JPS5933895A - Method of forming electric circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates generally to methods of manufacturing electrical circuits having high density or closely spaced conductors or leads. The present invention relates particularly to high-yield batch manufacturing processes for forming high-density circuits and their interconnects, and it is entirely intended that the interconnects be readily adapted for use with conventional bonding methods. ing.

Electrical connection of one point to another in an electronic circuit is possible by many means and in a wide range of densities. These electrical interconnection methods in microelectronics technology include point-to-point wiring, traditional (and recently evolving) printed circuit boards, thick- and thin-film hybrid circuits, redundant and non-redundant elastomer conductors, and chips. There are mask alignment all-polarized patterns that are carried out in the state. The increasing complexity of integrated circuits and other electronic devices has created a need to interconnect conductor patterns at ever higher densities. In order to achieve this target km, it is necessary to make full use of all of the above-mentioned techniques or to do something more than that. When we try to achieve high resolution, that is, a thin line structure,
An attendant problem necessarily arises of providing a means to electrically interconnect the dense conductors with other system components, such as peripheral drive circuitry.

The problem of high-density electrical interconnection is particularly
This particularly occurs in the field of printing technology, collectively known as image bars. As used herein, "image bar" refers to a device that converts a data set into a "hard copy", ie, a corresponding set of symbols, typically on paper. Although paper is the ultimate receptor for the transformed data set, the printing process need not be straightforward. That is, there are many image/print bars in the form of intermediate receptors. This term is writing element (transducer)
It also includes all forms of printbars in which the play writes pixels (pixels) of a page-width line. When the media to be printed passes the normal bar, -a full page is written. The transducer is then selectively driven according to the direction of input data flow. For example, this data flow is carried out by a computer,
Word processor, mask input scanner, or reading J4!
It occurs from 2shivers etc. "Read bar" means a device capable of capturing a visible image and converting it into an electronic data set representing it. An example of a reading bar is a JCCD scanner array that electronically reads printed information. In a system sense, these devices are complementary to the image bar; however, from an interconnection standpoint they are described here. In particular, the technique of the invention also applies to read bars.

The recording process is carried out directly or indirectly using the image bar. Directly includes, for example, gas discharge electrography in which a charge is applied to a treated insulating receptor (e.g. paper), and indirectly includes, for example, by forming an image on an intermediate receptor and then developing this image. How to transfer onto paper.

Direct printing methods also include partial width or full width inksheet arrays. Indirect methods also include light emitting diode arrays, liquid crystal light valve arrays, thin film magnetic hand arrays, and 6m electroluminescence arrays.

The required transducer density will of course depend on the type of print (eg, special fonts, graphics, etc.) and the desired resolution. To achieve high resolution, it is common to all image bar technologies that the image elements be arranged in a row with a size spacing of 200-600 elements/inch (approximately 8-24 elements/1Trl). Medium 400 elements/inch (approximately 16
(or about 4,000 elements per 10 I/te (254 mm) bar).91 Assuming the same element size and spacing for simplification, the interconnection problem is reduced to 1.
．． This is equivalent to interconnecting a conductor pattern of 25 mils (0.00125 inches or approximately 60 .mu.m) with 1.25 mil (30 .mu.m) spacing. Of course, this analysis is based on the assumption that each transducer must be controlled by its own drive circuit or switch. Here, the switch supplies the appropriate current or voltage for printing. Interconnection requirements are less pressing when converters and drive circuits can be multiplexed. However, even in this case, the interconnection problem cannot be solved easily or economically using conventional methods. Historically, both one-to-one converter and drive circuit configurations as well as multiplex configurations have encountered the difficulty of connecting drive lines to their respective drive circuits without significant "fan-out."

Therefore, there is a need to reduce the severity of the problem of interconnecting closely spaced conductors.

Additionally, new manufacturing methods are needed to package and mechanically support high-density electrical circuit arrays and their associated interconnects. The complete manufacturing system, including drive circuitry and connections to auxiliary equipment, must have sufficient mechanical integrity for normal processing of the resist and subsequent steps in making image bars, for example.

