GB2079539A - Electrical circuit assemblies - Google Patents
Electrical circuit assemblies Download PDFInfo
- Publication number
- GB2079539A GB2079539A GB8111458A GB8111458A GB2079539A GB 2079539 A GB2079539 A GB 2079539A GB 8111458 A GB8111458 A GB 8111458A GB 8111458 A GB8111458 A GB 8111458A GB 2079539 A GB2079539 A GB 2079539A
- Authority
- GB
- United Kingdom
- Prior art keywords
- layer
- aluminium
- circuit assembly
- thin
- highly conductive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/01—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate comprising only passive thin-film or thick-film elements formed on a common insulating substrate
- H01L27/016—Thin-film circuits
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/01—Chemical elements
- H01L2924/01046—Palladium [Pd]
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Parts Printed On Printed Circuit Boards (AREA)
Abstract
A thin film circuit assembly comprises a conductive aluminum layer 14 supported directly or indirectly by a resistive layer 12 and electrical interconnection members 24 bonded directly to the aluminium by ultrasonic or thermocompression bonding techniques. <IMAGE>
Description
SPECIFICATION
Electrical circuit assemblies
This invention relates to electrical circuit assemblies each having a thin highly conductive layer supported on a thin resistive layer, the thin resistive layer being supported on a major surface of an at least substantially planar substrate. Usually the thin highly conductive layer has a thickness less than 6 micrometres, and a sheet resistivity of less than 0 1 ohm per square. The thin resistive layer usually has a thickness less than 0 02 micrometre, and a sheet resistivity greater than 100 ohms per square, and conveniently comprises a nickelchromium alloy.
It is known to provide a thin highly conductive layer of gold.
An initially continuous thin highly conductive layer may be supported on the thin resistive layer, and subsequently the thin continuous highly conductive layer is formed into the desired shape in plan of a constituent layer of a required conductor pattern of the electrical circuit assembly, for example, by selectively etching portions of the thin initially continuous conductive layer. Such a constituent layer of the conductor pattern is also considered to be a thin highly conductive layer.
Alternatively the thin highly conductive layer is deposited initially in the shape in plan of the required conductor pattern, upon selected portions of the thin resistive layer, for example, the other portions of the thin resistive layer being covered by a mask during the deposition process step for the highly conductive layer, and subsequently the mask is removed, leaving the required highly conductive layer on the thin resistive layer. Portions of the thin resistive layer supporting the highly conductive layer of the conductor pattern are considered to be portions of the conductor pattern.
The thin resistive layer may be an initially continuous layer, portions of which may be removed selectively either before or after the deposition of the highly conductive layer thereon.
The conductor pattern provides at least a constituent part of terminals of the circuit assembly, which terminals are required to be bonded to one type of electrical interconnection members, for example. said one type of electrical interconnection members comprising leads extending from, but not included within, the circuit assembly; or comprising conductive mounting bumps, which may, or may not, be included within the circuit assembly. Said one type of electrical interconnection members are required to be bonded to the terminals in any convenient way. It may be required to solder these electrical interconnection members to the terminals employing a tin-based solder.
Further, the conductor pattern may provide required electrical interconnections between constituent electrical circuit elements of the circuit assembly, such as silicon semiconductor devices, having aluminium contacts, and always provides electrical interconnections between the circuit elements and the terminals.
Pads may be provided by the electrical interconnection portions of the conductor pattern, and the highly conductive material of these pads is required to be bonded to another type of electrical interconnection members, comprising parts of the electrical circuit assembly, for example, said other type of electrical interconnection members, comprising wires, or conductive mounting bumps, or the conctacts, or the terminals, of the constituent electrical circuit elements of the circuit assembly, said other type of electrical interconnection members being between the pads and at least some of the constituent circuit elements of the circuit assembly.
Usually there are very many more of said other type of electrical interconnection members required to be bonded to the pads, and usually these other type of electrical interconnection members are smaller, than said one type of electrical interconnection members.
