Electrical component resistant to damage by infrared radiation

In an electrical component that contains materials that can physically and/or chemically change under the influence of heat (infrared) radiation required during processing of the component and which in particular, is suitable for employment on printed circuits, a surface layer that reflects the heat (infrared) radiation is arranged at the outside of the component.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to an electrical component that contains 
materials which can physically and/or chemically change under the 
influence of heat (infrared) irradiation of the type required during 
circuit assembly steps involving the component and which, in particular, 
is suitable for employment on printed circuits. 
2. Description of the Prior Art 
Fastening electrical components on printed circuit boards ensues, for 
example, with a reflow soldering. The printed circuit board together with 
the components arranged thereon are heated by infrared radiation to such 
an extent that the solder melts and produces the required, reliable 
electrical and mechanical connection between the components and the 
metallic interconnects. In the case of components having heat-sensitive 
materials, for example electrical capacitors having plastic films, special 
care is therefore required to insure that the materials are not damaged or 
modified due to the heating produced by the infrared radiation. For 
example, there is a risk that the plastic foils (of, for example, 
polyethylene terephthalate) in the capacitors may melt under the influence 
of heat, so that the electrical values of the capacitor are changed. 
A further heat treatment with infrared radiation takes place in what are 
referred to as pre-heating paths (drying paths for fluxing agent) wherein 
the above-recited risks for electrical components can likewise occur. 
Heretofore, one could only attempt to minimize these difficulties in the 
heat treatment of the electrical components with infrared radiation by 
correctly observing the maximum temperatures and maximum treatment times 
prescribed by the manufacturer. A risk of damage is still present, 
however, because exact predictions about the effects of heating components 
with infrared irradiation are difficult to make, since the localized 
heating is dependent on many parameters (for example, spacing, wavelength 
and energy of the radiation, reflection and absorption at the component, 
etc.). Damage to the component cannot be precluded even given the greatest 
possible care. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to improve a component of the type 
initially described such that undesired heating by infrared radiation is 
diminished. 
This object is inventively achieved in an electrical component having a 
surface layer that reflects the heat (infrared) radiation disposed on the 
outside of the component. 
The advantage is thereby achieved that an absorption of the infrared 
radiation in the component is avoided to a great extent, and thus the 
undesired heating is prevented. 
The reflective layer is preferably composed of a metallization (for 
example, of aluminum) that is arranged on a plastic film, or directly on 
the component, or is composed of a metal foil. 
The electrical component is preferably a layered or stacked capacitor, or a 
wound capacitor, that has possibly been pressed flat. 
The electrical component can have contact surfaces at its end faces that 
are manufactured according to Schoop's metal spraying process. The 
reflective layer thereby preferably has at least one side with a free edge 
that is arranged in the region of a Schoop layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a capacitor body 7 as a stacked or layered capacitor. The 
capacitor body 7 is composed of dielectric films 3 and 4 arranged above 
one another that have at least one side provided with regeneratable metal 
layers 1 and 2. 
Contact layers 10 and 11 are arranged at the end faces 5 and 6 of the 
capacitor body 7. These contact layers are produced, for example, 
according to Schoop's metal spraying method and serve the purpose of 
electrically connecting the metal layers 1 and 2 that extend to the end 
faces 5 and 6 in alternation to one another. 
Plastic foils 20 and 21 are arranged at the outside of the capacitor body 
7, these plastic foils 20 and 21 having a surface layer 22 produced, for 
example, by vapor-deposition that reflects heat (infrared) radiation. If 
the layer 22 is metallic, metal-free edge strips 23 and 24 are arranged at 
the sides that prevent shorts between the oppositely polarized contact 
layers 10 and 11. Shorts can also be prevented by separating the potential 
in the surface 22. 
The plastic films 20 and 21 together with the surface layers 22 are 
expediently co-wound to form the winding during the manufacture of the 
master capacitor from which the individual components are cut. 
FIG. 2 shows another embodiment wherein the capacitor body 9 is composed of 
a winding that has been pressed flat. The regeneratable metal layers that 
are not visible in FIG. 2 are also applied onto plastic films in this 
capacitor and are conducted to the end faces 12 and 13 in alternation and 
are connected to one another at that location by the contact layers 14 and 
15. 
A surface layer 25 that reflects heat (infrared) radiation is arranged at 
the outside of the capacitor body 9, this surface layer 24 being produced, 
for example, by direct vapor-deposition of a metal (for example, aluminum) 
onto the capacitor body 9. A metal-free edge strip 26 is arranged parallel 
to the contact layer 14 in order to avoid shorts between the contact 
layers 14 and 15. As in the exemplary embodiment shown in FIG. 1, shorts 
between the contact layers 14 and 15 given a capacitor body 9 that has 
been pressed flat can also be prevented by a separation of potential in 
the surface 25. 
In addition to the embodiments shown in the drawings, of course, other 
versions of surface layers are also possible. Given an insulating covering 
of the contact layers, thus, the surface layer can cover the entire 
exterior of the capacitor since shorts cannot arise in that case. It is 
also possible to cover the sides, which become exposed in film or layered 
capacitors due to detachment from the master capacitor with a reflective 
layer. It should be taken into consideration, however, that the majority 
of the heat radiation is received by the outside surface of the component 
facing away from the printed circuit board, so that covering this surface 
is fundamentally adequate in most applications. Since, however, a 
distinction between an upper side and an under side, i.e. the exterior 
side facing toward or, respectively, away from the printed circuit board, 
is not possible given modern machine-equipping methods, at least these two 
sides (the upper side and under side in FIGS. 1 and 2) should be protected 
by a surface layer. 
The subject matter of the invention thus assures that a substantial 
preservation of the components is achieved when treating heat-sensitive, 
electrical components with infrared radiation, so that a destruction of 
the components is avoided even given inconsistent treatment times. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventors to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of their contribution to the art.