Patent Publication Number: US-4319302-A

Title: Antistatic equipment employing positive and negative ion sources

Description:
BACKGROUND OF THE INVENTION 
     This application is a continuation-in-part of my prior application Ser. No. 80,272, filed Oct. 1, 1979. 
    
    
     This invention relates generally to antistatic treatment of electrically charged objects and more particularly concerns improvements in ion generation and dispensing apparatus for altering the static charge on work surfaces. 
     In manufacturing electrical circuit boards, it is found that static charges develop in the conductive circuitry. Such charges can and do at times injure sensitive electrical components on such boards, whereby expensive scrappings of the boards becomes necessary. Insofar, as I am aware, no way was known prior to the present invention to eliminate this problem. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide apparatus and method characterized as overcoming the above described problems as well as problems with the equipment or products where electrical neutralization is necessary. Basically, the apparatus of the invention comprises: 
     (a) first and second tip means aimed generally longitudinally forwardly, said first tip means spaced laterally from said second tip means, 
     (b) insulative structure extending about said tip means, 
     (c) and circuit means to supply high voltage of relatively positive polarity to the first tip means and high voltage of relatively negative polarity to the second tip means. 
     As will appear, the circuit means may include a source of alternating high voltage, rectifiers and capacitors in parallel branches to which the tips are respectively connected and isolation resistors, the rectifiers poled to product positive voltage at one tip during one-half cycle and negative voltage at the other tip during the other half cycle; and tips are located in parallel, spaced insulative tubes or ducts which are open ended, and a larger tube or duct receives the smaller tubes all in such manner that air flow through all tubes occurs to enhance the neutralizing effect; the spacing of the tips from the forward ends of the tubes is selected of adjusted to enhance ion projection and/or to vary relative positive and negative in production; and pivoted housing structure is provided for the tubes. Accordingly, the work such as circuit boards is alternately bathed in positive and negative ions sufficiently mixed to neutralize the work. 
     It is another object of the invention to provide a method of generating and dispersing ions for electrically neutralizing articles, and employing tips means as referred to, the method including the steps: 
     (a) supplying high voltage of relatively positive polarity to the first tip means during first time intervals to generate positive ions, and 
     (b) supplying high voltage of relatively negative polarity to the second tip means during second time intervals to generate negative ions, 
     (c) said first and second time intervals occurring in alternating sequence, and 
     (d) causing said ions to travel onto at least one of said articles. 
     Further, the articles may comprise circuit boards having electrical components which become statically neutralized; enhancement of neutralization is achieved by flowing gas such as air forwardly about the tips and toward the article or articles, and the positive and negative voltages are approximately equal in absolute value, for neutralization purposes. 
     The invention improves over the devices described in U.S. Pat. Nos. 3,308,344 to Smith et al, and 3,976,916 to Saurenman. 
     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following description and drawings in which: 
    
    
     DRAWING DESCRIPTION 
     FIG. 1 is a frontal view of apparatus incorporating the invention; 
     FIG. 2 is an enlarged vertical section on lines 2--2 of FIG. 1; 
     FIG. 3 is a circuit diagram; and 
     FIGS. 4 and 5 are plan views showing modifications. 
    