SUMMARY OF THE INVENTION In accordance with the present invention, a method of forming high density conductive circuit patterns and electrical interconnections thereon is provided. In particular, a method is provided for forming high density conductors and their individual interconnects, where the interconnects are arranged in a two-dimensional (area) array to create bond points compatible with existing interconnect technology.

The first step is to form a thin layer of photosensitive material of uniform thickness on the smooth surface of a tetraelectric substrate. Then photosensitive material P
A pattern is formed by processing using the near-odlin graph method,
A selected portion of the smooth surface of the substrate is exposed. The exposed portions of the substrate are then electroplated to form the desired conductive circuit pattern.

This circuit pattern is then covered with a layer of insulating material.

A path is then formed through the layer of insulating material to expose the underlying conductive circuit pattern. , the paths are spaced apart from each other in a smooth, defined two-dimensional array, and the spacing between adjacent paths is greater than the spacing between adjacent conductors in the underlying circuitry. The multilayer board is then immersed in a plating bath and electroplated through the valley paths to cover the insulating layer to the desired thickness and form the raised mushroom interconnects to the conductive circuit. form. Finally, an additional layer of insulating material is added to the raised surface to provide mechanical support for the entire structure and maintain electrical isolation between interconnects. Although not required, the top of the raised interconnect may be removed to create a flat bonding pad. In this case, the height is 9
Preferably, the thickness, or height, of the interconnect is increased and a final layer of insulating material is added. Thereafter, both the interconnects and the overlying insulating layer are removed to create a substantially flat surface in which flat bonding is performed.

As an alternative to the previously described method, a two-step electroplating process is used to create the conductive circuit pattern. In this process, the first
conductive material to the same thickness as the patterned layer of photosensitive material. A second conductive material is then plated over the electroplated pattern of the first conductive material to create a circuit of desired ffi degree. The first conductive material is then etched selectively with respect to the second conductive material to separate the formed circuit from the conductive substrate.

Yet another method involves electroforming a conductive substrate through a patterned layer of photosensitive material.
Create a conductive circuit pattern. In a manner similar to that described above, the photosensitive material is overlaid by electroplating through the paths formed to form the interconnections of the raised portions. However, since this method employs electroforming, the formed circuit can be mechanically separated from the conductive substrate.

Embodiment FIG. 1 shows a preferred method of manufacturing a circuit according to the present invention. First, a suitable conductive substrate 10 is prepared. Although a wide range of materials can be used for the substrate 10, a brass plate has been found to be particularly suitable. This 2# conductive substrate 10 is used to ensure dimensional stability during post-processing! It will be clear to those skilled in the art that it must have a thickness of about 4. The upper surface 12 of the substrate 10 is polished to an ultra-smooth surface. [Ultra-smooth surface means that the upper surface 12 of the processed substrate 10 is approximately 2
Micro inch (2X 10-' inch - 5.08X1
0"-5ni) RM S finish. This definition means that the finish is on average 2 microinches (5-08X 10"mm) over the entire surface in question.
It can be understood as a technical term indicating that fluctuations in the amount of water are inevitable. A surface finish of approximately 2 microinches (5.08 x 10-5 mm) is preferred, but between 2 and 10 microinches (5.08
,08X 10-5mm~2-54X 10-'nv
It was found that surface finishes in the range n) were also light. Such surface finishing may be accomplished by any suitable means known in the art, such as diamond fly cutting. It should be noted that this surface finishing step is an important step in making the plating of the fine line conductive surface pattern described below uniformly reproducible.

A uniform thin film layer of photosensitive material is then applied to the treated optical surface 12 of the substrate 10. It is preferable that this thickness be as thin as possible under the condition that the thickness is just enough to ensure continuous coating without pinholes. The thickness of this layer is generally preferably in the range of 1 to 15 μm.

