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Dielectric thickness and foil thickness both influence heatspreading 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. See Heavy Copper Application section on page 11.The following graphs depict both the thermal impedance value andcase temperature when relating dielectric and foil thickness.

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

Standard Circuit Layer Thickness Heat Spreading Capability

MATERIALWEIGHTREFERENCE THICKNESS(oz/ft
2 )inchesµm 1 0.0014 35 2 0.0028 70 3 0.0042 105 Copper 4 0.0056 140
(Zinc Treatment) 5 0.0070 178 6 0.0084 210 8 0.0112 280 10 0.0140 350 NOTE: Copper foil is NOTmeasured for thickness as a control method.Instead, it is certified to an area weight requirement per IPC-4562. The nominal thickness given on 1 oz. copper is 1.35 mils/25.7µm.CAUTION! Values in IPC-4562 (Table 1.1) are not representative ofmechanical thickness.

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