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http://www.coolermaster.com/index.php?LT=english&Language_s=2&url_place=discovery_detail&serial=10
2003-09-22 On Cu/Al Radiators
The amazing Moor Law predicts that the number of transistors on the integrated circuits will be doubled every two years. In order to improve the operation performance, semi-conductors engineers have kept improving the integrity of the transistors on the silicon chips, thus making it verified over and over again. Since 1971, the number of the transistors in a single chip has risen by over 1800 times. The increased integrity has also become one of the driving forces for the prosperity of the computer industry.
The CPU currently used adopts the manufacturing technology with 130 nanometers (0.13 micron) line width. The CPUs manufactured with the production process of 90 nanometers will be put into the market, and the R &D in the production process including LADI and EUV has successfully come out. All these show that there is an ample room in technical development for the CPU with higher manufacturing density and faster operation. The density of future CPU integrated transistors will be multiplied, namely, the number of the transistors integrated in a given area will be multiplied.
However, the total energy consumption and the heat generated therefrom will be increased accordingly. More importantly, the electric energy consumed by CPU will be transformed into the heat energy, which is not only the growth in the value of the power, but also concentrated in a smaller space, thus resulting in a unprecedented difficulty in the heat dissipation. If such problem can\'t be solved effectively, the high density integrated technology can not be applied, which is a big bottleneck to block the CPU development. Take P4 3.06G CPU from Intel as an example, there are 55 million transistors integrated in a die area of 11.9x12.1 mm2 , with the biggest heat dissipation power of 70W. The heat problem of future CPU with over P4 3.6GHZ is a severe challenge facing CPU radiator manufacturers.
In order to achieve a good effect in heat dissipation, many manufacturers have demonstrated some very extreme heat dissipating products, such as water radiators and liquid nitrogen radiators, to try to solve the imminent heat dissipation problems. As a matter of fact, these products are still under commercially advertising, not used yet for CPU heat dissipation. This can be attributed to two factors. First, the reliability and quality of these products have not been verified, and no standard framework has been set up, thus unable to be popularized. Second, the air radiators can remain there for a rather long period. A good heat sink structure and heat flow design can still satisfy the cooling requirements. The air radiators have a big room for improvement in efficiency. For example, the application of Cu and Al bonding technology for the heat sinks can substantially increase the cooling effects of air radiators.
CPU is a high density heat source. The heat should be pushed over a larger area, which will be emitted into the air by way of forced convection action of the fan, thus attaining the goal of heat dissipation. The heat is pushed onto the surface of the heat sink from the core of CPU, which is a thermal conduction process. With the high thermal conductive materials used, the heat sinks are quite helpful to the increased thermal conductivity. For example, the thermal conductivity of Al is 735KJ/(M.H.K), and the thermal conductivity of Cu is 1386KJ(M.H.K). Under the otherwise equal conditions, the heat conducted by copper almost doubles that by aluminum at a given time.
It can be seen from left that if the heat sinks are made by copper instead of aluminum, it will result in a considerable improvement in the thermal conduction.
Thus, it will have a remarkable ??curative??effect on highly-concentrated heat of CPU. However, there are some factors which have to be considered, i.e. the specific weight of copper is bigger than that of aluminum, which is not in conformity with the weight limit of heat sinks; the hardness of red copper is lower than that of Aluminum alloy AL6063, and some of its machining properties (i.e. slotting) are not as good as aluminum??s; the melting point of copper is much higher than that of aluminum, which is not good to extrusion.
Therefore, we have adopted the technology of Cu and AL bonding. Cu can offer high thermal conductivity, which can transfer the heat to the fins of Al materials, and then dispersed into the air by the convection action of the fan, thus having the weight controlled, and limiting the production, meanwhile achieving some improvements in effects.
At present, the markets are flooded with various Cu/Al CPU radiators. Various processes are adopted to combine Cu and AL. The most commonly used is brazing, screw locking, the combination of thermal expansion and cold contraction, mechanical extrusion, etc.
1.Brazing Operation
Brazing is a kind of welding method by which metallic materials, which have lower melting points than the substrate materials, are used as the solder, and under the temperature lower than the melting point of the substrates but higher than that of the solder, the liquid flux are used to moisten the substrates, fill the joint clearance, and then make it condensed into a firm interface.
