MXPA96006645A - Disruptive distance from circuit board - Google Patents

Abstract

The present invention relates to a disruptive distance of printed circuit board characterized by: a plurality of surface mounting devices placed on a surface of a printed circuit board, said surface mounting devices being separated from each other by a distance predetermined and cooperate to form a disruptive distance between them to discharge energies excessively

Description

DISRUPTIVE DISTANCE OF PRINTED CIRCUIT BOARD Field of the invention This invention relates to disruptive distances for protecting electrical circuits and especially at disruptive distances associated with a printed circuit board.

BACKGROUND OF THE INVENTION A disruptive distance intended to protect a circuit from the damaging effects of a high voltage wave by providing a bypass path for the wave before the circuit. The disruptive distance determines the bridge within the circuit for the momentary oscillation or wave discharge and determines the specific potential of such discharge. The location of the desired discharge is determined by the circuit involved, the source of such momentary oscillations and the preferred discharge path. The differential voltage necessary for the discharge is determined by the separation between the two conductive points comprising the spark gap. The discharge potential required is established by determining the sources of momentary or wave oscillation and the desired level of protection, which, for example, can be determined by regulatory requirements Prior disruptive distance technologies include discrete disruptive distances (Figures 1A and 1B) or the most cost-effective disruptive printed circuit board (PCB) distances (Figures 2A and 2B). Disruptive distances are generally constructed with light-emitting diodes that end within a glass, ceramic or plastic body on respective conductive surfaces with a fixed spacing between them. There are two categories of discrete disruptive distances, one sealed with a controlled atmosphere as shown in Figure 1A and the other, not sealed at normal atmosphere as shown in Figure 1B. Both types require a sizable amount of mounting space (eg, on a PCB) and both require physical location and careful orientation during assembly due to separation and other mechanical considerations. Discrete disruptive distances, while tending to be more expensive than printed circuit breaker distances, are somehow more durable and typically exhibit a more controlled discharge potential. The construction of printed circuit boards (PCBs) comprising one or more layers of a rigid or flexible insulator (e.g. fiberglass or plastic) and one or more layers of a conductive material (e.g. conductive ink) where several circuit components are electrically connected by conductive "traces".

As shown in Figures 2A and 2B, a PCB spark gap uses conductive traces (eg, copper) from the PCB that are positioned at a fixed distance from one another and provides a controlled point for unloading the momentary or potential oscillation not wanted. The PCB disruptive distance may have a perforated slot in the board laminate between the nodes, depending on the voltage and energy potentials involved. Disruptive PCB distances are relatively easy to manufacture accurately and repetitively since there are few variables introduced through physical tolerance and placement (compared to discrete spark gap). Disruptive PVCB distances provide predictable operation and are relatively cheap, costing perhaps little more than the current cost of the board material. A disadvantage of the disruptive spacing of printed circuit board is evident with repeated discharges, catastrophic events or constant long-term discharge. In those situations, the surface of the printed circuit board and the copper sheet degrade rapidly with respect to the separation between the conductive nodes due to the vaporization of the sheet. Since distance separation increases the voltage potential required for an arc through space, space increases and the location of the arc can be less controlled. the board laminate can withstand the damage during unloading catastrophic and long-term due to the intense heat that can result from such an event. There are several useful techniques to improve PCB spark gap. For example, the problems associated with sheet vaporization can be delayed by increasing the thickness of the sheet or, in a type of PCB slot of disruptive distance, by increasing the length of the slot (while retaining the same width) . Unfortunately, the area of the PCB required to implement a disruptive distance increases with this technique and vaporization will eventually degrade performance. Another technique is the use of multiple distances separated in series so that the energy of the disruption is dissipated over two distances (Figure 2B). This technique also decreases the degradation of the leaf at the expense of the PCB area. It is therefore noted that it is desirable to provide a spark gap that eliminates or reduces the above-described limitations of the disruptive distances of the prior art.

Brief Description of the Invention This invention relates to an improvement of the above-described PCB spark gap type using surface mount devices (SMDs) which are facing one another and welded to respective PCB conductors of the spark gap BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described with reference to the accompanying drawings in which: Figures 1 and 2, previously referred to, show the disruptive distances of the type known in the prior art; Figure 3A shows the plan and side view of a preferred embodiment of the invention; Figure 3B shows the plan view and side view of an alternative embodiment of the invention; Figure 4 shows an isometric view of one embodiment of the invention; Figure 5 shows a plan and side view of the preferred embodiment of the invention shown in Figure 3A; and Figure 6 shows the plan and side view of another alternate embodiment of the invention. The similar reference designation in the different Figures refers to the same or similar elements.

Detailed description Referring to Figures 3A and 5, a PCB disruptive distance mode is illustrated according to the teachings of the invention. The PCB includes a non-conductive or laminated substrate 100 and a conductive layer that includes the conductors 200 and 300 formed on the laminate 100. conductors 200 and 300 are separated and electrically isolated from one another to form a spark gap 400. Spark gap 400 is enhanced by the addition of surface mount devices (SMDs) 210 and 310 that have been welded to conductors 200 and 300 , respectively. The distance 400 as illustrated includes a slot perforated through the laminate 100. However, it is not necessary for the practice of the invention to perforate such a slot. The SMD 210 is electrically and mechanically connected to the conductor 200 by means of the welding fillet 220 and the welding fillet 221 at conductive ends 230 and 231. The SMD is electrically and mechanically connected to the conductor 300 by means of the welding fillet 320 and the welding fillet 321 at conductive ends 230 and 231. The actual distance 400 through which electrical energy in the form of a disruption will move is initially formed by the space between conductors 200 and 300. Those conductors may experience some vaporization so that they wear to where the distance between the SMD 210 and the SMD 310 is formed. The amount of conductor between an SMD and the edge of the conductor is determined by the positioning tolerance of the SMD process used and the formation of the fillets. of welding. A first electrode of the spark gap 400 is formed by the conductor 200 and the weld fillet 220 and a second electrode is formed by the conductor 300 and the weld fillet 320. A disruption will jump from one electrode to the other when the differential voltage potential between the two electrodes exceeds the level dependent on the width of the distance and the dielectric strength of the material (for example, air in the case of a groove, or fiberglass). ). The conductive sheet between the SMD 210 or 310 can be formed to provide a defined point so that the welding fillets 220 and 320 flow within this shape. In this way the location of the bow and consequently the level of differential voltage required to induce the arching can be controlled more closely. This defined point promotes the discharge at the desired potential and location, in contrast to a rounded or wide discharge surface which will be less controlled. Considering only the first electrode, the electrical energy presented to the electrode due to the arc jump will be dissipated by the conductor 200, the welding fillet 220 and the conducting end 230 of the SM D 210. In addition, the heat generated (among other factors) by The I2R losses within the conductive materials of the electrode will be transferred to any adjacent materials, such as the SMD 210 and the laminate 100. In the disruptive distance of the prior art of Figure 2B, the electrical and thermal energies would be dissipated only by Copper and laminate, resulting in conductor wear and laminating, as previously described By using surface mounting devices and their associated welding fillets and Conductor ends, the mass available to absorb the heat from the copper is increased and the damage is reduced for the copper and the adjacent laminate. In addition, the larger cross-sectional area provided by the solder fillets and conductive ends directly reduces I2R losses by decreasing < resistance to current flow during an arc jump, thereby reducing the amount of heat generated. The invention can be practiced, as illustrated in the drawings, with or without the "shorting" of the SMD 210 and the SMD 310 by the conductors 200 and 300 respectively. However, additional copper under the SMDs provides additional protection by reducing the electrical resistance (ie, lower I2R losses) and increasing the thermal mass (ie, absorbing more heat without damage). Additional increases in thermal mass can be made by using different solder compounds. For example, a particular solder compound can be selected because of its characteristic high specific heat. A particular solder compound can also be selected due to a particular flow or curing characteristic, whereby an unusually thick solder joint can be formed. The SMDs used can be welded to the copper layers of a PCB using standard techniques and tolerances. For example, the methods of wave or reflow, the techniques of vapor phase and infrared In addition, the type of current component of the SMD used is not critical when the device is "short-circuited" as described above. When the device is not "short-circuited", the selection of the component is more important and a low-impedance component (for example, a bridge-type SMD) is an appropriate selection. As a practical matter, it has been found that SMD resistors tend to be mechanically stronger than SMD capacitors and are therefore more desirable, although either can be used. In a similar way, the tolerance of the selected device is not critical. As such, the electrically rejected parts can still be used if they retain the appropriate mechanical characteristics (i.e., they are not cracked, etc.). furthermore, SMDs do not need to be specifically stored for use in disruptive distances and SMDs ordered for other purposes can be used. The invention can also be practiced using the configuration of Figure 4, where two opposing SMDs are used to form the disruptive distance 400. The variations of the arrangement of Figure 4 are shown in Figures 3A and 3B. Figure 3A shows a first pair 210A, B of SMDs mounted on the first conductor 200 as opposed to a second pair 310Á.B of SMDs mounted on the second conductor 300, with the spark gap 400 comprising the two pairs of opposite SMDs, this configuration provides some redundancy where there are two surfaces defined for arc jump. Through the provision of two such surfaces the durability of the spark gap increases since any significant degradation in the defined surfaces of a set of opposing SMDs will eventually result in bowing between the other set of opposing SMDs. Figure 3B shows a further improvement of the arrangement shown in Figure A. A third pair 510A, B of SMDs mounted on a third conductor 500 between the first 210A.B and the second 310A, B pairs of SMDs mounted, forming a second disruptive distance 400B. This arrangement allows a division of the arc jump energy between the two distances 400A and 400B, thereby reducing the stresses on the individual elements comprising the disruptive distances. For example, assuming identical arc jump voltages, the individual spark gap in the arrangement of Figure 3A will necessarily be wider than either of the two spark gap in the arrangement of Figure 3B and the dissipated thermal and electrical energies will be dissipated by fewer components in the layout of Figure 3A. Therefore, the arrangement of Figure 3B allows a greater energy distance than the arrangement of Figure 3A without increasing the degradation of the associated components. The invention can also be practiced using the configuration of Figure 6, where a first SMD 210A and, optionally, a second SMD 210B are mounted on the first conductor 200 opposite a second conductor 300.

Disruptive distance 400 comprises the distance between the first conductor, including the conductive surfaces of one or more SMDs mounted thereto and, the second conductor. The mode is improved over the prior art by providing increased protection from arc-induced damage to one side of the spark gap. When compared to previous PCB disruptive distances, the cost increases will be minimal, essentially consisting of the cost of two or more SMDs and their placement on the PCB. In addition, the use of SMDs instead of the discrete spark gap of Figure 1A takes advantage of the benefits of surface mounting techniques (eg precise and repeatable component placement, etc.). the SMD placement must be selected so that the combination of the worst case of mechanical tolerance and positioning errors of the selected placement / welding process will ensure that there will always be some amount of conductor not covered by the component at the edge of the distance. The purpose of this placement is to guarantee the welding connection and a defined point for the initial discharge start. A disruptive distance can be constructed using either SMD components 805 or 1206. For example, tests conducted on one embodiment of the invention as shown in Figure 3A having end-to-end positioning accuracy of the SMD pair of approximately 5 000 and free space from side to side (central line to central line) of approximately 100 thousand have provided good results. The guidelines of the placement process require 200 mils of copper beyond the end of an SMD, although this distance may be decreased depending on, for example, the level of protection sought. Due to the factors of the assembly procedure (for example component welding) the centerline free space from side to side must adhere to 90 thousand from center line to center line for SMD size 805 and 100 thousand from center line to line central for the SMD of size 1206. The end free space required to obtain a welding fillet of 5 thousand also provides adequate electrical and mechanical connection. The experiments include the momentary oscillations and waves executed on the arrangement of Figure 3A with the previous physical direction being executed with very satisfactory results. The conducted test consisted of more than 20 waves. 6KV and 0.5uf using the SMDS of connection bridge types. It was found that the driver had virtually no degradation. Similar experiments were performed on the prior art arrangement of Figure 2A resulting in significant degradation of the copper. It has been shown that the spark gap of the invention is useful as a continuous discharge or momentary oscillation device. It will be evident to those with experience in the technique, that although the invention has been described in terms of examples specific, modifications and changes can be made to the described embodiments without departing from the essence of the invention. It is therefore understood that the claims are intended to cover all modifications arising from the treaty and previous examples.

Claims (3)

1. A disruptable printed circuit board spacing characterized by: a plurality (210, 310) of surface mounting devices positioned on a surface (200, 300) of a printed circuit board (100); said surface mounting devices are separated from one another by a predetermined distance (400) and cooperate to form a disruptive distance between them to discharge excessively high energies.

2. A disruptive distance characterized by: one or more (210, 310) surface mounting devices placed on a first surface (200); the first surface (200) and the devices separated from a second surface (300) by a predetermined distance (400) and cooperating with the second surface to form between them a distance susceptible to electrical arcing.

3. An improved PCB spark gap characterized by: a plurality of conductive elements positioned on the non-conductive surface; the conductive elements are separated from one another by a predetermined distance and cooperate to form a distance between them susceptible to electrical arcing; the conducting elements being comprised of surface mounting devices.