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. Other than that, aluminum in itself acts as a suitable metal substrate and is less costly.
(a close up on an IMS PCB)
1. 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 to Aluminum PCBs.
From the name, you can already tell 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. What's more, there's the presence of a thin layer of thermal, dielectric material 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're planning on using applications that have 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 a long time compared to other materials like fiberglass.
（Technician repairing pcb layout with soldering iron）
2. The basic structure of aluminum PCBs
An IMS has four significant layers, all of which play different roles and have distinct materials.
Circuit copper layer
This layer consists of an electrolytic copper foil that ranges 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 in 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 has the function of insulating, bonding, and dissipating heat from the board during current flow.t
Metal substrate
Inarguably, 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. Factors you should consider when searching for a reliable metal plate are 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 efficiency in conductivity or mechanical properties 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 at 250. The layer commonly has a thickness of 1mm.
3. 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 be knowing.
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. There will be a formation of a core of multilayer constructions 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. What’s more, their application is cost-effective since you won’t need to purchase 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-layer of thermally conductive dielectrics. The design constitutes one or more layers of circuitry found in the dielectric with blind vias representing thermal or signal vias.
An advantage to using multilayer IMS PCB is the straightforward and operative solution they offer 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.
4. The Advantages and Disadvantages of Aluminum PCBs
Just like any other PCB, these thermally conductive PCBs present their strengths and weaknesses. Contrary to traditional PCBs, IMS performs favorably and better despite having a few downsides. The table below summarizes a few notable points.
5. What are the performance aspects of aluminum PCBs?
Thermal Dissipation
There are the FR4 and CEM3, and then there’s 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 the heat dissipation.
Thermal expansion performance
You need to solve the challenge of dissipation and solve thermal expansion and contraction, especially in the expansion problem of surface mount technology (SMT). Regarding that, components on the board with different materials will have an improved life shell alongside staying reliable for a more extended period.
Dimensional 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 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.
6. Typical application areas of aluminum PCBs
Aluminum PCBs apply to various technological equipment. They include but not limited to;
- Audio equipment: For instance, input and output amplifiers and power amplifiers.
- Power supply equipment, such as DV/AC converters and switching regulators.
- Communication electronic equipment
- Power modules, e.g., bridges, solid-state relays, converters, and power rectifiers.
- Office automation equipment
(a close up of a motherboard)
7. 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 leads the etched image to have a vast difference in the trace surface and baseboard. Thus, printing becomes difficult.
A quick way to solve this problem is by 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.
8. How to Store Aluminum PCBs
MCPCBs have a downside of attracting moisture, coloring to yellow, or becoming black. Consider doing so within 48 years after you’ve opened the vacuum package if you are to use it. Should it stay longer without usage, ensure you store it in a dark and moist-free environment.
(aluminum Pcb on LED)
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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