HPL (High Power Lighting)

HPL is specifically formulated for high power lighting LED applications with demanding thermal performance requirements.

Optimal Design - Circuit Design

Cost Effective Materials Circuit
Design Part
Fabrication Design
Guidelines Electrical
Design Advanced Processes

Material Utilization
Independent of the fabrication method chosen, square or rectangular designs will utilize the material most efficiently. The usable area of an 457 x 610mm (18.0" x 24.0") panel is 432 x 584mm (17.0" x 23.0") and a 508 x 610mm (20.0" x 24.0") is 483 x 584mm (19.0" x 23.0"). For best cost value, maximize use of this usable area.The shape of the part effects cost, so please reference the section on part singulation for helpful guidelines.

Figure 2: Layout for Effective Use of Space

Part size is an important consideration in cost control. In Figure 2, part size is 146 x 142mm (5.75" x 5.59") and panel utilization is 90%.This high utilization was achieved by reducing part size from the original 146 x 145mm (5.75" x 5.71") - only a 3mm change.The result is an increase in parts per panel from 8 to 12 utilizing the same amount of material (30% gain in panel utilization).

Base Plate Finish

•	When using aluminum, a brushed finish is typical. Other finishes like anodize and irridite are available for additional cost. With copper, a brushed finish is also typical but may oxidize from handling and atmospheric conditions. Other finishes like nickel are available to prevent oxidation but will drive cost up.
•	When considering finishing the part edge and/or through hole edge, please note that an unfinished edge is more economical.

Surface Finish

•	Green is the most commonly used soldermask color in the industry, and as a result it is the most cost effective. Other colors such as black, white, red and blue are also available.
•	If possible, try to include legend (nomenclature) in the soldermask design. If not possible, consider white costs less than black.
•	Regarding solder pad finish, HASL and Pb-free HASL are the most cost effective finishes. Other surface finishes such as ENIG, Ag, NiPdAu (for gold wire bond surfaces), and OSP (in panel and array form only) are available.

Selecting a Circuit Layer

	Current Carrying Capabilities The circuit layer is the component-mounting layer in Thermal Clad. Current carrying capability is a key consideration because this layer typically serves as a printed circuit, interconnecting the components of the assembly. The advantage of Thermal Clad is that the circuit trace interconnecting components can carry higher currents because of its ability to dissipate heat due to I2R loss in the copper circuitry.	Temperature rise comparison graph depicts the significant difference between Bergquist Dielectric HT and FR-4. Additional comparison charts regarding all Bergquist Dielectrics are available. Note: No base metal used in calculation.

	Temperature rise comparison graph depicts the significant difference between Bergquist Dielectric HT and FR-4. Additional comparison charts regarding all Bergquist Dielectrics are available. Note: No base metal used in calculation.


	Heat Spreading Capabilities Dielectric thickness and foil thickness both influence heat spreading capability in Thermal Clad. Heat spreading is one of the most powerful advantages derived from IMS. By increasing copper conductor thickness, heat spreading increases and brings junction temperature down. In some cases very heavy copper can be utilized along with bare die to eliminate the need for a standard packaged component. The following graphs depict both the thermal impedance value and case temperature when relating dielectric and foil thickness.	Standard Circuit Layer Thickness Note: Copper foil is NOT measured for thickness as a control method. Instead, it is certified to an area weight requirement per IPC-4562. The nominalthickness given on 1 oz. copper is 0.0014"/35 μm. Caution! Values in IPC-4562 (Table 1.1) are not representative of mechanical thickness.

Designing A Non-Rectangular Array

Comparing An Array In Three Different Considerations

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Non-rectangular designs typically require additional spacing in the array for milling or punching the shape. Often a combination of scoring and milling/punching is required to create the part shape and allow parts to be separated from the array after assembly. Additional process steps and reduced material utilization can impact cost.


•	Will assembled components require parts to be spaced further apart? This can result in multiple score lines and reduced material utilization. Consider part orientation in the array. Alternating orientation may allow components to nest, maximizing material utilization. In Figure 8 parts are spaced further apart and use more material as compared to the common score lines used in Figures 9 and 10.

Figure 9: Improved Design

Figure 10: Optimized Design

Design Considerations For Better Material Utilization

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Are rails required for assembly? Rails consume material that will be discarded after parts are separated from the array. When designing an array, size and number of rails should be considered to optimize panel utilization. The reduced rail design in Figure 9 uses less material than Figure 8, and even less material is required for the design with no rails in Figure 10.

Figure 8:Original Array Design