Cleaning and liquid contact with solids – Apparatus – With movable means to cause fluid motion
Reexamination Certificate
2001-06-15
2003-09-30
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
With movable means to cause fluid motion
C134S111000, C134S198000, C134S199000, C134S902000, C134S067000, C095S241000, C095S243000, C095S260000, C438S906000
Reexamination Certificate
active
06626196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrangement for the degassing small high-aspect ratio drilled holes or vias which are present in panels prior to wet chemical processing of the panels. Moreover, more particularly, the present invention is directed to the degassing of vias which are formed in printed circuit boards prior to the copper plating of the vias in order to remove any air or gas bubbles from the vias tending to inhibit the reliable plating thereof. In addition to the foregoing, the invention is also directed to a method for implementing the degassing of the small high-aspect ratio drilled holes which are provided in the panels or printed circuit boards prior to the wet chemical processing of the latter, such as the copper plating of the surface areas of the drilled holes or vias.
In the technology directed to the manufacture of electronic packages, especially modules comprising semiconductor devices and printed circuit boards, the modules are frequently provided with considerable numbers of vias or holes, ranging up to 2000 to 3000 in numbers, which are frequently required to have their surfaces copper plated, to produce PTH's (plated through holes). In attempting to implement the copper plating of such small diameter holes or vias, which normally each possess diameters within a range of about 0.001 to 0.002 inches at high aspect ratios of 6-8:1, difficulties are at times encountered in being able to satisfactorily completely wet or plate the inside of the holes due to the occluding presence of air or gas bubbles. Consequently, in the event that even if a single hole is not adequately copper-plated, then the entire apertured module comprising of the printed circuit board must be discarded, and resultingly leading to considerable economic losses. With respect to the foregoing, it is of extreme importance to be able to provide an adequate wetting of the holes or vias which are present in the printed circuit boards or modules prior to the effectuating of an electroless copper plating pre-cleaning process step, in order to ensure that all of the interior surfaces of the vias or holes are adequately prepared for the electroless copper plating process. This, in effect, would then prevent any potential internal separation phenomena to occur due to a lack of adequate pre-cleaning of the inner planes of the copper material which being applied to the surfaces areas the vias or holes, inasmuch as, if any air or air bubbles were to remain in the holes during the electroless plating process step, the copper plating would fail to fully deposit on the via or hole surfaces, thereby resulting in internal plating separation causing an open circuit and potential failure of the electronic product being equipped with the specific printed circuit board or module.
Basically, in order to implement the removal of gasses or air bubbles from a liquid bath environment which is employed in the processing of articles, for example, such as modules comprising printed circuit boards incorporating a multiplicity of holes or vias which are to be copper plated in an electroless copper plating process, it is imperative that a suitable degassing step is implemented. This may be preferably carried out through the utilization of an ultrasonic prewetting in a deionized water or other suitable liquid bath preceding cleaning for the electroless plating process, thereby enabling all of the vias or holes to be degassed; in effect, having air removed and the vias or holes filled with liquid; thereby allowing subsequent process cleansing solutions to easily flow into the respective holes or vias in order to facilitate the electroless copper plating process.
In order to implement the comprehensive degassing of the liquids; in effect, the removal of any occluded air or gas bubbles, specific physical conditions must be satisfactorily met. Firstly, the liquid in the bath which is utilized in order to initially prewet the modules or panels containing the vias or small holes, and with the bath being constituted of either deionized water or other suitable liquids, must be fully degassed, preferably through the application of ultrasonic energy or any other process in which normal levels of dissolved air entrained in the liquid within the tank and/or entering the tank must be depleted and removed therefrom. Secondly, the apertured modular panels or printed circuit boards within the tank must be exposed to ultrasonic energy in order to promote the displacement and/or the dissolution of air or gas bubbles from the small holes or vias. In essence, failure to employ both of the foregoing conditions would result in the process being ineffective for adequately prewetting all of the small-diameter high-aspect ratio holes or vias, although potentially for small diameter holes or vias with small aspect ratios, agitation in a fully degassed tank (without ultrasonic energy) may be sufficient to dissolve and eliminate all of the air bubbles which are present in the bath or liquid.
2. Discussion of the Prior Art
Although numerous processes have been developed in various technologies which are directed to the degassing of liquids utilized in the cleaning of articles of the most diverse types, these have not been found to be fully satisfactorily, although complex systems utilize ultrasonic vibrators and energy generators in order to degass the liquids.
Sasaki et al. U.S. Pat. No. 5,810,037 discloses an ultrasonic treatment apparatus for articles immersed in a cleaning liquid which are subjected to a cavitation phenomenon caused by an ultrasonic vibrator. The cleaning liquid is then conveyed to a degassing vessel and thereafter re-circulated to the cleaning vessel subsequent to gas being dissolved in the degassing vessel and the bubbles separated out and maintained in a vacuum.
Philips, et al. U.S. Pat. No. 6,210,470 discloses an ultrasonic gas separator wherein gas bubbles in a moving fluid is collected in a chamber arranged adjacent a conduit conveying the fluid. An ultrasonic transducer is adapted to cooperate with a reflector to create a particular ultrasonic wave pattern so as to remove gas bubbles and enable these to be collected exteriorly of the flow of the fluid.
Long U.S. Pat. No. 6,071,385 discloses a racking fixture for electrochemical processing wherein gases trapped in components are adapted to be removed through suitable ultrasonic applications.
Chung, et al. U.S. Pat. No. 6,042,635 discloses a method for wetting a filter element, and wherein a vibration device will cause pressurized liquid to have entrained air bubbles in a filter element to be separated therein from a liquid and exhausted from the system.
Ohmi et al. U.S. Pat. No. 6,039,814 discloses a cleaning method employing a degassed cleaning liquid with applied ultrasonics, whereby particular ultrasonic frequencies are utilized to remove air bubbles through the intermediary of water vapor from a degassing device containing a liquid.
Kraus Jr. et al. U.S. Pat. No. 5,834,625 discloses an apparatus and a method for debubbling a discrete sample of a liquid through the intermediary of an ultrasonic device which causes air or gas bubbles to be exhausted from essentially high viscous liquids through the formation of ultrasonic waves.
Nicholls, et al. U.S. Pat. No. 5,653,860 discloses a system for the ultrasonic removal of air bubbles from the surface of an electroplated article, and wherein the mechanical vibrations produced by the ultrasonic transducer results in vibrations removing air bubbles and gases from the article surfaces.
Hackett U.S. Pat. No. 5,368,364 discloses a system for removing bubbles from small cavities consisting of blind via holes in a semiconductor wafer by immersing the article and cavities in a liquid medium. The bubbles are enabled to flow freely to enable the processing within the cavities to commence in a suitable degassed liquid.
Shibano, U.S. Pat. Nos. 4,907,611 and 4,865,060 each disclose ultrasonic washing apparatuses whereby air bubbles are removed from a liquid washing specific a
Downes, Jr. Francis J.
Galasco Raymond T.
Lehman Lawrence P.
Topa Robert D.
Gulakowski Randy
International Busines Machines Corporation
Kornakov M.
Samodovitz, Esq. Arthur J.
Scully Scott Murphy & Presser
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