High Quality Heat Sink

With the development of electronic technology, the efficiency of electronic components is relatively improved, and the amount of heat is also increasing. In order to maintain their normal working conditions, efficient heat dissipation is quite important. The heat sink to dissipate the heat generated by the operation of electrical components and improve their work efficiency. Heat sink is mostly made of aluminum alloy, brass or bronze in plate, sheet, or multiple sheet shapes. For example, the CPU central processing unit in the computer, the power tube and the line tube in the TV set, and the power amplifier tube in the power amplifier all use heat sinks.

Types of heat transfer:

1. Nature convection: the flow caused by the uneven temperature field of the fluid without relying on external forces such as pumps or fans.

2. Force convection: Convection of liquid or gas under the influence of external force.

(Heatsink with fan)

3. Liquid cooling: Use a pump to circulate the liquid in the heat pipe and dissipate the heat.

(Liquid cooling plate)

The history of heat sink:

As is well-known, the operating temperature of electronic equipment determines its service life and stability. In order to keep the working temperature of PC within a reasonable range, heat dissipation must be carried out. With the enhancement of PC computing power, the problem of power consumption and heat dissipation has increasingly become an unavoidable problem.

Generally speaking, the major heat sources in PC include CPU, motherboard, graphics card and other components such as hard disk. A considerable part of the electric energy consumed during their work will be converted into heat. Especially for the current high-end graphics card, it can easily reach 200W power consumption, and the heating capacity of its internal components can not be underestimated. In order to ensure its stable operation, it is more necessary to dissipate heat effectively.

The first generation - an era without the concept of heat dissipation

In November 1995, the birth of voodoo graphics card brought our vision into the 3D world. Since then, PC has almost the same level of 3D processing ability as arcade, creating a real era of 3D processing technology. Since then, the development of graphics chips has been out of control. The core working frequency has been increased from 100MHz to 900MHz, and the texture filling rate has soared from 100 million per second to 42 billion per second (GTX480). In the face of such a big change in performance, the heat is very large. Cooling equipment such as air cooling, heat pipe and semiconductor refrigeration chip are also applied to the graphics card. Today, let's introduce the development and trend of mainstream graphics card cooling equipment.

When the voodoo graphics card was first launched, there were no heat dissipation facilities, and the parameters on the core were exposed to us. Compared with the current mainstream graphics card, there was no saying of GPU at that time. The processing power of the main core chip on the graphics card is even weaker than the current network card, so the heat is almost zero, and there is almost no need for heat dissipation.

Second generation - Application of heat sink

In August 1997, NVIDIA entered the 3D graphics chip market again and released NV3, that is, Riva 128 graphics chip. Riva 128 is a 128bit 2D and 3D accelerated graphics core with a core frequency of 60MHz. The heating of the core has gradually become a problem, and the application of heat sink has officially entered the field of graphics card.

The third generation -- the arrival of the era of air cooling and heat dissipation

The release of tnt2 was like a heavy bullet shot into 3dfx's heart. The core frequency is 150MHz, which supports almost all 3D acceleration features at that time, including 32-bit rendering, 24 bit z-buffer, anisotropic filtering, panoramic anti aliasing, hardware convex concave mapping, etc. The performance enhancement means the increase of heating, but there is no great progress in technology. The 0.25 micron is still used, so the passive method of heat sink can no longer meet the current requirements, Active cooling mode start using in graphics card.

The cooling system twinturbo-ii (the second generation fully covered dual turbine cooling fan), the cooling fins completely cover the whole graphics card. When starting, the air will go out and in through two fans in one direction, which can effectively take away the heat of the chip and video memory quickly. Moreover, two ball bearing fans can effectively reduce noise, and the metal heat dissipation net makes the service life longer.

Although the high-speed fan is the best way to solve the heat dissipation problem, some friends can't stand the noise of fan while enjoying the 3D games. Fortunately, the application of heat pipe technology just solves this problem. It is generally composed of core heat absorption block, back heat absorption block, two large-area heat sinks and a heat pipe. As a passive heat conduction device, the heat pipe quickly transfers the heat from the heat absorption section to the heat release section through the phase state change of the internal working fluid, and then returns to the heat absorption section by relying on the internal capillary structure. It cycles back and forth without power consumption and noise. Moreover, it has strong heat conduction ability. It realizes the rapid heat transfer in a limited space, so as to increase the heat dissipation area, It is an effective means to greatly improve the effect of passive heat dissipation. However, this heat dissipation method still has disadvantages, because the heat dissipation capacity is not strong enough and can only be used on the middle-end card. If this technology is to be used in the high-end, a fan must be added.

Heat dissipation calculation principle

The general method of heat dissipation is to install the device on heat sink, the heat sink dissipates the heat into the air, and the heat will be dissipated through natural convection eventually.

Generally speaking, the heat flow (P) from the radiator to air can be represented by the following:

In formula P=hA η △ T

H is the total heat transfer conductivity of the heat sink (w / cm2 ℃),

A is the surface area of the heat sink (cm2),

η For heat sink efficiency,

△T is the difference between the maximum temperature of the heat sink and the environment temperature (℃).

In the formula above, h is determined by radiation and convection (natural convection, forced convection and material)

η It is mainly determined by the material size and thickness of the heat sink used. Generally speaking, materials with high thermal conductivity, such as aluminum (2.12w / cm²℃) and copper (3.85w/cm²℃）is quite poor.

η Is determined by the component of the heat sink. (influence of heat sink structure)

In a word, the larger the surface area of the heat sink and the greater difference temperature between heat sink and ambient, make more effective the heat radiation of heat sink.

Heat resistance

Parameter:

Rt-----Total internal resistance, ℃/W

Rtj---- Internal thermal resistance of semiconductor devices, ℃/W

Rtc----- Interface thermal resistance between semiconductor device and heat sink, ℃/W

Rtf----- Heat resistance of heat sink, ℃/W

Tj----- Semiconductor device junction temperature, ℃

Tc----- Semiconductor device shell temperature, ℃

Tf----- Heat sink temperature, ℃

Ta----- Environment temperature, ℃

Pc----- Service power of semiconductor devices, W

△Tfa----- Heat sink temperature rise, ℃

Heat dissipation calculation formula:

Rtf=(Ti-Ta)/Pc-Rti-Rtc

The thermal resistance RFF of heat sink is the main basis for selecting heat sink. TJ and RTJ are the parameters provided by semiconductor devices, PC is the parameters required by design, and RTC can be found in the thermal design professional books.

(1) Calculated total thermal resistance Rt:

Rt=(Timax-Ta)/Pc

(2) Calculate the heat sink thermal resistance RTF or temperature rise △ TFA

RTF = RTJ - RTC

△Tfa=Rtf × Pc

(3) According to the working conditions of heat sink (natural cooling or forced air cooling), select the heat sink according to RT or △ TFA and PC, and check the heat dissipation curve (RTF curve or △ TA line) of the selected heat sink. When the value found on the curve is less than the calculated value, the suitable heat sink is found.

Thermal conductivity

Thermal conductivity means in per unit length and per K, how much w energy can be transmitted, unit: w / m.

"W" refers to the power unit, "m" representing the length unit meter, and "K" is the absolute temperature unit.

The larger the value, the better the thermal conductivity.

Thermal conductivity (unit: w / MK)
Ag	429	CU	40L
Au	317	AL	237
Fe	80	Pd	34.8
AL1070	226	AL1050	209
AL6063	201	AL6061	155
AL1100	218—222	AL3003	155—193
SUS	24.5

AL6063: Common material for aluminum extrusion

AL6061: CNC maching metal:

AL1100 or AL1050: AL fin common material

C1100: Cu fin common material

C1020: Common material of heat pipe

ADC12 or ADC 10 or A380: Die casting material

Classification of Heat sink

1. According to the material used, it can be divided into:

a. Aluminum heat sink

b. Copper heat sink

c. Copper aluminum combined heat sink

d. Heat pipe fin

2. According to the manufacturing process, it can be divided into:

a. Extruded heat sinks

This is an excellent heat dissipation material widely used in modern heat dissipation, most of the manufacturers use AL6063-T5 high quality aluminum, its purity can reach more than 98%, it has strong heat conduction capacity, low density and low price, so it has been favored by major manufacturers.

b. Forging and casting heat sink:

Common used in LED, the shape: heat sink with rounded pin

c. AL skiving fin heat sink

Advantages: heat dissipation area (solves the problem of aluminum extruded heat sink, because the fin is too dense)

Disadvantages: Suitable for small batch production, high cost (compared with aluminum extruded heat sink)

d. Copper skiving heat sink:

Advantages: good heat dissipation performance, which solves the problem of copper extrusion.