As used herein, the term "photosensitive material" means that the exposed areas are processed and the unexposed areas are not processed (
refers to a material capable of forming a continuous film that is sensitive to light or other radiation (or vice versa). Treatment generally involves treatment using a solvent that selectively dissolves. This type of material can be applied to any suitable material meeting the above definition, provided that it is applied in a thin film layer with a controlled uniform thickness to form a high-intensity WI pattern (such as a line or dot). Physiophyllinaceae is used in the process described here. Known photoresists are included within this range of materials and are the preferred photosensitive materials useful in the process described herein. Shiso play (
5hipley) AZ1350J is an example of a photoresist that has proven to be very well suited. Ordinary methods such as day-resolution coating, streak-ray coating, spin coating, etc. On the other hand, a uniform thin film layer of this type of resist is formed. Laminated photopolymer resists such as Rlston (Flj, ■, trademark of DuPont Nemaux & Co.) have been found to be particularly unsuitable. This is because a sufficiently thin film, that is, a large development aspect ratio cannot be obtained.

However, this does not negate the possibility that technological improvements will be made in the future to create a hard photoresist film with the resolution required in this paper. Of course, if something of this kind were developed, it would fall within the scope of the present invention.

A desired conductor (circuit) pattern is formed in the resist layer by photolithography using conventional techniques compatible with the resist used. Various techniques such as exposure, development, etc. are well known to those skilled in the art and will not be described in detail here. After this photolithography process, the structure shown in FIG. 1a is obtained.

For simplicity and clarity of explanation, the resist lines 14 forming the mask pattern are shown in a repeating pattern. This mask pattern selectively exposes a portion of the smooth surface 12 of the substrate 10, and that portion is later plated to form a desired conductive circuit pattern. The process of the present invention is particularly suited for forming closely spaced leads and their interconnects so that the exposed pattern can be an array of fine wire conductors. In other applications, the exposure pattern could be of various shapes, such as buspars or individual recording styli (for electrography).

The patterned structure of Figure 1a is then placed in a plating bath. The liquid is selected to be suitable for the conductive material for electroplating the substrate 10. Since nickel is preferred as the conductive material, a suitable nickel bath is used, such as bright nickel sulfate or other bright nickel plating bath.

The plating process is controlled such that nickel plating is deposited over the brass substrate 10 and the resist 114 to form a conductor or busper 18 having a mushroom-shaped cross section as shown in FIG. 1b. Another particularly preferred example of this conductor plating process is shown in FIG. In this example, two types of conductive materials are used to form the plated buspar. In FIG. 6, the resist line 64 and the substrate 60 are connected to the element 1 of FIG.
Corresponds to 4 and 10. The masked substrate is plated with a first conductive material "line" 62 to the same thickness as the resist layer originally patterned. That is, the height of the line 62 is made the same as the upper surface of the resist line 64.

This plating is of course carried out in a suitable plating bath for the first conductive material. The partially plated assembly is then immersed in a new bath to plate the first conductive material with a second conductive material to create larger busbars 66 (busbars 66 are larger than the originally plated conductor wires 62). ).

Preferably, copper is selected as the first electrically conductive material (ie, conductor wire 62) and nickel is selected as the second electrically conductive material (ie, buspar 66). This two-step plating process is preferred by selectively etching the copper wire 62 with respect to the nickel busbar 66 when the entire process is complete, thereby creating a smooth "flat bottom" along the busbar 66.
This is because a flexible circuit can be obtained.

After forming the array of plated busbars 18, the assembly is coated with a layer of insulating material 11.

Layer 11 is 0.0005 to 0.002 inches (0.012
7~D. Preferably, a thick resist film is applied with a thickness in the range of 0.0508 mm). However, any patternable polymer may be used as layer 11. As shown in FIG. 1c, the insulating layer 11 is patterned (e.g. by photolithography when layer 11 consists of resist);
The path 13 to the bus spar 18 is formed by processing. An important aspect of the invention is that the pattern of paths 13 is selected to effectively spread the interconnection points of bussers 18 into two-dimensional space. This is shown in more detail in FIG. Second
In the figure, adjacent pass bars 18a and 18b are provided with Tayu paths 13a and 13b alternately spaced apart from each other. With such an arrangement, the dense one-dimensional interconnection problem becomes
It will be appreciated that the solution is a low density, easily achievable two-dimensional array. A wide range of patterns can be employed for the paths and next step contact bumps (described in detail below).

