Aluminum PCBs: A Comprehensive Guide to Help You Understand
Every printed circuit board ever manufactured meets specific criteria to which it ought to work. For aluminum PCBs, we need to know a lot. It has many differences from ordinary PCB boards.
The PCB contains a copper-clad lamination and aluminum-based metalcore.? Also, aluminum acts as a suitable metal substrate and is less costly.
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What Are Aluminum PCBs
When you hear the names Aluminum Clad, Aluminum base, Metal Clad Printed Circuit Board (MCPCB), Insulated Metal Substrate (IMS), Thermally Conductive PCBs, etc., do know that the PCB type in question is synonymous with Aluminum PCBs.?
You can already tell from the name that aluminum PCBs contain aluminum as one of the materials.
Indeed, these PCBs have a metal core at the base material, with aluminum being one of the critical components.
Moreover, there's a thin layer of thermal, dielectric, and electrically insulating material.?
Why use Aluminum PCBs
Since the emergence of aluminum PCB technology in the 1970s, several industries and individuals have augmented demand for production.
Suppose you plan on using applications with heat dissipation and wish to control the temperatures. In that case, Aluminum PCB is the right choice for you.
Aluminum is known for transferring heat away from significant components on the board. In doing so, your PCB is kept free from the dangers of heat damage.
Moreover, it is highly durable and can serve you longer than other materials like fiberglass.
The basic structure of aluminum PCBs
An IMS has four significant layers, all of which have different roles and distinct materials.?
Circuit copper layer
This layer comprises an electrolytic copper foil ranging from 1 to 10 ounces (oz).
During its manufacture, the designer etches the copper material to form a printed circuit.
Its function is to apprehend the assembly and connect devices for ease of functionality.
It being an IMS, the substrate layer carries a higher current. Nonetheless, it still possesses a similar thickness and width to an FR-4 stiffener.
Insulating/ Dielectric layer
The dielectric layer is best known for its thermal conduction. In thickness, manufacturers estimate them to be approximately 50μm to 200μm thick. It can insulate, bond, and dissipate heat from the board during current flow.t
Metal substrate
This layer defines an IMS by totally distinguishing it from other PCBs. In other words, the insulating layer consists of a metal core made of an aluminum substrate.
When searching for a reliable metal plate, you should consider cost-effectiveness, strong point, firmness, mass, thermal coefficient, and, most importantly, thermal conductivity.?
With that said, an aluminum plate meets all the criteria above. Even better, you can enhance its conductivity or mechanical properties efficiency by adding other leaves—for instance, copper, iron, and silicon steel plates.?
The metal base membrane layer
The base membrane, made of an aluminum alloy substrate, protects the aluminum substrate layer from unnecessary etching and scraping.
Depending on the degree of heat, the coating can be lower than 120 or 250. The layer commonly has a thickness of 1mm.
What are the types of aluminum PCBs?
Even though all aluminum clads work the same way, i.e., in heat dissipation, different types have individual characteristics based on their design and structure. The following are the types of aluminum clads that you should know.
Through-hole aluminum PCB
When we design through-hole aluminum PCB, the manufacturer backfills and pre-drills a single aluminum layer and then applies the laminate material.
A core of multilayer constructions will be formed after this process.
Afterward, they laminate the thermal materials on the two sides of the board with thermal bonding materials. The final touch involves drilling on the assembly.?
Flexible aluminum PCB
A flexible aluminum PCB is a recently marketed circuit board with a polyimide resin integrated with ceramic filters upon purchase.?
The two materials’ essence is to increase insulation, flexibility (you can twist or fold the PCB to any shape and retain the form), and thermal efficiency.
Moreover, their application is cost-effective since you won’t need connectors or cables.
It’s disadvantageous because you can’t alter or modify the final product once you acquire a specific shape.?
Multilayer aluminum printed circuit board
Multilayer aluminum PCBs have multiple layers of thermally conductive dielectrics. The design constitutes one or more dielectric circuitry layers, with blind vias representing thermal or signal vias.?
An advantage to using multilayer IMS PCB is their straightforward and operative solution for heat conductivity in complex products. Contrary to that, they’re costly and can’t easily engage in heat transfer in single-layer designs. Their application is often in power supply products.?
High thermal conductivity aluminum PCB
In this type of PCB, the insulating layer is an epoxy resin material. The epoxy resin should have excellent thermal conductivity.
High-frequency aluminum PCB
With high-frequency aluminum PCB, the insulating layer has a polyolefin or polyimide material. Other times, it can be woven fiberglass between an epoxy resin. The purpose of the materials is to improve the flexibility of the PCB.?
Advantages and Disadvantages of Aluminum PCBs
Advantages
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LEDs assembled on an aluminum PCB
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Disadvantages
What are the performance aspects of aluminum PCBs?
Thermal Dissipation
There are the FR4 and CEM3, and then the aluminum substrate. The former are known as poor conductors of high thermal temperatures.
