Process for etching workpieces

Details Process for etching workpieces Process for etching workpieces

1990-07-10

1991-12-31

Powell, William A.

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

134 10, 134 27, 134103, 156640, 156656, 1566591, 156666, 156345, B44C 122, C23F 102

Patent

active

050768859

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The invention refers to a process for etching workpieces containing copper, in particular copper laminated printed circuit boards, in which
a) The workpieces are subjected to a strong alkaline etching agent containing a copper tetramine complex and chloride ions, whereby the effective copper tetramine complex is decomposed to form an ineffective copper diamine complex
b) The etching agent is regenerated by the addition of ammonia ions, chloride ions, water and oxygen
c) After etching, the workpieces are washed with a washing liquid to remove any remaining etching agent
The invention furthermore refers to an etching system for executing this process, with:
a) An etching machine in which workpieces containing copper, in particular copper laminated printed circuit boards, are subjected to a strong alkaline etching agent containing a copper tetramine complex and chloride ions, whereby the effective copper tetramine complex is decomposed to form an ineffective copper diamine complex
b) A regeneration system in which the etching agent is prepared for regeneration with oxygen by the addition of ammonia ions, chloride ions and water
c) At least one washing device following the etching machine, in which any remaining etching agent is removed from the workpieces by a washing liquid.
Such a process or such an etching system respectively is described in the DE-PS 24 34 305. In this etching system several washing devices are provided in the form of a cascade. They all use water as the washing liquid. This water passes through the various washing devices in the cascade in the direction opposite to the direction of movement of the workpieces, so that the last washing device when viewed in the direction of movement contains the cleanest washing liquid.
In practice the following has become apparent:
During operation of the existing etching system the workpieces processed in the etching machine carry the etching agent, which contains a relatively high concentration of copper ions, into the first washing device in the washing cascade. If this first washing device was operated in the neutral area then the copper located in the area containing the etching agent would be precipitated as copper hydroxide and would collect as sludge in the sump of the first washing device. This would lead to incorrect operation both of the pumps and the jets in this washing device.
In the existing etching system it is also necessary to maintain the washing liquid in the first washing device at a strong alkaline level, at a pH value close to 10, through the addition of ammonia. Under these conditions no copper hydroxide is precipitated from the etching agent carried into the washing device. However, it is then no longer possible to process workpieces in this etching system in cases where a material which is released by alkaline solutions is used as the etching resist. Such etching resist materials which are removed by alkaline solutions would be released from the substrate in the washing device.
The objective of the invention involved here is to provide a process of the type stated at the outset in which also those workpieces can be treated which are coated with an etching resist which is soluble in an alkaline solution.
This task is solved by the invention in that:
d) Directly after the etching process the workpieces are washed with a mainly neutral solution of a regeneration salt containing the necessary ammonia ions and chloride ions
e) After use, the initial solution is added as a washing liquid for regenerating the etching agent, whereby ammonia is also added for adjusting the pH value.
The invention is based upon the fact that a neutral washing liquid can be used without the risk of precipitation of copper hydroxide if this solution is a neutral solution of the regeneration salt. Apparently this allows the high concentration of salt in the initial solution. The initial solution is thus used twice--once as the washing liquid for the washing process directly following the etching process and once in its actual function for regener

REFERENCES:
patent: 4058431 (1977-11-01), Haas
patent: 4741798 (1988-05-01), Haas

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