The choice of structure will be determined by many factors, including the spacing and number of buspars, the means and method of interconnection from the contact bumps to auxiliary devices, etc.

5 In the example shown in FIG. 4, the paths (contact bumps) are a filled two-dimensional array. This figure is simplified for illustrative purposes. Referring to FIG. 2, the end view of this filled lay interconnect structure is precisely shown. In FIG. 4, the adjacent passper 41a.

41b+41Cj411 are alternate interconnection parts 4
It has 2a142b1420j42cl. This staggered pattern is folded back to provide the necessary interconnections for the remaining buspars as shown in FIG. 4, forming a two-dimensional "fill" pattern. The interconnect bumps 42a 942b e 420t are suitable for backflow soldering or conventional interconnection techniques such as elastomer connections.
Of course, dimensions and intervals such as 42d are taken.

FIG. 5 shows yet another structure. In this figure, the paths and interconnects are shown in a circumferential array. As with the filled array structure of FIG. 4, the spacing between adjacent passpers (interconnects) is increased to facilitate interconnection with contact pads 56 on balance 54 using conventional wire bonds 58. The pattern of the periphery or bumps 50 is created to have the following effect. Many other patterns and interconnection techniques may be used in addition to the examples of FIGS. 4 and 5.

After the paths are formed, the assembly ffi is again immersed in a suitable bath and plated to form interconnections to the buspar 18. In this process, each path 1 is
3 to form a raised bump interconnect 15 over the insulating layer 11. The bump interconnections 15 made in this way are large (buspar 1
8), it has a round, mushroom-shaped shape, and exhibits a symmetrical shape, as clearly shown in Figure 2.

After that, an encapsulant layer 17 of insulating material is added,
While electrically insulating between the raised interconnection parts 15,
Mechanically integrated structure. Preferably, the insulating material layer 17
consists of a polymeric material such as liquid epoxy. This epoxy can be coated thickly (10 mils - 0.254 mm or more) and cured. The epoxy layer 17 can also be coated to a thickness such that the entire upper portion of the interconnect 15 is exposed (as opposed to a complete encapsulation as shown in FIG. 1e). These exposed contact bump portions would then provide contacts for connection to the attached electronics. However, it is particularly advantageous to completely coat the contact bumps 15, as shown in FIG. 1e. This step is followed by removing a portion of the capsular polymer layer 17 and a portion of the interconnect 15, for example by polishing or plasma etching, to create a flat bonding pad that is aligned with a substantially flat surface. . This is shown in Figure 1f, which shows a flat bonding pad with a four-conductor material.
Additional (and optional) steps for adding gold flashing, 19, for example, are also shown.

As a final step, the completed circuit is separated from the substrate 10. In the preferred embodiment, this is accomplished by selectively etching the copper conductor lines 62 with respect to the nickel busbars 66 in a suitable solvent, as described in FIG.

The above objective was to provide a complete set of high density electronic circuits and associated Q interconnects. According to this aspect of the invention, approximately 400 lines/inch (15,7 lines/m
It is particularly desirable to make thin wire conductors with a dimensional spacing of 1 m ). This density is possible with the process described herein and would result in the individual busbars 18 of FIG. 1 being spaced 2.5 mils (63.5 μm) center to center. Then mushroom-shaped interconnect 157il - center to center 60 mil C0,76
2rr1m) with a diameter of approximately 15 mils (0,3
81 mm) (approximately 10 mil-0, resulting in a flat bonding pad with a diameter of 254 nm). These achievable bonding pad spacings are compatible with conventional interconnect technology, allowing for easy connection with auxiliary electronic devices.

