FAQ's | Questions and answers on the subject of electronics cooling

ALUTRONIC's portfolio includes over 250 standard profiles, which can be easily filtered and sorted by geometric and/or thermal parameters using the Heat Sink Finder.

If you still cannot find a suitable profile, you can set up customized extrusions.

This offers the following advantages:

• Optimisation of the mass-to-surface ratio leads to cost savings due to a smaller amount of material and shorter machining time during cutting.
• Optimisation of the profile cross-section leads to a more efficient cooling effect
• Assembly functions such as screw channels, sockets, plateaus or insertion slots are already integrated in the profile
• Reduction of the number of components in enclosure solutions through combination profiles
• Exclusivity through exclusive right of use
• Short delivery times at low costs through stockpiling in combination with framework agreements, provided that the minimum pressing quantity specified by the aluminium extrusion plants is adhered to, depending on the market situation.

It is important for designers to know that, especially for "large" profiles with a wrap circle of >350mm, limit dimensions and shape tolerances according to the standards below can assume values that are significantly higher than the values of the more familiar DIN ISO 2768-1 or DIN ISO 2768-2 (standard for general tolerances for length and angle dimensions as well as shape and position).
For example, the cross-sectional dimensions of a profile with a wrap circle of 200mm to 300mm may include maximum deviations of ±2.5mm; the convexity or concavity in this case may be up to 1.8mm.

The valid standards for limit dimensions and shape tolerances of extruded profiles made of aluminium and aluminium alloys are:
- DIN EN 12020-2: valid for wrap-around circles of >350mm, replaces DIN 17615-3, which is no longer valid.
- DIN EN 755-9: valid for wrap-around circles of >800mm, replaces DIN 1748-4 which is no longer valid.

DIN EN 12020-2 differs from DIN EN 755-9, apart from the size restriction, in the following aspects in particular:
- Valid for precision profiles exclusively of the alloys EN AW-6060 and EN AW-6063.
- Mainly for architectural applications
- Stricter requirements with regard to visible surfaces
- Tighter limit dimensions and shape tolerances

Since DIN EN 755-9 does not have a lower limit with regard to the wrap circle, pressing plants can also produce profiles with a wrap circle >350mm according to DIN EN 755-9 if the tolerances of 12020-2 are too low for reliable production.
In addition, special agreements deviating from the standards may be necessary between manufacturer and buyer for complex profiles. 

If the tolerances of these standards do not fit the application, ALUTRONICers are ready to work with the designer to develop and manufacture customised adaptations through machining and surface processing.

The mass and surface area of a heat sink are two important factors that can affect heat dissipation. A heat sink with a larger mass tends to be able to absorb and store more heat before releasing it to the environment. A larger surface area, on the other hand, can dissipate more heat to the environment.

The ratio of mass to surface area depends on the shape of the heat sink. A heatsink with a larger surface area relative to mass tends to dissipate heat more effectively than a heatsink with a smaller surface area relative to mass.

However, there are other factors to consider, such as the performance of the component that needs to be cooled and the environmental conditions. A small heat sink with a low mass may be more effective than a large heat sink with a higher mass and larger surface area under certain conditions.

Therefore, it is important to consider various factors when choosing a heat sink to ensure effective heat dissipation.

LME (London Metal Exchange) is the abbreviation for the London Metal Exchange, which is one of the oldest and largest metal trading centres in the world.
Along with Singapore and New York, the reference prices for metals, including aluminium, are determined here daily on the basis of supply and demand.
As a raw material price, the LME price for aluminium is a factor that fundamentally influences the costs of extruded aluminium profiles.
However, the prices of extruded profiles are not only dependent on the LME price, there are also other influencing factors such as:
 

• Exchange rate: as the aluminium price is traded on the exchange in US dollars, changes in exchange rates also affect prices.
• Billet premium: For the production of extruded profiles, the aluminium billets have to be remelted into special billets, the costs for this are called "billet premium".
• Special surcharges: These include, for example, costs as a result of sharply increased energy prices.
• Profile cross-section: The larger and more complex the profile, the higher the price usually is.
• Surface condition: A surface treatment such as anodising, coating or special optical requirements increase the costs.
• Quantity: The larger the order quantity, the lower the price per unit can be.
• Competition: If there are many suppliers of a certain type of extrusion on the market, this can lead to lower prices, while a limited number of suppliers can lead to higher prices.
• Transport costs: Transport costs can be factored into the price depending on the delivery route and transport medium.

 
In summary, the LME price for aluminium as a raw material price is an important factor in determining the cost of extruded profiles.
The actual price can deviate significantly from this for the reasons mentioned above

According to the Arrhenius equation, the probability of failure of an electronic component doubles at a temperature increase of only 10K due to thermal ageing, and increases tenfold at 25K. For this reason, the aim should be to use every possibility of cooling the components, taking into account the generally valid rule: "As much as necessary as little as possible".

