Title of Invention	A PROCESS FOR THE FABRICATION OF IMPROVED CONDUCTOR FOR POWER THICK FILM HYBRID MICROCIRCUITS /MICROWAVE INTEGRATED CIRCUITS(PHMC)
Abstract	A process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits by preparing known thick film conductors selected from Pd-Ag, Pt-Ag, Pd-Pt-Ag on thick film circuits by conventional methods; surface cleaning the thick film conductor paths obtained by known methods; shorting the conductor paths by known means; electroplating the conductors with copper in a standard conventional electroplating bath to grow a desired plating thickness of 4µm; removing shorting done from conductor paths; cleaning the resultant copper plated conductor paths on thick film substrate in distilled water.

Title of Invention

A PROCESS FOR THE FABRICATION OF IMPROVED CONDUCTOR FOR POWER THICK FILM HYBRID MICROCIRCUITS /MICROWAVE INTEGRATED CIRCUITS(PHMC)

Abstract

A process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits by preparing known thick film conductors selected from Pd-Ag, Pt-Ag, Pd-Pt-Ag on thick film circuits by conventional methods; surface cleaning the thick film conductor paths obtained by known methods; shorting the conductor paths by known means; electroplating the conductors with copper in a standard conventional electroplating bath to grow a desired plating thickness of 4µm; removing shorting done from conductor paths; cleaning the resultant copper plated conductor paths on thick film substrate in distilled water.

