Introduction
Metal core printed circuit boards (MCPCB) refer to boards which incorporate a metal plate or substrate as the central layer instead of the typical FR4 dielectric. Metals like aluminum, copper or iron alloys can be used as the core material in MCPCBs.
The high thermal conductivity of the metal core enables heat dissipation from mounted electronic components. This makes MCPCBs well suited for thermal management in applications with high power devices.
This article provides a detailed comparison between the different metal core materials used in PCBs covering properties, performance, applications, pros/cons and costs.
Aluminum Core MCPCB
Aluminum is the most common metal base material used in metal core PCBs due to its combination of good thermal performance, ease of fabrication and lower cost:
Typical properties:
- Thermal conductivity: 130 W/mK
- Coefficient of thermal expansion (CTE): 23 ppm/°C
- Density: 2.7 g/cm3
- Specific heat capacity: 0.9 J/g°C
- Availability of alloys like 6061, 5052, 2024 etc.
Key attributes:
- Excellent heat dissipation performance
- Cost effective material and processing
- Lightweight
- Well-established PCB technology
- Can be easily machined or punched
- Recyclable
Typical thickness range:
- 0.5mm to 6mm plates
- 1mm to 2mm is common
Applications:
- LED lighting
- Power converters
- Motor drives
- Power supplies
- Solar inverters
- Automotive electronics
Aluminum MCPCBs offer the best balance of thermal performance, manufacturability and cost for most mid-to-high power electronic circuits.
Copper Core MCPCB
Copper provides significantly higher thermal conductivity than aluminum. This makes it useful for very demanding thermal applications:
Properties:
- Thermal conductivity: 400 W/mK
- CTE: 17 ppm/°C
- Density: 8.9 g/cm3
- Specific heat capacity: 0.39 J/g°C
Benefits:
- Extremely high thermal conductivity
- Well-established PCB technology
- Widely available
- Can be fabricated using standard FR4 processes
- Solderable and recyclable
Typical thickness range:
- 0.25mm to 4mm
- 0.5mm to 2mm common
Applications:
- High power LED lighting
- RF power amplifiers
- Power modules
- Solar microinverters
- High density computer systems
The excellent thermal performance of copper MCPCB justifies its higher cost in applications where thermal dissipation is critical for reliability.
Iron Alloy Core MCPCB
Iron alloys containing nickel, cobalt, aluminum etc. offer a lower cost alternative to copper for improved thermal conductivity over aluminum:
Properties vary by composition:
- Thermal conductivity: Up to 65 W/mK
- CTE: 10-15 ppm/°C
- Density: 7-8 g/cm3
- Specific heat capacity: 0.44-0.46 J/g°C
Benefits:
- Higher thermal conductivity than aluminum
- Lower cost than copper
- Compatible with FR4 fabrication
- High strength for thin cores
Typical thickness range:
- 0.1mm to 3mm plates
- 0.2mm to 0.5mm common
Applications:
- LED lighting
- Industrial electronics
- Telecom systems
- Automotive
Iron alloys like iron-nickel-cobalt provide a good compromise between performance and cost for an intermediate thermal conductivity core material.
Comparing Metal Core PCB Materials
Key properties of the main metal core PCB base materials:
| Parameter | Aluminum | Copper | Iron Alloy |
|---|---|---|---|
| Thermal conductivity | 130 W/mK | 400 W/mK | Up to 65 W/mK |
| CTE | 23 ppm/°C | 17 ppm/°C | 10-15 ppm/°C |
| Density | 2.7 g/cm3 | 8.9 g/cm3 | 7-8 g/cm3 |
| Specific heat | 0.9 J/g°C | 0.39 J/g°C | 0.44-0.46 J/g°C |
| Cost | Low | High | Medium |
| Common thickness | 1-3mm | 0.5-2mm | 0.1-0.5mm |
General material selection guidelines:
- Aluminum – Cost-driven applications where thermal conductivity >130 W/mK is sufficient
- Copper – Where maximum heat dissipation is critical
- Iron alloy – Applications constrained by weight or cost but need higher thermal performance than aluminum
Metal Core MCPCB Fabrication
Fabricating metal core PCBs requires specialized processes compared to standard FR4 PCB construction:
Base Metal Preparation
The metal is cut into specified panel sizes and thicknesses. Holes are punched for mounting components if needed. The surfaces are chemically cleaned.
Dielectric Layer Lamination
Thin dielectric films like polyimide or FR4 prepregs are laminated onto the metal core under pressure and temperature. Bonding agents help adhesion.
Circuit Formation
Similar to rigid PCB fabrication, the circuit layers are formed on the dielectric layers using processes like photolithography, plating and etching.
Component Assembly
Components can be conventionally soldered. For higher heat tolerance, sintering of silver paste or transient liquid phase bonding is used.
Enclosure Integration
The metal core MCPCB can sometimes directly serve as a housing or enclosure surface for mechanical stiffness, shielding and heat spreading.<img src=”https://drive.google.com/uc?export=view&id=1pNpZjav6MG438K0wGShZbZ8eqy3llH-S” alt=”metal core PCB fabrication” style=”width:500px;height:300px;”>
The specialized materials, processes and integration considerations involved in metal core PCB manufacturing demand working with an expert supplier.