First of all, one should strive to reduce the thermal resistance of the heat sink by optimising it, e.g. by enlarging the surface and blackening it. In addition to improving the heat exchange with the air, increasing the surface area has the negative effect of increasing the pressure loss of the natural air flow, so that "at some point" a further increase in the heat sink surface area will lead to a build-up of heat. From this moment on, the heat sink can only be operated sensibly with forced air flow.

From this follows:

Forced ventilation is always worthwhile when cooling with natural convection does not make sense for economic reasons, e.g. because a special profile would have to be set up or the heat sink would have to be reworked at great expense.

Forced ventilation is mandatory if cooling with natural convection is not possible or not sufficient for technical reasons.

The performance data, or more precisely the thermal resistance Rth of heat sinks, is generally determined empirically, i.e. in the laboratory, by applying an impressed power loss PV as a heat flow to the heat sink via its baseplate and determining the temperature difference Du between the heat sink and the environment. Alternatively, this determination can also be carried out by simulation programs.

The determined value of the thermal resistance is therefore the only thermal parameter with which heat sinks of different designs, materials and manufacturers can be compared.

This is particularly worth mentioning because this "characteristic value" depends on the following influencing variables and measurement parameters, among others:

• Ratio of the heating surface of the heat source to the base surface of the heat sink
• (absolute) temperature of heat sink and environment
• Radiation losses of the heat source
• (absolute) power of the heat source
• Position of the temperature measurement point on the heat sink
• When determining thermal resistances with forced convection, further influences such as flow type and flow losses are added (see also à pressure chamber).

It is worth noting that there are neither guidelines nor standards regarding the determination of thermal resistance, according to which the data must be recorded.

A serious manufacturer of heat sinks will therefore not only state exactly under which conditions he has measured the thermal resistance, he will also choose a practical measuring method in order to be able to present realistic results.

At ALUTRONIC, all values given in the catalogue have been measured under the following conditions, unless otherwise stated in the data sheet:

• Natural convection
• Matt black anodised heat sink
• Vertical arrangement of fins
• A heat source with 40% of the floor area in the centre of the heat sink
• Temperature measurement between semiconductor and heat sink mounting surface
• Use of heat-conducting paste
• Measurement of the ambient temperature at a distance of one metre (1m) from the object to be measured

First of all: A heat pipe is not a heat sink and cannot replace one, but a heat sink is often needed to operate a heat pipe.

In somewhat unscientific, but therefore understandable terms, a heat pipe is a tubular component that exploits the phenomenon that a relatively large amount of energy is required for evaporation in order to change the aggregate state of substances, e.g. from liquid to gaseous. This amount of energy is released again when the state of aggregation is changed back from gaseous to liquid, i.e. condensation.

In scientific terms, a passive component, also generally referred to as a heat pipe, uses the enthalpy of evaporation of the medium in it as a heat exchanger between at least two points, which are referred to as heat source (= evaporator) and heat sink (= condenser). The transport zone is located between these two points.

Due to special structures in the interior that promote capillary action, the heat pipe can be operated in any position within certain limits, which distinguishes it from the 2-phase thermosiphon.

The following aspects are important in practice:

• The ability of a heat pipe to transport a certain amount of heat depends on length, cross-section, internal structure, working medium, position, thus a heat pipe should be matched to the application.
• A heat pipe can only be operated within its operating limits, which result from the application in terms of temperature and heat flow. In detail, these limits are viscosity limit, sound velocity limit, interaction limit, capillary force limit and boiling limit.
• The heat conduction is up to 1000 times better compared to a solid copper rod of identical outer geometry.
• Gravity has a positive or negative effect on the return transport of the liquid medium, depending on its position; the influence factor on the heat flow is between 0.6 and 1.6.

"Eloxal" is the abbreviation for electrolytic oxidation of aluminium. This process is used to apply a protective layer to aluminium and wrought aluminium alloys.

This protective layer serves primarily as protection against chemical (e.g. corrosion) and mechanical (e.g. wear) stress and preserves a decorative appearance that may have been achieved through pre-treatment. 

Further positive effects of the anodising process are an increase in surface hardness, improvement of tribological properties and an increase in electrical insulation.

The special process also makes it possible to colour the anodised layer. Alutronic offers the colours blue and black as standard. Due to the darker surface, the proportion of heat radiation and thus the thermal resistance of the heat sink increases with rising temperature.

In addition to the "conventional anodising process", ALUTRONIC also offers the option of hard anodising aluminium components. This special process makes the layer much thicker, denser and harder than anodising, which also significantly improves the electrical insulation or dielectric strength.

