Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-03-21
2001-10-30
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S225000, C204S297060, C204S279000
Reexamination Certificate
active
06309517
ABSTRACT:
BACKGROUND OF INVENTION
This invention is a unique arrangement of a plating device for electroplating work pieces with metallic deposits. It is often desirable to process the work pieces using conveyorized equipment. When the work pieces are flat sheets or plates with through holes, such as printed circuit boards, they are often processed through operations in which solutions are forced through the holes. Examples of this include: drilling smear removal, drilling burr residue removal, applying materials to hole walls to make nonconductive hole walls conductive, stripping of metallic deposits from hole walls, and development of coatings out of holes.
The most commonly used conveyorized equipment for such applications has a horizontal roller conveyor on which the work pieces are placed. The work pieces are carried horizontally through processing chambers where solutions are pumped or sprayed onto the surfaces and into the through holes. Other less common processing equipment has a conveyor with vertical rollers. The vertical rollers are usually accompanied by horizontal guide wires or rails to keep the work pieces vertical while being transported through the processing chambers. Inside the processing chambers, solutions are pumped or sprayed onto the surfaces and into the through holes.
Up to this time, it has been common practice to process work pieces through several operations using conveyorized equipment to prepare them for plating of metallic deposits onto essentially the entire planar surface and the surfaces of the through holes. Even though conveyorized equipment is used for many manufacturing steps prior to electroplating, in order to perform the actual plating operation, the work pieces are usually removed from the conveyorized equipment, attached to electrically conductive racks, and electroplated in dip tanks. Even when conventional automated plating machines are used to transport the work pieces through the plating tanks for the electroplating operation, it is still necessary to unload work pieces from the conveyorized equipment and manually place them onto the rack of the automated plating machine. It is desirable to plate the work pieces as they are transported through the conveyorized equipment. Such in line plating, without removing the work pieces from the conveyorized equipment, would reduce processing time and labor.
Automatic plating machines originally designed for decorative or engineering electroplating which transport parts through dip tanks on carousels or programmed hoists have been used to successfully plate flat work pieces with through holes. However, this type of plating equipment is not well suited to other manufacturing operations where solutions must be sprayed or pumped through the holes in the work pieces. This is especially true when the diameter of the holes is small in relation to the thickness of the panels. For these non-plating operations, the work pieces are usually processed in conventional horizontal conveyorized equipment or vertical conveyorized equipment described above.
Automatic plating machines originally designed to electroplate wire or continuous strips of metal, such as reel to reel plating of electronic component lead frames, are not suitable for use with discreet flat work pieces such as printed circuit boards. Because wire and strips are continuous, they are easily electrified by applying an electric potential difference between convenient points along the work piece. However, flat panels are discreet work pieces rather than continuous strips. The electrification of discreet work pieces is not possible using wire or reel to reel plating machines.
Several conveyorized plating machines for printed circuits boards and other similar work pieces have been developed. Most such conveyorized machines are designed for plating a limited part of the planar surface of the work piece, such as contact tabs. The area on which the plated deposit is applied is usually limited to one or more edges of the panel. Examples of this type of machine are disclosed in U.S. Pat. No. 4,035,245, 4,186,062, and 4,377,461. Whereas these types of machines are well suited for plating the margins of flat work pieces, they are not suitable for plating the entire planar surfaces and the surface of through holes.
Several other plating machines designed to simultaneously plate essentially the entire planar surfaces and the surfaces of through holes of flat work pieces have been proposed. Examples of these include those disclosed in U.S. Pat. No. 4,385,967, 4,401,522, 4,755,271, 5,417,828, and 5,658,441. Whereas machines of these types can successfully plate essentially the entire planar surfaces and the surfaces of through holes of the work pieces, all of these machines have one or more specific problems as will be more fully explained hereinafter.
The apparatus disclosed in U.S. Pat. No. 4,385,967 issued to Brady et al transports the work pieces placed horizontally on a conveyor having horizontal rollers. Using this type of machine, work pieces may be processed through normal nonelectrified operations using conventional horizontal processing equipment mated to the plating apparatus. When work pieces reach the point in the manufacturing operations at which electroplating is required, one edge of each panel engages a series of electrified, driven contact wheels. The contact wheels transport the work pieces through the plating chamber and provide electrical connection to the work pieces. One or more of the electrified contact wheels is in electrical contact with the work piece during the entire time the work piece is in the plating chamber. Whereas this apparatus does allow the continuous processing of work pieces through conventional horizontal conveyorized equipment and through the disclosed apparatus without unloading and reloading, the contact wheels receive undesired electroplated deposits. Although the contact wheels are shielded from the electrolyte solution, they still accumulate electroplated deposit. These accumulated electroplated deposits interfere with electrical contact with the work pieces. When such buildup of electrodeposited metal occurs, the deposit must be removed from the contact wheels. Because of the location of the contact wheels, and because of the design of the wheel driving mechanism, removal of the contact wheels for cleaning is difficult and entails substantial time and labor. Additionally, the work pieces must be carefully positioned so that one edge of each panel is aligned properly to engage with the contact wheels. This need for alignment necessitates use of a repositioning mechanism immediately before the work pieces enter the contact wheel area. Otherwise, work pieces not repositioned immediately before entering the plating zone may not properly engage the electrified contact wheels. Furthermore, the supporting device that carries the edge of the work pieces opposite the contact wheels must be adjusted for each different width panel. All panels processed must have a common width or the machine must be taken out of service while the support device is adjusted for a new panel width. This limitation prevents continuous processing of mixtures of work pieces of significantly different widths. Taking the machine out of service for width adjustments dramatically limits it usefulness for many factories that process work pieces of differing widths. In addition, the contact wheels are offset outside the zone where the electrolyte makes continuous contact with the work pieces. This offset is required to allow space for the shielding to protect the contact wheels from making electrical contact with large volumes of the electrolyte. Such shielding is necessary to minimize electrodeposition of metal onto the contact wheels. However, as disclosed by Brady, the portion of the work piece which contacts the contact wheels, that lies between the contact wheels and the zone where the electrolyte washes over the work piece will not be plated. Thus, the work pieces may have no through holes that require plating in this unusually wide area. This res
Condra Richard Carroll
Johnson Richard Malcolm
Dwight Larry B.
Nicolas Wesley A.
Oliver Sales Company
Valentine Donald R.
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