Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
2000-09-01
2003-05-06
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
C361S119000, C361S117000, C361S091100, C361S088000, C333S185000, C174S002000
Reexamination Certificate
active
06560087
DESCRIPTION:
FIG. 3A , read in connection with the corresponding view shown in FIG. 4 , is a cross sectional view of a metal shield of a filter in accordance with one embodiment of the present invention. The grounded metal shield 104 (or 105 as shown in FIG. 1 ) includes a slot 106 . The slot 106 includes a first section 106 A, providing intimate contact with bottom surface 100 b of circuit board 100 and with a portion of top surface 100 a of circuit board 100 .
Slot 106 further includes a second section 106 B defining a space between the top surface 100 a of circuit board 100 and shield 104 . A conductive trace 200 is positioned on top surface 100 a of circuit board 100 within second section 106 B of slot 106 . A space of dimension d is formed between the surface of conductive trace 200 and the top of slot 106 in the region of 106 B. The dimension d of the space relates to the dielectric constant of the material, or air, located within the space. If a voltage surge passes through the filter along conductive trace 200 , a spark is generated within the space, and the current is shunted to ground via the grounded metal shield 104 .
It is believed that a space having the dimension d of about 0.013 inches will spark at a voltage surge of about 1000 volts passing through the conductive trace. Accordingly, d should be selected within a range of about 0.010 to 0.020 inches to provide a 1000-2000V surge protection rating.
FIG. 3A also shows that the metal shield preferably includes a raised boss member 110 , which increases the effective thickness of the metal shield to more closely match the width of the shield-receiving slot 101 ( FIG. 1 ) cut through the circuit board 100 . It is difficult to cut a slot through the circuit board that matches the relatively small thickness of the metal shield.
The metal shield 104 is made from a conductive metal, such as tin plated steel, which is grounded to the housing of the filter. The circuit board 100 is made from an electrically insulating material, an example of which is glass-epoxy composite. The conductive trace 200 is made from a conductive material, an example of which is solder-covered copper.
FIG. 3B , read in connection with the corresponding view shown in FIG. 5 , is a cross sectional view of the metal shield of a filter in accordance with another embodiment of the present invention. The metal shield 104 (or 105 as shown in FIG. 1 ) includes a slot 206 . Slot 206 includes a first section 206 A, providing intimate contact with a portion of bottom surface 100 b of circuit board 100 and a portion of top surface 100 a of circuit board 100 .
Slot 206 also includes a second section 206 B defining a space between top surface 100 a of circuit board 100 and shield 104 . Slot 206 further includes a third section 206 C defining a space between bottom surface 100 b of circuit board 100 and shield 104 .
A conductive trace 200 is located on top surface 100 a of the circuit board 100 within the second section 206 B. A space of dimension d 2 is formed between the surface of the conductive trace 200 and slot 206 in the region of 206 B. An electrically conductive plated through-hole 201 passes from the top of conductive trace 200 , through circuit board 100 , and through a conductive contact pad 202 located on bottom surface 100 b of circuit board 100 . A space having the dimension d 3 is formed between the surface of conductive contact pad 202 and slot 206 in the region of 206 C.
The dimensions of the spaces d 2 and d 3 relate to the dielectric constant of the material, or air, located within the respective spaces. If a voltage surge passes through the filter along conductive trace 200 , a spark is generated within the space, and the current is shunted to ground via the grounded metal shield 104 . The through-hole 201 is plated with a conductive material, an example of which is copper.
It is believed that a space having the dimension d 2 (or d 3 ) of about 0.013 inches will spark at a voltage surge of about 1000 volts passing through the conductive trace. Accordingly, d 2 (or d 3 ) should be select
REFERENCES:
patent: 4451803 (1984-05-01), Holdsworth et al.
patent: 4485447 (1984-11-01), Ericsson
patent: 5150087 (1992-09-01), Yoshie et al.
patent: 5262754 (1993-11-01), Collins
patent: 5768084 (1998-06-01), Chaudhry et al.
Louise William
Maguire Joseph N.
Marland Dale W.
Zennamo, Jr. Joseph A.
Burr & Brown
Eagle Comtronics, Inc.
Rodriguez Isabel
Sircus Brian
LandOfFree
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