|Publication number||WO2001042801 A1|
|Publication date||14 Jun 2001|
|Filing date||10 Oct 2000|
|Priority date||9 Dec 1999|
|Publication number||PCT/2000/28017, PCT/US/0/028017, PCT/US/0/28017, PCT/US/2000/028017, PCT/US/2000/28017, PCT/US0/028017, PCT/US0/28017, PCT/US0028017, PCT/US028017, PCT/US2000/028017, PCT/US2000/28017, PCT/US2000028017, PCT/US200028017, WO 0142801 A1, WO 0142801A1, WO 2001/042801 A1, WO 2001042801 A1, WO 2001042801A1, WO-A1-0142801, WO-A1-2001042801, WO0142801 A1, WO0142801A1, WO2001/042801A1, WO2001042801 A1, WO2001042801A1|
|Inventors||Albert T. Yuen, Pierre H. Mertz|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Referenced by (4), Classifications (11), Legal Events (6)|
|External Links: Patentscope, Espacenet|
Patent Application of
Method and Apparatus for Combined Alignment and Heat Drain of Stacked Processing Stages
Field of Invention
The present invention relates to a method and an apparatus for combined alignment and heat drain of stacked processing stages and in particular to a method and apparatus for combined alignment and heat drain of individual modules of an optical multiplex transceiver.
Background of the Invention
The demand for speed of signal processing in a computer and for capacity in signal communication between several computers is ever increasing. A technique to meet the demand for high signal transmission is optical multiplexing such as wavelength division multiplexing (WDM) and time division multiplexing (TDM) . In the WDM technique, the spectrum of a light beam transmitted in an optical fiber is divided into a number of wavelength divisions, which represent independent signal strings for transmitting information. Each wavelength division is an independent signal carrier. Hence, the advantage of optical multiplexing is its ability to transmit simultaneously in a single optical fiber a high number of information.
In a number of optoelectronic processing stages (OPS) optical signals of distinct wavelength are either collinear emitted or collinear received. These OPS are typically monolithically grown structures with a planar bottom and top surface. The optical signals are emitted or received perpendicular to the planar top surface.
US. Pat. No. 5,487,124 discloses a bi-directional wavelength division multiplex transceiver module, wherein a semi-translucent mirror is used to separate wavelength division multiplexed signals and redirect them to individual OPS' s.
Recent research achievements allow the fabrication of semi- translucent OPS' s with distinct translucent /opaque properties such that they work simultaneously as an optical bandwidth filter and an optoelectronic converter. These OPS' s are made opaque only for the spectrum of their predetermined wavelength division and are sufficiently translucent for the remaining light spectrum. In case of a receiver, a number of stacked OPS' s with distinct absorption spectra are sequentially arranged and absorb the wavelength divisions of a through passing light beam. In case of an emitter each OPS adds its signal in the distinct wavelength division to the passing light beam. As a result, the effort of multiplex transceivers to combine/separate the individual wavelength divisions and direct them from/to the corresponding OPS is significantly reduced such that the number of OPS in a single multiplex transceiver can be increased.
Optical multiplex systems are superior to electrical transmission systems, because they are noise free and enable a much longer transmission distance. These advantages are not only utilized for communication between computers or individual circuit boards but also within a stacked multichip circuit.
US. Pat. No. 5,568,574 discloses modulator-based photonic chip-to-chip interconnections for dense three-dimensional multichip module integration. In this invention, a number of OPS' s are embedded within individually manufactured semiconductor structures that perform logical operations and are placed in tightly stacked processing stages (PS) above each other. The OPS' s are placed in corresponding alignment in each of the semiconductor structures such that the optical signal beams travel vertically through the semiconductor stack. Thus, circuit boards with their two- dimensional conductive connections between the individual chips are replaced by a three-dimensional structure.
Semi-translucent OPS open up new possibilities for highly compact, tightly stacked PS. The high processing capacity in such PS produces heat. In conventional two-dimensional arrayed circuits and optoelectronic devices heat dissipation is relatively simple to achieve, since sufficient air contact surface is available for heat exchange. A heat absorbing air stream is thereby either thermally stimulated or provided by a fan.
