Metal fusion bonding – Process of disassembling bonded surfaces – per se
Reexamination Certificate
2001-10-04
2003-04-22
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Process of disassembling bonded surfaces, per se
C228S191000, C228S019000, C228S020100, C228S006200
Reexamination Certificate
active
06550669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates heating nozzles integral with a vacuum pickup tube for soldering and unsoldering electronic components to and from printed circuit boards (PCBs), and more particularly to such nozzle-pickup and placement devices for very small electronic components.
2. Background Information
Repair of components mounted onto PCBs typically requires solder reflow and removal of the defective components, followed by precision placement and solder reflow for installation of replacement components. The electronic industry has developed a myriad of different electronic and electrical components that has made repair more difficult. Generally the components, both active and passive, have become much smaller, and the packaging of very large scale integration (LSI) chips has made many solder joints relatively inaccessible for repair.
Many LSI chip packages have solder joints beneath large square or rectangular chip packages, e.g. Ball Grid Arrays (BGA) and J leaded devices. Other LSI packages include large chip packages with peripheral gull wing leads.
In response, the repair industry has developed some specialized soldering/desoldering devices for these LSI packages. For example, U.S. Pat. No. 5,419481, to Lasto et al. describes a device specifically adapted for the BGA packages, and U.S. Pat. No. 5,579,979, to Kurpiela describes a device specifically adapted for the Gull Wing package. Both of these inventions feature square nozzles with a center suction device and means to direct hot air to the solder connections on the underneath for a BGA and J leaded packages and to the periphery for the Gull Wing. The U.S. Pat. No. 5,579,979 invention includes an additional contact heating element.
Both of these patented inventions have fixed mechanical designs for the locations of the heated areas and the vacuum pickup since these are designs pointed at specific packages. Inherently these devices are not effective when used to repair small components or components of different shapes and contours. For example, the above referenced patented devices have a fixed mechanical relationship between the suction cup end of the pickup tube and the shroud surrounding the tube that defines the heated locations. Obviously, if the suction cup is not close enough or touching the package it will not hold the package for removal, or if the suction cup is moved closer, the hot airflow will be blocked from heating the very small component solder connections.
Other repair devices use vacuum pickup tubes of {fraction (3/16)} and ¼ inch outside diameters which can be effectively used for larger components, but when applied to smaller components the larger tubes interfere with adjacent components limiting the effective use of these devices.
However, along with the development of the larger chip packages there has been a parallel development of smaller active and passive devices, often single electronic devices, where the size has become very small, e.g. 0.010″×0.020″ in cross section. Moreover, the components themselves often have different shapes, and are densely populated on PCBs. The above described heating and pickup devices are not effective repairing these smaller components or larger, differently shaped components, and repair of such components remains a continuing problem.
SUMMARY OF THE INVENTION
The present invention addresses the limitations of the above described devices while providing other advantages as described below.
A soldering/desoldering and pickup/placement device for repairing components is described with a nozzle with an entrance through which heated gas enters and a second end shaped to focus and vent the heated gas onto the solder connections of components to be replaced. The nozzle is attached, and a preferred embodiment, to a plate that is positioned above the defective component and a hollow center syringe needle that is arranged to move vertically within the second end of the nozzle. A vacuum source is connected to a distal end of the hollow center and the proximate end terminates with the hollow center opening arranged to intimately contact the defective component to be repaired. Heated air, nitrogen, or helium is directed by the nozzle onto the soldered joints of the defective component, and, when the solder reflows, the vacuum operates to secure the component to be repaired to the proximate end of the syringe needle for removal. In a preferred embodiment, the syringe needle with the attached defective component may be raised through the nozzle or, in another preferred embodiment, the entire nozzle and defective component may be raised so that the defective component may be discarded. A replacement component can be attached to the proximate needle end and repositioned at the same location where the defective component was removed. The heated air then will melt the solder that reflows joining the new component to the PCB.
A mechanical system vertically moves the nozzle and syringe needle, but may also move the syringe needle with respect to the nozzle. The mechanism is arranged to position the proximate end of the syringe needle about centered in the nozzle opening and allows the needle end to move from a position before to a position beyond the second end of the nozzle. There may also be a “break-away” puff of gas pressure to break the contact between the syringe needle and the component. A vacuum sensor may also be used to detect when the component is in contact with the syringe needle. Force sensors are well known in the art and detects when the end of the syringe needle contacts the defective component on the PCB or when picking up the replacement component.
In some assemblies, the syringe needle is encompassed by a co-axial tube. Here the outer shape of the tube and the inner shape of the nozzle are arranged to focus the heated gas onto the soldered connections of the defective component.
In another embodiment, the nozzle is fixed to a mounting plate assembly that may be positioned with the nozzle above the PCB defective component. Here the nozzle opening is large enough to accommodate the defective component fitting through the nozzle's opening. In one preferred embodiment, the nozzle and the syringe needle and co-axial tube are connected as one assembly. In this case the PCB is roughly located by hand below the nozzle assembly, and, when the syringe needle and co-axial tube are vertically moved with respect to the PCB and the nozzle assembly, a floating washer between the nozzle and mounting plate assembly automatically seals the tube and the syringe needle with respect to the nozzle assembly when they are repositioned. The seal forces the heated gas to flow through the nozzle tip.
In another preferred embodiment, the second end of the nozzle has a transverse dimension of less than 0.25 inches, and where the syringe needle outside dimension is less than 0.01 to 0.05 inches.
REFERENCES:
patent: 4274576 (1981-06-01), Shariff
patent: 4295596 (1981-10-01), Doten et al.
patent: 4752025 (1988-06-01), Stach et al.
patent: 4767047 (1988-08-01), Todd et al.
patent: 4914513 (1990-04-01), Spigarelli et al.
patent: 5251266 (1993-10-01), Spigarelli et al.
patent: 5419481 (1995-05-01), Lasto et al.
patent: 5579979 (1996-12-01), Kurpiela
patent: 5598965 (1997-02-01), Scheu
patent: 5785237 (1998-07-01), Lasto et al.
patent: 6043458 (2000-03-01), Fortune
O'Neil John
Walz Mark J.
Cesari and McKenna LLP
Elve M. Alexandra
Genrad, Inc.
Paul, Esq. Edwin H.
Tran Len
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