Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
2001-04-06
2003-09-16
Paladini, Albert W. (Department: 2125)
Coherent light generators
Particular temperature control
Heat sink
C372S050121
Reexamination Certificate
active
06621839
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a method for contacting a high-power diode laser bar and a high-power diode laser bar-contact arrangement of electrical contacts with minor thermal function.
b) Description of the Related Art
High-power diode laser bars (HDBs) are semiconductor laser components of at least two semiconductor laser emitters of high optical output power which work essentially optically independent from one another. Their average optical line output densities exceed 1 watt/mm component width, their optical output power exceeds 10 watts cw per component. The reflection surfaces of the semiconductor laser resonators or cavities are called ‘facets’ and can be reflection-coated or antireflection-coated. HDBs are typically formed of a doped semiconductor substrate of a thickness of 10 or 100 &mgr;m on which a pn junction has been epitaxially grown. HDBs have two electrodes—an anode and a cathode—located on the substrate side and epitaxy side with respect to the HDB. Individual operation of single emitters is made possible by constructing the electrode so as to be electrically separated on the epitaxy side with respect to the emitter. The electrodes of an HDB can have metallization, but may also not be metallized.
HDBs must be contacted in order to operate. A contact by which an HDB is connected can realize different functions. These functions may include: supply of current to the HDB, dissipation of heat from the HDB and mechanical fixing of the HDB. The contact can perform its function for HDBs particularly well when the connection between the contact and the HDB is a material engagement. In the following, by electrical contact for the HDB is also meant the plurality of contact bodies which have the same electrical polarity and are at a distance from one another spatially. In this sense, for example, a series of electric bond wires at the cathode of the HDB forms an individual electrical (n-)contact. Likewise, a series of conductor paths on ceramic, for example, which are provided for epitaxy-side contacting of the HDB with its anodes which are provided for individual operation of the emitters forms an individual electrical (p-)contact. An electrical contact for an HDB can accordingly comprise a plurality of mechanical contacts.
By high-power diode laser (HDL) is meant an HDB which is connected in a material engagement with an electrically positive (p-)contact at the anode of the HDB and an electrically negative (n-)contact at the cathode of the HDB. By definition, the HDB of an HDL has exactly two electrical contacts—a positive and a negative contact—which are fixed to the HDB at the epitaxy side and substrate side.
During operation of the HDL, the HDB also generates, in addition to optical output, considerable thermal output (losses), particularly in the area of the pn junction of its emitter near the epitaxy side of the HDB. The electrical contacts of the HDB take on a thermal function in addition in that thermal output of the HDB is dissipated through them. If both electrical contacts of the HDL have the same thermal resistance, more thermal output (heat) is dissipated via the epitaxy-side contact than via the substrate-side contact.
An electrical contact for the HDB is defined as an electrical contact with major thermal function when more than one third of the thermal output generated in the HDB in continuous wave (cw) operation is dissipated through it. An electrical contact for the HDB is defined as an electrical contact with minor thermal function when, at most, one third of the thermal output generated in the HDB in cw operation is dissipated through it.
According to this definition, an HDB which is operated in cw mode requires at least one electrical contact with relevant thermal function. Operating in pulsed mode, both electrical contacts can have minor thermal function by definition insofar as the thermal output averaged over time does not exceed two thirds of the value of the thermal peak output in the pulse.
An example of an electrical contact with relevant thermal function is a metallized diamond body to which the HDB is soldered over a large area on the epitaxy side and through which 90% of the heat that is produced in the HDB during operation is dissipated.
An example of an electrical contact with minor thermal function is a series of bond wires which have been bonded to the substrate-side metallized electrode of the HDB and through which 1% of the heat produced in the HDB is dissipated in cw operation.
Another example of an electrical contact with minor thermal function is a copper-tungsten substrate to which the HDB has been soldered on the epitaxy side and through which 31.5% of the pulse peak heat output produced in the HDB or 90% of the heat output produced in the HDB averaged over time is dissipated in pulsed operation with a duty factor of 35% averaged over time.
The material-engagement connection of an HDB and an electrical contact involves a more or less highly pronounced joint zone between the two connection members. The material-engagement assembly between an HDB and an electrical contact is carried out in a material-engagement assembly process, a joining process, by a joining method. The joining process can be carried out using an additional joining material.
The joining process starts when the joint members are brought into contact with one another or with an additional joining material. It is finished when a material-engagement connection is achieved whose properties perform the intended function for which it is produced. These properties may include: sufficient electric conductivity, sufficient thermal conductivity, sufficient mechanical strength.
Joining processes for connecting the HDB with electrical contacts with minor thermal function according to the prior art are bonding and soldering.
Arrangements of HDBs and an electrical contact of minor thermal function according to the prior art have a joint zone between the HDB and electrical contact which is constructed as a bonding weld or solder joint. The joint zones differ depending on the joining method in that the joint zone between the HDB and electrical contact is formed by an additional joining material, the solder, in the case of soldering, whereas with bonding, the joint zone requires no additional joining material.
With bonding, the electrical contact, for example, one or more bond wires, is connected with the HDB by its metallization through local ultrasound, pressure and/or heat action. The mechanical forces occurring locally during the bonding process can overload and damage the HDB. Because of the small diameter of bond wires and the high currents occurring during the operation of the HDL, the HDB must be connected with large number of bond wires which can only be arranged sequentially. The contacting of the HDB with bond wires is also disadvantageous in that the HDB must be provided with a particularly thick metallization to compensate for the inhomogeneous input of current into the HDB. Finally, wire bonding processes result in an increased space requirement around the HDB. This is disadvantageous for the flexibility of the assembly process as well as for the capacity of the HDL to be integrated in systems.
During soldering, a material-engagement connection between the metallization of the HDB and the metallic or metallized electrical contact is achieved with the assistance of a soldering material. The connection relies on diffusion processes between the solder material and the metallization materials of the HDB and electrical contact. The diffusion processes start immediately after the metals and solder are brought into contact at a melting temperature of the solder or eutectic temperature of the metal and solder.
The soldering process is disadvantageous because of the required heat action and its consequences: The two joint members, namely, the HDB and the electrical contact, generally have different thermal expansion coefficients. When cooled below the solidification temperature of the solder joint at room temperature o
Haensel Hartmut G.
Lorenzen Dirk
Schroeder Matthias
Jenoptik Aktiengesellschaft
Paladini Albert W.
Reed Smith LLP
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