US. Pat. No. 5,280,191 discloses a packaging for pairs of optical devices having thermal dissipation means. The invention discloses a design of a duplex transceiver with secondary circuitry and a heat sink for cooling. The heat sink is a sheet metal part, which provides flat areas with low thermal convection.
US. Pat. No. 5,513,073 discloses an optical device heat spreader and thermal isolation apparatus. In this invention of a duplex transceiver, the optoelectronic devices are connected to a heat spreader card, which is thermally isolated from the transceiver board. The heat spreading card is a flat sheet metal piece kept in a insolating distance to the transceiver board.
In tightly stacked PS the ratio between air contact surface and generated heat decreases unfavorably. In addition to that, alignment features surrounding the central circuitry interrupt the heat flow to the remaining air contact surfaces at the sides of the PS.
US. Pat. No. 4,985,805 discloses a device for the cooling of optoelectronic components and a flange joint used therefor. A number of processing stages are stacked above a heat drain base plate. The vertical alignment and heat drain from the processing stages to the base plate is accomplished by vertical metal plates that are laterally attached to the processing stages with screws. The vertical metal plates have no designated alignment features, such that the achievable precision is not sufficient for stacked multiplexing PS. The metal plates have a certain elasticity such that the screw attachment does not provide sufficient contact over the lengths and widths of the PS. Because of their bulkiness, screw connections are generally unfavorable for microelectronic assemblies .
Therefore, there exists a need for a method and apparatus to align a number of processing stages and simultaneously drain their processing heat. The current invention addresses this problem.
High capacity electrical circuitry is generally very sensitive to electromagnetic fields. Therefore, there exists a need for stacked processing stages to shield them against peripheral electromagnetic fields. The current invention addresses this need. Typically, solid leads and solder pins are used to provide solid electrical ground. In stacked processing stages the available area is limited. Therefore, there exists a need to utilized existing features for a stable electrical ground. The current invention addresses this need.
Objects and Advantages
Accordingly, it is a primary object of the present invention to provide a method and apparatus to simultaneously align a number of tightly stacked processing stages, drain their processing heat and keep them below a predetermined temperature.
It is a further object of the present invention to provide a stable voltage ground for stacked processing stages.
It is a further object of the present invention to provide a faraday shield for stacked processing stages.
Summary of the Invention
The invention achieves alignment and simultaneous cooling of stacked processing stages (PS) with a number of parallel heat drain profiles (HDP) that protrude through soldering holes of each PS establishing mechanical and thermal connections. The contour lengths and the heights of the soldering holes define bridging areas between PS and HDP. The HDP' s are held in position within a heat sink base, which is typically placed on one end of the PS stack. The heat sink base has ribs to increase its air contact surface. The alignment profiles are made of a thermally conductive material like for instance aluminum or copper based alloys.
Each PS has a central processing area (CPA) where the optoelectronic and electronic circuitry is placed. A surrounding ring structure (SRS) captures the radially travelling thermal energy that is produced in the CPA and drains it in the bridging areas to the HDP. The draining capacity is directly proportional to the size of the bridging area, the average temperature difference between the PS' s and the HDP' s at the bridging area and the quality of the snug fit.
The HDP' s are placed in sufficient proximity on the SRS to drain the captured thermal energy such that the temperature difference within the SRS and subsequently within the CPA remains within a predetermined temperature range. The thermal energy travels inside the HDP towards the heat sink base where it is dissipated into the surrounding atmosphere.
Thermal energy flows from a thermal source with a high temperature level to a thermal drain with a low temperature level resulting in a temperature gradient along the thermal path. Materials with good thermal conductivity like aluminum and copper are a first factor for helping to obtain the flat temperature gradients. The second factor is the size of the section area of the thermal path, which affects directly the slope of the temperature gradient for a given thermal energy flow. In the current invention, each processing stage drains a certain thermal energy at a maximum allowable temperature to the HDP's, raising its temperature level and adding a step in the temperature gradient. The HDP has to have a minimum section area such that the average temperature in the HDP at the most distant PS remains sufficiently below the PS temperature such that enough thermal energy can bridge over.