Consequently, at least said other type of electrical interconnection members are required to be bonded to the pads in a wholly reliable manner, and thus, it is required that these electrical interconnection members are not soldered to the pads.
It is required that the thin highly conductive layer does not form at least significant amounts of disadvantageous intermetallic compounds with other metals included in the electrical circuit assembly. and under normally-encountered operating conditions for the assembly. Thus, diffusion of the material of the thin resistive layer into the thin highly conductive layer, or vice versa, can adversely affect the properties of either layer. In addition, the formation of significant amounts of intermetallic compounds, at regions within the circuit assembly at which bonds are formed with electrical interconnection members, can adversely affect the strengths of the bonds.
Further it is required that the highly conductive layer is of a material which is easily deposited.
In addition, it is requied that the thin highly conductive layer is of a material which, when deposited, is securely bonded to other contiguous layers of the circuit assembly. The contiguous layers may be of electrical insulating material, or resistive material, or another highly conductive material.
It is an object of the present invention to provide such an electrical circuit assembly of a novel and advantageous construction, and in particular having the required characteristics referred to above.
According to the present invention an electrical circuit assembly includes a thin resistive layer supported upon one major surface of an at least substantially planar substrate, and supported upon the thin resistive layer, either directly or indirectly, is a thin highly conductive layer of aluminium, and at least electrical interconnection members of the circuit assembly, between the thin highly conductive layer and constituent electrical circuit elements of the circuit assembly, are also of aluminium, and are bonded directly to the thin highly conductive layer of aluminium by employing ultrasonic or thermo-compression bonding techniques.
Such aluminium-to-aluminium bonds are desirable because they can be provided in a wholly reliable manner, not least because, inherently, significant amounts of an intermetallic compound are not formed at the bond regions. In addition, the bonds are more reliable, and less complex, than if the electrical interconnection members are to be soldered to the aluminium layer. Hence, possibly at least the majority of the required bonds associated with the circuit assembly are provided in this advantageous manner.
Aluminium is also an advantageous material for the thin highly conductive layer because it is easily deposited; and because when deposited, it is securely bonded to suitable contiguous layers, such as a dielectric layer of silicon oxide, or layers of other metals, such as a nickel layer. A nickel layer, advantageously, completes the bonding pads comprising terminals for the circuit assembly. Electrical interconnection members, associated with the circuit assembly, to be bonded to the terminals, and usually of aluminium, conveniently may be soldered to the nickel layers of the terminals by employing a suitable tin-based solder.
If the thin highly conductive layer of aluminium is likely to form an undesired interme- tallic compound with the material of the thin resistive layer on which it is supported, for example, if the thin resistive layer is of a nickel-chromium alloy, a suitable barrier layer, at least substantially to prevent the formation of the undesired intermetallic compound, can be provided between the thin highly conductive layer of aluminium and the other metal layer. A suitable barrier layer is of palladium.
Aluminium adheres well to palladium when deposited thereon, and palladium adheres well to a thin resistive layer of a nickelchromium alloy when the palladium is deposited thereon. Similarly, suitable barrier layers may be provided between the thin highly conductive layer of aluminium and another metal required within the circuit assembly, and with which, otherwise, the aluminium layer would be contiguous, and with which, otherwise, the aluminium layer would form an undesired intermetallic compound. However, in accordance with the present invention, such a barrier layer is not provided on at least the pads or parts of the thin highly conductive layer to be bonded to the required electrical interconnection members provided between the constituent electrical circuit elements of the circuit assembly and the aluminium layer.
The present invention will now be described by way of example, with reference to the accompanying drawing, which is a sectional elevation of part of an embodiment of an electrical circuit assembly in accordance with the present invention.
