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Aluminum PCB Manufacturer: General Introduction of Aluminum PCB

Posted:01:58 PM September 26, 2022 writer: NextPCB

What is an Aluminum Printed Circuit Board (PCB)?

An Aluminum PCB is just like a regular PCB, but it uses Aluminum as the base material instead of FR-4 to enhance the thermal and electrical properties of the circuit board. 

As we know, Aluminum is a good conductor of electricity; hence between the aluminum laminate and copper layer, a layer of dielectric material is laid on it to stop the current from spreading all over the laminate.

The heat dissipation rate of an aluminum PCB is higher, and it offers a stable dielectric constant, which ensures minimum loss tangent and accurate delivery of signal under high thermal and mechanical stress.

Structure of Aluminum PCB

The structure of an Aluminum PCB consists of three materials.   

Circuit Copper Layer

It is a conducting layer that make-up the signal traces. The standard thickness of a copper layer on a PCB is 1-3 ounces. But, it may go up to 10 ounces. However, not every manufacturer provides this particular service. But do not worry, the NextPCB got your back as we are willing to deliver your required specifications in minimum time.

Insulating Layer

The insulating layer has the purpose of resisting current from flowing all over the laminate. Also, it carries the heat and transfers it to the aluminum core to dissipate it at a faster rate. 

Metal Substrate

Metal substrate means a metal such as aluminum as the base material. The substrate of a PCB describes the temperature tolerance, mechanical strength and insulation property of the PCB. Hence, using a metal-backed or aluminum PCB has several advantages over a PCB with standard fiber-glass laminate.

Advantages and Disadvantages of Aluminum PCB

Advantages of Aluminum PCB

Aluminum-backed PCB offers several advantages over a standard fibre-glass PCB. A short list of its benefits is as follows.

Budget Friendly

Aluminum is significantly cheaper than copper. Copper is also harder to set as the core of the PCB, whereas aluminum is a flexible material and does not require intense skills to handle. That's why more manufacturers are ready to work with aluminum-backed PCBs and provide lower manufacturing prices than copper or other metal-backed PCBs. 

Flexibility

The flexibility of Aluminum makes it a perfect substrate for smaller devices that generate high heat. Aluminum as the base material provides excellent mechanical strength while being easily folded to fit into small spaces.

Higher Thermal Capability

The heat transferring capability of an aluminum PCB is excellent. Moderate to high-frequency PCBs require a stable dielectric constant (DK) to offer controlled impedance; the thermal stress of the PCB affects the stability of the dielectric constant. Hence, incorporating Aluminum as the base material of the PCB increases the signal integrity and lifespan of the printed circuit board.  

Lightweight and Durable

Aluminum is 30% lighter than copper[1] and has a lower environmental impact than other metals. The PCBs made up of aluminum are more reliable and robust in many aspects, such as mechanical and thermal stress. Aluminum-backed PCBs have higher physician durability, which reduces the risk of breakage and cracks.

Disadvantages of Aluminum PCB

Nothing is perfect. Every good thing has some downsides. Some of the disadvantages of an Aluminum PCB are as follows.

Manufacturing Process

The manufacturing process of an aluminum-core PCB is different and usually more intense than the manufacturing process of a fibre-glass PCB. Aluminum or other metal-based PCBs may require special machinery and skills to manufacture, which increases the manufacturing cost of the PCB.

Poor Vibration Stress Management

No doubt, Aluminum is the best material for flexible PCBs, but the only downside is that it can not tolerate vibration stress for a long time.
Only Suitable for High-Temperature devices

If the PCB does not have to deal with a high temperature, investing in the aluminum PCB may not justify the cost.

Application of Aluminum PCB

The main feature of an aluminum PCB is its thermal conductivity. Aluminum PCBs are perfect for devices that require high thermal tolerance and mechanical support. Higher heat conductivity helps maintain current and protect components and PCB traces against heat damage.
Aluminum PCBs are a significant current handler and have a wide application in rapid switching devices. The LED industry has reported an increasing demand for aluminum PCBs, as-such they have seen in many devices with surface mount LEDs and other lightning devices.

Storage Conditions of Aluminum PCB

Aluminum is a Metal That neither absorbs water nor is oxidized. But, aluminum PCBs have a condition that once they are manufactured, they are required to keep in a dark and dry place as when they are exposed to moisture and light, the colour of the PCB starts getting a shade of black Or yellow. That's why most manufacturers recommend using aluminum-based PCBs within 24 hours of unboxing.

Aluminum Layer Thickness

The thickness of the aluminum layer depends on the requirements of the printed circuit board. However, the standard thickness of the aluminum layer varies between 100-150um. 

Aluminum-backed PCBs have two types of insulation layers. One is FR-4, and the other is polypropylene (a type of epoxy resin). On the aluminum laminate, a layer of polypropylene with a thickness of 100-150um is furnished to create a barrier between the copper layer and aluminum laminate. However, FR-4 separates and supports copper layers. The thickness of FR-4 remains the same as in standard PCBs, which is 150um.

The stack-up of aluminum PCB with its thickness looks like this:

Aluminum PCB Thickness

The thickness of the aluminum base is the thickness of the plate selected by the customer minus the thicknesses above.

Why is Aluminum Used in Circuit Boards?

Aluminum has a higher heat conductivity and provides a stable dielectric constant (DK). These properties of aluminum make it the desired substrate for high-temperature, rapid switching and high-frequency devices.

The aluminum-backed PCBs have a significant crack resistance, which makes aluminum a competitive substrate for devices that undergoes rough environmental conditions, such as missiles and military equipment.

Performance of Aluminum PCB

Aluminum PCBs provide extraordinary performance in many aspects. The properties of aluminum are much similar to copper, but the high edge of aluminum is that it is cheaper than copper with significantly good performance. 

Thermal Dissipation

Thermal dissipation of a material refers to its capability of escaping the heat away from the board. 
The thermal dissipation property of aluminum is 10-times higher than the standard PCB substrate FR-4. This property of aluminum-backed PCB improves and helps stabilise the performance of circuit boards under high thermal stress.

Thermal Expansion

Thermal expansion refers to the stretching and contraction of a PCB under the influence of temperature. The expansion of material with rising temperature is a property of matter. Different materials have an individual rate of expansion or contraction, which somehow affects the performance. The coefficient of thermal expansion of aluminum is (23 x 10-6 per °C) higher than that of FR-4 (10 x 10-6 per °C)[2]. A Higher coefficient of thermal expansion reduces the risk of PCB cracking and is beneficial for surface mount assembling. 

Dimensional Stability

The dimensional stability of a substrate defines the change in the measurements of a board during the curing process. Aluminum has better dimensional stability than fibre-glass laminates; aluminum shows a difference of only 2-3% of its size when heated under a temperature of 30-150 C. Higher dimensional stability of aluminum helps in avoiding the bulking of insulation and the formation of thermal bridges between the signal traces.  

Stable Dielectric Constant

Metal PCBs such as aluminum-backed PCBs provide a stable dielectric constant, which is essential to minimize the loss-tangent and maintain signal integrity. As we know, the dielectric constant is inversely proportional to temperature[3]. The heat management property of aluminum decreases the fluctuation of the dielectric constant by maintaining a table temperature.

Classification of Aluminum PCB

Aluminum PCBs have a wide application in numerous devices with different specifications. Based on their applications, aluminum PCBs are classified into four main types.  

Flexible Aluminum PCB

Aluminum is a naturally flexible material; when treated especially, it opens the doors of opportunities for smaller devices by providing flexible PCBs that can fold and convert into any shape to fit in a smaller space. The demand for flexible PCBs is increasing[4] day by day as the size of devices is getting smaller. However, the cost of a flexible PCB is considerably higher than a rigid PCB.

Hybrid Aluminum PCB

In general, hybrid PCBs use a different material for layers of the PCB. The hybrid aluminum PCB is a combination of different materials to enhance the performance of the board. For example, when a standard FR-4 PCB adds ups a layer of aluminum, its heat dissipation property reaches another level. The manufacturing process of hybrid PCBs is complex and time taking. Thus, hybrid aluminum PCBs are not a norm and are only used by high-tech companies. 

