DE102005026404A1 - Printed circuit for protected ceramic component - Google Patents

Abstract

A printed circuit board comprising electronics components mounted on said board (12) including at least one ceramic component comprising first and second outer contacts having first and second conductive receptacles printed on said board, respectively Region (14A, 14B), said printed circuit board comprising means (18) for creating a thermal asymmetry between the two conductive receiving regions of the ceramic component to eliminate any risk of ignition of the printed circuit board. To avoid plate.

Description

Field of the invention

The The present invention relates to the field of ceramic mounting Components on a printed circuit, and in particular a printed circuit architecture, which in case of failure or breakdown of these ceramic components ensures protection against the risks of fire.

The Ceramic components, such as capacitors, which are on the printed circuits are subject to failures, which with different causes, such as a delamination, a thermal Shock or mechanical or electrical restrictions, which can bring a breakage of the ceramic component associated are. This break is of the kind that he has a short circuit of low impedance generated by increasing the local temperature at the component a flaming of the printed circuit, on which he is mounted, and in extreme cases a destruction of the Product in which the circuit and the various others can be produced by her carried components.

A classic solution This problem is with the ceramic component one Resistor in series, thereby limiting the produced Overall performance is possible. However, such a solution consuming due the implementation difficulty implied by them, as well due to the additional sizing the printed circuit that needs it. Further brings they have a significant limit on electromagnetic compatibility, for example due to high frequency filtering.

object and definition of the invention

The The present invention therefore has the object of the aforementioned inconveniences by proposing a printed circuit architecture, which is simple, that is without complementary implementation of components, and what any risk of ignition of this circuit in case of a Breaking the ceramic components mounted on this circuit reliable avoids.

These Targets are achieved through a printed circuit board, which includes electronic and / or passive components, which are based on this Plate are mounted, of which at least one ceramic component one first and a second outside contact comprising, which with a first and second conductive receiving area are connected, which are printed on this plate, characterized characterized in that it comprises a device for generating a thermal Asymmetry between said two conductive receiving areas of the Ceramic component includes, to avoid any risk of ignition of the mentioned to avoid printed circuit board.

By doing this particularly simple structure avoids the risk of ignition of the printed circuit board it prevents any destruction of the product containing them. According to a preferred embodiment includes this device for generating a thermal asymmetry a metallized surface huge extent which by means of thermal bridges with one of these conductive Recording areas are connected to one another thermally like an energy dissipation device to behave. This metallized surface of large scale is between 2 times and 10 times the area of this outer contact the ceramic component included.

According to one another embodiment includes this device for generating a thermal asymmetry an opening, which in this plate between this first and second conductive recording area realized directly under this ceramic component. Preferably there is this opening from a slot whose length is larger as the one of those conductive Reception Areas.

According to one more another embodiment includes this device for generating a thermal asymmetry immediately at the beginning of the other of said conductive recording areas a conductor track, which has a constriction zone to a To produce melting effect, in the case of heating the ceramic component a Cause interruption of this trace. advantageously, this narrowed track is connected to a metallized hole, traversing the board of the printed circuit therefore an additional Role as a thermal brake plays by restricting energy to these Conductor track is concentrated. This narrowed track extends preferably in a large scale to the metallized surface, which one of these conductive Recording areas surrounding, opposite direction.

The ceramic component may be a capacitor or component composed of high temperature dielectric materials is set, such as components based on BaTiO3, TiO2 or SrZrO3, not doped.

The Invention equally applies a method of protection a printed circuit board against overheating ceramic components mounted on this plate, and by means of fixing devices with those printed on this plate conductive Recording areas are connected, characterized in that a thermal asymmetry between these two conductive recording areas The ceramic component is made to withstand any risk of ignition to prevent this printed circuit board.

According to the considered embodiments This thermal asymmetry is generated by means of a large-scale metallized surface, which using thermal bridges with one of these conductive Recording areas is connected to thermally like a heat dissipation device too behave, or by a trace, which immediately before or at the beginning of the other of these conductive recording areas one Has constriction zone, or by means of a between this first and second conductive recording area directly below This ceramic component arranged opening, these generation modes can be combined with each other.

