Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Reexamination Certificate
2002-10-18
2004-11-16
Nicolas, Wesley A. (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
C205S133000, C205S148000, C205S125000, C205S131000, C204S22400M, C204S198000
Reexamination Certificate
active
06818115
ABSTRACT:
BACKGROUND OF THE INVENTION
For the printed circuit boards of existing and future high technology products, the problems of plating voids and poor plating distribution are becoming increasingly difficult due to the increase in aspect ratio. Printed circuit boards keep getting thicker and holes keep getting smaller. When a plating void is detected in a printed circuit board, the board is rejected because of an open circuit.
Additionally, poor plating distribution can cause “dogbone” effects or, even worse, rejection of the board because of the fact that the minimum required thickness cannot be achieved inside of the (micro) via holes.
The present electrolytic plating invention seeks to overcome or minimize these kinds of problems.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an electrolytic plating system in which the vibrator is mounted on a free, movable part of the flight bar. The vibrator is not mounted on one of the massive (rigid) parts of the line. In prior art systems, a significant loss of vibration energy occurs through absorption by the massive parts on which the vibrator is mounted. The mounting of the present invention allows all of the energy to be carried forward to the printed circuit boards in the plating line. Additionally, the energy transfer is more even compared to prior art systems.
The manner in which the vibration energy is carried to the product is more efficient and results in a dramatic reduction in plating voids.
The present invention also provides improved flow of the electrolyte through the holes of the printed circuit boards, which generates an improved throwing power of plating inside of the through holes and blind vias. The improved flow is accomplished by an increase in laminar flow along the printed circuit boards.
The laminar flow along the printed circuit boards is increased on one side of the panel and generates an underpressure in the through hole. Because of this underpressure, electrolyte is drawn from the other side of the panel through the hole to generate a better plating distribution. By bath movement, the laminar flow is moved from one side of the panel to the other side. Accordingly, the underpressure is also moved from one side to the other side and the eletrolyte is then drawn through the hole in the opposite direction.
The increased flow is generated first by an eductor system that is placed under specially designed floating shields. The resulting eductor system works like a venturi, so the volume of electrolyte that is pumped through the eductor is increased 5 times when leaving the eductor. Second, the floating shield itself also creates a venturi flow because of it special design. The electrolyte exiting this floating shield has much higher and better laminar flow as compared to standard plating designs.
REFERENCES:
patent: 4696729 (1987-09-01), Santini
patent: 2001/0045360 (2001-11-01), Omasa
patent: 2003/0010625 (2003-01-01), Gramarossa et al.
van Kempen Hein
Weber Daniel J.
Dunlap Codding & Rogers P.C.
Nicolas Wesley A.
Viasystems Group, Inc.
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