Through-Hole Aluminum PCB

Aluminum is a good conductor of electricity. Hence if used as the core of the PCB, it can carry the current and spread it to the whole circuit board. To deal with this condition, the through-hole aluminum laminates are drilled and filled with a dielectric material before the arrangement of layers to isolate the aluminum layer from touching the legs of the components. After the filling of dielectric material on the places of the component's legs, the aluminum is stacked and cured to convert into a PCB. Then the PCB is drilled and electroplated with a conducting material to make the holes conducting once again.

Multi-Layer Aluminum PCB

Multi-layer Aluminum PCBs use multiple insulating layers to separate the copper layers from one another. The multi-layer aluminum PCBs can use more than one layer of aluminum as the core, depending on the requirements of the circuit board. The different signal layers in a multi-layer aluminum PCB are connected through blind or buried vias as thermal vias and signal paths.

Manufacturing Process of Aluminum PCB

The manufacturing process of a 2-layer aluminum PCB is quite similar to the manufacturing process of standard PCBs.

Preparing the Aluminum Laminates

The first step of manufacturing an aluminum PCB is the preparation of the laminate to process it for the further process. The preparation of aluminum laminate includes the washing and dusting of laminate to remove dust that can later cause shorts and open circuits. At NextPCB, we execute this process with automatic machines to prevent laminates from scratching.

Printing of Circuits 

The second step of the fabrication includes the printing of electronic circuits on the copper layers. This process includes a UV plotter that converts the circuit on the copper layer and cures it for further process.
Once copper layers have finished with the process of printing, they go for an alkaline wash, which etches the uncured excess copper.

Drilling of Positioning Holes on Aluminum Laminates

The positioning holes are necessary to drill as they work as a guide while stacking all the dielectric, aluminum and copper layers together.
At NextPCB, we punch positioning holes using a punch press.

Stack-up and Curing

After the punching holes, we stacked all the layers in the required manner, screwed the layers together and moved them for curing at a high temperature under a considerable amount of pressure.

Solder Masking

Once the PCB is ready, a layer of liquid epoxy resin is applied on it to create a barrier between the outer copper layer and the environment to prevent the outer copper layer from oxidation and short circuits.

Application of Surface Finish 

After the solder masking of the PCB, it's time to electroplate some solderable material on the exposed area of PCB traces; for example, immersion gold, immersion silver and other suitable surface finish. The plating of the surface finish helps avoid solder and heat bridges.

Testing

The last step of PCB manufacturing is the testing of the circuit boards. At NextPCB, we check and run several tests to ensure that we deliver high-quality, error-free aluminum PCBs.

The above was a guide for a single-layer aluminum PCB. For two-layer aluminum PCBs, we manufacture a standard two-layer PCB and then bind it with the aluminum base. The two-layer PCB is not directly bound with the aluminum base, though a layer of dielectric material is sandwiched between aluminum and copper to isolate the two conducting layers.

However, for two-sided boards, the aluminum laminate is drilled and filled with a resin material to isolate the walls of the aluminum laminate from vias and through holes. Then the filled resin is drilled and electroplated with a conducting material to connect two layers of opposite sides.

Manufacturing Difficulties of Aluminum PCB

Aluminum PCBs are not a standard and integrate special features. Hence, they have some manufacturing difficulties that NextPCB can overcome; by using different techniques. 

Application of Solder Mask

The aluminum PCB generally utilizes thick copper. Due to this, there's a difference created between the traces and the base of the board, as the copper traces are thicker than the base, which makes the printing of the solder mask quite hard and uneven. To tackle this situation, NextPCB uses the two-time solder mask technique. However, in some cases, the board is first filled with resin and then goes for the printing of the solder mask to make sure an even layer of solder mask.

Mechanical Manufacturing

Mechanical manufacturing includes the process of drilling the holes, moulding and v-sourcing. The mechanical stress during the manufacturing of the PCB may affect the electrical strength of the PCB. Therefore, we at NextPCB utilize special high-tech equipment to prevent mechanical stress on the PCB. And also, follow the necessary parameters for drilling to prevent burr from generating. 

NextPCB's Aluminum PCB Solution

NextPCB's engineering solutions have a wide range of abilities that are designed to increase the performance of your aluminum PCB. Some of NextPCB's engineering solutions are  

Controlled Impedance

If your aluminum printed circuit board demands controlled impedance, modelling is significant for ensuring OEM quality of the board that operates between 100 MHz to 3GHz. The NextPCB also facilitates you with services like tailoring signal reflections to minimize signal loss and increase signal integrity.

