Process for the Manufacture of Substrates to Interconnect Electronic Components and Articles Made by Said Process

The present invention will be more fully described and will be better understood from the following further description of preferred embodiments of the invention taken with the appended drawings in which:

FIG. 1 is a top plan view of an interconnection substrate of the present invention;

FIG. 2 is an exploded view, in perspective of a chip carrier, chip, and cover, to which the invention is particularly adapted:

FIG. 3 is a perspective view of the chip carrier of FIG. 2 when viewed from the bottom;

FIG. 4 is a sectional view through a section of an interconnection substrate showing the preinsulated conductor before high energy ablation of the coating and insulation;

FIG. 5 is a top plan view of the section of FIG. 4;

FIG. 6 is a sectional view similar to FIG. 4 but showing the exposed conductor after formation of the interfacing cavity;

FIG. 7 is a top plan view of the section of FIG. 6;

FIG. 8 is a sectional view similar to FIGS. 4 and 6 but showing the conductor and conductor pad after plating;

FIG. 9 is a top plan view of the section of FIG. 8;

FIG. 10 is a schematic plan view of an apparatus for carrying out part of the process and for producing the cavities of the instant invention;

FIG. 11 is a side view, in elevation, of the schematic apparatus of FIG. 10;

FIG. 12 is a sectional view of the interconnection substrate of the instant invention showing the interconnection between the conductor or wire, a chip carrier and chip;

FIG. 13 is a sectional view of the interconnection substrate of one embodiment of the instant invention showing the circuit with a metal base and surface conductor;

FIG. 14 is a view similar to FIG. 13 but showing interconnection between the conductor or wire and a chip and without the chip carrier.

FIG. 15 is a view similar to FIG. 14 but showing the embodiment in which the circuit, when completed, is to be removed from the metal base;

FIG. 16 is a view similar to FIG. 15 but showing the exposed conductor after formation of the cavity; and

FIG. 17 is a view similar to FIGS. 15 and 16 but showing the conductor and conductor pad after plating, with the processing metal base removed and the circuit bonded to a permanent base.

Referring to the drawings, particularly FIG. 1, the circuit generally designated 2, includes the interconnection substrate 4 having mounted thereon chip carrier, chip and cover assemblies 12. Chip carriers 12 are connected to surface pads and may be connected to power and ground bus bars 14, 16 formed on the surface of substrate 4.

Chip carriers 12 vary in size, depending upon the complexity and size of the chip carried therein. As best shown in FIG. 2, chip carrier 12 is made up of a body 6, having a recessed center top portion 20 and a flat bottom portion 22, FIG. 3. For purposes more apparent later herein, recessed center top portion 20 has a plurality of contacts 24 spaced therearound. Bottom 22 and the sides of body 6 are provided with a plurality of contacts 26 spaced around the carrier sides and extending onto bottom surface 22, FIG. 3. Chip 10, FIG. 2, has a plurality of contacts 30 extending around the top edge of the chip.

Chip 10 is assembled in recess 20 of body 6 with contact 30 of chip 10 connected to contacts 24 in recess 20 of body 6. With chip 10 in recess 20 and contacts 30 and 24 connected, cover 32, FIG. 2, is placed over recess 20, covering the recess and the chip 10 therein. As will be later described, contacts 26 of body 6 to be connected to the circuit 2 are mounted on and soldered to contact pads on the substrate after the circuit is fabricated and the desired contact pads are formed thereon. As will also be described later herein, contacts 30 in chip 10 may be connected, by soldering, wire bonding or other appropriate means, directly to the contact pads on the substrate, once such contact pads are formed, and carrier body 6 with cover 32 are not used.

Referring next to FIGS. 4-9, in this illustrated embodiment, base 42, which may be plastic, glass fiber reinforced plastic, ceramic or coated metal is coated with an adhesive 44 activatable by ultrasonic energy. Metal wire 46 coated with an insulating coating 48 is scribed onto and embedded in adhesive 44 in accordance with the teachings and disclosures of the aforementioned '602 and '914 patents and the '082 application the disclosures of which, as already noted, are incorporated herein by reference. The substrate, with the wire scribed thereon in the preprogrammed pattern, may be heated and baked to further cure the adhesive in which the scribed wire is embedded and to remove and drive off volatiles from the adhesive. A liquid material 50 is then cast over the scribed wires. The exposed surface of the liquid 50 is brought into contact with the surface of a film, such as a polyester, which will not adhere to the coating, the coating is cured or hardened at a temperature below 100.degree. C. and the non-adherent film is removed. Such a procedure is disclosed and described in the aforementioned ' 380 U.S. patent, the disclosure of which is incorporated herein by reference. The exposed surface of the liquid 50 might also be spread and leveled with a knife, doctor blade or roller or might be flowed, ponded or puddled onto the wire scribed board before the material 50 is cured or hardened. In any event, a smooth, flat, planar surface is thus provided on the substrate. The dried and cured coating forms layer 50 over the wire scribed board. A thin adhesive coating 52, such as epoxy rubber, may be applied over layer 50 and dried or cured so as to form a coating over the board for adhering the metal subsequently applied by printing, plating or the like.