Another manufacturing process is shown in FIG. As briefly mentioned earlier, this process uses electroforming (as opposed to electroplating) to create dense circuit patterns on conductive substrates. Those familiar with photographic production, and particularly plating processes, will understand that conductive patterns created by electroforming can be peeled off (i.e., mechanically separated) from the temporary conductive support with relative ease. It will be. The method shown in FIG. 7 is clearly distinguished from the process of FIG. 1 and the variant of FIG. 6 in this respect. In FIGS. 1 and 6, a chemical separation or etching step is required to separate the completed circuit from the support.

FIG. 7 shows several steps in making a circuit according to different steps. On a conductive substrate 70 or mandrel is an array of conductive busbars 72 or styli coated with an insulating shaped coating 74, such as hardened epoxy. In order to form this wrapped thin line circuit pattern, first, a conductive substrate 70 is prepared for electroforming.

As with the above steps, it is an essential requirement of the present invention to first prepare a substrate. Also, as in the process mentioned above, 1
．． In this case as well, it is necessary to finish the substrate 70 with an ultra-smooth surface.
Also, the bus bar 18) shown in FIG. 1 can be formed not in a twilled shape but in a thin layered shape.

The thin layer growth creates a uniform buspar that provides the basis for the precise formation of raised bump interconnects in the next step. The conductive substrate 70 should be chosen with care. The range of choices includes conventional electroformed or plated mandrels such as brass, copper, chrome on glass or stainless steel. Clean the brass or copper and use an etching solution to remove the mandrel from the stylus array. On the other hand, with either chrome on glass or stainless steel, the array can be mechanically stripped from the mandrel. Since mechanical peeling is preferred, the latter type of mandrel is preferred here. A mechanically removable mandrel generally requires approximately 2 to 10 microinches of conductive material (metal).
) It is possible to polish the finished surface of EMS.

First, a suitable photosensitive material PI such as a resist is added to such a substrate TO. Then prepare suitable artwork for patterning the desired stylus array.
Used to peel off the resist layer.

Develop and process using traditional methods to transfer the artwork pattern to Resist. Stylus array 72 is then electroformed onto substrate 70 using a patterned resist mask. The remaining resist is removed again using conventional techniques, leaving the stylus 72 on the mandrel. The entire array of lights is then shaped coated with an insulating material consisting of 1 or liquid epoxy. The epoxy is fully cured to form a shaped coating 14. As mentioned above, relatively thick <(10 mils)
0,254 mm or more) When coated with epoxy,
It provides mechanical support for the conductor array and maintains the degree of mechanical bonding required during normal handling of the resist and subsequent material addition and curing. Dimensional changes are controlled by the choice of epoxy, catalyst, and curing cycle. Additionally, because curing the epoxy is a non-bulky, condensing chemical reaction, the wrinkle and bleaching problems associated with known techniques using thick solvent cast polymer films are avoided.

This known method suffers from the disadvantage that, especially when using solvent-cast polymer films, large amounts of hygroscopic solvent often have to be removed.

The coated stylus array is then separated from the mandrel or substrate 70. The mandrel side of the play (ie, the side of the coated array that was previously adjacent to the smooth surface of substrate 70) is coated with a layer of a suitable photosensitive material as shown in Figure 7b. The layer is, for example, a resist having a thickness of about 0.5 to 2 mils (12.7 to 50.8 .mu.m), preferably less than 1 mil (25.4 .mu.m). Using suitable artwork, a stylus can be selectively passed through the resist layer 76 by patterning a set of aligned paths 78'fc as shown in the top view of FIG. 4 or FIG. Perform etching up to 72.

Next, dip the assembly in a suitable solvent and remove the stylus 72.
is selectively electroplated to create large mushroom lands or raised bump interconnects 71. Preferably, stylus 74 and interconnect 71 are both formed of nickel. It will be appreciated that this plating process requires making electrical contacts to each individual stylus/busper. This contact is a common busper (not shown)
Or it can be constructed, for example, by a group of busbars conveniently in contact with the individual styli at the ends of the circuit pattern.

