CA1297206C - Electrostatic discharge protection for a printed circuit board - Google Patents

Electrostatic discharge protection for a printed circuit board

Info

Publication number
CA1297206C
CA1297206C CA 609934 CA609934A CA1297206C CA 1297206 C CA1297206 C CA 1297206C CA 609934 CA609934 CA 609934 CA 609934 A CA609934 A CA 609934A CA 1297206 C CA1297206 C CA 1297206C
Authority
CA
Grant status
Grant
Patent type
Prior art keywords
printed circuit
circuit board
conductor path
approximately
plurality
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA 609934
Other languages
French (fr)
Inventor
Ronald Charles Robinson
Ronald Gordon Field
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nortel Networks Ltd
Original Assignee
Nortel Networks Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Grant date

Links

Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00Printed circuits
    • H05K1/02Details
    • H05K1/0213Electrical arrangements not otherwise provided for
    • H05K1/0254High voltage adaptations; Electrical insulation details; Overvoltage or electrostatic discharge protection ; Arrangements for regulating voltages or for using plural voltages
    • H05K1/0257Overvoltage protection
    • H05K1/026Spark gaps
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00Printed circuits
    • H05K1/02Details
    • H05K1/0213Electrical arrangements not otherwise provided for
    • H05K1/0254High voltage adaptations; Electrical insulation details; Overvoltage or electrostatic discharge protection ; Arrangements for regulating voltages or for using plural voltages
    • H05K1/0257Overvoltage protection
    • H05K1/0259Electrostatic discharge [ESD] protection
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00Screening of apparatus or components against electric or magnetic fields
    • H05K9/0067Devices for protecting against damage from electrostatic discharge
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09209Shape and layout details of conductors
    • H05K2201/0929Conductive planes
    • H05K2201/09354Ground conductor along edge of main surface

Abstract

ELECTROSTATIC DISCHARGE PROTECTION
FOR A PRINTED CIRCUIT BOARD

Abstract of the Disclosure A printed circuit path, which connects to a reference potential point, is provided along a portion, or more, of a printed circuit board (PCB) assembly which requires protection from electrostatic discharge (ESD). This printed circuit board path has a plurality of intentionally pointed protrusion integrally formed along its length and which point preferably toward the direction from which the electrostatic discharge is likely to approach the printed circuit board assembly; ie. through housing mating edges or housing surface openings. The pointed conductor path is locate closer to the ESD regions to concern than other circuit paths or component solder pads. The pointed protrusion preferentially attract electrostatic discharges to itself rather than allow the discharges to strike other paths or components further in on the PCB assembly, thereby avoiding component damage.

- i -

Description

~2~7~36 ELECTROSTP.TIC DISC~IARGE PROTECTION
FOPc A PRINTED CIRC~JIT BOARD

Field of the Invention The present invention relates generally to electrostatic discharge protection o~ electronic circuits.
More speci~ically, the present invention relates to electrostatic discharge protection for a print~d circuit bsard .

Back~round of the Invention In general, products containing printed circuit board ~PCB) assemblies must be protected from electrostatic discharge (ESD), which results, in some cases, from a userls natural electrostatic charge build up and consequ~nt discharge with touching of the product housing near an opPning. Electrostatic discharge protection is necessary to prevent, or to reduce, damage to the sensitive components on the PCB assembly. Damage resulting from an electrostatic discharge may range from a brief intermittent fault to a catastrophic fault wherein the circuit is no longer capable of functioning. Standard~ have been set by cha International EleckrotQchnical Commission to ensure proper protection against electrostatic discharge within electronic components.
one such standard requires that talephone sets be made to withstand an eleatrostatic discharge of 15,000 volts.
Typically this high-energy ESD is capable of destroying solid-state components in the telephone set.
Many methods of preventing electrostatic discharge from occurring exist in the prior art. One method is to position the telephone set's PCB perimeter ~ar enough in from the walls of the plastic housing of the telephone set so that a 15,000 volt electro~tatic discharge at the plastic housing ~annot jump from the plastic housing to the printed circuit ~5 board. Positioning a PCB in such a manner creates an air gap which by virtue of its length prevents an electrostatic discharge from arcing, up to a given k~lovolt level dependent on the size of th~ air gap. However, positionlng a PCB in d~

