Radiator in our daily lives is very rich kind of radiator. There notebook radiator, car radiator, etc.
The CPU Die usually less than 2 cm2, but the consumption has reached tens, hundreds of watts, if not timely transfer heat out of the heat accumulation in Die in once, it will lead to serious consequences.
Radiator, the most important is its base as much as possible in a short time can absorb the heat of the CPU releases that moment absorbing capacity, which can perform only with the metal of high thermal conductivity coefficient. For metal thermal conductivity material, the specific heat and thermal conductivity are two important parameters.
Thermal conductivity is defined as: per unit length per K, the number W of energy can be transmitted in units of W / mK. Where "W" refers to the thermal power units, "m" is the length in meters, and the "K" is the absolute temperature units. The greater the value, the better the thermal performance. Here are some common metal thermal conductivity coefficient table:
Thermal conductivity (Unit: W / mK)
Silver Copper 401 429
Golden Aluminum 237 317
Lead iron 80 34.8
1070 aluminum alloy aluminum alloy 209 2261050
6063 aluminum alloy aluminum alloy 155 2016061
It can be seen, silver and copper are the best thermal conductivity material, followed by gold and aluminum. However, gold, silver is too expensive, so the fins are primarily made of aluminum and copper. However, due to the copper density, complex process, more expensive, so now fans usually use more lighter aluminum, of course, for air-cooled heat sink, in addition to considering the material when the thermal conductivity, but also must consider heat capacity of the radiator, combination of these two parameters, the advantages of aluminum is manifested. However, this article will only discuss aspects of thermal conductivity, for those we discussed in detail in the next section.
Heat sink spare parts
To improve the heat transfer capacity of the heat sink base, the choice of a material having high thermal conductivity on the one hand, but also other heat sources such as the combination of the CPU and the heat sink to solve the tightness of the base problem. According to the law of heat conduction, under the premise of a fixed material, conductivity is proportional to the contact area, the contact is inversely proportional to the distance. The larger contact area, the faster the heat can dissipate, but the CPU for its Die is fixed, so the combination of distance is even more important.
Although in theory, be able to heat the base sheet in intimate contact and the CPU, but objectively speaking, regardless of how the two contact surfaces smooth, or have a gap between them, i.e. the presence of air, and the poor thermal conductivity of air , which requires excellent design, strong gripping force to the heat sink clip tightly buckle in the CPU, in addition, the need for better thermal conductivity and can use some deformed thing instead of air to fill these gaps, such as thermal grease or heat tape. Ideally, the clip is firmly fixed to the heat sink in the CPU, the CPU heat sink and contacts in parallel in order to maintain full contact area, a number of small voids between them is completely filled with grease to maintain the minimum contact resistance.
Die casting Heat sink parts
However, it must be clear that, whatever the thermal grease or thermal tape, which can only be a supporting role, as compared with the base material copper heat sink, the thermal resistance is many times larger. To achieve the heatsink base to maximize heat transfer capability, but also must ensure the smooth and flat heat sink base, so you can really reduce the gap between the radiator and the contact surface of the CPU.
Radiator bottom surface treatment process / chemical passivation fly Sea
The bottom surface treatment processes used include:
Drawing process (grinding)
Drawing process is the use of the most underside treatment process. When using a drawing of a surface with a certain roughness and hardness of the tool, such as the common sandpaper, filing, etc., on the surface of the object handle one-way, repeated or rotating friction, with clipping effects tools to remove rough surface friction surface treatment projections; course, while polished projections also cause scratches on the original flat surface. Therefore should be used from coarse to fine gradual process, gradually reducing the treated surface roughness.
Drawing process characteristics: a parallel grinding marks
Disc milling process (cutting)
Refers to the disk milling process, after the heat sink is fixed by the bottom surface of the high-speed rotation of the cutting tool surface of the radiator, the tool is always rotated in the same plane, the cutting out of the bottom surface is very smooth. Same with the drawing process, tool tray finer milling process used, the higher the degree of cutting out the bottom of the formation. Higher manufacturing costs disc milling process, but relatively drawing only twenty-three process, when comparing the province, and the effect is ideal.
Disc milling process features: curved grinding marks
CNC machine tools
CNC machine tools used in flat bottom surface of the heat sink is mainly used in the processing technology is still milling. However, the traditional dish of different milling, CNC milling tool can precisely control the relative distance between the microcontroller and the heat sink between. After the tool contacts the bottom surface of the heat sink, the relative motion between the horizontal direction, to the traditional disk milling cutter gap left untreated section cutting, to achieve the full effect of the plane, and not to any subsequent treatment can generally get a mirror effect flatness can be less than 0.001mm.
Other processes
In addition to these types, there are other processes on the radiator end processing, such as polishing, "flying sea chemical passivation" is more polished radiator considerations of aesthetics, the underside of the heat sink flatness improvement quality performance is better.
As we said earlier, no matter how underside radiator processing, this mechanical process can not be made completely standard flat surface between the CPU and heat sink or voids exist gully always inevitable. These voids present in the conductivity of the air radiator has a great influence, known, high heat resistance of the air, and therefore must be used to reduce the thermal resistance of other substances, or else transfer performance of the heat sink will be larger discount can not even play a role. This is the origin of the heat medium. Its role is to fill the gap between large and small heat source and heat sink, such as CPU, increasing the contact area between the heat source and heat sink.
3 Performance Parameters
Since the thermal grease is a form of chemical substances, so it is also reflected in their work characteristics related performance parameters. Just understand the meaning of these parameters, you can determine the performance level of a thermal grease products.
Operating Temperature
Temperature is an important parameter to ensure that the thermal grease in a solid state or liquid state, the temperature is too high, thermal grease will decrease due to liquid viscosity; temperature is too low, it will become solid due to increased viscosity, both of kind of situation is not conducive to heat dissipation. Thermal grease operating temperature is generally -50 ℃ ~ 180 ℃. For thermal grease operating temperature, generally do not have to worry about, after all, it is difficult to CPU temperature outside this range by conventional means, unless you plan to use liquid nitrogen refrigeration - that temperatures will be out of action most of the thermal grease.
Aluminium die casting heat sink parts
Thermal conductivity
Compared with conventional radiators material, thermal grease thermal conduction system is much smaller, the current general specification, the thermal conductivity coefficient of thermal grease on the requirements for the 1.13W/mK, compared with copper 401W/mk, the gap can not be on the same day and language, but compared with air, is still high a lot. This also shows that the underside is smooth radiator how important it is, how shameless some manufacturers claim that its flat underside enough just by thermal grease filled radiator without affecting its cooling capacity argument.
Thermal Coefficient
Thermal coefficient of heat conduction of said objects on obstruction effect. The concept of thermal resistance is very similar, but also with similar units (℃ / W), that is, when the object continued to heat power 1W, temperature difference between the heat conduction path ends. Thermal resistance is clearly better, since the same ambient temperature and the thermal power, the lower the thermal resistance, the lower the heating temperature of the object. The size of the thermal resistance and thermal conductivity of the material used grease has a great relationship.
Permittivity
For some there is no metal cover to protect the CPU, the dielectric constant is a very important parameter, which is related to whether there is a short inside your computer problems. Standard thermal grease are used preferably in an insulating material, but some special grease (grease such as silver, etc.) may have a conductivity. Of course, the current CPU are fitted with a metal roof for thermal and protect the core, so do not worry about thermal grease overflow problem caused by a short circuit, but also when applied thermal grease must be careful not to mistakenly applied to other places such as the motherboard.
Heat sink thermal grease used in mainstream permittivity greater than 5.1.
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