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Coefficient Of Thermal ExpansionAnd Solder Joints Electrical connections toBase Plate

Solder joint fatigue can be minimized by selecting the correctbase layer to match component expansion. The major concern with thermal expansion is the stress the solder joint experiences in power (or thermal) cycling. Solder joints are not mechanically rigid. Stress induced by heating and cooling will cause the joint to fatigue as it relieves stress. Large devices, extreme temperature differential, badly mismatched materials, or a minimum solder thickness will all place increased cyclic strain on solder joints.Solder joint fatigue is typically first associated with passive,ceramic components and with the device termination. The assembly section on page 20 covers these issues in greater detail. If a connection to the base plate is desired, copper is the mostcompatible base layer to use. When using electrical or thermal vias, it is important to match the circuit and base coefficients of thermal expansion as closely as possible. Otherwise, excess plated-hole stress will occur during thermal cycles.Other base layer materials can beused for connection, but will require different connection schemes.

Costs

The most cost effective base layers are Aluminum and Copperbecause they represent industry standards. Copper is more expensive than Aluminum when comparing the like thicknesses, but can be the less expensive option if design considerations allow for a thinner layer. As an example, typically the cost of 0.040" (1.0 mm) Copper is equal to the cost of 0.125" (3.2 mm) Aluminum.

Thickness

Copper and aluminum Thermal Clad is normally purchased inone of the standard-gauge thicknesses shown in the table below. Non-standard thicknessesare also available.Standard sizes include 16" x 19" and 18" x 24" sheets (usablearea: 15" x 18" and 17" x 23"). Other sizes are available upon request.

Surface Finish

Aluminum and copper base layers come with a uniformcommercialquality brushed surface. Aluminum is also availableanodized with choices of clear, black, blue and red colors.

Inches Millimeters 0.020 0.51 0.030 0.76

Standard Thermal Clad Materials

0.040 1.02

Available in:•16"(406mm) x 19"(482mm)Usable Area: 15" (381 mm) x 18" (457.2 mm)•18" (457.2 mm) x 24" (609.6 mm)Usable area: 17" (451.8 mm) x 23" (584.2 mm)

0.062 1.57 0.080 2.03 0.093 2.36 0.125 3.18

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