~9~21~
such a mann~r is not always possible as an objective in telephone design is to make the set as physically small as possible so that it takes up a minimum amount of space on a desk or table, and so that it is aesthetically pleasing.
Another method is to increase the ESD jump distance, and hence the ~SD voltage maximum, by having an internal plastic barricade molded as part of the plastic housing. This forces any ESD to arc a greater distancs than it otherwise would and khus prevents an axc from initiating at a given voltage level.
A further method is to put an insulated cover or sleeving over the region of concern which effectively increases the available arc jump distance.
Yet another method is to suspend, or otherwise locate, a wire, soldered to the electrostatic ground at one end, from the PC~ much like a lightening arrestor so that it will attract ESD at a particularly sensitlve location to prevent it from gettiny further into the circuitry.
While all of the abova methods are effective, they each can add to the complexity of the design of the telephone ~et or necessitate that the telephone set be made larger to accommodate the electrostatic discharge protection.
Information regarding the state of the prior art may be found in the following references- United States Patent 4,821,320 issued April 11, 1989 in the name o T.J.
Andert et al.; United States Patent 4,667,266 issued May 19, 1987 in the name of Masuo]ca et al.; United States Patent 4,532,419 i~sued July 30, 1985 in the name of M. Takeda; and United States Patent 4,531,176 issued July 23, 1985 in the name of R.L~ Beecher.

Summary of the Invention ~ he present invention provides a simple, effective, and inexpensive way of preventing electrostatic discharge from entering further into the circuitry while not increasing the size or complexity of a surrounding housing.
The present in~ntion uses a PCB conductor path, connected to a source of reference potential, which is placed near the ~9'7~

perimeter of the PCB adjacent to a probable housing mating edge breakdown region or at a region of the PCB near an opening in the housing, as for example where a button or the like may protrude. By so placing such a conductor path, the electrostatic discharge tends to jump to this path. To prevent the possibility of the ESD jumping past the perimeter conductor path, the conductor path is designed so as to have pointed, or nearly pointed, protrusions extending from the path at intermittent locations. The protrusions act like lighting rods by using the principle that an electrostatic discharge is more likely to jump to sharp objects than to smooth objects. In other words, the protrusions attract the ESD, thereby preventing the ESD from striking elsewhere on the PCB.
Stated in other terms the present invention is a method of reducing electrostatic discharge damage to a printed circuit board, the method comprising the steps of:
providing at least one conductor path connected to a source of reference potential, the at least one conductor path placed alony at least one portion of at least one edge of the printed circuit board; and, providing a plurality of approximately pointed protrusions along the length of the at least one conductor path, each of said protrusions being an integral part oE said at least one conductor path and having a base approximately equal to the width of said at least one conductor path and an apex approximately half of the width of said at least one conductor path from said base; wherein each of said plurality of approximately pointed protrusions has its apex near said at least one edge of said printed circuit board and wherein each of said plurality of approximately pointed protrusi.ons is nearer to said at least one edge than any other conductor on said p-rinted circuit board.
Stated in yet other terms the present invention is a printed circuit board, the printed circuit board being formed from a dielectric substrate and having thereon a plurality of conductor paths for interconnecting electrical 72~6 components thereon, the printed circuit board comprising:
at least one conductor path for connection to a source of reference potential, for providing protection against electrostatic discharge,the at least one conductor path placed along at least one portion of at least one edge of the printed circuit board; the at least one conductor path having formed therewith a plurality of approximately pointed protrusions along the length of the at least one conductor path, each of said protrusions being an integral part of said at least one conductor path and having a base approximately equal to the width of said at least one conductor path and an apex approximately half of the width of said at least one conductor path from said base; wherein each of said plurality of approximately pointed protrusions has its apex near said at least one edge of said printed circuit board and wherein each of said plurality of approximately pointed protrusions is nearer to said at least one edge than any other conductor on said printed :. 3a ~29~ 6 Brief Description o~ the Drawings The invention will be readily understood by the following description o~ a preferred embodiment, by way of example, in conjunction with the accompanying diagrammatic drawings, in which:
Figure 1 is a top plan view of a printed circuit board incorporating the present invention:
Figure 2 is a partial top plan view of an electrostatic discharge conductor path according to the present invention.