    
     DETAILED DESCRIPTION 
     In accordance with the invention, first and second tip means are provided, to be aimed generally longitudinally forwardly (see arrow 10 in FIG. 2). In the illustrated embodiment, the first and second tip means take the form of first and second tips 11a and 12a respectively at the forward ends of longitudinally elongated needles 11 and 12. The two needles, and their associated tips are laterally spaced apart so that ions of differing polarity may be delivered therefrom, in alternating sequence, with minimum interference. 
     Insulative structure extends about the tip means, and in the example shown takes the form of first and second generally parallel, forwardly elongated plastic tubes 13 and 14 respectively extending about the first and second tips 11a and 12a, as well as about needles 11 and 12. Note that the tips are spaced inwardly from the forward ends of the tubes, for protection and for minimizing mutual interference as respects ion delivery. An outer and larger diameter plastic tube 15 extends about the two smaller tubes, and is also open ended. A vertical strut 16 extends diametrically across the bore of the outer tube and is attached thereto at 17 and 18. A horizontal strap 19 is attached at 20 to the strut, and also to the tops of the two smaller tubes, to support them near the center of the larger tube. Strut 16 extends between the smaller tubes, as seen in FIG. 1. This construction facilitates optimum air flow forwardly through all the tubes, as described below. Insulative tubes 13, 14 and 15 may consist of polyvinyl chloride. 
     Means is also provided to supply flowing gas (such as air) to pass forwardly through the tubes 13-15, thereby to aid in transporting the charged ions, generated by the tips 11a and 12a, beyond the tubes and onto work such as circuit boards indicated at 21 in FIG. 3. Such means is shown in FIG. 2 to include a fan 22 supported and driven to rotate in outer tube 15 by an electric motor 23. The latter may be suitably supported at 24 by tube 15, to provide a very simple and effective construction in combination with all three tubes 13-15. The open-endedness of all the tubes facilitates air flow through and about tubes 13 and 14 to optimally maintain the flow of ions directed toward and onto the work. 
     Further as appears in FIGS. 1 and 2, structure is provided to pivotally support the outer tube 15 so that the latter and tubes 13 and 14 may pivot as a unit about an axis 124 generally normal to the longitudinal direction 10. As shown, such structure advantageously includes a housing 25 defining an interior zone 26 in which the tubes 13-15 are located, the housing having a front wall 27 with a through opening 28 in alignment with the outer tube 15 and parallel tubes 13 and 14. Support means including trunnions 29 on the housing side walls and bearings 130 on a bracket 131 pivotally support the housing to pivot about horizontal axis 124, whereby the ion generally tips 11a and 12a and associated tubes 13-15 may be selectively aimed at work such as the circuit boards 21. As will be seen, ions of alternately negative and positive polarity may thus be caused to flow onto the circuit board, or boards, to electrically neutralize same. 
     Further in accordance with the invention, circuit means is provided to supply high voltage of relatively positive polarity to one tip, and high voltage of relatively negative polarity, to the other tip. An example of such circuit means is shown in FIG. 3 to include a source 30 of alternating voltage. That source may comprise an AC, 115 volt, 60 cycle source, and a transformer 31 having a primary coil 31a connected across that source. High voltage derived from the secondary coil 31b is applied through the circuitry 32 to the two tips 11a and 12a. Such circuitry includes parallel branches 33 and 34 connected in series with coil 31b, a first rectifier (as for example a diode) 35 connected in one branch 33, and a second rectifier (as for example a reversed) diode 36 connected in the other branch 34. The first branch 33 also includes first capacitance 37 connected in series with rectifier 35, and the second branch includes second capacitance 38 connected in series with the second rectifier 36. The first tip 11a and needle 11 are connected to the first branch at 39 between the rectifier 35 and capacitor 37; and the second tip 12a and needle 12 are connected to the second branch at 40 between rectifier 36 and capacitor 38. The circuit means also includes isolation resistances 41 and 42 respectively connected between point 39 and needle 11, and between point 40 and needle 12. As an example, when about 3800 VAC is developed across secondary coil 31b, about 6,000 volts positive is developed during one-half cycle at tip 11a, and about 6,000 volts negative is developed during the other half cycle at tip 12a, with circuit elements having values as follows: 
     
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value or identification                                                   
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diodes                                                                    
35      High voltage rectifier 10,000 PRV, 25 miliamps                    
36      High voltage rectifier 10,000 PRV, 25 miliamps                    
capacitors                                                                
37      .01 MFD.                                                          
38      .01 MFD.                                                          
resistance                                                                
41      22 meg 1/2 Watt                                                   
42      22 meg 1/2 Watt or vary to equalize voltage output                
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     It is found the invention enables electrical neutralization of the components of circuit boards, to eliminate or prevent build-up of static charges that would harm, or interfere with operation of circuit board components. 
     The circuitry 30, 31 and 32 of FIG. 3 is conveniently contained within zone 50 in the housing. An on-off switch 41 is located on the front wall 27 of the housing; and an on-off indicator light 42 is also located on that front wall. Motor 23 may be electrically connected across the AC source, as shown in FIG. 3. Diodes 35 and 36 are oppositely poled, as shown. 
     In the plan view of FIG. 4, the tubes 113 and 114 correspond to tubes 13 and 14 above, and large diameter tube 115 corresponds to large diameter tube 15, above. Needles 111 and 112 in the tubes project axially forwardly, and they have tips 111a and 112a. The tubes have forward ends 113a and 114a which are circular and spaced forwardly of the tips. In this regard, the tips are located sufficiently rearwardly of the tube forward ends as to optimize, or nearly optimize ion projection forwardly from the needles. Forward air streams through tubes are indicated at 109. A tube mounting strut 116 corresponds to strut 16. Sources of positive and negative voltage appear at 106 and 107, and are connected to the needles as shown. They may take the form of the means described in FIG. 3. Tubes 113, 114 and 115 may consist of insulative plastic material. 
     More specifically, a line 140 extending from the first tip 111a to forward edge 113a defines an angle α  with the axis 141 of the first tube 113. Similarly, a line 142 extending from the second tip 112a to forward edge 114a defines an angle β with the axis 143 of the second tube. Each of the angles α and β is less than about 45° and preferably is between about 30° and 40° for best results in terms of ion production. 
     Further, the needles and their tips are supported within the tubes, as for example by supports 150 and 151. One or both of the latter may allow adjustment of the supported needle or needles in an axial direction, to vary the spacing of the tip or tips from the forward end or ends of the tubes. Accordingly, for example, if the amount of negative ions produced by tip 111a is too great in relation to the amount of positive ions produced by tip 112a, tip 111a may be adjustably displaced forwardly to decrease its negative ion production. Conversely, tip 112a may be adjustably displaced forwardly to decrease positive ion production if that result is desired. Thus, the relative intensities of positive and negative ion production or dispersal by the tips have an adjustably selected or selectable relationship. 
     FIG. 5 shows that a similar or the same result can be achieved by adjusting the position of the tube forwardmost ends relative to the tips, which have fixed positions. Note sleeves 113&#39; and 114&#39; on the tubes, defining edges 113a and 114a. The sleeves are slidably adjustable on the tubes, as shown.