Referring next to FIGS. 10 and 11, the wire scribed and adhesive coated substrate of FIG. 4 is mounted on and registered with table 60 of `X`- `Y` table machine, generally designated 62, numerically controlled, such as with a floppy disc computer controller 64, and preprogrammed to move table 60 and the substrate attached thereto through a preset sequence. A high energy source, such as laser 70, capable of being focused and applied as a vertical beam to the substrate on the table is projected through tube 72 and is applied vertically such as through a mirror and mirror head 74. An Everlase 150 Watt CO.sub.2 laser manufactured by Coherent Inc., has been found to be particularly adaptable as a high energy laser source of use in the instant invention. Computer drive 64 not only controls the movement and stopping of `X`- `Y` table 62 but also controls the pulsing of laser 70. Thus, as table 60 and the scribed substrate mounted thereon is moved from point-to-point and then stopped by control 64, at each stop laser 70 is pulsed.

As best shown in FIGS. 6 and 7, with the wire scribed and rubber epoxy coated substrate of FIG. 4 mounted on table 60, table 60 and computer drive 64 are preprogrammed so as to align conductor 46 with the beam from mirror head 74. When the conductor 46 is so aligned, table 60 and the substrate mounted thereon is stopped and the high energy source is pulsed. The high energy source, in the described embodiment a laser, may be pulsed once during each stop or a series of pulses might be applied. The power of the energy source is adjusted so as to apply the energy to the substrate at the desired absorption level. In any event, the rubber epoxy coating and the coating over the conductor are heated, vaporized and flashed off. Insulation 48 is exposed to the beam and with the coating is vaporized and flashed off. The metal in the conductor or wire 46, which in the preferred embodiment is copper, reflects the energy beam and remains intact. Thus, as best shown in FIGS. 6 and 7, a substantially cylindrical cavity is formed from the surface into the substrate leaving the conductor or wire in the opening partially bare and exposed.

After the preprogrammed pattern of cavities or openings in the board surface has been completed, the walls of the cavities, rubber epoxy coated surface and exposed wire are cleaned and metal plated. This may be accomplished by electroless plating or with a combination of electroless and electroplating, the cavity and outer epoxy rubber surface being first sensitized with a catalyst applid after high energy formation of the cavity or incorporated during initial casting and coating application. The catalyst sensitized surface is first electrolessly plated to form a thin coating of metal on the surface along the cavity walls and around the exposed wire and then the electroless metal deposition might be built up in thickness by electroplating or further electroless plating.

After the substrate and cavities have been plated, conductor pads, and ground and power planes or conductors might be formed on the surface by masking and etching in any of the manners conventionally followed in preparing circuit board surfaces. These planes may also be formed prior to wire-scribing such that they are on the interior of the carrier board. Thus, as best shown in FIGS. 8 and 9, the walls of the conductor cavities are coated at 80 with metal, such as copper, and conductor pads 82 and planes 84, FIG. 13, are formed on the board surface. As best shown in FIG. 12, chip carrier 12 is electrically connected at carrier contact 26 by solder joint with conductor pad 82. As best shown in FIG. 12, chip 10 might be mounted and cemented by cement 79 and directly connected to conductor pad 82 by solder joint 81, wire bonding or other appropriate means to chip conductor 30 in which case carrier 12 would not be used.

The embodiment of the invention illustrated in FIGS. 15, 16, and 17, is similar to the embodiment already described and is formed in substantially the same manner. Where the two embodiments differ is that, while the embodiment already described produces a substrate with an integral base used for stability during processing and as a part of the final product, the embodiment of FIGS. 15, 16, and 17 utilizes a base for processing only. Thus, metal base 42 is copper plated with plating 100. Adhesive 44' is adhered to copper plating 100, wires 48' are applied or scribed and coatings 50', 52' are applied in the manner as in the aforedescribed embodiment.