Detailed Description o~ the Invention Figure 1 illustrates a printed circuit board 20 having a plurality of conductor paths 14. Conductor paths 14 ]5 are provided to interconnect electrical circuitry (not shown) affixed to the PCB 20 via lands 16. According to the present invention, placed along a portion of the perimeter of the PCB
20 is an electrostatic discharge conductor path 10 which is connected to a source of reference potential ~not shown).
The conduator path 10 is placed along the perimeter of the RCB 20 so as to aat as a direct path for any electrostatic discharge which may occur around the parting line of a plastic housing encasing the PCB 20. The conductor path 10 is not covered or coated with insulating solder resist thereby facilitating a conductive path for an electrostatic discharge. In practice, the conduator path 10 need only be placed along the edge, or edges, of the PCB 20 nearest the region o~ the plastic housing that will result in an electrostatic discharg~ breakdown, thereby reducing the area needed to accommodate the conduator path 10 and consequently leaving more room for other conductor paths 14 on the PCB
20.
To ensure that an electrostatic discharge will not jump over the conductor path 10, pointed, or nearly pointed, protrusions 12 (further illustrated in Figure 2) are plaeed along the length of the conductor path 10. ~he apexes of the protrusions 12 are placed towards the edge or edges of the PCB 20 and extend beyond any other conductor paths 14 or ~g7~

lands 16 that may appear on the edges of the PCB 20. The protrusions 12 pxovide a sharp edge which attracts an electrostatic discharge onto conductor path 10.
It can be noted that the protrusions 12 may b~
regularly or irregularly spaced along the length of conductor path 10. The determination as to the location of the protrusions 12 will depend on the amount of protection reguired at a particular location on PCB 20.
The protrusions need not be specifically shaped as shown in the Figures; they could be rectangular protrusions, or regular and/or irragular pointed configurations protruding along the length of the at least one conductor path. The distinguishing ~eature o~ the protrusion is its sharp or nearly-sharp points pref~rably pointing towards the direction from which the ESD might enter the PCB, as for example through the mating edges of the housing pieces. The size of the protrusions are in general controlled by the amount of available space on the PCB and the acceptable closeness of them to the ESD entry regions.
In a preferred em~odiment, the width of the conductor path 10 is approximately 0.02 inches. Each o~ the protrusions 12 has a base of approximately 0.02 inches and an apex approximately 0.01 inches from the conductor path 10.
The present invention provides a simple yet relatively effective method o~ reducing electrostatic discharge damage to components on a printed circuit board.
Numerous other modifications, variations, and adaptations may be made to the particular embodiments of the invention described above without departing from the scope of the claims.

Claims (6)

1. A method of reducing electrostatic discharge damage to a printed circuit board said method comprising the steps of:
providing at least one conductor path connected to a source of reference potential, said at least one conductor path placed along at least one portion of at least one edge of said printed circuit board; and, providing a plurality of approximately pointed protrusions along the length of said at least one conductor path, each of said protrusions being an integral part of said at least one conductor path and having a base approximately equal to the width of said at least one conductor path and an apex approximately half of the width of said at least one conductor path from said base;
wherein each of said plurality of approximately pointed protrusions has its apex near said at least one edge of said printed circuit board and wherein each of said plurality of approximately pointed protrusions is nearer to said at least one edge than any other conductor on said printed circuit board.
2. A method of reducing electrostatic discharge damage to a printed circuit board as claimed in claim 1 wherein said plurality of approximately pointed protrusions are approximately equidistantly spaced.
3. A printed circuit board, said printed circuit board being formed from a dielectric substrate and having thereon a plurality of conductor paths for interconnecting electrical components thereon, said printed circuit board comprising:
at least one conductor path for connection to a source of reference potential, for providing protection against electrostatic discharge, said at least one conductor path placed along at least one portion of at least one edge of said printed circuit board;
said at least one conductor path having formed therewith a plurality of approximately pointed protrusions along the length of said at least one conductor path, each of said protrusions being an integral part of said at least one conductor path and having a base approximately equal to the width of said at least one conductor path and an apex approximately half of the width of said at least one conductor path from said base;
wherein each of said plurality of approximately pointed protrusions has its apex near said at least one edge of said printed circuit board and wherein each of said plurality of approximately pointed protrusions is nearer to said at least one edge than any other conductor on said printed circuit board.
4. A printed circuit board as claimed in claim 3 wherein said plurality of protrusions are approximately equidistantly spaced.
5. A printed circuit board as claimed in claim 3 wherein said plurality of approximately pointed protrusions are placed at locations along said conductor path where electrostatic discharge will occur.
6. A printed circuit board, said printed circuit board being formed from a dielectric substrate and having thereon a plurality of conductor paths for interconnecting electrical components thereon, said printed circuit board comprising:
at least one conductor path for connection to a source of reference potential, for providing protection against electrostatic discharge, said at least one conductor path placed along at least one portion of at least one edge of said printed circuit board;

