Electroless Copper 4000 process

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Product Description
Electroless Copper 4000 is designed to give unsurpassed interconnect reliability for multilayer applications, as well as superior coverage on all PTH applications. It has been formulated to give a bright, smooth uniform copper deposit of 60 microinches in 30 minutes.

The bath exhibits exceptional stability and is designed to operate at elevated temperatures which, depending on factors such as tank configuration and loading, can in many cases eliminate volume growth.

Another important factor is that when the bath is cooled to room temperature, plating ceases, which cuts losses due to costly plate-out and reduces maintenance of the system.
Solution makup
Deionized Water Balance
Electro-Brite Copper 4000 M 12.00% by volume
Electro-Brite Copper 4000 A 2.20% by volume
Electro-Brite Copper 4000 B 1.80% by volume

Mixing Instructions:
  • Fill tank to 50% of final volume with deionized water.
  • With mixing, add the required amount of 4000 M.
  • Slowly add the required amount of 4000 A. Mix.
  • Slowly add the required amount of 4000 B. Mix.
  • Dilute to the final volume with deionized water and mix thoroughly.
Operating conditions
  Nominal Range
4000A 100% (2.0 g/L) 90 - 110% (1.8 - 2.2 g/L)
4000B 100% (7.5 g/L) 90 - 110% (6.75 - 8.25 g/L)
4000M 0.120 M 0.105 - 0.135 M
Formaldehyde 100% (4.5 g/L) 90 - 110% (4.0 - 5.0 g/L)
Temperature 49°C (120°F) 43 - 54°C (110 - 125°F)
Time 60 microinches (1.5 microns) in 30 minutes.
Recommended process cycle
  1. Cleaner/Conditioner ML-373
  2. Rinse
  3. 10% sulfuric acid dip (optional)
  4. Rinse
  5. Cu Prep III, or Cu Prep II
  6. Rinse
  7. Pre-Dip PD-472
  8. Catalyst C-473
  9. Rinse
  10. Rinse
  11. Accelerator (optional)
  12. Rinse
  13. Electroless Copper 4000
  14. Rinse
  15. 10% sulfuric acid dip
  16. Rinse
  17. Copper Inhibitor L.D. (optional)
  18. Rinse (optional)
  19. Dry
Bath operation and maintenance
Components

4000 A - Copper, formaldehyde: used for initial bath make-up and working replenishment
4000 B - Caustic: used for initial bath make-up and working replenishment
4000 C - Chelator: used for working replenishment
4000 M - Chelator: Used for initial bath make-up, and working replenishment based on depletion

Maintenance and replenishment can be based on square feet of work processed or by analytical control. (Procedures are included at the end of the data sheet.)

Replenishment based on workload

The following additions are based on a plating rate of 60 microinches of copper per 30 minutes. Replenishment should be made either continually or at regular intervals in order to maintain the bath components within range.

Surface Area 4000 A 4000 B 4000 C
1.0 ft2 13.4 ml 11.3 ml 5.7 ml
1.0 m2 144 ml 122 ml 61.1 ml


To maintain the solution level, remove a volume of bath equal to the volume of Electroless Copper 4000 A and Electroless Copper 4000 B to be added.

A precipitate will form when the Copper 4000 A is added to the bath. For this reason the concentrate should be added into the inlet of the recirculation system or to the weir overflow tank.

During the course of the day, extra formaldehyde may be needed beyond that which is available in the Copper 4000 A concentrate.

4000 M is not consumed in the deposition of copper, it is lost by drag-out only. Depending on working replenishment, it may be necessary to add 4000 M to maintain the proper operating concentration and should be analyzed daily, especially when the workload is heavy or when the bath has been transferred or diluted.

Replenishment via an automatic controller

If a controller is used to monitor copper and make adds, it should be set to the following ratio:

4000 A 4000 B 4000 C
1.0 0.9 0.4


Morning Replenishment

After a nightly or weekend shutdown, the formaldehyde and caustic concentrations will be lower than optimal.
Analyze the 4000 A concentration using the procedure included at the end of the data sheet and use the following chart to make the add. Do this before analyzing the caustic and formaldehyde concentrations.
Add the required amount of 4000 A. Remember to first bail out whatever volume is to be added to the bath.
After adding the required 4000 A volume, analyze the caustic and formaldehyde concentrations. To raise the caustic level, add 4000 B, and to raise the formaldehyde level, add formaldehyde.
4000 C is not replenished by hand each morning. It is generally only added through working replenishment.

To raise: by: add:
4000 A 10% (0.20 g/L) 8.3 ml/gal of 4000 A
4000 B 10% (0.75 g/L) 7.9 ml/gal of 4000 B
4000 M 0.01 M 37.9 ml/gal of 4000 M
Formaldehyde 10% (0.45 g/L) 4.7 ml/gal of Formaldehyde (37%)


Note: 4000 A contains formaldehyde. A 10% add to Copper 4000 A will result in a 10% increase in copper, a 10% increase in formaldehyde and a 5% loss in 4000 B. Therefore, an addition of 4000 B is required to maintain the caustic level whenever an addition of 4000 A is made.

Bath Life

Though it is difficult to predict the life of an electroless copper solution, the rise in specific gravity is an indication of when the solution is spent.
When the specific gravity reaches 1.12 at 24ºC (75°F), a decrease in bath performance can be expected. At this point, the bath should be diluted by 30% or changed entirely.
 
 


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