When the cavities are subsequently filled with metal, as best shown in FIG. 17, metal to metal contact is not only provided between the hole filling metal 80' and exposed wire 48' but may also be provided with copper plating 100. Thus, when metal base 42, is removed, as shown in FIG. 17, the exposed surface of plating 100 may be masked and etched to form isolated conductor pads and power or ground distribution busses. The circuit is mounted on base 102, FIG. 17, which may be of metal or any other support material coated with an adhesive 104 which, in the case of a metal base, should also be dielectric.

In the preferred embodiments of the invention, the dielectric base is mounted on and affixed to a rigid stable base while the wire is scribed, the liquid coating is applied, leveled, flattened and cured in accordance with the teachings of the '380 U.S. patent, the cavities in the circuit to expose the wires or conductors are formed by high energy beams and the holes are electrolessly plated or electroplated. In the instance of the embodiment of FIGS. 4-9, the base is permanently affixed and remains a part of the finished circuit. In the embodiment of FIGS. 15-17, the metal base upon which the circuit is mounted and affixed for processing is removed, the processed circuit, with the high energy formed cavities filled with electroless or electroplated metal is bonded to a base, which may be a dielectrically coated metal base or base of dielectric material or some other dielectrically coated material. A plurality of processed circuits, each affixed to and mounted on a metal base for processing and subsequently removed therefrom, might be laminated and connected, one on the other, and before or after laminating might be mounted and affixed to a dielectric base or a dielectric coated base.

In the preferred embodiments of the invention, the conductor or wire extends through the high-energy-formed cavity at the time of plating. This provides better electrical contact and mechanical strength between the conductor and cavity plating metal than could be provided when attempting to drill through a 2 to 4 mil diameter wire with a 6-12 mil diameter drill.

In the practice of the instant invention, encapsulating coating 50, 50' may be cast, in situ, over the wire scribed circuit. Voids between the coating and the wire scribed circuit surface may be removed with a doctor blade or roller applied to the exposed surface of coating 50, 50'. Rather than casting coating 50, 50' in situ, the coating material may be a low temperature thermosetting or ultra-violet curing material, such as an epoxy, a polyamide or an acrylic, and may be cast on the surface between the surface and a pre-formed sheet and applied over the wire scribed circuit with a doctor blade, roller or platen to level the coating between the sheet and wire scribed circuit. In any event, encapsulating coating 50, 50' forms a planar surface over the irregular wire scribed circuit and is cured or hardened before cavities are formed in the circuit. Coating 50, 50' should be of a material or contain an additive so that the coating can be cured or hardened at low temperature or by low temperature radiation, such as ultraviolet radiation. A coating process such as disclosed and described in the aforementioned '380 U.S. patent, is satisfactory. Additional planar coatings may, of course, be added to the circuit or the desired characteristics of these coatings, such as adhesion may be incorporated in encapsulating coating 50, 50'.

Circuits produced in accordance with the instant invention, particularly the embodiment of FIGS. 15-17, may be laminated, one over the other. In carrying out such lamination, dielectric coating or adhesives should be used between the circuits to maintain circuit integrity.

In the practice of the instant invention cavity forming with a high energy beam, such as a laser, has been found to be particularly useful. However, as already noted, other means, such as a drill bit, abrasive, chemical or high speed jet might also be employed. Other high energy beams absorbable by the material being drilled, but not the condcutor or wire, and capable of volatilizing the material and insulation on the conductor or wire, may be employed.

The following examples serve to illustrate certain preferred embodiments of the present invention. The purpose is not, in any way, to limit the scope of the present invention.

A 0.018-inch thick metal alloy sheet core of 64% iron and 36% nickel was clad on both of its planar surfaces with copper metal sheets having a thickness of 0.006 inch. The copper surfaces were treated with black oxide solution to promote adhesion. The substrate base was laminated on each side with copper foil 0.0014 inches in thickness and a semi-cured fiberglass-reinforced epoxy resin sheet. The lamination took place at a pressure of 375 psi and 350.degree. F. for a period of 25 minutes. The substrate base was then baked at a temperature of 350.degree. F. for 1 hour in order to effect full curing of the epoxy resin.

The substrate base was then brushed in order to clean the surface. Circuit patterns were formed on one side of the substrate base by exposing a dry film photoresist to an ultraviolet light source and developing the pattern. The other side of the substrate base was encapsulated by photoresist material.

The substrate base was then exposed to a ferric chloride-water solution to remove exposed copper metal from the surface of the substrate base. The remaining photoresist was removed from the surface and the substrate base treated with black oxide solution to promote adhesion.

