What Are the Pros and Cons of a Large Heatsink?

A heat sink is a device that dissipates heat-prone electronic components in electrical appliances. It is mostly made of aluminum alloy, brass or bronze in plate shape, sheet shape, multi-piece shape. Heat sinks, power tubes in televisions, row tubes, and power amplifier tubes in power amplifiers all use heat sinks. In general, the heat sink should be coated with a layer of thermal grease on the contact surface between the electronic components and the heat sink, so that the heat emitted by the components is more effectively transmitted to the heat sink, and then radiated to the surrounding air through the heat sink.

heat sink

A heat sink is a device that dissipates heat-prone electronic components in electrical appliances. It is mostly made of aluminum alloy, brass or bronze in plate shape, sheet shape, multi-piece shape. Heat sinks, power tubes in televisions, row tubes, and power amplifier tubes in power amplifiers all use heat sinks. In general, the heat sink should be coated with a layer of thermal grease on the contact surface between the electronic components and the heat sink.

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2013 China (Shanghai) Electronic Thermal Material Exhibition

Exhibition time: November 11, 2013 --- November 12, 2013

Exhibition time: November 13, 2013 --- November 15, 2013

Withdrawal time: November 15, 2013 --- November 15, 2013

Exhibition venue: Shanghai New International Expo Center

2014 China (Shenzhen) Electronic Thermal Material Exhibition

Exhibition time: April 7, 2014 --- April 8, 2014

Exhibition time: April 9, 2014 --- April 12, 2014

Withdrawal time: April 12, 2014 --- April 12, 2014

Venue: Shenzhen Convention and Exhibition Center ^[1]

Make

As we all know, the operating temperature of electronic devices directly determines its service life and stability. To keep the operating temperature of PC components within a reasonable range, in addition to ensuring that the temperature of the PC operating environment is within a reasonable range, it must also be Perform heat treatment. With the enhancement of PC computing capabilities, power consumption and heat dissipation issues have become increasingly unavoidable.

Generally speaking, the major heat sources in PCs include CPUs, motherboards, graphics cards, and other components such as hard disks. A considerable part of the power they consume when they work is converted into heat. Especially for the current high-end graphics cards, power consumption can reach 200W at any time, and the heat generated by its internal components cannot be underestimated. To ensure stable operation, it is necessary to effectively dissipate heat.

The first generation-an era without cooling concepts

In November 1995, the birth of the Voodoo graphics card brought our vision into the 3D world. Since then, PCs have almost the same level of 3D processing capabilities as arcades, creating a true era of 3D processing technology. Since then, the development of graphics chips

Any device has certain losses during operation, and most of the losses become heat. Low power devices have low losses and do not require heat sinks. High-power devices have large losses. If no heat dissipation measures are taken, the die temperature can reach or exceed the allowable junction temperature, and the device will be damaged. Therefore, a heat sink must be added. The most commonly used method is to install the power device on the radiator, and use the radiator to dissipate heat to the surrounding space. If necessary, add a cooling fan to enhance cooling and heat dissipation at a certain wind speed. In some large-scale equipment, mobile cold water cooling plates are also used on the power devices, which have better heat dissipation effect. The heat dissipation calculation is to determine the proper heat dissipation measures and heat sinks through calculation under certain working conditions. The power device is mounted on the heat sink. Its main heat flow direction is transmitted from the die to the bottom of the device, and the heat is dissipated to the surrounding space through the heat sink. If there is no fan to cool at a certain wind speed, this is called natural cooling or natural convection heat dissipation.

There is a certain thermal resistance in the heat transfer process. The thermal resistance transmitted from the device die to the bottom of the device is R JC, the thermal resistance between the bottom of the device and the heat sink is R CS, the thermal resistance of the heat sink to dissipate heat to the surrounding space is R SA, and the total thermal resistance R JA = R JC + R CS + R SA. If the maximum power loss of the device is PD and the allowable junction temperature of the device is TJ and the ambient temperature is TA, the allowable total thermal resistance R JA can be obtained by the following formula.

R JA (TJ-TA) / PD

Then calculate the maximum allowable thermal resistance R SA of the radiator to the ambient temperature as

R SA ((T_ {J} -T_ {A}} \ over {P_ {D}})-(R JC + R CS)

In order to leave room for design, the TJ is generally set to 125 ° C. The ambient temperature should also consider the worse case, generally set TA = 40 60 . The size of R JC is related to the size and package structure of the die, and can generally be found in the device data sheet. The size of R CS is related to the mounting technology and the package of the device. If the device is installed with a thermal grease or a thermal pad and then installed with a heat sink, its R CS value is typically 0.1 0.2 ° C / W; if the bottom surface of the device is not insulated, and additional mica sheet insulation is required, its R CS can reach 1 ° C / W. PD is the actual maximum power loss, which can be calculated according to the operating conditions of different devices. In this way, R SA can be calculated, and a suitable radiator can be selected according to the calculated R SA value.