Aluminum MCPCB Pros and Cons
Benefits of aluminum metal core PCBs:
- Excellent thermal conductivity for heat dissipation
- Cost-effective material and fabrication
- Lightweight construction
- Mature, established manufacturing processes
- Readily machinable or punchable
- Solderable and recyclable
Limitations of aluminum MCPCBs:
- Lower thermal conductivity than copper or alloy cores
- Higher CTE than copper causes greater component warping stresses
- Susceptible to corrosion in harsh environments
- Lower stiffness than steel or copper cores when very thin
- Not suitable for high frequency or precision circuits
Aluminum strikes the best balance between cost, performance and manufacturability for most commercial thermal management PCB applications.
Copper MCPCB Pros and Cons
Advantages of copper metal core PCBs:
- Extremely high thermal conductivity
- Well-established PCB manufacturing processes
- Widely available material supply
- Can often reuse fabrication lines for rigid FR4 PCBs
- High temperature soldering capability
- Recyclable material
Drawbacks of using copper as metal core:
- Substantially higher cost than aluminum
- Heavy weight increases product weight
- Thermal expansion issues when paired with non-CTE matched components
- Lower brilliance compared to aluminum with LEDs
- Lower dielectric strength than aluminum at thinner gauges
- Requires nickel plating for solderability
The unmatched thermal performance of copper justifies its usage where removing heat is absolutely critical for application success.
Iron Alloy MCPCB Pros and Cons
Benefits of iron alloy metal core PCBs:
- Higher thermal conductivity than aluminum
- Lower density than copper provides weight savings
- Cost is between aluminum and copper
- High yield and tensile strengths when thin
- Manufacturing processes similar to FR4 PCBs
Challenges with iron alloys for metal core PCBs:
- Thermal conductivity still lower than copper
- Material options not as diverse as aluminum or copper alloys
- More difficult to fully recycle
- Higher loss at high frequencies than aluminum or copper
- Lower stiffness than aluminum or copper at identical thickness
Iron alloys offer a viable intermediate option where cost or weight are key constraints but thermal performance must exceed aluminum.
Cost Comparison
Metal core PCB cost considerations:
- Metal core PCBs have higher fabrication cost than FR4 PCBs due to specialized materials, processes and lower panel utilization.
- However, the ability to remove heat from high power components results in overall system cost savings.
- Aluminum core is the most economical metal base material. Iron alloy adds moderate cost increment over aluminum. Copper core can double the cost over aluminum.
- But metal core PCB cost is typically a small fraction of overall system cost for an electronic product. The thermal and reliability benefits justify the premium.
- Cost reduces in high production volumes due to improved material utilization and manufacturing efficiency.
Applications of Metal Core PCBs
Some common application areas where metal core PCBs provide benefits include:
LED Lighting
The high power LEDs used require metal core PCBs for heat extraction. Aluminum is widely used but copper or iron allows driving LEDs at higher currents for greater luminosity.
Power Converters
Switching converters and inverters for power electronics require metal core PCBs to manage substantial heat dissipation from components like inductors and FETs.
Motor Drives
Motor drives work under challenging operating temperatures. Metal core PCBs allow efficient thermal management in the tightly packed drives.
Servers
Within data centers, high compute density server blades need effective cooling to maintain reliability.
RF Power Amplifiers
High frequency RF amplifiers using GaAs or GaN ICs benefit from the electrical and thermal conductivity of copper metal core PCBs.
Aerospace & Defense
Rugged aluminum or copper core PCBs meet demanding thermal and mechanical performance requirements in aerospace and military applications.
Conclusion
Metal core PCB technology enables integration of electronic components and systems with higher power densities by effectively managing dissipated heat. Aluminum, copper and iron alloys provide a range of core material options to suit different design constraints and applications. Aluminum MCPCBs offer the best value for most cost-driven commercial applications demanding higher thermal conductivity than standard FR4 PCBs. Where maximum heat transfer is critical for product functioning, the highest performing copper MCPCBs are the optimal choice despite increased cost. Iron alloys provide a middle ground alternative. With each material having unique benefits and tradeoffs, designers must make informed selections to match the metal PCB technology used to the specific thermal, weight, frequency, mechanical and cost requirements of the application.
FAQs
What are some key considerations when selecting metal core PCB thickness?
Some guidelines for choosing thickness:
- Thicker cores allow mounting larger, higher power components
- Thinner cores weigh less but have reduced stiffness
- Thicker cores increase trace lengths if routing on outer layers
- Optimal thickness balances weight, cost and layout space
What fabrication challenges are common with metal core PCBs?
Some potential issues include:
- Delamination or cracking due to CTE mismatches
- Voids or lack of adhesion with dielectric bonding
- Drilling precision on thicker metal cores
- Higher scrap rates and lower panel utilization
- Warping when cooling after lamination
How are components assembled on MCPCBs?
Assembly options:
- Conventional SMT soldering for moderate temperature parts
- Sintered silver joints for high power devices
- Transient liquid phase soldering where high heat capacity is required
- Press fit pins, clips or thermal adhesives for selective mounting
What alternatives exist to using metal core PCBs for thermal management?
Some options are:
- Thick copper planes within conventional PCBs
- Thermal cladding, gap pads or vias for heat extraction
- Heat sinks, heat pipes or cold plates attached to PCBs
- Liquid cooled plates with internal fluid circulation
- Insulated metal substrate PCBs
Are electrically insulating coatings required on metal cores?
Yes, the metal core must be coated with insulating dielectric films on both sides to avoid electrical shorts. This adds material cost but allows routing signals like conventional PCBs.