The patterned surface was then coated with an encapsulating resin according to the following procedure:

A pair of rigid rollers, mounted parallel to each other, were adjusted to provide a controlled encapsulation thickness. A filled, thermosetting epoxy resin which cures at room temperature was thoroughly mixed with an amount of curing agent sufficient to ensure complete polymerization of the system. This mixture was placed into a bell jar and the bell jar evacuated with a vacuum pump. The mixture was uniformly applied to the patterned surface of the substrate base. The substrate base was then placed in a vacuum chamber to remove any air in the mixture. After removal from the vacuum chamber, one edge of the substrate base was placed into the preset gap between the rigid rollers. One edge of a 0.004-inch thick release-treated polyester carrier sheet on which was coated a 0.0027-inch thick sheet of wiring adhesive was placed in contact with and parallel to the gap edge of the substrate base. The substrate base, carrier sheet and adhesive were then drawn through the gap in order to bond the adhesive to the resin surface such that the surface of the adhesive was substantially flat.

The encapsulating resin was allowed to cure at room temperature for a period of 8 hours. The substrate base was then baked for period of 30 minutes at a temperature of 150.degree. F. After baking, the substrate base was placed onto a computer-controlled X-, Y- positioning table with the adhesive-coated surface exposed. An energized wiring head assembly was brought into close proximity with the adhesive surface and an insulated copper wire 0.0025 inch in diameter was placed between the head assembly and the adhesive surface. The table was moved to predetermined locations and the head assembly was directed to dispense the insulated wire and to bond it to the adhesive surface and thereby form a precise wire-scribed circuit pattern. The substrate base was then baked for a period of 90 minutes at a termperature of 200.degree. F.

The wire scribed circuit pattern was then coated with an encapsulating resin coating and adhesive sheet to stabilize the position of the scribed wirer and to form a flat, planar surface in accordance with the procedure described above. The adhesive sheet in this procedure was specifically-adapted for processing in semi-additive plating techniques. This adhesive sheet was 0.0012 inch thick. After being drawn through the rollers, the substrate base was allowed to cure at room temperature for 8 hours and then baked at 150.degree. F. for 90 minutes.

The substrate base was then placed onto an X-, Y- positioning table with the adhesive surface exposed and the beam of a carbon dioxide laser was directed at the adhesive surface at predetermined locations. The laser beam vaporized and removed the materials surrounding the copper wire, and formed cavities which were between 0.010 and 0.012 inch in diameter.

The substrate base was then placed in an oven and baked for 30 minutes at a temperature of 250.degree. F. The temperature of the oven was then increased to 350.degree. F. and the substrate base was baked for an additional 90 minutes. The substrate base was cleaned by an ultrasonically-agitated cleaning solution and rinsed in order to remove any dirt or debris from the laser-generated cavities. The substrate base and cavities were further cleaned by immersion for forty minutes in a solution of potassium permanganate in water which was maintained at a pH of about 13.5. After this immersion, the substrate base was immersed for 3 minutes in a permanganate neutralization solution of stannous chloride and hydrochloric acid in water. This solution was maintained at room temperature. Immediately thereafter, the substrate base was immersed in a second neutralization solution having a reduced stannous chloride concentration for three minutes. The substrate base was rinsed in running water for 6 minutes.

A palladium/tin catalyst was applied to the substrate base to activate it. It was then immersed in an electroless copper plating solution of the type commonly used for the manufacture of printed circuits until a very thin layer of copper metal had been deposited on its surface. It was removed from the electroless copper plating solution and rinsed in running water for 60 seconds. The substrate base was then electroplated to increase the thickness of its surface copper deposit.

The substrate base was then brushed and coated with a dry film photoresist which was exposed and developed as described above to form a circuit pattern on the substrate base. It was then again electroplated in order to increase the thickness of the copper deposit in those areas which had been exposed by patterning the photoresist. The substrate base was rinsed in running water and immersed in a commercially available tin/lead electroplating solution. In order to deposit tin/lead on all exposed copper surfaces.

The photoresist was removed from the surfaces of the substrate base and then exposed to a copper etching solution which did not dissolve or remove the tin/lead plating, preserving the desired circuit pattern while all undesired copper metal was dissolved and removed.

The substrate base was rinsed in running water and then baked for 30 minutes at 150.degree. F. The temperature was increased to 350.degree. F. and the substrate base baked for an additional 120 minutes. The substrate base was then subjected to conventional fabrication operations such as cutting to size, and drilling mounting holes to produce a finished wire-scribed circuit board.