The main operating procedures include material pre-treatment, assembly, heating welding, cooling and post-treatment. The most commonly used brazing is Tin brazing. A very reliable oxidized layer (Al2O3) is produced on the Al surface, thus resulting in a great difficulty in the brazing operation of Cu and Al. This is the biggest obstacle in the brazing operation, which must be removed or after being decomposed by the chemical reaction, then have a Tin layer or other easy to braze materials electroplated, thus Cu and Al can be easily brazed together.
The Cu base on the heat sinks is for thermal conduction purpose, which requires not only the mechanical strength, and more importantly, a large welding area (good welding effect). Only by this, the heat dissipation effects can be improved otherwise, no effects will be achieved. Rather, it will be made even worse than other solid Al alloy heat sinks. The most serious problem in the Cu and Al brazed heat sinks currently used is poor welding effects, or unstable quality. No inspection means or inspection criterions are available now for the effective welding of almost all the brazed heat sinks. The quality can't be judged by only visional checks. The following diagrams are the brazing interfaces measured under the non-destructive scanning detector. (The samples are taken from the retail market at random. After continuous improvements, the welding effects have been considerably increased).
In the left diagrams, the red fraction indicates poor brazing, while the blue indicates good bonding. But the overall welding effect is relatively poor and non-stable. Many tests and strictly controlled production specifications resulted in the qualified products. Please see the scanned diagram on the right side.
The welding effect of the samples in the above diagrams exceeds 90%, but it is really difficult to guarantee the stable brazing quality in the production.
2. Screw Locking
Tests proved that a high performance heat dielectric is placed between the bottom and the Copper block, and fastened with the screws after a 80kgf force is applied. Thus it will produce the same thermal dissipation effects as the Cu/AL brazing, and achieve the desired effects. Compared to the brazing operation, it can offer simple operation, stable quality, simplified manufacturing process and less equipment cost. Main procedures include Cu wafer skiving, leveling( flatness<0.1mm), boring, the heat dielectric coated for boring, tapping, cleaning, hard pre-compression procedures, two-stage locking operation, fixing the torque force for locking screws. During the manufacturing process, the Cu and Al flatness and roughness, and the torque force for locking screws must be kept under control, so as to improve the efficiency. This is a good Cu/AL bonding method.
If the heat dielectric used has poor quality, or the copper block has poor flatness, no heat can successfully be conducted to the surface of AL heat sinks, thus resulting in the lower effects. Further, the locking force of the screws and the purity of Cu materials are also the adverse factors.
3.The Combination of Heat Expansion and Cold Contraction
On the bottom of the AL heat sink is a round hole (o=D1) and a copper rod (o =D1+0.1MM) (see below). When the AL heat sink is heated to 400°C, it will be expanded and the hole size is expanded to over D1+0.2MM. A special-purpose machine is used to cram the copper rod at the room temperature into the round hole of the AL heat sink. After being cooled and contracted, the copper rod and Al heat sink will be well bonded together. This is also a reliable method, which offers a very high Cu / Al reliability and the optimum density. However, the dimensions of the Cu rod and the round hole, and the quality of the surface roughness must be brought under good control. These will produce some effects on the thermal dissipation effects.
4. Mechanical Extrusion.
By mechanical extrusion, the copper block with a larger diameter than AL bore size will be mechanically extruded with the Al heat sink together. AL is ductile, so Cu can be well bonded with AL heat sink at the room temperature. This method will also bring about a good effect. However, it has a fatal disadvantage, that is, during the process that the copper is extruded into the AL hole, the interior surface of such hole is easily skived by the copper, thus seriously effecting the conduction of the heat. This kind of problems can be avoided by rational arrangement of interference, and the optimized design of the copper block.
