Wednesday, August 3, 2011

Electroless Copper

Electroless copper is a coating process of copper with no electrical involved on this coating method. Electroless has been applied for coating to metal and non metal materials, but operator often exposed to formaldehyde and difficult to remove waste stream of this process, so they often seek other alternative of better process. The deficiency of this process is as follows:

  • Use of formaldehyde as reducing agent.
  • The process is unstable, requiring stabilizing additives to avoid copper precipitation.
  • Many complex agents are non Environmental friendly, such as EDTA, are used.
  • The large number of process and rinse tanks causes high water consumption.

There are four basic process of copper electroless; cleaning, activation, acceleration and deposition. Only micro etch, that is associated with sulfuric dip, and anti tarnish baths are likely to be non proprietary chemistries. Usually all shop purchase a series of proprietary chemistries from single vendor that use for several process bath line.

Cleaning.
To cleaning segment begins with a cleaner conditioner to remove organics and condition the hole barrels for the subsequent uptake of catalyst, followed by microetch step. Cleaner conditioner mostly consist of common alkaline solutions.

Activation and Acceleration.
Activation process is to make the metal surface active to be coated, for this process usually use hydrochloric acid and possibly tin or sodium chloride. The activation bath itself consists of hydrochloric acid and possibly tin or sodium chloride.

Copper Deposition.
Electroless copper bath can divided into two types. Heavy deposition baths and light deposition bath. Heavy deposition bath will produce copper coating for about 75 to 125 micro inches and light deposition bath will produce about 20 to 40 micro inches.

On the light deposition process must be followed by electrolytic copper plating immediately. The main constituent of electroless copper chemistry are sodium hydroxide, formaldehyde, EDTA and copper salt.