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Connection Techniques

Connection techniques common throughout the industry arebeing used successfully on Thermal Clad IMS substrates. Surface mount connectors are manufactured using plastic molding materials with thermal coefficients of expansion that roughly match the characteristics of the baseplate metal. However, the plastic molding compounds do have a different thermal capacity and thermal conductivitythat can cause stress in the assembly as it cools aftersoldering and during any significant temperature excursion. Process- caused thermal mechanical stress is specific to the solder reflow process used. For this reason, designs that capture the metal pin withoutrigidity are preferred, particularly if the major dimension ofthe connector is large.

Pin Connectors

Pin connectors and pin headers are often used in Thermal Cladassembly when an FR-4 panel is attached to a Thermal Clad assembly. The differential coefficient of expansion between the control panel and the base metal will cause stress in the solder joint and dielectric. The most advanced designs incorporate stress relief in the fabrication of the pin. Redundant header pins are often used to achieve high current carrying capacity.

Wire Bonding – Direct Die

Wire bonding is particularly useful in design of packages withchip on board (COB) architecture. The technique uses surface mount and interconnect capability of Thermal Clad in a highly efficient thermal design.To use this technique with Thermal Clad, it is important to prepareinterconnection sites of the circuit layer for wire bonding. For alu- minum wire bonding to the circuit layer, a electroless nickel- immersion gold plating is required. For applications requiring gold wire bonding a electroless nickel – wire bondable gold or a palladium – immersion gold is required. The specific requirements for the plating are typically customer supplied within standard plating capabilities. These surface finishes are very solder compatible and meet wetting requirements for solder die mounting processes.
Manufacturers such as AutoSplice and Zierick have off the shelf pins ideal forIMS applications. Custom pins and connectors are also available. Wire soldering on Thermal Clad. Flex attachment on Thermal Clad.

Power Connections

Only a few companies supply spade or threaded fastenerconnectorsfor surface mount power connections. In many casesthese are lead frame assemblies soldered to the printed circuit pads and bent to accommodate the shell used for encapsulation. Designs incorporating stress relief and a plastic retainer suitable for high amperage are also available.

Edge Connectors

When using edge connectors as part of the Thermal Clad printedwiring pattern, it is suggested that interfacing conductors be finished with a hard gold plating over sulfamate nickel plating. A 45°chamfer is recommended when using an edge connector. Remember to maintain the minimum edge to conductor distance to prevent shorting. 21