AN1703 - APPLICATION NOTE

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Any solder temperature profile should be within these limits. The soldering process causes considerable

thermal stress to a semiconductor component. This has to be minimized to ensure a reliable and extended

lifetime of the device. When the entire device is heated to a high temperature, failure to complete soldering

within a short time could result in device failure. Therefore, in order to minimize the thermal stress to which

the devices are subject, the device should always be preheated (max 120sec at 125

a device without preheating can cause excessive thermal shock and stress that can result in damage to

the device.

Voids pose a difficult reliability problem for large surface mount devices. Pockets of air under the package

result in poor thermal contact and the resulting high thermal resistance leads to complete failure. Because

of co-planarity problems, weight balance is critical.

The quality of the solder joints is very important for two reasons: firstly, poor quality solder joints result

directly in poor reliability, and secondly, solder thickness significantly affects the thermal resistance. Thus

a tight control of this parameter results in thermally efficient and reliable solder joints. Thermal conductivity

in the region of 0.5°C/W can easily be lost through uneven solder and poor co-planarity of tabs and leads.

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to change without notice. This publication supersedes and replaces all information previously supplied.

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