said at least one conductor path having formed therewith a plurality of approximately pointed protrusions along the length of said at least one conductor path, the protrusions being integrally formed therewith;
wherein said at least one conductor path is approximately 0.02 inches in width and each of said approximately pointed protrusions has a base of approximately of 0.02 inches and an apex approximately 0.01 inches from said conductor path;
wherein each of said plurality of approximately pointed protrusions has its apex near said at least one edge of said printed circuit board and wherein each of said plurality of approximately pointed protrusions is nearer to said at least one edge than any other conductor on said printed circuit board.
CA 609934 1989-08-30 1989-08-30 Electrostatic discharge protection for a printed circuit board Expired - Fee Related CA1297206C (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA 609934 CA1297206C (en) 1989-08-30 1989-08-30 Electrostatic discharge protection for a printed circuit board

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA 609934 CA1297206C (en) 1989-08-30 1989-08-30 Electrostatic discharge protection for a printed circuit board

Publications (1)

Publication Number Publication Date
CA1297206C true CA1297206C (en) 1992-03-10

Family

ID=4140529

Family Applications (1)

Application Number Title Priority Date Filing Date
CA 609934 Expired - Fee Related CA1297206C (en) 1989-08-30 1989-08-30 Electrostatic discharge protection for a printed circuit board

Country Status (1)

Country Link
CA (1) CA1297206C (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1478214A2 (en) * 2003-05-16 2004-11-17 Hewlett-Packard Development Company, L.P. Method and apparatus for protecting a circuit assembly from electrostatic discharge
WO2005042095A1 (en) * 2003-10-02 2005-05-12 Medtronic, Inc. Circuit board construction for handheld programmer
DE102006061300A1 (en) * 2006-12-22 2008-06-26 Conti Temic Microelectronic Gmbh Electric printed circuit board for protecting microprocessors against electrostatic discharge has protective strip conductors on both sides of the printed circuit board running round on the outer edge of the printed circuit board
US7561921B2 (en) 2003-10-02 2009-07-14 Medtronic, Inc. Neurostimulator programmer with internal antenna
US7991479B2 (en) 2003-10-02 2011-08-02 Medtronic, Inc. Neurostimulator programmer with clothing attachable antenna
US9248298B2 (en) 2003-10-02 2016-02-02 Medtronic, Inc. Medical device programmer with selective disablement of display during telemetry

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1478214A2 (en) * 2003-05-16 2004-11-17 Hewlett-Packard Development Company, L.P. Method and apparatus for protecting a circuit assembly from electrostatic discharge
EP1478214A3 (en) * 2003-05-16 2005-07-27 Hewlett-Packard Development Company, L.P. Method and apparatus for protecting a circuit assembly from electrostatic discharge
WO2005042095A1 (en) * 2003-10-02 2005-05-12 Medtronic, Inc. Circuit board construction for handheld programmer
US7561921B2 (en) 2003-10-02 2009-07-14 Medtronic, Inc. Neurostimulator programmer with internal antenna
US7729766B2 (en) 2003-10-02 2010-06-01 Medtronic, Inc. Circuit board construction for handheld programmer
US7991479B2 (en) 2003-10-02 2011-08-02 Medtronic, Inc. Neurostimulator programmer with clothing attachable antenna
US9248299B2 (en) 2003-10-02 2016-02-02 Medtronic, Inc. Medical device programmer
US9248298B2 (en) 2003-10-02 2016-02-02 Medtronic, Inc. Medical device programmer with selective disablement of display during telemetry
DE102006061300A1 (en) * 2006-12-22 2008-06-26 Conti Temic Microelectronic Gmbh Electric printed circuit board for protecting microprocessors against electrostatic discharge has protective strip conductors on both sides of the printed circuit board running round on the outer edge of the printed circuit board

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