In a word, there are many kinds of methods for Cu/AL combination, but the interface quality must be guaranteed. Otherwise, the thermal dissipation effects are not as good as the solid AL Alloy heat sinks. New manufacturing processes need continuous verification, continuous improvement, and finally the anticipated effects can be achieved. But when choosing the Cu/Al radiators, do not just judge from its appearance, but make tests and comparisons. Only by this, can you have a superior Cu/AL radiator.
http://www.coolermaster.com/index.php?LT=english&Language_s=2&url_place=discovery_detail&serial=10
2003-09-22 On Cu/Al Radiators
The amazing Moor Law predicts that the number of transistors on the integrated circuits will be doubled every two years. In order to improve the operation performance, semi-conductors engineers have kept improving the integrity of the transistors on the silicon chips, thus making it verified over and over again. Since 1971, the number of the transistors in a single chip has risen by over 1800 times. The increased integrity has also become one of the driving forces for the prosperity of the computer industry.
The CPU currently used adopts the manufacturing technology with 130 nanometers (0.13 micron) line width. The CPUs manufactured with the production process of 90 nanometers will be put into the market, and the R &D in the production process including LADI and EUV has successfully come out. All these show that there is an ample room in technical development for the CPU with higher manufacturing density and faster operation. The density of future CPU integrated transistors will be multiplied, namely, the number of the transistors integrated in a given area will be multiplied.
However, the total energy consumption and the heat generated therefrom will be increased accordingly. More importantly, the electric energy consumed by CPU will be transformed into the heat energy, which is not only the growth in the value of the power, but also concentrated in a smaller space, thus resulting in a unprecedented difficulty in the heat dissipation. If such problem can\'t be solved effectively, the high density integrated technology can not be applied, which is a big bottleneck to block the CPU development. Take P4 3.06G CPU from Intel as an example, there are 55 million transistors integrated in a die area of 11.9x12.1 mm2 , with the biggest heat dissipation power of 70W. The heat problem of future CPU with over P4 3.6GHZ is a severe challenge facing CPU radiator manufacturers.
In order to achieve a good effect in heat dissipation, many manufacturers have demonstrated some very extreme heat dissipating products, such as water radiators and liquid nitrogen radiators, to try to solve the imminent heat dissipation problems. As a matter of fact, these products are still under commercially advertising, not used yet for CPU heat dissipation. This can be attributed to two factors. First, the reliability and quality of these products have not been verified, and no standard framework has been set up, thus unable to be popularized. Second, the air radiators can remain there for a rather long period. A good heat sink structure and heat flow design can still satisfy the cooling requirements. The air radiators have a big room for improvement in efficiency. For example, the application of Cu and Al bonding technology for the heat sinks can substantially increase the cooling effects of air radiators.
CPU is a high density heat source. The heat should be pushed over a larger area, which will be emitted into the air by way of forced convection action of the fan, thus attaining the goal of heat dissipation. The heat is pushed onto the surface of the heat sink from the core of CPU, which is a thermal conduction process. With the high thermal conductive materials used, the heat sinks are quite helpful to the increased thermal conductivity. For example, the thermal conductivity of Al is 735KJ/(M.H.K), and the thermal conductivity of Cu is 1386KJ(M.H.K). Under the otherwise equal conditions, the heat conducted by copper almost doubles that by aluminum at a given time.
It can be seen from left that if the heat sinks are made by copper instead of aluminum, it will result in a considerable improvement in the thermal conduction.
Thus, it will have a remarkable ??curative??effect on highly-concentrated heat of CPU. However, there are some factors which have to be considered, i.e. the specific weight of copper is bigger than that of aluminum, which is not in conformity with the weight limit of heat sinks; the hardness of red copper is lower than that of Aluminum alloy AL6063, and some of its machining properties (i.e. slotting) are not as good as aluminum??s; the melting point of copper is much higher than that of aluminum, which is not good to extrusion.
Therefore, we have adopted the technology of Cu and AL bonding. Cu can offer high thermal conductivity, which can transfer the heat to the fins of Al materials, and then dispersed into the air by the convection action of the fan, thus having the weight controlled, and limiting the production, meanwhile achieving some improvements in effects.
At present, the markets are flooded with various Cu/Al CPU radiators. Various processes are adopted to combine Cu and AL. The most commonly used is brazing, screw locking, the combination of thermal expansion and cold contraction, mechanical extrusion, etc.
1.Brazing Operation
Brazing is a kind of welding method by which metallic materials, which have lower melting points than the substrate materials, are used as the solder, and under the temperature lower than the melting point of the substrates but higher than that of the solder, the liquid flux are used to moisten the substrates, fill the joint clearance, and then make it condensed into a firm interface.