Disadvantages: high cost, heavy weight, high hardness, difficult to process (relative to AL)

g. Heat sink with insert copper

Advantages: low cost and mass production

Disadvantages: structure

It is mostly used for computer CPU. The contact part is changed to copper block. Copper has fast heat absorption and heat conduction energy

With the characteristics of strong force, it can quickly bring a large amount of heat energy generated by CPU operation to the surface copper block, and the copper block is closely combined with the aluminum extruded heat sink, so that a large amount of heat energy can quickly diffuse to the aluminum extruded heat sink and be taken away by the rotation of the fan.

i. bonded heat sink

Advantages:

This technology can be arbitrarily combined and matched with copper and aluminum fins and copper and aluminum base, and can also effectively avoid the disadvantages of new thermal resistance caused by uneven heat conduction of various welding pastes in the welding process, large size heat sink can be produced

Disdvantages:

Make customers have more selectivity and diversity of thermal solutions. However, due to the particularity of its processing, the cost of mass production is still too high

Cooling plate

The design of cooling plate:

The cooling plate is a compact and thin plate-shaped, with fluid channels arranged inside, so as to generate convection between the fluid and the cooling plate and dissipate the thermal power consumption of high-power electronic components which on the surface of the cooling plate.

The application advantage of cooling plate is that it can dissipate more heat in per unit area, so the heat sink structure can be miniaturized. The disadvantage of cooling system is that it must be used in the system with fluid medium, the maintenance is complex, and the reliability of components is high.

Water cooling plate design basis

P: power consumption

Tc, Tj: Tc refers to the surface temperature of heat sink, Tj refers to chip junction temperature.

Tin: Water inlet temperature

Δ TC: Surface temperature rise of heat sink, Δ T = (Tc-Tin)/P

Tout: outlet water temperature

△ TW: inlet and outlet water temperature rise, △ TW = Tout-Tin

Ta: Environment temperature

Fluid: EGW x%, or PGW x%, or water

△ ts: Temperature difference of each chip on the heat sink surface

Pressure: fluid Pressure drop

Reliability of water cooling plate

1) Strength - the product meets the requirements for structural use

2) Pressure holding test - the product meets the requirements for sealing under high pressure operation in the system

3) Leakage test - the product meets the requirements for leakage per unit time under certain pressure conditions

4) Corrosion resistance requirements - the raw materials used by the product meet the requirements for years of corrosion resistance and no leakage

5) Vibration requirements - the product meets the requirements for sealing under certain vibration conditions. And the structure is not damaged, the tightness is not reduced.

6) Other, such as flatness, roughness, screw drawing force, screw preload, etc

Processing technology of water cooling plate:

1) CNC channel type: CNC (grooving) + argon arc welding, CNC (grooving) + brazing, CNC (grooving) + vacuum brazing, CNC (grooving) + friction stir welding, CNC (grooving) + O ring

2) Deep hole processing form: gun drill + argon welding , gun drill + twist piece + argon welding, gun drill + O ring, gun drill + twist piece + O ring

3) Casting form: gravity casting buried pipe, gravity casting + argon welding · gravity casting + brazing, gravity casting + vacuum brazing welding, gravity casting + friction stir welding

4) Coil welding form: CNC aluminum plate + copper pipe + epoxy, CNC aluminum plate + steel pipe + epoxy, CNC aluminum plate + copper pipe + tin welding

5) Ultra thin water cooling plate process: wide flat tube welding, stamping sheet diffusion welding, stamping sheet brazing, stamping sheet vacuum brazing

6) Extruded water plate form: array shunt hole water plate, ultra-thin battery water cooling plate

Surface treatment

1. Sand blasting

Sand blasting is a method that uses compressed air to blow out quartz sand at high speed to clean the surface of parts. It is also called sand blowing. It not only removes rust, but also removes oil. For coating, it is very suitable for removing rust on the surface of parts; Modify the surface of the part; The high-strength bolt connection in steel structure is an advanced method. Because the high-strength connection uses the friction between the joint surfaces to transfer force, it has high requirements for the quality of the joint surface. The joint surface must be treated with sand blasting.

Sand blasting is used for complex shape, easy to remove rust manually, low efficiency and poor site environment.

