Mounting and Installing - Why Do Core Boards Have Electrically Active Substrates? Which are Common Cathode (-)? Which are Common Anode (+)?

Short Answer: good thermal performance at high current densities. A list of common cathode (-) and common anode parts (+) is provided below.

Luminus Devices utilizes a core board design for many low voltage high current LED devices. The LED chips are bonded directly to the copper core board. This gives the best possible path for heat extraction through the back surface of the device.

LED chips using high thermal conductivity submounts typically are electrically conductive (vertical chips) which leads to what is called common cathode (-) and common anode (+) configuration*.  A common cathode core board has connections on both the negative connector pin and the bottom of the copper substrate and vice versa.

The voltage for these devices is low.  For instance, the voltage between the common cathode (-) and isolated anode (+) of the CFT-90-WDH at 22.5 A is 3.5 V.

The system designer has a number of choices in incorporating core board electrical isolation. Suggestions can be found in: "Mounting Recommendations for Luminus High Power Chip on Board Devices", "How do I pick a TIM?" and Design Guidelines for SFT Chipsets Assembly. 

Devices with Common Cathode (-) Configuration

• CFT-90-W
• CBT-90-RX
• PT-120/PT-121-RAX
• CBM-120-UV

Devices with Common Anode (+) Configuration

• CBT-140-WCS
• CBT-140-WDH
• CBT-90-G
• CBT-90-B
• PT-120/PT-121-G
• PT-120/PT-121-B
• PT-39-DR-L51
• PT-39-G-L51
• CBT-90-UV
• CBM-90-IR
• CBM-120-FR

* Anode and cathode are confusing nomenclatures because they refer to the direction of electron flow during operation rather than a fixed component polarity.  For LEDs in forward bias, the convention is cathode (-) and anode (+).  

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