Thermal Materials : Thermal Substrates : Fans and Blowers : Membrane Switches : Touch Screens

• T-Clad Product Overview
• Dielectrics
  • Selection
  • Characteristics
  • Summary
  • Product Family FAQ's
• Base Metal Layer
• Optimal Design
  • Cost Effective Materials
  • Circuit Design
  • Part Fabrication
  • Design Guidelines
  • Electrical Design
  • Advanced Processes
• LEDs
  • Introduction
  • Temp. Effect
  • PCB Comparison
  • HPL
  • T-Clad PA
  • TIM Solutions
  • Standard Configurations
• Reliability Testing
• Applications
• Specialty Applications
• IsoEdge Heat Plate
• Assembly Recommendations
• Awards and Certifications
• T-Clad Selection Guide
• LED Solutions Brochure
• T-Clad Optimal Design White Paper
• Assembly Resources
  

LED Applications

Bergquist offers a standard and custom thermally conductive insulated metal substrate (IMS) circuit boards specifically for LED applications which replace conventional FR-4 PCBs. Better thermal management allows more forward current to be applied to the LED, while still maintaining desired die temperatures, which means more light and possibly reducing the number of LEDs required to achieve the desired light output. With proper thermal management, Power LED lifetimes can be extended considerably.

A Power LEDs light output and life expectance are directly attributed to how well the LED is managed thermally. As the LED generates heat, the dielectric of the Bergquist Thermal Clad insulated metal substrate quickly transfers it to the aluminum base, significantly improving the LEDs performance.

The Effect of Temperature

The LEDs color, or wavelength, will change with temperature. As the die temperature increases, the wavelength of the color increases.This is particularly important with white light.The human eye can differentiate small color changes in white light.When Power LEDs are populated in an array, consistent thermal resistance from one die to the next assures consistent color. Because of the comparatively low thermal resistance Thermal Clad offers versus FR-4, die temperature is less affected by slight variances in the junction-to-case thermal resistance that occurs with tin eutectic or epoxydie mounting techniques. It is also possible to pack the die more closely in an assembly that utilizes good thermal management techniques, thereby reducing the effects of temperature. Generally, a 50 percent drop in light output for a constant-forward current indicates end-of-life for Power LEDs.With proper thermal management, Power LED lifetimes can exceed 100,000 hours.

Light output of the same LED die on different circuit board materials at a maintained die temperature of 50°C.

 

Circuit Board Comparison Models

Insulated Metal Substrates (IMS®) and standard FR-4 are commonly used circuit board materials in conjunction with Power LEDs. Bergquist’s Thermal Clad IMS is a thin, thermally conductive layer bonded to an aluminum or copper substrate for heat dissipation (see illustration below).The key to Thermal Clad’s superior performance lies in its dielectric layer. This layer offers electrical isolation with high thermal conductivity and bonds the base metal and circuit foil together. Other manufacturers use standard prepreg as the dielectric layer, but prepreg doesn’t provide the high thermal conductivity and resulting thermal performance required to help assure the lowest possible operating temperatures and brightest light output for high-intensity LEDs.Thermal Clad circuit board materials are available from The Bergquist Company in three different thermal conductivities, High Temperature (HT), Multi-Purpose (MP) and Low Thermal Impedance (LTI).

Packaging Conclusion

There are several options available for thermal management of Power LEDs. The most critical thermal path in the stack is the one with the highest thermal resistance. Good practice suggests that you reduce the thermal resistance of that layer with Thermal Clad instead of FR-4.  

Liqui-Bond® Adhesive
Liqui-Bond is a thermally conductive liquid silicone adhesive that cures to a solid bonding elastomer. Liqui-Bond features excellent low and high-temperature mechanical and chemical stability. It can be supplied in either a tube or mid-sized container form.
• High thermal conductivity
• Easy dispensing
• Can achieve a very thin bond line
• Heat cure

 

Bond-Ply® Adhesive
Bond-Ply is a thermally conductive, pressure sensitive adhesive tape, available in either fiberglass reinforced or unreinforced. With its ability to have a high bond strength, it can eliminate the need for screws, clipmounts or fasteners.
• Good thermal performance
• Immediately bonds to target surface
• Eliminates need for mechanical
fasteners or screws
• Alternative to heat-cure adhesives

TIC® Thermal Interface Compound
TIC is a high performing, thermally conductive grease designed for use as a thermal interface between an aluminum base and a heat sink or metal casing.The compound wets-out the thermal surfaces and flows to produce the lowest impedance for your LED application.
• High thermal performance
• Good thermal conductivity
• Can be screened
• No post “cure” required
• Room temperature storage
• Exceptional value

 

Gap Pad® and Gap Filler
Gap Pad and Gap Filler are cost-effective, filled, thermally conductive interface materials. With shock dampening abilities, the Gap Pad line is recommended for applications that require a minimum amount of pressure between components. It’s “gel-like” modulus makes it well suited in areas where conformity may be a priority.
• Exceptional thermal conductivity
• Electrically isolating
• Highly conformable, low hardness
• Efficient gap filling material for minimizing component stress

 

Gap Pad® and Gap Filler Silicone-Free
Gap Pad and Gap Filler are also available in a silicone-free form.These thermally conductive polymers are designed to have similar mechanical benefits as silicone materials.They are ideal for sensitive applications that do not allow silicone, such as underwater pools and automotive lighting applications.
• Good thermal conductivity
• Highly conformable, low hardness
• Naturally tacky on both sides
• Ideal option for silicone sensitive applications