A layer 73 of insulating material is then added to the bump interconnect 71 of FIG. 7d. Preferably, this layer is a shaped epoxy coating that matches the coefficient of thermal expansion of layer 74. For example layer 7
The same liquid epoxy used in step 4 may be added and cured. Preferably, the shaping coating 73 is thicker than the bump interconnect 71, as shown in FIG. 7e. This complete coverage as in the process of FIG. 1 is not necessarily necessary; for example, the thickness may be such that the top of the interconnect 71 is exposed. When using the preferred full-cover process, the top of interconnect 71 is then exposed by partially removing both interconnect 71 and shaping coating 73. This can be done using polishing, plasma etching, ion etching, or any other suitable means. The result is a substantially flat surface having an array of flat bonding pads with a cross-sectional structure as shown in Figure 7f. Please feel free to ask for goldflash.
g) may be applied to the bonding pad 75.

At this stage, the circuit is complete and ready to be interconnected with auxiliary electronics and incorporated into, for example, an image bar. Buspar 72 (and first
Because the density of the bussers 18 in the figure has been changed (ie, the effective lead spacing has been expanded in a two-dimensional plane), conventional techniques such as wire bonding can be used. Alternatively, conventional back flow solder or elastomer could be used to connect to the aligned contact array on the back of the secondary mold carrier.

For clarity, the method of the present invention has been described for a simple conductor/busbar array.

Although the invention has been described in terms of an array thereof and a particular method of making the same, many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the present invention includes all such alternatives, modifications, and variations within the spirit and scope of the present invention.

[Brief explanation of the drawing]

Figures 1a to 1f show the entire valley process of the manufacturing method according to the invention. FIG. 2 is a fragmentary equidistant drawing of the structure formed by the method of FIG. 1. Figure 6 is the first
It is an enlarged view of a part of the figure. FIG. 4 is a schematic illustration of a filled lay structure with bump interconnects arranged to receive, for example, a land grid array package. FIG. 5 schematically illustrates the arrangement of bump interconnects in a peripheral array structure and wire bonding to tips. FIG. 6 shows a method different from that of FIG. 1, in which two electroplating steps are used to form the conductive pattern. Figures 7a to 7f show yet another method in which electroforming is entirely employed to form the conductor pattern. 10.60,70... Board 13,78... Route 1
8.66.72... Bus bar 15.71... Bump interconnection agent Akira Asamura 7 F/G, 6 FIG 4 b 5 2 FIG, 7a FIG, 7b F/G7c FIG 7d F/G7e FIG? f

Claims (1)

[Claims] (1) Forming a uniform thick film of photosensitive material on the smooth surface of a conductive substrate; b) Processing the photosensitive material using a photolithographic method to selectively form a photosensitive material on the smooth surface of the substrate; The process of exposing the part. (1) electrically peeling a four-conductor circuit pattern on the exposed portion of the smooth surface; (2) covering the conductive circuit pattern with an insulating material layer; and (e) forming a path through the insulating material layer. forming and selectively exposing said conductive circuit pattern; forming a bump interconnect with a predetermined thickness and adding a layer of insulating material of a predetermined thickness to
A method for forming an electric circuit, including a step of electrically insulating between parts. +217) forming a uniform thick film of photosensitive material on the smooth surface of a conductive substrate, and a) processing the photosensitive material by photolithography to form selective portions of the smooth surface of the substrate. (b) Electroforming a conductive circuit pattern on the exposed portion of the smooth surface; (d) Coating the conductive circuit pattern with an insulating material; and (e) (a) applying a layer of photosensitive material of a predetermined thickness to the surface of said (b) said path previously adjacent to said substrate; and g) said forming a path through a layer of photosensitive material to selectively expose the conductive circuit pattern; a) electroplating through the valley path to coat the photosensitive material to a selected thickness; creating raised bump interconnects to the four-conductor circuit; f) applying a layer of insulating material to a predetermined thickness to provide electrical isolation between the interconnects; A method of forming an electrical circuit.