Design Rule Checks (DRCs)

PCB designing is complex. While designing a PCB, the engineers have to use the basic rules of electronics and PCB designing. For example, when designing a PCB, the designer makes sure that the chip layout meets the necessary parameters and PCB design rules. However, it is possible to make a mistake or neglect the fundamentals of PCB designing. But do not worry NextPCB, with its highly accurate DRC software, is ready to examine your layout to make sure that the layout is fully optimized and uses the maximum available space.

Design For Manufacturability (DFM)

NextPCB encourages PCB designs that optimize the manufacturing process at every stage, namely fabrication, assembly, testing, delivery and support after delivery. The NextPCB is willing to work with you on projects that follow and promotes the best manufacturing practices to enhance the performance and quality of the circuit boards.

File Conversions

If you have outdated CAD-generated DFX or DWG files that require a conversion to the latest Gerber files, do not worry. Because NextPCB can convert your old DWX or DWG files to the current version of Gerber files to fasten up the PCB manufacturing process.

Surface Finishes

The surface finish is the coating of conducting material on the open or exposed copper traces on the outer layers of the PCB. Electroplating a conducting material on the exposed traces is crucial as it protects the copper from oxidation and corrosion. The type of surface finish that you should use always depends on the requirements of the circuit. However, it is necessary to choose an accurate finish by considering several aspects and environmental conditions. 

NextPCB offers various surface finishes for PCBs, including the following:
Immersion gold
Immersion silver
Immersion tin
Hot air soldering level (HASL)
Lead-free HASL
Organic solderability preservative (OSP)
Hard gold
Electroless-nickel electroless-palladium immersion gold (ENEPIG)

Edge Plating

Edge plating involves electroplating the edges or corners of the PCB with a conducting material to ensure higher electromagnetic compatibility (EMC), signal integrity and heat dissipation. A benefit of edge plating is that it provides a non-interrupting and strong connection all over the PCB; it also minimizes the chances of equipment failures. NextPCB usually recommends ENIG or nickel-gold as the surface finish for edge plating. The process of edge plating requires very sharp skills and cautious handling to make edge plating long-lasting.
NextPCB can provide you with high-quality edge plating for your PCBs. As quality matters for us, we perform all kinds of necessary tests on edge plating to guarantee a well-functioning PCB for your device.

Electronic Components Sourcing

At NextPCB, we not only manufacture, test and assemble the boards but also source high-quality original components. If you are having trouble finding your desired components, send us a query. We will provide you with your required components, including Resistors, Potentiometers, Capacitors, Diodes, transistors, transformers, ICs, connectors, heat sinks and what else you can imagine.

To initiate the process of component sourcing with us, contact us and send the bill of material (BOM). The bill of material should contain appropriate information about the components, quantity and its designated manufacturer (if possible).

Layer Stacking

In layer stacking, different layers, sometimes with different materials, are stacked to produce a single PCB with all the required features. Layer stacking has several advantages, such as it reduces the manufacturing cost of the PCB and providing better electromagnetic compatibility for internal layers.

NextPCB can provide you with high-quality multi-layer aluminum PCBs within a very short amount of time. The multi-layer boards can have three or more conductive layers depending on your demand. We are willing to dive into the journey of appropriate stacking for your multilayer Aluminum-backed PCB.

Conclusion

Aluminum-backed PCB is a type of metal-backed PCB. The use of metal in circuit boards increases heat dissipation and provides a stable dielectric constant. Let aside properties, the cost of aluminum-backed PCBs is relatively lower than that of copper-backed PCBs.

Aluminum PCBs are robust against thermal and physical stress and, due to their high coefficient of thermal expansion, resist PCB cracks and leakage of current. A benefit of using aluminum PCBs is that; it has a high current handling capacity and performs well for rapid switching devices. With additional features, such as edge plating and high-quality surface finishes, the aluminum-backed PCBs provide high-end performance, even against rough environmental conditions. The rising demand for heat tolerance, rapid switching and high current handling is increasing the use of aluminum PCBs, especially in LED products.

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