The preferred application of the invention is an optical multiplex transceiver mainly consisting of several optoelectronic PS' s (OPS' s) . The HDP' s are arranged along the direction of the signal light beam. The heat sink base is typically an extrusion profile with cooling ribs and straight holes where the HDP's are soldered in. It is positioned preferably opposite of the cable connecting side. The HDP' s have a preferably circular contour, which allows a high fabrication precision with relatively little machining effort. The OPS are stacked next to the heat sink base leaving a certain gap for air circulation. A number of functional stages are placed between the OPS or at the end of the stack as they are known for optical transceiver devices.
Solder ball connections are arrayed on the OPS to provide electrical signal transmission between them. Each OPS may have on a side an array of laterally extending solder pins that connect the multiplex transceiver mechanically and electrical with a printed circuit board. The solder pins are preferably surface mount an edge of the OPS. The connection with the printed circuit board is optionally provided by edge castellations as they are known to those skilled in the art. The heat sink remains thermally insulated within a certain insulating distance to the printed circuitry board.
The HDP' s provide an electrical ground for the OPS by connecting them to the heat sink. The circular arrangement of the HDP' s provides thereby a favorable faradic shield effect against peripheral electromagnetic noise.
Brief Description of the Figures
Fig. 1 shows a first perspective view of the preferred embodiment of the invention with the adapter side of the multiplex transceiver being visible.
Fig. 2 shows a second perspective view of the preferred embodiment of the invention with the heat sink side of the multiplex transceiver being visible.
Fig. 3 shows a side view of the preferred embodiment of the invention and a corresponding graph visualizing the temperature distribution in the heat drain profiles. Fig. 4 shows a front view of an example of a single optoelectronic processing stage with superimposed isothermal curves.
Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.
The invention performs four main tasks : first to align the processing stages; second to drain sufficient thermal energy from the processing stages; third to keep the stage peak temperature sufficiently below a critical level for a most unfavorable surrounding air temperature and hampering influences like dust on the heat sink; and fourth to provide a stable electrical ground to all stages. In the following, the four main tasks are described in detail.
Fig. 1 shows a perspective view of a preferred application of the invention for an optical multiplex transceiver. It is appreciated that the method and apparatus of the invention may be applied to any processing device, which at least partially consists out of stacked processing stages as they are known to those skilled in the art.
An exemplary number of processing stages 2a, 2b, 2c are stacked together with a first functional stage 3 and a second functional stage 4 on the heat drain profiles 5a-d. The heat drain profiles 5a-d drain the heat created during the functional operation of the processing stages 2a, 2b, 2c in the heat drain direction 9a into a heat sink base 1. Each of the processing stages 2a, 2b, 2c has a solder pin array 8a, 8b, 8c, which consist of surface mounted solder pins that extend laterally from socket shoulders 10a, 10b, 10c as it is known to those skilled in the art. The solder pin arrays 8a, 8b, 8c form a solder pin matrix 11, which provides a two dimensional mechanical connection and a number of electrical contacts in a final assembly position on a printed circuit board (not shown) . It is appreciated that the solder pins may be edge castellations as they are known to those skilled in the art. The solder pin arrays 8a, 8b, 8c may also drain some heat.
The heat drain profiles 5a-d are pressed into base holes 12a-d (see Fig. 2) of the heat sink base 1. The heat sink base 1 is preferably an extruded profile made of aluminum or copper based material with an extrusion direction parallel to the main heat drain direction 9a. Design features of extruded fabricated profiles are generally parallel, which allows a precise alignment of the heat drain profiles 5a-d. In an optional reaming operation the precision of the dimension and parallel orientation of the base holes 12a-d can be additionally increased.
The heat drain profiles 5a-d are made of a core material with a high thermal conductivity and have a preferably circular section, which allows them to be manufactured with the requisite precision. The core material is preferably an aluminum based material or a copper based material. Optional surface coatings like for instance gold or silver coating prevent oxidation and raise the thermal contact conductivity of the heat drain profiles 5a, 5b, 5c, 5d.
The processing stages 2a, 2b, 2c carry in a central processing area the processing circuitry and are stacked on the heat drain profiles 5a-d with their soldering holes 14 (see Fig. 2) . The soldering holes 14 have sufficient tolerance in shape, orientation and position to the heat drain profiles 5a-d to avoid strain on the assembled processing stages 2a, 2b, 2c. To fixate the processing stages 2a, 2b, 2c and to establish thermal and electrical conductivity the heat drain profiles 5a-d are soldered in the soldering holes 14.
Thermal energy is generated as a by-product of the operational function of the processing circuitry in the central processing area of the processing stages 2a, 2b, 2c. This radial energy is radially transmitted to the periphery where the soldering holes are located. Each processing stage 2a, 2b, 2c has a maximum thermal processing energy (MTPE) that is generated during full stage operation and during a given time unit (TU) . The thermal energy causes a rise of the stage temperature, which has to remain with a safety distance 60 (see Fig.3) below a critical level 61 (see Fig.3) under worst conditions. The worst conditions are defined by a high surrounding air temperature 45 and eventual reduction of the cooling capacity of the heat sink base 1 because of deposited dust that may clog the ribs 16.
The soldering holes 14 are of a hole material with high thermal contact conductivity (TCC) and define with their section length and their height a bridging area. The TCC and the size of the bridging area define a maximum thermal bridging energy (MTBE) that can bridge from one of the processing stages 2a, 2b, 2c onto the heat drain profiles 5a-d during TU and at a given bridging temperature difference (BTD) between the stage hole temperatures 41a-c
(see Fig.3) and a local profile temperature. The MTPE together with a safety margin energy is MTBE. The safety margin energy covers eventual corrosion in the bridging areas, which may reduce the TCC.
The first functional stage 3 may carry the lens system as it is known for optical transceivers. The second functional stage 4 features the design elements required for aligning and accessing a cable plug of a fiber optic cable as known to those skilled in the art. Exemplary alignment features for such a cable plug are the alignment pins 6a, 6b. Exemplary access features are the plug slots 7a, 7b where receiving and emitting light beams pass through.
Fig. 2 shows a perspective view of the optical multiplex transceiver as described above with its heat sink base 1 being visible. The heat sink base 1 has a preferably rectangular section hull contour with a number of cooling ribs 16 being placed between the corner bases 17 that hold the heat drain profiles 5a-d with their base holes 12a-d.
The corner bases 17 have a corner base width 22 where the thermal energy drained from the heat drain profiles 5a-d passes through and onto a heat sink core 18. The heat sink core 18 in the center of the heat sink 1 receives a thermal energy that is drained from the heat drain profiles 5a-d in the corner bases 17 and distributes it evenly to the cooling ribs 16, which increase the air contact surface of the heat sink base 1. The heat sink base 1 is kept in a decoupling distance 19 to the adjacent processing stage 2a to avoid thermal shorting of the designated thermal path and to provide full air contact for the heat sink 1.
It is noted that the cooling ribs 16 may be placed at any location of the heat sink base 1.
The metallic materials of the heat drain profiles 5a-d are electrically conductive to allow for electrical power delivery, electrical ground and/or electrical signal transmission between the individual stages. The heat drain profiles 5a-d are preferably utilized to provide a ground and a faraday shield for the optical processing stages 2a, 2b, 2c. The heat drain profiles 5a-d ground thereby the optical processing stages 2a, 2b, 2c the heat sink base 1. The circular arrangement of the heat drain profiles 5a-d provide a faraday shield effect thereby to shield the optoelectronic receiver/emitter structures 24a, 24b (see Fig. 4) and the supporting electronic circuitry 23 against peripheral electromagnetic noise.