Full Text	This invention relates to a process for the -fabrication of improved conductor for power thick film hybrid microcircuits/microwiave integrated circuits (PHMCs) . For fabrication of power thick film hybrid circuits, high conductivity materials are required for handling high currents. For handling a high current, required width of conventional Pd-Ag, Pt-Pd-Ag, Pt-Ag conductor which are normally used is ten times larger as compared to a conventional Cu-thick film conductor. In the process of the present invention, in order to achieve high current capacity with smaller width of conventional conductor such as Pd-Ag, Pt-Pd-Ag, Pt-Ag, the conventional conductor is electroplated with Cu in a standard plating bath to obtain an improved conductor for PHMCs. Manufactures of Hybrid Micro Circuit in India have not adopted fabrication of Cu-thick film conductor technology due to .requirement of additional equipment/ infrastructure. So far considering the need of PHMCs for automobiles, power electronic applications, utilization of a new low cost fabrication process for fabrication of power thick film conductor will be useful for manufacturing PHMCs. The hitherto known process for fabrication of conductor for Power Thick Film Hybrid Microcircuits (PHMCs) is to use high conductivity materials such as Cu thick film conductor on peramic base. Resistivity of fired Cu thick film conductor is ~1.5m ohm/sq. Use of Cu thick film conductor requires pure Nitrogen atmosphere (Oxygen inductor is printed, dried and fired after fabrication of resistors. In conventional process of thick film hybrid microcircuits, first the conductor pattern of. conductivity materials such as Pd-Ag, Pt-Pd-Ag is printed, dried and fired then resistor pattern is printed, dried & fired in air atmosphere. Such fired conductor materials have resistivity 25m ohm/sq. Therefore for handling a given current required width of conventional Pd/Ag, Pt-Pd-Ag, Pt-Ag, conductor is ten times larger as compared to a conventional Cu-thick film conductor. The hitherto known processes have the following drawbacks: 1. Cu thick film material requires pure Nitrogen (Oxygen ppm) for its process. 2. Resistors are printed & fired prior to conductor formation. This requires precise alignment of various resistor patterns which is an unconventional technique in thick film process. 3. Process cost is very high due to Nitrogen consumption. 4. Requires ten times larger width in-case of Pd-Ag, Pt-Ag, Pd-Pt-Ag conductor for handling a given current as compared to Cu-thick film conductor. Cost is one of the major parameter in producing power thick film HMCs. For handling high current required for power hybrid cu-thick film conductor is used, Cu thick film conductor can handle about 10 times larger current as compared to conventional thick film conductor viz. Pd-Ag, Pt-Ag and Pd-Ag-Pt. The existing process of Cu-thick film fabrication requires an additional Nitrogen atmosphere conveyor belt firing furnace (cost Rs. 50 lakhs) and large consumption of nitrogen gas. Considering these requirements fabrication of Cu-thick film conductor may form about 2 0* of a power HMCs cost . The main object of the present invention is to provide a process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits. Another object is to provide a process compatible with thick film materials having high conductivity which are required for Power Hybrid Microcircuits/Microwave Integrated circuits. Yet another object of the process of the present invention is to improve the conductivity of conventional air fired conductor material such as Pd-Ag, Pt-Ag, Pd-Pt-Ag by electroplating of Cu. In the process of the present invention the surface of thick film Pd-Ag, Pt-Ag, Pd-Pt-Ag conductor is cleaned by a rubber buffing. Desired conductor path are shorted by soldering a wire or wire bonding technique. Cu is electroplated in a standard bath to grow a desired thickness. After electroplating, the thick film circuit is cleaned in distilled water and shorting wires are removed off by desoldering or pulling. Thick film substrate so formed is now ready for components attachment. Accordingly, the present invention provides a process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits which comprises : i) preparing known thick film conductors selected from Pd-Ag, Pt-Ag, Pd-Pt-Ag on thick film circuits by conventional methods; ii) surface cleaning the thick film conductor paths obtained in step (i) by known methods; iii) shorting the conductor paths by known means; iv) electroplating the conductors with copper in a standard conventional electroplating bath to grow a desired plating thickness of 4µm; v) removing shorting done in step (iii) from conductor paths; vi) cleaning the resultant copper plated conductor paths on thick film substrate in distilled water. In an embodiment of the present invention the surface cleaning may be done using known methods such as rubber buffing. In another embodiment the shorting of conductor paths is done by using known means such as soldering a wire, wire bonding techniques. The following example is given by way of illustration of the process of the present invention and therefore should not be construed to limit the scope of the present invention. Example-1 Thick film circuit is fabricated on alumina substrate by screen printing and firing of conductor/resistor compositions. The Pd-Ag conductor material is fired in air. Resistivity of fired conductor is 25 mohm/sq. Thick film circuit comprises of conductor (1), Resistor (2) and alumina substrate (3) as shown in fig.1. Surface of the Thick film circuit is then cleaned by rubber buffing. In this process of cleaning only conductor surface gets cleaned without affecting the resistor's surface. Conductor paths are shorted by soldering of wire using hand/reflow technique/wire bonding (4) for shorting as shown in fig.2. Solder flux is cleaned in flux removal solution is available in the market. Now Cu film of thickness of 4 µm with current 10 mA for 5 minutes on conductor path is deposited in a plating ,bath to get resistivity of: the conductor t.o J .1.5 in ohm/aq. C'u electroplated thick film conductor(5) is shown in fig 3. After plating, the circuit is cleaned in Deionised water. Shorted wires are then removed off by desoldering or by breakinq the bonded wires as shown in fig. 4. The thick film substrate is now ready for components attachment using reflow technique. The plating bath comprises of D.C. power supply (6) , positive terminal connected to Cu electrode (7) and negative terminal connected to thick film circuit (8), Container (9), air agitation tube (10) and plating sulution having CuS04 75 gm/liter and H2SO4 30 cc per liter (11) as shown in fig. S. The main advantages of the process of the present invention are as follows: 1. Compatible with thick film process. 2. Nitrogen not required. Hence it is a low cost, as it does not require such as Nitrogen firing conveyor belt furnace. Nitrogen gas. 3. High conductivity material does not get deposited on resistors. 4. No masking required during the electroplating process. 5. Reduced conductor width (as compared to standard thick film conductor) for a given current capacity. We claim : 1. A process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits which comprises : i) preparing known thick film conductors selected from Pd-Ag, Pt-Ag, Pd-Pt-Ag on thick film circuits by conventional methods; ii) surface cleaning the thick film conductor paths obtained in step (i) by known methods; iii) shorting the conductor paths by known means; iv) electroplating the conductors with copper in a standard conventional electroplating bath to grow a desired plating thickness of 4µm; v) removing shorting done in step (iii) from conductor paths; vi) cleaning the resultant copper plated conductor paths on thick film substrate in distilled water. 2. A process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits substantially as herein describe with reference to examples accompanying this specification.

Full Text

This invention relates to a process for the -fabrication of improved conductor for power thick film hybrid microcircuits/microwiave integrated circuits (PHMCs) . For fabrication of power thick film hybrid circuits, high conductivity materials are required for handling high currents. For handling a high current, required width of conventional Pd-Ag, Pt-Pd-Ag, Pt-Ag conductor which are normally used is ten times larger as compared to a conventional Cu-thick film conductor. In the process of the present invention, in order to achieve high current capacity with smaller width of conventional conductor such as Pd-Ag, Pt-Pd-Ag, Pt-Ag, the conventional conductor is electroplated with Cu in a standard plating bath to obtain an improved conductor for PHMCs. Manufactures of Hybrid Micro Circuit in India have not adopted fabrication of Cu-thick film conductor technology due to .requirement of additional equipment/ infrastructure. So far considering the need of PHMCs for automobiles, power electronic applications, utilization of a new low cost fabrication process for fabrication of power thick film conductor will be useful for manufacturing PHMCs.
The hitherto known process for fabrication of conductor for Power Thick Film Hybrid Microcircuits (PHMCs) is to use high conductivity materials such as Cu thick film conductor on peramic base. Resistivity of fired Cu thick film conductor is ~1.5m ohm/sq. Use of Cu thick film conductor requires pure Nitrogen atmosphere (Oxygen
inductor is printed, dried and fired after fabrication of resistors. In conventional process of thick film hybrid microcircuits, first the conductor pattern of. conductivity materials such as Pd-Ag, Pt-Pd-Ag is printed, dried and fired then resistor pattern is printed, dried & fired in air atmosphere. Such fired conductor materials have resistivity 25m ohm/sq. Therefore for handling a given current required width of conventional Pd/Ag, Pt-Pd-Ag, Pt-Ag, conductor is ten times larger as compared to a conventional Cu-thick film conductor.
The hitherto known processes have the following drawbacks:
1. Cu thick film material requires pure Nitrogen (Oxygen ppm) for its process.
2. Resistors are printed & fired prior to conductor formation. This requires precise alignment of various resistor patterns which is an unconventional technique in thick film process.
3. Process cost is very high due to Nitrogen consumption.
4. Requires ten times larger width in-case of Pd-Ag, Pt-Ag, Pd-Pt-Ag conductor for handling a given current as compared to Cu-thick film conductor. Cost is one of the major parameter in producing power thick film HMCs. For handling high current required for power hybrid cu-thick film conductor is used, Cu thick film conductor can handle about 10 times larger current as compared to conventional thick film conductor viz. Pd-Ag, Pt-Ag and Pd-Ag-Pt. The existing process of Cu-thick film fabrication requires an additional Nitrogen atmosphere

conveyor belt firing furnace (cost Rs. 50 lakhs) and large consumption of nitrogen gas. Considering these requirements fabrication of Cu-thick film conductor may form about 2 0* of a power HMCs cost .
The main object of the present invention is to provide a process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits. Another object is to provide a process compatible with thick film materials having high conductivity which are required for Power Hybrid Microcircuits/Microwave Integrated circuits.
Yet another object of the process of the present invention is to improve the conductivity of conventional air fired conductor material such as Pd-Ag, Pt-Ag, Pd-Pt-Ag by electroplating of Cu.
In the process of the present invention the surface of thick film Pd-Ag, Pt-Ag, Pd-Pt-Ag conductor is cleaned by a rubber buffing. Desired conductor path are shorted by soldering a wire or wire bonding technique. Cu is electroplated in a standard bath to grow a desired thickness. After electroplating, the thick film circuit is cleaned in distilled water and shorting wires are removed off by desoldering or pulling. Thick film substrate so formed is now ready for components attachment.

Accordingly, the present invention provides a process for the fabrication of improved conductor for power thick film hybrid microcircuits/microwave integrated circuits which comprises :
i) preparing known thick film conductors selected from Pd-Ag, Pt-Ag,
Pd-Pt-Ag on thick film circuits by conventional methods; ii) surface cleaning the thick film conductor paths obtained in step (i)
by known methods; iii) shorting the conductor paths by known means; iv) electroplating the conductors with copper in a standard
conventional electroplating bath to grow a desired plating thickness
of 4µm; v) removing shorting done in step (iii) from conductor paths; vi) cleaning the resultant copper plated conductor paths on thick film
substrate in distilled water.

In an embodiment of the present invention the surface cleaning may be done using known methods such as rubber buffing.
In another embodiment the shorting of conductor paths is done by using known means such as soldering a wire, wire bonding techniques.
The following example is given by way of illustration of the process of the present invention and therefore should not be construed to limit the scope of the present invention.
Example-1
Thick film circuit is fabricated on alumina substrate by screen printing and
firing of conductor/resistor compositions. The Pd-Ag conductor material is fired in
air. Resistivity of fired conductor is 25 mohm/sq. Thick film circuit comprises of
conductor (1), Resistor (2) and alumina substrate (3) as shown in fig.1. Surface of
the Thick film circuit is then cleaned by rubber buffing. In this process of cleaning
only conductor surface gets cleaned without affecting the resistor's surface.
Conductor paths are shorted by soldering of wire using hand/reflow technique/wire
bonding (4) for shorting as shown in fig.2. Solder flux is cleaned in flux removal
solution is available in the market. Now Cu film of
thickness of 4 µm with current 10 mA for 5 minutes on

conductor path is deposited in a plating ,bath to get resistivity of: the conductor t.o J .1.5 in ohm/aq. C'u electroplated thick film conductor(5) is shown in fig 3. After plating, the circuit is cleaned in Deionised water. Shorted wires are then removed off by desoldering or by breakinq the bonded wires as shown in fig. 4. The thick film substrate is now ready for components attachment using reflow technique. The plating bath comprises of D.C. power supply (6) , positive terminal connected to Cu electrode (7) and negative terminal connected to thick film circuit (8), Container (9), air agitation tube (10) and plating sulution having CuS04 75 gm/liter and H2SO4 30 cc per liter (11) as shown in fig. S.
The main advantages of the process of the present invention are as follows:
1. Compatible with thick film process.
2. Nitrogen not required. Hence it is a low cost, as it does not require such as Nitrogen firing conveyor belt furnace. Nitrogen gas.
3. High conductivity material does not get deposited on resistors.

4. No masking required during the electroplating process.
5. Reduced conductor width (as compared to standard thick film conductor) for a given current capacity.

We claim :
1. A process for the fabrication of improved conductor for power thick film
hybrid microcircuits/microwave integrated circuits which comprises :
i) preparing known thick film conductors selected from Pd-Ag, Pt-Ag,
Pd-Pt-Ag on thick film circuits by conventional methods; ii) surface cleaning the thick film conductor paths obtained in step (i)
by known methods; iii) shorting the conductor paths by known means; iv) electroplating the conductors with copper in a standard
conventional electroplating bath to grow a desired plating thickness
of 4µm; v) removing shorting done in step (iii) from conductor paths; vi) cleaning the resultant copper plated conductor paths on thick film
substrate in distilled water.
2. A process for the fabrication of improved conductor for power thick film
hybrid microcircuits/microwave integrated circuits substantially as herein
describe with reference to examples accompanying this specification.

Documents:

2449-del-1997-abstract.pdf

2449-del-1997-claims.pdf

2449-del-1997-complete specification (granted).pdf

2449-del-1997-correspondence-others.pdf

2449-del-1997-correspondence-po.pdf

2449-del-1997-description (complete).pdf

2449-del-1997-drawings.pdf

2449-del-1997-form-1.pdf

2449-del-1997-form-19.pdf

2449-del-1997-form-2.pdf

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Patent Number

228263

Indian Patent Application Number

2449/DEL/1997

PG Journal Number

29/2008

Publication Date

26-Sep-2008

Grant Date

08-Dec-2006

Date of Filing

28-Aug-1997

Name of Patentee

Council of Scientific and Industrial Research

Applicant Address

RAFI MARG,NEW DELHI-110001,INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	Yogendra Kumar Jain	Central Electronics Engineering Research Institute Pilani-333031.
2	Harish Chandra Pandey	Central Electronics Engineering Research Institute Pilani-333031.

PCT International Classification Number

H01L 21/82

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA