Indian Patents. 213221:"A PROCESS FOR THE FABRICATION OF IMPROVED METALLISED CERAMIC SUBSTRATE USEFUL FOR ASSEMBLY OF SEMICONDUCTOR DEVICES"

Title of Invention	"A PROCESS FOR THE FABRICATION OF IMPROVED METALLISED CERAMIC SUBSTRATE USEFUL FOR ASSEMBLY OF SEMICONDUCTOR DEVICES"
Abstract	NO ABSTRACT

Full Text	The present invention relates to a process for the fabrication of improved metallised ceramic substrate useful for assembly of semiconductor devices. The utility of the present invention is to provide a process for the fabrication of improved metallization on ceramic substrate for assembly of semiconductor devices. Using this process the leaching resistance of fabricated conductors with Sn/Pb solder also improves. Features of the metallized ceramic substrate are very good adherence, solderable with Sn/Pb solder and high leaching resistance compared to standard thick film metallisation. For assembly of semiconductor devices such as high current rectifiers etc. the metallized ceramic substrate must possess the above features.For this purpose Pd-Ag or Pt-Ag thick film metallisation on ceramic is used.To achive this, the hitherto known process employes a thick film conductor layer on ceramic substrate. This is fabricated by screen printing drying & firing processes. Reference may be made to 1. "Power Hybrid Circuit design and manufacture "by Haim Taraseiskey 2. "Hand book of thick film hybrid microelectronics" by Charles .A Harper. wherein the ceramic substrate is metallized with a thick metallic layer of Pt-Ag orPd-Ag by screen printing, drying and firing processes. The hitherto known process has the following drawbacks: 1. It uses materials such as Pt or Pd which are rare in occurance and are costly. 2. The thick film conductors have lower leaching resistance as compared with copper with Sn/Pb solder There is a large demand of metallized ceramic substrates for packaging of semiconducter devices. The process using Pd-Ag or Pt-Ag for such metallisation is rather costly. Further more the leaching resistance is also lower with the commonly used Sn/Pb solder. The main object of the present invention is to provide a process for the fabrication of improved metallised ceramic substrates useful for assembly of semiconductor devices, which obviates the drawbacks as detailed above. Another object of the present invention is to provide a low cost process for the fabrication of improved metallisation on ceramic substrate for assembly of semiconductor devices. In the present invention silver thick film metallisation on ceramic substrate is about five times cheaper as compared to Pd-Ag or Pt-Ag thickfilm materials Subsequent electroplating of copper and nickel is also a cheap process. Therefore, overall the present invention is about four times cheaper than the existing process. Hence considering the large demand of metallised ceramic substrates for assembly of semiconductor devices, utilisation of a new low cost metallisation will be very useful for assembly of semiconductor devices. Still another object of the present invention is to provide much higher leaching resistance as compared with standard thick film metallisation with Sn/Pb solder, thus the present invention obviates the drawbacks of the prior art as state above. Accordingly the present invention provides a process for the fabrication of improved metallised ceramic substrate useful for assembly of semiconductor devices which comprises (i) preparing silver metal film on a ceramic substrate by conventional methods, (ii) electroplating the ceramic substrate having silver metal film obtained in step (i), with copper in a standard electroplating bath to get copper plated ceramic substrate, (iii) cleaning and electroplating the above said copper plated ceramic substrate obtained in step (ii) with nickel in a standard electroplating bath, cleaning the said plated ceramic substrate followed by drying the metallized ceramic substrate by known methods. In an embodiment of the present invention the desired silver thick film pattern is formed by using a known method of thick film process such as screen printing, drying and firing techniques. In another embodiment of the present invention copper & nickel is electroplated by using known means such as pin point contact jig method in the standard plating baths. The present invention provides a process for the fabrication of improved metallised substrate useful for assembly of semiconductor device^, which comprises, preparing known film metallisation such as silver on ceramic substrate by conventional methods, electroplating the silver metallisation with fcopper in a standard conventional electroplating bath to grow a desired plating thickness, cleaing it in distilled water, then electroplating the above with nickel in a-standard conventional electroplating bath to grow a plating thickness, cleaning the above in distilled water, then drying in an oven. In the process of the present invention the detailed steps are as follows: 1. Silver thickfilm paste is printed on ceramic substrate by screen printing technique to get the wet print thickness of 35-40µm. 2. The printed pattern of silver is dried at 125.° - 150.°C for 10-15 minutes in an oven 3. The dried pattern of silver is fired at 750.°-850.°C peak firing temperature for 10- 15 minutes in conveyor belt furnace. 4. Metallised ceramic substrate thus obtained through steps 1 to 3 is electroplated with copper using standard copper plating bath. The plating thickness of 0.3-0.5 µm is build-up. 5. The substrate obtained in step 4 is cleaned in distilled water. 6. Cleaned ceramic substrate obtained in step 5 is further electroplated with nickel using standard nickel plating bath. The plating thickness of 0.3-0.5µm is build up. 7. Cleaning of nickel plated ceramic substrate as obtained in step 6 is performed in distilled water. 8. Drying of the cleaned ceramic substrate obtained in step 7 is done in an oven at 100.M 10.°C for 10-15 minutes. Silver has very low leaching resistance with Sn/Pb(60:40) solder due to its chemical affinity. Leaching resistance of Ag is increased by adding Pd or Pt. Nickel or copper has high leaching resistance with Sn/Pb(60:40) solder as compared to Pd-Ag or Pt-Ag. Therefore in the present invention nickel metallisation improves the leaching resistance with Sn/Pb solder as compared to Pd-Ag or Pt-Ag thick film metallisation on ceramics substrate. The copper is used as an adhesive layer between Ag & nickel. The unique combination of Ag-Cu-Ni has been used for preparing the metallized ceramic substrate. Ag film is used an adhesive conductive layer between the ceramic substrate and the Cu film. Nickel plating over copper protects copper from oxidation and provides favourable environment for copper-nickel interaction resulting in better adherence. The present invention not only improves the leaching resistance with Sn/Pb solder but also makes the metallisation cost effective as compared to Pd-Ag or Pt-Ag metallisation on ceramic substrates where high current densities are to be used. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example: 1 The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 35µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 750°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. Example:2 The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 35µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 850°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. Example: 3 The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 40µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 750°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. Example: 4 The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 40µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 850°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. The main advantages of the process of the present invention are as follows: 1. About four times cheaper than Pt-Ag or Pd-Ag metallisation. 2. Rare earth materials not required. 3. Higher leaching resistance with Sn/Pb solder as compared to Pd-Ag or Pt-Ag materials. We Claim: 1. A process for the fabrication of improved metallised ceramic substrate useful for assembly of semiconductor devices, which comprises: . (i) characterised in that preparing silver metal film on herein described a ceramic substrate by conventional methods; (ii) electroplating the ceramic substrate having silver metal film obtained in stepi) with copper in a standard electroplating bath to get copper plated ceramic substratet herein described, (iii) cleaning and electroplating the above said copper plated ceramic substrate obtained in step ii)with nickel as herein described in a standard electroplating bath,cleaning the said plated ceramic substrate followed by drying the metallised ceramic substrate by known methods. 2. A process as claimed in claim 1, wherein the silver metal thin metal film on ceramic substrate is formed by using known methods of thick film process such as screen printing, drying and filtring. 3. A process as claimed in claim 1, wherein the electroplating of copper and nickel is done by using known methods such as standard plating bath with pin point contact jig. 4. A process for the fabrication of improved metallised substrate useful for assembly of semiconductor devices, substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for the fabrication of improved metallised ceramic substrate useful for assembly of semiconductor devices.
The utility of the present invention is to provide a process for the fabrication of improved metallization on ceramic substrate for assembly of semiconductor devices. Using this process the leaching resistance of fabricated conductors with Sn/Pb solder also improves.
Features of the metallized ceramic substrate are very good adherence, solderable with Sn/Pb solder and high leaching resistance compared to standard thick film metallisation. For assembly of semiconductor devices such as high current rectifiers etc. the metallized ceramic substrate must possess the above features.For this purpose Pd-Ag or Pt-Ag thick film metallisation on ceramic is used.To achive this, the hitherto known process employes a thick film conductor layer on ceramic substrate. This is fabricated by screen printing drying & firing processes. Reference may be made to
1. "Power Hybrid Circuit design and manufacture "by Haim Taraseiskey
2. "Hand book of thick film hybrid microelectronics" by Charles .A Harper.
wherein the ceramic substrate is metallized with a thick metallic layer of Pt-Ag orPd-Ag by screen printing, drying and firing processes. The hitherto known process has the following drawbacks:
1. It uses materials such as Pt or Pd which are rare in occurance and are costly.
2. The thick film conductors have lower leaching resistance as compared with
copper with Sn/Pb solder
There is a large demand of metallized ceramic substrates for packaging of semiconducter devices. The process using Pd-Ag or Pt-Ag for such metallisation is rather costly. Further more the leaching resistance is also lower with the commonly used Sn/Pb solder.
The main object of the present invention is to provide a process for the fabrication of improved metallised ceramic substrates useful for assembly of semiconductor devices, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a low cost process for the fabrication of improved metallisation on ceramic substrate for assembly of semiconductor devices. In the present invention silver thick film metallisation on ceramic substrate is about five times cheaper as compared to Pd-Ag or Pt-Ag thickfilm materials Subsequent electroplating of copper and nickel is also a cheap process. Therefore, overall the present invention is about four times cheaper than the existing process. Hence considering the large demand of metallised ceramic substrates for assembly of semiconductor devices, utilisation of a new low cost metallisation will be very useful for assembly of semiconductor devices.
Still another object of the present invention is to provide much higher leaching resistance as compared with standard thick film metallisation with Sn/Pb solder, thus the present invention obviates the drawbacks of the prior art as state above.
Accordingly the present invention provides a process for the fabrication of improved metallised ceramic substrate useful for assembly of semiconductor devices which comprises (i) preparing silver metal film on a ceramic substrate by conventional methods, (ii) electroplating the ceramic substrate having silver metal film obtained in step
(i), with copper in a standard electroplating bath to get copper plated ceramic substrate, (iii) cleaning and electroplating the above said copper plated ceramic substrate obtained in step (ii) with nickel in a standard electroplating bath, cleaning the said plated ceramic substrate followed by drying the metallized ceramic substrate by known methods.
In an embodiment of the present invention the desired silver thick film pattern is formed by using a known method of thick film process such as screen printing, drying and firing techniques.
In another embodiment of the present invention copper & nickel is electroplated by using known means such as pin point contact jig method in the standard plating baths.
The present invention provides a process for the fabrication of improved metallised substrate useful for assembly of semiconductor device^, which comprises, preparing known film metallisation such as silver on ceramic substrate by conventional methods, electroplating the silver metallisation with fcopper in a standard conventional electroplating bath to grow a desired plating thickness, cleaing it in distilled water, then electroplating the above with nickel in a-standard conventional electroplating bath to grow a plating thickness, cleaning the above in distilled water, then drying in an oven.
In the process of the present invention the detailed steps are as follows:
1. Silver thickfilm paste is printed on ceramic substrate by screen printing technique
to get the wet print thickness of 35-40µm.
2. The printed pattern of silver is dried at 125.° - 150.°C for 10-15 minutes in an
oven
3. The dried pattern of silver is fired at 750.°-850.°C peak firing temperature for 10-
15 minutes in conveyor belt furnace.
4. Metallised ceramic substrate thus obtained through steps 1 to 3 is electroplated
with copper using standard copper plating bath. The plating thickness of 0.3-0.5
µm is build-up.
5. The substrate obtained in step 4 is cleaned in distilled water.
6. Cleaned ceramic substrate obtained in step 5 is further electroplated with nickel
using standard nickel plating bath. The plating thickness of 0.3-0.5µm is build up.
7. Cleaning of nickel plated ceramic substrate as obtained in step 6 is performed in
distilled water.
8. Drying of the cleaned ceramic substrate obtained in step 7 is done in an oven at
100.M 10.°C for 10-15 minutes.
Silver has very low leaching resistance with Sn/Pb(60:40) solder due to its chemical affinity. Leaching resistance of Ag is increased by adding Pd or Pt. Nickel or copper has high leaching resistance with Sn/Pb(60:40) solder as compared to Pd-Ag or Pt-Ag. Therefore in the present invention nickel metallisation improves the leaching resistance with Sn/Pb solder as compared to Pd-Ag or Pt-Ag thick film metallisation on ceramics substrate. The copper is used as an adhesive layer between Ag & nickel.
The unique combination of Ag-Cu-Ni has been used for preparing the metallized ceramic substrate. Ag film is used an adhesive conductive layer between the ceramic substrate and the Cu film. Nickel plating over copper protects copper from oxidation and provides favourable environment for copper-nickel interaction resulting in better adherence.
The present invention not only improves the leaching resistance with Sn/Pb solder but also makes the metallisation cost effective as compared to Pd-Ag or Pt-Ag metallisation on ceramic substrates where high current densities are to be used.
The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example: 1
The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 35µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 750°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. Example:2
The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 35µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 850°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a
standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. Example: 3
The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 40µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 750°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a

standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven. Example: 4
The desired silver thickfilm pattern is fabricated on ceramic substrate by screen printing, drying & firing processes. Wet print thickness of silver is 40µm. Drying is done at 150°C for 15 minutes in an oven. Firing of dried silver is done in a conveyor belt furnace at peak firing temperature of 850°C for 10 minutes. Now copper film of about 0.5 µm is electroplated on silver metallisation at current density of 50 mA/cm2 for 15 seconds in a standard copper plating bath. After cleaning in distilled water, nickel is electroplated of about 0.5 µm thick at current density of 50mA/cm2 for 15 seconds in a standard nickel plating bath. After this, metallized ceramic is cleaned in distilled water & then dried at 150°C for 10 minutes in an oven.
The main advantages of the process of the present invention are as follows:
1. About four times cheaper than Pt-Ag or Pd-Ag metallisation.
2. Rare earth materials not required.
3. Higher leaching resistance with Sn/Pb solder as compared to Pd-Ag or Pt-Ag
materials.

We Claim:
1. A process for the fabrication of improved metallised ceramic substrate useful
for assembly of semiconductor devices, which comprises: .
(i) characterised in that preparing silver metal film on herein described a ceramic substrate by conventional

methods;
(ii) electroplating the ceramic substrate having silver metal film obtained in stepi) with copper in a standard electroplating bath to get copper plated ceramic substratet herein described,
(iii) cleaning and electroplating the above said copper plated ceramic substrate
obtained in step ii)with nickel as herein described in a standard electroplating bath,cleaning the

said plated ceramic substrate followed by drying the metallised ceramic substrate by known methods.
2. A process as claimed in claim 1, wherein the silver metal thin metal film on
ceramic substrate is formed by using known methods of thick film process
such as screen printing, drying and filtring.
3. A process as claimed in claim 1, wherein the electroplating of copper and
nickel is done by using known methods such as standard plating bath with pin
point contact jig.
4. A process for the fabrication of improved metallised substrate useful for
assembly of semiconductor devices, substantially as herein described with
reference to the examples.

Documents:

160-del-2000-claims.pdf

160-del-2000-correspondence-others.pdf

160-del-2000-correspondence-po.pdf

160-del-2000-description (complete).pdf

160-del-2000-form-1.pdf

160-del-2000-form-19.pdf

160-del-2000-form-2.pdf

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Patent Number

213221

Indian Patent Application Number

160/DEL/2000

PG Journal Number

01/2008

Publication Date

04-Jan-2008

Grant Date

24-Dec-2007

Date of Filing

25-Feb-2000

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	YOGENDRA KUMAR JAIN	CENTRAL ELECTRONIC ENGINEERING RESEARCH INSTITUTE, PILANI-333031, RAJASTHAN, INDIA.
2	HARISH CHANDRA PANDEY	CENTRAL ELECTRONIC ENGINEERING RESEARCH INSTITUTE, PILANI-333031, RAJASTHAN, INDIA.
3	SATISH KUMAR BHATNAGAR	CENTRAL ELECTRONIC ENGINEERING RESEARCH INSTITUTE, PILANI-333031, RAJASTHAN, INDIA.

PCT International Classification Number

H01L 39/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA