related to various methods and parameters. Various modifications in form and detail of the devices described above, as well as other aspects of the invention, will be apparent to persons skilled in the art upon reading this description. It is therefore contemplated that the following claims will embrace any such modifications or variations to the described embodiments as falling within the true spirit and scope of the present invention.

For example, while the embodiments of fig. 3-10 show gold or gold plated balls, other conductive materials may be used, including solder, copper, and silver. In addition, although the conductors used to form the electrical connection between the two metal layers in the embodiments of FIGS. 3-10 are spherical, other shapes are possible.

Claims (17)

1. A method of forming an electrically conductive connection between first and second electrically conductive layers separated by an insulating layer, comprising:

forming a via in the first layer;

forming a via in the insulating layer; and

conductive balls are disposed within the vias to establish a conductive connection between the first and second conductive layers.

2. The method of claim 1, wherein positioning the conductive balls comprises pressing the conductive balls into the vias.

3. The method of claim 1, wherein positioning the conductive balls comprises ultrasonically welding the conductive balls to the first and second conductive layers.

4. A method of forming an electrically conductive connection between first and second metal layers separated by an insulating layer, comprising:

forming a via in the first layer;

forming a via in the insulating layer; and

metal balls are disposed within the vias to establish an electrically conductive connection between the first and second conductive layers.

5. The method of claim 4, wherein positioning the metal ball comprises pressing the metal ball into the via.

6. The method of claim 4, wherein positioning the metal balls comprises ultrasonically welding the metal balls to the first and second conductive layers.

7. The method of claim 4, further comprising forming a via through the second metal layer prior to disposing the metal balls.

8. The method of claim 7, wherein the first and second metal layers and the insulating layer are part of a workpiece, the method comprising:

the workpiece is placed on the support fixture prior to the placing operation.

9. The method of claim 8, wherein the support fixture has a space between its surface and the passage of the workpiece.

10. The method of claim 9, further comprising:

the metal ball is pressed into the passage and against the support fixture.

11. The method of claim 10, wherein the metal balls are made of at least one of: gold, silver, copper.

12. A circuit, comprising:

a first conductive layer having a via;

a second conductive layer;

an insulating layer between the first and second conductive layers, the insulating layer having vias aligned with the vias of the first conductive layer;

conductive balls are disposed within the vias to form conductive connections between the first and second conductive layers.

13. The circuit of claim 12, wherein the second conductive layer includes a via aligned with the vias of the first conductive layer and the insulating layer.

14. The circuit of claim 13, wherein the conductive balls are made of one of the following materials: gold, silver, copper.

15. A head suspension assembly comprising:

a metal suspension;

a metal layer on the suspension;

an insulating layer between the metal layer and the metal suspension, wherein the metal layer and the insulating layer each have aligned vias;

conductive balls disposed within the vias conductively connect the metal suspension to the metal layer.

16. The head suspension assembly of claim 15 wherein the suspension has vias aligned with the vias of the metal layer and the insulating layer.

17. The head suspension assembly as recited in claim 15 wherein the conductive balls are made of one of gold, silver, and copper.