The sand blasting machine has sand blasting guns of various specifications. As long as it is not a particularly small box, the gun can be put in to dry.

The supporting products of the pressure vessel----The head, adopts sand blasting to remove the oxide skin on the surface of the workpiece. The diameter of quartz sand is 1.5m~3.5mm.

There is a kind of processing that uses water as a carrier to drive the emery to process parts, which is one of sandblasting.

2.Surface treatment of aluminum alloys

1). Electroplating process of aluminum alloy

Due to the chemical and physical properties of aluminum and its alloys, the electroplating on aluminum parts is much more difficult than that on steel substrate, and some special treatments must be carried out. The following is the electroplating process flow of automobile aluminum alloy wheel hub

Polishing - shot peening (selective) → ultrasonic wax removal → water washing → alkali etching and oil removal → water washing → acid etching (light out) → water washing → zinc dipping → water washing → dezincification → water washing → zinc dipping → water washing → electroplating dark nickel → water washing → acid bright copper I → water washing → polishing → ultrasonic wax removal → water washing → cathodic electrolytic oil removal → water washing → activation → water washing → semi bright nickel → high sulfur nickel → bright nickel → nickel sealing → water washing → chromium plating → water washing

2). Electroless plating process of aluminum alloy

Electroless nickel plating on aluminum alloy is more and more accepted by manufacturers because of its excellent performance. Electroless nickel plating is also known as nickel phosphorus plating. The aluminum alloy surface (computer heat sink, hard disk, etc.) adopts the following process

Normal temperature chemical degreasing → running water cleaning x 2 → thermal degreasing → running water cleaning x 2 → alkali corrosion → running water cleaning x 3 → acid pickling → running water cleaning x 2 → primary zinc immersion → running water cleaning x 2 → 20% nitric acid → running water cleaning × 3 → secondary zinc dipping → running water cleaning x3 → (1-5%) ammonia pre dipping → pre plating chemical nickel → running water cleaning x2 → pure water cleaning → medium phosphorus bright chemical nickel or high phosphorus bright chemical nickel → running water cleaning x3 → passivation → running water cleaning x3 → drying and drying → inspection → packaging

The aluminum substrate on the surface of electronic components such as semiconductor devices often requires electroless nickel plating and electroless gold plating due to the need of welding. The process flow is as follows:

Degreasing → alkali etching → polishing → first zinc dipping → dezincification → pretreatment solution → second zinc dipping → electroless nickel plating → pickling prepreg → electroless gold plating →final treatment

3. Passivation

Passivation is to treat the metal in Nitrite, nitrate, Chromate or Dichromate solution to make a layer of chromate passivation film on the metal surface. It is often used as the post-treatment of zinc and cadmium coatings to improve the corrosion resistance of coatings, the protection of non-ferrous metals, and the adhesion of paint films.

Passivation process of aluminum and aluminum alloy:

Chromate treatment of aluminum and its alloys can obtain another chemical conversion film completely different from anodization. Its composition is the same as chromate film of zinc and cadmium, which is a complex compound of chromium.

Difference between aluminum anode and chromate --- Conductive and non-conductive

Common-used finish of aluminum extrusion heat sink: 1.Clean 2.Anodizing 3.Chromate

Common-used finish of copper heat sink: Anti-oxidation

4. Nickel plating

The method of plating a layer of nickel on metal or some non-metal by electrolytic or chemical methods is called nickel plating. Nickel plating includes electroplating and electroless nickel plating.

Electroplating is in an electrolyte composed of nickel salt, conductive salt, PH buffer, and wetting agent, metallic nickel is used for the anode. When direct current is applied, a uniform and dense nickel plating layer will be deposited on the plated parts. Bright nickel is obtained from the plating solution with brightener, while dark nickel is obtained from the electrolyte without brightener.

Electroless plating is also called autocatalytic plating. The specific process refers to the process in which metal ions in aqueous solution are reduced by reducing agent and precipitated on the surface of solid matrix under certain conditions. As defined in ASTM b374 (American Society for testing and materials), autocatalytic plating is "deposition of a metallic coating by a controlled chemical reduction that is catalyzed by the metal or alloy being deposited". This process is different from displacement plating. The coating can be continuously thickened , and the plated metal itself also has catalytic ability.

Electroless nickel plating is commonly used in heat dissipation industry due to the good solderability.

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