The illustrated electrical circuit assembly has a planar substrate 10, of a glazed ceramic, with major surfaces 11, 5 centimetres square. On one major surface 11 of the substrate 10 is deposited a thin resistive layer 12 of a nickel-chromium alloy having a sheet resistivity of 300 ohms per square. The thin resistive layer 12 is deposited in a sputtering process, and the layer has a uniform thickness of 0 01 micrometre, the layer being deposited in an initially continuous form. The thin resistive layer 12 adheres well to the substrate.
Next a layer of palladium 13 is deposited upon the thin resistive layer. The palladium layer 13 has a uniform thickness of 0-06 micrometre, and is deposited in an initially continuous form, the palladium being evaporated by employing a resistance heating furnace. The palladium layer 13 adheres well to the thin resistive layer.
An initially continuous thin layer of aluminium 14 is deposited upon the palladium layer.
The aluminium layer 14 has a uniform thickness of 1~5 micrometre, and adheres well to the palladium layer. The aluminium 14 is evaporated onto the palladium layer employing a resistance heating furnace. The palladium layer prevents the diffusion of the material of the thin resistive layer into the thin aluminium layer.
In a first photolithographic etching step, portions of the aluminium layer, the palladium layer, and the thin resistive layer, each selectively are etched, these layers being etched sequentially employing as etchants, respectively, a mixture of phosphoric and nitric acids, a mixture of potassium iodide and iodine, and a mixture of hexanitro-ammonium cerate and acetic acid. In a second photolithographic etching step, further portions of the aluminium layer and the palladium layer each selectively are etched, and these two layers are etched sequentially. By the two photolithographic etching steps, together, there is defined the required conductor pattern 15, 16 and the constituent thin film resistors 17 of the circuit assembly. The portions of the thin resistive layer and the palladium layer remaining and supporting the remaining aluminium portions, are considered to be also portions of the conductor pattern.
Alternatively, a thin aluminium layer of the desired shape in plan of the conductor pattern is provided by depositing the palladium and the aluminium selectively upon the appropri ate portions of the thin resistive layer being covered by a mask during the palladium and aluminium deposition process steps, and subsequently the mask is removed in any convenient way. The palladium and the aluminium either are not deposited upon the mask, or any palladium and aluminium deposited upon the mask are removed with the masking material. The shape in plan of the conductor pattern 15, 16 is such that terminals 15 for the circuit assembly are provided adjacent to the periphery of the major surface of the substrate supporting the conductor pattern, the conductor pattern providing a constituent part of the terminals 15.The terminals 15 are completed by providing a layer of nickel 20 upon each of the portions of aluminium of the terminals, so that one type of electrical interconnection members 21 can be bonded in a reliable manner to the terminals employing a suitable tin-based solder 22. Said one type of electrical interconnection members 21, also required to be of a material capable of being soldered in a reliable manner, comprise leads extending from, but not included within, the circuit assembly; or they may comprise conductive mounting bumps, which, if provided within the circuit assembly, are formed in any convenient way. The nickel layers 20 adhere well to both the aluminium layer, and to the solder 22.It is required that only the terminal portions of the aluminium layer are coated with nickel 20, and the nickel may be deposited selctively on these portions by masking the remainder of the conductor-providing surface of the assembly at this stage, subsequently the masking material being removed, leaving the desired nickel layers. Alternatively an initially continuous layer of nickel is deposited, and the desired nickel layers of the terminals are provided by employing a photolithographic etching step in which the underlying layers of the circuit assembly are unaffected.
The nickel is deposited upon the aluminium layer by being evaporated in an electrical resistance furnace.
If it is not required to bond these said one type of electrical interconnection members to the terminals of the circuit assembly by soldering, the nickel layers are not provided, the terminals comprising only portions of the conductor pattern. Hence, these electrical interconnection members are required to be of a material capable of being bonded in a reliable manner to the portions of the aluminium layer included within the terminals. Desirably, intermetallic compounds in the bonding regions associated with the terminals are obviated by these electrical interconnection members also being of aluminium. Reliable bonds can be made between the aluminium layers and aluminium electrical interconnection members, by employing ultrasonic or thermo-compression bonding techniques.The formation of significant amounts of intermetallic compounds, at regions within the circuit assembly at which bonds are formed with electrical interconnection members, can adversely affect the strengths of the bonds.
