FIELD OF THE INVENTION
[001] The present invention generally relates to ESD protection of the electronic components in PCB. More particularly, the present invention relates to ESD protection of the electronic components in PCB with the help of a child component of High Mount Stop Lamp (HMSL). 5
BACKGROUND OF THE INVENTION
[002] Electrostatic discharge is the sudden flow of electricity/charge caused by a contact (either electrical short or dielectric breakdown) when differently-charged objects are brought close together. A certain materials become electrically charged after they come into frictional 10 contact with a different material (e.g. rubbing glass with fur, or a plastic comb through the hair).ESD becomes very critical parameter when dealing with components based on semiconductors like LED, transistors, diodes, resistors because of their low operating voltage range. 15
[003] ESD damages the electrical characteristics of a semiconductor device. The ESD event may cause metal melt, junction breakdown, oxide failure or terminal short. The device's circuitry may get damaged causing the device to stop functioning totally or at least 20 partially.
[004] Conventionally in PCBs protection is incorporated in the circuit design against sudden voltage surges by use of diodes. However, this method is effective only when the ESD occurs through terminals of 25
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PCB i.e. sudden discharge charge follows along the designed circuit only
[005] However in PCB, the ESD can be transferred through other surrounding components e.g., screw mounted nearby to PCB 5 electronic devices.
[006] For example in the Figure 1 PCB is mounted on housing (10) and screws (5) are used to mount the inner lens (20). These screws (5) are open to environment/human touch. During assembly of HMSL on 10 vehicle or while handling of HMSL, Electric Charge can get accumulated on the screw (5) and it can further get transferred to PCB components (15) though air gap (0.25 mm) between PCB (15) and screw (5) as shown in section A-A.
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[007] Air acts as an insulator; however when the Electrostatic potential (charge imbalance) exceeds the dielectric strength of air (3KV/mm) leading to ionization of air making it conductive & hence, sudden charge flow from screw to the surrounding electronic components leading to functional failure. 20
[008] The dielectric strength of material can be described as the maximum electric field that a pure material can withstand under ideal conditions without breaking down i.e. without experiencing failure of its insulating properties. 25
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[009] US8337061 relates to an illuminating device for vehicles, in particular a tail light, with a housing containing at least one light source, a support accommodating the light source, and a reflector, and with a diffusion lens for covering an opening of the housing. The reflector, which is provided with an electrically conductive 5 coating, is assigned charge dissipation path in such a manner that, when electrostatic charging of the reflector occurs, a dissipation current flows along the dissipation path to a connection to earth of the illuminating device.
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[0010] A charge dissipation means proposed in a preferred embodiment of the invention is a charge conductive path having a first end in direct contact with the reflector and a second end in direct contact with an earth connection of the support or a central plug connector arrangement of the illuminating device. Acontrolled charge 15 dissipation from an electrostatically charged reflector can be preferably achieved this way in bypassing electrically conductive surfaces of the support. Reflectors in the meaning of this invention are any and all plastic surfaces which are apt to get electrostatically charged and which are disposed in contact with or close to a light 20 source support.
[0011] US 20130001596 discloses a method and apparatus for providing electro-static discharge (ESD) protection to light emitting diode (LED) systems on printed circuit boards (PCBs). Protection is 25 provided by ESD diodes deposited on the PCBs configured as flexible substrates. Various deposition techniques are employed including
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chemical vapor deposition, pulsed laser deposition and atomic layer deposition.
[0012] Conventionally this problem is also avoided by use of copper track around hole of PCB which acts as an ESD ring (35) as 5 shown in figure 2. Electrostatic charge have tendency to find the shortest path/lowest resistance path for discharging. This copper ring (35) acts as nearest sink for the charge and this Copper ring (35) is further grounded in the PCB, thus protecting the components.
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[0013] Though this method is effective yet it adds up to the cost of the part. Further the introduction of another part in already complicated PCBs of these days it increases the complexity of the manufacturing process of the PCB.
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[0014] In all the above mentioned prior arts, none of the prior art teaches ESD protection of PCB using the mechanical structure.
OBJECTS OF THE INVENTION
[0015] It is therefore an object of the present invention to design a HMSL in such a way that the electric Charge accumulated on the 20 screw is not passed to the PCB thereby damaging its components.
Another object of the present invention is to design the HMSL in such a way that the screw and PCB are separated by the inner lens of HMSL.
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SUMMARY OF THE INVENTION
[0016] The invention is related to ESD protection of the electronic components in PCB by use of mechanical structure. In the present invention a child component of LED based High Mount Stop Lamp (typically inner lens) is used to provide protection against 5 damage due to Electrostatic Discharge.
[0017] Typically the HMSL is designed in such a way that the screw is used to mount the inner lens through the housing & screw is exposed to outside environment. Hence, the mounting screws can act 10 as carrier of electrostatic charge either through environment/human body etc.& the charge can be further discharged/transferred to the vicinity of PCB making electronic component susceptible to failure/malfunction due to electrical overstress.
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[0018] According to the present invention, the child component, inner lens made up of preferably polycarbonate, is extended further so as to cover entire screw. Since, Polycarbonate material has dielectric strength about 5 times that of air, it insulates the screw thereby avoiding the need of addition of ESD ring (35) (copper track) in the 20 PCB. Thus, reducing the cost and complexity of the PCB.
BRIEF DESCRIPTIONS OF THE ACCOMPANYING DRAWINGS
[0019] The above brief description, as well as further objects, features and advantages, of the present invention can be fully 25
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appreciated by reference to the following detailed description. These features of the present invention will become more apparent upon reference to the drawings, wherein:
Fig. 1: Existing assembly of HMSL
Fig. 2: A-A Section of Existing Assembly of HMSL 5
Fig. 3: ESD protection of PCB using copper ring
Fig. 4: Existing assembly of HMSL having Copper Ring
Fig. 5: Assembly of HMSL according to the present invention.
DETAIL DESCRIPTION OF THE INVENTION
[0020] The present invention will be described in detail below 10 with reference to an embodiment as shown in the drawing.
[0021] Electrostatic discharge is the sudden flow of electricity/charge caused by a contact (either electrical short or dielectric breakdown) when differently-charged objects are brought 15 close together. A certain materials become electrically charged after they come into frictional contact with a different material (e.g. rubbing glass with fur, or a plastic comb through the hair). ESD becomes very critical parameter when dealing with components based on semiconductors like LED, transistors, diodes, resistors because of their 20 low operating voltage range.
[0022] ESD damages the electrical characteristics of a semiconductor device. The ESD event may cause metal melt, junction
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breakdown, oxide failure or terminal short. The device's circuitry may get damaged causing the device to stop functioning totally or at least partially. In HMSL the screw is used to mount the inner lens through the housing & screw is exposed to outside environment. Hence, the mounting screws can act as carrier of electrostatic charge either 5 through environment/human body etc. & the charge can be further discharged/ transferred to the vicinity of PCB making electronic component susceptible to failure/malfunction due to electrical overstress.
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[0023] According to the present invention, the electric charge itself is not allowed to pass to the PCB (15) and its components by increasing the dielectric resistance between screw (5) and PCB (35) thus increasing the resistance to the charge flow between them.
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[0024] According to the present invention, one of the existing child components of HMSL i.e. Inner lens (20) is used to provide ESD protection as shown in Fig. 5.
[0025] Further, according to the present invention, the length of 20 the boss (30) of child component, pref. Inner lens (20), is increased.
[0026] Ref. to Fig. 5, the design of HMSL consists of a screw (5), which is inserted in housing (10) of a HMSL (100). A PCB (15) 25 is separated from said screw (5) with the help of extended legs of said
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boss (30) of said child component (20), pref. Inner lens, and an outer lens (25) is connected to said housing (10).
[0027] Said child component (20) could be inner lens, light guide, light bar or reflector which are made of insulating material 5 having dielectric constant within the range of 10-40 KV/mm selected from, but not limited to, Polycarbonate Acrylonitrile butadiene styrene (ABS), Nylon (PA6), Polybutylene Terephthalate (PBT), Polymethyl-Methacrylate (PMMA), Polypropylene (PP).
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[0028] The boss (30) is made to pass through the PCB (15) insulating the screw (5) from the PCB (15) and in turn protecting the PCB (15) from ESD generated through screw (5).
[0029] In the conventional design (Fig. 2), said screw (5) was 15 separated from said PCB (15) having an air gap of approx. 0.25 mm between them, however according to the present invention, said screw (5) and said PCB (15) are separated from each other by approx 1.8 mm of insulating material of said child component (20), preferable inner lens made of Polycarbonate. 20
[0030] Referring to the comparison between the convention HMSL design and the HMSL design according to the present invention, shown in Fig. 4 and Fig. 5, it can be seen that the boss (30) is passed through said PCB (15) resulting in the insulation of said PCB 25 (15) from said screw (5) and in turn protecting said PCB (15) from
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ESD through said screw (5) because the dielectric strength of an insulating material of said child component (20) such as Polycarbonate is higher than that of air.
[0031] Since the dielectric strength of Polycarbonate is approx. 5 5 times higher than that of air i.e. PC can withstand 5 times more electrostatic potential than air, it obviates the need of providing extra insulation resulting in the elimination of copper ring.
[0032] The level of ESD protection which can be achieved using 10 this invention depends on the dielectric constant of material selected and the thickness of the material.

WE CLAIM:
1. A High Mount Stop Light (HMSL) design for ESD protection of PCB, wherein
A child component (20) fastened to a housing (10) and a PCB 5 (15) using a fastening means (5);
Said child component (20) having extended legs of boss (30), passes through said PCB (15) in such a way that it insulates said fastening means (5) from said PCB (15) to produce said HMSL design for ESD protection of PCB. 10
2. The HMSL design as claimed in claim 1, wherein said child component (20) is selected from a group of inner lens, light guide, light bar or reflector.
3. The HMSL design as claimed in claim 1, wherein said child component (20) is manufactured from insulating material having dielectric constant within the range of 10-40 Kv/mm.
4. The HMSL design as claimed in claim 1, wherein said child 20 component is selected from Polycarbonate (PC), Acrylonitrile butadiene styrene (ABS), Nylon (PA6), Polybutylene Terephthalate (PBT), Polymethyl-Methacrylate (PMMA), Polypropylene (PP).
5. The HMSL design as claimed in claim 1, wherein said fastening
means is selected from screw, bolt or rivet made from
conductive material.