Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1998-05-28
2001-05-01
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S844000, C029S845000
Reexamination Certificate
active
06223431
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the general subject of electronic circuit assemblies and processes used in the fabrication thereof. More particularly, the present invention relates to a method for providing an electrical ground connection between a printed circuit board and a metallic substrate.
BACKGROUND OF THE INVENTION
Many types of electronic devices, such as electronic ballasts for gas discharge lamps, require an electrical ground connection between a printed circuit board and a metallic base or substrate. Typically, the metallic base or substrate is composed of a material such as galvanized steel or aluminum that is incapable of forming a reliable direct solder connection with the printed circuit board.
One of the most common arrangements for providing a ground connection employs a simple mounting screw that is driven through a hole in the printed circuit board and into a corresponding hole in the base. The printed circuit board typically includes one or more ground jumper wires for making contact with a bottom surface of the head of the screw. This approach has several disadvantages. First, it is extremely difficult to automate. Secondly, due to the amount of mechanical stress it places on the printed circuit board, it is ill-suited for assemblies with very thin circuit boards, such as flex-circuits.
An alternative approach employs flexible “tab” structures on the base. After the printed circuit board is placed onto the base, the tabs are bent or twisted into tight friction contact with the ground jumper wires. This approach is known to have significant problems, such as inadvertent fracturing of the ground jumper wires. Like the mounting screw approach, this approach is also difficult to automate and is not well-suited for assemblies that include very thin printed circuit boards.
A third approach employs a metallic ground plug having surfaces that are receptive to solder. The metallic ground plug is fabricated, and a hole is formed in the base or substrate. The prefabricated ground plug is then inserted into the hole in the substrate, and solder is deposited into a hole on the printed circuit board and onto the ground plug to form an electrical connection between the ground plug and a ground trace on the printed circuit board. This approach has the advantage of being particularly well-suited for thin printed circuit boards, since it places little physical stress on the circuit board itself.
Existing “ground plug” approaches have a number of disadvantages, however. First, since the ground plug is fabricated in an independent process, insertion of the prefabricated ground plug into the hole in the substrate usually requires complex “pick-and-place” machinery. Secondly, since a significant amount of time may elapse between the processes of fabricating the ground plug, forming the hole in the substrate, and inserting the ground plug into the hole in the substrate, significant deposition of environmental impurities and/or oxidation may occur on the contact surfaces of the ground plug and the hole in the substrate. Consequently, the quality and reliability of the resulting electrical connection between the ground plug and substrate may be unfavorably affected.
What is needed therefore is a method for providing a reliable, high quality electrical ground connection between a printed circuit board and a metallic substrate that is well-suited for high-volume automated assembly with thin printed circuit boards, that is efficient with regard to process steps and process time, and that may be implemented without a need for expensive, complicated machinery. Such a method would represent a significant advance over the prior art.
REFERENCES:
patent: 3397453 (1968-08-01), Gwyn, Jr.
patent: 4110904 (1978-09-01), Johnson
patent: 5275970 (1994-01-01), Itoh et al.
patent: 5295299 (1994-03-01), Takahashi
patent: 5661088 (1997-08-01), Tessier et al.
patent: 2734461 (1979-02-01), None
patent: 646314 (1950-11-01), None
Doikas Peter
Geis David
Merwin Jeffrey D.
Bessone Carlo S.
Osram Sylvania Inc.
Trinh Minh
Young Lee
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