The conductor pattern also provides electrical interconnections 16 between constituent circuit elements 17 of the circuit assembly and the terminals 15, and may provide electrical interconnections 16 between the constituent circuit elements. Pads may be provided by the electrical interconnection portions of the conductor pattern, and the aluminium of these pads is required to be bonded to another type of electrical interconnection members 24 between the pads and at least some of the constituent circuit elements of the circuit assembly, and comprising part of the electrical circuit assembly.These other type of electrical interconnection members 24 comprise wires; or they may comprise conductive mounting bumps, of the contacts, or the terminals, of the constituent electrical circuit elements of the circuit assembly, and are between the pads and at least some of the constituent circuit elements of the circuit assembly. Usually there are very many more of said other type of electrical interconnection members 24 required to be bonded to the pads, and usually these other type of electrical interconnection members are smaller, than said one type of electrical interconnection members. Consequently, at least said other type of electrical interconnection members are required to be bonded to the pads in a wholly reliable manner, and thus, it is required that these electrical interconnection members are not soldered to the pads.As indicated above, desirably intermetallic compounds in the bonding regions are obviated, so that reliable bonds are obtained, by the electrical interconnection members being of aluminium, and the aluminium electrical interconnection members are bonded to the thin highly conductive layer of aluminium by employing the reliable ultrasonic or thermo-compression bonding techniques. Inherently, with such aluminium-toaluminium bonds no intermetallic compound is formed at the bond regions. In addition, the bonds are more reliable, and less complex, than if the electrical interonnection members are to be soldered to the aluminium layer.
This type of bond is used for possibly at least the majority of bonds associated with each electrical circuit assembly in accordance with the present invention.
When an electrical interconnection member, between a constituent electrical circuit element and the thin highly conductive layer of aluminium, comprises an aluminium wire, conveniently the wire is wedge-bonded to the aluminium layer, as indicated at 25.
It is possible to operate the circuit assembly at higher temperatures than otherwise would be the case if the formation of intermetallic compounds in significant amounts does not occur in the bonding regions at these high temperatures.
The electrical circuit assembly is completed by at least the major substrate surface bearing the conductor pattern, and the constituent electrical circuit elements, being encapsulated, for example, by being covered with a suitable potting compound, or being covered by a closure member, with the space between the closure member and the substrates being substantially evacuated, or filled with an inert gas, such as nitrogen; or by the circuit assembly being mounted with other such electrical circuit assemblies within a more complex electrical circuit assembly, which more complex electrical circuit assembly is encapsulated, for example, in one of the ways referred to above; to ensure stability in the manner of operation of the electrical circuit assembly under normally-encountered operating conditions.
The substrate may be of any suitable material, for example, having a high coefficient of thermal conductivity, and a coefficient of thermal conductivity, and a coefficient of linear expansion substantially the same as that of the resistive material, the palladium, and the aluminium. The thin resistive layer may be deposited directly upon the substrate if the substrate is of electrical insulating material, such as glass, or a glazed ceramic, or an asfired-ceramic, or sapphire, or silica.
If portions of the thin resistive layer are required selectively to be removed, for exam ple, in a photolithographic etching step, this removal may be either before or after the deposition of the aluminium layer.
The constituent circuit elements of the circuit assembly may have any convenient form.
if they comprise silicon semiconductor devices, having aluminium contacts, these contacts may be bonded directly to the thin highly conductive layer of aluminium. If the constituent circuit elements comprise modules having aluminium terminals, these terminals may be bonded directly to the thin highly conductive layer of aluminium.