Higher temperatures can lead to an overall electrical components failure in the PCB, should you stick to the FR4 and CEM3.?
An aluminum substrate works to curb the damage that may be brought about by heat dissipation.
Thermal expansion performance
You need to solve the dissipation challenge and thermal expansion and contraction, especially in the expansion problem of surface mount technology (SMT) expansion problem.
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Regarding that, components on the board with different materials will have an improved life shell and stay reliable for extended periodsDimensional stability performance
An aluminum substrate is more stable than the insulating substrate in the PCB.
For instance, if you heat the board from 30° C to 140 - 150° C, the aluminum substrate’s dimensional change will range from 2.5 to 3.0%
Other performance introduction
In addition to the three main performance aspects of an aluminum-clad PCB, using an aluminum substrate, PCB alternates with a brittle ceramic substrate for better protection.
Furthermore, the substrate advances the board’s heat resistance and physical properties, reducing the workload and manufacturing costs.?
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Typical application areas of aluminum PCBs
Aluminum PCBs apply to various technological equipment. They include but not limited to;
Aluminum PCB Board for LED
These specialized LED boards feature a thin dielectric layer sandwiched between the copper traces and the aluminum base.
This dielectric provides excellent thermal conductivity to transmit the heat from the components and copper traces to the aluminum base.
It is electrically insulating to keep the traces and components from shorting on the aluminum layer below.
This layered construction ensures high-power LED circuits function at the optimal temperature, preventing failure or inefficient performance.
Difficulties and solutions encountered in the production of aluminum PCBs.
Copper etching
Ideally, the copper foil you use in the circuit layer should be thick. A higher standard than this, which is more than 3oz, will force you to compensate for the etching’s width requirement.
Failure to do so will make the width intolerant to the etching. Therefore, you need to control the etching factors carefully, compensation being a major one.?
Solder mask printing
A thick copper foil in this PCB design hinders solder mask printing of aluminum PCBs.
In other words, a thick layered trace copper makes the etched image have a vast difference in the trace surface and baseboard. Thus, printing becomes difficult.?
Quickly solving this problem is using a quality solder mask oil. Alternatively, you can fill in the resin before the solder mask.
Machine-made
Manufacturing an IMS involves drilling mechanically, molding, and v-scoring, among others, centered on the internal via or holes.
To combat this, use the electric milling and professional milling cutter for manufacturing products of a lower volume.
Additionally, adjust the drilling parameters to stop burr production.?
How to Store Aluminum PCBs
MCPCBs have a downside of attracting moisture, coloring yellow, or becoming black. Consider doing so within 48 hours after you’ve opened the vacuum package if you are to use it.
Store it in a dark and moist-free environment if it stays longer without usage.?
Aluminum PCB vs. FR4 PCB
Price
Aluminum metal is costlier than FR4 (fiberglass), making aluminum PCBs more expensive.
Thermal Conduction
Metal is more thermally conductive than fiberglass, and this advantage makes aluminum the ideal base material for PCBs with multiple LEDs and other heat-generating components.
Technological Practices
Because aluminum is electrically conductive, the board must have a thermal bridge or dielectric between the traces and the metal base.
The aluminum base supports the circuit and doubles as the heat sink, while the thin circuit-layer PCB sits on the dielectric.
However, FR4 does not need an insulation layer because it is not electrically conductive.
On the downside, FR4 is not as thermally conductive as aluminum. Therefore, you’ll need heat sinks to dissipate the heat from the hot spots.
Aluminum PCB vs. Copper Base PCB
Price
Copper metal is more expensive than aluminum, meaning copper-based PCBs are costlier.
Thermal Conduction
Copper is two times better at thermal conductivity than aluminum, making copper-based PCBs more efficient at dissipating heat.
Technological Practices
Copper PCBs are ideal for high-frequency circuits and should have thicker traces to handle the high current transmission. The typical trace thickness range is 35-280μm.
The board should also have an insulating layer between the foil and copper base because the material is electrically conductive.
Aluminum PCB vs. Ceramic PCB
Price
Although manufacturers initially used ceramic PCBs to build high-end electronics, the technology is becoming cheaper. It is gradually replacing aluminum and even FR4 in standard PCBs.
Thermal Conduction
Aluminum is more thermally conductive than ceramic materials, but the opposite is true in PCBs. Since ceramic is not electrically conductive, these PCBs don’t need a dielectric to insulate the traces from the base.
Therefore, electronic components dissipate heat directly to the ceramic, making the assembly more efficient at evacuating the heat and eliminating hot spots.
Technological Practices
Ceramic PCBs have higher inertia and stability than aluminum and share compatible CTEs with leadless ceramic chip carriers.
Therefore, they can overcome thermal cycle failures. And they are less complex to manufacture because they don’t need an insulating dielectric layer.
Summary：
Generally, aluminum PCBs are good in heat dissipation, use surface mount technology, replace the ceramic substrate with an aluminum substrate, have reduced production volume compared to other PCBs, and are cost-effective.?
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