Supports – Miscellaneous
Reexamination Certificate
2001-10-09
2003-04-29
Wood, Kimberly (Department: 3632)
Supports
Miscellaneous
C248S901000, C359S871000, C359S223100, C359S819000
Reexamination Certificate
active
06554244
ABSTRACT:
The invention relates to a device for supporting a miniaturized, especially an electronic or optical, component, according to the preamble of claim 1.
DE 195 33 426 A describes a mechanical fastening system for modular, microoptical elements, preferably held in a housing, on a baseplate for the production of an optical or opto-electronic layout. A support is formed with a central platform which carries a single module. At least three legs which are fastened to the baseplate, for example by laser spot welding or soldering, are connected to the platform in an articulated manner, preferably by means of hinges. This known fastening system makes it possible to support optical components in a shock-proof and vibration-proof manner.
It is the object of the invention further to develop a device for supporting a component according to the preamble of claim 1 in such a way that the effect of temperature changes on the position of the component can be compensated as substantially as possible.
This object is achieved, according to the invention, by the features of the characterizing clause of claim 1.
Advantageous further developments of the subject of the invention are described in the subclaims.
Basic concepts of inventive devices and methods are described below.
In a method for surface-mounting three-dimensional, miniaturized, optical devices which are suitable for automated conveyor-belt assembly with six degrees of freedom on a support plate of optical, electronic and miniaturized mechanical components by a flux-free and precise laser soldering method, some modifications have been made to the holding parts for the “TRIMO SMD” technique (three-dimensional miniaturized surface mounted devices) in order to improve the results which can be obtained by this technique.
The support device is now composed of at least two parts which are characterized by low machining precision: a standard holding part, which is produced by die forming, for example of a 0.1 mm thick metal sheet, and the support for the optical element. The shape and the dimensions of the holding parts are customary and in particular have been designed so that they can hold various optical support parts. The standard holding part is formed from a ball socket base, which is covered with a thin tin layer, and from two metal flaps which are arranged perpendicular to the base of the holding part. These flaps are extremely expedient since they permit fixing of the holding part to the optical support part and moreover also enable the holding part to be easily gripped by a robot.
The optical element is usually positioned roughly (±0.2 mm) inside the support part and held by adhesive bonding or mechanical force, which is generally applied by a spring.
Each support part is specially processed in order to hold an optical element, a lens, an optical fiber or a laser diode. The distance between the focal axis and the base of the holding part can be exactly set by moving the position of the optical support part inside the holding part. They can readily be assembled beforehand in various ways, such as by laser spot welding, adhesive bonding or electrical resistance spot welding. As soon as assembly is complete, the holding part can be fixed to a support plate.
Since the two parts which form the support device are completely independent, they can be produced from different materials. One restriction is that the standard holding part must be produced from a metal which can be wetted with tin, otherwise a layer which can be wetted with tin has to be applied to the spherical base of the holding part. This layer, which can be produced in various ways, such as, for example, by physical vapor deposition or electroplating, is rapidly attacked by the liquid tin—unless it is very thick—and tends to dissolve. After a short time, it is no longer possible sufficiently to guarantee that it constitutes a resistant and suitable boundary layer between the holding part and the support plate. The deposition of a layer which can be wetted with tin thus does not improve the fixing conditions and does not improve the costs and the complexity of the holding part.
The material for the production of the holding part must have sufficient deformability to withstand the die forming process but at the same time it may not be too weak or too soft, in order to guarantee rigid fixing. Usually, the holding part is produced from CuBe (copper-beryllium), nickel, invar or copper.
The optical support part is usually produced by processing a 1 mm thick sheet of either CuBe or invar or stainless steel or Al
2
O
3
. The choice of material depends on how the two parts are to be assembled.
Since the holding part is produced using a 0.1 mm thick metal sheet, it is characterized by high heat resistance, which enables the optical support part to be heat-insulated. This prevents damage to the optical support part during exposure to laser radiation. The heat flow which reaches the base of the holding part encounters considerable difficulties in being removed along the holding part, owing to its high heat resistance. Only a small quantity of heat can reach the optical support part, with the result that no dangerous heating-up is caused, and this slight heating can therefore be neglected.
The fact that the energy delivered by the laser remains limited to a small part of the holding part during the soldering process makes it possible to limit energy wastage and to use a less powerful laser station.
If the holding part contains an active element which generates heat, such as a laser diode or an electrical resistance, the high heat resistance of the holding part is even a disadvantage. Unless the heat generated by it were removed, the active element would inevitably be caused to fail, owing to its continuous heating-up.
The small dimensions do not permit the holding part to be provided with a radiator (heat sink). The use of the support plate as a radiator which can remove most of the heat generated is an appealing and possible solution. It can be achieved only if the support plate is produced using a material having high thermal conductivity, and also only if the heat can flow to the support plate. An inevitable consequence of this second point of view is the reduction in the heat resistance of the holding part. Where a large quantity of heat has to be removed, a sapphire support plate must be used (thermal conductivity 41 Wm
−1
/K
−1
). In all other cases, it is more advantageous to produce the support plate from materials which have a much lower thermal conductivity, such as Pyrex, Al
2
O
3
, zerodor, quartz and float glass. The float glass is least suitable because it can break during the soldering process since it does not withstand thermal shocks.
The soldering process, which is carried out, on a sapphire support plate, is actually extremely problematic owing to its high thermal conductivity. The amount of energy which has to be emitted by the laser in order to cause the tin layer to melt is much greater than the energy which would be required in the case of a support plate having a lower thermal conductivity. The existing ratio of the energy values which are required for a sapphire support plate and for any other support plate can be up to a factor of 2. The necessity of a much more powerful laser soldering station consequently requires a greater investment for purchasing the laser and also higher utilization costs.
If the support plate acts as a radiator, the holding part should be capable of transmitting to it the heat generated by the active element. This cannot actually be achieved if the holding part is characterized by high heat resistance. At the same time, if the holding part is characterized by low intrinsic heat resistance, the heat generated by the laser during the soldering process would rapidly reach the optical element and would then damage it. The heat resistance of the holding part must change during the process: a high resistance during the soldering process and a low resistance after the fixing means has been produced. This can be achieved by fill
Remy De Graffenried Christian
Scussat Marco Antonio
Leica Geosystems AG
Rothwell Figg Ernst & Manbeck
Wood Kimberly
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