The thin resistive layer may be of other materials than a nickel-chromium alloy. The thin highly conductive layer of aluminium may be deposited directly upon the thin resistive layer, without a barrier layer in between, if significant amounts of an intermetallic compound, which can adversely affect the properties of either layer, is not likely to be formed under normally encountered operating conditions for the circuit assembly.
Other metal layers may be provided within the circuit assembly, and these other metal layers may be required to be contiguous with the thin highly conductive layer of aluminium.
However, if significant amounts of undesired intermetaliic compounds are likely to be formed by the aluminium and such another metal layer, a barrier layer is provided therebetween.
In general, a circuit assembly in accordance with the present invention, and having only two or three contiguous metal layers, possibly at least in the majority of bonding regions associted therewith, has the desirable performance characteristics of known, but more complex, constructions of such circuit assemblies in this respect, having a greater number of contiguous metal layers in such bonding regions, for example, a circuit assembly in which a nickel-chromium resistive layer is coated with titanium, palladium and gold.
It is required that the aluminium layer is securely bonded to other, contiguous, layers of the circuit asembly. Usually, the aluminium adheres well to any other metal, or metal alloy, layer which may be deposited thereon.
In addition, aluminium generally adheres well to layers of electrical insulating material, for example, a layer of silicon oxide which conveniently can be provided.
Electrical circuit assemblies in accordance with the present invention, including a conductor pattern, at least partially, comprising aluminium, is not as likely to be damaged by radiation as such assemblies having a conductor pattern of a metal of a higher atomic weight, for example, when the conductor pattern is of gold.
Aluminium is also an advantageously stable material, because of the formation of thin oxide layers upon its exposed surfaces.
Claims (8)
1. An electrical circuit assembly including a thin resistive layer supported upon one major surface of an at least substantially planar substrate, and supported upon the thin resistive layer is a thin highly conductive layer of aluminium, and at least electrical interconnection members of the circuit assembly, between the thin highly conductive layer and constituent electrical circuit elements of the circuit assembly, are also of aluminium, and are bonded directly to the thin highly conductive layer of aluminium by employing ultrasonic or thermo-compression bonding techniques.
2. A circuit assembly as claimed in claim 1 in which the aluminium electrical interconnection members, between the thin highly conductive layer of aluminium and the constituent electrical circuit elements of the circuit assembly, comprise wires.
3. A circuit assembly as claimed in any one of the preceding claims in which the thin resistive layer is of a nickel-chromium alloy.
4. A circuit assembly as claimed in any one of the preceding claims in which a barrier layer is provided between the thin resistive layer and the thin highly conductive layer of aluminium.
5. A circuit assembly as claimed in any one of the preceding claims in which a barrier layer is provided between the thin highly conductive layer of aluminium and another metal layer of the circuit assembly.
6. A circuit assembly as claimed in claim 4 or claim 5 in which the barrier layer is of palladium.
7. A circuit assembly as claimed in any one of the preceding claims in which terminals for the circuit assembly are completed by providing layers of nickel on portions of the thin aluminium layer, electrical interconnection members to be soldered to the nickel layers of the terminals by employing a suitable tin-based solder.
8. An electrical circuit assembly substantially of any one of the different forms described herein, with reference to the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8111458A GB2079539B (en) | 1980-04-22 | 1981-04-13 | Electrical circuit assemblies |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8013163 | 1980-04-22 | ||
| GB8111458A GB2079539B (en) | 1980-04-22 | 1981-04-13 | Electrical circuit assemblies |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2079539A true GB2079539A (en) | 1982-01-20 |
| GB2079539B GB2079539B (en) | 1983-10-12 |
Family
ID=26275272
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8111458A Expired GB2079539B (en) | 1980-04-22 | 1981-04-13 | Electrical circuit assemblies |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2079539B (en) |
-
1981
- 1981-04-13 GB GB8111458A patent/GB2079539B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2079539B (en) | 1983-10-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |