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Dielectric Performance Considerations

Peel StrengthStorage Modulus Operating Thermal CladMaterials Above Tg

This chart depicts the storage modulus of the material over a temperature range. Allof our dielectrics are robust, but you will want to choose the one that best suits your operating temperature environment. See Assembly Recommendations on pages 20-21 for additional information. This charts depicts the stability of the dielectric electrical properties over a range oftemperatures. The flatter the line, the more stable. Note the stability of our high temperature dielectric, HT to a temperature of 175° C. This chart graphs the stability of the bond strength between the dielectric and thecircuit layer during temperature rise. Although bond strength goes down at higher temperatures, it maintains at least 3 lbs. even at 175° C.

Dielectric StabilityCoefficient of Thermal Expansion

Thermo Mechanical Analysis (TMA) measures the dimensional stability of materials during temperature changes, monitoring the Coefficient of Thermal Expansion (CTE). Note: In the application, the CTE of the base material is a dominant contributorto thermal mechanical stress. See pages 12-13 for base layer selection.CTE OF IMS BOARDS - The concerns in exceeding Tg in standard FR4 materialsfrom a mechanical standpoint should be tempered when using Thermal Clad. The ceramic filler in the polymer matrix of Thermal Clad dielectrics results in considerably lower Z-axis expansion than in traditional FR-4 materials, while the low thickness of the dielectric means significantly less strain on plated-through-hole (PTH) connections due to expansion. . The dielectric materialabove T There is a potential benefit of relieving residualstress on the dielectric interfaces, in solder joints, and other interconnects due to CTE mismatches by choosing a dielectric with Tg below the operating temperature Above the Tg of the material, mechanical and electrical propertiesbegin to change. Mechanical changes of note are reduction of peel strength of the copper foil, an increase in the CTE, and decreasing storage modulus.
g is in its elastomeric state (much lower storage modulus),allowing some of the stresses to relax. Changes in electricalproperties must also be considered in operation above Tg, althoughthey are typically only important at frequencies above 1 MHz. Effects to consider are changes in the permitivity, dielectric lossand breakdown strength of the material. Important Note: ManyThermal Clad products have ULrating up to 45% higher than their glass transition temperature and are used extensively in applications above rated T . 8
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