The heat sink base 1 has an extrusion height 20 to provide sufficient mechanical interlocking length with the heat drain profiles 5a-d and sufficient surface of the heat sink 1. Extrusion profiles have a minimum wall thickness and gap width that is limited by the fabrication technique. Thus a maximum section contour length is defined, which leaves the extrusion height 20 as the only variable factor to increase the heat sink surface necessary to exchange the sum thermal energy generated by all processing stages 2a, 2b, 2c under worst climatic conditions. As a result, the extrusion height 20 typically exceeds significantly the main thermal exchange length 32 (see Fig. 3) between the heat drain profiles 5a-d and the heat sink base 1. The reduction of the TCC caused by the optional electrical insulation layer increases the thermal exchange length 32 within the extrusion height 20 and the overall cooling performance remains unaltered.
The rectangular design typically used for electronic circuitry and subsequently the typical election of four heat drain profiles 5a-d limits the amount of electrical transmission paths between the individual processing stages 2a, 2b, 2c. Optional ball grid arrays 15a, 15b correspondingly placed on all processing stages 2a, 2b, 2c provide additional electrical transmission paths. Fig. 2 shows the optional ball grid arrays 15 only on one side of the processing stage 2a without contacting an adjacent processing stage and is shown solely for purposes of visualization. It is appreciated that anybody skilled in the arts may place the optional ball grid arrays 15a, 15b between the processing stages 2a, 2b, 2c to establish functioning electrical path between them.
Fig. 3 shows the optical multiplex transceiver as described above in side view together with a corresponding graph that visualizes the temperature relations of the preferred application of the invention. The horizontal axis of the graph corresponds to the dimensions of the optical multiplex transceiver in the main heat drain direction 9a and the secondary heat drain direction 9b. The vertical axis of the graph represents temperatures. The values and relations shown in this graph are shown for the sole purpose for visualization without any claim for accuracy. Given is an surrounding air temperature 45 with a maximum level of typically 85 degrees centigrade, which results in a maximum level of the stage peak temperatures 41a-c for a maximum thermal energy generated in the processing stages 2a-c. Each of the processing stages 2a-c has a stage hole temperature 42a-c at the contact surface of the bridging area of the soldering holes 14. For purposes of visualization circumferential variations of the stage hole temperature 42a-c are neglected in Fig. 3.
The level differences between the stage peak temperatures
41a-c and their corresponding stage hole temperatures 42a-c are defined by the radial thermal conductivity within the processing stages 2a-c. Optional thermally conductive layer structures with radial orientation increase the radial conductivity. Electrical leads, which are typically made from copper based materials with good thermal conductivity properties connect the central processing area with the ball grid arrays, and hence serve simultaneously to reduce the radial thermal conductivity of the processing stages 2a-c.
The drain profile temperature curve 43 visualizes the temperature of the heat drain profiles 5a-d at various locations. For the purpose of visualization, radial temperature variations of the heat drain profiles 5a-d are neglected in Fig. 3.
In the exemplary visualization of the graph each of the processing stages 2a-c has the same TCC and the same average GBTD between the drain profile temperature curve 43 and the stage hole temperatures 42a-c. As a result, the curve segments 43c, 43e, and right part of 43g are shown in the graph to be parallel and having the bridging decline angle 47a-c. The left part of curve segment 43g is declining towards the first and second functional stages 3, 4, which do not generate heat and thus have a cooling influence on the heat drain profiles 5a-d. As a result, the main heat drain direction 9a is inverted in the peak 48 to the secondary heat drain direction 9b.
The first functional stage 3, which preferably carries the lenses to focus the passing light beams is close to the heat generating processing stage 2c and has a relatively small surface contact to surrounding air. The lowest temperature 432 of the first functional stage is therefore only insignificantly below the curve segment 43h. The hole temperature 431 of the first functional stage is located between lowest temperature 432 and curve segment 43h at a location dependent on the relation between internal thermal conductivity (ITC) and the thermal bridging conductivity (TBC) in the bridging area.
The second functional stage 4 has more surface exposed to the cooling air and is separated by the first functional stage 3 from the next heat producing processing stage 2c. Hence, its lowest temperature 442 and its hole temperature 441 are significantly below the curve segment 43i .