For the production of heat sinks using the cold extrusion process, pure aluminium such as EN AW-1050 (Al 99.5) or also pure copper is usually used. The thermal conductivity of pure metals is generally higher than that of alloyed metals such as EN AW 6060 (AlMgSi0.5), which is frequently used in extrusion.

Due to the forming process and the resulting minimisation of voids and air bubbles, this high thermal conductivity is even improved.

Since the air can move three-dimensionally along the surface in comparison to extruded profiles in the case of heat sinks that are frequently pressed into a pin shape, the heat dissipation performance is optimised. 

The shape retention and the surfaces are of such good quality at relatively low tooling costs that mechanical reworking is required only rarely and to a minor extent.

The production of heat sinks by means of impact extrusion is therefore always an option when it comes to rather small, customer-specific series and the heat sink as such should also be rather small with the highest possible efficiency.

The cooling performance can be further enhanced by black anodising and the installation of a fan directly in the heat sink.

The machining of a heat sink accounts for a large proportion of the costs of a heat sink, in addition to the actual material price.

It therefore makes sense to take the mechanical finishing into account and minimise it as early as the selection or design of the raw profile.

It should also be taken into account that the small heat sinks in particular often have very filigree fin structures, which can bend or even break very easily.

There are various criteria for determining the suitable and optimal heat sink, such as the geometric dimensions "width", "height", "base thickness", "length", the permissible maximum thermal resistance Rth,KK as well as the maximum power loss PV to be expected.

The Heat Sink Finder from Alutronic is the ideal tool to include these criteria completely or only partially in the selection. The results can be output as a list and optimised, for example, according to the mass coating or also the weight per metre to minimise costs. Alternatively, for each profile suggested by the Heat Sink Finder, a graph with the thermal resistances dependent on length and power loss can be created and evaluated.

The explanatory video illustrates the relationships in detail.

The carbon footprint of a heat sink refers to the amount of greenhouse gas emissions generated during the production of the heat sink. The carbon footprint is usually measured in tonnes of carbon dioxide equivalent (tCO2e) and includes all direct and indirect emissions that occur during the life cycle of the heat sink, including manufacture, transport, use and disposal.

The exact size of a heatsink's carbon footprint depends on many factors, such as the type of material from which the heatsink is made, the manufacturing process, the type of transport, the energy supply used in the manufacture and operation of the heatsink, and the way the heatsink is used and disposed of.

To minimise the carbon footprint of a heat sink, there are several approaches, such as:

Using recycled materials to reduce the need for manufacturing virgin raw materials.
Using renewable energy sources in the manufacture and operation of the heat sink to reduce energy consumption and therefore CO2 emissions
Optimisation of manufacturing methods to minimise waste and emissions
Design optimisation to minimise the size and weight of the heatsink, which reduces transportation and thus CO2 emissions
Longer life of the heat sink to reduce the need for replacement or disposal.
By implementing these approaches, the carbon footprint of a heat sink can be reduced.

Yes, there are several ways to influence the carbon footprint of a heat sink:

Purchase decision: Before you buy a heat sink, you can find out about the energy efficiency of the product and choose a more environmentally friendly option. There are energy efficiency labels that can help you identify energy efficient equipment.

Maintenance: Regular maintenance of the heatsink can help improve the energy efficiency of the appliance and thus reduce the carbon footprint. This includes, for example, cleaning the cooling fins and replacing outdated or damaged components.

Use: You can also influence the carbon footprint of the heat sink by the way you use it. For example, you can set the temperature of the unit to the minimum required for your needs and ensure that you switch off the unit when it is not in use.

Disposal: When you dispose of the heat sink at the end of its life, you can ensure that it is properly recycled or disposed of to minimise its impact on the environment.

Yes, the alloy of the heat sink can play a role in its carbon footprint. Some alloys are more energy intensive and carbon intensive to manufacture than others. For example, the production of aluminium alloys is usually more energy intensive than the production of copper alloys.

Higher energy intensity usually means higher greenhouse gas emissions, which can increase the carbon footprint of the product. Therefore, it is important to also consider the materials used when choosing a heat sink.

Some manufacturers, including ALUTRONIC, also use recycled materials or materials from renewable sources to reduce their CO2 emissions. You can look for such products to minimise the carbon footprint of your heat sink.

However, it is also important to note that the choice of material alone is not enough to determine the carbon footprint of a heatsink. The entire life cycle of the product, including manufacturing, transport, use and disposal, contributes to its environmental impact.

Es gibt verschiedene Maßnahmen, die Sie ergreifen können, um die Wärmeableitung Ihres Kühlkörpers zu verbessern:

Platzierung: Stellen Sie sicher, dass der Kühlkörper korrekt auf dem Bauteil montiert ist und der Kontakt zwischen dem Kühlkörper und dem Bauteil eng ist. Eine unzureichende Montage kann die Wärmeableitung beeinträchtigen.

Kühlkörpergröße: Überprüfen Sie, ob die Größe des Kühlkörpers angemessen ist, um die Wärmeabgabe zu bewältigen. Ein zu kleiner Kühlkörper kann die Wärme nicht effektiv ableiten, während ein zu großer Kühlkörper zu teuer sein kann und Platzprobleme verursachen kann.

Kühlkörperdesign: Überprüfen Sie das Design des Kühlkörpers, um sicherzustellen, dass es für den spezifischen Zweck optimiert ist. Ein effektives Kühlkörperdesign kann die Wärmeableitung verbessern.

Lüfter: Wenn Ihr Kühlkörper einen Lüfter hat, stellen Sie sicher, dass er ordnungsgemäß funktioniert und die Luftzirkulation verbessert. Eine schlechte Luftzirkulation kann die Wärmeableitung beeinträchtigen.

Kühlkörpermaterial: Wenn möglich, wählen Sie einen Kühlkörper aus einem Material mit einer hohen Wärmeleitfähigkeit wie Kupfer oder Aluminium. Diese Materialien können dazu beitragen, die Wärmeableitung zu verbessern.

Zusätzliche Wärmeableitung: Wenn der Kühlkörper nicht ausreicht, um die Wärme effektiv abzuleiten, können Sie zusätzliche Wärmeableitungsteile wie Wärmeleitfolien oder Wärmeleitpaste verwenden, um die Wärmeableitung zu verbessern.

When installing and mounting a heat sink, there are several factors to consider to ensure effective cooling. Here are some important points:

Orientation: make sure the heatsink is properly oriented to ensure optimal heat transfer. The heat sink should be oriented so that the largest surface area of the heat sink is in contact with the heat source.

Thermal paste: Use a thermal paste between the heat sink and the component to be cooled. The thermal paste helps to avoid air bubbles between the heat sink and the component and improves heat transfer.

Fastening: Make sure the heat sink is securely fastened to ensure sufficient heat transfer. Inadequate fastening may result in the heat sink not remaining in close contact with the component.

Cleaning: Clean the component to be cooled to ensure that no contaminants or impurities interfere with heat transfer.

Air circulation: Make sure that the air circulation around the heat sink is sufficient. Poor air circulation can result in the heat sink not effectively dissipating its heat to the environment.

Power supply: If the heatsink has a fan, make sure the fan is properly connected and powered for optimal cooling.

Component temperature: Ensure that the operating temperature of the component to be cooled is within the permissible range. Excessive operating temperature can reduce the life of the component and affect its performance.

By following these tips, you can ensure that your heat sink functions optimally and protects the component to be cooled from overheating.

With forced, i.e. fan-driven cooling, the following phenomena occur, which can be reduced or minimised with a pressure chamber depending on the application: 

1. Path of least resistance: The air strives to flow through a path that is as free or low in obstructions as possible. Therefore, it can happen that the air does not flow through the heat sink as desired, but bypasses it or leaves it halfway; this is also referred to as the "bypass phenomenon".
    
2. Dead water: In the centre of the fan is the fan hub, which serves to position the motor and fix the fan blades. There is no air flow in this area, so the air behind the hub is undirected and slow. In terms of flow depth, this area roughly encompasses the hub radius and is referred to as the "dead water zone".

Especially high-performance heat sinks with a high aspect ratio (ratio between fin height and spacing) can be additionally equipped with a pressure chamber when used with a fan. This channels the air flow and compensates for the dead water, thus ensuring a more uniform flow through the heat sink by virtually storing air under pressure before it flows through; hence the term "pressure chamber".

In the field of cooling systems, Alutronic offers assemblies with and without pressure chambers in order to provide the greatest possible variety for the customer in this product line as well.

The thermal resistance Rth [K[W] describes the resistance of a body to conduct a heat flow [W] through it and thus the temperature difference [K] between entry and exit, i.e. from or to the neighbouring bodies or substances. For this reason, two components are always specified for thermal resistance, e.g. RthjC for "between chip "Junction" and case "Case"").

The heat capacity C [J/K] describes the temperature increase [K] of a body as a result of a supplied amount of heat [J=Nm=Ws].

Both quantities are object or component related, i.e. not material properties.

For each substance or material there is both a material-specific thermal resistance Rl [mK/W] (whereby in the literature the (specific) thermal conductivity l or k [W/mK] is given as the reciprocal value) and a specific heat capacity c [J/kgK].

For aluminium (99.5%), for example:

lAl = 236W/mK

cAl = 0.9kJ/kg

The heat capacity does not normally play a role in heat sink design, as the heat sink should not store the heat but dissipate it as efficiently as possible to the environment.

It can be calculated as follows:

CH = cAl x mH 

with

CH: heat capacity of the heatsink 

cAl: specific heat capacity of aluminium

mH: mass of the heat sink