Metal core PCB is not very common in consumer products, but it can be found everywhere in industries, aerospace, lighting systems, power electronics and other fields that require high reliability. High-power systems generate a lot of heat, and it is necessary to quickly remove the heat to prevent component failure. Similarly, low-power systems may be exposed to high heat, and heat needs to be quickly removed to prevent damage to circuit boards and components.
Metal core PCB design (including DFM) follows many basic design rules that are the same as those of typical PCB on FR4. If you want to design a new product in any of the above fields, you may need to use a metal core plate to control the temperature. In this article, we will briefly introduce the structure of metal core PCB and some important design points to be considered before planning to use metal core PCB design. These boards have special manufacturing requirements, but the right design company can help to meet these requirements and ensure that PCB can be mass-produced.
Application of metal core PCB design
Metal core PCB can find its place in almost any application where a lot of heat is generated when the equipment is running. These plates are not ideal substitutes for ceramics, because they are a low-cost option, and they provide higher thermal conductivity, which can remove heat from important parts. When looking for circuit boards for systems with strong heat dissipation, they are often a starting point. Some applications of metal core PCB include:
LED unit: Usually, a board with high-power LEDs is manufactured on a metal core PCB. These boards can provide a firm base for high-power LEDs (SMD and through holes), while radiating high heat into the metal core board.
Power conversion and management: Hybrid electric vehicles, industrial equipment, base station telecommunication equipment and municipal power distribution system all operate with high power. In these fields, metal core PCB is very common.
Solar Energy Equipment: Solar energy equipment needs to be particularly strong and operate at high temperature and high DC voltage/current. Similar PCB design can be implemented in geothermal facilities.
Military (e.g., submersible, airplane): Metal-core PCB can quickly dissipate heat, keeping electrons away from electronic devices that may be located near high heat sources such as engines or exhaust systems.
In many other fields, high reliability and structural rigidity are also crucial, which makes metal core board an excellent choice. Once you start studying the stacking and layout requirements of these boards, it becomes less obvious how to actually design them. Can you make multi-layer metal core board? Can we have two sides? How to deal with vias in the manufacturing process? These are all important issues related to DFM of metal core PCB.
DFM for metal core PCB
Like other PCBs, if you want to ensure a successful manufacturing operation, you need to follow certain DFM guidelines. The process of metal core board is different from the typical PCB lamination process involving glass woven laminate, so they tend to adopt different DFM rules. The following figure shows a typical stack of double-sided metal core PCB.
Please note that this laminate can be technically adapted as a multilayer board, in which each side of the metal core has multiple dielectrics. Alternatively, you can make the circuit board single-sided with the back of the metal core exposed. When designing metal core PCB, the following manufacturing points should be paid attention to:
Metal core grounding
The metal backing on the PCB can work like a large ground plane or a large heat sink. If the board needs to use high-speed/high-frequency circuit blocks, using the back metal plate as a larger grounding layer can provide some shielding. If a power plane is used on the board, it can also provide some plane capacitance.
In addition, the metal core can be used as a large heat sink, especially if it is exposed. The latter aspect is very useful when the board needs to be installed near a high heat source. In this case, when connecting the top side to the standard power supply, it is best not to ground the back side. This can prevent grounding loops. This will also directly dissipate heat into a very large radiator, which helps to lower the surface temperature.
Holes in a single panel
The holes can be placed on the metal core PCB, and can be used as mounting holes or standard through holes on double panels. If holes are only used for mounting through-hole assemblies on a single panel, these holes should not be plated to prevent short circuit. This is done by drilling holes in the mounting holes and filling the holes with non-conductive epoxy resin or gel. Then, plug the holes so that the installation can be carried out on the upper layer.
Holes in double panels
In a double-sided metal core PCB, some components may be installed on both sides, and plated vias need to be placed between signal layers. Electroplating through holes are formed by pre-drilling → insulating filler → re-drilling → electroplating process, so some difficulties will be encountered in manufacturing. This process will take extra time and lead to extra costs, but it is designed to prevent short-circuiting of vias. In PCB layout, it is best to use anti-pad to represent the area around the through hole that needs to be filled with insulating filling material. Make sure to adjust the size of via solder pads so as to comply with IPC-2221 standard.
DFM is similar to standard PCB in other aspects of PCB design with metal core, although CAD tools are not used to design these boards. The front end of electric equipment needs to follow some small rules, especially IPC-2221 (creepage and release rules), as well as other national defense and aerospace standards.