Short description of drawings

The Characteristics and advantages of the present invention crystallize to be better understood from the following description, which is in descriptive and not in a limiting way with reference to the attached drawings is made, in which:

the 1 to 3 explain the mounting of a ceramic component on a printed circuit according to various embodiments of the invention, and

the 4 the assembly of a ceramic component on a printed circuit according to the prior art explained.

Detailed description a preferred embodiment

The 4 discloses a double-sided conventional printed circuit architecture in which a ceramic component 10 on an upper side of an insulating circuit board 12 is mounted, which comprises conductors or tracks, including the conductive receiving areas 14A and 14B , by which they through their external contacts 10A and 10B is brought into electrical contact. This electrical contact is conventionally ensured by means of heat-fixing devices, for example by means of brazing or soldering / welding. In the illustrated example, which is not intended to be limiting, the ceramic component is, for example, a multilayer capacitor in CMS package.

in the Fall of a failure, such as an overvoltage in the ceramic component is the heat released by this element when the degradation temperature of the printed circuit board for more exceeded a few seconds This is a carbonization of this printed circuit board below of the ceramic component, which can become conductive by becoming conductive this lot (by creating a new passage way for the stream) causes a short circuit of this component, as the origin of a Ignition of the printed circuit (of course under Reservation of a minimum of oxygen).

Furthermore, according to the invention, and as is the preferred embodiment of 1 It is proposed to improve the thermal drainage under the ceramic component by creating a thermal asymmetry (of the order of 200 ° C.) between the two conductive receiving regions of the component. To do this, one of the conductive recording areas 14A , which is referred to as a cold zone, by means of thermal bridges 16 (advantageously four in number) with a metallized surface of large scale 18 which behaves thermally like a dissipation device, while the other is a conductive receiving region 14B , which is referred to as a warm zone, is largely reduced (typically the extent of external contact) so as not to dissipate but also does not behave like an antenna of electromagnetic radiation. By a large scale surface is meant a surface 2 to 10 times larger than that of the external contact of the ceramic component bonded to this hot zone.

The heat conduction obtained in this way can be further improved by the area 18 by means of metallized holes 20 connecting one side to the other are connected to a similar surface (not shown) on the other side of the printed circuit board.

In the second embodiment of the invention, according to 2 , is the printed circuit board 12 with one between the conductive recording areas 14A and 14B directly under the ceramic component incorporated opening 22 provided in order to eliminate the path, which in the case of carbonizing the printed scarf tung plate could take the electricity. In fact, this carbonization in a precise zone may cause the contact of other potentials around that zone to be in contact, thus causing a short circuit. In this way you can avoid any short circuit and interrupt the process of ignition. This configuration here has a direct effect on the effects of the breakdown and on the other hand has no influence on the electromagnetic compatibility, and is particularly easy to implement. The opening 22 may take the form of perforations (not shown), or better, a slot whose length is greater than that of the receiving areas, and whose width is the largest, which corresponds to the manufacturing conditions of the printed circuit board and the knowledge of the Phenomenon of failure of the ceramic component (which gives information regarding the currents and the times that occur in the periods of the out-of-control device) is compatible.

Another embodiment of the invention, which equally allows one to create a thermal asymmetry between the conductive receiving regions of the component to stop the phenomenon of the progression of the heat, advantageously just after its beginning, is in this 2 and in the 3 shown dotted. It consists in the conductor track at the hot zone immediately before or at the beginning of the recording area of the ceramic component, a constriction zone 24A . 24B having a role as a fuse (in the case of over-current), or as a breaker by mechanically breaking the conductor in the case of rapidly increasing the temperature.

The dimensioning of this narrowed orbit (whose length is Lf and whose width is lf) can be effected using the following simplified formula for the calculation of lfmax, where the length Lf is chosen to be the largest possible, to obtain the effects of a breaker in the Case of over-current (detachment of the web, stretches) but less than a fixed value Lmax imposed by the conditions of electromagnetic radiation: Ifmax = 81.937 [Ipm / (ef / 25.4) .6732 XTF .4281 x0,0674] 1,485

Tf

die Schmelz-Temperatur (in °C) des Kupfer ist, welches die Gedruckte-Schaltung-Platte bedeckt,

Ef

die Dicke (in Mikrometern) der gemäß der verwendeten Technologie fixierten Kupfer-Lage ist (sei es 35, 70 oder 105 Mikrometer) ist.

Where Ipm is the peak current (in amperes) circulating at least in the component due to avalanche,

tf

the melting temperature (in ° C) of the copper covering the printed circuit board is

ef

the thickness (in microns) of the copper layer fixed according to the technology used is (35, 70 or 105 microns).

On get that way for example, for a current of 10 A and a of 105 microns a lfmax of 416 microns.

How special of the 3 As shown, this melting effect can be increased by using the narrowed trace with a metallized hole 26 The traversal of the printed circuit board then plays an additional role as a thermal brake to transfer the energy to this small narrowed trace piece 24B Concentrate this hole with the recording area 14B the component in the warm zone connects. Preferably, the fusible part becomes 24B furthest away from the metallized surface of large scale 18 arranged, which surrounds the cold zone, that is, it is from the recording area 14B extends in the opposite direction to this cold zone.

The The present invention has an implementation which is particularly Cheap and less expensive is, as it concerns essentially nothing, as the design of the Printed circuit board. It allows an intrinsic robustness as they do not coincide with the probability of failure Component is connected. On the other hand, it limits the thermal accident locally around the failing component.

Of course, limited the present invention is not limited to the single assembly of a ceramic capacitor, as previously described. One can actually consider by analogy draw on the printed circuit other types of components to assemble their bodies out high-temperature dielectric materials such as components based on BaTiO3, TiO2 or SrZrO3, not doped.

Claims (11)

Printed circuit board, which on this plate ( 12 ) mounted electronic and / or passive components, including at least one ceramic component ( 10 ), which have a first and a second external contact ( 10A . 10B ), which are provided with first and second conductive receiving areas printed on this plate ( 14A . 14B ), characterized in that it comprises a device ( 18 ; 22 ; 24A . 24B ) for creating a thermal asymmetry between said two conductive receptacles In order to avoid any risk of ignition of the printed circuit board mentioned above, the ceramic components are included in the ranges. A printed circuit board according to claim 1, characterized in that said device for generating a thermal asymmetry comprises a metallized surface of large scale ( 18 ), which by means of heat bridges ( 16 ) with one of said conductive recording areas ( 14A ) to thermally behave as an energy dissipation device. Printed circuit board according to claim 2, characterized that said metallized surface of large extent between 2 times and 10 times the surface said outer contact the ceramic component comprises. A printed circuit board according to claim 1 or claim 2, characterized in that said thermal asymmetry generating means comprises an aperture ( 22 ) realized in said plate between said first and second conductive receiving regions directly beneath said ceramic component. Printed circuit board according to claim 4, characterized in that that this opening is formed by a slot whose length is greater than that of said conductive Reception Areas. Printed circuit board according to one of claims 1 to 5, characterized in that said device for generating a thermal asymmetry immediately at the beginning of the other of said conductive recording areas ( 14B ) comprises a track which comprises a constriction zone ( 24A . 24B ) to produce a melting effect such that in the case of heating the ceramic component, an interruption of this conductor is caused. Printed circuit board according to claim 6, characterized in that this narrowed conductor track ( 24B ) with a metallized hole ( 26 ), the traversal of the printed circuit board then playing an additional role as a thermal brake by concentrating the energy on this narrowed track. Printed circuit board according to claim 7, characterized in that this conductor track ( 24B ) in a large scale to the metallized area ( 18 ), which one of these conductive recording areas ( 14A ), opposite direction extends. A printed circuit board according to any one of claims 1 to 8, characterized in that this ceramic component is a capacitor is. A printed circuit board according to any one of claims 1 to 8, characterized in that said ceramic component is made of high temperature dielectric materials is composed as components based on BaTiO3, TiO2 or SrZrO3, not doped. Method for protecting a printed circuit board ( 12 ) against overheating of ceramic components ( 10 ), which are mounted on this plate, and with on this plate printed conductive receiving areas ( 14A . 14B ), characterized in that a thermal asymmetry is created between these two conductive receiving areas of the ceramic component to prevent any risk of ignition of this printed circuit board.