Having a constant TCC in all stages and having constant thermal properties of the heat drain profiles 5a-d over their length in the example visualized in Fig. 3, the thermal energy bridges proportional to the bridging temperature difference BTD between the contact surface of the soldering holes 14 and the drain profile surface in the bridging areas. It is appreciated that anybody skilled in the art may vary the TCC between or within each of the processing stages 2a-c and the heat sink base 1. It is also appreciated that anybody skilled in the art may vary the thermal properties, geometric shapes, and numbers of the heat drain profiles 5a-d over their length without diverting from the scope of the invention. The curve segments 43b, 43d, 43f show the temperature decline with the conduction decline angle 46 in the heat drain profiles 5a-d over the traveling length of the thermal energy. The conduction decline angle 46 is dependent on the material specific thermal conductivity and the size of the section area of the heat drain profiles 5a- d as it is known to those skilled in the art. Since thermal energy is imposed on the heat drain profiles 5a-d at the curve segments 43c, 43e, 43g they have the bridging decline angles 47a-c. For the constant TCC and BTD in the bridging decline angles 47a-c are proportional to the imposed and drained thermal energy.
At the peak 48 the thermal flow changes from the direction towards the heat sink base 1 to the direction towards the first and second functional stages 3, 4. Reducing the TCC of the first and second functional stages moves the peak 48 towards the left end of the processing stage 2c and results in less energy and less thermal load imposed onto the first and second functional stages 3,4.
The heat sink base 1 has a heat sink hole temperature 44 and the heat sink core temperature 44b, which has level discrepancies over its length dependent on the mass of the heat sink core 18. For the purpose of visualization, the heat sink core temperature 44b is defined as constant over the heat drain direction 9. In the exemplary monolithic heat sink base 1 the thermal conductivity between the base holes 12a-d and the heat sink core 18 dependents mainly on the corner base width 22 and is represented by the third decline angle 49.
The heat sink base 1 receives the sum thermal energy from all heat generating processing stages 2a-c, except the thermal energy that is transmitted onto the first and second functional stages 3,4 and a certain energy amount that is transmitted to the surrounding air along the thermal path. The heat sink base 1 transmits the thermal energy mainly via convection to the surrounding air. As it is known to those skilled in the art, the thermal exchange energy at TU between heat sink base 1 and the surrounding air is dependent on the size of the air contact surface, the air flow characteristic around the heat sink base 1, the convection temperature difference (CTD) between heat sink temperature 44b and surrounding air temperature 45 and the TCC between surrounding air and air contact surface. It is appreciated that anybody skilled in the art may change the design of the heat sink base 1.
The heat drain profiles 5a-d drain the sum thermal energy over the main thermal exchange length 32. The curve segment 43a approaches asymptotically the hole temperature 44 such that the temperature difference in the secondary thermal exchange length 33 is at low level insignificant for thermal energy exchange is.
In the following, the heat transfer of the invention is described against the main heat drain direction 9a since the surrounding air temperature 45 at the very end of the thermal path defines the profile peak temperature 48 and consequently the stage peak temperatures 41a-c. The base hole temperature 44 is a result of the given surrounding air temperature 45 and depends on it as described above.
Between thermal path point 50 and 51 the temperature rises in the heat drain profiles 5a-d according to the curve segment 43a. The higher the temperature difference to the base hole temperature 44, the more thermal energy is drained from the heat drain profiles 5a-d and the steeper the curve segment 43a becomes . Between thermal path point 51 and 52 the temperature rises with the thermal conductivity angle 46, which is defined by the section size and the thermal conductivity of the material of the heat drain profiles 5a-d.
Between thermal path point 52 and 53 the temperature rises with the thermal conductivity angle 47a, which is defined by the thermal energy generated in the processing stage 2a at TU and is imposed over the hole heights 21a on the heat drain profiles 5a-d within. The stage hole temperature 42a and consequently the stage peak temperature 41a rise above the level of curve segment 43c to the point where the BTD is sufficient to drain the generated thermal energy to the heat drain profiles 5a-d.