The main operating procedures include material pre-treatment, assembly, heating welding, cooling and post-treatment. The most commonly used brazing is Tin brazing. A very reliable oxidized layer (Al2O3) is produced on the Al surface, thus resulting in a great difficulty in the brazing operation of Cu and Al. This is the biggest obstacle in the brazing operation, which must be removed or after being decomposed by the chemical reaction, then have a Tin layer or other easy to braze materials electroplated, thus Cu and Al can be easily brazed together.
The Cu base on the heat sinks is for thermal conduction purpose, which requires not only the mechanical strength, and more importantly, a large welding area (good welding effect). Only by this, the heat dissipation effects can be improved otherwise, no effects will be achieved. Rather, it will be made even worse than other solid Al alloy heat sinks. The most serious problem in the Cu and Al brazed heat sinks currently used is poor welding effects, or unstable quality. No inspection means or inspection criterions are available now for the effective welding of almost all the brazed heat sinks. The quality can't be judged by only visional checks. The following diagrams are the brazing interfaces measured under the non-destructive scanning detector. (The samples are taken from the retail market at random. After continuous improvements, the welding effects have been considerably increased).
In the left diagrams, the red fraction indicates poor brazing, while the blue indicates good bonding. But the overall welding effect is relatively poor and non-stable. Many tests and strictly controlled production specifications resulted in the qualified products. Please see the scanned diagram on the right side.
The welding effect of the samples in the above diagrams exceeds 90%, but it is really difficult to guarantee the stable brazing quality in the production.
2. Screw Locking
Tests proved that a high performance heat dielectric is placed between the bottom and the Copper block, and fastened with the screws after a 80kgf force is applied. Thus it will produce the same thermal dissipation effects as the Cu/AL brazing, and achieve the desired effects. Compared to the brazing operation, it can offer simple operation, stable quality, simplified manufacturing process and less equipment cost. Main procedures include Cu wafer skiving, leveling( flatness<0.1mm), boring, the heat dielectric coated for boring, tapping, cleaning, hard pre-compression procedures, two-stage locking operation, fixing the torque force for locking screws. During the manufacturing process, the Cu and Al flatness and roughness, and the torque force for locking screws must be kept under control, so as to improve the efficiency. This is a good Cu/AL bonding method.
If the heat dielectric used has poor quality, or the copper block has poor flatness, no heat can successfully be conducted to the surface of AL heat sinks, thus resulting in the lower effects. Further, the locking force of the screws and the purity of Cu materials are also the adverse factors.
3.The Combination of Heat Expansion and Cold Contraction
On the bottom of the AL heat sink is a round hole (o=D1) and a copper rod (o =D1+0.1MM) (see below). When the AL heat sink is heated to 400°C, it will be expanded and the hole size is expanded to over D1+0.2MM. A special-purpose machine is used to cram the copper rod at the room temperature into the round hole of the AL heat sink. After being cooled and contracted, the copper rod and Al heat sink will be well bonded together. This is also a reliable method, which offers a very high Cu / Al reliability and the optimum density. However, the dimensions of the Cu rod and the round hole, and the quality of the surface roughness must be brought under good control. These will produce some effects on the thermal dissipation effects.
4. Mechanical Extrusion.
By mechanical extrusion, the copper block with a larger diameter than AL bore size will be mechanically extruded with the Al heat sink together. AL is ductile, so Cu can be well bonded with AL heat sink at the room temperature. This method will also bring about a good effect. However, it has a fatal disadvantage, that is, during the process that the copper is extruded into the AL hole, the interior surface of such hole is easily skived by the copper, thus seriously effecting the conduction of the heat. This kind of problems can be avoided by rational arrangement of interference, and the optimized design of the copper block.
In a word, there are many kinds of methods for Cu/AL combination, but the interface quality must be guaranteed. Otherwise, the thermal dissipation effects are not as good as the solid AL Alloy heat sinks. New manufacturing processes need continuous verification, continuous improvement, and finally the anticipated effects can be achieved. But when choosing the Cu/Al radiators, do not just judge from its appearance, but make tests and comparisons. Only by this, can you have a superior Cu/AL radiator.