Small radiators (or heat sinks) are made of aluminum alloy sheet through stamping process and surface treatment, while large radiators are formed by extrusion of aluminum alloy, and then processed by mechanical processing and surface treatment. They are available in various shapes and sizes for devices with different device installations and different power consumption. Radiators are generally standard parts, and profiles can also be provided. Users can cut non-standard radiators into certain lengths according to requirements. The surface treatment of the heat sink has electrophoretic paint or black oxygen polarization treatment, the purpose of which is to improve heat dissipation efficiency and insulation performance. It can be increased by 10 15% under natural cooling, 3% under ventilated cooling, and the electrophoretic paint can withstand 500 800V.

Radiator manufacturers give thermal resistance values or relevant curves for different types of radiators, and give different thermal resistance values under different heat dissipation conditions.

A power operational amplifier PA02 (product of APEX) is used as a low-frequency power amplifier, and its circuit is shown in Figure 1. The device is packaged in an 8-pin TO-3 metal case. Device operating conditions

It is as follows: The working voltage VS is 18V; the load impedance RL is 4; the working frequency can reach 5kHz under DC conditions; the ambient temperature is set to 40 ° C; natural cooling is used.

Checking the PA02 device data shows that the typical value of the quiescent current IQ is 27mA and the maximum value is 40mA; the RJC (from the die to the case) of the device is typically 2.4 / W and the maximum value is

2.6 ° C / W.

The power consumption of the device is PD:

PD = PDQ + PDOUT

Where PDQ is the power consumption of the device's internal circuit, and PDOUT is the power consumption of the output power. PDQ = IQ (VS + | -VS |), PDOUT = V ^ {2} _ {S} / 4RL, substitute the above formula

PD = IQ (VS + | -VS |) + V ^ {2} _ {S} / 4RL = 37mA (36V) + 18V2 / 4 4 = 21.6W

The quiescent current in the formula is 37mA.

Radiator thermal resistance R SA calculation: R SA ((T_ {J} -T_ (A)) \ over {P_ {D}})-(R_ {JC} + R_ {CS}})

In order to leave room, TJ is set to 125 ° C, TA is set to 40 ° C, R JC is set to the maximum value (R JC = 2.6 ° C / W), R CS is set to 0.2 ° C / W, (PA02 is directly installed on the radiator,

Thermal grease). Substituting the above data into the formula

R SA {125 -40 } \ over {21.6W}-(2.6 / W + 0.2 / W) 1.135 / WHSO4 The thermal resistance is 0.95 / W at natural convection, which can meet the requirements of heat dissipation.

Precautions

1. The maximum power consumption value in the device data cannot be taken in the calculation, but it must be calculated according to the actual conditions; the maximum junction temperature in the data is generally 150 ° C.

There is room in the plan to take 125 ° C, and the ambient temperature cannot be taken to 25 ° C (to consider the actual temperature of the summer and the chassis).

2. The installation of the radiator should consider the direction that is favorable for heat dissipation, and the heat dissipation holes must be opened at the corresponding position on the chassis or chassis

).

3. If the case of the device is an electrode, the mounting surface is not insulated (not insulated from the internal circuit). Mica gaskets must be used for insulation during installation to prevent short circuits.

4. The pins of the device should pass through the heat sink, and holes should be drilled in the heat sink. To prevent the pins from touching the hole wall, a PTFE sleeve should be put on.

5. In addition, different types of heat sinks have different thermal resistances under different heat dissipation conditions, which can be changed during design, that is, the thermal resistance of these heat sinks can be referred to in practical applications.

To calculate, and can use a similar structure shape (cross-sectional area, perimeter) of the profile composed of heat sinks to substitute.

6. In the above calculations, some parameters are set, which may differ from the actual values, and the size of the substitute model is not exactly the same, so it should be used as a mold during mass production.

Tests are to be conducted to confirm whether the radiator selection is appropriate, and if necessary, some modifications (such as the length of the profile or the change of the profile type) can be made for mass production.

IDT thermal data

Considering the power consumption of microelectronic devices, thermal management is critical to the optimal performance of any electronic product. Microelectronics

The operating temperature of the component determines the speed and reliability of the product. IDT is actively committed to strengthening the research and development of its products and packages to achieve optimal speed and

reliability. However, product performance is often affected by implementation, so careful handling of factors that affect operating temperature can help maximize performance.

The most important factors affecting device operating temperature include power consumption, air temperature, package construction, and cooling devices. These factors determine together

The operating temperature of the product. The following is the equation currently used to calculate the operating temperature

QJA = (TJ-TA) / PQJC = (TJ-TC) / PQCA = (TC-TA) / PQJA = QJC + QCATJ = TA + P [QJA]

TC = TA + P [QCA]

QJA = package thermal resistance from die to ambient air (degrees per watt)

QJC = Package Thermal Resistance from Die to Package Housing (Celsius per Watt)

QCA = package thermal resistance from package enclosure to ambient air (degrees per watt Celsius)

TJ = average die temperature (degrees Celsius)

TC = package case temperature (Celsius)

TA = ambient air temperature (degrees Celsius)

P = power (Watts)

The above equation is the current method for determining package temperature. The industry sometimes adopts more precise and complex methods, but accordingly needs to get more