A 0.018-inch thick metal alloy sheet core of 64% iron and 36% nickel was clad on both of its planar surfaces with copper metal sheets having a thickness of 0.006 inch. The copper surfaces were treated with black oxide solution to promote adhesion. The substrate base was laminated on each side with copper foil 0.0014 inche in thickness and a semi-cured fiberglass-reinforced epoxy resin sheet. The lamination took place at a pressure of 375 psi and 350.degree. F. for a period of 25 minutes. The substrate base was then baked at a temperature of 350.degree. F. for 1 hour in order to effect full curing of the epoxy resin.

The substrate base was then brushed in order to clean the surface. Circuit patterns were formed on one side of the substrate base by exposing a dry film photoresist to an ultraviolet light source and developing the pattern. The other side of the substrate base was encapsulated by photoresist material.

The substrate base was then exposed to a ferric chloride-water solution to remove exposed copper metal from the surface of the substrate base. The remaining photoresist was removed from the surface and the substrate base treated with black oxide solution to promote adhesion.

After patterning, thin,single-sided copper-clad laminated sheets were applied to each side of the substrate base laminating semi-cured fiberglass reinforced epoxy sheets as the bonding medium as in Example 1. The substrate base was then baked in order to cure the epoxy resin fully.

Circuit patterns were formed on the substrate base as described above in Example 1, except they were in the form of circular areas which were between 0.008 and 0.010 inch in diameter. The copper metal was dissolved and removed from the circular areas, and the photoresist was removed as in Example 1.

The substrate base was then placed onto a computer-controlled X-, Y- positioning table with the circular areas exposed. The table was moved to predetermined locations in order to vaporize and remove the cured epoxy resin layer between the two copper layers in the circular areas using a carbon dioxide laser as in Example 1.

The substrate base was then cleaned and rinsed as described in Example 1. The substrate base was then activated using a palladium/tin catalyst. It was immersed in an acidic copper sulfate plating solution and electroplated to deposit copper metal in the cavities. After this plating operation, the substrate base was removed from the solution, rinsed in running water for 2 minutes and dried.

The substrate base was then encapsulated, wired and processed in accordance with Example 1.

The procedures of Example 1 were followed except that the metal alloy sheet used as the core was composed of 58% iron and 42% nickel, and it was not clad with copper metal sheets. Mechanical roughening techniques were employed in order to promote adhesion.

The procedures of Example 2 were followed except that the metal alloy core was replaced by a thin laminate consisting of a 0.005-inch thick fiberglass reinforced epoxy resin sheet bonded on each side with composite metal sheets. These composite metal sheets consided of 0.0045-inch thich metal alloy cores (64% iron and 36% nickel) both sides of which were clad with 0.00075-inch thick cooper metal.

A metal alloy core of 64% iron and 36% nickel and which was 0.006 inch thick was clad on each surface with copper metal sheets having a thickness of 0.002 inch. This metal alloy core was placed onto an X-, Y- positioning table, the table was moved to predetermined locations, and 0.042-inch diameter holes were mechanically drilled through the core.

The copper surfaces of the drilled metal alloy sheet were treated to promote adhesion through the use of a commercially available black oxide treatment solution.

Several sheets of semi-cured fiberglass reinforced eopxy resin were used to fill drilled holes in the core, and a sheet of copper foil 0.0014 inch thick was laminated to one side of the drilled metal alloy core as described in Example 1.

Another sheet of copper foil 0.0014 inch thick was then laminated to the other side of the drilled metal alloy core in the same manner. After application of the copper foil to each side of the drilled metal alloy core, the resulting substrate base was baked for 60 minutes at a temperature of 350.degree. F. to fully cure the epoxy resin.

The substrate base was then brushed in order to remove dirt, dust, oxide and similar foreign material from the surface of the copper foil. A dry film photoresist was then applied to each side of the substrate base in order to form circuit patterns on each side of the substrate base.

The substrate base was then exposed to ferric chloride solution as described in Example 1 to dissolve exposed copper metal. The remaining photoresist material was removed and the copper exposed to black oxide.

The substrate base was then encapsulated with resin and adhesive and scribed with wire, one side at a time, according to the procedures of Example 1.

The substrate base was then baked for 30 minutes at 250.degree. F. The baking temperature was then increased to 350.degree. F. and the substrate base baked for an additional 90 minutes.

The substrate base was then placed onto the X-, Y- positioning table described above, the table was moved to the same locations in which holes were drilled earlier, and 0.020 inch diameter holes were mechanically drilled through the layers on the substrate base.

The substrate base was then subjected to the cleaning/adhesion promotion treatment and plated in accordance with the process described in Example 1, above.

The terms and expressions which have been employed are used in terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claims.