Between thermal path point 53 and 54 the temperature raises with the thermal conductivity angle 46. Between thermal path point 54 and 55 the temperature rises with the thermal conductivity angle 47b, which is defined by the thermal energy generated in the processing stage 2b at TU and is imposed over the hole heights 21b on the heat drain profiles 5a-d within. The stage hole temperature 42b and consequently the stage peak temperature 41b rise above the level of curve segment 43c to the point where the BTD is sufficient to drain the generated thermal energy to the heat drain profiles 5a-d. Between thermal path point 55 and 56 the temperature rises with the thermal conductivity angle 46.
Between thermal path point 56 and 57 the temperature rises with the thermal conductivity angle 47c, which is defined by the thermal energy generated in the processing stage 2c at TU and is imposed over the hole heights 21c on the heat drain profiles 5a-d within. The stage hole temperature 42c and consequently the stage peak temperature 41c rise above the level of curve segment 43g to the point where the BTD is sufficient to drain the generated thermal energy onto the heat drain profiles 5a-d. At the profile peak temperature 48 the heat drain direction 9a inverts and flows in secondary heat drain direction 9b towards first and second functional stages 3, 4 and is drained as described above.
Hence, the temperature increase over the thermal path as described above results in a maximum level of the stage peak temperature 41c. For a most unfavorable high level of the surrounding air temperature 45, the sum thermal conductivity of the thermal path is at a level to have the maximum level of the stage peak temperature 41c with a minimal safety temperature margin 60 below the a maximum operation temperature 61.
Fig.4 shows the front view of one of the processing stages 2a-c with superimposed isothermal temperature lines visualizing the lateral temperature distribution. The exemplary processing stage 2 has in its central area an optoelectronic receiver structure 24a, an optoelectronic emitter structure 24b and supporting electronic circuitry 23 in immediate surrounding. Electrical conductive leads 25 emanate in radial direction from the supporting electronic circuitry 23 and connect with the ball grid arrays 15a, 15b. The processing heat generated by the circuitry results in the shown stage peak temperature 41. The thermal energy that is produced flows radially away and is captured at peripheral ring structure 26 and redirected towards the soldering holes 14. Over the thermal path in the processing stage 2 the temperature declines according to the local thermal conductivity. The temperature decline is visualized by the isothermal temperature lines 41I-III and 42I-III with constant temperature differences. Since the thermal conductivity of the central processing area is low the isothermal temperature lines are closer together. The radial conductive leads 25 increase the thermal conductivity. The peripheral ring structure 26 has a good thermal conductivity, which results in a larger distance between the isothermal temperature lines. The peripheral ring structure 26 has sufficient mass around the soldering holes 14 such that the circumference temperature discrepancies along the circumference are kept below a maximum level .
The circumferential temperature discrepancies result in thermal expansion differences of the heat drain profiles 5a-d, which alter their straightness and impose radial mechanical tensions onto the processing stages 2a-c. The maximum level of the circumferential temperature difference is the level, at which the straightness of the heat drain profiles remains within a predetermined limit.
It is appreciated that the soldering holes 14 may be shaped such that they contact the heat drain profiles 5a-d only on a portion of their circumference and that the heat drain profiles 5a-d may have a noncircular section shape with a cooling feature like for instance cooling ribs.
It is appreciated that the heat drain profiles 5a-d may be connected to each other at a portion or all over their length such that they may form a singular profile with preferably hollow section shape. The stages 2a-c, 3, and 4 may be stacked and aligned there within without diverting from the scope of the invention. Precision alignment features may be utilized between individual optoelectronic processing stages 2a, 2b, 2c to position the optoelectronic processing stages 2a, 2b, 2c with a higher precision than it is provided by the heat drain profiles 5a-d. It is appreciated that the invention may be utilized for vertical-cavity surface-emitting laser and edge-emitting laser as they are known to those skilled in the art .
Accordingly , the scope of the invention should be determined by the following claims and their legal equivalents :
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|International Classification||H05K7/14, H05K7/20, G02B6/42, H01L33/64|
|Cooperative Classification||G02B6/4272, G02B6/4277, G02B6/4269, H05K7/1429, H01L33/642, G02B6/4266|
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