DTE – Direct Thermal Exchange Technology

Although traditional MCPCBs were originally conceived for use in the power-supply industry, these substrates are the most widely used in production of LED products. There are many names for these products; Aluminum Clad, Aluminum Base, Metal Clad (MCPCB), Insulated Metal Substrate (IMS or IMPCB) and Thermally Conductive PCBs. All these references refer to the same design. A thin layer of thermally conductive, but electrically insulating, dielectric laminated between a metal base and a copper foil. The copper foil is etched into the desired circuit pattern and the metal base draws heat away from this circuit through the thin dielectric.

LEDs require heat dissipation that standard PCB material can’t handle. The solution is a dielectric material that provides 1-2 W/mK of thermal conductivity. Standard PCB material typically has a thermal conductivity of 0.5 W/mK, which is not enough for the current high-intensity LEDs. Metal clad PCB materials will increase the life of your LEDs with advantages that include increased heat dissipation, reduced thermal expansion and increased dimensional stability.

Styles of MCPCB’s

 

Traditional (Non-direct Thermal Path) – A traditional MCPCB consists of a metal core layer (typically aluminum or copper), a continuous dielectric layer and a copper circuit          layer. It protects electronic components by removing heat through the thermally conductive dielectric layer to the metal base heatsink. (See Traditional Non-Direct Thermal)

Direct Thermal Path – The Direct Thermal Exchange Methodology can be broken down into two designs.

• The first consists of a three dimensional metal core (typically aluminum or copper), a dielectric layer and a copper circuit layer. It functions by removing heat directly from the components to the thermal transfer pads on the top of the PCB and dissipates the head to the metal base heatsink. (See Direct Thermal)
• The second consists of a splash pad that is drilled and plated through to a Cu heatsink. It functions by removing heat directly from the components to the splash pad on the top of the PCB and dissipates the head through the plated holes to the metal base heatsink. (No depiction noted)

Considerations

• What’s the thermal conductivity of MCPCB material? Dielectric materials range from 0.5 W/mK (Typical FR4) to 8W/mK for very high end materials. Typical MCPCB’s require between 1-2W/mK in order to provide reasonable operating temperatures. See the Thermal comparison chart (Table 1).
• Can I get a different dielectric thickness between the metal and circuit layer? Yes, most material suppliers offer material is various thicknesses. See the Thermal comparison chart (Table 1).
• Can I do more than one layer with an MCPCB? Yes, typical multilayer MCPCB’s are up to 4 layers.
• Can I put plated through-holes on an MCPCB? Yes, traditional multilayer MCPCB’s can be created with plated through holes. Be warned that the process can add considerable costs depending on the complexity of the required fabrication of the heatsink.
• What metals can be used? Typical metals include Aluminum and Copper alloys.
• What is the most cost effective MCPCB? Single sided aluminum backed
• How quick can a MCPCB be manufactured? A traditional single sided MCPCB can be produced within 3 business days, whereas a traditional multi-layer will take up to 5 business days. Designs utilizing the Direct Thermal path can take up to 10-15 business days depending on the design complexity.

 

Keeping MCPCB Designs Cost Friendly

There are several important factors when designing a circuit board which will help keep your price per unit as low as possible.

• Copper Weight – Stick with 1-2 oz. Cu foil. Thicker starting foil can significantly increase board spacing requirements.
• Final Finish – Try to stay away from expensive surface finishes such as ENIG / Immersion Au
• Board Size – The typical panel sizes are usually 18”x24” or 21”x24”. A half inch is required around the full panel for handling/manufacturing so you are left with 17”x 23” or 20”x23” respectively of manufacturable space. Try to design your MCPCB array to utilize as much of that space as posable.
• High End Dielectric Prepreg – Target your design around a dielectric material that provides 1-2 W/mK of thermal conductivity. The high end materials come at a significant cost.
• Complex CNC Routing – CNC routing can be one of the most challenging aspects of manufacturing MCPCB’s. If at all possible keep the routing to a minimum and utilize V-scoring as much as possible.
• V-Scoring – Keep the design simple enough to for V-Scoring, CNC routing can add considerable costs.
• Number of Layers – Keep the layer count as low as possible. Not only does increasing the layer count have an impact on pricing but it often reduces the thermal conductivity of the dielectric.
• Metal Core – Stick with an aluminum based alloy if possible. Cu alloys will add significant cost.

 

When you add extra features to a design like heavy copper foil, blind/filled vias, complex machining/profiling and expensive surface finishes, these features and processes will typically add an extra 40-50% in price and will be costly for production volume

  

HT Pho-Tronics MCPCB Capabilities.

• Single layer or Multiple Layer Traditional MCPCB
• Conductivity from 1.2 – 4.2 (°W/m-K)
• Dielectric thickness for 2.5 – 6 mil
• Direct Thermal Path Single or Multiple layer MCPCB
• MCPCB Al base plates 30 – 125 mil
• MCPCB Cu base plates 30 – 93 mil
• MCPCB copper foil thickness 1 – 6 oz.
• Machined features such as counter bore / counter sink
• Brilliant White solder mask for LED Applications

Typical products utilizing MCPCB’s

• Automotive:

• Head lights
• Tail light assemblies
• Dash board
• Interior lighting.

• Military:

• Head lights
• Running lights
• Spot lights
• Signal beacons
• High power flash lights

• Aerospace:

• Aircraft landing lights
• Running lights
• Cabin mood lighting systems
• Spot light and general lighting.

• Consumer:

• Street lighting
• Traffic control lighting
• Interior building lights
• Landscape lighting
• Camping gear.

• Medical:

• Operating room lighting
• Surgical lighting tools
• High power scanning technology

 

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